• Allison J Bethune, David A Houlden, Terry S Smith, Albert J Yee, Rajiv Midha, and Manoj Singrakhia.
• Sunnybrook and Women's HSC, Surgical Neuromonitoring, 2075 Bayview Ave, Suite B506, Toronto, ON, Canada M4N 3M5. allison.bethune@utoronto.ca
• J Clin Monit Comput. 2007 Feb 1; 21 (1): 41-7.

ObjectiveIntra-operative systemic changes impairing peripheral nerve function are not commonly detected with electrophysiology. This case presentation illustrates how somatosensory evoked potential (SSEP) monitoring can detect global changes in peripheral nerve excitability during spine surgery.MethodsA posterior thoracic spine fixation was performed on a young male with multiple traumatic injuries. Bilateral tibial nerve SSEPs were intraoperatively recorded, along with the right median nerve SSEP for control.ResultsA rapid, progressive loss of tibial and median nerve potentials (followed by cortical SSEP loss) occurred 90 min after anaesthetic induction. Oxygenation and fluid volume were adequate throughout the case, despite mean airway resistance being elevated (33 cmH(2)0) and blood pressure being low (80/45 mmHg). Corresponding to the decrease in peripheral nerve responses was a drop in end-tidal CO(2) partial pressure (PaCO(2)) from 37 to 25 mmHg. Approximately, 100 min later, the peripheral and cortically generated SSEPs recovered in 2 of 3 limbs monitored. On emergence from anesthesia it was clear that the patient had bitten and kinked the endotracheal tube thus increasing the airway resistance. Ventilation difficulties were magnified with the patient's prone position. Post-operatively there were no sensorimotor deficits.ConclusionsSomatosensory evoked potential monitoring during spine surgery can detect uncommon generalized nerve conduction block, and further alert surgical teams to a systemic impairment. This was discovered to result from a compromised endotracheal tube. This can apply in various monitoring situations, as the changes affecting the SSEPs were not related to surgical manipulation.

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