A previously healthy 45-year-old male undergoes an elective hernia repair under spinal anesthesia. Postoperatively, he complains of difficulty voiding. Bladder catheterization shows a post-void residual of 300cc of urine. This patient would most likely benefit from which of the following medications?

Question

A previously healthy 45-year-old male undergoes an elective hernia repair under spinal anesthesia.  Postoperatively, he complains of difficulty voiding.  Bladder catheterization shows a post-void residual of 300cc of urine.  This patient would most likely benefit from which of the following medications?

Quizplus · Accepted Answer

This patient most likely has postoperative urinary retention, which occurs in up to 25% of patients after lower abdominal surgery. A normal post-void residual urine volume in the bladder is less than 50cc. Anesthesia and analgesia contribute to all of the following: over-distention of the bladder, a decreased micturition reflex, decreased contractility of the bladder detrusor muscle, and incomplete emptying. Contraction of the detrusor muscle is stimulated by muscarinic cholinergic agonists. Bethanechol, a muscarinic agonist, often improves bladder-emptying in patients with post-surgery urinary retention. (Choice A) Finasteride is prescribed for patients with bladder outlet obstruction secondary to prostatic hypertrophy. Finasteride is a 5α-reductase inhibitor that decreases the local conversion of testosterone to dihydrotestosterone in the prostate, thereby promoting shrinkage of the gland over 6 to 12 months. Since this patient's incomplete bladder emptying is due to weak detrusor muscle contraction rather than prostatic hypertrophy, finasteride would not be likely to improve his acute condition. (Choice B) Phenylephrine is an alpha-agonist with some selectivity for α1 receptors. The occupation of α1 receptors in the bladder actually encourages the trigone and sphincter to contract. Phenylephrine promotes, rather than alleviates, urinary retention. (Choice D) Oxybutynin is an antimuscarinic agent commonly used for urge incontinence. If given, it will worsen this patient's condition. (Choice E) Imipramine has anticholinergic activity, and would thus worsen this patient's condition! Educational Objective: Postoperative urinary retention, with incomplete bladder emptying, is a common complication thought to involve decreased micturition reflex activity, decreased contractility of the bladder detrusor, and/or increased vesical sphincter tone. This condition may be treated with a muscarinic agonist (bethanechol) or an α1 blocking drug.

A Previously Healthy 45-Year-Old Male Undergoes an Elective Hernia Repair