Passive Leg Raise Maneuver Research Articles

Evaluation of four cardiac output measurement techniques during a modified passive leg raise maneuver in anesthetized dogs

Introduction: Modified passive leg raise maneuver (PLRM) is a successful volumetric predictor of fluid responsiveness in dogs during experimental induction and correction of hypovolemia using invasive pulmonary artery thermodilution (PACTD) for measuring cardiac output (CO). In this study, other CO methods, minimally-invasive esophageal Doppler (ESD), transesophageal echocardiography (TEE), arterial pressure waveform analysis (APW), noninvasive electrical velocimetry (EV), were investigated during PLRM in anesthetized dogs.

Dynamic and Static Cardiac Function Measurements During Sepsis.

Dynamic and Static Cardiac Function Measurements During Sepsis.

Use of a modified passive leg raise maneuver as a volumetric predictor of fluid responsiveness during experimental induction and correction of hypovolemia in anesthetized dogs

Introduction: Modified passive leg raise maneuver (PLR) was studied as a predictor of fluid responsiveness, via transient effects on cardiac output (CO) and plethysmographic variability index (PVI) in dogs during induction and correction of hypovolemia.

Mortality Benefit From the Passive Leg Raise Maneuver in Guiding Resuscitation of Septic Shock Patients: A Systematic Review and Meta-Analysis of Randomized Trials.

Fluid therapy plays a major role in the management of critically ill patients. Yet assessment of intravascular volume in these patients is challenging. Different invasive and non-invasive methods have been used with variable results. The passive leg raise (PLR) maneuver has been recommended by international guidelines as a means to determine appropriate fluid resuscitation. We performed this systematic review and meta-analysis to determine if using this method of volume assessment has an impact on mortality outcome in patients with septic shock. This study is a systematic review and meta-analysis. We searched available data in the MEDLINE, CINAHL, EMBASE, and CENTRAL databases from inception until October 2020 for prospective, randomized, controlled trials that compared PLR-guided fluid resuscitation to standard care in adult patients with septic shock. Our primary outcome was mortality at the longest duration of follow-up. We screened 1,425 article titles and abstracts. Of the 23 full-text articles reviewed, 5 studies with 462 patients met our eligibility criteria. Odds ratios (ORs) and associated 95% confidence intervals (CIs) for mortality at the longest reported time interval were calculated for each study. Using random effects modeling, the pooled OR (95% CI) for mortality with a PLR-guided resuscitation strategy was 0.82 (0.52 -1.30). The included studies were not blinded and they ranged from having low to high risk of bias using the Cochrane Risk of Bias Tool. Our analysis showed there was no statistically significant difference in mortality among septic shock patients treated with PLR-guided resuscitation vs. those with standard care.

Venous Pulse Wave Velocity variation in response to a simulated fluid challenge in healthy subjects

PurposeThe evaluation of a mini or simulated fluid challenge is still a complex and open issue in the clinical setting and it is of paramount significance for the fluid therapy optimization. We here investigated the capacity of a new hemodynamic parameter, the venous Pulse Wave Velocity (vPWV), to detect the effect of passive leg raising (PLR). Materials and methodsIn 15 healthy volunteers (7 M, 8 F, age 26 ± 3) venous pressure pulses were elicited by pneumatic compressions of the left hand and proximally detected by ultrasound for calculation of the vPWV. We also non-invasively measured the basilic vein (BV) cross-sectional perimeter, and peripheral venous pressure (PVP). The PLR manoeuvre was performed twice to evaluate reliability of the assessment. ResultsThe PLR had an overall statistically significant effect on the entire set of variables (MANOVA, p < 0.05): vPWV increased from 2.11 ± 0.46 to 2.30 ± 0.47 m/s (p = 0.01; average increase: 10%). This effect was transient and dropped below 5% after about 3 min. A significant increase was also exhibited by BV size and PVP. In consecutive measurements vPWV showed little intra-subject variability (CoV = 8%) and good reliability (ICC = 0.87). Finally, the vPWV responses to the two PLRs exhibited good agreement (paired T-test: p = 0.96), and moderate reliability (ICC = 0.57). ConclusionThese results demonstrated that vPWV can be non-invasively, objectively and reliably measured in healthy subjects and that it is adequate to detect small pressure/volume variations, as induced by PLR-from-supine. These characteristics make it suitable for clinical applications.

