Pulse pressure variations to predict fluid responsiveness: influence of tidal volume

Fluid responsiveness in acute respiratory distress syndrome patients: a post hoc analysis of the HEMOPRED study

PURPOSE

Optimal fluid management in patients with acute respiratory distress syndrome (ARDS) is challenging due to risks associated with both circulatory failure and fluid overload. The performance of dynamic indices to predict fluid responsiveness (FR) in ARDS patients is uncertain.

METHODS

This post hoc analysis of the HEMOPRED study compared the performance of dynamic indices in mechanically ventilated patients with shock, with and without ARDS, to predict FR, defined as an increase in aortic velocity time integral (VTI)  > 10% after passive leg raising (PLR).

RESULTS

Among 540 patients, 117 (22%) had ARDS and were ventilated with a median tidal volume of 7.6 mL/kg [6.9-8.4] and a median positive end-expiratory pressure of 7 cmH2O [5-9]. FR was observed in 45 ARDS patients (39% vs 44% in non-ARDS patients, p = 0.384). Reliability of dynamic indices to predict FR remained consistent in ARDS patients, though with different thresholds. Collapsibility index of the superior vena cava (ΔSVC) showed the best predictive performance in both ARDS (area under the curve [AUC] = 0.763 [0.659-0.868]) and non-ARDS (AUC = 0.750 [0.698-0.802]) patients. A right to left ventricle end-diastolic area ratio  > 0.8 or paradoxical septal motion were strongly linked to the absence of FR (> 80% specificity). FR was not associated with intensive care unit (ICU) mortality (47% vs. 46%, p = 1). However, hypovolemia, defined as an aortic VTI increase  > 32% during PLR (median increase in patients with a partial SVC collapse) was independently associated with ICU mortality (odds ratio [OR] = 1.355 [1.077-1.705], p = 0.011), as well as pulse pressure variation (OR = 1.014 [1.001-1.026], p = 0.034).

CONCLUSION

Performance of dynamic indices to predict FR appears preserved in ARDS patients, albeit with distinct thresholds. Hypovolemia, indicated by a  > 32% increase in aortic VTI during PLR, rather than FR, was associated with ICU mortality in this population.

A Clinician's Guide to Understanding Bias in Critical Clinical Prediction Models

This narrative review focuses on the role of clinical prediction models in supporting informed decision-making in critical care, emphasizing their 2 forms: traditional scores and artificial intelligence (AI)-based models. Acknowledging the potential for both types to embed biases, the authors underscore the importance of critical appraisal to increase our trust in models. The authors outline recommendations and critical care examples to manage risk of bias in AI models. The authors advocate for enhanced interdisciplinary training for clinicians, who are encouraged to explore various resources (books, journals, news Web sites, and social media) and events (Datathons) to deepen their understanding of risk of bias.

Assessment of fluid responsiveness using pulse pressure variation, stroke volume variation, plethysmographic variability index, central venous pressure, and inferior vena cava variation in patients undergoing mechanical ventilation: a systematic review and meta-analysis

IMPORTANCE

Maneuvers assessing fluid responsiveness before an intravascular volume expansion may limit useless fluid administration, which in turn may improve outcomes.

OBJECTIVE

To describe maneuvers for assessing fluid responsiveness in mechanically ventilated patients.

REGISTRATION

The protocol was registered at PROSPERO: CRD42019146781.

INFORMATION SOURCES AND SEARCH

PubMed, EMBASE, CINAHL, SCOPUS, and Web of Science were search from inception to 08/08/2023.

STUDY SELECTION AND DATA COLLECTION

Prospective and intervention studies were selected.

STATISTICAL ANALYSIS

Data for each maneuver were reported individually and data from the five most employed maneuvers were aggregated. A traditional and a Bayesian meta-analysis approach were performed.

RESULTS

A total of 69 studies, encompassing 3185 fluid challenges and 2711 patients were analyzed. The prevalence of fluid responsiveness was 49.9%. Pulse pressure variation (PPV) was studied in 40 studies, mean threshold with 95% confidence intervals (95% CI) = 11.5 (10.5-12.4)%, and area under the receiver operating characteristics curve (AUC) with 95% CI was 0.87 (0.84-0.90). Stroke volume variation (SVV) was studied in 24 studies, mean threshold with 95% CI = 12.1 (10.9-13.3)%, and AUC with 95% CI was 0.87 (0.84-0.91). The plethysmographic variability index (PVI) was studied in 17 studies, mean threshold = 13.8 (12.3-15.3)%, and AUC was 0.88 (0.82-0.94). Central venous pressure (CVP) was studied in 12 studies, mean threshold with 95% CI = 9.0 (7.7-10.1) mmHg, and AUC with 95% CI was 0.77 (0.69-0.87). Inferior vena cava variation (∆IVC) was studied in 8 studies, mean threshold = 15.4 (13.3-17.6)%, and AUC with 95% CI was 0.83 (0.78-0.89).

CONCLUSIONS

Fluid responsiveness can be reliably assessed in adult patients under mechanical ventilation. Among the five maneuvers compared in predicting fluid responsiveness, PPV, SVV, and PVI were superior to CVP and ∆IVC. However, there is no data supporting any of the above mentioned as being the best maneuver. Additionally, other well-established tests, such as the passive leg raising test, end-expiratory occlusion test, and tidal volume challenge, are also reliable.

Effects of dynamic versus static parameter-guided fluid resuscitation in patients with sepsis: A randomized controlled trial

Background

Fluid resuscitation is an essential component for sepsis treatment. Although several studies demonstrated that dynamic variables were more accurate than static variables for prediction of fluid responsiveness, fluid resuscitation guidance by dynamic variables is not standard for treatment. The objectives were to determine the effects of dynamic inferior vena cava (IVC)-guided versus (vs.) static central venous pressure (CVP)-guided fluid resuscitation in septic patients on mortality; and others, i.e., resuscitation targets, shock duration, fluid and vasopressor amount, invasive respiratory support, length of stay and adverse events.

Methods

A single-blind randomized controlled trial was conducted at Thammasat University Hospital between August 2016 and April 2020. Septic patients were stratified by acute physiologic and chronic health evaluation II (APACHE II) <25 or ≥25 and randomized by blocks of 2 and 4 to fluid resuscitation guidance by dynamic IVC or static CVP.

Results

Of 124 patients enrolled, 62 were randomized to each group, and one of each was excluded from mortality analysis. Baseline characteristics were comparable. The 30-day mortality rates between dynamic IVC vs. static CVP groups were not different (34.4% vs. 45.9%, p=0.196). Relative risk for 30-day mortality of dynamic IVC group was 0.8 (95%CI=0.5-1.2, p=0.201). Different outcomes were median (interquartile range) of shock duration (0.8 (0.4-1.6) vs. 1.5 (1.1-3.1) days, p=0.001) and norepinephrine (NE) dose (6.8 (3.9-17.8) vs. 16.1 (7.6-53.6) milligrams, p=0.008 and 0.1 (0.1-0.3) vs. 0.3 (0.1-0.8) milligram⋅kilogram -1, p=0.017). Others were not different.

Conclusions

Dynamic IVC-guided fluid resuscitation does not affect mortality of septic patients. However, this may reduce shock duration and NE dose, compared with static CVP guidance.

Predicting Fluid Responsiveness Using Carotid Ultrasound in Mechanically Ventilated Patients: A Systematic Review and Meta-Analysis of Diagnostic Test Accuracy Studies

BACKGROUND

A noninvasive and accurate method of determining fluid responsiveness in ventilated patients would help to mitigate unnecessary fluid administration. Although carotid ultrasound has been previously studied for this purpose, several studies have recently been published. We performed an updated systematic review and meta-analysis to evaluate the accuracy of carotid ultrasound as a tool to predict fluid responsiveness in ventilated patients.

METHODS

Studies eligible for review investigated the accuracy of carotid ultrasound parameters in predicting fluid responsiveness in ventilated patients, using sensitivity and specificity as markers of diagnostic accuracy (International Prospective Register of Systematic Reviews [PROSPERO] CRD42022380284). All included studies had to use an independent method of determining cardiac output and exclude spontaneously ventilated patients. Six bibliographic databases and 2 trial registries were searched. Medline, Embase, Emcare, APA PsycInfo, CINAHL, and the Cochrane Library were searched on November 4, 2022. Clinicaltrials.gov and Australian New Zealand Clinical Trials Registry were searched on February 24, 2023. Results were pooled, meta-analysis was conducted where possible, and hierarchical summary receiver operating characteristic models were used to compare carotid ultrasound parameters. Bias and evidence quality were assessed using the Quality Assessment of Diagnostic Accuracy Studies (QUADAS) tool and the Grading of Recommendations, Assessment, Development, and Evaluations (GRADE) guidelines.

RESULTS

Thirteen prospective clinical studies were included (n = 648 patients), representing 677 deliveries of volume expansion, with 378 episodes of fluid responsiveness (58.3%). A meta-analysis of change in carotid Doppler peak velocity (∆CDPV) yielded a sensitivity of 0.79 (95% confidence interval [CI], 0.74-0.84) and a specificity of 0.85 (95% CI, 0.76-0.90). Risk of bias relating to recruitment methodology, the independence of index testing to reference standards and exclusionary clinical criteria were evaluated. Overall quality of evidence was low. Study design heterogeneity, including a lack of clear parameter cutoffs, limited the generalizability of our results.

CONCLUSIONS

In this meta-analysis, we found that existing literature supports the ability of carotid ultrasound to predict fluid responsiveness in mechanically ventilated adults. ∆CDPV may be an accurate carotid parameter in certain contexts. Further high-quality studies with more homogenous designs are needed to further validate this technology.

Use of stepwise lung recruitment maneuver to predict fluid responsiveness under lung protective ventilation in the operating room

Recent research has revealed that hemodynamic changes caused by lung recruitment maneuvers (LRM) with continuous positive airway pressure can be used to identify fluid responders. We investigated the usefulness of stepwise LRM with increasing positive end-expiratory pressure and constant driving pressure for predicting fluid responsiveness in patients under lung protective ventilation (LPV). Forty-one patients under LPV were enrolled when PPV values were in a priori considered gray zone (4% to 17%). The FloTrac-Vigileo device measured stroke volume variation (SVV) and stroke volume (SV), while the patient monitor measured pulse pressure variation (PPV) before and at the end of stepwise LRM and before and 5 min after fluid challenge (6 ml/kg). Fluid responsiveness was defined as a ≥ 15% increase in the SV or SV index. Seventeen were fluid responders. The areas under the curve for the augmented values of PPV and SVV, as well as the decrease in SV by stepwise LRM to identify fluid responders, were 0.76 (95% confidence interval, 0.61-0.88), 0.78 (0.62-0.89), and 0.69 (0.53-0.82), respectively. The optimal cut-offs for the augmented values of PPV and SVV were > 18% and > 13%, respectively. Stepwise LRM -generated augmented PPV and SVV predicted fluid responsiveness under LPV.

