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  • Title: Middle ear pressure changes after nitrous oxide anesthesia and its effect on postoperative nausea and vomiting.
    Author: Nader ND, Simpson G, Reedy RL.
    Journal: Laryngoscope; 2004 May; 114(5):883-6. PubMed ID: 15126749.
    Abstract:
    OBJECTIVES/HYPOTHESIS: This study was designed to explore the relationship between changes in middle ear pressure associated with inhalational anesthesia and the incidence of postoperative nausea and vomiting (PONV). STUDY DESIGN: Prospective, randomized. METHODS: Middle ear compartment pressures were measured by tympanometry in 27 randomly assigned knee arthroscopy patients throughout the surgical procedure as well as into recovery. RESULTS: A positive correlation between the maximum positive pressure (MPP) and maximum negative pressure (MNP) gradient and PONV was demonstrated (P <.05). The incidence of PONV in the nitrous oxide (N2O) treatment group was 6 of 16 patients, whereas only 2 of 11 patients in the control group developed nausea, vomiting, and vertigo symptoms. Those patients that did not experience PONV demonstrated a median MPP of 155 with a median MNP of -52. The patients that experienced PONV exhibited a median MPP of 179 with a median MNP of -164. This demonstrates a significant increase in the incidence of PONV in the N2O treatment group. CONCLUSIONS: Barometric changes in the middle ear contribute to the incidence of PONV induced by N2O.
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