Comparison of clonidine, morphine or placebo mixed with bupivacaine during continuous spinal anaesthesia

To compare intraoperative anaesthetic and haemodynamic effects of clonidine-bupivacaine, morphine-bupivacaine and placebo-bupivacaine combinations during continuous spinal anaesthesia.

Thirty six geriatric patients, undergoing knee replacement using continuous spinal anaesthesia were randomly assigned to: Placebo (n = 12), clonidine (n = 12) and morphine (n = 12), where 1 ml saline, 0.15 mg clonidine or 0.15 mg morphine were mixed with 10 mg bupivacaine 0.5%. Anaesthetic variables studied were maximal sensory level and degree of motor block, duration of surgical analgesia and duration of anaesthesia. Changes in systolic arterial pressure and vasopressor requirements were evaluated.

Maximal sensory level and degree of motor block were comparable among the groups. Before surgery two patients in the placebo group, three in the clonidine and one in the morphine group received one additional ml bupivacaine 0.5% because of inadequate anaesthesia and were not considered for determination of duration of surgical analgesia. In the remainder, 1/9 in the clonidine group, 8/10 in placebo and 8/11 in morphine (P < 0.05) received reinjection of bupivacaine for surgical pain. These injections were given about 2 1/2 hr after the initial intrathecal injection, the duration of anaesthesia being about four hours. During the first 30 min after the initial injection the decrease in systolic pressure was greater in the clonidine and morphine than in the placebo group (P < 0.05). Thereafter, vasopressor requirements were higher only in the clonidine group (P < 0.05).

In elderly patients 0.15 mg clonidine but not 0.15 mg morphine prolonged surgical analgesia when added to 10 mg plain bupivacaine.