Making it safe to fly: Singapore’s first Hypoxic Challenge Test for children

24 Jul 2026 | Special Delivery

Key points:

KKH is Singapore’s first healthcare provider to offer the Hypoxic Challenge Test (HCT) for children.
HCT determines if children with chronic respiratory conditions can maintain safe blood oxygen levels during air travel.
Provides families with definitive guidance on whether it is safe for their child to fly with or without supplemental oxygen.
Suitable for children with chronic respiratory diseases or conditions with muscle weakness. A referral can be made to the KKH Respiratory Medicine Service for assessment.

For families of children with chronic respiratory conditions, the prospect of air travel can bring as much anxiety as it does excitement. This is because taking a plane may cause breathing difficulty in a child with decreased lung function, posing health risks.

During a flight, the ambient air in the pressurised cabin of a commercial flight drops to an oxygen saturation of about 15 per cent. This is lower than that of sea level at approximately 21 per cent. While most people can continue breathing normally and maintain safe blood oxygen levels, those with chronic lung disease or respiratory muscle weakness can experience significant drops in their blood oxygen levels, which can be life-threatening.

Due to this risk, families of affected children often avoid air travel with their child, fly with in-flight oxygen as a precautionary step, or simply take a gamble and fly without precautions.

Singapore’s first Hypoxic Challenge Test for children

First of its kind in Singapore, the Hypoxic Challenge Test (HCT) helps doctors determine whether a child with chronic respiratory disease or muscle weakness can breathe safely and comfortably, and maintain safe blood oxygen levels in an aircraft cabin.

Test results empower parents with concrete data that helps them take appropriate measures to mitigate and prevent life-threatening emergencies mid-flight. The assessment also provides peace of mind to parents that the child is able to maintain safe levels of oxygen throughout the flight either independently or with supplemental oxygen support.

Serving as a “preflight oxygen test”, HCT simulates in-flight conditions where a child breathes ambient oxygen concentration of about 15 per cent for 20 minutes. Rather than relying on estimates, it determines the exact flow rate of supplemental oxygen required for the child to maintain safe levels of oxygen saturation during a flight.

Who is eligible to undergo a HCT?

Eligible
1. Infants (> 40 weeks corrected age) and children with a history of severe chronic neonatal lung disease.	2. Patients with a history of severe respiratory disease or respiratory muscle weakness, and one or more of the following: a. SpO2 (blood oxygen saturation level) < 95% at rest or during exercise b. FEV1 (forced expiratory volume at one second) persistently ≤ 50% predicted, or severely abnormal FVC (forced vital capacity), defined as FVC z-score more negative than -4.0 c. On long term oxygen therapy in the last six months d. On nocturnal or whole-day non-invasive positive pressure respiratory support (e.g. CPAP, BiPAP) e. Known hypercapnia (abnormally elevated levels of carbon dioxide in the bloodstream)
HCT is not recommended for
1. Infants who are born premature and have not reached their corrected age of term, as testing is not a reliable guide of oxygen requirement in them. Note: They should have in-flight oxygen available, and delivered at 1–2L/min if they develop abnormally rapid and shallow breathing (tachypnoea), the skin between the ribs pulls inwards while the baby breathes (recessions), or other signs of respiratory distress.	2. Children with an ongoing or recent acute respiratory infection.

How is a HCT done?

Method of conducting the HCT may differ based on the child’s age and ability to cooperate with instructions.

Children older than four years: The test is usually conducted using a venturi mask connected to purified nitrogen gas. Children younger than four years: The test is usually done with the child (and parent, if the child is very young or has special needs) sitting in an enclosed chamber.
The child (and parent) breathes air with approximately 15 per cent oxygen saturation for a usual test duration of 20 minutes.
The child’s (and parent’s) baseline heart rate and blood oxygen saturation level in room air are recorded before commencing the test, and monitored continuously during the test by a pulmonary function technologist. A respiratory service doctor is present for rapid response in the rare event of a medical emergency.
If the child develops a drop in saturation levels below pre-defined thresholds during the test, supplemental oxygen will be given.
After the test, the child (and parent) will be exposed to ambient air, and their heart rate and blood oxygen saturation level will continue to be observed for a further 15 minutes. Following the test, the doctor will discuss the test results with the parents or caregivers. A detailed report and a memo with recommendations to the airline based on the report will also be shared.

What are the implications of the test results?

A doctor’s memo can be issued explaining the test results and recommendations (if any) for in-flight supplemental oxygen. This can help parents make advance arrangements with the air travel service provider.

The types of test results can include:

'Fit to fly’, where in-flight oxygen is not recommended	If the child maintains SpO2 ≥ 90% during the test without supplemental oxygen, in-flight oxygen is not recommended. It safe for the child to fly without supplemental oxygen
‘Fit to fly’, but in-flight oxygen is recommended	If the child needs supplemental oxygen (2 or 4L/min) to maintain SpO2 ≥ 90% during the test, in-flight oxygen is recommended at that specific flow rate.
Not ‘fit to fly’	If, despite supplemental oxygen at 4L/min flow rate, the child is not able to maintain SpO2 ≥ 90% during the test, air travel is NOT recommended for the child.

Refer a patient

Hypoxic Challenge Test (HCT) is offered as an outpatient service at the respiratory laboratory at KKH.Community health professionals and paediatricians are encouraged to keep a look out for children with chronic respiratory diseases, or diseases associated with respiratory muscle weakness, who may benefit from objective assessment of their ‘fitness to fly’ – in terms of their ability to maintain safe levels of oxygen saturation during flight.

For such patients, referral to the Respiratory Medicine Service can be made via KKH Central Appointments at +65 6294 4050 or centralaapt@kkh.com.sg.

Acknowledgments

Dr Justin Wee Liang Yi, Dr Thomas Adi Kurnia Susanto, Ms Tan Soh Gin and the Respiratory Lab team at KK Women’s and Children’s Hospital

Dr Biju Thomas, Head and Senior Consultant, Respiratory Medicine Service, KKH

Dr Biju Thomas was trained in India, Australia and the United Kingdom. His clinical and research interests include asthma, bronchiectasis, flexible bronchoscopy and paediatric sleep medicine.Dr Biju also holds academic appointments with the Duke-NUS Medical School, NUS Yong Loo Lin School of Medicine and NTU Lee Kong Chian School of Medicine.

Prior to his appointment at KKH, Dr Biju was a consultant in paediatric respiratory medicine at the Royal Manchester Children’s Hospital, United Kingdom. He is a member of the European Respiratory Society and a fellow of the Royal College of Paediatrics and Child Health.

Contributed by

Biju Thomas Head ＆ Senior Consultant at Respiratory Medicine Service at KK Women's and Children's Hospital