Background: In this study, we examined the ability of resonance Raman spectroscopy to measure tissue hemoglobin oxygenation (R-StO2) noninvasively in critically ill patients and compared its performance with conventional central venous hemoglobin oxygen saturation (ScvO2).
Methods: Critically ill patients (n = 138) with an indwelling central venous or pulmonary artery catheter in place were consented and recruited. R-StO2 measurements were obtained by placing a sensor inside the mouth on the buccal mucosa. R-StO2 was measured continuously for 5 min. Blood samples were drawn from the distal port of the indwelling central venous catheter or proximal port of the pulmonary artery catheter at the end of the test period to measure ScvO2 using standard co-oximetry analyzer. A regression algorithm was used to calculate the R-StO2 based on the observed spectra.
Results: Mean (SD) of pooled R-StO2 and ScvO2 were 64(7.6) % and 65(9.2) % respectively. A paired t test showed no significant difference between R-StO2 and ScvO2 with a mean(SD) difference of -1(7.5) % (95% CI: -2.2, 0.3%) with a Clarke Error Grid demonstrating 84.8% of the data residing within the accurate and acceptable grids. Area under the receiver operator curve for R-StO2's was 0.8(0.029) (95% CI: 0.7, 0.9 P < 0.0001) at different thresholds of ScvO2 (≤60%, ≤65%, and ≤70%). Clinical adjudication by five clinicians to assess the utility of R-StO2 and ScvO2 yielded Fleiss' Kappa agreement of 0.45 (P < 0.00001).
Conclusions: R-StO2 has the potential to predict ScvO2 with high precision and might serve as a faster, safer, and noninvasive surrogate to these measures.
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