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Middle ear pressure changes after nitrous oxide anesthesia and its effect on postoperative nausea and vomiting
Nader D Nader1, George Simpson, Roberta L Reedy
1Department of Anesthesiology, Veteran's Administration, Western New York Healthcare Center, Buffalo, NY 14215, USA. nnader@buffalo.edu
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.