Critical Care: Miscellaneous Critical Care |

Assessment of Pulse Oximetry Waveforms Before and After Hemodialysis and Ultrafiltration in Critically Ill Patients May Reflect Changes in Intravascular Volume Status FREE TO VIEW

Ken Stern, MD; Shadman Chowdhury, BS; Elaine Kaptein, MD; Ray Pillai, MD; Ahmet Baydur, MD
Author and Funding Information

University of Southern California, Los Angeles, CA

Copyright 2016, American College of Chest Physicians. All Rights Reserved.

Chest. 2016;150(4_S):331A. doi:10.1016/j.chest.2016.08.344
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SESSION TITLE: Miscellaneous Critical Care

SESSION TYPE: Original Investigation Poster

PRESENTED ON: Wednesday, October 26, 2016 at 01:30 PM - 02:30 PM

PURPOSE: Patients undergoing intermittent hemodialysis (HD) with ultrafiltration (UF) frequently experience hypotension which potentially can result in end-organ injury. Prior research has shown that pulse O2 saturation (SpO2) waveform may correlate with changes in intravascular volume. This study assessed the ability of the changes in pulse oximetry waveform patients before and after UF to reflect changes in intravascular volume.

METHODS: Of a convenience sample of 16 ICU patients with renal failure in 46 encounters of hemodialysis, we analyzed the pulse O2 saturation waveform retrieved by telemetry before and after undergoing UF. Variation in the amplitude of the SpO2 wave was measured as the difference between end-inspiration and end-expiration [ΔP = (max-min)/{(max+min)/2}] over five respiratory cycles before onset and at completion of UF. We also measured the difference in the peak values of the SpO2 waveform at end-inspiration and end-expiration [ΔS = (peakmax-peakmin)/{(max+min)/2}]. Net ultrafiltrate volume removed was plotted against ΔS and ΔP and the changes in ΔS and ΔP for five respiratory cycles were compared using Wilcoxon rank sum test. Large variability of waveforms among respiratory cycles and thus in ΔS and ΔP for individual patients were noted. Therefore, in a subset of 10 encounters, we assessed the effect of increasing the number of respiratory cycles from five to thirty on the coefficient of variation for ΔS and ΔP to determine the optimum number of cycles to be ultimately analyzed.

RESULTS: We initially found close correlations between ΔS and net ultrafiltrate volume removed (r=0.60, p<0.02). No significant change in ΔP was found. The number of respiratory cycles required to achieve a variation <10% for ΔS varied from 5 to 30 and was achieved in 9 of 10 samples for 30 cycles. For ΔP, a variation of <10% was only achieved in 4 of 10 encounters for 30 cycles. Upon reviewing the variability of the data, an additional sample of convenience of 15 ICU patients with renal failure in 34 encounters of hemodialysis was obtained, each encounter preceded within 24 hours by inferior vena cava ultrasound (IVC US) collapsibility index assessment of intravascular volume prior to ultrafiltration. The SpO2 waveform was digitized and is currently being analyzed.

CONCLUSIONS: To our knowledge, this is the first study evaluating pulse O2 saturation waveform variations before and after volume removal by ultrafiltration. The main findings in this study suggest an increase in pulse O2 saturation waveform variation with respiratory cycles after ultrafiltration. With further analysis, we will be able to compare rapid volume removal by ultrafiltration to changes in pulse O2 saturation waveform variation.

CLINICAL IMPLICATIONS: These findings suggest a potential clinical application of pulse O2 saturation waveform variability in evaluating changes in intravascular volume status and potentially predicting and avoiding intradialytic hypotension.

DISCLOSURE: The following authors have nothing to disclose: Ken Stern, Shadman Chowdhury, Elaine Kaptein, Ray Pillai, Ahmet Baydur

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