Are We Always Right? Evaluation of the Performance and Knowledge of the Passive Leg Raise Test in Detecting Volume Responsiveness in Critical Care Patients: A National German Survey

Background: In hemodynamically unstable patients, the passive leg raise (PLR) test is recommended for use as a self-fluid challenge for predicting preload responsiveness. However, to interpret the hemodynamic effects and reliability of the PLR, the method of performing it is of the utmost importance. Our aim was to determine the current practice of the correct application and interpretation of the PLR in intensive care patients. Methods: After ethical approval, we designed a cross-sectional online survey with a short user-friendly online questionnaire. Using a random sample of 1903 hospitals in Germany, 182 hospitals with different levels of care were invited via an email containing a link to the questionnaire. The online survey was conducted between December 2021 and January 2022. All critical care physicians from different medical disciplines were surveyed. We evaluated the correct points of concern for the PLR, including indication, contraindication, choice of initial position, how to interpret and apply the changes in cardiac output, and the limitations of the PLR. Results: A total of 292 respondents participated in the online survey, and 283/292 (97%) of the respondents completed the full survey. In addition, 132/283 (47%) were consultants and 119/283 (42%) worked at a university medical center. The question about the performance of the PLR was answered correctly by 72/283 (25%) of the participants. The limitations of the PLR, such as intra-abdominal hypertension, were correctly selected by 150/283 (53%) of the participants. The correct effect size (increase in stroke volume ≥ 10%) was correctly identified by 217/283 (77%) of the participants. Conclusions: Our results suggest a considerable disparity between the contemporary practice of the correct application and interpretation of the PLR and the practice recommendations from recently published data at German ICUs.

Consistency of data reporting in fluid responsiveness studies in the critically ill setting: the CODEFIRE consensus from the Cardiovascular Dynamic section of the European Society of Intensive Care Medicine

PURPOSE

To provide consensus recommendations regarding hemodynamic data reporting in studies investigating fluid responsiveness and fluid challenge (FC) use in the intensive care unit (ICU).

METHODS

The Executive Committee of the European Society of Intensive Care Medicine (ESICM) commissioned and supervised the project. A panel of 18 international experts and a methodologist identified main domains and items from a systematic literature, plus 2 ancillary domains. A three-step Delphi process based on an iterative approach was used to obtain the final consensus. In the Delphi 1 and 2, the items were selected with strong (≥ 80% of votes) or week agreement (70-80% of votes), while the Delphi 3 generated recommended (≥ 90% of votes) or suggested (80-90% of votes) items (RI and SI, respectively).

RESULTS

We identified 5 main domains initially including 117 items and the consensus finally resulted in 52 recommendations or suggestions: 18 RIs and 2 SIs statements were obtained for the domain "ICU admission", 11 RIs and 1 SI for the domain "mechanical ventilation", 5 RIs for the domain "reason for giving a FC", 8 RIs for the domain pre- and post-FC "hemodynamic data", and 7 RIs for the domain "pre-FC infused drugs". We had no consensus on the use of echocardiography, strong agreement regarding the volume (4 ml/kg) and the reference variable (cardiac output), while weak on administration rate (within 10 min) of FC in this setting.

CONCLUSION

This consensus found 5 main domains and provided 52 recommendations for data reporting in studies investigating fluid responsiveness in ICU patients.

Measurement error of pulse pressure variation

Dynamic preload parameters are used to guide perioperative fluid management. However, reported cut-off values vary and the presence of a gray zone complicates clinical decision making. Measurement error, intrinsic to the calculation of pulse pressure variation (PPV) has not been studied but could contribute to this level of uncertainty. The purpose of this study was to quantify and compare measurement errors associated with PPV calculations. Hemodynamic data of patients undergoing liver transplantation were extracted from the open-access VitalDatabase. Three algorithms were applied to calculate PPV based on 1 min observation periods. For each method, different durations of sampling periods were assessed. Best Linear Unbiased Prediction was determined as the reference PPV-value for each observation period. A Bayesian model was used to determine bias and precision of each method and to simulate the uncertainty of measured PPV-values. All methods were associated with measurement error. The range of differential and proportional bias were [- 0.04%, 1.64%] and [0.92%, 1.17%] respectively. Heteroscedasticity influenced by sampling period was detected in all methods. This resulted in a predicted range of reference PPV-values for a measured PPV of 12% of [10.2%, 13.9%] and [10.3%, 15.1%] for two selected methods. The predicted range in reference PPV-value changes for a measured absolute change of 1% was [- 1.3%, 3.3%] and [- 1.9%, 4%] for these two methods. We showed that all methods that calculate PPV come with varying degrees of uncertainty. Accounting for bias and precision may have important implications for the interpretation of measured PPV-values or PPV-changes.

CAROTID ARTERY ULTRASOUND FOR ASSESSING FLUID RESPONSIVENESS IN PATIENTS UNDERGOING MECHANICAL VENTILATION WITH LOW TIDAL VOLUME AND PRESERVED SPONTANEOUS BREATHING

ABSTRACT

Objective : This study aimed to investigate whether changes in carotid artery corrected flow time (ΔFTc bolus ) and carotid artery peak flow velocity respiratory variation (Δ V peak bolus ) induced by the fluid challenge could reliably predict fluid responsiveness in mechanically ventilated patients with a tidal volume < 8 mL/kg Predicted Body Weight while preserving spontaneous breathing. Methods : Carotid artery corrected flow time, Δ V peak, and hemodynamic data were measured before and after administration of 250 mL crystalloids. Fluid responsiveness was defined as a 10% or more increase in stroke volume index as assessed by noninvasive cardiac output monitoring after the fluid challenge. Results : A total of 43 patients with acute circulatory failure were enrolled in this study. Forty-three patients underwent a total of 60 fluid challenges. The ΔFTc bolus and Δ V peak bolus showed a significant difference between the fluid responsiveness positive group (n = 35) and the fluid responsiveness negative group (n = 25). Spearman correlation test showed that ΔFTc bolus and Δ V peak bolus with the relative increase in stroke volume index after fluid expansion ( r = 0.5296, P < 0.0001; r = 0.3175, P = 0.0135). Multiple logistic regression analysis demonstrated that ΔFTc bolus and Δ V peak bolus were significantly correlated with fluid responsiveness in patients with acute circulatory failure. The areas under the receiver operating characteristic curves of ΔFTc bolus and Δ V peak bolus for predicting fluid responsiveness were 0.935 and 0.750, respectively. The optimal cutoff values of ΔFTc bolus and Δ V peak bolus were 0.725 (sensitivity = 97.1%, specificity = 84%) and 4.21% (sensitivity = 65.7%, specificity = 80%), respectively. Conclusion : In mechanically ventilated patients with a tidal volume < 8 mL/kg while preserving spontaneous breathing, ΔFTc bolus and Δ V peak bolus could predict fluid responsiveness. The predictive performance of ΔFTc bolus was superior to Δ V peak bolus .

Surviving Sepsis Campaign Research Priorities 2023

OBJECTIVES

To identify research priorities in the management, epidemiology, outcome, and pathophysiology of sepsis and septic shock.

DESIGN

Shortly after publication of the most recent Surviving Sepsis Campaign Guidelines, the Surviving Sepsis Research Committee, a multiprofessional group of 16 international experts representing the European Society of Intensive Care Medicine and the Society of Critical Care Medicine, convened virtually and iteratively developed the article and recommendations, which represents an update from the 2018 Surviving Sepsis Campaign Research Priorities.

METHODS

Each task force member submitted five research questions on any sepsis-related subject. Committee members then independently ranked their top three priorities from the list generated. The highest rated clinical and basic science questions were developed into the current article.

RESULTS

A total of 81 questions were submitted. After merging similar questions, there were 34 clinical and ten basic science research questions submitted for voting. The five top clinical priorities were as follows: 1) what is the best strategy for screening and identification of patients with sepsis, and can predictive modeling assist in real-time recognition of sepsis? 2) what causes organ injury and dysfunction in sepsis, how should it be defined, and how can it be detected? 3) how should fluid resuscitation be individualized initially and beyond? 4) what is the best vasopressor approach for treating the different phases of septic shock? and 5) can a personalized/precision medicine approach identify optimal therapies to improve patient outcomes? The five top basic science priorities were as follows: 1) How can we improve animal models so that they more closely resemble sepsis in humans? 2) What outcome variables maximize correlations between human sepsis and animal models and are therefore most appropriate to use in both? 3) How does sepsis affect the brain, and how do sepsis-induced brain alterations contribute to organ dysfunction? How does sepsis affect interactions between neural, endocrine, and immune systems? 4) How does the microbiome affect sepsis pathobiology? 5) How do genetics and epigenetics influence the development of sepsis, the course of sepsis and the response to treatments for sepsis?

CONCLUSIONS

Knowledge advances in multiple clinical domains have been incorporated in progressive iterations of the Surviving Sepsis Campaign guidelines, allowing for evidence-based recommendations for short- and long-term management of sepsis. However, the strength of existing evidence is modest with significant knowledge gaps and mortality from sepsis remains high. The priorities identified represent a roadmap for research in sepsis and septic shock.

The effects of respiratory rate and tidal volume on pulse pressure variation in healthy lungs-a generalized additive model approach may help overcome limitations

Pulse pressure variation (PPV) is a well-established method for predicting fluid responsiveness in mechanically ventilated patients. The predictive accuracy is, however, disputed for ventilation with low tidal volume (VT) or low heart-rate-to-respiratory-rate ratio (HR/RR). We investigated the effects of VT and RR on PPV and on PPV's ability to predict fluid responsiveness. We included patients scheduled for open abdominal surgery. Prior to a 250 ml fluid bolus, we ventilated patients with combinations of VT from 4 to 10 ml kg-1 and RR from 10 to 31 min-1. For each of 10 RR-VT combinations, PPV was derived using both a classic approach and a generalized additive model (GAM) approach. The stroke volume (SV) response to fluid was evaluated using uncalibrated pulse contour analysis. An SV increase > 10% defined fluid responsiveness. Fifty of 52 included patients received a fluid bolus. Ten were fluid responders. For all ventilator settings, fluid responsiveness prediction with PPV was inconclusive with point estimates for the area under the receiver operating characteristics curve between 0.62 and 0.82. Both PPV measures were nearly proportional to VT. Higher RR was associated with lower PPV. Classically derived PPV was affected more by RR than GAM-derived PPV. Correcting PPV for VT could improve PPV's predictive utility. Low HR/RR has limited effect on GAM-derived PPV, indicating that the low HR/RR limitation is related to how PPV is calculated. We did not demonstrate any benefit of GAM-derived PPV in predicting fluid responsiveness.Trial registration: ClinicalTrials.gov, reg. March 6, 2020, NCT04298931.

Passive leg raising test induced changes in plethysmographic variability index to assess fluid responsiveness in critically ill mechanically ventilated patients with acute circulatory failure

BACKGROUND

Passive leg raising (PLR) reliably predicts fluid responsiveness but requires a real-time cardiac index (CI) measurement or the presence of an invasive arterial line to achieve this effect. The plethysmographic variability index (PVI), an automatic measurement of the respiratory variation of the perfusion index, is non-invasive and continuously displayed on the pulse oximeter device. We tested whether PLR-induced changes in PVI (ΔPVIPLR) could accurately predict fluid responsiveness in mechanically ventilated patients with acute circulatory failure.

METHODS

This was a secondary analysis of an observational prospective study. We included 29 mechanically ventilated patients with acute circulatory failure in this study. We measured PVI (Radical-7 device; Masimo Corp., Irvine, CA) and CI (Echocardiography) before and during a PLR test and before and after volume expansion of 500 mL of crystalloid solution. A volume expansion-induced increase in CI of >15% defined fluid responsiveness. To investigate whether ΔPVIPLR can predict fluid responsiveness, we determined areas under the receiver operating characteristic curves (AUROCs) and gray zones for ΔPVIPLR.