Management of cardiovascular insufficiency in ICU: the BEAT approach.

A large number of patients admitted to ICU display hemodynamic deterioration at some time during their stay. The management of acute hemodynamic derangement of any cause can be difficult and has to be accomplished quickly and correctly as delayed and inappropriate resuscitation treatments carry increased mortality. Cardiovascular insufficiency shows end-organ hypoperfusion-associated dysfunction, thus decreasing level of consciousness, falling urine output, ileus, new onset tachypnea and the presence of skin mottling are important clinical clues to cardiovascular deterioration and should be promptly looked for and if detected alert the bedside clinician that further assessment and potentially treatment is necessary. Although measures of serum lactate are useful to document the presence of tissue hypoperfusion, they are non-specific in defining its etiology. In a patient with acute hemodynamic instability, we propose a step-by-step approach as follows: 1) rapid initial ultrasound assessment of heart function; 2) pathophysiological understanding of heart and circulation interaction; 3) functional hemodynamic monitoring; and 4) treatment. We named such approach BEAT, which stands for: browse the heart, measure the elastances, assess volume status, and treat. Combining bedside echocardiography, including the evaluation of the interaction between the heart and the circulation, with FHM offers the opportunity to personalize the hemodynamic management to the specific requirements.

Passive Leg Raise: Feasibility and Safety of the Maneuver in Patients With Undifferentiated Shock.

Passive leg raise (PLR), in combination with technologies capable of capturing stroke volume changes, has been widely adopted in the management of shock. However, dedicated evaluation of safety, feasibility, and receptiveness of patients and nursing staff to PLR maneuver is missing. A noninterventional, prospective trial recruited adult patients with onset of undifferentiated shock within 24 hours with persistent vasopressor requirements despite fluid resuscitation. A standardized PLR maneuver was used to compare two noninvasive hemodynamic monitoring systems, each without significant impact on the performance of the maneuver. Safety and efficacy of the PLR were evaluated via subjective and objective measures. Objective measures of patient comfort and tolerance were evaluated through changes in vital signs, sedation, and analgesia requirements. Nurses and awake patients completed surveys on their experience. Seventy-nine patients were enrolled. Testing was aborted in 2 cases for medical reasons (one patient developed rapid atrial fibrillation, second had profound desaturation). Of all, 5.4% of patients required additional vasopressor support after completion of the PLR maneuver due to persistent hypotension and 4.1% of patients required additional sedation. Among awake patients (N = 35), 6% reported pain and 29% reported discomfort. A total of 11% of nurses reported minor technical difficulties with the maneuver. Passive leg raise maneuver leads to a few serious but reversible complications in a selected population of hemodynamically unstable patients. Although it provides relevant diagnostic information, it may impact patient care. Treating physician should be aware of infrequent but possible complications and appreciate the impact of the maneuver on patients' comfort and nursing workload.

