Clinical relevance of pulse pressure variations for predicting fluid responsiveness in mechanically ventilated intensive care unit patients: the grey zone approach

Predictors, Prevalence, and Outcomes of Early Crystalloid Responsiveness Among Initially Hypotensive Patients With Sepsis and Septic Shock

OBJECTIVES

The prevalence of responsiveness to initial fluid challenge among hypotensive sepsis patients is unclear. To avoid fluid overload, and unnecessary treatment, it is important to differentiate these phenotypes. We aimed to 1) determine the proportion of hypotensive sepsis patients sustaining favorable hemodynamic response after initial fluid challenge, 2) determine demographic and clinical risk factors that predicted refractory hypotension, and 3) assess the association between timeliness of fluid resuscitation and refractoriness.

DESIGN

Secondary analysis of a prospective, multisite, observational, consecutive-sample cohort.

SETTING

Nine tertiary and community hospitals over 1.5 years.

PATIENTS

Inclusion criteria 1) suspected or confirmed infection, 2) greater than or equal to two systemic inflammatory response syndrome criteria, 3) systolic blood pressure less than 90 mm Hg, greater than 40% decrease from baseline, or mean arterial pressure less than 65 mm Hg.

MEASUREMENTS AND MAIN RESULTS

Sex, age, heart failure, renal failure, immunocompromise, source of infection, initial lactate, coagulopathy, temperature, altered mentation, altered gas exchange, and acute kidney injury were used to generate a risk score. The primary outcome was sustained normotension after fluid challenge without vasopressor titration. Among 3,686 patients, 2,350 (64%) were fluid responsive. Six candidate risk factors significantly predicted refractoriness in multivariable analysis: heart failure (odds ratio, 1.43; CI, 1.20-1.72), hypothermia (odds ratio, 1.37; 1.10-1.69), altered gas exchange (odds ratio, 1.33; 1.12-1.57), initial lactate greater than or equal to 4.0 mmol/L (odds ratio, 1.28; 1.08-1.52), immunocompromise (odds ratio, 1.23; 1.03-1.47), and coagulopathy (odds ratio, 1.23; 1.03-1.48). High-risk patients (≥ three risk factors) had 70% higher (CI, 48-96%) refractory risk (19% higher absolute risk; CI, 14-25%) versus low-risk (zero risk factors) patients. Initiating fluids in greater than 2 hours also predicted refractoriness (odds ratio, 1.96; CI, 1.49-2.58). Mortality was 15% higher (CI, 10-18%) for refractory patients.

CONCLUSIONS

Two in three hypotensive sepsis patients were responsive to initial fluid resuscitation. Heart failure, hypothermia, immunocompromise, hyperlactemia, and coagulopathy were associated with the refractory phenotype. Fluid resuscitation initiated after the initial 2 hours more strongly predicted refractoriness than any patient factor tested.

Nonischemic Causes of Cardiogenic Shock

Although cardiogenic shock is uncommon in the emergency department, it is associated with high mortality. Most cardiogenic shock is caused by ischemia, but nonischemic etiologies are essential to recognize. Clinicians should optimize preload, contractility, and afterload. Volume-responsive patients should be resuscitated in small aliquots, although some patients may require diuresis to improve cardiac output. Vasopressors are important to restore end-organ perfusion, and inotropes improve contractility. Intubation and positive pressure ventilation impact hemodynamics, which, depending on volume status, may be beneficial or deleterious. Knowing indications for mechanical circulatory support is important for timely consultation or transfer as indicated.

Relationship between Microcirculatory Perfusion and Arterial Elastance: A Pilot Study

Background

Arterial elastance (Ea) represents the total afterload imposed on the left ventricle, and it is largely influenced by systemic vascular resistance (SVR). Although one can expect that Ea is influenced by peripheral endothelial function, no data are available to support it in patients. The aim of this study was to investigate the relationship between Ea, SVR, and microvascular perfusion in critically ill patients undergoing the fluid challenge (FC).

Methods

A prospective study in patients receiving a fluid challenge. A pulse wave analysis system (MostCare, Vygon, France) was used to estimate Ea and an incident dark field (IDF) handheld device (Braedius Medical BV, The Netherlands) to evaluate the sublingual microcirculation. Microvascular perfusion was assessed using the proportion of small-perfused vessels (PPV). Relative changes in each variable were calculated before and after FC; fluid responsiveness was defined as an increase in the cardiac index by at least 10% from baseline.

Results

We studied 20 patients requiring a fluid challenge (n=10 for hypotension; n=5 for oliguria; n=3 for lactate values greater than 2 mmol/l; n=2 for tachycardia), including 12 fluid responders. There was a strong correlation between Ea and SVR (r² = 0.75; p < 0.001) and only a weak correlation between Ea and PPV at baseline (r² = 0.22; p=0.04). Ea decreased from 1.4 [1.2–1.6] to 1.2 [1.1–1.4] mmHg/mL (p=0.01), SVR from 1207 [1006–1373] to 1073 [997–1202] dyn ∗ s/cm⁵ (p=0.06), and PPV from 56 [51–64] % to 59 [47–73] % (p=0.25) after fluid challenge. Changes in Ea were significantly correlated with changes in SVR, but not with changes in PPV.

Conclusions

The correlation between Ea and indexes of microvascular perfusion in the sublingual region is weak. The impact of microcirculatory perfusion on the arterial load is probably limited.