RESULTS

Of the 29 patients, 27 (93.1%) received norepinephrine. The median tidal volume was 7.0 [IQR: 6.6-7.6] mL/kg ideal body weight. Nineteen patients (65.5%) were classified as fluid responders (increase in CI > 15% after volume expansion). Relative ΔPVIPLR accurately predicted fluid responsiveness with an AUROC of 0.89 (95%CI: 0.72-0.98, p < 0.001). A decrease in PVI ≤ -24.1% induced by PLR detected fluid responsiveness with a sensitivity of 95% (95%CI: 74-100%) and a specificity of 80% (95%CI: 44-97%). Gray zone was acceptable, including 13.8% of patients. The correlations between the relative ΔPVIPLR and changes in CI induced by PLR and by volume expansion were significant (r = -0.58, p < 0.001, and r = -0.65, p < 0.001; respectively).

CONCLUSIONS

In sedated and mechanically ventilated ICU patients with acute circulatory failure, PLR-induced changes in PVI accurately predict fluid responsiveness with an acceptable gray zone.

TRIAL REGISTRATION

ClinicalTrials.govNCT03225378.

Reliability of pulse pressure and stroke volume variation in assessing fluid responsiveness in the operating room: a metanalysis and a metaregression

BACKGROUND

Pulse pressure and stroke volume variation (PPV and SVV) have been widely used in surgical patients as predictors of fluid challenge (FC) response. Several factors may affect the reliability of these indices in predicting fluid responsiveness, such as the position of the patient, the use of laparoscopy and the opening of the abdomen or the chest, combined FC characteristics, the tidal volume (Vt) and the type of anesthesia.

METHODS

Systematic review and metanalysis of PPV and SVV use in surgical adult patients. The QUADAS-2 scale was used to assess the risk of bias of included studies. We adopted a metanalysis pooling of aggregate data from 5 subgroups of studies with random effects models using the common-effect inverse variance model. The area under the curve (AUC) of pooled receiving operating characteristics (ROC) curves was reported. A metaregression was performed using FC type, volume, and rate as independent variables.

RESULTS

We selected 59 studies enrolling 2,947 patients, with a median of fluid responders of 55% (46-63). The pooled AUC for the PPV was 0.77 (0.73-0.80), with a mean threshold of 10.8 (10.6-11.0). The pooled AUC for the SVV was 0.76 (0.72-0.80), with a mean threshold of 12.1 (11.6-12.7); 19 studies (32.2%) reported the grey zone of PPV or SVV, with a median of 56% (40-62) and 57% (46-83) of patients included, respectively. In the different subgroups, the AUC and the best thresholds ranged from 0.69 and 0.81 and from 6.9 to 11.5% for the PPV, and from 0.73 to 0.79 and 9.9 to 10.8% for the SVV. A high Vt and the choice of colloids positively impacted on PPV performance, especially among patients with closed chest and abdomen, or in prone position.

CONCLUSION

The overall performance of PPV and SVV in operating room in predicting fluid responsiveness is moderate, ranging close to an AUC of 0.80 only some subgroups of surgical patients. The grey zone of these dynamic indices is wide and should be carefully considered during the assessment of fluid responsiveness. A high Vt and the choice of colloids for the FC are factors potentially influencing PPV reliability.

TRIAL REGISTRATION

PROSPERO (CRD42022379120), December 2022. https://www.crd.york.ac.uk/prospero/display_record.php?RecordID=379120.

Respiratory variation in the internal jugular vein does not predict fluid responsiveness in the prone position during adolescent idiopathic scoliosis surgery: a prospective cohort study

BACKGROUND

Respiratory variation in the internal jugular vein (IJVV) has not shown promising results in predicting volume responsiveness in ventilated patients with low tidal volume (Vt) in prone position. We aimed to determine whether the baseline respiratory variation in the IJVV value measured by ultrasound might predict fluid responsiveness in patients with adolescent idiopathic scoliosis (AIS) undergoing posterior spinal fusion (PSF) with low Vt.

METHODS

According to the fluid responsiveness results, the included patients were divided into two groups: those who responded to volume expansion, denoted the responder group, and those who did not respond, denoted the non-responder group. The primary outcome was determination of the value of baseline IJVV in predicting fluid responsiveness (≥15% increases in stroke volume index (SVI) after 7 ml·kg-1 colloid administration) in patients with AIS undergoing PSF during low Vt ventilation. Secondary outcomes were estimation of the diagnostic performance of pulse pressure variation (PPV), stroke volume variation (SVV), and the combination of IJVV and PPV in predicting fluid responsiveness in this surgical setting. The ability of each parameter to predict fluid responsiveness was assessed using a receiver operating characteristic curve.

RESULTS

Fifty-six patients were included, 36 (64.29%) of whom were deemed fluid responsive. No significant difference in baseline IJVV was found between responders and non-responders (25.89% vs. 23.66%, p = 0.73), and no correlation was detected between baseline IJVV and the increase in SVI after volume expansion (r = 0.14, p = 0.40). A baseline IJVV greater than 32.00%, SVV greater than 14.30%, PPV greater than 11.00%, and a combination of IJVV and PPV greater than 64.00% had utility in identifying fluid responsiveness, with a sensitivity of 33.33%, 77.78%, 55.56%, and 55.56%, respectively, and a specificity of 80.00%, 50.00%, 65.00%, and 65.00%, respectively. The area under the receiver operating characteristic curve for the baseline values of IJVV, SVV, PPV, and the combination of IJVV and PPV was 0.52 (95% CI, 0.38-0.65, p=0.83), 0.54 (95% CI, 0.40-0.67, p=0.67), 0.58 (95% CI, 0.45-0.71, p=0.31), and 0.57 (95% CI, 0.43-0.71, p=0.37), respectively.

CONCLUSIONS

Ultrasonic-derived IJVV lacked accuracy in predicting fluid responsiveness in patients with AIS undergoing PSF during low Vt ventilation. In addition, the baseline values of PPV, SVV, and the combination of IJVV and PPV did not predict fluid responsiveness in this surgical setting.

TRAIL REGISTRATION

This trial was registered at www.chictr.org (ChiCTR2200064947) on 24/10/2022. All data were collected through chart review.

Effect of tidal volume change on pressure-based prediction of fluid responsiveness in children

INTRODUCTION

It is known that pulse pressure variation and systolic pressure variation cannot predict fluid responsiveness in children. In adults, the ability of these dynamic parameters to predict fluid responsiveness is improved by increasing tidal volume. We planned to investigate whether pulse pressure variation or systolic pressure variation can predict fluid responsiveness in children when augmented by increasing tidal volume by conducting a prospective study.

METHODS

We enrolled children younger than 7 years who underwent cardiac surgery for atrial septal defect or ventricular septal defect. After sternum closure, pulse pressure variation and systolic pressure variation were continuously recorded while changing the tidal volume to 6, 10, and 14 mL/kg. Fluid loading was done with 10 mL/kg of crystalloids for 10 min, and stroke volume index was measured via transesophageal echocardiography. Children whose stroke volume index increased by more than 15% after the fluid loading were defined as responders to fluid therapy. We set primary outcome as the predictability of pulse pressure variation and systolic pressure variation for fluid responsiveness and measured the area under the curve of receiver operating characteristics curve.

RESULTS

Twenty-six children were included, of which 15 were responders. At the tidal volume of 14 mL/kg, the area under the curves of receiver operating characteristics curves of pulse pressure variation and systolic pressure variation were 0.576 (p = .517) and 0.548 (p = .678), respectively. The differences in dynamic parameters between responders and nonresponders were not significant.

DISCUSSION

Failure of pulse pressure variation or systolic pressure variation at augmented tidal volume in children may be due to difference in their arterial compliance from those of adults. Large compliance of thoracic wall may be another reason.

CONCLUSIONS

Augmented pulse pressure variation or systolic pressure variation due to increased tidal volume cannot predict fluid responsiveness in children after simple cardiac surgery.

Pressure- vs. volume-controlled ventilation and their respective impact on dynamic parameters of fluid responsiveness: a cross-over animal study

BACKGROUND AND GOAL OF STUDY

Pulse pressure variation (PPV) and stroke volume variation (SVV), which are based on the forces caused by controlled mechanical ventilation, are commonly used to predict fluid responsiveness. When PPV and SVV were introduced into clinical practice, volume-controlled ventilation (VCV) with tidal volumes (VT) ≥ 10 ml kg- 1 was most commonly used. Nowadays, lower VT and the use of pressure-controlled ventilation (PCV) has widely become the preferred type of ventilation. Due to their specific flow characteristics, VCV and PCV result in different airway pressures at comparable tidal volumes. We hypothesised that higher inspiratory pressures would result in higher PPVs and aimed to determine the impact of VCV and PCV on PPV and SVV.

METHODS

In this self-controlled animal study, sixteen anaesthetised, paralysed, and mechanically ventilated (goal: VT 8 ml kg- 1) pigs were instrumented with catheters for continuous arterial blood pressure measurement and transpulmonary thermodilution. At four different intravascular fluid states (IVFS; baseline, hypovolaemia, resuscitation I and II), ventilatory and hemodynamic data including PPV and SVV were assessed during VCV and PCV. Statistical analysis was performed using U-test and RM ANOVA on ranks as well as descriptive LDA and GEE analysis.

RESULTS

Complete data sets were available of eight pigs. VT and respiratory rates were similar in both forms. Heart rate, central venous, systolic, diastolic, and mean arterial pressures were not different between VCV and PCV at any IVFS. Peak inspiratory pressure was significantly higher in VCV, while plateau, airway and transpulmonary driving pressures were significantly higher in PCV. However, these higher pressures did not result in different PPVs nor SVVs at any IVFS.

CONCLUSION

VCV and PCV at similar tidal volumes and respiratory rates produced PPVs and SVVs without clinically meaningful differences in this experimental setting. Further research is needed to transfer these results to humans.

Cardio-respiratory interactions in acute asthma

Asthma encompasses of respiratory symptoms that occur intermittently and with varying intensity accompanied by reversible expiratory airflow limitation. In acute exacerbations, it can be life-threatening due to its impact on ventilatory mechanics. Moreover, asthma has significant effects on the cardiovascular system, primarily through heart-lung interaction-based mechanisms. Dynamic hyperinflation and increased work of breathing caused by a sharp drop in pleural pressure, can affect cardiac function and cardiac output through different mechanisms. These mechanisms include an abrupt increase in venous return, elevated right ventricular afterload and interdependence between the left and right ventricle. Additionally, Pulsus paradoxus, which reflects the maximum consequences of this heart lung interaction when intrathoracic pressure swings are exaggerated, may serve as a convenient bedside tool to assess the severity of acute asthma acute exacerbation and its response to therapy.

Cardiopulmonary interactions-which monitoring tools to use?

