Experimental study on the optimum flow rate and pressure for selective cerebral perfusion.

The optimum flow rate and pressure for selective cerebral perfusion during moderate hypothermia (25 degrees C) were investigated in 36 mongrel dogs. Cerebral perfusion was performed for 90 minutes at a flow rate of 100% (the physiologic flow rate), 50%, 25%, and 0%, or no flow (cerebrocirculatory arrest). Somatosensory evoked potentials were monitored to assess brain function. An excess lactate level was considered an index of anaerobic cerebral metabolism, and histopathologic evaluation was performed. Somatosensory evoked potentials showed no abnormalities at flow rates of 100% and 50%, but became abnormal in some dogs at 25% and in all dogs under no-flow conditions. The excess lactate level only increased at a no-flow rate, but not significantly. Histopathologic evaluation showed no ischemic changes at flow rates of 100% and 50%, but there were slight ischemic changes at 25% and severe ischemic damage at no flow. The mean carotid arterial pressure was 63.1 +/- 5.9, 39.8 +/- 6.2, 24.9 +/- 6.0, and 11.3 +/- 3.5 mm Hg at a flow rate of 100%, 50%, 25%, and no flow, respectively. These results suggest that the safe range of flow rates for cerebral perfusion during moderate hypothermia is more than 50% of the physiologic level with a carotid arterial pressure of about 30 mm Hg or more.