Co-administration of pethidine and clonidine: a spinal anaesthetic technique for total hip replacement.

Co-administration of pethidine 0.75 mg kg-1 and clonidine 75 micrograms intrathecally provided good intraoperative anaesthesia for total hip replacement, similar to that obtained using 0.5% isobaric bupivacaine. Sensory and motor block were of shorter duration than that after 0.5% isobaric bupivacaine and 0.5% isobaric bupivacaine with morphine 0.5 mg (P < 0.001 sensory block, P < 0.001 motor block). Postoperative morphine consumption, measured using a patient-controlled system, was similar to that in patients in the bupivacaine only group (pethidine-clonidine: median 39 mg/24 h; bupivacaine: median 34 mg/24 h) but greater than that in the bupivacaine-morphine group (median 8 mg/24 h) (P < 0.001). Visual analogue pain scores after operation were similar to those with bupivacaine alone at all but one of the recording times but were greater than those in patients who received bupivacaine and morphine at 4, 6 and 10 h after operation (P < 0.001, P < 0.04, P < 0.02). The combination did not offer any major advantage over conventional agents.