V Goll et al. Anesth Analg 2001; 92:112-7.

Reviewed by: R. Prasad, MD

Summary:

• Supplemental intraoperative oxygen (80% vs. 30%) prevents PONV after gynecological laparoscopic surgery.
• Ondansetron is no more effective than 80% oxygen.

• Overall, a very interesting study.
• As mentioned in their discussion section, a larger number of patients may have demonstrated (to statistical significance) that ondansetron was more effective than control.
• Nevertheless, there was a trend suggesting some benefit from ondansetron, but still less effective than 80% oxygen
• They gave ondansetron at start of surgery, rather than at end. However, used 8mg. Also, surgeries relatively short (~1.5hrs). So, perhaps their comparisons are similar to actual practice.

• Power analysis: based on efficacy of ondan in prelim study, needed 216pts for 90% power to detect 50% dec in PONV
• 240 pts, 80/group
• Exclusions: pregnant, breast-feeding, menopausal, obese, kidney/liver dz, CNS injury, vertebrobasilar a insuff, vestibular dz, cytostatic therapy, preop vomiting or antiemetics
• Randomized 3 groups

• Standardized anesthetic: midaz premed, isoflurane, NMB/refersal. O2 given in PACU for at least 2h for all. All personnel reporting PONV blinded to intraop mgmt.

• No diff in demographics, hemodynamics, anesthetic mgmt, confounding factors (smoking, alcohol use, h/o motion sickness and PONV)
• Pain scores higher in 30% O vs. 80% O (VAS 21+/-16 vs. 15+/-17)

• No diff in longterm outcomes (physical fnct and mental status scores at 24hrs, pt satisfaction, time to liquid/solid food, time to discharge from PACU)

• Possible mechanisms
• hyperoxia decreases dopamine release from carotid bodies. However, unlikely to continue to have dec N/V after ox supp stopped
• intestinal hypoxia or ischemia (e.g., from colon manipulation, or increased intraabd pressures during laparoscopy) causes serotonin release