Respiratory changes in aortic blood velocity as an indicator of fluid responsiveness in ventilated patients with septic shock

A Carotid Doppler Patch Accurately Tracks Stroke Volume Changes During a Preload-Modifying Maneuver in Healthy Volunteers

Objectives:

Detecting instantaneous stroke volume change in response to altered cardiac preload is the physiologic foundation for determining preload responsiveness.

Design:

Proof-of-concept physiology study.

Setting:

Research simulation laboratory.

Subjects:

Twelve healthy volunteers.

Interventions:

A wireless continuous wave Doppler ultrasound patch was used to measure carotid velocity time integral and carotid corrected flow time during a squat maneuver. The Doppler patch measurements were compared with simultaneous stroke volume measurements obtained from a noninvasive cardiac output monitor.

Measurements and Main Results:

From stand to squat, stroke volume increased by 24% while carotid velocity time integral and carotid corrected flow time increased by 32% and 9%, respectively. From squat to stand, stroke volume decreased by 13%, while carotid velocity time integral and carotid corrected flow time decreased by 24% and 10%, respectively. Both changes in carotid velocity time integral and corrected flow time were closely correlated with changes in stroke volume (r² = 0.81 and 0.62, respectively). The four-quadrant plot found a 100% concordance rate between changes in stroke volume and both changes in carotid velocity time integral and changes in corrected flow time. A change in carotid velocity time integral greater than 15% predicted a change in stroke volume greater than 10% with a sensitivity of 95% and a specificity of 92%. A change in carotid corrected flow time greater than 4% predicted a change in stroke volume greater than 10% with a sensitivity of 90% and a specificity of 92%.

Conclusions:

In healthy volunteers, both carotid velocity time integral and carotid corrected flow time measured by a wireless Doppler patch were useful to track changes in stroke volume induced by a preload-modifying maneuver with high sensitivity and specificity.

Performance of the Hypotension Prediction Index with non-invasive arterial pressure waveforms in non-cardiac surgical patients

An algorithm derived from machine learning uses the arterial waveform to predict intraoperative hypotension some minutes before episodes, possibly giving clinician’s time to intervene and prevent hypotension. Whether the Hypotension Prediction Index works well with noninvasive arterial pressure waveforms remains unknown. We therefore evaluated sensitivity, specificity, and positive predictive value of the Index based on non-invasive arterial waveform estimates. We used continuous hemodynamic data measured from ClearSight (formerly Nexfin) noninvasive finger blood pressure monitors in surgical patients. We re-evaluated data from a trial that included 320 adults ≥ 45 years old designated ASA physical status 3 or 4 who had moderate-to-high-risk non-cardiac surgery with general anesthesia. We calculated sensitivity and specificity for predicting hypotension, defined as mean arterial pressure ≤ 65 mmHg for at least 1 min, and characterized the relationship with receiver operating characteristics curves. We also evaluated the number of hypotensive events at various ranges of the Hypotension Prediction Index. And finally, we calculated the positive predictive value for hypotension episodes when the Prediction Index threshold was 85. The algorithm predicted hypotension 5 min in advance, with a sensitivity of 0.86 [95% confidence interval 0.82, 0.89] and specificity 0.86 [0.82, 0.89]. At 10 min, the sensitivity was 0.83 [0.79, 0.86] and the specificity was 0.83 [0.79, 0.86]. And at 15 min, the sensitivity was 0.75 [0.71, 0.80] and the specificity was 0.75 [0.71, 0.80]. The positive predictive value of the algorithm prediction at an Index threshold of 85 was 0.83 [0.79, 0.87]. A Hypotension Prediction Index of 80–89 provided a median of 6.0 [95% confidence interval 5.3, 6.7] minutes warning before mean arterial pressure decreased to < 65 mmHg. The Hypotension Prediction Index, which was developed and validated with invasive arterial waveforms, predicts intraoperative hypotension reasonably well from non-invasive estimates of the arterial waveform. Hypotension prediction, along with appropriate management, can potentially reduce intraoperative hypotension. Being able to use the non-invasive pressure waveform will widen the range of patients who might benefit.

Clinical Trial Number: ClinicalTrials.gov NCT02872896.

Is dynamic arterial elastance a predictor of an increase in blood pressure after fluid administration in pediatric patients with hypotension? Reanalysis of prospective observational studies

BACKGROUND

Dynamic arterial elastance (Ea_dyn ) has been proposed to predict an increase in mean arterial pressure (MAP) after volume expansion in hypotensive adults. We aimed to evaluate the clinical usefulness of Ea_dyn as a predictor of arterial pressure response after fluid loading in pediatric patients with hypotension.

METHODS

We re-analyzed data of 63 hypotensive children (age, ≤5 years), collected from three previous prospective observational studies about fluid responsiveness. Pulse pressure variation (PPV), stroke volume variation (SVV), and respiratory variation in aortic blood flow velocity (ΔVpeak) were used to calculate Ea_dyn (PPV/SVV) and modified Ea_dyn (PPV/ΔVpeak). Preload-dependent patients were defined as those with ΔVpeak ≥12% before fluid loading. Patients were classified as pressure responders, if their MAP increased ≥15% after fluid administration.

