Oxygen saturation monitoring using resonance Raman spectroscopy

Abstract

Background The knowledge of hemoglobin oxygen saturation (SO2) and tissue oxygenation is critical to identify the presence of shock and therapeutic options. The resonance vibrational enhancement of hemoglobin allows measurement of oxy- and deoxy species of hemoglobin and resonance Raman spectroscopy (RRS-StO2) has been successfully used to measure aggregate microvascular oxygenation. We tested the hypothesis that noninvasive oxygen saturation measured by RRS-StO2could serve as surrogate of systemic central venous SO2. Methods In anesthetized rats, measurements of RRS-StO2made in oral mucosa, skin, muscle, and liver were compared with measurements of central venous SO2using traditional multi-wavelength oximetry. Various oxygenation levels were obtained using a stepwise hemorrhage while over 100 paired blood samples and Raman-based measurements were performed. The relationships between RRS-StO2and clinically important systemic blood parameters were also evaluated. RRS-StO2measurements were made in 3-mm diameter tissue areas using a microvascular oximeter and a handheld probe. Results Significant correlations were found between venous SO2and RRS-StO2measurements made in the oral mucosa (r = 0.913, P < 0.001), skin (r = 0.499, P < 0.01), and liver (r = 0.611, P < 0.05). The mean difference between sublingual RRS-StO2and blood sample SO2values was 5.4 ± 1.6%. Sublingual RRS-StO2also correlated with lactate (r = 0.909, P < 0.01), potassium (r = 0.757, P < 0.01), and pH (r = 0.703, P < 0.05). Conclusions Raman-based oxygen saturation is a promising technique for the noninvasive evaluation of oxygenation in skin, thin tissues, and solid organs. Under certain conditions, sublingual RRS-StO2measurements correlate with central venous SO2.