Changes in aortic blood flow induced by passive leg raising predict fluid responsiveness in critically ill patients

Abstract

Introduction: Esophageal Doppler provides a continuous and non-invasive estimate of descending aortic blood flow (ABF) and corrected left ventricular ejection time (LVETc). Considering passive leg raising (PLR) as a reversible volume expansion (VE), we compared the relative abilities of PLR-induced ABF variations, LVETc and respiratory pulsed pressure variations (DeltaPP) to predict fluid responsiveness.

Methods: We studied 22 critically ill patients in acute circulatory failure in the supine position, during PLR, back to the supine position and after two consecutive VEs of 250 ml of saline. Responders were defined by an increase in ABF induced by 500 ml VE of more than 15%.

Results: Ten patients were responders and 12 were non-responders. In responders, the increase in ABF induced by PLR was similar to that induced by a 250 ml VE (16% versus 20%; p = 0.15). A PLR-induced increase in ABF of more than 8% predicted fluid responsiveness with a sensitivity of 90% and a specificity of 83%. Corresponding positive and negative predictive values (PPV and NPV, respectively) were 82% and 91%, respectively. A DeltaPP threshold value of 12% predicted fluid responsiveness with a sensitivity of 70% and a specificity of 92%. Corresponding PPV and NPV were 87% and 78%, respectively. A LVETc of 245 ms or less predicted fluid responsiveness with a sensitivity of 70%, and a specificity of 67%. Corresponding PPV and NPV were 60% and 66%, respectively.

Conclusion: The PLR-induced increase in ABF and a DeltaPP of more than 12% offer similar predictive values in predicting fluid responsiveness. An isolated basal LVETc value is not a reliable criterion for predicting response to fluid loading.

Figure 1

Study protocol.

Figure 2

Relationship between changes in ABF induced by PLR and VE. Abbreviations: ABF = aortic blood flow; PLR = passive leg raising; VE = volume expansion. Results are expressed as percentage variation from Base 1 value for PLR and from Base 2 value for VE.

Figure 3

ROC curves comparing delta ABF, LVETc and ΔPP to discriminate responders and non-responders. Abbreviations: ROC = Receiver Operating Characteristic; ABF = aortic blood flow; PLR = passive leg raising; LVETc = left ventricular ejection time corrected for heart rate; ΔPP = respiratory variation of pulse pressure.

Figure 4

Boxplots and individual values of change in ABF, LVETc and ΔPP in responders and non-responders. Abbreviations: ABF = aortic blood flow; LVETc = left ventricular ejection time corrected for heart rate; ΔPP = respiratory variation of pulse pressure. Asterisk, p < 0.05 for responders versus non-responders.