ALFENTANIL DOSE-RESPONSE RELATIONSHIPS FOR RELIEF OF POSTOPERATIVE PAIN

The aim of this study was to characterize within-patient alfentanil do se-response curves for the relief of spontaneous postoperative pain an d to test the closeness of relationships 1) between pain intensity and alfentanil analgesic requirements, and 2) between alfentanil requirem ents for analgesic and nonanalgesic (sedative and miotic) effects. The effects of alfentanil were studied in 23 patients after elective abdo minal surgery. During a 40- to 60-min testing session, the patient rec eived two intravenous (IV) injections of saline (placebo) and up to si x 3-mu g/kg increments of alfentanil at 5-min intervals. The patient r ated the pain intensity with a visual analog scale, and in a subgroup of 15 patients the blinded observer rated patients' sedation and measu red pupil diameter. Spontaneous postoperative pain was completely reli eved in all patients with cumulative doses of alfentanil ranging from 6 to 18 mu g/kg. The within-patient alfentanil dose-analgesic response curves were primarily quantal in nature: a precipitous decrease in pa in intensity (representing greater than or equal to 2/3 of the total e ffect) after the injection of only one of the increments of alfentanil was observed in 15 of 23 patients. When the analgesic effect of alfen tanil was presented as the collective response of a group of individua ls, the quantal nature of the response was concealed by the wide inter individual variability of the response. No statistically significant r elationship was noted between predrug pain intensity and the cumulativ e dose of alfentanil necessary to produce pain relief. A strong correl ation was found between interpatient variabilities in the analgesic an d sedative effects of alfentanil (r = 0.75, P < 0.002). At the same ti me, the relationship between alfentanil requirements for pain relief a nd that for pupil constriction did not demonstrate any significant cor relation. The results suggest that, in a population of patients with p ostoperative pain, the intensity of spontaneous pain cannot be the pri mary factor determining the dose of alfentanil necessary for its relie f.