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Retinal large vessel oxygen saturations correlate with early blood loss and hypoxia in anesthetized swine.

BACKGROUND
Noninvasive monitoring would likely improve trauma care. Using laser technology, we monitored the oxygen saturation in retinal vessels during exsanguination and hypoxia.


METHODS
Seven anesthetized swine were bled at 0.4 mL/kg/min for 40 minutes. During exsanguination, retinal venous saturation (SrvO2) was measured using an eye oximeter, and central venous saturation (SvO2) 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 (SaO2) and retinal artery oxygen saturation (SraO2) were measured at each increment.


RESULTS
During exsanguination, SrvO2 correlated with blood loss (r = -0.93) and SvO2 (r = 0.94). SraO2 correlated with SaO2 during incremental hypoxia (R2 = 0.93 +/- 0.15).


CONCLUSIONS
In this model of exsanguination, retinal venous oxygen saturation correlates with blood volume and with central venous oxygen saturation. The SraO2 correlates with SaO2 during graded hypoxia. Use of an eye oximeter to noninvasively monitor trauma patients appears promising and warrants further study.