EFFICACY OF TRANSCRANIAL MOTOR-EVOKED MYOGENIC POTENTIALS TO DETECT SPINAL-CORD ISCHEMIA DURING OPERATIONS FOR THORACOABDOMINAL ANEURYSMS

Objective: Motor-evoked myogenic potentials after transcranial electri cal stimulation monitor the vulnerable motoneuronal system of the spin al cord, This study reports our initial experiences with motor-evoked potentials to assess the adequacy of spinal cord perfusion during oper ations for thoracoabdominal aneurysms, Methods: In 20 patients undergo ing thoracoabdominal aneurysm operations, myogenic motor-evoked potent ials were recorded, In 18 patients retrograde aortic perfusion was use d, When spinal cord ischemia was detected, distal flow or mean arteria l pressure was increased in an attempt to restore cord perfusion, By m eans of sequential crossclamping, motor-evoked potentials were also us ed to identify intercostal or lumbar arteries that needed to be reimpl anted. Results: Reproducible motor-evoked potentials could be recorded in all patients, During retrograde perfusion, nine patients showed a rapid decrease in the amplitude of motor-evoked potentials to less tha n 25% of baseline, indicating spinal cord ischemia, In five patients i schemic changes in motor-evoked potentials could be reversed by increa sing distal and proximal blood pressures, In four patients ischemic ch anges during crossclamping necessitated segmental artery reimplantatio n, In three of these four patients intercostal or lumbar arteries were reattached, In one patient reimplantation of segmental arteries was n ot possible; this patient awoke paraplegic. Segmental arteries were li gated after confirmation of intact motor-evoked potentials during aort ic clamping in eight patients. None of these patients had a neurologic deficit, The absence of motor-evoked potentials at the end of the pro cedure always indicated a postoperative motor deficit. Conclusion: Dur ing operations for thoracoabdominal aneurysms, monitoring of motor-evo ked potentials is an effective technique to detect spinal cord ischemi a within minutes, This modality can be used to guide the management of distal aortic perfusion techniques and may also help to identify segm ental arteries that need to be reattached.