The use of anxiolytic and parasympathomimetic agents in the treatment of postoperative urinary retention following anorectal surgery. A prospective, randomized, double-blind study.

Approximately 30 percent of patients undergoing anorectal surgery will develop acute urinary retention. The cause of this complication is poorly understood. Anxiety, anal distention, bladder distention as a result of vigorous hydration during surgery, and reflex inhibition of the urinary bladder detrusor muscle secondary to pain have been postulated as contributing factors. A four-armed prospective, double-blind, randomized trial was carried out to determine whether an anxiolytic agent (midazolam, 5 mg intramuscularly) and/or a parasympathomimetic agent (bethanechol, 10 mg subcutaneously) reduce the incidence of postoperative urinary retention following anorectal surgery. One hundred thirty-two patients (ages, 18 to 50 years), in acute urinary retention 6 to 12 hours following anorectal surgery, were enrolled. Sixty-nine percent of patients responded to bethanechol. Side effects were minimal. Midazolam alone had no effect on retention. Bethanechol and midazolam in combination resulted in less retention than midazolam and a placebo (P less than 0.05). Bethanechol alone was better than a placebo (P less than 0.002). Mean intraoperative intravenous fluid volume for the entire study group was 900 cc. Initial postoperative urinary volumes of patients who failed the treatment protocol were significantly higher than in those responding to bethanechol (mean of 527 cc vs. 241 cc, P less than 0.001). The use of an anxiolytic agent was not effective in the treatment of postoperative urinary retention. Bladder distention may increase the incidence of urinary retention. Bethanechol, in a dose of 10 mg subcutaneously, significantly lowered the incidence of postoperative urinary catheterization and should be considered as initial treatment of postoperative urinary retention following anorectal surgery.