Incremental hyperoxic normovolemic hemodilution was utilized to progressively decrease oxygen delivery (Do2) in anesthetized rabbits. At decreasing D02, we compared systemic responses related to the adequacy of Do2, i.e. mixed venous oxygen saturation (SvO2), oxygen consumption (V02), and arterial lactate concentrations, to near infrared spectroscopy (NIRS) of the brain, a regional measure of intracellular oxygen availability. We sought concomitantly to define critical SvO2 and D02, beyond which whole body V02 begins to decline and arterial lactate concentrations increase. NIR Spectroscopy provided the means to test the hypothesis that systemic indicators of inadequate Doe would not accurately reflect the oxygenation of a critical organ such as the brain. In thirteen rabbits anesthetized with fentanyl, paralyzed and artificially ventilated at an FIO2 of 0.60, hemodilution produced an early decrease in mixed venous oxygen saturation. When mixed venous oxygen saturation decreased below approximately 50'%, arterial lactate concentrations began to increase significantly. Further decreases in oxygen delivery precipitated a decline in systemic Vo2. Finally, NIRS revealed an increase in the reduction level of brain cytochrome a,a3 after systemic parameters of oxygen delivery had been altered. Analysis of the data indicated that falling SvO2 predicted inadequate D02 to tissue during early hemodilution under narcotic/relaxant anesthesia and that the brain showed evidence of intracellular hypoxia only after systemic parameters such as SvO2 were affected markedly.
- mixed venous oxygen saturation
- near infrared spectroscopy
- oxygen consumption
ASJC Scopus subject areas
- Emergency Medicine
- Cardiology and Cardiovascular Medicine