Assessing the risk of hypoxia in flight: the need for more rational guidelines.

This study aimed to test the hypothesis that advice currently given by respiratory physicians to potentially hypoxic patients planning air travel varies and is not evidence-based. A prospective observational study was performed, surveying respiratory physicians in England and Wales. Sixty-two per cent responded. Nearly two-thirds worked in district general hospitals, a quarter in university hospitals, and the rest in tertiary referral (specialist) centres or a combination thereof. Most provide advice routinely; most of the remainder do on request or if concerned. Assessments comprise spirometry, blood gas level measurement, oximetry, predictive equations and hypoxic challenge tests. Twenty-five per cent of physicians measuring blood gas levels recommend in-flight oxygen when arterial oxygen tension (Pa,O2) <7.3 kPa, 50% when Pa,O2 is 7.3-8.0 kPa. Over two-thirds using spirometry recommend oxygen when the forced expiratory volume in one second <40% of the predicted value. Half recommend oxygen when arterial oxygen saturation (Sa,O2) <90%, 33% when Sa,O2 is 90-94%. Fewer than 10% of district hospital physicians (and none in other hospitals) use predictive equations. More than half of specialists but fewer than 10% of district hospital physicians perform hypoxic challenge tests. The risk of hypoxia at altitude is recognized by most respiratory physicians in England and Wales, but assessment methods and criteria for recommending oxygen vary widely. This suggests that most current advice is not evidence-based. Evidence-based guidelines are required.