RESULTS

Mean Ea_dyn (SD) was 1.06 (0.47) in pressure responders (n=39) and 0.99 (0.48) in nonresponders (n = 24) (mean difference, 0.08; 95% confidence interval [CI], -0.19-0.34; P = .567). Additionally, mean modified Ea_dyn was 1.27 (0.64) in responders and 1.11 (0.43) in nonresponders (mean difference, 0.17; 95% CI, -0.13-0.46; P = 0.269). Both Ea_dyn (AUC 0.506; 95% confidence interval [CI], 0.337 to 0.675; P = 0.948) and modified Ea_dyn (AUC 0.498; 95% CI, 0.328-0.669; P = 0.983), as well as other dynamic variables, could not predict pressure responsiveness in children. Sub-group analysis revealed similar findings in both in 39 preload-dependent and hypotensive patients (26 pressure responders and 13 nonpressure responders).

CONCLUSION

Both Ea_dyn and modified Ea_dyn cannot predict whether blood pressure increases with fluid administration in pediatric patients with hypotension.

Comparison of pulse pressure variation versus echocardiography-derived stroke volume variation for prediction of fluid responsiveness in mechanically ventilated anesthetized dogs

OBJECTIVE

To evaluate the ability and accuracy of aortic flow velocity-time integral variation (ΔVTI) and peak aortic velocity variation (ΔVpeak) compared with pulse pressure variation (PPV) to predict fluid responsiveness in mechanically ventilated dogs.

STUDY DESIGN

Prospective clinical study.

ANIMALS

A group of 50 mechanically ventilated dogs with spontaneous hypotension during orthopedic or oncologic surgery.

METHODS

Investigations were performed in the surgery room. When mean arterial pressure (MAP) decreased to <65 mmHg, measurements were performed before and after a fluid challenge (lactated Ringer's solution 5 mL kg^-1 over 15 minutes). Responders were defined as a change in stroke volume (SV; transesophageal Doppler) ≥15%. Data were analyzed using paired/unpaired t test or Mann-Whitney/Wilcoxon test when appropriate and receiver operating characteristics (ROC) curves; a p value <0.05 was considered statistically significant.

RESULTS

After the fluid challenge, 35 (70%) of 50 dogs were responders with significant increases in SV and decreases in PPV; 15 dogs were nonresponders. ΔVTI and ΔVpeak correlated with a 15% increase in SV. The optimum cut-off value for PPV was 15.6% (sensitivity, 88%; specificity, 100%), for ΔVTI was 10.65% (sensitivity, 65%; specificity, 100%) and for ΔVpeak was 10.15% (sensitivity, 80%; specificity, 100%). The area under the ROC curve for PPV was (0.93 ± 0.08) and for ΔVpeak was (0.89 ± 0.09), before fluid challenge. The gray zone area spread from 6.15% to 15.6% for PPV (18 dogs), 2.45% to 10.65% for ΔVTI (22 dogs) and 0.6% to 10.15% for ΔVpeak (25 dogs).

CONCLUSIONS

When using mechanical ventilation, ΔVTI and ΔVpeak predicted fluid responsiveness with the same ability as PPV, based on the area under the ROC curve analysis. However, PPV showed great accuracy demonstrated by a narrower gray zone that included fewer individuals.

CLINICAL RELEVANCE

ΔVTI and ΔVpeak can be used as indices of fluid responsiveness in anesthetized dogs.

Arterial Pulse Pressure Variation with Mechanical Ventilation

Fluid administration leads to a significant increase in cardiac output in only half of ICU patients. This has led to the concept of assessing fluid responsiveness before infusing fluid. Pulse pressure variation (PPV), which quantifies the changes in arterial pulse pressure during mechanical ventilation, is one of the dynamic variables that can predict fluid responsiveness. The underlying hypothesis is that large respiratory changes in left ventricular stroke volume, and thus pulse pressure, occur in cases of biventricular preload responsiveness. Several studies showed that PPV accurately predicts fluid responsiveness when patients are under controlled mechanical ventilation. Nevertheless, in many conditions encountered in the ICU, the interpretation of PPV is unreliable (spontaneous breathing, cardiac arrhythmias) or doubtful (low Vt). To overcome some of these limitations, researchers have proposed using simple tests such as the Vt challenge to evaluate the dynamic response of PPV. The applicability of PPV is higher in the operating room setting, where fluid strategies made on the basis of PPV improve postoperative outcomes. In medical critically ill patients, although no randomized controlled trial has compared PPV-based fluid management with standard care, the Surviving Sepsis Campaign guidelines recommend using fluid responsiveness indices, including PPV, whenever applicable. In conclusion, PPV is useful for managing fluid therapy under specific conditions where it is reliable. The kinetics of PPV during diagnostic or therapeutic tests is also helpful for fluid management.

Leveraging Device-Arterial Coupling to Determine Cardiac and Vascular State

OBJECTIVE

Limitations in available diagnostic metrics restrict the efficacy of managing therapies for cardiogenic shock. In current clinical practice, cardiovascular state is inferred through measurement of pulmonary capillary wedge pressure and reliance on linear approximations between pressure and flow to estimate peripheral vascular resistance. Mechanical circulatory support devices residing within the left ventricle and aorta provide an opportunity for both determining cardiac and vascular state and offering therapeutic benefit. We leverage the controllable mode of operation and transvalvular position of an indwelling percutaneous ventricular assist device to assess vascular and, in turn, cardiac state through the effects of device-arterial coupling across different levels of device support.