Corrected carotid flow time and passive leg raise as a measure of volume status

BackgroundThe aim of this study was to investigate the value of corrected carotid flow time (FTc) with passive leg raise (PLR) as a non-invasive marker of volume status in end stage renal disease (ESRD) patients. MethodsProspective observational study of ESRD patients presenting to the Emergency department requiring hemodialysis. The common carotid artery was evaluated in long axis. Flow time measurements pre- and post-dialysis as well as before and after PLR were recorded. Results54 patients were enrolled, of which, 30 (55%) were male. The mean age was 47.4 years. The mean volume of fluid removed was 3.89 ± 0.91 L. In the pre-dialysis cohort, the mean FTc was 340.16 ms (95% CI, 330.36–349.95). Following PLR, the mean FTc was 341.34 ms (95% CI 331.74–350.94). In the post hemodialysis cohort, the mean FTc was 302.48 ms (95% CI, 293.63–311.32). Following the PLR maneuver, the mean FTc was 340.49 ms (95% CI 331.97–349.02). The mean decrease in corrected carotid flow time was 19.15 ms (95% CI, 22.86–41.17), 32.02 ms (95% CI 4.05–34.25) and 41.17 ms (95% CI, 36.47–54.76) for patients who had <3 L, 3-4 L and >4 L removed, respectively. In patients without CHF, the mean decrease in FTc after hemodialysis was 38.80 ms (95% CI, 30.12–47.49) whereas for CHF patients the mean decrease was 35.60 ms (95% CI, 25.05–46.15). ConclusionCorrected flow time in conjunction with passive leg raise seem to correlate with volume status in hemodialysis patients.

Volume responsiveness assessed by passive leg raising and a fluid challenge: a critical review focused on mean systemic filling pressure.

This review applied cardiovascular principles relevant to the physiology of venous return in interpreting studies on the utility of a passive leg-raising manoeuvre to identify patients who do (responders) or do not respond to a subsequent intravenous volume challenge with an increase in cardiac output. Values for cardiac output, mean arterial and central venous pressure, and the calculated cardiovascular variables mean systemic filling pressure analogue, heart efficiency, cardiac power indexed by volume state and volume efficiency, before and after passive leg raising as well as before and after fluid volume challenge, were extracted from published studies. Eleven studies including 572 patients and 52% responders were analysed. Cardiac output increased by 12% in responders during passive leg raising and by 22% following a volume challenge. No statistically significant differences were found between responders and non-responders in cardiac output, mean arterial or central venous pressure before the passive leg-raising manoeuvre or the volume challenge. In contrast, the calculated mean (SD) systemic filling pressure analogue, reflecting the intravascular volume, was significantly lower in responders (14.2 (1.8) mmHg) than non-responders (17.5 (3.4) mmHg; p = 0.007) before the passive leg-raising manoeuvre, as well as before fluid volume challenge (14.6 (2.2) mmHg vs. 17.6 (3.5) mmHg, respectively; p = 0.02). The scalar measure volume efficiency was higher in responders at 0.35 compared with non-responders at 0.10. Non-responders also demonstrated deteriorating heart efficiency of -15% and cardiac power of -7% when given an intravenous fluid volume challenge. The results demonstrate that the calculation of mean systemic filling pressure analogue and derived variables can identify patients likely to respond to a fluid volume challenge and provides scalar results rather than merely a dichotomous outcome of responder or non-responder.

Echocardiography and passive leg raising in the postoperative period: A prospective observational study.

Signs of hypovolaemia are frequent in the postoperative period, but not all patients need or respond to fluid administration. An increase in cardiac output (CO) after passive leg raising (PLR) has been demonstrated to be useful as a volume response predictor in non-surgical, spontaneously breathing patients. The objective of this study was to evaluate the accuracy of transthoracic echocardiography after PLR to predict fluid responsiveness in post-surgical patients. A prospective observational study. A tertiary hospital between January and July 2015. Fifty-one spontaneously breathing postoperative patients with suspected hypovolaemia (arterial hypotension, oliguria, tachycardia or delayed capillary refill) were considered for the study. Demographic and personal data were collected, as well as heart rate variations, mean arterial pressure during PLR and after administering 500 ml of Ringer's lactate solution. CO was measured by transthoracic echocardiography. The primary outcome was measurement of CO before and after PLR and Ringer's lactate administration. Forty-one patients were included in the study (six patients were excluded because of a poor echocardiographic window and four because of misalignment of the Doppler and outflow tract of the left ventricle). Twenty-two patients (54%) were considered responders to fluid therapy, with an increase of stroke volume greater than or equal to 15% after 500 ml lactated Ringer's infusion. The highest area under the curve was found for an increase in CO (0.91 ± 0.05; 95% confidence interval 0.78 to 0.97). An increase in CO greater than 11% after the PLR manoeuvre predicts a volume response with 68% sensitivity and 100% specificity. This is the first study showing that measurement of CO after PLR can predict volume response in spontaneously breathing postoperative patients.

