A systematic review 1 including 2 retrospective case series with a total of 9 subjects was abstracted in DARE. Additionally 7 citations, either letters in peer-reviewed journals or opinions of organisations, were identified. One case series (n=6) reported that decompression illness (DCI) symptoms worsened in 4 patients when the altitude of the helicopter rose above 700 to 1 000 feet (213 to 304 m) above ground level, but were resolved at 500 feet above ground level. No symptoms were noted in the other 2 patients when the helicopter stayed below 500 feet (152 m) above ground level. The other case series (3 patients who experienced symptoms on a commercial flight after hypobaric high-altitude military training) reported no complications in any of the 3 patients when the helicopter stayed below 1 000 feet (304 m) above ground level. None of the expert opinions cited clinical trials or prospective cohort studies. Expert opinions recommended a maximum altitude of 500 to 1 000 feet but did not specify whether this was above sea level or ground level.
Comment: The quality of evidence is downgraded by limitations in study quality (case series and expert opinions only).
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