METHODS

Vascular state is determined by measuring changes in the pressure waveforms induced through intentional variation in the device generated blood flow. We evaluate this impact by applying a lumped parameter model to quantify state-specific vascular resistance and compliance and calculate beat-to-beat stroke volume and cardiac output in both animal models and retrospective patient data without external calibration.

RESULTS

Vascular state was accurately predicted in patients and animals in both baseline and experimental conditions. In the animal, stroke volume was predicted within a total root mean square error of 3.71 mL (n = 482).

CONCLUSION

We demonstrate that device-arterial coupling is a powerful tool for evaluating patient and state specific parameters of cardiovascular function.

SIGNIFICANCE

These insights may yield improved clinical care and support the development of next generation mechanical circulatory support devices that determine and operate in tandem with the supported organ.

Ultrasound Assessment of the Change in Carotid Corrected Flow Time in Fluid Responsiveness in Undifferentiated Shock

OBJECTIVES

Adequate assessment of fluid responsiveness in shock necessitates correct interpretation of hemodynamic changes induced by preload challenge. This study evaluates the accuracy of point-of-care Doppler ultrasound assessment of the change in carotid corrected flow time induced by a passive leg raise maneuver as a predictor of fluid responsiveness. Noninvasive cardiac output monitoring (NICOM, Cheetah Medical, Newton Center, MA) system based on a bioreactance method was used.

DESIGN

Prospective, noninterventional study.

SETTING

ICU at a large academic center.

PATIENTS

Patients with new, undifferentiated shock, and vasopressor requirements despite fluid resuscitation were included. Patients with significant cardiac disease and conditions that precluded adequate passive leg raising were excluded.

INTERVENTIONS

Carotid corrected flow time was measured via ultrasound before and after a passive leg raise maneuver. Predicted fluid responsiveness was defined as greater than 10% increase in stroke volume on noninvasive cardiac output monitoring following passive leg raise. Images and measurements were reanalyzed by a second, blinded physician. The accuracy of change in carotid corrected flow time to predict fluid responsiveness was evaluated using receiver operating characteristic analysis.

MEASUREMENTS AND MAIN RESULTS

Seventy-seven subjects were enrolled with 54 (70.1%) classified as fluid responders by noninvasive cardiac output monitoring. The average change in carotid corrected flow time after passive leg raise for fluid responders was 14.1 ± 18.7 ms versus -4.0 ± 8 ms for nonresponders (p < 0.001). Receiver operating characteristic analysis demonstrated that change in carotid corrected flow time is an accurate predictor of fluid responsiveness status (area under the curve, 0.88; 95% CI, 0.80-0.96) and a 7 ms increase in carotid corrected flow time post passive leg raise was shown to have a 97% positive predictive value and 82% accuracy in detecting fluid responsiveness using noninvasive cardiac output monitoring as a reference standard. Mechanical ventilation, respiratory rate, and high positive end-expiratory pressure had no significant impact on test performance. Post hoc blinded evaluation of bedside acquired measurements demonstrated agreement between evaluators.

CONCLUSIONS

Change in carotid corrected flow time can predict fluid responsiveness status after a passive leg raise maneuver. Using point-of-care ultrasound to assess change in carotid corrected flow time is an acceptable and reproducible method for noninvasive identification of fluid responsiveness in critically ill patients with undifferentiated shock.

Getting to know a familiar face: Current and emerging focused ultrasound applications for the perioperative setting

Ultrasound technology is available in many pediatric perioperative settings. There is an increasing number of ultrasound applications for anesthesiologists which may enhance clinical performance, procedural safety, and patient outcomes. This review highlights the literature and experience supporting focused ultrasound applications in the pediatric perioperative setting across varied disciplines including anesthesiology. The review also suggests strategies for building educational and infrastructural systems to translate this technology into clinical practice.

Effect of Systolic Cardiac Function on Passive Leg Raising for Predicting Fluid Responsiveness: A Prospective Observational Study

BACKGROUND

Passive leg raising (PLR) represents a "self-volume expansion (VE)" that could predict fluid responsiveness, but the influence of systolic cardiac function on PLR has seldom been reported. This study aimed to investigate whether systolic cardiac function, estimated by the global ejection fraction (GEF) from transpulmonary-thermodilution, could influence the diagnostic value of PLR.

METHODS

This prospective, observational study was carried out in the surgical Intensive Care Unit of the First Affiliated Hospital of Sun Yat-sen University from December 2013 to July 2015. Seventy-eight mechanically ventilated patients considered for VE were prospectively included and divided into a low-GEF (<20%) and a near-normal-GEF (≥20%) group. Within each group, baseline hemodynamics, after PLR and after VE (250 ml 5% albumin over 30 min), were recorded. PLR-induced hemodynamic changes (PLR-Δ) were calculated. Fluid responders were defined by a 15% increase of stroke volume (SV) after VE.

