[The usefulness of combined measurements of transcranial Doppler sonogram and somatosensory evoked potentials during hypothermic cardiopulmonary bypass].

Serial and simultaneous measurements of the blood flow velocity of the middle cerebral artery (MCA-V) by transcranial Doppler sonography (TCD) and somatosensory evoked potentials (SEP) were performed in 7 adult patients during hypothermic cardiopulmonary bypass (CPB). CPB was instituted by alpha-stat blood gas management until the rectal temperature stabilized at 24 to 28 degrees C and gas management was converted from alpha to pH-stat by adding 4-7% of CO2 gas into the oxygenator for 10 minutes. MCA-V during hypothermic CPB by alpha-stat management was identical with normothermic prebypass MCA-V. However it significantly increased after pH-stat conversion, suggesting that CO2 reactivity was preserved even in the hypothermic situation above 24 degrees C of body temperature. Latency of all wave components of SEP and central conduction time (CCT) prolonged and wave voltages decreased as the body temperature dropped and SEP waves almost completely recovered following the temperature resumed to the prebypass temperature. There were no significant changes developed in latency and wave forms of SEP by conversion of the blood gas management from alpha-stat to pH-stat. The combined technique of TCD and SEP for detecting the real time changes of cerebral blood flow and brain function is considered to be useful to minimize the brain damage during open heart surgery.