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Annual Congress of Malaysian Thoracic Society Symposium 4B Air-Travel Related Disorders Physiological changes with altitude – Who are the high risk passengers? Lim Boon Khaw Malaysia We are living in a jet age. Commercial airliners are getting increasingly sophisticated, efficient and safe. If sea-level cabin pressure could be maintained continuously in all aircrafts, the role of the physician would be simplified greatly. Regardless of aircraft, exposing patients to changing ambient pressures is therefore unavoidable. Atmospheric physics potentially affect all air travellers, some more than others. Hence, it is important to understand the physical changes at high altitude. Here, we review the human responses to pressure changes and discuss who are at risk. 35
Annual Congress of Malaysian Thoracic Society Symposium 4B Air-Travel Related Disorders Evaluation of “Fitness” for Patients with Respiratory Diseases Planning Air Travel Hooi Lai Ngoh Malaysia Every year nearly 2 billion passengers travel by air. Air travel is potentially hazardous for patients with lung diseases (from hypobaric hypoxia) and physicians need to be able to offer practical advice. The advent of larger aircraft that can undertake longer flights and the increasing proportion of elderly in the population will result in increasing numbers of passengers with medical ailments. Modern aircraft are pressurised to cabin altitudes of 1,524 - 2,438 m (5,000 - 8,000 ft). At 8,000 ft, the partial pressure of oxygen would be equivalent to breathing 15.1% oxygen at sea level and in healthy persons, PaO2 will fall to 7.0 – 8.5 kPa / 53 – 64 mm Hg (SpO2 85 – 91%). The British Thoracic Society (BTS) and Aerospace Medical Association (AsMA) have published guidelines for respiratory patients planning air travel. Pre-flight assessment for adults should include history and physical examination focussing on cardiopulmonary disease, dyspnoea and previous flying experience. Other useful tests include spirometry, SpO2 by pulse oximetry and measurement of blood gas tensions. It has been recommended that those with sea level SpO2 of < 92% (BTS) or PaO2 < 70 mm Hg (AsMA) require in-flight oxygen and those already on supplemental oxygen at sea level will need increased flow at cruising altitude. Hypoxic challenge test or hypoxic altitude simulation test which is done with the subject breathing a hypoxic mixture of 15% oxygen in nitrogen, is the gold standard to estimate the expected in-flight PaO2. Those with low expected in-flight will require oxygen supplementation ie., PaO2 < 50 mm Hg according to BTS (SpO2 < 85%) and < 55 mm Hg according to AsMA guidelines. The AsMA advocates a 50-metre walk test as a simple and practical test of cardio-respiratory reserve to exercise but there is little evidence to validate this approach. Other walk tests have been used and of these, the 6-minute test has been standardised and validated. BTS guidelines mention the use of hypoxaemia-predicted equations if the hypoxic challenge test is not available. Simulation of cabin conditions in a hypobaric chamber, the ideal test, is not generally available and is mainly used for research and training purposes. Those with infectious tuberculosis should not fly until rendered non-infectious by effective treatment. Patients with current closed pneumothorax should not fly until 1 week after radiological resolution and the time lapse should be 2 weeks for those with traumatic pneumothorax. Patients should not fly until 2 weeks after major thoracic surgery, for an uncomplicated procedure. Those with chronic respiratory illness who have unstable disease should be dissuaded from flying. Advice for patients with various specific respiratory diseases will be touched upon. For normal term infants, it is best to avoid flying until 1 week after birth. Infants born preterm and those who had neonatal lung disease are more susceptible to developing hypoxaemia during air travel. Hypoxic challenge test may be needed for children at risk of hypoxaemia, with titration of oxygen requirement if SaO2 falls below 90%. 36
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