Bethanechol Chloride for the Prevention of Postoperative Urinary Retention After Anal Surgery Under Spinal Anesthesia

Abstract

Background: Postoperative urinary retention is a commonly encountered problem after anal surgery particularly under spinal anesthesia. Bethanechol chloride, a muscarinic cholinergic receptor agonist was used to determine whether it could prevent this problem. Methods: One hundred six patients with mean age of 37 ± 9 who underwent anal surgery under spinal anesthesia from January to August 2007 were included in this nonblinded randomized prospective experimental study. Forty-six patients were given bethanechol chloride 25mg/tab 1 hour post-op then another dose after 4-6 hours. Intravenous fluid was limited to <750 ml perioperatively and patients were asked to void within 6-8 hours post-op. Those with the urge to void but unable to do so within the hour or had hypogastric pain (VAS > 8) were immediately catheterized and the amount drained recorded. Results: The study showed that the number of patients catheterized in the bethanechol group was significantly lower (6.52% vs 23.33%, P=0.038) and the mean amount of urine drained was less than the control (<400cc, P=0.001). Using Z test, the proportion of patients catheterized in the bethanechol group was significantly lower than the control (P=0.0097). No significant relationship was noted between the patient's age (<50 or >50) and gender with regards to urinary retention (P=0.254 and P=0.187, respectively). The number needed to treat (NNT) showed that six patients treated with bethanechol are needed to prevent one patient from experiencing urinary retention. Conclusion: Although bethanechol chloride did not completely prevent the development of postoperative urinary retention, its use was associated with reduced need for catheterization. Key words: Bethanechol chloride, postoperative urinary retention, spinal anesthesia