RESULTS

Twenty-five out of 38 patients were responders in the GEF <20% group, compared to 26 out of 40 patients in the GEF ≥20% group. The thresholds of PLR-ΔSV and PLR-Δ cardiac output (PLR-ΔCO) for predicting fluid responsiveness were higher in the GEF ≥20% group than in the GEF <20% group (ΔSV: 12% vs. 8%; ΔCO: 7% vs. 6%), with increased sensitivity (ΔSV: 92% vs. 92%; ΔCO: 81% vs. 80%) and specificity (ΔSV: 86% vs. 70%; ΔCO: 86% vs. 77%), respectively. PLR-Δ heart rate could predict fluid responsiveness in the GEF ≥20% group with a threshold value of -5% (sensitivity 65%, specificity 93%) but could not in the GEF <20% group. The pressure index changes were poor predictors.

CONCLUSIONS

In the critically ill patients on mechanical ventilation, the diagnostic value of PLR for predicting fluid responsiveness depends on cardiac systolic function. Thus, cardiac systolic function must be considered when using PLR.

TRIAL REGISTRATION

Chinese Clinical Trial Register, ChiCTR-OCH-13004027; http://www.chictr.org.cn/showproj.aspx?proj=5540.

What is the lowest change in cardiac output that transthoracic echocardiography can detect?

Background

In critically ill patients, changes in the velocity-time integral (VTI) of the left ventricular outflow tract, measured by transthoracic echocardiography (TTE), are often used to non-invasively assess the response to fluid administration or for performing tests assessing fluid responsiveness. However, the precision of TTE measurements has not yet been investigated in such patients. First, we aimed at assessing how many measurements should be averaged within one TTE examination to reach a sufficient precision for various variables. Second, we aimed at identifying the least significant change (LSC) of these variables between successive TTE examinations.

Methods

We prospectively included 100 haemodynamically stable patients in whom TTE examination was planned. Three TTE examinations were performed, the first and the third by one operator and the second by another one. We calculated the precision and LSC (1) within one examination depending on the number of averaged measurements and (2) between measurements performed in two successive examinations.

Results

In patients in sinus rhythm, averaging three measurements within an examination was enough for obtaining an acceptable precision (interquartile range highest value < 10%) for VTI. In patients with atrial fibrillation, averaging five measurements was necessary. The precision of some other common TTE variables depending on the number of measurements is provided. Between two successive examinations performed by the same operator, the LSC was 11 [5–18]% for VTI. If two operators performed the examinations, the LSC for VTI significantly increased to 14 [8–26]%. The LSC between two examinations for other TTE variables is also provided.

Conclusions

Averaging three measurements within one TTE examination is enough for obtaining precise measurements for VTI in patients in sinus rhythm but not in patients with atrial fibrillation. Between two TTE examinations performed by the same operator, the LSC of VTI is compatible with the assessment of the effects of a 500-mL fluid infusion but is not precise enough for assessing the effects of some tests predicting preload responsiveness.

Electronic supplementary material

The online version of this article (10.1186/s13054-019-2413-x) contains supplementary material, which is available to authorized users.

The utility of point-of-care ultrasound in the assessment of volume status in acute and critically ill patients

BACKGROUND

Volume resuscitation has only been demonstrated to be effective in approximately fifty percent of patients. The remaining patients do not respond to volume resuscitation and may even develop adverse outcomes (such as acute pulmonary edema necessitating endotracheal intubation). We believe that point-of-care ultrasound is an excellent modality by which to adequately predict which patients may benefit from volume resuscitation.

DATA RESOURCES

We performed a search using PubMed, Scopus, and MEDLINE. The following search terms were used: fluid responsiveness, ultrasound, non-invasive, hemodynamic, fluid challenge, and passive leg raise. Preference was given to clinical trials and review articles that were most relevant to the topic of assessing a patient's cardiovascular ability to respond to intravenous fluid administration using ultrasound.

RESULTS

Point-of-care ultrasound can be easily employed to measure the diameter and collapsibility of various large vessels including the inferior vena cava, common carotid artery, subclavian vein, internal jugular vein, and femoral vein. Such parameters are closely related to dynamic measures of fluid responsiveness and can be used by providers to help guide fluid resuscitation in critically ill patients.

CONCLUSION

Ultrasound in combination with passive leg raise is a non-invasive, cost- and time-effective modality that can be employed to assess volume status and response to fluid resuscitation. Traditionally sonographic studies have focused on the evaluation of large veins such as the inferior vena cava, and internal jugular vein. A number of recently published studies also demonstrate the usefulness of evaluating large arteries to predict volume status.

Prediction of fluid responsiveness in ventilated patients

Fluid administration is the first-line therapy in patients with acute circulatory failure. The main goal of fluid administration is to increase the cardiac output and ultimately the oxygen delivery. Nevertheless, the decision to administer fluids or not should be carefully considered, since half of critically ill patients are fluid unresponsive, and the deleterious effects of fluid overload clearly documented. Thus, except at the initial phase of hypovolemic or septic shock, where hypovolemia is constant and most of the patients responsive to the initial fluid resuscitation, it is of importance to test fluid responsiveness before administering fluids in critically ill patients. The static markers of cardiac preload cannot reliably predict fluid responsiveness, although they have been used for decades. To address this issue, some dynamic tests have been developed over the past years. All these tests consist in measuring the changes in cardiac output in response to the transient changes in cardiac preload that they induced. Most of these tests are based on the heart-lung interactions. The pulse pressure or stroke volume respiratory variations were first described, following by the respiratory variations of the vena cava diameter or of the internal jugular vein diameter. Nevertheless, all these tests are reliable only under strict conditions limiting their use in many clinical situations. Other tests such as passive leg raising or end-expiratory occlusion act as an internal volume challenge. To reliably predict fluid responsiveness, physicians must choose among these different dynamic tests, depending on their respective limitations and on the cardiac output monitoring technique which is used. In this review, we will summarize the most recent findings regarding the prediction of fluid responsiveness in ventilated patients.

