Resonance Raman Spectroscopy Derived Tissue Hemoglobin Oxygen Saturation in Critically Ill and Injured Patients

ABSTRACT Background: In this study, we examined the ability of resonance Raman spectroscopy to measure tissue hemoglobin oxygenation (R-StO 2 ) noninvasively in critically ill patients and compared its performance with conventional central venous hemoglobin oxygen saturation (ScvO 2 ). Methods: Critically ill patients (n = 138) with an indwelling central venous or pulmonary artery catheter in place were consented and recruited. R-StO 2 measurements were obtained by placing a sensor inside the mouth on the buccal mucosa. R-StO 2 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 ScvO 2 using standard co-oximetry analyzer. A regression algorithm was used to calculate the R-StO 2 based on the observed spectra. Results: Mean (SD) of pooled R-StO 2 and ScvO 2 were 64(7.6) % and 65(9.2) % respectively. A paired t test showed no significant difference between R-StO 2 and ScvO 2 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-StO 2 's was 0.8(0.029) (95% CI: 0.7, 0.9 P < 0.0001) at different thresholds of ScvO 2 (≤60%, ≤65%, and ≤70%). Clinical adjudication by five clinicians to assess the utility of R-StO 2 and ScvO 2 yielded Fleiss’ Kappa agreement of 0.45 ( P < 0.00001). Conclusions: R-StO 2 has the potential to predict ScvO 2 with high precision and might serve as a faster, safer, and noninvasive surrogate to these measures.