Detecting central-venous oxygen desaturation without a central-venous catheter: Utility of the difference between invasively and noninvasively measured blood pressure.

Objective: The objective was to determine whether central-venous oxygen saturation (ScvO2<70%) can be detected from the difference between invasively and noninvasively measured systolic blood pressure (BP) (ie, ΔBP defined as arterial BP minus noninvasive BP).
Methods: This is a cross-sectional study at a single medical and surgical intensive care unit in Japan. All hypotensive patients admitted to intensive care unit were eligible. Arterial BP was measured via a radial-artery catheter, and noninvasive BP on the same side was measured via a brachial cuff. ScvO2 was measured by gas analysis of blood sampled from a central-venous chatheter (CVC). We calculate the area under the curve for ΔBP as an indicator of ScvO2<70%.
Results: Usable data were obtained from the records of 111 patients. The median and interquartile range of ΔBP and ScvO2 were -4mm Hg (-11, 6) and 67% (60.9, 73.9), respectively. The area under the curve of ΔBP as an indicator of ScvO2<70% was 0.81 (95% confidence interval [CI], 0.73-0.89). With a cutoff ΔBP of 0, sensitivity was 65.7% (95% CI, 53.1-76.8), specificity was 97.7% (95% CI, 88.0-99.8), and positive predictive value was 97.8 (95% CI, 88.2-99.9).
Conclusions: ΔBP can indicate whether ScvO2 is lower than 70%. When that difference is greater than 0, ScvO2 is very likely to be lower than 70%.
(Copyright © 2016 Elsevier Inc. All rights reserved.)