Effect of timing of morphine administration during remifentanil-based anaesthesia on early recovery from anaesthesia and postoperative pain.

BACKGROUND: Since the time to peak analgesic effect of intravenous morphine can be longer than 40-60 min in volunteers, the goal of this study was to evaluate the effect of the timing of intraoperative morphine administration on early postoperative pain. METHODS: A total of 120 adult patients undergoing laparoscopic cholecystectomy were studied. Anaesthesia was induced with remifentanil and etomidate and maintained with remifentanil and sevoflurane/nitrous oxide. Morphine 150 micrograms kg-1 was given randomly at three different times during surgery, and a fourth group received placebo. Times to eyes opening and extubation were measured, and pain was evaluated in the post-anaesthesia care unit (PACU) using a visual analogue scale (VAS). Morphine 2-3 mg was given when the VAS score was > or = 50 mm. The four groups were, according to the time elapsed from morphine administration to the end of surgery, group 1 (n = 30): placebo; group 2 (n = 33): < 20 min; group 3 (n = 30): 20-40 min; group 4 (n = 27): > 40 min. RESULTS: Recovery from anaesthesia and pain scores were similar in all groups. However, mean (SD) morphine consumption was 5.7 (4.7) mg in group 1, 4.4 (4.2) mg in group 2, 4.7 (4.7) mg in group 3, and 2.2 (4.0) mg in group 4 (P < 0.05, group 1 vs 4). Morphine was required in only 38% of patients in group 4 compared with 83%, 67% and 69% in groups 1, 2, and 3, respectively (P < 0.01, group 1 vs 4). CONCLUSIONS: The timing of intraoperative morphine administration did not affect the early recovery from anaesthesia. However, the reduction in the number of patients requiring morphine in the PACU when morphine had been given more than 40 min before the end of surgery supports this practice, rather than administration closer to the end of surgery.

No clinical evidence of acute opioid tolerance after remifentanil-based anaesthesia.

We have prospectively assessed whether remifentanil-based anaesthesia is associated with clinically relevant acute opioid tolerance, expressed as greater postoperative pain scores or morphine consumption. Sixty patients undergoing elective gynaecological, non-laparoscopic, surgery were randomly assigned to receive remifentanil (group R, n=30) or sevoflurane (group S, n=30) based anaesthesia. Postoperative analgesia was provided with morphine through a patient-controlled infusion device. Mean (SD) remifentanil infusion rate in group R was 0.23 (0.10) microg kg(-1) min(-1) and mean inspired fraction of sevoflurane in group S was 1.75 (0.70)%. Mean (SD) cumulative morphine consumption during the first 24 postoperative hours was similar between groups: 28.0 (14.2) mg (group R) vs 28.6 (12.4) mg (group S). Pain scores, were also similar between groups during this period. These data do not support the development of acute opioid tolerance after remifentanil-based anaesthesia in this type of surgery.