Non-invasive assessment of fluid responsiveness using CNAP™ technology is interchangeable with invasive arterial measurements during major open abdominal surgery

BackgroundDynamic variables of fluid responsiveness (FR), such as pulse pressure variation (PPV), have been shown to predict the response to a fluid challenge accurately. A recently introduced non-invasive technology based on the volume-clamp method (CNAP™) offers the ability to measure PPV continuously (PPVCNAP). However, the accuracy regarding the prediction of FR in the operating room has to be proved. MethodsWe compared PPVCNAP with an invasive approach measuring PPV using the PiCCO technology (PPVPiCCO). We studied 47 patients undergoing major open abdominal surgery before and after a passive leg-raising manoeuvre and i.v. fluid resuscitation. A positive response to a volume challenge was defined as ≥15% increase in stroke volume index obtained with transpulmonary thermodilution. Bootstrap methodology was used with the grey zone approach to determine the area of inconsistency regarding the ability of PPVPiCCO and PPVCNAP to predict FR. ResultsIn response to the passive leg-raising manoeuvre, PPVPiCCO predicted FR with a sensitivity of 81% and a specificity of 72% [area under the curve (AUC) 0.86] compared with a sensitivity of 76% and a specificity of 72% (AUC 0.78) for PPVCNAP. Regarding the volume challenge in the operating room, PPVPiCCO predicted FR with a sensitivity of 87% and a specificity of 100% (AUC 0.97) compared with a sensitivity of 91% and specificity of 93% (AUC 0.97) for PPVCNAP. The grey zone approach identified a range of PPVPiCCO values (11–13%) and PPVCNAP values (7–11%) for which FR could not be predicted reliably. ConclusionsNon-invasive assessment of FR using PPVCNAP seems to be interchangeable with PPVPiCCO in patients undergoing major open abdominal surgery. Clinical trial registrationNCT02166580.

The diagnostic utility of sonographic carotid flow time in determining volume responsiveness

ObjectiveWe aimed to predict volume responsiveness and to assess the diagnostic accuracy of carotid flow time (FTc) with the change in hydration status before and after a passive leg raise (PLR) maneuver. MethodsParticipants who presented at a community health fair in a dehydrated state following a prolonged fast while observing the month of Ramadan were recruited. Sonographic FTc measurements were obtained in the semi-Fowler position and after a PLR maneuver while participants were in a fasting state and repeated approximately 3 hours after breaking their fast. ResultsIn total, 123 participants with mean age of 47±14 years, 55% male, were enrolled. Participants had fasted for an average of 16.9 hours and consumed an average of 933 mL between the 2 ultrasound measurements. Mean FTc values were significantly lower in the fasting state compared with the nonfasting state (312±22 vs 345±25milliseconds, P value < .001). Relative increases in FTc following a PLR maneuver demonstrated strong discrimination of volume status (area under the receiver operating curve: 0.86 [95% confidence interval, 0.81-0.91]). ConclusionsThe use of point-of-care ultrasound to measure FTc may provide a noninvasive alternative to determine fluid status. Percentage change in FTc of ≥5% provides a reliable diagnostic accuracy for predicting fluid status.

