Objective: To determine the sparing effect of clonidine (C) on fentanyl (F) demand in burned patients under PCA.
Study design: Prospective, randomized, double blind study versus placebo.
Patients: Twelve consecutive patients with mean burn surface area of 20 +/- 9%, studied between the third and the eighth day post-burn.
Methods: F was delivered by a PCA pump (bolus: 1 mg.kg-1). In the morning, burn patients received additional F (5 mg.kg-1) before hydrotherapy. After randomisation, C or placebo (P) were alternatively infused over 24 hours. Demands for F during the morning, the afternoon and the evening were noted. Pain scores were measured on a visual analogic scale. In eight patients, plasma levels of F (pF) were iteratively measured. Heart rate, arterial pressure, respiratory rate and SpO2 were monitored.
Results: Analgesic demands were 19.5/day under P and 9.5 under C (P < 0.0001). Pain reoccurred for pF of 4.1 under C vs 5.7 under P (P < 0.05) with same pain scores in the two groups. After a pain stimulus, pain scores were lower under F, despite lower pF (P < 0.05). Arterial pressure and heart rate were significantly lowered during the first hour of C infusion.
Conclusion: Doses of F and pF required to reach analgesia were very high. Adding C decreases by 50% the F demand and lowers pF. Minor haemodynamic effects were observed during the first hour of C infusion.