Quest for the holy grail: Assessment of echo-derived dynamic parameters as predictors of fluid responsiveness in patients with acute aneurysmal subarachnoid hemorrhage

Background:

Acute aneurysmal subarachnoid hemorrhage (aSAH) is a potentially devastating event often presenting with a plethora of hemodynamic fluctuations requiring meticulous fluid management. The aim of this study was to assess the utility of newer dynamic predictors of fluid responsiveness such as Delta down (DD), superior vena cava collapsibility index (SVCCI), and aortic velocity time integral variability (VTIAoV) in patients with SAH undergoing neurosurgery.

Materials and Methods:

Fifteen individuals with SAH undergoing surgery for intracranial aneurysmal clipping were enrolled in this prospective study. Postinduction, vitals, anesthetic parameters, and the study variables were recorded as the baseline. Following this, patients received a fluid bolus of 10 ml/kg of colloid over 20 min, and measurements were repeated postfluid loading. Continuous variables were expressed as mean ± standard deviation and compared using Student's t-test, with a P < 0.05 considered statistically significant. The predictive ability of variables for fluid responsiveness was determined using Pearson's coefficient analysis (r).

Results:

There were 12 volume responders and 3 nonresponders (NR). DD >5 mm Hg was efficient in differentiating the responders from NR (P < 0.05) with a sensitivity and specificity of 90% and 85%, respectively, with a good predictive ability to identify fluid responders and NR; r = 0.716. SVCCI of >38% was 100% sensitive and 95% specific in detecting the volume status and in differentiating the responders from NR (P < 0.05) and is an excellent predictor of fluid responsive status; r = 0.906. VTIAoV >20% too proved to be a good predictor of fluid responsiveness, with a sensitivity and specificity of 100% and 90%, respectively, with a predictive power; r = 0.732.

Conclusion:

Our study showed that 80% of patients presenting with aSAH for intracranial aneurysm clipping were fluid responders with normal hemodynamic parameters such as heart rate and blood pressure. Among the variables, SVCCI >38% appears to be an excellent predictor followed by VTIAoV >20% and DD >5 mmHg in assessing the fluid status in this population.

A bedside ultrasound technique for fluid therapy monitoring in severe hypovolemia: Tissue Doppler imaging of the right ventricle

Fluid therapy is one of the main issues for hemodynamic resuscitation. Tissue Doppler imaging (TDI) of the right ventricle (RV) with bedside ultrasound (BUS) technique is a new dynamic method to identify fluid responsiveness in patients with hypotension. Here, we present the case of a hypotensive patient monitored with TDI measurements of RV. A 75-year-old male patient was admitted to the emergency department (ED) with the complaint of diarrhea. He was in severe hypovolemia, with hypotension, tachycardia, and tachypnea. His laboratory results were normal. BUS was performed on the patient by the ED physician. The velocity of the excursion of the tricuspid valve measured at presentation was 14.47 cm/s and, together with collapsed inferior vena cava (IVC), this finding led to the decision to begin fluid therapy immediately. The patient underwent 2 L of fluid therapy with 0.9% NaCl in a 2-h period. Control BUS after fluid therapy revealed decreased TDI velocity of tricuspid annulus to 11.81 cm/s and dilated IVC not collapsing sufficiently with respiration. The patient received his maintenance therapy after admission to the internal medicine department and was discharged from the service after 3 days. TDI in fluid responsiveness may find a clinical role in the future by the clinical studies.

Critical care ultrasonography in circulatory shock

PURPOSE OF REVIEW

The objective was to define the role of ultrasound in the diagnosis and the management of circulatory shock by critical appraisal of the literature.

RECENT FINDINGS

Assessment of any patient's hemodynamic profile based on clinical examination can be sufficient in several cases, but many times unclarities remain. Arterial catheters and central venous lines are commonly used in critically ill patients for practical reasons, and offer an opportunity for advanced hemodynamic monitoring. Critical care ultrasonography may add to the understanding of the hemodynamic profile at hand. Improvements in ultrasound techniques, for example, smaller devices and improved image quality, may reduce limitations and increase its value as a complementary tool. Critical care ultrasonography has great potential to guide decisions in the management of shock, but operators should be aware of limitations and pitfalls as well. Current evidence comes from cohort studies with heterogeneous design and outcomes.

SUMMARY

Use of ultrasonography for hemodynamic monitoring in critical care expands, probably because of absence of procedure-related adverse events. Easy applicability and the capacity of distinguishing different types of shock add to its increasing role, further supported by consensus statements promoting ultrasound as the preferred tool for diagnostics in circulatory shock.

Assessment of adequacy of volume resuscitation

PURPOSE OF REVIEW

It has recently become evident that administration of intravenous fluids following initial resuscitation has a greater probability of producing tissue edema and hypoxemia than of increasing oxygen delivery. Therefore, it is essential to have a rational approach to assess the adequacy of volume resuscitation. Here we review passive leg raising (PLR) and respiratory variation in hemodynamics to assess fluid responsiveness.