Characteristics Associated With Fluid Responsiveness and Fluid Toxicity Demonstrated by Passive Leg Raise Maneuver in Septic Patients in a Mozambican Emergency Department

Characteristics Associated With Fluid Responsiveness and Fluid Toxicity Demonstrated by Passive Leg Raise Maneuver in Septic Patients in a Mozambican Emergency Department

Carotid Doppler flowmetry correlates poorly with thermodilution cardiac output following cardiac surgery.

It remains unclear whether measuring carotid arterial flow by the time velocity integral using vascular Doppler ultrasound can be used to monitor cardiac output and volume responsiveness. The carotid Doppler flow (time velocity integral and peak flow velocity variation) was assessed in triplicate by an intensivist with formal vascular ultrasound training. Thirty-three patients admitted following coronary by-pass surgery were studied before and after a passive leg-raising manoeuvre to investigate volume responsiveness (more than 10% increase in cardiac output) along with indices of arterial load measuring cardiac output by thermodilution. Pearson's correlation coefficient and area under the curve (AUC) by receiver operating characteristics were calculated. A significant correlation between carotid Doppler flow and cardiac output was demonstrated in post-operative cardiac surgery patients (r = 0.80 [95%CI 0.61-0.89]), including relative changes following passive leg raising (r = 0.79 [95%CI 0.60-0.89]) that showed a mean difference of 2% with wide limits of agreements (-19% to 16%). Changes in carotid Doppler flow following passive leg raising correlated with the baseline arterial resistance but not with compliance or effective elastance. A peak flow variation > 10% before passive leg raising discriminated responders to the manoeuvre with an AUC of 0.81 [95% CI 0.55-0.95]. Weak correlations between common carotid Doppler flow and cardiac output mean that the methods cannot be used interchangeably in post-operative cardiac surgery patients.

Assessing Fluid Responsiveness in Spontaneously Breathing Patients.

The primary objective of this study was to test if fasting volunteers exhibit fluid responsiveness using noninvasive hemodynamic measurements. The secondary objective was to test a passive leg raise (PLR) maneuver as a diagnostic predictor of fluid responsiveness. This was a quasi-experimental design involving healthy volunteers. Subjects were excluded for pregnancy and congestive heart failure. Following a 12-hour fast, subjects had baseline hemodynamic monitoring recorded using noninvasive, continuous pulse contour analysis. Subjects then had a PLR maneuver performed, followed by an intravenous bolus of crystalloid. A rise in stroke volume ≥ 10% from baseline with the bolus was considered consistent with fluid responsiveness, and the same rise with a PLR was consistent with a positive PLR maneuver. The primary outcome was the change in stroke volume with a fluid bolus. Univariate analysis assessed changes in hemodynamic parameters. Logistic regression analysis determined the test characteristics of the PLR in predicting subjects who were ultimately fluid responsive. Forty subjects completed the study. The mean change in stroke volume with a crystalloid bolus was 19% (95% confidence interval [CI] = 16% to 21%). Thirty-six (90%) subjects were fluid responsive. The mean PLR response for the overall cohort was 16% (95% CI = 12% to 19%), and 26 (65%) subjects had a positive PLR maneuver. The PLR was 72% sensitive (95% CI = 55% to 85%) and 100% specific (95% CI = 40% to 100%) for predicting the presence of fluid responsiveness. Noninvasive assessment of fluid responsiveness in healthy volunteers and prediction of this response with a PLR maneuver is achievable. Further work is indicated to test these methods in acutely ill patients.

The value of internal jugular vein collapsibility index in sepsis.