Monitoring of pulse pressure variation using a new smartphone application (Capstesia) versus stroke volume variation using an uncalibrated pulse wave analysis monitor: a clinical decision making study during major abdominal surgery

Pulse pressure variation (PPV) and stroke volume variation (SVV) can be used to assess fluid status in the operating room but usually require dedicated advanced hemodynamic monitors. Recently, a smartphone application (Capstesia™), which automatically calculates PPV from a picture of the invasive arterial pressure waveform from any monitor screen (PPV_CAP), has been developed. The purpose of this study was to compare PPV_CAP with SVV from an uncalibrated pulse wave analysis monitor (SVV_PC). In 40 patients undergoing major abdominal surgery, we compared PPV_CAP with SVV_PC at post-induction, pre-incision, post-incision, end of surgery, and during every hypotensive episode (mean arterial pressure < 65 mmHg). We classified PPV_CAP and SVV_PC into three categories reflecting the thresholds used for the decision to administer fluids: no fluid administration (PPV and SVV < 9%), gray zone (PPV and SVV 9-13%), and fluid administration (PPV and SVV > 13%). The agreement between SVV_PC and PPV_CAP for these three categories was measured by the number of concordant paired measurements divided by the total number of paired measurements and Cohen's kappa coefficient. In the 549 pairs of PPV-SVV data obtained, the overall agreement of PPV_CAP with SVV_PC was 79%, and the kappa coefficient was moderate (0.55). The highest agreement and kappa coefficient value were observed after the induction of anesthesia before surgical incision. PPV_CAP and SVV_PC would have resulted in completely opposite clinical decisions regarding fluid administration in 1% of the cases. In this clinical decision making study in patients undergoing major abdominal surgery, we observed a moderate agreement between PPV_CAP and SVV_PC with regard to categories used to guide fluid administration. Trial Registration: Clinical Trials.gov (NCT03137901).

Is goal-directed fluid therapy based on dynamic variables alone sufficient to improve clinical outcomes among patients undergoing surgery? A meta-analysis

Background

Whether goal-directed fluid therapy based on dynamic predictors of fluid responsiveness (GDFTdyn) alone improves clinical outcomes in comparison with standard fluid therapy among patients undergoing surgery remains unclear.

Methods

PubMed, EMBASE, the Cochrane Library and ClinicalTrials.gov were searched for relevant studies. Studies comparing the effects of GDFTdyn with that of standard fluid therapy on clinical outcomes among adult patients undergoing surgery were considered eligible. Two analyses were performed separately: GDFTdyn alone versus standard fluid therapy and GDFTdyn with other optimization goals versus standard fluid therapy. The primary outcomes were short-term mortality and overall morbidity, while the secondary outcomes were serum lactate concentration, organ-specific morbidity, and length of stay in the intensive care unit (ICU) and in hospital.

Results

We included 37 studies with 2910 patients. Although GDFTdyn alone lowered serum lactate concentration (mean difference (MD) − 0.21 mmol/L, 95% confidence interval (CI) (− 0.39, − 0.03), P = 0.02), no significant difference was found between groups in short-term mortality (odds ratio (OR) 0.85, 95% CI (0.32, 2.24), P = 0.74), overall morbidity (OR 1.03, 95% CI (0.31, 3.37), P = 0.97), organ-specific morbidity, or length of stay in the ICU and in hospital. Analysis of trials involving the combination of GDFTdyn and other optimization goals (mainly cardiac output (CO) or cardiac index (CIx)) showed a significant reduction in short-term mortality (OR 0.45, 95% CI (0.24, 0.85), P = 0.01), overall morbidity (OR 0.41, 95% CI (0.28, 0.58), P < 0.00001), serum lactate concentration (MD − 0.60 mmol/L, 95% CI (− 1.04, − 0.15), P = 0.009), cardiopulmonary complications (cardiac arrhythmia (OR 0.58, 95% CI (0.37, 0.92), P = 0.02), myocardial infarction (OR 0.35, 95% CI (0.16, 0.76), P = 0.008), heart failure/cardiovascular dysfunction (OR 0.31, 95% CI (0.14, 0.67), P = 0.003), acute lung injury/acute respiratory distress syndrome (OR 0.13, 95% CI (0.02, 0.74), P = 0.02), pneumonia (OR 0.4, 95% CI (0.24, 0.65), P = 0.0002)), length of stay in the ICU (MD − 0.77 days, 95% CI (− 1.07, − 0.46), P < 0.00001) and in hospital (MD − 1.18 days, 95% CI (− 1.90, − 0.46), P = 0.001).

Conclusions

It was not the optimization of fluid responsiveness by GDFTdyn alone but rather the optimization of tissue and organ perfusion by GDFTdyn and other optimization goals that benefited patients undergoing surgery. Patients managed with the combination of GDFTdyn and CO/CI goals might derive most benefit.

Electronic supplementary material

The online version of this article (10.1186/s13054-018-2251-2) contains supplementary material, which is available to authorized users.

Mandatory criteria for the application of variability-based parameters of fluid responsiveness: a prospective study in different groups of ICU patients

BACKGROUND AND OBJECTIVE

Stroke volume variation (SVV) has high sensitivity and specificity in predicting fluid responsiveness. However, sinus rhythm (SR) and controlled mechanical ventilation (CV) are mandatory for their application. Several studies suggest a limited applicability of SVV in intensive care unit (ICU) patients. We hypothesized that the applicability of SVV might be different over time and within certain subgroups of ICU patients. Therefore, we analysed the prevalence of SR and CV in ICU patients during the first 24 h of PiCCO-monitoring (primary endpoint) and during the total ICU stay. We also investigated the applicability of SVV in the subgroups of patients with sepsis, cirrhosis, and acute pancreatitis.

METHODS

The prevalence of SR and CV was documented immediately before 1241 thermodilution measurements in 88 patients.

RESULTS

In all measurements, SVV was applicable in about 24%. However, the applicability of SVV was time-dependent: the prevalence of both SR and CV was higher during the first 24 h compared to measurements thereafter (36.1% vs. 21.9%; P<0.001). Within different subgroups, the applicability during the first 24 h of monitoring ranged between 0% in acute pancreatitis, 25.5% in liver failure, and 48.9% in patients without pancreatitis, liver failure, pneumonia or sepsis.

CONCLUSIONS

The applicability of SVV in a predominantly medical ICU is only about 25%-35%. The prevalence of both mandatory criteria decreases over time during the ICU stay. Furthermore, the applicability is particularly low in patients with acute pancreatitis and liver failure.

