Relation between pulse oximetry plethysmographic waveform amplitude induced by passive leg raising and cardiac index in spontaneously breathing subjects

IntroductionPrevious studies suggested that variation of pulse oximetric plethysmographic (POP) waveform amplitude (ΔPOP) could predict fluid responsiveness in mechanically ventilated patients. Our objective was to correlate the variations of ΔPOP and the variations of cardiac index (CI) induced by passive leg raising (PLR) in spontaneously breathing volunteers.MethodsWe studied 26 spontaneously breathing volunteers using a pulse oximeter attached to the middle finger. We assessed hemodynamic variables, including ΔPOP (%) (POPmax − POPmin)/[(POPmax + POPmin)/2] and CI determined by transthoracic echocardiography at baseline (eg, semirecumbent position), during PLR at 60°, and back to baseline.ResultsCardiac index significantly increased from 2.2 to 2.5 L/min·m2 (P < .01) at 60° PLR. Conversely, ΔPOP significantly decreased from 22% to 15% (P < .01) at 60° PLR. There was a weak correlation between CI and ΔPOP variations at 60° PLR (r = 0.40; P < .01). The area under curve of the receiver operating characteristic curve for ΔPOP as a predictor of an increase of CI of 15% was not significant (0.67 ± 0.10; P = .16).ConclusionThe variation of ΔPOP induced by PLR is not an accurate predictor of increase in CI.