Rapid, accurate, and reproducible assessment of intravascular volume status is crucial in order to predict the efficacy of volume expansion in septic patients. The aim of this study was to verify the feasibility and usefulness of the internal jugular vein collapsibility index (IJV-CI) as an adjunct to the inferior vena cava collapsibility index (IVC-CI) to predict fluid responsiveness in spontaneously-breathing patients with sepsis. Three stages of sonographic scanning were performed. Hemodynamic data were collected using the Ultrasonic Cardiac Output Monitor 1A system (Uscom, Ltd., Sydney, NSW, Australia) coupled with paired assessments of IVC-CI and IJV-CI at baseline, after passive leg raise (PLR), and again in semi-recumbent position. Fluid responsiveness was assessed according to changes in the cardiac index (CI) induced by PLR. Patients were retrospectively divided into 2 groups: fluid responder if an increase in CI (ΔCI) ≥15% was obtained after PLR maneuver, and non-responder if ΔCI was <15%. Total of 132 paired scans of IJV and IVC were completed in 44 patients who presented with sepsis and who were not receiving mechanical ventilation (mean age: 54.6±16.1 years). Of these, 23 (52.2%) were considered to be responders. Responders had higher IJV-CI and IVC-CI before PLR maneuver than non-responders (p<0.001). IJV-CI of more than 36% before PLR maneuver had 78% sensitivity and 85% specificity to predict responder. Furthermore, less time was needed to measure venous diameters for IJV-CI (30 seconds) compared with IVC-CI (77.5 seconds; p<0.001). IJV-CI is a precise, easily acquired, non-invasive parameter of fluid responsiveness in patients with sepsis who are not mechanically ventilated, and it appears to be a reasonable adjunct to IVC-CI.

Field Ultrasound Evaluation of Central Volume Status and Acute Mountain Sickness

To investigate whether ultrasonography can be used for field volume status assessment and to determine whether a detectable difference in intravascular volume exists in individuals with acute mountain sickness (AMS) compared with those without. Study was performed at the Himalayan Rescue Association Clinic in Manang, Nepal, located on the Annapurna trekking circuit at an altitude of 3519 m (11545 feet). A convenience sample was taken from individuals trekking over 5 to 8 days from 760 m (2490 feet) to 3519 m (11,545 feet), comparing asymptomatic trekkers vs those who experienced AMS. Subjects were evaluated for AMS based on the Lake Louise AMS Questionnaire (LLS ≥ 3 indicates AMS). After medical screening examination, both groups (control, n = 51; AMS, n = 18) underwent ultrasonography to obtain measurements of inferior vena cava collapsibility index (IVC CI) and left ventricular outflow tract velocity-time integral (LVOT VTI) before and after a passive leg raise (PLR) maneuver. There was no statistically significant difference between groups regarding change in heart rate before and after PLR, or IVC CI; however, there was a statistically significant greater increase in LVOT VTI after PLR maneuver in control group subjects compared with those with AMS (18.96% control vs 11.71% AMS; P < .01). Ultrasonography is a useful tool in the assessment of intravascular volume at altitude. In this sample, we found ultrasonographic evidence that subjects with AMS have a higher intravascular volume than asymptomatic individuals. These data support the hypothesis that individuals with AMS have decreased altitude-related diuresis compared with asymptomatic individuals.

Both passive leg raising and intravascular volume expansion improve sublingual microcirculatory perfusion in severe sepsis and septic shock patients

To assess sublingual microcirculatory changes following passive leg raising (PLR) and volume expansion (VE) in septic patients. This prospective study was conducted in two university hospital intensive care units and included 25 mechanically ventilated patients with severe sepsis or septic shock who were eligible for VE in the first 24 h of their admission. Pulse pressure variation (ΔPP), cardiac output (CO) and sublingual microcirculation indices were assessed at five consecutive steps: (1) semi-recumbent position (Baseline 1), (2) during PLR manoeuvre (PLR), (3) after returning to semi-recumbent position (Baseline 2), (4) at the time when VE induced the same degree of preload responsiveness as PLR (VE(∆PP = PLR)) and (5) at the end of VE (VE(END)). At each step, five sublingual microcirculation sequences were acquired using sidestream darkfield imaging to assess functional capillary density (FCD), microcirculatory flow index (MFI), proportion of perfused vessels (PPV) and flow heterogeneity index (FHI). The PLR, VE(∆PP = PLR) and VE(END) induced a significant increase in CO and a significant decrease in ΔPP compared to Baseline 1 and Baseline 2 values. Both PLR and VE induced significant increases in FCD, MFI and PPV and a significant decrease in FHI compared to Baseline 1 and Baseline 2 values. In preload responsive severe septic patients examined within the first 24 h of their admission, both PLR and VE improved sublingual microcirculatory perfusion. At the level of volume infusion used in this study, these changes in sublingual microcirculation were not explained by changes in rheologic factors or changes in arterial pressure.

