Passive leg raise offers promise in predicting fluid responsiveness
"Like this ... kind of"
Passive Leg Raise Improved Management of Patients in Shock* (*some assembly required)
Providing the right amount of fluid is vital in a critically ill patient, as both too little and too much can result in poor outcomes. Yet even with this understanding, the clinical assessment of fluid responsiveness remains a challenge because the most rigorously tested dynamic techniques require invasive monitoring and mechanical ventilation. Further, the former gold standard Swan-Ganz pulmonary artery catheter was not shown to be helpful in managing fluid balance in patients with ARDS, and strong observational data suggests routine use of PACs is actually harmful, for unknown reasons. Only 50% of hemodynamically unstable patients are volume responsive, but we need something better than just a coin flip to determine who should receive fluids and who shouldn't. Lifting a patient's legs has been estimated to provide a 200-300 mL bolus of fluid, by mobilizing pooled venous blood back to the heart. Marik and colleagues asked whether this quick and easy test was also accurate at identifying patients whose blood pressure would improve with IV fluids, reporting their findings in a recent issue of Chest.
What They Did
This was a single center, retrospective electronic chart review of 34 patients admitted to the ICU. These patients were selected because they had data available for continuous stroke volume index (measured by bioreactance); passive leg raise maneuver; and carotid bloodflow (by ultrasonography). Since these authors practiced in this ICU (at Sentara Norfolk General Hospital, associated with Eastern Virginia Medical School in Norfolk, Virginia), it was unblinded, more of a case series from this institution's critical care practice, where they had previously incorporated formal testing of passive leg raise into the routine management of hemodynamically unstable patients. A few notes about the methodology:
In all patients stroke volume index (SVI) was measured and stabilized prior to any maneuvers being performed.
Passive Leg Raise (PLR): All patients were placed in the semi-recumbent 45° position and then moved to the supine position with legs elevated 45°. See how passive leg raise is done.
The change in stroke volume index was recorded as the maximum change in the first three minutes from baseline.
Carotid and brachial bloodflow were obtained by ultrasound doppler during this time as well.
After passive leg raise, all patients got a 500 cc bolus of crystalloid to determine true fluid responsiveness.
Patients were "true fluid responders" when they had a >10% increase in stroke volume index from baseline after receiving 500 mL crystalloid.
Patients were excluded if they were not in sinus rhythm. Ventilators were set on pressure control ventilation to target plateau pressure < 30 cmH2O to achieve tidal volume 6-8 mL/kg ideal body weight.
What They Found
18 of 34 patients were considered true fluid responders
PLR was 94% sensitive and 100% specific for predicting fluid responsiveness.
Fluid responders had higher left ventricular ejection fractions (p=0.02), but the LVEF did not correlate with percent change in SVI
Carotid bloodflow increased by significantly more after the passive leg raise maneuver in responders compared to non-responders (p<0.001)
There was a strong correlation between percent change in SVI by PLR and percent change carotid bloodflow (p=0.003)
What It Means
Paired with stroke volume indices in a heterogenous group of hemodynamically unstable patients in sinus rhythm, passive leg raising was a sensitive and specific maneuver to predict fluid responsiveness in this small study. Furthermore, if one is ultrasound savvy, passive leg raise maneuver can be paired with carotid visualization to potentially eliminate the need for cardiac output monitoring. This small study will need to be replicated in larger cohorts. But when a patient is in shock, one really wants to know whether giving fluid will cause her blood pressure (not stroke volume index) to go up. The authors didn't report the mean arterial pressures before-and-after passive leg raise and fluid challenges, probably either because the data was not available, or because there was no detectable difference.
Clinical Takeaway: When trying to ascertain a patient's fluid responsiveness, our current choices are gestalt (i.e., high uncertainty) and an invasive pulmonary artery catheter of doubtful benefit and possible harm. Using passive leg raise as a test routinely could help, and it's hard to see how it could hurt. (Passive leg raising is already a standard maneuver taught in emergency medicine training.) Ultimately, its effectiveness could be reduced by limited availability of the non-invasive stroke volume index monitoring, or the availability of trained ultrasonographers. Without these higher-tech adjuncts, passive leg raise doesn't perform as well as a test (i.e., many patients' blood pressure won't change noticeably). Marik, PE et al. The use of bioreactance and carotid Doppler to determine volume responsiveness and bloodflow redistribution following passive leg raising in hemodynamically unstable patients. Chest 2013; 143(2):364-370. Passive leg raise demonstration (a video produced by Edwards Lifesciences, who were not associated with this article or the authors):