[Does intrathecal clonidine prolong the effect of spinal anesthesia with hyperbaric mepivacaine? A randomized double-blind study].

BACKGROUND

Clonidine, an alpha 2-receptor agonist, has been reported to prolong the blocking actions of local anaesthetics. The aim of this study was to investigate the effects of spinally injected clonidine on the duration of spinal anaesthesia by mepivacaine and on the postoperative demand for analgesics.

METHODS

Forty-five patients who had transurethral urological surgery under spinal anaesthesia were randomized to 3 groups (n = 15 each) and studied in a double-blind fashion. Group I received 80 mg mepivacaine 4% only, while in group II mepivacaine was combined with 75 micrograms clonidine intraspinally and in group III with 150 micrograms clonidine. Onset time, spread of anaesthesia, duration of sensory and motor blockade, regression of anaesthesia and postoperative demand for analgesics were recorded. In addition heart rate and mean arterial pressure were measured at regular intervals.

RESULTS

Clonidine had no effect on the onset time and spread or intensity of spinal anaesthesia. The higher dose of clonidine significantly prolonged the duration of sensory blockade by 50 min and the duration of motor block by 40 min, while 75 micrograms had no significant effect. Heart rate and mean arterial pressure were significantly reduced in both clonidine groups when compared to plain mepivacaine. There was no significant reduction in postoperative analgesic demand.

CONCLUSION

While clonidine prolonged sensory analgesia, there was also an undesirable prolongation of motor block postoperatively. In addition, there was a significant and long lasting reduction in heart rate and mean arterial pressure in both clonidine groups. Unfavourably, postoperative demand of analgesics was not reduced by spinal injection of clonidine. Thus, the routine addition of clonidine for spinal anaesthesia with local anaesthetics is not recommended.