Effects of core body temperature on changes in spinal somatosensory-evokedpotential in acute spinal cord compression injury - An experimental study in the rat

Study Design. Acute spinal cord injury was induced by a clip compression mo del in rats to approximate spinal cord injury encountered in spinal surgery . Spinal somato-sensory-evoked potential neuromonitoring was used to study the electrophysiologic change. Objectives. To compare and correlate changes in evoked potential after acut e compression at different core temperatures with postoperative neurologic function and histologic change, to evaluate current intraoperative neuromon itoring warning criteria for neural damage, and to confirm the protective e ffect of hypothermia in acute spinal cord compression injury by electrophys iologic, histologic, and clinical observation. Summary of Background Data. With the increase in aggressive correction of s pinal deformities, and the invasiveness of surgical instruments,the inciden ce of neurologic complication appears to have increased despite the availab ility of sensitive intraoperative neuromonitoring techniques designed to al ert surgeons to impending neural damage. Many reasons have been given for t he frequent failures of neuromonitoring, but the influence of temperature-a very important and frequently encountered factor - on evoked potential has not been well documented. Specifically, decrease in amplitude and elongati on of latency seem not to have been sufficiently taken into account when in traoperative neuromonitoring levels were interpreted and when acceptable in traoperative warning criteria were determined. Methods. Experimental acute spinal cord injury was induced in rats by clip compression for two different intervals and at three different core tempera tures. Spinal somatosensory-evoked potential, elicited by stimulating the m edian nerve and recorded from the cervical interspinous C2-C3, was monitore d Immediately before and after compression, and at 15-minute intervals for 1 hour. Results. spinal somatosensory-evoked potential change is almost parallel to temperature-based amplitude reduction and latency elongation. Significant neurologic damage induced by acute compression of the cervical spinal cord produced a degree of effect on the amplitude of spinal somatosensory-evoked potential in normothermic conditions that differed from the effect in mode rately hypothermic conditions. Using the same electromonitoring criteria, m oderately hypothermic groups showed a significantly higher false-negative r ate statistically (35%) than normothermic groups (10%). Conclusions. Systemic cooling may protect against the detrimental effects o f aggressive spinal surgical procedures, There is still not enough publishe d information available to establish statistically and ethically acceptable Intraoperative neuromonitoring warning and intervention criteria conclusiv ely. Therefore, an urgent need exists for further investigation. Although a reduction of more than 50% in evoked potential still seems acceptable as a n indicator of impending neural function loss, maintenance of more than 50% of baseline evoked potential is no guarantee of normal postoperative neura l function; especially at lower than normal temperatures.