Setup of Neurophysiological Monitoring with tcMEP/SSEP During Thoracoabdominal Aneurysm Repair

Abstract

The article describes a procedure for the intraoperative neurophysiological placement of electrodes to control the spinal cord function during thoracoabdominal aortic aneurysm repair. Intraoperative monitoring is performed by motor-evoked myogenic potentials after transcranial electric stimulation (tcMEP) and somatosensory-evoked potentials (SSEP). In tcMEP, the stimulating percutaneous needle electrodes are placed at C3 and C4 according to the 10 - 20 system for EEG recordings. TcMEP are recorded from the anterior tibial and gastrocnemius muscles on both sides. The SSEP electrodes are placed laterally and caudally onto the malleolus medialis in order to stimulate the tibial nerve. The stimulus is documented via electrodes attached to the scalp within the sensory cortex region. The application of the electrodes is both easy to learn and can be performed without further difficulties. Once attached, the electrodes provide a quick assessment and interpretation of spinal cord function. The identification of external sources of disturbance during the monitoring (e. g. insufficient impedance, unfavourable electrode positioning, and technical interference caused by medical equipment) enables the supervisor to differentiate between normal and abnormal neurological responses. TcMEP and SSEP allow an adequate, direct, and reliable intraoperative assessment of spinal cord function, enabling the surgeon to diagnose an impending ischaemia and act accordingly. This measurement technique provides the surgical team with a means of integrating neurological aspects during thoracoabdominal aneurysm repair.