Pulse pressure variation and pleth variability index as predictors of fluid responsiveness in patients undergoing spinal surgery in the prone position

Background

This study investigated the ability of pulse pressure variation (PPV) and pleth variability index (PVI) to predict fluid responsiveness of patients undergoing spinal surgery in the prone position.

Patients and methods

A total of 53 patients undergoing posterior lumbar spinal fusion in the prone position on a Jackson table were studied. PPV, PVI, and hemodynamic and respiratory variables were measured both before and after the administration of 6 mL/kg colloid in both the supine and prone positions. Fluid responsiveness was defined as a 15% or greater increase in stroke volume index, as assessed by esophageal Doppler monitor after fluid loading.

Results

In the supine position, 40 patients were responders. The areas under the receiver operating characteristic (ROC) curves for PPV and PVI were 0.783 [95% CI 0.648–0.884, P<0.001] and 0.814 (95% CI 0.684–0.908, P<0.001), respectively. The optimal cut-off values of PPV and PVI were 10% (sensitivity 75%, specificity 62%) and 8% (sensitivity 78%, specificity 77%), respectively. In the prone position, 27 patients were responders. The areas under the ROC curves for PPV and PVI were 0.781 (95% CI 0.646–0.883, P<0.001) and 0.756 (95% CI 0.618–0.863, P<0.001), respectively. The optimal cut-off values of PPV and PVI were 7% (sensitivity 82%, specificity 62%) and 8% (sensitivity 67%, specificity 69%), respectively.

Conclusion

Both PPV and PVI were able to predict fluid responsiveness; their predictive abilities were maintained in the prone position.

Prediction of fluid responsiveness in mechanically ventilated cardiac surgical patients: the performance of seven different functional hemodynamic parameters

Background

Functional hemodynamic parameters such as stroke volume and pulse pressure variation (SVV and PPV) have been shown to be reliable predictors of fluid responsiveness in mechanically ventilated patients. Today, different minimally- and non-invasive hemodynamic monitoring systems measure functional hemodynamic parameters. Although some of these parameters are described by the same name, they differ in their measurement technique and thus may provide different results. We aimed to test the performance of seven functional hemodynamic parameters simultaneously in the same clinical setting.

Methods

Hemodynamic measurements were done in 30 cardiac surgery patients that were mechanically ventilated. Before and after a standardized intravenous fluid bolus, hemodynamics were measured by the following monitoring systems: PiCCOplus (SVV_PiCCO, PPV_PiCCO), LiDCO_rapid (SVV_LiDCO, PPV_LiDCO), FloTrac (SVV_FloTrac), Philips Intellivue (PPV_Philips) and Masimo pulse oximeter (pleth variability index, PVI). Prediction of fluid responsiveness was tested by calculation of receiver operating characteristic (ROC) curves including a gray zone approach and compared using Fisher’s Z-Test.

Results

Fluid administration resulted in an increase in cardiac output, while all functional hemodynamic parameters decreased. A wide range of areas under the ROC-curve (AUC’s) was observed: AUC-SVV_PiCCO = 0.91, AUC-PPV_PiCCO = 0.88, AUC-SVV_LiDCO = 0.78, AUC-PPV_LiDCO = 0.89, AUC-SVV_FloTrac = 0.87, AUC-PPV_Philips = 0.92 and AUC-PVI = 0.68. Optimal threshold values for prediction of fluid responsiveness ranged between 9.5 and 17.5%. Lowest threshold values were observed for SVV_LiDCO, highest for PVI.

Conclusion

All functional hemodynamic parameters tested except for PVI showed that their use allows a reliable identification of potential fluid responders. PVI however, may not be suitable after cardiac surgery to predict fluid responsiveness.

Trial registration

NCT02571465, registered on October 7th, 2015 (retrospectively registered).

[Intraoperative fluid therapy during esophagectomy followed by repair]

AIM

To optimize fluid therapy in transhiatal eshophagectomy by using of goal-oriented infusion therapy based on stroke volume variation.

MATERIAL AND METHODS

Our trial enrolled 30 patients who underwent transhiatal esophagectomy followed by repair for the period 2011-2014. Patients were divided into 2 groups. The first group (LT) included 16 patients with liberal fluid therapy. The second group (GDT) consisted of 14 patients in whom goal-oriented fluid therapy was performed. Goal-oriented fluid therapy was implemented via stroke volume variation (SVV).

RESULTS

Infusion rate was 6.7 ml/kg/h and 11.5 ml/kg/h in the main and control groups, respectively. Morbidity rate was 28.6% (n=4) and 62.5% (n=10) in the main and control groups respectively. Clavien-Dindo IV complications were lung atelectasis (n=2, 14%), pneumonia (n=1, 7%). Hydrothorax required puncture was noted in 1 (7%) case. Acute respiratory failure as complication IVa was in 1 (9%) patient. In the control group complications were registered in 10 (62.5%) patients. Complications I-II degree included lung atelectasis (n=4, 25%), cervical anastomosis failure (n=1, 6%); complications IVa were observed in 8 cases (50%). It was significant respiratory failure with reduced PO2/FiO2<300. Patients of the main group required less time for postoperative mechanical ventilation (120 [90-300] vs. 315 [215-810] min (p=0.02) and ICU-stay (0.83 [0.7-0.8] vs. 1.75 [1.25-2.75] (p=0.0022).

Applicability of respiratory variations in stroke volume and its surrogates for dynamic fluid responsiveness prediction in critically ill patients: a systematic review of the prevalence of required conditions

Objective

The present systematic review searched for published data on the prevalence of required conditions for proper assessment in critically ill patients.

Methods

The Medline, Scopus and Web of Science databases were searched to identify studies that evaluated the prevalence of validated conditions for the fluid responsiveness assessment using respiratory variations in the stroke volume or another surrogate in adult critically ill patients. The primary outcome was the suitability of the fluid responsiveness evaluation. The secondary objectives were the type and prevalence of pre-requisites evaluated to define the suitability.

