Spinal anesthesia with meperidine. Effects of added alpha-adrenergic agonists: epinephrine versus clonidine.

We determined the effects of intrathecally administered epinephrine and clonidine on the duration and quality of a meperidine spinal block. Forty-five patients scheduled for orthopedic surgery, divided into three groups, received spinal anesthesia with 1 mg/kg 5% meperidine, alone or with 200 microg epinephrine or 2 microg/kg clonidine. Using a double-blind method, the onset, extension, and duration of sensory block (to pinprick) and the duration and degree of motor block (Bromage scale) were assessed. Hemodynamic responses, duration of postoperative analgesia, degree of sedation, and occurrence of side effects were also recorded. The addition of epinephrine to the meperidine solution prolonged the sensory block (P<0.01) but did not affect its onset or extent. A similar potentiating effect was demonstrated for clonidine (P<0.001). The duration and degree of motor block were increased by addition of both epinephrine and clonidine. A tendency toward bradycardia and a decrease of mean arterial pressure was potentiated by clonidine but not by the epinephrine. Only the addition of clonidine prolonged the postoperative analgesia (P<0.001), but was associated with an increased sedation score. The incidence of other side effects did not differ between the groups. We conclude that coadministration of epinephrine or clonidine with meperidine enhances the duration and degree of spinal anesthesia and that adding clonidine prolongs the duration of postoperative analgesia.