RETRACTOR ON THE ILIAC ARTERY
An anterior discectomy and interbody fusion, posterior decompression, instrumentation and fusion from L4 to S1 were performed on a 59-year-old female. The neurotechnologist used somatosensory evoked potentials to monitor the tibial and ulnar nerves and dermatome evoked potentials of the L4, L5 and S1 nerve roots.  Oxygen saturation was monitored from the left great toe.

Baseline studies of the tibial and ulnar nerves, L4, L5 and S1 dermatomes were well-developed and repeated. During the anterior discectomy and graft impaction at L4 - L5, the blood oxygen saturation readings could not be obtained. In addition, the left tibial nerve, left L4, L5 and S1 dermatomes showed prolonged cortical latency exceeding 10 percent. The amplitudes of all lower extremity responses were reduced by greater than 50 percent. However, responses recorded from the contralateral side and ulnar nerves showed no significant deviation from baseline suggesting that anesthetic agents were not a factor. The neurotechnologist verified that the O2 monitor was functioning properly.

A discussion with the surgeon regarding the abnormal readings ensued. The surgeon noted that a retractor was placed on the left iliac artery. The retractor was released and subsequent evoked potential recordings returned to approximate baselines. A 97 percent reading of the oxygen saturation was noted and maintained through closure. No known neurological deficits were observed.