[The incidence of postoperative nausea and vomiting is not effected by routinely applied manual pre-oxygenation during induction of anesthesia]

Abstract

Objective: To evaluate whether routine pre-intubation positive pressure mask ventilation (PPMV) influences the incidence of postoperative nausea and vomiting (PONV).

Design: Prospective, randomised single blinded study.

Patients: 669 ASA class I-III patients of either sex (number calculated as follows: incidence of PONV = 30%, group difference = 25%, a-error < 5%, statistical power = 90%) scheduled for elective surgery (no eye, neck, nose or ear surgery) of at least 30 min duration.

Interventions: Approval by the local ethical committee and informed written consent was obtained. After preoxygenation (3 min) and induction of anesthesia with fentanyl (1-2 micrograms.kg-1 b.w.) and thiopental (5 mg.kg-1 b.w) patients were divided into two groups: group 1 patients (without PPMV, n = 333) received succinylcholine 30s after thiopental followed by tracheal intubation. Group 2 patients (with PPMV, n = 336) were ventilated by mask for at least 30s after thiopental injection, followed by succinylcholine and, after another 120s of PPMV, tracheal intubation. All anesthetics were performed by 15 anesthesiologists (8 certified staff members, 7 residents).

Measurements: Primary endpoint: incidence of PONV during the first 24 h postoperatively. Secondary end point: relation between PONV and medical qualification of the anesthesiologists.

Null hypothesis: significant difference in PONV between groups.

Statistics: contingency tables with chi-square and Fisher's exact test, Kruskal-Wallis-test (for categorical variables); ANOVA with post-hoc Scheffe (for continuous variables), p < 0.05.

Main results: No difference was found in the incidence of nausea (30.6% vs. 28%, p = 0.5) or vomiting (20.1% vs. 17%, p = 0.32) regardless whether the patients received PPMV or not. Women were nearly three times more likely to suffer from PONV (35.2% vs. 13.8%, p < 0.0001). Distribution of age, weight, height, anesthetic duration and surgical procedures were comparable between groups. The degree of medical qualification did not influence the incidence of PONV (p = 0.543).

Conclusion: Since neither routine pre-intubation positive pressure mask ventilation nor the medical qualification of the anesthesilogist affect the incidence of PONV neither variable needs to be taken into account in studies concerning PONV.