Hypoxia in airline passengers
Editor - Morgan emphasized the importance of proper preparation of
airline passengers with respiratory disease1. When using the guidelines of
the British Thoracic Society, it should be taken into account that these
are based on data of studies among awake and comfortably seated passengers
or study subjects. However, immobility, cramped seating conditions, sleep
and drowsiness, as occur in passengers on long-haul flights, may hinder
proper respiratory activities. Moreover, the lower ambient pressure in the
cabin leads to gastro-intestinal distension (1.4x expansion at 8000 ft),
which may limit downward movements of the diaphragm and proper pulmonary
We have measured oxygen saturation of haemoglobin (SaO2; ear pulse-
oximetry) in 15 resting healthy subjects seated in a hypobaric chamber
with an inside ambient pressure of 75.8 kPa, which equals 8000 ft cabin
altitude, commonly encountered in commercial airliners. Mean SaO2 was 90 %
(SD ± 1.9; range 85-93) after 30 min of exposure2. The subjects stayed
for 8 hours in the hypobaric chamber, and when they were dozing off or
sleeping, we found much lower SaO2 levels (80%, range 78-85) at cabin
altitudes of 8000 ft. When these drowsy subjects were stimulated to
ventilate properly, SaO2 levels increased significantly. We conclude that
at some stages of flight SaO2 levels in passengers may be critically
lower than is generally assumed. Therefore, pre-flight preparation of
passengers with respiratory disease should also address proper seating,
body position while sleeping, ventilation exercises, abstaining from
alcohol (causes drowsiness and dehydration), and techniques to discreetly
pass out gases from the gastro-intestinal tract.
Respiratory problems may be more frequent than reported. Diagnosis of
onboard medical incidents is often made by other passengers or crew with
various medical backgrounds. In some cases hypoxia presents as a hypoxic
syncope3 and may be reported as such. Syncope is reported to account for 9
to 26% of in-flight emergencies. Some of these cases may well be caused
by mild to moderate respiratory disease.
Ries M. Simons, consultant Aviation Medicine
Aerospace Medicine Group, TNO-Human Factors Institute, Soesterberg, The
1. Morgan MDL. Air travel and respiratory disease. BMJ 2002; 325:
2. Harinck E, Hutter PA, Hoorntje TM, Simons M, de Bruijn D, Fischer JC,
Meijboom EJ. Air travel in adults with cyanotic congenital heart disease.
Circulation 1996; 93:272-276.
3. Westendorp RGJ, Blauw GJ, Fröhlich M, Simons M. Hypoxic Syncope. Aviat
Space Environ Med 1997; 68:410-414.
Competing interests: No competing interests