Regional tissue oxygenation during hemorrhage: can near infrared spectroscopy be used to monitor blood loss?

We investigated whether near infrared spectroscopy could be used to monitor regional tissue oxygenation during uncompensated hemorrhage in man. A Somanetics INVOS 4100 oximeter was used to measure regional hemoglobin oxygen saturation in the cerebral cortex (CsO2, left frontal area) and from the left calf muscle (PsO2) in 40 volunteers donating 470 mL of the whole blood. A Critikon 2001 Cerebral Redox Instrument was used to monitor total (tHb), oxygenated (O2Hb), and deoxygenated (HHb) hemoglobin in the right calf muscle. The oxygenation index, [HbD] = [O2Hb] - [HHb] was derived. CsO2 decreased by a mean (95% CI) of 2 (1-3.3%) (P < 0.001), PsO2 decreased by a mean (95% CI) of 3.2 (1.7-4.6%) (P < 0.001), and HbD decreased by a median (95% CI) of 6.4 (2.65-10.16) delta microM/cm (P < 0.001) during blood collection. There was an inverse correlation between blood loss and CsO2 (R = -0.59, P < 0.001), PsO2 (R = -0.61, P < 0.001), and HbD (R = -0.5, P < 0.001). Regional tissue oxygenation decreases in proportion to uncompensated blood loss. Near infrared spectroscopy may potentially be developed into a transfusion trigger.