Introduction Commercial airplanes fly with an equivalent cabin FiO₂ of 0.15 leading to reduced oxygen saturation (SpO₂) in passengers. Although guidelines exist, the evidence-base for recommending supplemental O₂ when flying in children with complex congenital heart disease (CHD) is practically non-existent. We conducted hypoxic challenge tests (HCT) to determine which children need a pre-flight assessment.

Methods Children<16 years with complex CHD were recruited; exclusions were SpO₂ <75%; pulmonary hypertension; oxygen requirement; or concomitant respiratory disease. Children had a standard HCT in a sealed body plethysmograph with FiO₂ of 0.15. We measured SpO₂, pulse rate, transcutaneous CO₂ (PtcCO₂), corrected QT interval (QTc), and total Hb by co-oximetry (SpHb). Supplemental O₂ was given (which meant a ‘failed’ test) if (1) children with baseline SpO₂95%–100% desaturated to 85%, (2) or baseline SpO₂85%–94% desaturated to 15% of their baseline; (3) or baseline SpO₂75%–84% desaturated to 70%.

Results There were 68 children, mean age 3.3 years (range 10 weeks to 14.5 years); 53% were boys. Grouping by normal (≥95%) vs abnormal baseline SpO₂(75%–94%), both groups had a significant fall in SpO₂ (p<0.0001). 3/38 (8%) children failed with normal baseline SpO₂ vs 5/32 (16%) with abnormal baseline (non-significant difference). In terms of cardiac status, both groups had a significant fall in SpO₂ (p<0.0001); however in those with no residual for potential R-L shunt 0/27 failed vs those with residual potential R-L shunt or who had not undergone repair or who had palliative surgery in whom 8/41 (20%) failed (p<0.02). PtcCO₂ did not change significantly (i.e., no-one hyperventilated to compensate for hypoxia); pulse rate and QTc were not different between groups, and unaffected by the hypoxic state.

Conclusions This is the first evidence to help inform which children with CHD need a pre-flight HCT. We suggest all children with residual potential R-L shunt or who have not undergone repair or who have only had palliative surgery should be tested (as 20% are expected to need supplemental O₂), whereas those with no potential for R-L shunt need not be. Baseline SpO₂ does not help predict who will need supplemental O₂ when flying.