Results

Five studies were included (14,804 patients). High clinical and statistical heterogeneity was observed (I² = 98.6%), which prevented us from pooling the results into a meaningful summary conclusion. The most frequent limitation identified is the absence of invasive mechanical ventilation with a tidal volume ≥ 8mL/kg. The final suitability for the fluid responsiveness assessment was low (in four studies, it varied between 1.9 to 8.3%, in one study, it was 42.4%).

Conclusion

Applicability of the dynamic indices of preload responsiveness requiring heart-lung interactions might be limited in daily practice.

Should we measure the central venous pressure to guide fluid management? Ten answers to 10 questions

The central venous pressure (CVP) is the most frequently used variable to guide fluid resuscitation in critically ill patients, although its use has been challenged. In this viewpoint, we use a question and answer format to highlight the potential advantages and limitations of using CVP measurements to guide fluid resuscitation.

End-expiratory occlusion maneuver to predict fluid responsiveness in the intensive care unit: an echocardiographic study

BACKGROUND

In mechanically ventilated patients, an increase in cardiac index during an end-expiratory-occlusion test predicts fluid responsiveness. To identify this rapid increase in cardiac index, continuous and instantaneous cardiac index monitoring is necessary, decreasing its feasibility at the bedside. Our study was designed to investigate whether changes in velocity time integral and in peak velocity obtained using transthoracic echocardiography during an end-expiratory-occlusion maneuver could predict fluid responsiveness.

METHODS

This single-center, prospective study included 50 mechanically ventilated critically ill patients. Velocity time integral and peak velocity were assessed using transthoracic echocardiography before and at the end of a 12-sec end-expiratory-occlusion maneuver. A third set of measurements was performed after volume expansion (500 mL of saline 0.9% given over 15 minutes). Patients were considered as responders if cardiac output increased by 15% or more after volume expansion.

RESULTS

Twenty-eight patients were responders. At baseline, heart rate, mean arterial pressure, cardiac output, velocity time integral and peak velocity were similar between responders and non-responders. End-expiratory-occlusion maneuver induced a significant increase in velocity time integral both in responders and non-responders, and a significant increase in peak velocity only in responders. A 9% increase in velocity time integral induced by the end-expiratory-occlusion maneuver predicted fluid responsiveness with sensitivity of 89% (95% CI 72% to 98%) and specificity of 95% (95% CI 77% to 100%). An 8.5% increase in peak velocity induced by the end-expiratory-occlusion maneuver predicted fluid responsiveness with sensitivity of 64% (95% CI 44% to 81%) and specificity of 77% (95% CI 55% to 92%). The area under the receiver operating curve generated for changes in velocity time integral was significantly higher than the one generated for changes in peak velocity (0.96 ± 0.03 versus 0.70 ± 0.07, respectively, P = 0.0004 for both). The gray zone ranged between 6 and 10% (20% of the patients) for changes in velocity time integral and between 1 and 13% (62% of the patients) for changes in peak velocity.

CONCLUSIONS

In mechanically ventilated and sedated patients in the neuro Intensive Care Unit, changes in velocity time integral during a 12-sec end-expiratory-occlusion maneuver were able to predict fluid responsiveness and perform better than changes in peak velocity.

Detailing the cardiovascular profile in shock patients

Evaluation of the cardiovascular profile of critically ill patients is one of the most important actions performed in critically ill patients. It allows recognition that the patient is in shock and characterization of the type of circulatory failure. This step is crucial to initiate supportive interventions and to cure the cause responsible for the development of shock. Evaluation of tissue perfusion allows identification of the patient insufficiently resuscitated and also to trigger therapeutic interventions. Monitoring tissue perfusion can be achieved by lactate, venoarterial gradients in PCO₂, and central venous or mixed venous oxygen saturation. Ultimately, monitoring the microcirculation may help not only to identify alterations in tissue perfusion but also to identify the type of alterations: diffuse decrease in microvascular perfusion versus heterogeneity in the alterations, as in sepsis, with well perfused areas in close vicinity to poorly perfused areas. Regarding supportive therapy, a step-by-step approach is suggested, with fluid optimization followed by vasoactive support to preserve perfusion pressure and global and regional blood flows. The different variables should be integrated into decision and management pathways, and therapies adapted accordingly.

Assessment of potential heart donors: A statement from the French heart transplant community

Assessment of potential donors is an essential part of heart transplantation. Despite the shortage of donor hearts, donor heart procurement from brain-dead organ donors remains low in France, which may be explained by the increasing proportion of high-risk donors, as well as the mismatch between donor assessment and the transplant team's expectations. Improving donor and donor heart assessment is essential to improve the low utilization rate of available donor hearts without increasing post-transplant recipient mortality. This document provides information to practitioners involved in brain-dead donor management, evaluation and selection, concerning the place of medical history, electrocardiography, cardiac imaging, biomarkers and haemodynamic and arrhythmia assessment in the characterization of potential heart donors.

Change in cardiac output during Trendelenburg maneuver is a reliable predictor of fluid responsiveness in patients with acute respiratory distress syndrome in the prone position under protective ventilation

Background

Predicting fluid responsiveness may help to avoid unnecessary fluid administration during acute respiratory distress syndrome (ARDS). The aim of this study was to evaluate the diagnostic performance of the following methods to predict fluid responsiveness in ARDS patients under protective ventilation in the prone position: cardiac index variation during a Trendelenburg maneuver, cardiac index variation during an end-expiratory occlusion test, and both pulse pressure variation and change in pulse pressure variation from baseline during a tidal volume challenge by increasing tidal volume (VT) to 8 ml.kg^-1.

Methods

This study is a prospective single-center study, performed in a medical intensive care unit, on ARDS patients with acute circulatory failure in the prone position. Patients were studied at baseline, during a 1-min shift to the Trendelenburg position, during a 15-s end-expiratory occlusion, during a 1-min increase in VT to 8 ml.kg^-1, and after fluid administration. Fluid responsiveness was deemed present if cardiac index assessed by transpulmonary thermodilution increased by at least 15% after fluid administration.

