Abstract
The estimation of venous oxygen saturations using photoplethysmography (PPG) may be useful as a noninvasive continuous method of detecting changes in regional oxygen supply and demand (e.g. in the splanchnic circulation). The aim of this research was to compare PPG-derived peripheral venous oxygen saturations directly with venous saturation measured from co-oximetry blood samples, to assess the feasibility of non-invasive local venous oxygen saturation. This paper comprises two similar studies: one in healthy spontaneously-breathing volunteers and one in mechanically ventilated anaesthetised patients. In both studies, PPG-derived estimates of peripheral venous oxygen saturations (SxvO2) were compared with co-oximetry samples (ScovO2) of venous blood from the dorsum of the hand. The results were analysed and correlation between the PPG-derived results and co-oximetry was tested for. In the volunteer subjects,moderate correlation (r = 0.81) was seen between SxvO2 values and co-oximetry derived venous saturations (ScovO2), with a mean (±SD) difference of +5.65 ± 14.3% observed between the two methods. In the anaesthetised patients SxvO2 values were only 3.81% lower than SpO2 and tended to underestimate venous saturation (mean difference = –2.67 ± 5.89%) while correlating weakly with ScovO2 (r = 0.10). The results suggest that significant refinement of the technique is needed to sufficiently improve accuracy to produce clinically meaningful measurement of peripheral venous oxygen saturation. In anaesthetised patients the use of the technique may be severely limited by cutaneous arteriovenous shunting.
Highlights
Photoplethysmography (PPG), a fundamental technology behind the widely used pulse oximeter, is an optical technique that detects periodic blood volume changes in the tissue bed [1]
In the volunteer subjects,moderate correlation (r = 0.81) was seen between SxvO2 values and cooximetry derived venous saturations (ScovO2), with a mean (±SD) difference of ?5.65 ± 14.3% observed between the two methods
In the anaesthetised patients SxvO2 values were only 3.81% lower than SpO2 and tended to underestimate venous saturation while correlating weakly with & J
Summary
Photoplethysmography (PPG), a fundamental technology behind the widely used pulse oximeter, is an optical technique that detects periodic blood volume changes in the tissue bed [1]. J Clin Monit Comput (2017) 31:1213–1220 significantly [4] This concept is applicable to the body as a whole, and is the physiological basis of using mixed venous saturations (SvO2) as an indication of cardiac output in the assessment of global oxygen delivery. Peripheral venous saturations cannot replace or infer SvO2, direct correlation of central and peripheral venous saturations (SxvO2) has been found by Echiadis et al to be viable in certain cases where the supply or demand balance changes rapidly [4], which would suggest the potential use as continuous non-invasive monitor in critically ill patients. PPG-derived SxvO2 was recorded from awake volunteers breathing through a flow resistor to simulate mechanical ventilation and compared to peripheral venous co-oximetry sample values (ScovO2) obtained form the dorsal vein of the hand. Similar measurements were performed in mechanically ventilated anaesthetised patients
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