Heart-lung interactions occur due to the mechanical influence of intrathoracic pressure and lung volume changes on cardiac and circulatory function. These interactions manifest as respiratory fluctuations in venous, pulmonary, and arterial pressures, potentially affecting stroke volume. In the context of functional hemodynamic monitoring, pulse or stroke volume variation (pulse pressure variation or stroke volume variability) are commonly employed to assess volume or preload responsiveness. However, correct interpretation of these parameters requires a comprehensive understanding of the physiological factors that determine pulse pressure and stroke volume. These factors include pleural pressure, venous return, pulmonary vessel function, lung mechanics, gas exchange, and specific cardiac factors. A comprehensive knowledge of heart-lung physiology is vital to avoid clinical misjudgments, particularly in cases of right ventricular (RV) failure or diastolic dysfunction. Therefore, when selecting monitoring devices or technologies, these factors must be considered. Invasive arterial pressure measurements of variations in breath-to-breath pressure swings are commonly used to monitor heart-lung interactions. Echocardiography or pulmonary artery catheters are valuable tools for differentiating preload responsiveness from right ventricular failure, while changes in diastolic function should be assessed alongside alterations in airway or pleural pressure, which can be approximated by esophageal pressure. In complex clinical scenarios like ARDS, combined forms of shock or right heart failure, additional information on gas exchange and pulmonary mechanics aids in the interpretation of heart-lung interactions. This review aims to describe monitoring techniques that provide clinicians with an integrative understanding of a patient's condition, enabling accurate assessment and patient care.

Diagnostic Efficacy of Carotid Ultrasound for Predicting the Risk of Perioperative Hypotension or Fluid Responsiveness: A Meta-Analysis

Despite the acceptance of carotid ultrasound for predicting patients' fluid responsiveness in critical care and anesthesia, its efficacy for predicting hypotension and fluid responsiveness remains unclear in the perioperative setting. Electronic databases were searched from inception to May 2023 to identify observational studies focusing on the use of corrected blood flow time (FTc) and respirophasic variation in carotid artery blood flow peak velocity (ΔVpeak) for assessing the risks of hypotension and fluid responsiveness. Using FTc as a predictive tool (four studies), the analysis yielded a pooled sensitivity of 0.82 (95% confidence interval (CI): 0.72 to 0.89) and specificity of 0.94 (95% CI: 0.88 to 0.97) for the risk of hypotension (area under curve (AUC): 0.95). For fluid responsiveness, the sensitivity and specificity of FTc were 0.79 (95% CI: 0.72 to 0.84) and 0.81 (95% CI: 0.75 to 0.86), respectively (AUC: 0.87). In contrast, the use of ΔVpeak to predict the risk of fluid responsiveness showed a pooled sensitivity of 0.76 (95% CI: 0.63 to 0.85) and specificity of 0.74 (95% CI: 0.66 to 0.8) (AUC: 0.79). The current meta-analysis provides robust evidence supporting the high diagnostic accuracy of FTc in predicting perioperative hypotension and fluid responsiveness, which requires further studies for verification.

Predictors of fluid responsiveness in the operating room: a narrative review

Prediction of fluid responsiveness has been considered an essential tool for modern fluid management. However, most studies in this field have focused on patients in intensive care unit despite numerous research throughout several decades. Therefore, the present narrative review aims to show the representative method's feasibility, advantages, and limitations in predicting fluid responsiveness, focusing on the operating room environments. Firstly, we described the predictors of fluid responsiveness based on heart-lung interaction, including pulse pressure and stroke volume variations, the measurement of respiratory variations of inferior vena cava diameter, and the end-expiratory occlusion test and addressed their limitations. Subsequently, the passive leg raising test and mini-fluid challenge tests were also mentioned, which assess fluid responsiveness by mimicking a classic fluid challenge. In the last part of this review, we pointed out the pitfalls of fluid management based on fluid responsiveness prediction, which emphasized the importance of individualized decision-making. Understanding the available representative methods to predict fluid responsiveness and their associated benefits and drawbacks through this review will aid anesthesiologists in choosing the most reliable methods for optimal fluid administration in each patient during anesthesia in the operating room.

The haemodynamic effects of phenylephrine after cardiac surgery

BACKGROUND

Phenylephrine increases systemic- and pulmonary resistances and therefore may increase blood pressures at the expense of blood flow. Cardio-pulmonary bypass alters vasoreactivity and many patients exhibit chronotropic insufficiency after cardiac surgery. We aimed to describe the haemodynamic effects of phenylephrine infusion after cardiac surgery.

METHODS

Patients in steady state after low-risk cardiac surgery received incremental infusion rates of phenylephrine up to 1.0 μg/kg/min with the aim of increasing systemic mean arterial blood pressure 20 mmHg. Invasive haemodynamic parameters, including pulmonary wedge pressures, were captured along with echocardiographic measures of biventricular function before, during phenylephrine infusion at target systemic blood pressure, and 20 min after phenylephrine discontinuation.

RESULTS

Thirty patients were included. Phenylephrine increased mean arterial pressure increased from 78 (±9) mmHg to 98 (±10) mmHg with phenylephrine infusion. Also, pulmonary blood pressure as well as systemic- and pulmonary resistances increased. The ratio between systemic- and pulmonary artery resistances did not change statistically significantly (p = .59). Median cardiac output was 4.35 (interquartile range [IQR] 3.6-5.4) L/min at baseline and increased significantly with phenylephrine infusion (median Δcardiac output was 0.25 [IQR 0.1-0.6] L/min) (p = .012). Pulmonary artery wedge pressure increased from 10.2 (±3.0) mmHg to 11.9 (±3.4) mmHg (p < .001). This was accompanied by significant increases in central venous pressure. Phenylephrine infusion increased left ventricular end-diastolic volume from 105 (±46) mL to 119 (±44) mL (p < .001). All results of phenylephrine infusion were reversed with discontinuation.

CONCLUSION

In haemodynamically stable patients after cardiac surgery, phenylephrine increased PVR and SVR, but did not change the PVR/SVR ratio. Phenylephrine increased biventricular filling pressures and left ventricular end-diastolic area. Consequently, CO increased as ejection fraction was maintained. These findings do not discourage the use of phenylephrine after low-risk cardiac surgery.

REGISTRATION

clinicaltrial.gov (identifier NCT04419662).

Hemodynamic Implications of Prone Positioning in Patients with ARDS

This article is one of ten reviews selected from the Annual Update in Intensive Care and Emergency Medicine 2023. Other selected articles can be found online at https://www.biomedcentral.com/collections/annualupdate2023 . Further information about the Annual Update in Intensive Care and Emergency Medicine is available from https://link.springer.com/bookseries/8901 .

Does tidal volume challenge improve the feasibility of pulse pressure variation in patients mechanically ventilated at low tidal volumes? A systematic review and meta-analysis

BACKGROUND

Pulse pressure variation (PPV) has been widely used in hemodynamic assessment. Nevertheless, PPV is limited in low tidal volume ventilation. We conducted this systematic review and meta-analysis to evaluate whether the tidal volume challenge (TVC) could improve the feasibility of PPV in patients ventilated at low tidal volumes.

METHODS

PubMed, Embase and Cochrane Library inception to October 2022 were screened for diagnostic researches relevant to the predictability of PPV change after TVC in low tidal volume ventilatory patients. Summary receiving operating characteristic curve (SROC), pooled sensitivity and specificity were calculated. Subgroup analyses were conducted for possible influential factors of TVC.

RESULTS

Ten studies with a total of 429 patients and 457 measurements were included for analysis. The predictive performance of PPV was significantly lower than PPV change after TVC in low tidal volume, with mean area under the receiving operating characteristic curve (AUROC) of 0.69 ± 0.13 versus 0.89 ± 0.10. The SROC of PPV change yielded an area under the curve of 0.96 (95% CI 0.94, 0.97), with overall pooled sensitivity and specificity of 0.92 (95% CI 0.83, 0.96) and 0.88 (95% CI 0.76, 0.94). Mean and median cutoff value of the absolute change of PPV (△PPV) were 2.4% and 2%, and that of the percentage change of PPV (△PPV%) were 25% and 22.5%. SROC of PPV change in ICU group, supine or semi-recumbent position group, lung compliance less than 30 cm H₂O group, moderate positive end-expiratory pressure (PEEP) group and measurements devices without transpulmonary thermodilution group yielded 0.95 (95%0.93, 0.97), 0.95 (95% CI 0.92, 0.96), 0.96 (95% CI 0.94, 0.97), 0.95 (95% CI 0.93, 0.97) and 0.94 (95% CI 0.92, 0.96) separately. The lowest AUROCs of PPV change were 0.59 (95% CI 0.31, 0.88) in prone position and 0.73 (95% CI 0.60, 0.84) in patients with spontaneous breathing activity.

CONCLUSIONS

TVC is capable to help PPV overcome limitations in low tidal volume ventilation, wherever in ICU or surgery. The accuracy of TVC is not influenced by reduced lung compliance, moderate PEEP and measurement tools, but TVC should be cautious applied in prone position and patients with spontaneous breathing activity. Trial registration PROSPERO (CRD42022368496). Registered on 30 October 2022.

Non-invasive measurement of digital plethysmographic variability index to predict fluid responsiveness in mechanically ventilated children: A systematic review and meta-analysis of diagnostic test accuracy studies

BACKGROUND

To date, the use of the plethysmographic variability index (PVI) has not been recommended to guide fluid management in the paediatric surgical population. This systematic review and meta-analysis aimed to summarise available evidence about the diagnostic accuracy of digital PVI to predict fluid responsiveness in mechanically ventilated children.

METHODS

We searched the Pubmed, Embase and Web of Science databases, from inception to January 2022, to identify all relevant studies that investigated the ability of the PVI recorded at the finger to predict fluid responsiveness in mechanically ventilated children. Using a random-effects model, we calculated pooled values of diagnostic odds ratio, sensitivity, and specificity of PVI to predict the response to fluid challenge.

RESULTS

Eight studies met the inclusion criteria with a total of 283 patients and 360 fluid challenges. All the studies were carried out in a surgical setting. The area under the summary receiver operating characteristic curve of PVI to predict fluid responsiveness was 0.82. The pooled sensitivity, specificity, and diagnostic odds ratio of PVI for the overall population were 72.4% [95% CI: 65.3-78.7], 65.9% [58.5-72.8], and 9.26 [5.31-16.16], respectively.

CONCLUSION

Our results suggest that digital PVI is a reliable predictor for fluid responsiveness in mechanically ventilated children in the perioperative setting. The diagnostic performance of digital PVI reported in our work for discrimination between responders and non-responders to the fluid challenge was however not as high as previously reported in the adult population.

Point-of-care ultrasonography to predict fluid responsiveness in children: A systematic review and meta-analysis

BACKGROUND

Point-of-care ultrasonography (POCUS) is proposed as a valuable method for hemodynamic monitoring and several ultrasound-based predictors of fluid responsiveness have been studied. The main objective of this study was to assess the accuracy of these predictors in children.

METHODS

PubMed, Embase, Scopus, ClinicalTrials.gov, and Cochrane Library databases were searched for relevant publications through July 2022. Pediatric studies reporting accuracy estimates of ultrasonographic predictors of fluid responsiveness were included since they had used a standard definition of fluid responsiveness and had performed an adequate fluid challenge.

