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Flying on a wing and a prayer

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Spirometry predicts hypoxia during flights more accurately than hypoxic challenge. So Buchdahl et al found when they tested their initial premise—that in children with cystic fibrosis (CF) and chronic lung disease fingertip pulse oximetry beforehand could predict O2 desaturation in flight—by direct measurement during flights.

In a five year study of children with CF flying long haul on organised holidays, 10 of the 82 children developed desaturation <90% during the outward or return flight, two of whom needed in flight O2. Pulse oximetry one month before flying correctly predicted only two of the 10, spirometry predicted seven. Sensitivity for pulse oximetry was 20% and specificity 98% compared with 70% and 96% respectively for spirometry. Spirometry was the better predictor in this selected group, but not by much, the authors say.

Reliable measures for assessing likelihood of hypoxia are long overdue. Commenting in an editorial, Webb, from the Adult Cystic Fibrosis Unit in Manchester, UK, points to exclusion of the most severely affected children and probable attention to the children's medical fitness during their holiday as drawbacks to this latest study. He cites evidence, in adult patients, that resting O2 saturation or FEV1 did not correctly predict hypoxia during simulated flight conditions. The Manchester unit recommends in flight O2 for patients whose PaO2 drops below 6.6kPa during a simulated flight test.

Many other risk factors in CF complicate the picture. Emphasising the need for careful planning and preparation, Webb lists the minimum essentials for such patients planning a holiday abroad.