title: Retinal venous oxygen saturation correlates with blood volume.
abstract: OBJECTIVE
  To evaluate the sensitivity of retinal venous O2 saturation (SrvO2) for early blood loss and reinfusion. A secondary objective was to measure the correlation between SrvO2 and mixed venous O2 saturation (SvO2) 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. SrvO2 was measured using an eye oximeter (EOX) and SvO2 was measured using a fiber-optic catheter.
  
  
  RESULTS
  During blood loss, SrvO2 correlated with blood removed (r = -0.88, -0.97, -0.96) and SvO2 (r = 0.87, 0.98, 0.92). During reinfusion, SrvO2 correlated with blood re-infused (r = 0.63, 0.76, 0.82) and SvO2 (r = 0.80, 0.93, 0.96). SrvO2 decreased 1.22 +/- 0.60%/mL/kg of blood removed. The rate of decrease in SrvO2 per minute (deltaSrvO2) when blood was removed at 2.4 mL/kg/min was significantly greater than deltaSrvO2 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 O2 saturation correlated with blood volume and central venous O2 saturation. Unlike the rate of change in BP and heart rate, deltaSrvO2 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.
authors.affiliation: Department of Emergency Medicine, University of Alabama at Birmingham, 35233-7013, USA. kurt@qsb2.his.uab.edu
authors.forename: K R
authors.initials: KR
authors.lastname: Denninghoff
authors.forename: M H
authors.initials: MH
authors.lastname: Smith
authors.forename: L W
authors.initials: LW
authors.lastname: Hillman
authors.forename: D
authors.initials: D
authors.lastname: Redden
authors.forename: L W
authors.initials: LW
authors.lastname: Rue
mesh_terms: D000818:Animals; D001794:Blood Pressure; D001803:Blood Transfusion; D001810:Blood Volume; D005260:Female; D006339:Heart Rate; D006470:Hemorrhage; D010092:Oximetry; D010100:Oxygen / Q000378:metabolism*; D012169:Retinal Vein / Q000502:physiology*; D012680:Sensitivity and Specificity; D013552:Swine
chemical_list: D010100:Oxygen