PATIENT POSITIONING
A 42-year-old male was positioned and intubated for an anterior lumbar surgery. Prior to draping, his arms were placed in the cross position. Baseline studies of the tibial and ulnar nerves, L3, L4 and L5 dermatomes were obtained post induction. These identified well-developed reproducible cervical and cortical somatosensory and dermatome evoked potentials. However, the left ulnar nerve response showed a significant delay in latency and a decrease in cortical amplitude when compared to the right.

An impedance check was performed, and the impedance of all recording electrodes fell within acceptable limits of 2K ohms or less. Stimulating and recording electrodes were checked and found to be in the correct locations in the stimulation box and intact on the patient. Anesthesia was queried regarding the anesthetic regime, and no agents that affect somatosensory evoked potentials were administered. The surgeon was advised of abnormal findings of the left ulnar nerve.

Anesthesia was directed to reposition the arm. Subsequent recordings of the left ulnar nerve showed an improvement in cortical latency and increased amplitude.