RECENT FINDINGS

The use of ultrasound enhances the clinician's ability to detect and predict fluid responsiveness, whereas enthusiasm for this modality must be tempered by recent evidence that it is only reliable in apneic patients.

SUMMARY

The best predictor of fluid response for hypotensive patients not on vasopressors is a properly conducted passive leg raise maneuver. For more severely ill patients who are apneic, mechanically ventilated and on vasopressors, point of care echocardiography is the best choice. Increases in vena caval diameter induced by controlled positive pressure breaths are insensitive to arrhythmias and can be performed with relatively brief training. Most challenging are patients who are awake and on vasopressors; we suggest that the best method to discriminate fluid responders is PLR measuring changes in cardiac output.

Anesthesia-Associated Relative Hypovolemia: Mechanisms, Monitoring, and Treatment Considerations

Although the utility and benefits of anesthesia and analgesia are irrefutable, their practice is not void of risks. Almost all drugs that produce anesthesia endanger cardiovascular stability by producing dose-dependent impairment of cardiac function, vascular reactivity, and compensatory autoregulatory responses. Whereas anesthesia-related depression of cardiac performance and arterial vasodilation are well recognized adverse effects contributing to anesthetic risk, far less emphasis has been placed on effects impacting venous physiology and venous return. The venous circulation, containing about 65–70% of the total blood volume, is a pivotal contributor to stroke volume and cardiac output. Vasodilation, particularly venodilation, is the primary cause of relative hypovolemia produced by anesthetic drugs and is often associated with increased venous compliance, decreased venous return, and reduced response to vasoactive substances. Depending on factors such as patient status and monitoring, a state of relative hypovolemia may remain clinically undetected, with impending consequences owing to impaired oxygen delivery and tissue perfusion. Concurrent processes related to comorbidities, hypothermia, inflammation, trauma, sepsis, or other causes of hemodynamic or metabolic compromise, may further exacerbate the condition. Despite scientific and technological advances, clinical monitoring and treatment of relative hypovolemia still pose relevant challenges to the anesthesiologist. This short perspective seeks to define relative hypovolemia, describe the venous system’s role in supporting normal cardiovascular function, characterize effects of anesthetic drugs on venous physiology, and address current considerations and challenges for monitoring and treatment of relative hypovolemia, with focus on insights for future therapies.

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.

Advances in Diagnosis and Management of Hemodynamic Instability in Neonatal Shock

Shock in newborn infants has unique etiopathologic origins that require careful assessment to direct specific interventions. Early diagnosis is key to successful management. Unlike adults and pediatric patients, shock in newborn infants is often recognized in the uncompensated phase by the presence of hypotension, which may be too late. The routine methods of evaluation used in the adult and pediatric population are often invasive and less feasible. We aim to discuss the pathophysiology in shock in newborn infants, including the transitional changes at birth and unique features that contribute to the challenges in early identification. Special emphasis has been placed on bedside focused echocardiography/focused cardiac ultrasound, which can be used as an additional tool for early, neonatologist driven, ongoing evaluation and management. An approach to goal oriented management of shock has been described and how bed side functional echocardiography can help in making a logical choice of intervention (fluid therapy, inotropic therapy or vasopressor therapy) in infants with shock.

Fluid and Volume Monitoring

Background

Fluid resuscitation is not only used to prevent acute kidney injury (AKI) but fluid management is also a cornerstone of treatment for patients with established AKI and renal failure. Ultrafiltration removes volume initially from the intravascular compartment inducing a relative degree of hypovolemia. Normal reflex mechanisms attempt to sustain blood pressure constant despite marked changes in blood volume and cardiac output. Thus, compensated shock with a normal blood pressure is a major cause of AKI or exacerbations of AKI during ultrafiltration.

Methods

We undertook a systematic review of the literature using MEDLINE, Google Scholar and PubMed searches. We determined a list of key questions and convened a 2-day consensus conference to develop summary statements via a series of alternating breakout and plenary sessions. In these sessions, we identified supporting evidence and generated clinical practice recommendations and/or directions for future research.

Results

We defined three aspects of fluid monitoring: i) normal and pathophysiological cardiovascular mechanisms; ii) measures of volume responsiveness and impending cardiovascular collapse during volume removal, and; iii) measured indices of each using non-invasive and minimally invasive continuous and intermittent monitoring techniques. The evidence documents that AKI can occur in the setting of normotensive hypovolemia and that under-resuscitation represents a major cause of both AKI and mortality ion critically ill patients. Traditional measures of intravascular volume and ventricular filling do not predict volume responsiveness whereas dynamic functional hemodynamic markers, such as pulse pressure or stroke volume variation during positive pressure breathing or mean flow changes with passive leg raising are highly predictive of volume responsiveness. Numerous commercially-available devices exist that can acquire these signals.

Conclusions

Prospective clinical trials using functional hemodynamic markers in the diagnosis and management of AKI and volume status during ultrafiltration need to be performed. More traditional measure of preload be abandoned as marked of volume responsiveness though still useful to assess overall volume status.

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.

