Transintercostal-Evoked Spinal Cord Potential in Thoracic Aortic Surgery

Background: We have developed a novel method of measuring spinal cord-evoked potentials with stimulation and recording at the intercostal nerves (transintercostal-evoked spinal cord potential: Tic-ESCP). The purpose of this study was to examine the feasibility and accuracy of Tic-ESCP during thoracic aortic surgery. Methods: In addition to the conventional electrodes (cranial and intrathecal), stimulating and recording electrodes were placed on the intercostal nerves that were located at a cephalad and caudal level relative to the aneurysm after the pleura on the intercostal nerves was opened. Specially designed hook-type electrodes were anchored to the nerves and surroundings atraumatically and fixed on the pleura. The conventional transcranial motor-evoked potential (Tc-MEP) and Tic-ESCP were recorded simultaneously. Eight patients were examined in this study. Results: In all patients, Tic-ESCP could be clearly recorded with biphasic waveforms consisting of first a positive wave and a subsequent negative wave. In all 8 patients, the waveform of Tc-MEP and Tic-ESCP changed during aortic reconstruction. In 2 cases, the waveform of Tc-MEP and Tic-ESCP decreased below 50% of baseline during aortic clamping and the intercostal arteries were reconstructed with no resultant spinal cord injury. In 1 case with a shaggy aorta, Tc-MEP and Tic-ESCP had different values and each evoked potential could have reflected that regional spinal cord infarction and paraplegia had occurred. Conclusions: Tic-ESCP was clinically feasible and changes were compatible with the conventional Tc-MEP. The Tic-ESCP waveforms were simple and appeared to be specific to the spinal cord within the target range, in contrast to the other evoked potentials which are multimorphic and reflect the amplitudes at the brain and multiple levels of the spinal cord.