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

Introduction: Previous studies suggested that variation of pulse oximetric plethysmographic (POP) waveform amplitude (Delta POP) could predict fluid responsiveness in mechanically ventilated patients. Our objective was to correlate the variations of Delta POP and the variations of cardiac index (Cl) induced by passive leg raising (PLR) in spontaneously breathing volunteers. Methods: We studied 26 spontaneously breathing volunteers using a pulse oximeter attached to the middle finger. We assessed hemodynamic variables, including Delta POP (%) (POPmax - POPmin)/[(POPmax + POPmin)/2] and Cl determined by transthoracic echocardiography at baseline (eg, semirecumbent position), during PLR at 60 degrees, and back to baseline. Results: Cardiac index significantly increased from 2.2 to 15 L/min.m(2) (P < .01) at 60 degrees PLR. Conversely, Delta POP significantly decreased from 22% to 15% (P < .01) at 60 degrees PLR. There was a weak correlation between CI and Delta POP variations at 60 degrees PLR (r = 0.40; P < .01). The area under curve of the receiver operating characteristic curve for Delta POP as a predictor of an increase of Cl of 15% was not significant (0.67 +/- 0.10; P = .16). Conclusion: The variation of Delta POP induced by PLR is not an accurate predictor of increase in Cl. (C) 2010 Elsevier Inc. All rights reserved.