Electrophysiologic Deterioration in Surgery for Thoracic Disc Herniation: Impact of Mean Arterial Pressures on Surgical Outcome

Objective: Severe thoracic disc herniation leads to increased pressure in adjacent neural structures, which in turn can require an increase in mean arterial pressure (MAP) to maintain adequate spinal cord perfusion. We report a case series of three patients with severe thoracic disc herniation that experienced deteriorations in motor-evoked potentials (MEPs) and somatosensory evoked potentials (SSEPs) following induction of general anesthesia, but prior to decompression of the neural elements.

Methods: In-depth chart reviews were completed for each patient from their initial presentation to long-term post-operative course. Careful attention was taken with regards to MAP at induction of each operative case.

Results: The origin of the decreased signals in all patients was thought to relate to inadequate cord perfusion pressures. Two of the patients recovered pre-operative neurologic function while the third was left with mild post-operative paraparesis. Mean arterial pressures at time of deterioration were noted to be 58, 80, and 60 mmHg. These measurements represented MAPs approximately 65, 92, and 60 % those of baseline values, respectively.

Conclusion: Based on these experiences, the authors' institution has adopted new guidelines in the setting of thoracic disc herniations that includes pre-operative optimization of volume status, placement of an awake arterial line prior to induction of anesthesia, use of MEP and SSEP electrophysiologic monitoring, careful selection of anesthetic, and aggressive maintenance of MAPs >110 % of preoperative values at all times prior to decompression of the spinal cord.