Results

There were 33 patients included, among whom 14 (42%) exhibited cardiac arrhythmia at baseline and 15 (45%) were deemed fluid-responsive. The area under the receiver operating characteristic (ROC) curve of the pulse contour-derived cardiac index change during the Trendelenburg maneuver and the end-expiratory occlusion test were 0.90 (95% CI, 0.80–1.00) and 0.65 (95% CI, 0.46–0.84), respectively. An increase in cardiac index ≥ 8% during the Trendelenburg maneuver enabled diagnosis of fluid responsiveness with sensitivity of 87% (95% CI, 67–100), and specificity of 89% (95% CI, 72–100). The area under the ROC curve of pulse pressure variation and change in pulse pressure variation during the tidal volume challenge were 0.52 (95% CI, 0.24–0.80) and 0.59 (95% CI, 0.31–0.88), respectively.

Conclusions

Change in cardiac index during a Trendelenburg maneuver is a reliable test to predict fluid responsiveness in ARDS patients in the prone position, while neither change in cardiac index during end-expiratory occlusion, nor pulse pressure variation during a VT challenge reached acceptable predictive performance to predict fluid responsiveness in this setting.

Trial registration

ClinicalTrials.gov, NCT01965574. Registered on 16 October 2013. The trial was registered 6 days after inclusion of the first patient.

Electronic supplementary material

The online version of this article (doi:10.1186/s13054-017-1881-0) contains supplementary material, which is available to authorized users.

The ICM research agenda on critical care ultrasonography

PURPOSE

Critical care ultrasonography has utility for the diagnosis and management of critical illness and is in widespread use by frontline intensivists. As there is a need for research to validate and extend its utility, the Editor of Intensive Care Medicine included critical care ultrasonography as a topic in the ICM Research Agenda issue.

METHODS

Eleven international experts in the field of critical care ultrasonography contributed to the writing project. With the intention of developing a research agenda for the field, they reviewed best standards of care, new advances in the field, common beliefs that have been contradicted by recent trials, and unanswered questions related to critical care ultrasonography.

RESULTS

The writing group focused on the provision of training in critical care ultrasonography, technological advances, and some specific clinical applications.

CONCLUSIONS

The writing group identified several fields of interest for research and proposed ten research studies that would address important aspects of critical care ultrasonography.

Mini-fluid Challenge of 100 ml of Crystalloid Predicts Fluid Responsiveness in the Operating Room

BACKGROUND

Mini-fluid challenge of 100 ml colloids is thought to predict the effects of larger amounts of fluid (500 ml) in intensive care units. This study sought to determine whether a low quantity of crystalloid (50 and 100 ml) could predict the effects of 250 ml crystalloid in mechanically ventilated patients in the operating room.

METHODS

A total of 44 mechanically ventilated patients undergoing neurosurgery were included. Volume expansion (250 ml saline 0.9%) was given to maximize cardiac output during surgery. Stroke volume index (monitored using pulse contour analysis) and pulse pressure variations were recorded before and after 50 ml infusion (given for 1 min), after another 50 ml infusion (given for 1 min), and finally after 150 ml infusion (total = 250 ml). Changes in stroke volume index induced by 50, 100, and 250 ml were recorded. Positive fluid challenges were defined as an increase in stroke volume index of 10% or more from baseline after 250 ml.

RESULTS

A total of 88 fluid challenges were performed (32% of positive fluid challenges). Changes in stroke volume index induced by 100 ml greater than 6% (gray zone between 4 and 7%, including 19% of patients) predicted fluid responsiveness with a sensitivity of 93% (95% CI, 77 to 99%) and a specificity of 85% (95% CI, 73 to 93%). The area under the receiver operating curve of changes in stroke volume index induced by 100 ml was 0.95 (95% CI, 0.90 to 0.99) and was higher than those of changes in stroke volume index induced by 50 ml (0.83 [95% CI, 0.75 to 0.92]; P = 0.01) and pulse pressure variations (0.65 [95% CI, 0.53 to 0.78]; P < 0.005).

CONCLUSIONS

Changes in stroke volume index induced by rapid infusion of 100 ml crystalloid predicted the effects of 250 ml crystalloid in patients ventilated mechanically in the operating room.

A composite score associated with spontaneous operational tolerance in kidney transplant recipients

New challenges in renal transplantation include using biological information to devise a useful clinical test for discerning high- and low-risk patients for individual therapy and ascertaining the best combination and appropriate dosages of drugs. Based on a 20-gene signature from a microarray meta-analysis performed on 46 operationally tolerant patients and 266 renal transplant recipients with stable function, we applied the sparse Bolasso methodology to identify a minimal and robust combination of six genes and two demographic parameters associated with operational tolerance. This composite score of operational tolerance discriminated operationally tolerant patients with an area under the curve of 0.97 (95% confidence interval 0.94-1.00). The score was not influenced by immunosuppressive treatment, center of origin, donor type, or post-transplant lymphoproliferative disorder history of the patients. This composite score of operational tolerance was significantly associated with both de novo anti-HLA antibodies and tolerance loss. It was validated by quantitative polymerase chain reaction using independent samples and demonstrated specificity toward a model of tolerance induction. Thus, our score would allow clinicians to improve follow-up of patients, paving the way for individual therapy.

Predictors to Intravenous Fluid Responsiveness

Management with intravenous fluids can improve cardiac output in some surgical patients. Management with static preload indicators, such as central venous pressure and pulmonary artery occlusion pressure, has not demonstrated a suitable relationship with changes in the cardiac output induced by intravenous fluid therapy. Dynamic indicators, such as the variability of arterial pulse pressure or stroke volume variation, have demonstrated a suitable relationship. Since improvement in cardiac output does not guarantee an adequate perfusion pressure, in patients with hypotension, it is also necessary to know whether arterial pressure will also increase with intravenous fluid therapy. In this regard, the functional assessment of arterial load by dynamic arterial elastance could help to determine which patients will improve not only their cardiac output but also their mean arterial pressure.