Passive leg raising: keep it easy!

Dear Editor, We read with interest the recently published article by Lakhal et al. [1]. The authors confirmed that the passive leg raising (PLR) test was a good predictor of fluid responsiveness when its effects were assessed on cardiac output. This study increases the level of evidence that the PLR test can serve as a ‘‘self’’ volume challenge. The authors also confirmed previous studies including ours [2, 3] by showing that the PLR test was less predictive of fluid responsiveness if its effects were assessed on arterial pressure rather than directly on cardiac output. Nevertheless, we are concerned by the fact that the predictive value of the PLR effects on cardiac output was lower in the study by Lakhal et al. (area under the receiver operating characteristics curve of 0.83) than in all previous studies on this topic. Two reasons can be found in the manuscript to explain this surprising result. The first reason is that Lakhal et al. assessed the effects of PLR on cardiac output 1 min after the beginning of the PLR manoeuvre and used the intermittent thermodilution technique, which required repetitive injections of 3–7 cold boluses. Their way to proceed is highly questionable. Indeed, we already reported that the PLR test exerts its maximal effects within 1 min and that these effects might later decrease in some patients [5]. This justifies the use of continuous real-time cardiac output monitoring to be sure not to miss the maximal haemodynamic effects of PLR and thus to improve the accuracy of this test. Secondly, Lakhal et al. reported that the PLR manoeuvre did not significantly increase the central venous pressure in a large proportion of patients. We strongly believe that, in fact, this was due to the method by which the leg raise was performed, i.e. starting from the supine position and not from the semi-recumbent position. Indeed, we previously demonstrated that starting the manoeuvre from the supine rather than from the semi-recumbent position reduced the PLR effects on cardiac preload since it did not mobilize the blood volume of the splanchnic compartment [4]. Again, one can hypothesize that the way in which the authors performed the PLR test reduced its sensitivity. Thus, the results of the study by Lakhal et al. might be hardly applicable to current practice. We believe that, when PLR is performed in an appropriate way, i.e. starting from the semi-recumbent position and by using a real-time cardiac output monitoring technique [5], one can waive the cumbersome measurement of central venous pressure without reducing the accuracy of the PLR test.

Stroke volume and passive leg raising predict volume responsiveness in ICU patients: who is actually responsive?

With much interest we read the article by Thiel and coworkers [1], who clearly demonstrate how a completely non-invasive technique can be used to determine changes in cardiac stroke volume in response to a passive leg raise maneuver (PLR) and actual fluid administration. Still, I have some questions. First, we wonder why the authors chose to enroll only the patients who were a priori considered to require volume expansion. Especially with the use of a non-invasive technique and the PLR being part of routine practice, it would be very instructive to know which and how many patients from the general ICU population are actually fluid responsive or likely to be exposed to excess fluid administration. Second, why did the authors perform the volume expansion after the PLR with the patients again in the semi-recumbent position? Patients are put in this position to mobilize more volume for the actual PLR [2], but the stroke volume response is studied in the supine position (which is also the normal position for most ICU patients). Because of a decreased preload it is very likely that more fluid has to be administered to these patients to evoke a similar response in stroke volume Finally, did the authors anticipate this increased fluid requirement when they administered a rather large volume expansion (≥ 500 ml) in relation to the volume they estimated to be mobilized with the PLR (150 to 200 ml)? Could it be possible that these differences have influenced the sensitivity and specificity of calculations?