Urodynamic changes following intrathecal administration of morphine and fentanyl to dogs

The effect of intrathecal (i.t.) injection of morphine and fentanyl on the urinary bladder was studied by ascending cystogram in 18 anaesthetized dogs. Examinations were performed before and 60 and 120 minutes after i.t. injection of saline (group I), 0.03 mg/kg morphine (group II) and 1.5 microg/kg fentanyl (group III). A significant increase in maximal volume and compliance and a decrease in voiding pressure were observed, indicating relaxation of the detrusor muscle after i.t. administration of morphine or fentanyl. I.t. morphine produced greater and more prolonged bladder relaxation than i.t. fentanyl. We conclude that i.t. morphine and fentanyl cause variable degrees of urinary retention. As fentanyl produced milder and shorter bladder relaxation than morphine, it may be useful in patients with urinary disturbances.