RESULTS

Twenty-three studies involving 1028 fluid boluses were included, and 12 predictors were identified. A positive response to fluid infusion was observed in 59.7% of cases. The vast majority of participants were mechanically ventilated (93.4%). The respiratory variation in aortic blood flow peak velocity (∆Vpeak) was the most studied predictor, followed by the respiratory variation in inferior vena cava diameter (∆IVC). The pooled sensitivity and specificity of ∆Vpeak were 0.84 (95% CI, 0.76-0.90) and 0.82 (95% CI, 0.75-0.87), respectively, and the area under the summary receiver operating characteristic curve (AUSROC) was 0.89 (95% CI, 0.86-0.92). The ∆IVC presented a pooled sensitivity and specificity of 0.79 (95% CI, 0.62-0.90) and 0.70 (95% CI, 0.51-0.84), respectively, and an AUSROC of 0.81 (95% CI, 0.78-0.85). Significant heterogeneity in accuracy estimates across studies was observed.

CONCLUSIONS

POCUS has the potential to accurately predict fluid responsiveness in children. However, only ∆Vpeak was found to be a reliable predictor. There is a lack of evidence supporting the use of POCUS to guide fluid therapy in spontaneously breathing children.

Tidal volume challenge to predict preload responsiveness in patients with acute respiratory distress syndrome under prone position

Background

Prone position is frequently used in patients with acute respiratory distress syndrome (ARDS), especially during the Coronavirus disease 2019 pandemic. Our study investigated the ability of pulse pressure variation (PPV) and its changes during a tidal volume challenge (TVC) to assess preload responsiveness in ARDS patients under prone position.

Methods

This was a prospective study conducted in a 25-bed intensive care unit at a university hospital. We included patients with ARDS under prone position, ventilated with 6 mL/kg tidal volume and monitored by a transpulmonary thermodilution device. We measured PPV and its changes during a TVC (ΔPPV TVC6–8) after increasing the tidal volume from 6 to 8 mL/kg for one minute. Changes in cardiac index (CI) during a Trendelenburg maneuver (ΔCITREND) and during end-expiratory occlusion (EEO) at 8 mL/kg tidal volume (ΔCI EEO8) were recorded. Preload responsiveness was defined by both ΔCITREND ≥ 8% and ΔCI EEO8 ≥ 5%. Preload unresponsiveness was defined by both ΔCITREND < 8% and ΔCI EEO8 < 5%.

Results

Eighty-four sets of measurements were analyzed in 58 patients. Before prone positioning, the ratio of partial pressure of arterial oxygen to fraction of inspired oxygen was 104 ± 27 mmHg. At the inclusion time, patients were under prone position for 11 (2–14) hours. Norepinephrine was administered in 83% of cases with a dose of 0.25 (0.15–0.42) µg/kg/min. The positive end-expiratory pressure was 14 (11–16) cmH2O. The driving pressure was 12 (10–17) cmH2O, and the respiratory system compliance was 32 (22–40) mL/cmH2O. Preload responsiveness was detected in 42 cases. An absolute change in PPV ≥ 3.5% during a TVC assessed preload responsiveness with an area under the receiver operating characteristics (AUROC) curve of 0.94 ± 0.03 (sensitivity: 98%, specificity: 86%) better than that of baseline PPV (0.85 ± 0.05; p = 0.047). In the 56 cases where baseline PPV was inconclusive (≥ 4% and < 11%), ΔPPV TVC6–8 ≥ 3.5% still enabled to reliably assess preload responsiveness (AUROC: 0.91 ± 0.05, sensitivity: 97%, specificity: 81%; p < 0.01 vs. baseline PPV).

Conclusion

In patients with ARDS under low tidal volume ventilation during prone position, the changes in PPV during a TVC can reliably assess preload responsiveness without the need for cardiac output measurements.

Trial registration: ClinicalTrials.gov (NCT04457739). Registered 30 June 2020 —Retrospectively registered, https://clinicaltrials.gov/ct2/show/record/NCT04457739

Right ventricular and pulmonary artery pulse pressure variation and systolic pressure variation for the prediction of fluid responsiveness: an interventional study in coronary artery bypass surgery patients

PURPOSE

Predicting fluid responsiveness is essential when treating surgical or critically ill patients. When using a pulmonary artery catheter, pulse pressure variation and systolic pressure variation can be calculated from right ventricular and pulmonary artery pressure waveforms.

METHODS

We conducted a prospective interventional study investigating the ability of right ventricular pulse pressure variation (PPV_RV) and systolic pressure variation (SPV_RV) as well as pulmonary artery pulse pressure variation (PPV_PA) and systolic pressure variation (SPV_PA) to predict fluid responsiveness in coronary artery bypass (CABG) surgery patients. Additionally, radial artery pulse pressure variation (PPV_ART) and systolic pressure variation (SPV_ART) were calculated. The area under the receiver operating characteristics (AUROC) curve with 95%-confidence interval (95%-CI) was used to assess the capability to predict fluid responsiveness (defined as an increase in cardiac index of > 15%) after a 500 mL crystalloid fluid challenge.

RESULTS

Thirty-three patients were included in the final analysis. Thirteen patients (39%) were fluid-responders with a mean increase in cardiac index of 25.3%. The AUROC was 0.60 (95%-CI 0.38 to 0.81) for PPV_RV, 0.63 (95%-CI 0.43 to 0.83) for SPV_RV, 0.58 (95%-CI 0.38 to 0.78) for PPV_PA, and 0.71 (95%-CI 0.52 to 0.89) for SPV_PA. The AUROC for PPV_ART was 0.71 (95%-CI 0.53 to 0.89) and for SPV_ART 0.78 (95%-CI 0.62 to 0.94). The correlation between pulse pressure variation and systolic pressure variation measurements derived from the different waveforms was weak.

CONCLUSIONS

Right ventricular and pulmonary artery pulse pressure variation and systolic pressure variation seem to be weak predictors of fluid responsiveness in CABG surgery patients.

Fluid challenge in critically ill patients receiving haemodynamic monitoring: a systematic review and comparison of two decades

Introduction

Fluid challenges are widely adopted in critically ill patients to reverse haemodynamic instability. We reviewed the literature to appraise fluid challenge characteristics in intensive care unit (ICU) patients receiving haemodynamic monitoring and considered two decades: 2000–2010 and 2011–2021.

Methods

We assessed research studies and collected data regarding study setting, patient population, fluid challenge characteristics, and monitoring. MEDLINE, Embase, and Cochrane search engines were used. A fluid challenge was defined as an infusion of a definite quantity of fluid (expressed as a volume in mL or ml/kg) in a fixed time (expressed in minutes), whose outcome was defined as a change in predefined haemodynamic variables above a predetermined threshold.

Results

We included 124 studies, 32 (25.8%) published in 2000–2010 and 92 (74.2%) in 2011–2021, overall enrolling 6,086 patients, who presented sepsis/septic shock in 50.6% of cases. The fluid challenge usually consisted of 500 mL (76.6%) of crystalloids (56.6%) infused with a rate of 25 mL/min. Fluid responsiveness was usually defined by a cardiac output/index (CO/CI) increase ≥ 15% (70.9%). The infusion time was quicker (15 min vs 30 min), and crystalloids were more frequent in the 2011–2021 compared to the 2000–2010 period.

Conclusions

In the literature, fluid challenges are usually performed by infusing 500 mL of crystalloids bolus in less than 20 min. A positive fluid challenge response, reported in 52% of ICU patients, is generally defined by a CO/CI increase ≥ 15%. Compared to the 2000–2010 decade, in 2011–2021 the infusion time of the fluid challenge was shorter, and crystalloids were more frequently used.

Dynamic changes of pulse pressure but not of pulse pressure variation during passive leg raising predict preload responsiveness in critically ill patients with spontaneous breathing activity

PURPOSE

To evaluate whether the changes in arterial pulse pressure (PP) and/or pulse pressure variation (PPV) during passive leg raising (PLR) can be used to evaluate preload responsiveness in patients with spontaneous breathing activity.

MATERIALS AND METHODS

Patients ventilated with pressure support mode or totally spontaneously breathing were prospectively included. The values of PP and PPV were recorded before and at the end of PLR. The changes in cardiac index (CI) or the velocity-time integral (VTI) of the left ventricular outflow tract during PLR were tracked by the pulse contour analysis or transthoracic echocardiography. Patients exhibiting an increase in CI ≥ 10% or VTI ≥ 12% during PLR were defined as preload responders.

RESULTS

Among 33 patients included, 28 (80%) received norepinephrine and 14 were preload responders. The increase in PP > 2 mmHg in absolute value (4% in percentage) during PLR (PLR_PP) predicted preload responsiveness with an area under the receiver operating characteristic (AUROC) of 0.76 ± 0.09 (p = 0.003 vs. AUROC of 0.5). The changes in PPV during PLR, however, failed to predict preload responsiveness (p = 0.82 vs. AUROC of 0.5).

CONCLUSION

In patients with full spontaneous breathing activity, PLR-induced changes in PP had a fair ability to assess preload responsiveness even when norepinephrine was administered.

REGISTRATION NUMBER

ClinicalTrials.gov (NCT04369027).

How can assessing hemodynamics help to assess volume status?

In critically ill patients, fluid infusion is aimed at increasing cardiac output and tissue perfusion. However, it may contribute to fluid overload which may be harmful. Thus, volume status, risks and potential efficacy of fluid administration and/or removal should be carefully evaluated, and monitoring techniques help for this purpose. Central venous pressure is a marker of right ventricular preload. Very low values indicate hypovolemia, while extremely high values suggest fluid harmfulness. The pulmonary artery catheter enables a comprehensive assessment of the hemodynamic profile and is particularly useful for indicating the risk of pulmonary oedema through the pulmonary artery occlusion pressure. Besides cardiac output and preload, transpulmonary thermodilution measures extravascular lung water, which reflects the extent of lung flooding and assesses the risk of fluid infusion. Echocardiography estimates the volume status through intravascular volumes and pressures. Finally, lung ultrasound estimates lung edema. Guided by these variables, the decision to infuse fluid should first consider specific triggers, such as signs of tissue hypoperfusion. Second, benefits and risks of fluid infusion should be weighted. Thereafter, fluid responsiveness should be assessed. Monitoring techniques help for this purpose, especially by providing real time and precise measurements of cardiac output. When decided, fluid resuscitation should be performed through fluid challenges, the effects of which should be assessed through critical endpoints including cardiac output. This comprehensive evaluation of the risk, benefits and efficacy of fluid infusion helps to individualize fluid management, which should be preferred over a fixed restrictive or liberal strategy.

The association between carotid flow time and fluid responsiveness in children under general anesthesia

BACKGROUND

Fluid administration in children undergoing surgery requires precision, however, determining fluid responsiveness can be challenging. Ultrasound has been used widely in the emergency department and intensive care units as a noninvasive, bedside manner of determining volume status, but the intraoperative period presents unique challenges as often the chest and abdomen are inaccessible for ultrasound. We investigate whether carotid artery ultrasound, specifically carotid flow time, can be used to determine fluid responsiveness in children under general anesthesia.

METHODS

Prospective observational study of 87 children ages 1-12 years who were scheduled for elective noncardiac surgery. Ultrasound of the carotid artery and heart was performed at three time points: (1) after inhalational induction of anesthesia with the subject spontaneously breathing, (2) during positive pressure ventilation through endotracheal tube or supraglottic airway with tidal volume set at 8 ml/kg with PEEP of 10 cmH₂ O, and (3) after a 10 ml/kg fluid bolus. Carotid flow time and cardiac output were measured from saved images.

