Intraoperative monitoring of the bulbocavernosus reflex: the method and its problems

Objectives: This study evaluates the method of intraoperative neurophysiolo gical monitoring of the bulbocavemosus reflex (BCR) with reference to stimu lation and detection. Methods: The study was performed on a group of 65 patients, 53 men and 12 w omen, who underwent surgery for lower thoracic and lumbar spinal trauma, wi th no neurological deficit prior to dr following surgery. Stimulating elect rodes were placed on the dorsum of the penis or the clitoris. Single and do uble stimuli were used, as well as trains of 3, 4 and 5 stimuli. Detecting wire electrodes were introduced into the perianal region. Results: A single stimulus elicited the BCR in 50%, pairs in 75%, trains of 3 in 95%, and trains of 4 and 5 in 100% of patients. With placement of the detecting electrodes 2.5 cm deep to the skin, the BCR was detected in 13% of hemisphincters in women, and in 81% of hemisphincters in men. With contr olled intramuscular placement of detecting electrodes, the BCR was detected in 97% of hemisphincters in men. With bifocal detection the BCR amplitudes were 30-312 mV (median 90), and interside amplitude ratio was 0.05-1 (medi an 0.66); with monofocal detection, amplitudes and interside amplitude rati o were 30-560 mV (median 200) and 0.15-1 (median 0.86), respectively. Conclusions: A train of 3 electrical stimuli is optimal in eliciting the BC R in anesthetized patients. The low rate of elicitability in women was most probably due to inefficient stimulation. Detection was improved by control led intramuscular placement of electrodes. Monofocal detection yielded high er BCR amplitudes. Interside difference and interindividual variability of the BCR amplitude were considerable. (C) 2001 Elsevier Science Ireland Ltd. All rights reserved.