Testing anal sphincter tone predicts the effectiveness of caudal analgesia in children.

In this study, we examined the effectiveness of caudal blocks and correlated it with the laxity of the patients' anal sphincter before emergence from anesthesia in 178 children undergoing inguinal and/or penile surgery. Bupivacaine 0.25% in a volume of 0.6-1.25 mL/kg was used in all patients. The presence of a lax anal sphincter at the end of surgery correlated significantly with the reduced administration of narcotics intraoperatively and in the postanesthesia care unit (P < 0.001). The sensitivity of the sphincter tone test was 98.1% with a 95% confidence interval (CI) ranging from 94.3% to 99.6%. The specificity of the test was 94.4% with a 95% Cl of 72.0%-100%. The positive predictive value of this test in predicting adequate caudal block was excellent (99.4%) with a 95% CI of 96.1%-100%. The negative predictive value was better than average (85%) with a 95% Cl of 62.9%-95.4%. We conclude that a lax anal sphincter can predict the effectiveness of analgesia after pediatric caudal blockade. A tight sphincter may suggest the need to repeat the block before the child awakens, or consider alternate methods of postoperative analgesia.