Experimental Studies on Cerebral Protection during Aortic Arch Reconstruction : Optimal Cerebral Perfusion Flow and Electrophysiological Evaluation of Brain Function during Selective Cerebral Perfusion

Recently selective cerebral per fusion (SCP) has been established as a very useful method for cerebral protection during aortic arch reconstruction, but many details such as per fusion flow and pressure remain to be defined in order for this technique to be considered safe. It will also he necessary to define the cerebral functions which will serve best as diagnostic criteria for safety during such surgery. This study investigated for the optimal cerebral per fusion flow and evaluated the usefulness of motor evoked potentials (MEP) as a criterion for cerebral function. Somatosensory evoked potentials (SEP) and MEP were monitored to evaluate cerebral function in 44 adult mongrel dogs. The dogs were subjected to extracorporeal circulation (ECC). SCP was started when the brain temperature had cooled to 25℃ using ECC. After a 90-minute period of SCP, the dogs were rewarmed gradually to normal temperature. 34 out of the 44 dogs had been divided into four groups and subjected to the following cerebral per fusion flow rates. Group I (n=9) : 100% flow rate, i. e. the imposed per fusion was equal to the physiological flow as determined experimentally; Group II (n=10): 50% flow rate; Group III (n=8): 25% flow rate; Group IV (n=7): 0% flow rate (cerebrocirculatory arrest). In the remaining group (n=10), cerebral tissue blood flow before ECC and during SCP was measured by non-radioactive color-labelled microspheres. There was no significant difference between the observed changes in SEP and MEP. Cerebral function showed no abnormal findings as assessed by the final SEP and MEP after rewarming in both Groups I and II ; these potentials recovered almost completely to the pre-ECC values in all dogs. In Group III, SEP and MEP disappeared in 5 dogs (62.5%). In Group IV, SEP and MEP disappeared in all dogs. The observed cerebral tissue blood flow showed a clear correlation with the cerebral per fusion flow rate. It was concluded that (1) MEP is a useful monitor for cerebral function during ECC, (2) the safe range of cerebral per fusion flow of SCP under moderate hypothermia is 50-100% of the physiological flow rate, and (3) cerebral tissue blood flow depends on the cerebral per fusion flow