[Comparison of fentanyl and tramadol in pain therapy with an on-demand analgesia computer in the early postoperative phase].

17 patients undergoing cholecystectomy in non-opiate general anaesthesia received tramadol (n = 7) or fentanyl (n = 10) for immediate postoperative pain relief using the on-demand analgesia computer (ODAC). Heart rate, blood pressure, and respiratory rate were monitored at half-hourly intervals during the 6-h trial period. Arterial blood was withdrawn at hourly intervals for blood gas analyses and beta-endorphin plasma level assays. Fentanyl and tramadol serum levels were determined prior to each on-demand bolus injection during the first 2 h of the study. At the end of the trial period, the quality of analgesia was assessed retrospectively using a visual analog scale. Mean opiate consumption was 0.53 +/- 0.1 mg for fentanyl and 412 +/- 11.6 mg for tramadol, resulting in an equipotency ratio of about 1:980 (relating to body wt., consumption/h, and pain score). No correlation was found between body wt.-based opiate requirements and pain score. Heart rate increased slightly but significantly under both opiates. Fentanyl produced a significant drop in mean arterial pressure by a maximum of 16%, while tramadol left mean arterial pressure unchanged. Respiratory rate, which was elevated initially, dropped significantly in both groups. Arterial pO2 and pCO2 were within the normal range throughout the observation period, reflecting the absence of respiratory side effects. Opiate blood levels showed major inter- and intraindividual variations (minimal and maximal levels for fentanyl ranged from 0.44-3.44 ng/ml, for tramadol from 272-1,900 ng/ml) and were thus poor predictors of the quality of analgesia.(ABSTRACT TRUNCATED AT 250 WORDS)