[Evoked potentials monitoring in aortic surgery]

Somatosensory evoked potential (SSEP), evoked spinal cord potential (ESCP) and motor evoked potential (MEP) have been used to detect spinal cord ischemia during aortic surgery. SSEP evaluates the sensory pathway, and is recorded from the sensory cortex by peripheral nerve stimulation. The interval from the onset of ischemia to change is relatively long(5-10 minutes). It has less frequently been used because of the high false negative and false positive rate. ESCP is recorded from the spinal cord by direct stimulation of the cord. It reflects the function of spinal tract but not that of alpha motor neurons. It is resistant to anesthesia and both the sensitivity and specificity is high, but the interval from ischemia to change is relatively long. Together with the necessity of 2 epidural electrodes, its application in aortic surgery has become infrequent. Since the introduction of train pulse transcranial electrical stimulation, myogenic MEP have gained widespread acceptance. It evaluates motor pathways from the cortex to the muscle, and therefore is influenced by non-spinal factors such as peripheral nerve ischemia. Its vulnerability to anesthesia requires special anesthetic consideration, and baseline amplitude fluctuation is common. It is highly sensitive and shows changes in the early phase of spinal cord ischemia.