Methodology of motor evoked potentials in a rabbit model.

Spinal cord ischemia (SCI) is a devastating complication of aortic operations. Neuromonitoring using motor evoked potentials (MEPs) is a sensitive modality to detect SCI in humans. We describe a leporine SCI model using MEPs to test pharmaceutical therapeutics and other neuroprotective adjuncts. In 80 rabbits, methods to obtain MEPs in normotensive and ischemic rabbits were developed. The effects of isoflurane, propofol, apnea, and hypotension on lower extremity MEPs were studied. Lower extremity MEPs disappear upon SCI induction in 78 of 78 (100 %) rabbits. Prior to SCI induction and during apneic episodes, lower extremity MEPs were lost in all (100 %) and upper extremity MEPs in one (25 %). Isoflurane was used in four experiments, with loss of lower extremity MEPs in all four (100 %) and loss of upper extremity MEPs in zero. With propofol upper extremity, MEPs were obtainable in 80 of 80 rabbits (100 %) and lower extremity MEPs in 78 of 80 rabbits (97.5 %) prior to SCI induction. The presence of these lower extremity MEPs prior to SCI induction was not correlated with systolic or diastolic blood pressure. Disappearance of MEPs occurred in all 45 rabbits with postoperative lower extremity impairment. MEPs in the leporine model correlate closely with paraplegia. MEPs are influenced by inhaled anesthetics and apnea but not by hypotension alone. Propofol anesthesia provides reliable MEPs. This study provides the basis for a reproducible model of SCI to be used for novel therapeutic drug development.