British Journal of Anaesthesia 1998; 81: 653–659 Propofol and postoperative nausea and vomiting

Editor,—I read with interest the article by Bree and colleagues1 on combining propofol with morphine patient-controlled analgesia to prevent postoperative nausea and vomiting (PONV). They showed that addition of propofol did not decrease the incidence of PONV. I would like to suggest some explanations for their results. The authors correctly pointed out that the plasma concentration of propofol for 50% reduction in nausea scores in a group of postoperative patients was 343 ng ml 1.2 This concentration may be achieved with a bolus dose of propofol 10 mg followed by continuous infusion of 1 mg kg 1 h 1. Therefore, a 70-kg patient would receive 70 mg h 1. In Bree and colleagues’ study, the propofol treated group used a mean dose of propofol 9.8 (95% CI 7.5–12.1) mg h 1 for the first 24 h and 2.6 (95% CI 0.9–4.2) mg h 1 for the next 24 h. Indeed, the maximum dose of propofol used (in one patient) was 180 mg in a 4-h period (45 mg h 1). Hence, it is likely that their patients received sub-therapeutic doses of propofol for antiemetic effects. We have recently reported the use of patient-administered propofol for the treatment of PONV.3 In a randomized, doubleblind design, patients self administered propofol 20 mg or Intralipid (placebo) with a 5-min lockout interval, where no propofol could be administered. The propofol group had significant reductions in the degree of nausea (25% less nausea vs placebo), incidence of vomiting (12% vs 56%) and need for rescue antiemetic (17% vs 70%) compared with placebo. Placebo patients had a nine-fold increase in the risk of subsequent vomiting and a 10-fold increase in the likelihood of using rescue antiemetics. The propofol group received a mean dose of propofol 100 60 mg during the study (2 h). This was not associated with an increase in sedation compared with placebo. Propofol treated patients were also more satisfied with their control of PONV. When propofol is used for its antiemetic effects in comparative studies, it is important that therapeutic dose ranges are administered. T. J. GAN Department of Anesthesiology Duke University Medical Centre Durham, NC, USA