Evoked potentials in aortic surgery - method and implementation

Background The article exemplifies a procedure concerning the intraoperative neurophysiological placement technique of electrodes to control the spinal cord function during thoracoabdominal aortic aneurysm repair. Methods 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 located 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. Results The application method of the electrodes is both easy to understand and without further difficulties to perform. Once attached, the electrodes provide quick assessment and interpretation of spinal cord function. The identification of external sources of disturbance during the monitoring (e.g. insufficient impedance, unfavorable electrode positioning, and technical interferences caused by medical equipment) enables the supervisor to differentiate between normal and abnormal neurological responses. Conclusion TcMEP and SSEP allow an adequate, direct, and reliable intraoperative assessment of spinal cord function, enabling the surgeon to diagnose an impending ischemia and act accordingly. This measurement technique provides the surgical team with a means for integrating neurological aspects in thoracoabdominal aneurysm repair into the surgical focus.