Retrospective study of somatosensory evoked potential monitoring in deep hypothermic circulatory arrest

Background;. We evaluated the efficiency of median nerve somatosensory evok ed potentials (SEPs) monitoring in determining the optimal level of hypothe rmia in 62 consecutive patients operated on under deep hypothermic circulat ory arrest (CA). Methods. CA was started at 1 degrees C below the temperature at which both brainstem and cortical SEP components disappear. No additional method of ce rebral protection was used. Results. New neurological complications were observed in 15 patients: long- lasting in 11 and transient in 4. A retrospective analysis of SEP monitorin g identified the origin of the complications in 12 cases: early CA with inc omplete cooling due to emergency (3 cases); inefficient retrograde perfusio n through the femoral artery during cooling due to the dissection flap effe ct (4 cases); embolism during rewarming (2 cases); delayed embolism (2 case s); hemorrhagic shock (1 case). In 2 cases, neurological sequelae involved the lower limbs (extracerebral origin). One case without intraoperative SEP changes was neurologically abnormal preoperatively and did not change post operatively. There were no cases with sequelae due to excessive CA duration . Conclusions. The use of SEP monitoring to determine the optimal level of hy pothermia efficiently prevents neurological sequelae of CA. It helps in mon itoring the degree of cerebral protection during cooling (flap effect), and rewarming. (C) 1999 by The Society of thoracic Surgeons.