Investigation of Middle Ear Pressure Changes During Prone Position Under General Anesthesia Without Using Nitrous Oxide

Purpose: The effects of different body positions on the middle ear were reported in several studies, but there are no data about the effects on patients under general anesthesia. The aim of this study is to determine the effect of prone position on middle ear pressure (MEP) during general anesthesia without using nitrous oxide. Methods: Twenty patients under general anesthesia during prone position were included in the study. The performed anesthesia method was the same for all patients. Remifentanil was used for analgesia instead of nitrous oxide. MEPs were measured 5 times with a middle ear analyzer: before induction (BI), after intubation (AI), after turned to the prone position (PP1), at the end of the prone position (PP2), and after returned to the supine position (SP). Duration of prone position was also recorded. Results: Of the 20 patients were 11 women and 9 men with a 49 +/- 13 mean age. BI-AI, AI-PP1, PP1-PP2, and PP2-SP comparisons of both MEPs were statistically significant (P < 0.0001). Right mean MEPs were BI, -1 +/- 23 daPa; AI, 41 +/- 51 daPa; PP1, 124 +/- 76 daPa; PP2, 152 +/- 59 daPa; and SP, 63 +/- 29 daPa; whereas left mean MEPs were BI, -24 +/- 55 daPa; AI, 28 +/- 34 daPa; PP1, 132 +/- 67 daPa; PP2, 162 +/- 48 daPa; and SP, 70 +/- 89 daPa. Significant increases were detected at the start and continuation of the prone position. The mean duration of prone position was 98 +/- 51 per minute. Conclusions: The significant MEP increases during the prone position under general anesthesia depend on a number of reasons. Among them are inhaler agents, pressure changes in mucosal blood vessels due to venous congestion, and the mastoid bone volume. Further researches are required to determine and explain the mechanisms of increase in MEP during prone position.