Retinal venous oxygen saturation correlates with blood volume

Objectives: To evaluate the sensitivity of retinal venous O-2 saturation (SrvO(2)) for early blood loss and reinfusion. A secondary objective was to measure the correlation between SrvO(2) and mixed venous O-2 saturation (SvO(2)) during blood loss and reinfusion. Methods: Seven anesthetized swine were bled at 0.8 ml/kg/min to 16 mL/kg. Shed blood was re-infused at the same rate and the swine were allowed to equilibrate. After equilibration, repeat hemorrhages were performed at 1.6 ml/kg/min and 2.4 ml/kg/min. SrvO(2) was measured using an eye oximeter (EOX) and SvO(2) was measured using a fiber-optic catheter. Results: During blood loss, SrvO(2) correlated with blood removed (r = -0.88, -0.97, -0.96) and SvO(2) (r = 0.87, 0.98, 0.92). During reinfusion, SrvO(2) correlated with blood re-infused (r = 0.63, 0.76, 0.82) and SvO(2) (r = 0.80, 0.93, 0.96). SrvO(2) decreased 1.22 +/- 0.60%/mL/kg of blood removed. The rate of decrease in SrvO(2) per minute (Delta SrvO(2)) when blood was removed at 2.4 ml/kg/min was significantly greater than Delta SrvO(2) when blood was removed at 0.8 mL/kg/min (p < 0.007). The rates of change in blood pressure (BP) and pulse were not significantly different at any rate of blood removal. Conclusions: In this model, retinal venous O-2 saturation correlated with blood volume and central venous O-2 saturation. Unlike the rate of change in BP and heart rate, Delta SrvO(2) values were significantly different at different rates of blood removal. Use of an EOX to monitor for blood loss, estimate the rate of hemorrhage, and evaluate the response to therapy during resuscitation warrants further study.