RESULTS

Corrected carotid flow time (FTc) increased with initiation of positive pressure ventilation in both fluid responders and nonresponders (352.7 vs. 365.3 msec, p = .005 in fluid responders; 348.3 vs. 365.2 msec, p = .001 in nonresponders). FTc increased after fluid bolus in both responders and nonresponders (365.3 vs. 397.6 msec, p < .001 in fluid responders; 365.2 vs. 397.2 msec, p < .001 in nonresponders). However, baseline FTc during spontaneous ventilation or positive pressure ventilation prior to fluid bolus was not associated with fluid responsiveness.

DISCUSSION

Flow time increases with initiation of positive pressure ventilation and after administration of a fluid bolus. FTc may serve as an indicator of fluid status but does not predict fluid responsiveness in children under general anesthesia.

Passive leg raising-induced changes in pulse pressure variation to assess fluid responsiveness in mechanically ventilated patients: a multicentre prospective observational study

BACKGROUND

Passive leg raising-induced changes in cardiac index can be used to predict fluid responsiveness. We investigated whether passive leg raising-induced changes in pulse pressure variation (ΔPPV_PLR) can also predict fluid responsiveness in mechanically ventilated patients.

METHODS

In this multicentre prospective observational study, we included 270 critically ill patients on mechanical ventilation in whom volume expansion was indicated because of acute circulatory failure. We did not include patients with cardiac arrythmias. Cardiac index and PPV were measured before/during a passive leg raising test and before/after volume expansion. A volume expansion-induced increase in cardiac index of >15% defined fluid responsiveness. To investigate whether ΔPPV_PLR can predict fluid responsiveness, we determined areas under the receiver operating characteristic curves (AUROCs) and grey zones for relative and absolute ΔPPV_PLR.

RESULTS

Of the 270 patients, 238 (88%) were on controlled mechanical ventilation with no spontaneous breathing activity and 32 (12%) were on pressure support ventilation. The median tidal volume was 7.1 (inter-quartile range [IQR], 6.6-7.6) ml kg^-1 ideal body weight. One hundred sixty-four patients (61%) were fluid responders. Relative and absolute ΔPPV_PLR predicted fluid responsiveness with an AUROC of 0.92 (95% confidence interval [95% CI], 0.88-0.95; P<0.001) each. The grey zone for relative and absolute ΔPPV_PLR included 4.8% and 22.6% of patients, respectively. These results were not affected by ventilatory mode and baseline characteristics (type of shock, centre, vasoactive treatment).

CONCLUSIONS

Passive leg raising-induced changes in pulse pressure variation accurately predict fluid responsiveness with a small grey zone in critically ill patients on mechanical ventilation.

CLINICAL TRIAL REGISTRATION

NCT03225378.

Efficacy of using tidal volume challenge to improve the reliability of pulse pressure variation reduced in low tidal volume ventilated critically ill patients with decreased respiratory system compliance

Background

The prediction accuracy of pulse pressure variation (PPV) for fluid responsiveness was proposed to be unreliable in low tidal volume (Vt) ventilation. It was suggested that changes in PPV obtained by transiently increasing Vt to 8 ml/kg accurately predicted fluid responsiveness even in subjects receiving low Vt. We assessed whether the changes in PPV induced by a Vt challenge predicted fluid responsiveness in our critically ill subjects ventilated with low Vt 6 ml/kg.

Methods

This study is a prospective single-center study. PPV and other parameters were measured at a Vt of 6 mL/kg, 8 mL/kg, and after volume expansion. The prediction accuracy of PPV and other parameters for fluid responsiveness before and after tidal volume challenge was also analyzed using receiver operating characteristic (ROC) curves.

Results

Thirty-one of the 76 subjects enrolled in the study were responders (41%). Respiratory system compliance of all subjects decreased significantly (26 ± 4.3). The PPV values were significantly higher in the responder group than the non-responder group before (8.8 ± 2.7 vs 6.8 ± 3.1) or after (13.0 ± 1.7 vs 8.5 ± 3.0) Vt challenge. In the receiver operating characteristic curve (ROC) analysis, PPV₆ showed unsatisfactory predictive capability with an area under the curve (AUC) of 0.69 (95%CI, 0.57–0.79, p = 0.002) at a Vt of 6 mL/kg. PPV₈ andΔPPV_6–8 showed good predictive capability with an AUC of 0.90 (95% CI, 0.81–0.96, p < 0.001) and 0.90 (95% CI, 0.80–0.95, P < 0.001) respectively. The corresponding cutoff values were 11% for PPV₈ and 2% for ΔPPV_6–8.

Conclusions

PPV shows a poor operative performance as a predictor of fluid responsiveness in critically ill subjects ventilated with a tidal volume of 6 mL/ kg. Vt challenge could improve the predictive accuracy of PPV to a good but not excellent extent when respiratory system compliance decreased significantly.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12871-022-01676-8.

Respiratory-Cardiovascular Interactions During Mechanical Ventilation: Physiology and Clinical Implications

Positive-pressure inspiration and positive end-expiratory pressure (PEEP) increase pleural, alveolar, lung transmural, and intra-abdominal pressure, which decrease right and left ventricular (RV; LV) preload and LV afterload and increase RV afterload. The magnitude and clinical significance of the resulting changes in ventricular function are determined by the delivered tidal volume, the total level of PEEP, the compliance of the lungs and chest wall, intravascular volume, baseline RV and LV function, and intra-abdominal pressure. In mechanically ventilated patients, the most important, adverse consequences of respiratory-cardiovascular interactions are a PEEP-induced reduction in cardiac output, systemic oxygen delivery, and blood pressure; RV dysfunction in patients with ARDS; and acute hemodynamic collapse in patients with pulmonary hypertension. On the other hand, the hemodynamic changes produced by respiratory-cardiovascular interactions can be beneficial when used to assess volume responsiveness in hypotensive patients and by reducing dyspnea and improving hypoxemia in patients with cardiogenic pulmonary edema. Thus, a thorough understanding of the physiological principles underlying respiratory-cardiovascular interactions is essential if critical care practitioners are to anticipate, recognize, manage, and utilize their hemodynamic effects. © 2022 American Physiological Society. Compr Physiol 12:1-24, 2022.

Correlation between Carotid and Brachial Artery Velocity Time Integral and Their Comparison to Pulse Pressure Variation and Stroke Volume Variation for Assessing Fluid Responsiveness

Background

Fluid boluses are used in hemodynamically unstable patients with presumed hypovolemia, to improve tissue perfusion, in the perioperative period. Now less invasive methods, such as pulse pressure variation (PPV) and stroke volume variation (SVV) are increasingly being used. We investigated correlation between carotid and brachial artery velocity time integral (VTI) and compared both with PPV and SVV.

Methods

We recruited 27 patients undergoing supra-major abdominal surgeries. When indicated (hypotension or increased lactate), a fluid bolus was given after measuring carotid and brachial artery VTI, PPV, and SVV. The change in SV was noted and patients were categorized as responders if the SV increased by >15%. We performed Bland Altman Agreement and calculated best sensitivity and specificity for the parameters.

Results

Patients were found to be fluid responders on 29 instances. The correlation between PPV, SVV, carotid and brachial artery VTI was poor and the limits of agreement between them were wide. The Area under Curve (AUC) for PPV was 0.69, for SVV was 0.63, while those of Carotid and Brachial artery VTI (TAP and flow) were (0.53 and 0.54 for carotid) and (0.51 and 0.56 for brachial) respectively.

Conclusion

We found poor agreement and weak correlation between both VTi (TAP and flow) measured at carotid and brachial arteries, suggesting that the readings at brachial vessel cannot be used interchangeably with those at carotid artery. The PPV and SVV were better than these parameters for predicting fluid responsiveness; however, their predictive ability (AUROC), sensitivity and specificity were much lower than previously reported. Further studies in this area are therefore required (CTRI Reg No: CTRI/2017/08/009243).

How to cite this article

Joshi M, Dhakane P, Bhosale SJ, Phulambrikar R, Kulkarni AP. Correlation between Carotid and Brachial Artery Velocity Time Integral and Their Comparison to Pulse Pressure Variation and Stroke Volume Variation for Assessing Fluid Responsiveness. Indian J Crit Care Med 2022;26(2):179–184.

Central Venous-to-Arterial CO2 Difference-Assisted Goal-Directed Hemodynamic Management During Major Surgery-A Randomized Controlled Trial

BACKGROUND

Different goals have guided goal-directed therapy (GDT). Protocols aiming for central venous-to-arterial carbon dioxide gap (DCO2) <6 mm Hg have improved organ function in septic shock. Evidence for use of DCO2 in the perioperative period is scarce. We aimed to determine if a GDT protocol using central venous saturation of oxygen (SCvo2) and DCO2 reduced organ dysfunction and intensive care unit (ICU) stay in American Society of Anesthesiologist (ASA) I and II patients undergoing major surgeries compared to pragmatic goal-directed care.

METHODS

One hundred patients were randomized. Arterial and venous blood-gas values were recorded every 2 hours perioperatively for all patients. Intervention group (GrI) with access to both values was managed per protocol based on DCO2 and SCvo2. Dobutamine infusion 3 to 5 µg/kg/min started if DCO2 >6 mm Hg after correcting all macrocirculatory end points. Control group (GrC) had access only to arterial-gas values and managed per "conventional" goals without DCO2 or SCvo2. Patients were followed for 48 hours after surgery. Organ dysfunction, sequential organ failure assessment (SOFA) scores-primary outcome, length of stay in ICU, and duration of postoperative mechanical ventilation and hospital stay were recorded. The patient, surgeons, ICU team, and analyzer were blinded to group allocation.

RESULTS

The groups (44 each) did not significantly differ with respect to baseline characteristics. Perioperative fluids, blood products, and vasopressors used did not significantly differ. The GrI had less organ dysfunction although not significant (79% vs 66%; P = .2). Length of ICU stay in the GrI was significantly less (1.52; standard deviation [SD], 0.82 vs 2.18; SD, 1.08 days; P = .002). Mechanical ventilation duration (0.9 days in intervention versus 0.6 days in control; P = .06) and length of hospital stay did not significantly differ between the groups. Perioperative DCO2 (5.8 vs 8.4 mm Hg; P < .001) and SCvo2 (73.5 vs 68.4 mm Hg; P < .001) were significantly better in the GrI.

CONCLUSIONS

GDT guided by DCO2 did not improve organ function in our cohort. It resulted in greater use of dobutamine, improved tissue oxygen parameters, and decreased length of ICU stay. More evidence is needed for the routine use of DCO2 in sicker patients. In the absence of cardiac output monitors, it may be a readily available, less-expensive, and underutilized parameter for major surgical procedures.

Comparison of vena cava distensibility index and pulse pressure variation for the evaluation of intravascular volume in critically ill children

OBJECTIVE

In this study, the authors aimed to evaluate the effectiveness of the vena cava distensibility index and pulse pressure variation as dynamic parameters for estimating intravascular volume in critically ill children.

METHODS

Patients aged 1 month to 18 years, who were hospitalized in the present study's pediatric intensive care unit, were included in the study. The patients were divided into two groups according to central venous pressure: hypovolemic (< 8 mmHg) and non-hypovolemic (central venous pressure ≥ 8 mmHg) groups. In both groups, vena cava distensibility index was measured using bedside ultrasound and pulse pressure variation. Measurements were recorded and evaluated under arterial monitoring.