Predictors to Intravenous Fluid Responsiveness

Management with intravenous fluids can improve cardiac output in some surgical patients. Management with static preload indicators, such as central venous pressure and pulmonary artery occlusion pressure, has not demonstrated a suitable relationship with changes in the cardiac output induced by intravenous fluid therapy. Dynamic indicators, such as the variability of arterial pulse pressure or stroke volume variation, have demonstrated a suitable relationship. Since improvement in cardiac output does not guarantee an adequate perfusion pressure, in patients with hypotension, it is also necessary to know whether arterial pressure will also increase with intravenous fluid therapy. In this regard, the functional assessment of arterial load by dynamic arterial elastance could help to determine which patients will improve not only their cardiac output but also their mean arterial pressure.

Inferior vena cava collapsibility detects fluid responsiveness among spontaneously breathing critically-ill patients

PURPOSE

Measurement of inferior vena cava collapsibility (cIVC) by point-of-care ultrasound (POCUS) has been proposed as a viable, non-invasive means of assessing fluid responsiveness. We aimed to determine the ability of cIVC to identify patients who will respond to additional intravenous fluid (IVF) administration among spontaneously breathing critically-ill patients.

METHODS

Prospective observational trial of spontaneously breathing critically-ill patients. cIVC was obtained 3cm caudal from the right atrium and IVC junction using POCUS. Fluid responsiveness was defined as a≥10% increase in cardiac index following a 500ml IVF bolus; measured using bioreactance (NICOM™, Cheetah Medical). cIVC was compared with fluid responsiveness and a cIVC optimal value was identified.

RESULTS

Of the 124 participants, 49% were fluid responders. cIVC was able to detect fluid responsiveness: AUC=0.84 [0.76, 0.91]. The optimum cutoff point for cIVC was identified as 25% (LR+ 4.56 [2.72, 7.66], LR- 0.16 [0.08, 0.31]). A cIVC of 25% produced a lower misclassification rate (16.1%) for determining fluid responsiveness than the previous suggested cutoff values of 40% (34.7%).

CONCLUSION

IVC collapsibility, as measured by POCUS, performs well in distinguishing fluid responders from non-responders, and may be used to guide IVF resuscitation among spontaneously breathing critically-ill patients.

Use of 'tidal volume challenge' to improve the reliability of pulse pressure variation

This article is one of ten reviews selected from the Annual Update in Intensive Care and Emergency Medicine 2017. Other selected articles can be found online at http://ccforum.com/series/annualupdate2017. Further information about the Annual Update in Intensive Care and Emergency Medicine is available from http://www.springer.com/series/8901.

Changes in Stroke Volume Induced by Lung Recruitment Maneuver Predict Fluid Responsiveness in Mechanically Ventilated Patients in the Operating Room

Background

Lung recruitment maneuver induces a decrease in stroke volume, which is more pronounced in hypovolemic patients. The authors hypothesized that the magnitude of stroke volume reduction through lung recruitment maneuver could predict preload responsiveness.

Methods

Twenty-eight mechanically ventilated patients with low tidal volume during general anesthesia were included. Heart rate, mean arterial pressure, stroke volume, and pulse pressure variations were recorded before lung recruitment maneuver (application of continuous positive airway pressure of 30 cm H2O for 30 s), during lung recruitment maneuver when stroke volume reached its minimal value, and before and after volume expansion (250 ml saline, 0.9%, infused during 10 min). Patients were considered as responders to fluid administration if stroke volume increased greater than or equal to 10%.

Results

Sixteen patients were responders. Lung recruitment maneuver induced a significant decrease in mean arterial pressure and stroke volume in both responders and nonresponders. Changes in stroke volume induced by lung recruitment maneuver were correlated with those induced by volume expansion (r2 = 0.56; P &lt; 0.0001). A 30% decrease in stroke volume during lung recruitment maneuver predicted fluid responsiveness with a sensitivity of 88% (95% CI, 62 to 98) and a specificity of 92% (95% CI, 62 to 99). Pulse pressure variations more than 6% before lung recruitment maneuver discriminated responders with a sensitivity of 69% (95% CI, 41 to 89) and a specificity of 75% (95% CI, 42 to 95). The area under receiver operating curves generated for changes in stroke volume induced by lung recruitment maneuver (0.96; 95% CI, 0.81 to 0.99) was significantly higher than that for pulse pressure variations (0.72; 95% CI, 0.52 to 0.88; P &lt; 0.05).

Conclusions

The authors’ study suggests that the magnitude of stroke volume decrease during lung recruitment maneuver could predict preload responsiveness in mechanically ventilated patients in the operating room.

Applicability of stroke volume variation in patients of a general intensive care unit: a longitudinal observational study

Sinus rhythm (SR) and controlled mechanical ventilation (CV) are mandatory for the applicability of respiratory changes of the arterial curve such as stroke volume variation (SVV) to predict fluid-responsiveness. Furthermore, several secondary limitations including tidal volumes <8 mL/kg and SVV-values within the "gray zone" of 9-13% impair prediction of fluid-responsiveness by SVV. Therefore, we investigated the prevalence of these four conditions in general ICU-patients. This longitudinal observational study analyzed a prospectively maintained haemodynamic database including 4801 transpulmonary thermodilution and pulse contour analysis measurements of 278 patients (APACHE-II 21.0 ± 7.4). The main underlying diseases were cirrhosis (32%), sepsis (28%), and ARDS (17%). The prevalence of SR and CV was only 19.4% (54/278) in the first measurements (primary endpoint), 18.8% (902/4801) in all measurements and 26.5% (9/34) in measurements with MAP < 65 mmHg and CI < 2.5 L/min/m² and vasopressor therapy. In 69.1% (192/278) of the first measurements and in 65.9% (3165/4801) of all measurements the patients had SR but did not have CV. In 1.8% (5/278) of the first measurements and in 2.5% (119/4801) of all measurements the patients had CV but lacked SR. In 9.7% (27/278) of the first measurements and in 12.8% (615/4801) of all measurements the patients did neither have SR nor CV. Only 20 of 278 (7.2%) of the first measurements and 8.2% of all measurements fulfilled both major criteria (CV, SR) and both minor criteria for the applicability of SVV. The applicability of SVV in ICU-patients is limited due to the absence of mandatory criteria during the majority of measurements.

