Changes of motor evoked potentials during descending thoracic and thoracoabdominal aortic surgery with deep hypothermic circulatory arrest

Paraplegia is a serious complication of descending and thoracoabdominal aortic aneurysms (dTAAs and TAAAs) surgery. Motor evoked potentials (MEPs) enable monitoring the functional integrity of motor pathways during dTAA and TAAA surgery. Although MEPs are sensitive to temperature changes, there are few human data on changes of MEPs during mild and deep hypothermia. Therefore, we investigated changes of MEPs in deep hypothermic circulatory arrest (DHCA) in dTAA and TAAA surgery. Fifteen consecutive patients undergoing dTAA and TAAA surgery using DHCA were enrolled. MEPs were elicited and recorded during each degree Celsius change in nasopharyngeal temperature during both the cooling and rewarming phases. Hand and leg skin temperature were also recorded simultaneously. In the cooling phase MEP amplitude decreased lineally in both the hand and leg. The MEP disappeared at similar to 16A degrees C in both the hand and leg in 10 of 15 patients, but was still elicited in 5 patients. In the rewarming phase MEP in the hand recovered before the temperature reached 20A degrees C for eight patients and 25A degrees C for the other seven patients. In contrast, MEP in the leg recovered below 20A degrees C for two patients and 30A degrees C for three patients. For the other eight patients MEP waves did not recover during the rewarming phase. In the cooling phase of DHCA, MEP disappeared at similar to 16A degrees C in some patients but was still elicited in others. MEP recovered below 25A degrees C in the hand. Recovery of MEP in the leg was, however, extremely variable.