Laboratory assessment of fitness to fly in patients with lung disease: a practical approach.
To identify patients with respiratory disease, who may be at risk of developing respiratory distress during commercial air travel, a hypoxia inhalation test (HIT) can be performed. This paper reports our experience of using such a test combined with an interpretation algorithm in a routine respiratory function laboratory. Twenty-eight patients were studied. Baseline oxygen saturation (Sa,O2) was measured using a pulse oximeter. If Sa,O2 was < 90% no HIT was performed and the patient was assessed as unfit for air travel. If baseline Sa,O2 was > or = 90% an HIT was performed by the patient breathing through a 35% Venturi mask supplied with 100% nitrogen which reduced inspiratory oxygen fraction to 15.1+/-0.2%. Results were interpreted using a locally derived algorithm, and validation was attempted using a questionnaire to investigate subsequent symptoms during travel. All patients tolerated the assessment well. Twenty-two patients were assessed as "fit to fly" with a further two patients "fit to fly with supplemental O2". Four patients were considered unfit to fly. Hypoxic response could not be predicted from either forced expiratory volume in one second, or pretest saturation. Validation of such protocols is difficult, but the hypoxia inhalation test may be a useful tool for predicting hypoxia during air travel in patients with chronic respiratory disease.