The Diagnosis and Hemodynamic Monitoring of Circulatory Shock: Current and Future Trends

Circulatory shock is a complex clinical syndrome encompassing a group of conditions that can arise from different etiologies and presented by several different hemodynamic patterns. If not corrected, cell dysfunction, irreversible multiple organ insufficiency, and death may occur. The four basic types of shock, hypovolemic, cardiogenic, obstructive and distributive, have features similar to that of hemodynamic shock. It is therefore essential, when monitoring hemodynamic shock, to making accurate clinical assessments which will guide and dictate appropriate management therapy. The European Society of Intensive Care has recently made recommendations for monitoring hemodynamic shock. The present paper discusses the issues raised in the new statements, including individualization of blood pressure targets, prediction of fluid responsiveness, and the use of echocardiography as the first means during the initial evaluation of circulatory shock. Also, the place of more invasive hemodynamic monitoring techniques and future trends in hemodynamic and metabolic monitoring in circulatory shock, will be debated.

Pulse Pressure Variation Adjusted by Respiratory Changes in Pleural Pressure, Rather Than by Tidal Volume, Reliably Predicts Fluid Responsiveness in Patients With Acute Respiratory Distress Syndrome

OBJECTIVES

1) To evaluate the ability of pulse pressure variation adjusted by respiratory changes in pleural pressure to predict fluid responsiveness compared with pulse pressure variation alone. 2) To identify factors explaining the poor performance of pulse pressure variation in acute respiratory distress syndrome.

DESIGN

Prospective study.

SETTING

Forty-bed university hospital general ICU.

PATIENTS

Ninety-six mechanically ventilated acute respiratory distress syndrome patients requiring fluid challenge.

INTERVENTIONS

Fluid challenge, 500 mL saline over 20 minutes.

MEASUREMENTS AND MAIN RESULTS

Before fluid challenge, esophageal pressure was measured at the end-inspiratory and end-expiratory occlusions. Change in pleural pressure was calculated as the difference between esophageal pressure measured at end-inspiratory and end-expiratory occlusions. Hemodynamic measurements were obtained before and after the fluid challenge. Patients were ventilated with tidal volume 7.0 ± 0.8 mL/kg predicted body weight. The fluids increased cardiac output by greater than 15% in 52 patients (responders). Adjusting pulse pressure variation for changes in pleural pressure (area under the receiver operating characteristic curve, 0.94 [0.88-0.98]) and the ratio of chest wall elastance to total respiratory system elastance (area under the receiver operating characteristic curve, 0.93 [0.88-0.98]) predicted fluid responsiveness better than pulse pressure variation (area under the receiver operating characteristic curve, 0.78 [0.69-0.86]; all p < 0.01). The gray zone approach identified a range of pulse pressure variation/changes in pleural pressure values (1.94-2.1) in 3.1% of patients for whom fluid responsiveness could not be predicted reliably. On logistic regression analysis, two independent factors affected the correct classification of fluid responsiveness at a 12% pulse pressure variation cutoff: tidal volume (adjusted odds ratio 1.57/50 mL; 95% CI, 1.05-2.34; p = 0.027) and chest wall elastance/respiratory system elastance (adjusted odds ratio, 2.035/0.1 unit; 95% CI, 1.36-3.06; p = 0.001). In patients with chest wall elastance/respiratory system elastance above the median (0.28), pulse pressure variation area under the receiver operating characteristic curve was 0.94 (95% CI, 0.84-0.99) compared with 0.76 (95% CI, 0.61-0.87) otherwise (p = 0.02).

CONCLUSIONS

In acute respiratory distress syndrome patients, pulse pressure variation adjusted by changes in pleural pressure is a reliable fluid responsiveness predictor despite the low tidal volume (< 8 mL/kg). The poor predictive ability of pulse pressure variation in acute respiratory distress syndrome patients is more related to low chest wall elastance/respiratory system elastance ratios than to a low tidal volume.

Applicability of Pulse Pressure Variation during Unstable Hemodynamic Events in the Intensive Care Unit: A Five-Day Prospective Multicenter Study

Pulse pressure variation can predict fluid responsiveness in strict applicability conditions. The purpose of this study was to describe the clinical applicability of pulse pressure variation during episodes of patient hemodynamic instability in the intensive care unit. We conducted a five-day, seven-center prospective study that included patients presenting with an unstable hemodynamic event. The six predefined inclusion criteria for pulse pressure variation applicability were as follows: mechanical ventilation, tidal volume >7 mL/kg, sinus rhythm, no spontaneous breath, heart rate/respiratory rate ratio >3.6, absence of right ventricular dysfunction, or severe valvulopathy. Seventy-three patients presented at least one unstable hemodynamic event, with a total of 163 unstable hemodynamic events. The six predefined criteria for the applicability of pulse pressure variation were completely present in only 7% of these. This data indicates that PPV should only be used alongside a strong understanding of the relevant physiology and applicability criteria. Although these exclusion criteria appear to be profound, they likely represent an absolute contraindication of use for only a minority of critical care patients.

Respiratory variation in aortic blood flow peak velocity to predict fluid responsiveness in mechanically ventilated children: a systematic review and meta-analysis

BACKGROUND

Dynamic indices of preload have been shown to better predict fluid responsiveness than static variables in mechanically ventilated adults. In children, dynamic predictors of fluid responsiveness have not yet been extensively studied.

AIM

To evaluate the diagnostic accuracy of respiratory variation in aortic blood flow peak velocity (ΔVPeak) for the prediction of fluid responsiveness in mechanically ventilated children.

