Retinal Large Vessel Oxygen Saturations Correlate with Early Blood Loss and Hypoxia in Anesthetized Swine

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Abstract
Noninvasive monitoring would likely improve trauma care. Using laser technology, we monitored the oxygen saturation in retinal vessels during exsanguination and hypoxia. Seven anesthetized swine were bled at 0.4 mL/kg/min for 40 minutes. During exsanguination, retinal venous saturation (Srv O2) was measured using an eye oximeter, and central venous saturation (Sv O2) was measured using a fiber-optic catheter. After the shed blood was reinfused, the FiO2 was progressively decreased from 0.97 to 0.07. Femoral artery oxygen saturation (Sa O2) and retinal artery oxygen saturation (Sra O2) were measured at each increment. During exsanguination, Srv O2 correlated with blood loss (r = -0.93) and Sv O2 (r = 0.94). Sra O2 correlated with Sa O2 during incremental hypoxia (R2 = 0.93 +/- 0.15). In this model of exsanguination, retinal venous oxygen saturation correlates with blood volume and with central venous oxygen saturation. The Sra O2 correlates with Sa O2 during graded hypoxia. Use of an eye oximeter to noninvasively monitor trauma patients appears promising and warrants further study.