Urodynamic studies after intrathecal fentanyl and buprenorphine in the dog

Cystometrograms (CMG) and urethral pressure profiles (UPP) were used in six anesthetized dogs to study the urodynamic effects of intrathecal (IT) injections of fentanyl and buprenorphine. The CMG and UPP were examined for each of the two drugs in all dogs (four experiments per animal). The measurements were performed before and 15, 30, 60, 90, and 120 min after IT injection of either 1.5 micrograms/kg fentanyl or 2 micrograms/kg buprenorphine. Fifteen minutes after IT injection of fentanyl, reduction in bladder tone was already noted, followed by decreases in mean peak vesical pressure of 48.3% +/- 6.0 (SE) (P less than 0.05) and mean peak urethral pressure of 38% +/- 3.0 (P less than 0.05) between 30 and 60 min after injection. These decreases, occurring in each experiment, gradually lessened at 90 and 120 min. The effects of IT buprenorphine, a partial opioid agonist, on bladder and urethral dynamics were inconsistent and non-significant in all studies. Disturbances of micturition observed clinically after spinal opioid administration may be related to the decrease in intravesical pressure and the resulting highly compliant bladder. Relaxation of the urethral musculature seen 15 min after IT fentanyl may prevent overdistension of the bladder and its associated complications.