RESULTS

In total, 19 (47.5%) of the 40 subjects included in the study were assigned to the central venous pressure ≥ 8 mmHg group, and 21 (52.5%) to the central venous pressure < 8 mmHg group. A moderate positive correlation was found between pulse pressure variation and vena cava distensibility index (r = 0.475, p < 0.01), while there were strong negative correlations of central venous pressure with pulse pressure variation and vena cava distensibility index (r = -0.628, p < 0.001 and r = -0.760, p < 0.001, respectively). In terms of predicting hypovolemia, the predictive power for vena cava distensibility index was > 16% (sensitivity, 90.5%; specificity, 94.7%) and that for pulse pressure variation was > 14% (sensitivity, 71.4%; specificity, 89.5%).

CONCLUSION

Vena cava distensibility index has higher sensitivity and specificity than pulse pressure variation for estimating intravascular volume, along with the advantage of non-invasive bedside application.

Does the definition of fluid responsiveness affect passive leg raising reliability? A methodological ancillary analysis from a multicentric study

BACKGROUND

Fluid challenge (FC) is often adopted as gold standard used to assess the reliability of passive leg raising (PLR) in predicting fluid responsiveness in the intensive care unit (ICU). This study aimed to address the impact of the different definitions and timings used to assess FC response on PLR reliability.

METHODS

Ancillary study from a data set of a multicentric study in 85 ICU patient with acute circulatory failure who received a FC (500 mL of crystalloids in 10 minutes) within the first 48h of ICU admission, preceded by PLR in 30 patients. FC response was assessed considering the changes in cardiac index (CI) and stroke volume index (SVI) using different thresholds and at different timepoints.

RESULTS

The definitions of fluid responsiveness by using CI or SVI with a 15% increase after 10 minutes were associated to the best performances of the PLR [AUC (95% CI) 0.94 (0.83-1.01); vs. AUC (95% CI) 0.95 (0.87-1.02)]. The sensitivity of the PLR by adopting the CI or the SVI as reference variable ranged from 54.1% to 67.6% and from 81.5% to 100.0%; the specificity from 65.9% to 78.0% and from 79.5% to 100.0%, respectively. Considering all the subgroups, the number of responders 10 minutes after FC administration was higher as compared to 15 and 30 minutes (140 vs. 120 and 125, respectively, p < 0.05).

CONCLUSIONS

The reliability of the PLR test to predict fluid responsiveness depends on the definition of FC adopted. The timing of FC outcome assessment affected the overall fluid responsiveness.

Changes in pulse pressure variation to assess preload responsiveness in mechanically ventilated patients with spontaneous breathing activity: an observational study

BACKGROUND

Pulse pressure variation (PPV) is not reliable in predicting preload responsiveness in patients receiving mechanical with spontaneous breathing (SB) activity. We hypothesised that an increase in PPV after a tidal volume (V_T) challenge (TVC) or a decrease in PPV during passive leg raising (PLR) can predict preload responsiveness in such cases.

METHODS

This prospective observational study was performed in two ICUs and included patients receiving mechanical ventilation with SB, for whom the treating physician decided to test preload responsiveness. Transthoracic echocardiography was used to measure the velocity-time integral (VTI) of the left ventricular outflow tract. Patients exhibiting an increase in VTI ≥12% during PLR were defined as PLR+ patients (or preload responders). Then, a TVC was performed by increasing V_T by 2 ml kg^-1 predicted body weight (PBW) for 1 min. PPV was recorded at each step.

RESULTS

Fifty-four patients (Simplified Acute Physiology Score II: 60 (25) ventilated with a V_T of 6.5 (0.8) ml kg^-1 PBW, were included. Twenty-two patients were PLR+. The absolute decrease in PPV during PLR and the absolute increase in PPV during TVC discriminated between PLR+ and PLR- patients with area under the receiver operating characteristic (AUROC) curve of 0.78 and 0.73, respectively, and cut-off values of -1% and +2%, respectively. Those AUROC curve values were similar but were significantly different from that of baseline PPV (0.61).

CONCLUSION

In patients undergoing mechanical ventilation with SB activity, PPV does not predict preload responsiveness. However, the decrease in PPV during PLR and the increase in PPV during a TVC help discriminate preload responders from non-responders with moderate accuracy.

CLINICAL TRIAL REGISTRATION

NCT04369027 (ClinicalTrials.gov).

Novel Method of Calculating Pulse Pressure Variation to Predict Fluid Responsiveness to Transfusion in Very Low Birth Weight Infants

A novel technique was used to calculate pulse pressure variation. The algorithm reliably predicted fluid responsiveness to transfusion, with a receiver operating characteristic area under the curve of 0.89. This technique may assist clinicians in the management of fluids and vasoactive medications for premature infants.

Ability of Carotid Corrected Flow Time to Predict Fluid Responsiveness in Patients Mechanically Ventilated Using Low Tidal Volume after Surgery

Predicting fluid responsiveness in patients under mechanical ventilation with low tidal volume (VT) is challenging. This study evaluated the ability of carotid corrected flow time (FTc) assessed by ultrasound for predicting the fluid responsiveness during low VT ventilation. Patients under postoperative mechanical ventilation and clinically diagnosed with hypovolemia were enrolled. Carotid FTc and pulse pressure variation (PPV) were measured at VT of 6 and 10 mL/kg predicted body weight (PBW). FTc was calculated using both Bazett’s (FTcB) and Wodey’s (FTcW) formulas. Fluid responsiveness was defined as a ≥15% increase in the stroke volume index assessed by FloTrac/Vigileo monitor after administration of 8 mL/kg of balanced crystalloid. Among 36 patients, 16 (44.4%) were fluid responders. The areas under the receiver operating characteristic curves (AUROCs) for the FTcB at VT of 6 and 10 mL/kg PBW were 0.897 (95% confidence interval [95% CI]: 0.750–0.973) and 0.895 (95% CI: 0.748–0.972), respectively. The AUROCs for the FTcW at VT of 6 and 10 mL/kg PBW were 0.875 (95% CI: 0.722–0.961) and 0.891 (95% CI: 0.744–0.970), respectively. However, PPV at VT of 6 mL/kg PBW (AUROC: 0.714, 95% CI: 0.539–0.852) showed significantly lower accuracy than that of PPV at VT of 10 mL/kg PBW (AUROC: 0.867, 95% CI: 0.712–0.957; p = 0.034). Carotid FTc can predict fluid responsiveness better than PPV during low VT ventilation. However, further studies using automated continuous monitoring system are needed before its clinical use.

Dynamic Indices Fail to Predict Fluid Responsiveness in Patients Undergoing One-Lung Ventilation for Thoracoscopic Surgery

Thoracic surgery using CO₂ insufflation maintains closed-chest one-lung ventilation (OLV) that may provide the necessary heart–lung interaction for the dynamic indices to predict fluid responsiveness. We studied whether pulse pressure variation (PPV) and stroke volume variation (SVV) can predict fluid responsiveness during thoracoscopic surgery. Forty patients were enrolled in the study. OLV was performed with a tidal volume of 6 mL/kg at a positive end-expiratory pressure of 5 cm H₂O, while CO₂ was insufflated to the contralateral side at 8 mm Hg. Patients whose stroke volume index (SVI) increased ≥15% after fluid challenge (7 mL/kg) were defined as fluid responders. The predictive ability of PPV and SVV on fluid responsiveness was investigated using the area under the receiver-operator characteristic curve (AUROC), which was also assessed according to the right or left lateral decubitus position considering the intrathoracic location of the right-sided superior vena cava. AUROCs of PPV and SVV for predicting fluid responsiveness were 0.65 (95% confidence interval 0.47–0.83, p = 0.113) and 0.64 (95% confidence interval 0.45–0.82, p = 0.147), respectively. The AUROCs of indices did not exhibit any statistical significance according to position. Dynamic indices of preload cannot predict fluid responsiveness during one-lung ventilation with CO₂ gas insufflation.

Changes in arterial blood pressure characteristics following an extrasystolic beat or a fast 50 ml fluid challenge do not predict fluid responsiveness during cardiac surgery

Prediction of fluid responsiveness is essential in perioperative goal directed therapy, but dynamic tests of fluid responsiveness are not applicable during open-chest surgery. We hypothesised that two methods could predict fluid responsiveness during cardiac surgery based on their ability to alter preload and thereby induce changes in arterial blood pressure characteristics: (1) the change caused by extrasystolic beats and (2) the change caused by a fast infusion of 50 ml crystalloid (micro-fluid challenge). Arterial blood pressure and electrocardiogram waveforms were collected during surgical preparation of the left internal mammary artery in patients undergoing coronary artery bypass surgery. Patients received a fluid challenge (5 ml/kg ideal body weight). The first 50 ml were infused in 10 s and comprised the micro-fluid challenge. Predictor variables were defined as post-ectopic beat changes (compared with sinus beats preceding ectopy) in arterial blood pressure characteristics, such as pulse pressure and systolic pressure, or micro-fluid challenge induced changes in the same blood pressure characteristics. Patients were considered fluid responsive if stroke volume index increased by 15% or more after the full fluid challenge. Diagnostic accuracy was calculated by the area under the receiver operating characteristics curve (AUC). Fifty-six patients were included for statistical analysis. Thirty-one had extrasystoles. The maximal AUC was found for the extrasystolic change in pulse pressure and was 0.70 (CI [0.35 to 1.00]). The micro-fluid challenge method generally produced lower AUC point estimates. Extrasystoles did not predict fluid responsiveness with convincing accuracy in patients undergoing cardiac surgery and changes in arterial waveform indices following a micro-fluid challenge could not predict fluid responsiveness. Given a low number of fluid responders and inherently reduced statistical power, our data does not support firm conclusions about the utility of the extrasystolic method. CLINICAL TRIAL REGISTRATION: Unique identifier: NCT02903316. https://clinicaltrials.gov/ct2/show/NCT02903316?cond=NCT02903316&rank=1 .

Effects of positive end-expiratory pressure on the predictability of fluid responsiveness in acute respiratory distress syndrome patients

The prediction accuracy of pulse pressure variation (PPV) for fluid responsiveness was suggested to be unreliable in low tidal volume (VT) ventilation. However, high PEEP can cause ARDS patients relatively hypovolemic and more fluid responsive. We hypothesized that high PEEP 15 cmH₂O can offset the disadvantage of low VT and improve the predictive performance of PPV. We prospectively enrolled 27 hypovolemic ARDS patients ventilated with low VT 6 ml/kg and three levels of PEEP (5, 10, 15 cmH₂O) randomly. Each stage lasted for at least 5 min to allow for equilibration of hemodynamics and pulmonary mechanics. Then, fluid expansion was given with 500 ml hydroxyethyl starch (Voluven 130/70). The hemodynamics and PPV were automatically measured with a PiCCO2 monitor. The PPV values were significantly higher during PEEP15 than those during PEEP5 and PEEP10. PPV during PEEP15 precisely predicts fluid responsiveness with a cutoff value 8.8% and AUC (area under the ROC curve) of ROC (receiver operating characteristic curve) 0.847, higher than the AUC during PEEP5 (0.81) and PEEP10 (0.668). Normalizing PPV with driving pressure (PPV/Driving-P) increased the AUC of PPV to 0.875 during PEEP15. In conclusions, high PEEP 15 cmH₂O can counteract the drawback of low VT and preserve the predicting accuracy of PPV in ARDS patients.

