Effect of pentobarbital on cerebral regional venous O₂ saturation heterogeneity

Observed venous O₂ saturation inhomogeneity in the brain implies a microregional imbalance in O₂ supply/consumption. We hypothesized that this heterogeneity should be decreased by pentobarbital anesthesia through a reduction in regional metabolic heterogeneity. Male, Long-Evans, ∼ 350 g rats were either anesthetized with 50 mg/kg pentobarbital (n = 10) or used as a conscious control group (n = 10, catheters inserted two hours earlier under ether anesthesia). In each rat, regional cerebral blood flow was determined by [¹⁴C]iodoantipyrine and regional arterial and venous O₂ saturation were determined by microspectrophotometry. In the PB group, the mean blood pressure (107 ± 7 Torr), heart rate (362 ± 29 /min), average cerebral blood flow (63 ± 19 ml/min/100 g), and average cerebral O₂ consumption (3.7 ± 1.2 ml O₂/min/100 g) were lower than those values in the conscious group (128 ± 15, 474 ± 44, 112 ± 40, and 7 ± 3), respectively. O₂ extraction did not change after pentobarbital anesthesia. However, the dispersion of venous O₂ saturation narrowed. The distribution of O₂ saturations in 373 cerebral veins of anesthetized rats had a significantly reduced coefficient of variation [C.V. = 100 × (S.D./mean = 13] as compared to a C.V. of 18 in 320 veins in conscious rats. Thus, pentobarbital anesthesia reduced the microregional venous O₂ saturation inhomogeneity in the brain, creating a more uniform balance of oxygen supply and consumption.