Post Operative Nausea and Vomiting and Time to Discharge is Unchanged with 6 mg Initial Dose of Intravenous Morphine
Aaron A. Tebbs, M.D., Craig Curry, M.D., Andreas Taenzer, M.D., Catharine La Vopa, R.N. Maine Medical Center, Portland, ME

Background: Post-operative nausea and vomiting (PONV) is common after laparoscopic surgery and often leads to prolonged discharge from the post anesthesia care unit (PACU). Opioids are known to directly stimulate the chemoreceptor trigger zone (CTZ), however, at higher plasma concentrations they may actually suppress the CTZ and reduce PONV (1). We conducted a prospective, randomized, doubleblinded, clinical trial that demonstrated an increased initial dose of morphine improved pain control (2) while PACU discharge times and PONV rates remained unchanged.
Methods: 70 adult patients, ASA class I or II, undergoing elective laparoscopic procedures (Nissen fundoplication or Cholecystecomy) with a post-operative numeric pain scale (NPS) score > 5 were randomized into three groups (2, 4, or 6 mg initial dose of morphine). All patients underwent general anesthesia with propofol, a volatile anesthetic, nitrous oxide, and muscle relaxant. In addition, each patient received 4mg ondansetron fentanyl, toradol, and local anesthetic infiltration of the incision. In the PACU a rescue dose of 4 mg ondansetron was administered for PONV. After the initial dose of morphine the NPS
scores were recorded in 5 minute intervals and 25 mcg fentanyl boluses were given as needed throughout the PACU stay.
Results: 34.8% of the patients in the 6 mg morphine group required PONV rescue medication compared to

55.6% and 41.4% for the 4mg and 2mg groups, respectively. Total minutes in PACU were 61.5(6mg), 66.1(4mg) and 75.1 (2mg). There was no respiratory depression in any group. An unpaired t test showed no statistical difference between groups in PONV rates or total time in PACU.
Conclusion: The more rapid pain control (2) and similar PONV rates in the 6 mg initial dose of morphine group likely explains the unchanged total time in PACU. Since the higher initial dose of IV morphine offers more rapid pain control without increasing PONV or discharge times, a 6 mg loading dose of IV morphine should be considered when treating acute post-operative pain after laparoscopy.
References:
1. Barnes NM, Bunce KT, Naylor RJ, et al: The Action of Fentanyl to Inhibit Drug-Induced Emesis. Neuropharmacology 1991;30:1073-83
2. Tebbs A, Curry C, Taenzer A, LaVopa C Evaluation of Three Different Initial Doses of Intravenous Morphine. Sumitted for presentation at SAMBA, 2004

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