The warning criterion of intraoperative bulbocavernosus reflex monitoring in adult patients with lumbosacral intraspinal tumor

Abstract

Objective: There are currently no standard warning criteria for intraoperative neurophysiological monitoring (IONM) of bulbocavernosus reflex (BCR). This study aimed to preliminary detect a practical warning criterion for use in intraoperative BCR monitoring in adult patients with lumbosacral intraspinal tumor.

Methods: Adult patients with lumbosacral intraspinal tumor who underwent surgery with BCR monitoring were recruited. Patients were classified into four groups according to the amplitude decline rate of BCR responses at the end of surgery compared with the baseline: Group 1, <50%; Group 2, >50% and <75%; Group 3, >75% and <100%; Group 4, 100% (BCR disappeared). The sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) for three specified cutoff values of BCR amplitude decline rate at 50%, 75% and 100% to predict postoperative voiding function were calculated. Receiver operating characteristic curve analysis was used to determine the optimal cutoff value of BCR amplitude decline. Voiding function was evaluated based on subjective urinary symptoms and postvoid residual urine volume measurement at 1 month post-operatively.

Results: A total of 57 patients were included in the study. There were 33 (57.9%) males and the mean age was (51.2±15.3) years. There were 46 patients (26 males) in Group 1, 3 patients (2 males) in Group 2, 3 patients (1 male) in Group 3, and 5 patients (4 males) in Group 4. Two patients (2 males) in Group 1, 1 patient (0 male) in Group 2, 2 patients (0 male) in Group 3, and 4 patients (4 males) in Group 4 demonstrated worsened voiding function at 1 month post-operatively. When the warning criterion of BCR amplitude decline rate was set as 50%, the sensitivity, specificity, PPV, and NPV of BCR monitoring for worsened voiding were 77.8%, 91.7%, 63.6%, and 95.7% respectively. When the warning criterion was 75%, the sensitivity, specificity, PPV, and NPV were 66.7%, 95.8%, 75.0%, and 93.9% respectively. When the warning criterion was 100%, the sensitivity, specificity, PPV, and NPV were 44.4%, 97.9%, 80.0%, and 90.4% respectively. According to the ROC curve analysis, the optimal cutoff value of BCR amplitude decline for predicting voiding function at 1 month post-operatively was 66.5%. The area under curve, sensitivity, and specificity were 0.813, 77.8% and 95.8% respectively.

Conclusions: Intraoperative BCR monitoring is a valuable tool to be performed during surgery in adult patients with lumbosacral intraspinal tumor. The cutoff value of BCR amplitude decline rate at 100% (all or none criterion) can be used to predict postoperative voiding function, and the absence of BCR is a robust indication for poor voiding post-operatively. As a warning criterion, the cutoff value of BCR amplitude decline at 66.5% may be practical.