Balanced postoperative analgesia: effect of intravenous clonidine on blood gases and pharmacokinetics of intravenous fentanyl.

Agonist interactions in antinociceptive effects between clonidine and opioids can be used to reduce opioid requirements in surgical patients. However, clonidine can cause marked sedation and associated respiratory dysfunction. Thus, the benefit of using clonidine to reduce opioid use on respiration is questionable. This double-blind randomized study compared the analgesic efficacy, arterial blood gases, and pharmacokinetics of an intravenous (IV) infusion of fentanyl 75 micrograms/h and a mixture of fentanyl 25 micrograms/h plus clonidine 0.3 micrograms.kg-1.h-1 in 32 healthy young adults after surgery for scoliosis correction. Oxygen saturation (FIO2: 0.21) and respiratory rate were monitored as well as supplemental analgesia demands (IV ketoprofen via a patient-controlled device), pain, sedation, and hemodynamics. Oxygen and naloxone (5 micrograms.kg-1.min-1) were administered, respectively, if more than three episodes of oxygen saturation less than 90% were observed within 10 min and if PaCO2 was higher than 50 mm Hg. Pain relief, sedation, and ketoprofen requirements were similar in both groups. The number of episodes of arterial desaturation less than 90% (> 20 s) was 106 for four patients in the fentanyl group (versus none in the clonidine-fentanyl group). Naloxone was required in six patients and oxygen in two patients of the fentanyl group (versus none in the group receiving clonidine). Dopamine, 10 micrograms.kg-1.min-1, was required in one patient of the clonidine-fentanyl group to correct hypotension. Mean arterial blood pressure, plasma clearance, and the elimination rate constant of fentanyl were lower in the clonidine-fentanyl group than in the fentanyl group.(ABSTRACT TRUNCATED AT 250 WORDS)