Resonance Raman spectroscopy: a new technology for tissue oxygenation monitoring

Objective. To evaluate resonance Raman spectroscopy for the detection of changes in sublingual mucosal hemoglobin oxygen saturation (SmO2) in response to hemorrhage and resuscitation, and to compare SmO2 with other indicators of tissue oxygenation including central venous oxygen saturation (ScvO(2)), lactate, base excess, and shed blood volume. Design: Prospective single group pilot study. Setting: University laboratory. Subjects: Five Sprague-Dawley, rats. Interventions: Animals were anesthetized and instrumented for measurement of arterial and central venous blood gases. Raman spectroscopy was performed using a krypton ion laser providing excitation at 406.7 nm (5 mW). A 1-mm(2) region of the sublingual tongue surface was chosen for investigation. Animals were subjected to stepwise hemorrhage until approximately 50% of the blood volume was removed. At each hemorrhage and resuscitation interval, Raman spectroscopy was performed and corresponding arterial and central venous blood gas and lactate measurements were made. SmO2 was calculated as the ratio of the oxygenated heme spectral peak height to the sum of the oxy- and deoxyhemoglobin spectral peak heights. Raman spectroscopy-derived SmO2 measurements were compared with ScvO(2) as well as with other indicators of oxygenation. Measurements and Main Results: The mean difference between SmO2 and ScvO(2) for all paired measurements was 5.8 +/- 11.7 absolute saturation points. SmO2 was significantly (p < .0001) correlated with ScvO(2) (r = .80), lactate (r = -.78), base excess (r = .80), and shed blood volume (r = -.75). SmO2 and ScvO(2) showed similar levels of precision for predicting elevated lactate and base deficit. Conclusions: These studies demonstrate the ability of Raman spectroscopy to noninvasively track microvascular hemoglobin oxygenation in tissue and favorably correlate with other important indicators of tissue oxygenation such as ScvO(2), lactate, base deficit, and shed blood volume. The technique shows promise as a method to noninvasively monitor tissue oxygenation.