Chest
Volume 133, Issue 4, April 2008, Pages 1002-1005
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Topics in Practice Management
Hypoxia Altitude Simulation Test

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A large number of patients with underlying pulmonary disease travel by air each year and are therefore at risk for significant cardiopulmonary effects of induced hypoxia at higher altitudes. The hypoxia altitude simulation test provides a simple way to identify those patients at risk by simulating conditions encountered at high altitude. By asking the patient to breathe a mixture of gases with an oxygen saturation of 15.1%, the test simulates a cabin pressure of 8,000 feet and allows the physician to screen for hypoxia, significant symptoms, and arrhythmias. Repeating the test with supplemental oxygen ensure adequate treatment of those patients who have a decrease in the alveolar pressure of oxygen, significant symptoms, and/or arrhythmias.

Section snippets

Effects of Altitude and Air Travel

The most serious complications arising from air travel are those that involve neurologic, cardiac, or pulmonary complaints.4 Patients with underlying cardiopulmonary diseases are particularly at risk for medical emergencies because they may have a limited ability to compensate for the effects of the elevated cabin pressure. As airplanes ascend, the cabin pressure is maintained to a Po2 that corresponds to a maximum of 8,000 feet with a range from 5,000 to 8,000 feet (1,524 to 2,438 m),

Who Should Be Screened?

Several European, Canadian, and North American guidelines have attempted to identify patients at risk for air travel based on pulmonary disease.2,3,5 Most of these guidelines are based on patients with COPD, and there are some disparities between them. The statement2 by the British Thoracic Society is not only the most practical in terms of recommendations for screening but also one of the few to include patients not only with chronic obstructive lung diseases, but also those with restrictive

Test Performance

Henry Gong Jr et al7 first described the HAST in the American Review of Respiratory Diseases in 1984. Twenty-two patients with normocapnic chronic obstructive airway disease (chronic bronchitis and emphysema) were asked to breathe oxygen at concentrations of 20.9% (baseline), 17.1%, 15.1%, 13.9%, and 20.9% (recovery) while breath-by-breath ventilatory and gas exchange variables were measured. Pao2, oxygen saturation, PAo2, and alveolar-arterial Po2 gradients all decreased with decreasing oxygen

Billing and Supervision

The billing of an HAST is separated into the typical steps of a testing protocol. The test is first performed without supplemental oxygen. If hypoxia does not develop and no oxygen titration is required, the appropriate current procedural terminology billing code would be 94452. If desaturation occurs, however, and oxygen titration is required, billing code 94453 should be used instead. No pulse oximetry codes should be applied because they are included within the HAST codes. However, if

Interpretation and Significance

If the PAo2 during the HAST is > 55 mm Hg, no supplemental oxygen is recommended. If the PAo2, however, falls to < 50 mm Hg, the patient is asked to wear supplemental oxygen (usually at 2 L/min). The test is repeated with supplemental oxygen as well to ensure not only adequate treatment of hypoxia but also reversal of any symptoms described during the test. If the PAo2 is from 50 to 55 mm Hg, the test is considered borderline, and measurements with activity may be obtained.3

Values obtained from

Conclusions

With high incidence of cardiopulmonary disease and millions of people traveling by air, many people are at risk for significant hypoxia and respiratory symptoms while flying. Although cabin pressure is maintained at a maximum of 8,000 feet, which ensures normal oxygen saturation in most travelers, those with underlying cardiopulmonary disease may still be at risk. HAST testing provides the opportunity to not only assess for changes in PAo2 that may take place in flight but also for potential

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The authors have conflicts of interest to disclose.

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