Prediction of fluid responsiveness using lung recruitment manoeuvre in paediatric patients receiving lung-protective ventilation: A prospective observational study

BACKGROUND

Pressure-based dynamic variables are poor predictors of fluid responsiveness in children, and their predictability is expected to reduce further during lung-protective ventilation with a low tidal volume.

OBJECTIVE

We hypothesised that lung recruitment manoeuvre (LRM)-induced changes in dynamic variables improve their ability to predict fluid responsiveness in children.

DESIGN

Prospective observational study.

SETTING

Tertiary care children's hospital, single-centre study performed from June 2017 to May 2019.

PATIENTS

We included patients less than 7 years of age undergoing cardiac surgery. Neonates and patients with pulmonary hypertension, significant dysrhythmia, ventricular ejection fraction of less than 30% or pulmonary disease were excluded.

INTERVENTION

All patients were provided with lung-protective volume-controlled ventilation (tidal volume 6 ml kg-1, positive end-expiratory pressure 6 cmH2O). A LRM was applied with a continuous inspiratory pressure of 25 cmH2O for 20 s.

MAIN OUTCOME MEASURE

The ability of dynamic variables to predict fluid responsiveness was evaluated by the area under the receiver operating characteristic curve [area under the curve (AUC)]. Fluid responsiveness was defined as an increase in the cardiac index by more than 15% with crystalloid administration (10 ml kg-1).

RESULTS

Thirty patients were included in the final analysis, of whom 19 were responders. The baseline pleth variability index (PVI) (AUC 0.794, 95% confidence interval 0.608 to 0.919, P < 0.001) and LRM-induced PVI (AUC 0.711, 95% confidence interval 0.517 to 0.861, P = 0.026) could predict fluid responsiveness. The respiratory variation of pulse oximetry photoplethysmographic waveform and pulse pressure variation did not predict fluid responsiveness regardless of the LRM.

CONCLUSION

The PVI is effective in predicting fluid responsiveness in paediatric patients with lung-protective ventilation regardless of a LRM. However, the LRM did not improve the ability of the other dynamic variables to predict fluid responsiveness in these patients.

CLINICAL TRIAL REGISTRATION

www.clinicaltrials.gov identifier: NCT03184961.

Mini fluid chAllenge aNd End-expiratory occlusion test to assess flUid responsiVEness in the opeRating room (MANEUVER study): A multicentre cohort study

BACKGROUND

The fluid challenge response in surgical patients can be predicted by functional haemodynamic tests. Two tests, the mini-fluid challenge (mini-FC) and end-expiratory occlusion test (EEOT), have been assessed in a few small single-centre studies with conflicting results. In general, functional haemodynamic tests have not performed reliably in predicting fluid responsiveness in patients undergoing laparotomy.

OBJECTIVE

This trial is designed to address and compare the reliability of the EEOT and the mini-FC in predicting fluid responsiveness during laparotomy.

DESIGN

Prospective, multicentre study.

SETTING

Three university hospitals in Italy.

PATIENTS

A total of 103 adults patients scheduled for elective laparotomy with invasive arterial monitoring.

INTERVENTIONS

The study protocol evaluated the changes in the stroke volume index (SVI) 20 s (EEOT20) and 30 s (EEOT30) after an expiratory hold and after a mini-FC of 100 ml over 1 min. Fluid responsiveness required an increase in SVI at least 10% following 4 ml kg-1 of Ringer's solution fluid challenge infused over 10 min.

MAIN OUTCOME MEASUREMENTS

Haemodynamic data, including SVI, were obtained from pulse contour analysis. The area under the receiver operating characteristic curves of the tests were compared with assess fluid responsiveness.

RESULTS

Fluid challenge administration induced an increase in SVI at least 10% in 51.5% of patients. The rate of fluid responsiveness was comparable among the three participant centres (P = 0.10). The area under the receiver operating characteristic curves (95% CI) of the changes in SVI after mini-FC was 0.95 (0.88 to 0.98), sensitivity 98.0% (89.5 to 99.6) and specificity 86.8% (75.1 to 93.4) for a cut-off value of 4% of increase in SVI. This was higher than the SVI changes after EEOT20, 0.67 (0.57 to 0.76) and after EEOT30, 0.73 (0.63 to 0.81).

CONCLUSION

In patients undergoing laparotomy the mini-FC reliably predicted fluid responsiveness with high-sensitivity and specificity. The EEOT showed poor discriminative value and cannot be recommended for assessment of fluid responsiveness in this surgical setting.

TRIAL REGISTRATION

NCT03808753.

Perioperative hemodynamic optimization: from guidelines to implementation-an experts' opinion paper

Despite a large body of evidence, the implementation of guidelines on hemodynamic optimization and goal-directed therapy remains limited in daily routine practice. To facilitate/accelerate this implementation, a panel of experts in the field proposes an approach based on six relevant questions/answers that are frequently mentioned by clinicians, using a critical appraisal of the literature and a modified Delphi process. The mean arterial pressure is a major determinant of organ perfusion, so that the authors unanimously recommend not to tolerate absolute values below 65 mmHg during surgery to reduce the risk of postoperative organ dysfunction. Despite well-identified limitations, the authors unanimously propose the use of dynamic indices to rationalize fluid therapy in a large number of patients undergoing non-cardiac surgery, pending the implementation of a "validity criteria checklist" before applying volume expansion. The authors recommend with a good agreement mini- or non-invasive stroke volume/cardiac output monitoring in moderate to high-risk surgical patients to optimize fluid therapy on an individual basis and avoid volume overload. The authors propose to use fluids and vasoconstrictors in combination to achieve optimal blood flow and maintain perfusion pressure above the thresholds considered at risk. Although purchase of disposable sensors and stand-alone monitors will result in additional costs, the authors unanimously acknowledge that there are data strongly suggesting this may be counterbalanced by a sustained reduction in postoperative morbidity and hospital lengths of stay. Beside existing guidelines, knowledge and explicit clinical reasoning tools followed by decision algorithms are mandatory to implement individualized hemodynamic optimization strategies and reduce postoperative morbidity and duration of hospital stay in high-risk surgical patients.

Respiratory Variation in Aortic Blood Flow Velocity in Hemodynamically Unstable, Ventilated Neonates: A Pilot Study of Fluid Responsiveness

OBJECTIVES

To assess whether respiratory variation in aortic blood flow peak velocity can predict preload responsiveness in mechanically ventilated and hemodynamically unstable neonates.

DESIGN

Prospective observational diagnostic accuracy study.

SETTING

Third-level neonatal ICU.

PATIENTS

Hemodynamically unstable neonates under mechanical ventilation.

INTERVENTIONS

Fluid challenge with 10 mL/kg of normal saline over 20 minutes.

MEASUREMENTS AND MAIN RESULTS

Respiratory variation in aortic blood flow peak velocity and superior vena cava flow were measured at baseline (T0), immediately upon completion of the fluid infusion (T1), and at 1 hour after fluid administration (T2). Our main outcome was preload responsiveness which was defined as an increase in superior vena cava flow of at least 10% from T0 to T1. Forty-six infants with a median (interquartile range) gestational age of 30.5 weeks (28-36 wk) were included. Twenty-nine infants (63%) were fluid responders, and 17 (37%) were nonresponders Fluid responders had a higher baseline (T0) respiratory variation in aortic blood flow peak velocity than nonresponders (9% [8.2-10.8] vs 5.5% [3.7-6.6]; p < 0.001). Baseline respiratory variation in aortic blood flow peak velocity was correlated with the increase in superior vena cava flow from T0 to T1 (rho = 0.841; p < 0.001). The area under the receiver operating characteristic curve of respiratory variation in aortic blood flow peak velocity to predict preload responsiveness was 0.912 (95% CI, 0.82-1). A respiratory variation in aortic blood flow peak velocity cut-off point of 7.8% provided a 90% sensitivity (95% CI, 71-97), 88% specificity (95% CI, 62-98), 7.6 positive likelihood ratio (95% CI, 2-28), and 0.11 negative likelihood ratio (95% CI, 0.03-0.34) to predict preload responsiveness.

CONCLUSIONS

Respiratory variation in aortic blood flow velocity may be useful to predict the immediate response to a fluid challenge in hemodynamically unstable neonates under mechanical ventilation. If our results are confirmed, this measurement could be used to guide safe and individualized fluid resuscitation in critically ill neonates.

Do changes in pulse pressure variation and inferior vena cava distensibility during passive leg raising and tidal volume challenge detect preload responsiveness in case of low tidal volume ventilation?

Background

In patients ventilated with tidal volume (Vt) < 8 mL/kg, pulse pressure variation (PPV) and, likely, the variation of distensibility of the inferior vena cava diameter (IVCDV) are unable to detect preload responsiveness. In this condition, passive leg raising (PLR) could be used, but it requires a measurement of cardiac output. The tidal volume (Vt) challenge (PPV changes induced by a 1-min increase in Vt from 6 to 8 mL/kg) is another alternative, but it requires an arterial line. We tested whether, in case of Vt = 6 mL/kg, the effects of PLR could be assessed through changes in PPV (ΔPPV_PLR) or in IVCDV (ΔIVCDV_PLR) rather than changes in cardiac output, and whether the effects of the Vt challenge could be assessed by changes in IVCDV (ΔIVCDV_Vt) rather than changes in PPV (ΔPPV_Vt).

Methods

In 30 critically ill patients without spontaneous breathing and cardiac arrhythmias, ventilated with Vt = 6 mL/kg, we measured cardiac index (CI) (PiCCO2), IVCDV and PPV before/during a PLR test and before/during a Vt challenge. A PLR-induced increase in CI ≥ 10% defined preload responsiveness.

Results

At baseline, IVCDV was not different between preload responders (n = 15) and non-responders. Compared to non-responders, PPV and IVCDV decreased more during PLR (by − 38 ± 16% and − 26 ± 28%, respectively) and increased more during the Vt challenge (by 64 ± 42% and 91 ± 72%, respectively) in responders. ∆PPV_PLR, expressed either as absolute or as percent relative changes, detected preload responsiveness (area under the receiver operating curve, AUROC: 0.98 ± 0.02 for both). ∆IVCDV_PLR detected preload responsiveness only when expressed in absolute changes (AUROC: 0.76 ± 0.10), not in relative changes. ∆PPV_Vt, expressed as absolute or percent relative changes, detected preload responsiveness (AUROC: 0.98 ± 0.02 and 0.94 ± 0.04, respectively). This was also the case for ∆IVCDV_Vt, but the diagnostic threshold (1 point or 4%) was below the least significant change of IVCDV (9[3–18]%).

Conclusions

During mechanical ventilation with Vt = 6 mL/kg, the effects of PLR can be assessed by changes in PPV. If IVCDV is used, it should be expressed in percent and not absolute changes. The effects of the Vt challenge can be assessed on PPV, but not on IVCDV, since the diagnostic threshold is too small compared to the reproducibility of this variable.

Trial registration: Agence Nationale de Sécurité du Médicament et des Produits de santé: ID-RCB: 2016-A00893-48.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13054-021-03515-7.