Poor agreement between respiratory variations in pulse oximetry photoplethysmographic waveform amplitude and pulse pressure in intensive care unit patients

Abstract

BACKGROUND:: To identify fluid responsiveness, a correlation between respiratory variations in pulse pressure (ΔPP) and respiratory variations in pulse oximetry photoplethysmographic waveform amplitude (ΔPOP) in mechanically ventilated patients has been demonstrated. To evaluate the agreement between the two methods, knowledge about the repeatability of the methods is imperative. However, no such data exist. Based on knowledge of slow oscillation in skin blood flow, the authors hypothesized that the variability of ΔPOP would be larger than that of ΔPP when calculations were performed continuously over a long recording period. METHODS:: Respiration, continuous invasive blood pressure, pulse oximetry, and skin microcirculation were recorded in 14 mechanically ventilated intensive care unit patients. No intravenous fluid challenges were given, and no other interventions were performed during the measurements. Seventy consecutive comparisons between ΔPP and ΔPOP were calculated for each of the 14 patients. RESULTS:: For all patients, ΔPOP was 13.7 ± 5.8% and ΔPP was 5.8 ± 2.6% (P < 0.001). There was a larger intraindividual (8.94 vs. 1.29; P < 0.001) and interindividual (26.01 vs. 5.57; P < 0.001) variance of ΔPOP than of ΔPP. In six patients, there was no significant correlation between ΔPP and ΔPOP. A Bland-Altman plot showed poor agreement between the two methods. CONCLUSION:: A large variability of ΔPOP and a poor agreement between ΔPP and ΔPOP limits ΔPOP as a tool for evaluation of fluid responsiveness in intensive care unit patients. This is in contrast to ΔPP, which shows a small variability. © 2008, the American Society of Anesthesiologists, Inc. Lippincott Williams & Wilkins, Inc.