Prediction of hypoxaemia at high altitude in children with cystic fibrosis.

OBJECTIVE--To assess the usefulness of a hypoxic challenge in a laboratory at sea level in predicting acute desaturation at altitude in children with lung disease. DESIGN--Comparison of responses to hypoxic challenge in different settings. SUBJECTS--22 children (12 boys) aged 11 to 16 years with cystic fibrosis in whom the mean forced expiratory volume in one second was 64% (range 24-100%). SETTING--Lung function laboratory, the Alps, and aboard commercial jet aircraft. MAIN OUTCOME MEASURES--Spirometric lung function at sea level and finger probe oximetry with air and 15% oxygen. Oximetry during high altitude flight and on a mountain at altitude of 1800 m. RESULTS--Significant desaturation (range 0 to 12%) occurred with all hypoxic challenges (P < 0.002). The best predictor of hypoxic response from a single reading was the laboratory test (r2 = 76% for flight and r2 = 47% for mountain altitude), but the mean errors of prediction were not clinically significantly different. In six children who showed the greatest desaturation the laboratory test overestimated desaturation, but other predictors underestimated desaturation in three by up to 5%. CONCLUSIONS--The laboratory hypoxic challenge directly predicted the worst case of desaturation during flight and at equivalent high altitude. Spirometry and baseline oxygen saturations may underestimate individual hypoxic response. The test may have wider applications to other patients with stable chronic lung diseases, particularly in determining who needs supplementary oxygen during air travel and who should be advised against holidays at high altitude.