[Effects of anesthesia on postoperative micturition and urinary retention]

Postoperative micturition difficulties, considered as minor complications, have a high incidence. Acute urinary retention can follow all types of anaesthetics or operations. Surgical trauma to the pelvic nerves or to the bladder, postoperative oedema around the bladder neck, and pain-induced reflex spasm of the external and internal urethral sphincters may play a role in the development of urinary retention. Acute urinary retention is the most common complication of surgery for benign anorectal disease. The incidence of urinary retention is more likely to occur in old male patients. Preoperative urinary symptoms are not a prerequisite for developing postoperative urinary retention, although they are considered to be a risk factor. The type of anaesthetic, postoperative pain and its management may have little effect on the occurrence of postoperative urinary dysfunction. Studies on the urodynamic effects of various anaesthetic agents are rare. The parasympatholytic drugs increase bladder capacity, decrease the rate of bladder contractions and cause downward trends in urethral resistance. The barbiturates and halothane produce similar effects on urethral resistance. The anaesthetic agents decrease the intrabladder pressure and inhibit the micturition reflex. Halothane decreases bladder contractions and increases its capacity measured by the cystometrogram. Urinary retention is a side effect of opioids, particularly after intrathecal or epidural administration. Epidural morphine relaxes the detrusor muscle with a corresponding increase in the maximal bladder capacity. Spinal opioids influence the function of the lower urinary tract, by direct spinal action on the sacral nociceptive neurons and autonomic fibres, as well as by an effect on supraspinal centres. Naloxone increases detrusor pressure, decreases bladder capacity, and causes a need to void. Urinary retention is less common after a short-acting (lidocaine 5%) than after a long-acting agent (bupivacaine 0.5%). After spinal anaesthesia, detrusor strength and the ability to void restarts with the return of sacral sensation to pinprick. A single episode of bladder overdistention can result in significant morbidity. Overfilling of the bladder can stretch and damage the detrusor muscle, leading to atony of the bladder wall, so that recovery of micturition may not occur when the bladder is emptied. On the other hand, the excessive use of an indwelling catheter can lead to urinary tract infection, urethral stricture and prolonged hospital stay. Short-term prophylactic catheterisation is recommended in patients with obstructive symptoms. Patients at risk for urinary retention should be stimulated to void and provided a quiet environment in which to do so. They should be encouraged to seat, stand or ambulate as early as possible. The alpha 1 adrenergic receptor blocking agents have been used for treatment of organic or functional urinary retention. It is essential to make sure the bladder empties regularly in the postoperative period, especially in day-case surgery or in patients receiving opioid analgesia or after epidural anaesthesia.