Tissue Edema, Fluid Balance, and Patient Outcomes in Severe Sepsis: An Organ Systems Review

Severe sepsis and septic shock remain among the deadliest diseases managed in the intensive care unit. Fluid resuscitation has been a mainstay of early treatment, but the deleterious effects of excessive fluid administration leading to tissue edema are becoming clearer. A positive fluid balance at 72 hours is associated with significantly increased mortality, yet ongoing fluid administration beyond a durable increase in cardiac output is common. We review the pathophysiologic and clinical data showing the negative effects of edema on pulmonary, renal, central nervous, hepatic, and cardiovascular systems. We discuss data showing increased morbidity and mortality following nonjudicious fluid administration and challenge the assumption that patients who are fluid responsive are also likely to benefit from that fluid. The distinctions between fluid requirement, responsiveness, and tolerance are central to newer concepts of resuscitation. We summarize data in each organ system showing a predictable increase in morbidity and mortality with nonbeneficial fluid administration, providing a better framework for precision in volume management of the patient with severe sepsis.

Pearls and pitfalls in comprehensive critical care echocardiography

Critical care echocardiography is developing rapidly with an increasing number of specialists now performing comprehensive studies using Doppler and other advanced techniques. However, this imaging can be challenging, interpretation is far from simple in the complex critically ill patient and mistakes can be easy to make. We aim to address clinically relevant areas where potential errors may occur and suggest methods to hopefully improve accuracy of imaging and interpretation.

The Assessment of Intravascular Volume with Inferior Vena Cava and Internal Jugular Vein Distensibility Indexes in Children Undergoing Urologic Surgery

PURPOSE

The purpose of this work is to assess the predictive value, for fluid responsiveness (FR), of the inferior vena cava distensibility index (IVC-DI) and internal jugular vein distensibility index (IJV-DI) in pediatric surgical patients.

MATERIAL AND METHODS

Prior to being placed under general anesthesia, 24 surgical patients were enrolled. Baseline parameters were recorded with the patient in the semirecumbent position (Stage 1). Next, the passive leg raising (PLR) maneuver was carried out and a second measurement was recorded (Stage 2). Patients with an increase in the cardiac index (CI) of >10%, induced by PLR, were considered to be responders (R), otherwise they were classified as nonresponders (NR). At both stages, CI and DI of the IVC and IJV were measured.

RESULTS

Responders had higher IVC-DI and IVJ-DI than NR in stage 1 (both p <.001). In stage 2, IVC-DI and IJV-DI were not different in R and NR groups (p =.164, p =.201). Utilizing cut-off values of > 22.7% for IVC-DI and > 25% for IJV-DI, these parameters had positive correlation coefficients, both in R and NR of, respectively, 0.626 and 0.929.

CONCLUSIONS

The IVC-DI predicts FR in anesthetized pediatric patients and correlates well with the IJV-DI; both may be used as prediction markers of FR in children.

Respiratory variation in aortic blood peak velocity and caudal vena cava diameter can predict fluid responsiveness in anaesthetised and mechanically ventilated dogs

BACKGROUND AND M&MS

Dynamic preload indices, such as systolic pressure variation (SPV), aortic flow peak velocity variation (ΔVpeak) and distensibility index of the caudal vena cava (CVCDI), are reliable indices for predicting fluid responsiveness in humans. This study aimed to investigate the ability of these indices to predict fluid response in 24 healthy dogs undergoing general anaesthesia and mechanical ventilation. Aortic flow peak velocity variation (∆Vpeak), CVCDI, and SPV were calculated before volume expansion (5mL/kg bolus of lactated Ringer's solution). The aortic velocity time integral (VTI) was measured before and after volume expansion as a surrogate of stroke volume. Dogs were considered responders (n=9) when the VTI increase was ≥15% and non-responders (n=15) when the increase was <15%.

RESULTS AND CONCLUSIONS

Before volume expansion, ΔVpeak, CVCDI and SPV were higher in responders than in non-responders (P=0.0009, P=0.0003, and P=0.0271, respectively). Receiver operating characteristic (ROC) curves were plotted for the three indices. The areas under the ROC curves for SPV, ΔVpeak, and CVCDI were 0.91 (CI 0.73-0.99; P=0.0001), 0.95 (CI 0.77-1; P=0.0001), and 0.78 (CI 0.56-0.92; P=0.015), respectively. The best cut-offs were 6.7% for SPV (sensitivity, 77.78%; specificity, 93.33%), 9.4% for ΔVpeak (sensitivity, 88.89%; specificity, 100%), and 24% for CVCDI (sensitivity, 77.78%; specificity, 73.33). In conclusion, ΔVpeak, CVCDI, and SPV are reliable predictors of fluid responsiveness in healthy dogs undergoing general anaesthesia and mechanical ventilation.

