Effects of Commercial Air Travel
During commercial aircraft flight, the pressure within the cabin
is mandated to be no less than the barometric pressure at an altitude of 8000 ft
(typical cabin altitude, 1500 to 2438 m). During flight the ambient air PO2
could fall from 159 mm Hg at sea level to as low as 118 mm Hg. Two published reports
have measured actual cabin altitude as high as 2700 m, though in an older generation
of aircraft.[278]
[279]
The ensuing mild hypoxemia (arterial O2
saturation usually above 90%)
is generally well tolerated by normal individuals. However, during flight, patients
with impaired gas exchange because of chronic obstructive pulmonary disease or restrictive
disease may experience significant hypoxemia[280]
[281]
[282]
[283]
[284]
[285]
[286]
and symptoms of dyspnea, edema, wheezing, cyanosis, and chest pain.[283]
One way of evaluating the safety of commercial air travel or high-altitude
exposure in patients with lung disease is to measure blood gases or SpO2
while simulating exposure to high altitude in a hypobaric chamber. If a hypobaric
chamber is not available, several published algorithms can be used to predict PaO2
at altitude from PaO2
at ground level.
A method assuming a constant PaO2
/PAO2
ratio is slightly better (see Equations 5 to 7). Predicted PaO2
at altitude (PaO2 alt (predicted)
) can
be calculated from the ground-level blood gases (PaO2
GL
, PaCO2 GL
), ground-level calculated
alveolar PO2
(PAO2
GL
), and altitude alveolar PO2
(PAO2
alt
) by using the following equation, which is similar to Equation 8:
PaO2 alt (predicted)
= PAO2 alt
× (PaO2
GL
/PAO2 GL
) (13)
To calculate alveolar PO2
, a respiratory
exchange ratio of 0.8 is assumed.
It has been recommended that patients with baseline hypoxemia
as a result of lung or heart disease be considered for in-flight O2
administration.
[287]
Procedural details have been reviewed by
Stoller.
[288]
It has been reported that phlebothrombosis commonly occurs during
commercial aircraft flight[289]
; however pulmonary
thromboembolism is rare and more likely to be caused by prolonged relative immobility
rather than the mild hypoxia that may be experienced in commercial aircraft cabins
(typically 1520 to 2440 m).
