POSTOPERATIVE ANALGESIA BY INTRAVENOUS CLONIDINE

Clonidine, an alpha-2 adrenoreceptor agonist, has nonopiate antinociceptive properties, which might be an alternative for postoperative analgesia free of opioid-induced side effects. To document the analgesic properties of intravenous clonidine during the postoperative period, 50 ASA physical status 1 patients, immediately after spinal fusion, were randomly assigned to two groups, blindly administered either clonidine (5-mu-g/kg infused the 1st h and then 0.3-mu-g-1.kg-1.h-1 during 11 h) or a placebo. A visual analog scale graded from 0 (no pain) to 100 mm was used to assess pain before clonidine or placebo administration (T0), at the end of the loading dose (T1) and then every 2 h (T3, T5, T7, T9, and T11). Morphine (0.1 mg/kg) was administered intramuscularly after each pain measurement if the score was greater than 50 mm. No morphine was given at T0. Hemodynamics, blood gases and plasma clonidine concentrations were measured each time the pain score was measured. The pain score decreased from 42 +/- 5 to 26 +/- 3 mm (mean +/- standard error) in the clonidine group whereas it was unchanged in the placebo group despite a greater morphine requirement (dose for each patient: 3.8 +/- 1 vs. 10.8 +/- 1.2 mg). Clonidine delayed the onset of pain and the first request for morphine injection. Mean arterial pressure decreased to 74 +/- 2 mmHg in the clonidine group (-26 +/- 2 vs. -15 +/- 2% in the placebo group at T11) despite a significant increase in the cumulative fluid volume. Plasma clonidine concentration was 1.8 +/- 0.1 ng/ml at T1 and 1.4 +/- 0.1 ng/ml at T3 and progressively increased to 1.8 +/- 0.1 ng/ml at T11. In conclusion, intravenous clonidine is a possible approach to postoperative pain treatment in patients recovering from major surgery. However, the usefulness of this technique may be limited by a decrease in blood pressure if filling pressure is inadequate.