Respiratory Variation in Femoral Vein Diameter Has Moderate Accuracy as a Marker of Fluid Responsivity in Mechanically Ventilated Septic Shock Patients

Ultrasound (US) is considered the first step in evaluation of patients with shock; respiratory variation of the inferior vena cava (inferior vena cava collapsibility [IVCc]) is an important measurement in this scenario that can be impaired by patient condition or technical skills. The main objective of this study was to evaluate if respiratory variation of the femoral vein (femoral vein collapsibility [FVc]), which is easier to visualize, can adequately predict fluid responsiveness in septic shock patients. Forty-five mechanically ventilated septic shock patients in a mixed clinical-surgical, 30-bed intensive care unit were enrolled in this study. All patients underwent assessments of FVc, IVCc and cardiac output using a portable US device. The passive leg raising test was used to evaluate fluid responsiveness. FVc presented an area under the receiver operating characteristic curve of 0.678 (95% confidence interval: 0.519-0.837, p = 0.044) with a cutoff point of 17%, yielding a sensitivity of 62% and specificity of 65% in predicting fluid responsiveness. IVCc had greater diagnostic accuracy compared with FVc, with an area under the receiver operating characteristic curve of 0.733 (95% confidence interval: 0.563-0.903, p = 0.024) and a cutoff point of 29%, yielding a sensitivity of 47% and specificity of 86%. In conclusion, FVc has moderate accuracy when employed as an indicator of fluid responsiveness in spontaneously mechanically ventilated septic shock patients.

Predicting Fluid Responsiveness in Acute Liver Failure: A Prospective Study

BACKGROUND

The profound hemodynamic changes seen in acute liver failure (ALF) resemble the hyperdynamic state found in the later stages of septic shock. Vasopressor support frequently is required after initial volume therapy. Markers of preload dependency have not been studied in this patient group. Dynamic maneuvers such as passive leg raising or end-expiratory hold, which have shown good predictive accuracy in a general intensive care unit population, cannot be considered safe in this cohort because of the concerns of intracranial hypertension.

METHODS

Mechanically ventilated patients with ALF admitted to a tertiary specialist intensive care unit in shock and multiorgan failure were enrolled. Markers of fluid responsiveness derived from transpulmonary thermodilution, pulse contour analysis, and echocardiography were compared between responders (cardiac index ≥15%) and nonresponders to a colloid fluid challenge (5 mL/kg predicted body weight). The ability to predict fluid responsiveness of stroke volume variation, pulse pressure variation (PPV), and respiratory change in peak (delta V peak) left ventricular outflow tract velocity for preload dependency were analyzed.

RESULTS

Thirty-five patients (mean ± SD age, 38 [14] years, 13 male, 22 female]) were assessed after a single fluid challenge. Ten patients (29%) were fluid responders. Changes in cardiac index and stroke volume index in the cohort of 35 patients were correlated (R = 0.726 [99% confidence interval, 0.401-0.910]; P < .001). PPV predicted fluid responsiveness (area under the receiver operating characteristic curve [AUROC], 0.752 [95% confidence interval, 0.565-0.889]; P = .005; cutoff >9%). The AUROC for stroke volume variation was 0.678 ([95% confidence interval, 0.499-0.825]; P = .084; cutoff >11%). The AUROC for [delta] V peak before fluid bolus was 0.637 (95% confidence interval, 0.413-0.825; P = .322).

CONCLUSIONS

PPV based on pulse contour analysis predicted fluid responsiveness in ALF.

Strategies for Intravenous Fluid Resuscitation in Trauma Patients

Intravenous fluid management of trauma patients is fraught with complex decisions that are often complicated by coagulopathy and blood loss. This review discusses the fluid management in trauma patients from the perspective of the developing world. In addition, the article describes an approach to specific circumstances in trauma fluid decision-making and provides recommendations for the resource-limited environment.

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.

A review of hemodynamic monitoring techniques, methods and devices for the emergency physician

The emergency department (ED) is frequently the doorway to the intensive care unit (ICU) for a significant number of critically ill patients presenting to the hospital. Hemodynamic monitoring (HDM) which is a key component in the effective management of the critically ill patient presenting to the ED, is primarily concerned with assessing the performance of the cardiovascular system and determining the correct therapeutic intervention to optimise end-organ oxygen delivery. The spectrum of hemodynamic monitoring ranges from simple clinical assessment and routine bedside monitoring to point of care ultrasonography and various invasive monitoring devices. The clinician must be aware of the range of available techniques, methods, interventions and technological advances as well as possess a sound approach to basic hemodynamic monitoring prior to selecting the optimal modality. This article comprises an in depth discussion of an approach to hemodynamic monitoring techniques and principles as well as methods of predicting fluid responsiveness as it applies to the ED clinician. We review the role, applicability and validity of various methods and techniques that include; clinical assessment, passive leg raising, blood pressure, finger based monitoring devices, the mini-fluid challenge, the end-expiratory occlusion test, central venous pressure monitoring, the pulmonary artery catheter, ultrasonography, bioreactance and other modern invasive hemodynamic monitoring devices.

Data availability and feasibility of various techniques to predict response to volume expansion in critically ill patients

Objective:

The accuracy of various techniques to predict response to volume expansion in shock has been studied, but less well known is how feasible these techniques are in the ICU.

Methods:

This is a prospective observation single-center study of inpatients from a mixed profile ICU who received volume expansion. At time of volume expansion, we determined whether a particular technique to predict response was feasible, according to rules developed from available literature and nurse assessment.

Results:

We studied 214 volume expansions in 97 patients. The most feasible technique was central venous pressure (50%), followed by vena cava collapsibility, (47%) passive leg raise (42%), and stroke volume variation (22%). Aortic velocity variation, and pulse pressure variation, and were rarely feasible (1% each). In 37% of volume expansions, no technique that we assessed was feasible.

Conclusions:

Techniques to predict response to volume expansion are infeasible in many patients in shock.