METHOD

PubMed, Embase, and the Cochrane Database of Systematic Reviews were screened for studies relevant to the use of ΔVPeak to predict fluid responsiveness in children receiving mechanical ventilation. Clinical trials published as full-text articles in indexed journals without language restriction were included. We calculated the pooled values of sensitivity, specificity, diagnostic odds ratio (DOR), and positive and negative likelihood ratio using a random-effects model.

RESULTS

In total, six studies (163 participants) met the inclusion criteria. Data are reported as point estimate with 95% confidence interval. The pooled sensitivity, specificity, positive likelihood ratio, negative likelihood ratio, and DOR of ΔVPeak to predict fluid responsiveness for the overall population were 92.0% (84.1-96.7), 85.5% (75.6-92.5), 4.89 (2.92-8.18), 0.13 (0.07-0.25), and 50.44 (17.70-143.74), respectively. The area under the summary receiver operating characteristic curve was 0.94. Cutoff values for ΔVPeak to predict fluid responsiveness varied across studies, ranging from 7% to 20%.

CONCLUSION

Our results confirm that the ΔVPeak is an accurate predictor of fluid responsiveness in children under mechanical ventilation. However, the question of the optimal cutoff value of ΔVPeak to predict fluid responsiveness remains uncertain, as there are important variations between original publications, and needs to be resolved in further studies. The potential impact of intraoperative cardiac output optimization using goal-directed fluid therapy based on ΔVPeak on the perioperative outcome in the pediatric population should be subsequently evaluated.

The use of static and dynamic haemodynamic parameters before volume expansion: A prospective observational study in six French intensive care units

OBJECTIVE

The aim of the present study was to determine the use of static and dynamic haemodynamic parameters for predicting fluid responsiveness prior to volume expansion (VE) in intensive care unit (ICU) patients with systemic inflammatory response syndrome (SIRS).

METHODS

We conducted a prospective, multicentre, observational study in 6 French ICUs in 2012. ICU physicians were audited concerning their use of static and dynamic haemodynamic parameters before each VE performed in patients with SIRS for 6 consecutive weeks.

RESULTS

The median volume of the 566 VEs administered to patients with SIRS was 1000mL [500-1000mL]. Although at least one static or dynamic haemodynamic parameter was measurable before 99% (95% CI, 99%-100%) of VEs, at least one them was used in only 38% (95% CI, 34%-42%) of cases: static parameters in 11% of cases (95% CI, 10%-12%) and dynamic parameters in 32% (95% CI, 30%-34%). Static parameters were never used when uninterpretable. For 15% of VEs (95% CI, 12%-18%), a dynamic parameter was measured in the presence of contraindications. Among dynamic parameters, respiratory variations in arterial pulse pressure (PPV) and passive leg raising (PLR) were measurable and interpretable before 17% and 90% of VEs, respectively.

CONCLUSIONS

Haemodynamic parameters are underused for predicting fluid responsiveness in current practice. In contrast to static parameters, dynamic parameters are often incorrectly used in the presence of contraindications. PLR is more frequently valid than PPV for predicting fluid responsiveness in ICU patients.

A rational approach to fluid therapy in sepsis

Aggressive fluid resuscitation to achieve a central venous pressure (CVP) greater than 8 mm Hg has been promoted as the standard of care, in the management of patients with severe sepsis and septic shock. However recent clinical trials have demonstrated that this approach does not improve the outcome of patients with severe sepsis and septic shock. Pathophysiologically, sepsis is characterized by vasoplegia with loss of arterial tone, venodilation with sequestration of blood in the unstressed blood compartment and changes in ventricular function with reduced compliance and reduced preload responsiveness. These data suggest that sepsis is primarily not a volume-depleted state and recent evidence demonstrates that most septic patients are poorly responsive to fluids. Furthermore, almost all of the administered fluid is sequestered in the tissues, resulting in severe oedema in vital organs and, thereby, increasing the risk of organ dysfunction. These data suggest that a physiologic, haemodynamically guided conservative approach to fluid therapy in patients with sepsis would be prudent and would likely reduce the morbidity and improve the outcome of this disease.

Decrease in pulse pressure and stroke volume variations after mini-fluid challenge accurately predicts fluid responsiveness†

BACKGROUND

Dynamic indices, such as pulse pressure variation (PPV), are inaccurate predictors of fluid responsiveness in mechanically ventilated patients with low tidal volume. This study aimed to test whether changes in continuous cardiac index (CCI), PPV, and stroke volume variation (SVV) after a mini-fluid challenge (100 ml of fluid during 1 min) could predict fluid responsiveness in these patients.

METHODS

We prospectively studied 49 critically ill, deeply sedated, and mechanically ventilated patients (tidal volume <8 ml kg(-1) of ideal body weight) without cardiac arrhythmias, in whom a fluid challenge was indicated because of circulatory failure. The CCI, SVV (PiCCO™; Pulsion), and PPV (MP70™; Philips) were measured before and after 100 ml of colloid infusion during 1 min, and then after the additional infusion of 400 ml during 14 min. Responders were defined as subjects with a ≥15% increase in cardiac index (transpulmonary thermodilution) after the full (500 ml) fluid challenge. Areas under the receiver operating characteristic curves (AUCs) and the grey zones were determined for changes in CCI (ΔCCI100), SVV (ΔSVV100), and PPV (ΔPPV100) after 100 ml fluid challenge.

RESULTS

Twenty-two subjects were responders. The ΔCCI100 predicted fluid responsiveness with an AUC of 0.78. The grey zone was large and included 67% of subjects. The ΔSVV100 and ΔPPV100 predicted fluid responsiveness with AUCs of 0.91 and 0.92, respectively. Grey zones were small, including ≤12% of subjects for both indices.

CONCLUSIONS

The ΔSVV100 and ΔPPV100 predict fluid responsiveness accurately and better than ΔCCI100 (PiCCO™; Pulsion) in patients with circulatory failure and ventilated with low volumes.