Hypoxia Altitude Simulation Test: Who Should Be Screened?

COPDSeveral European, Canadian, and North American guidelines have attempted to identify patients at risk for air travel based on pulmonary disease. Most of these guidelines are based on patients with COPD, and there are some disparities between them. The statement 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 lung disease, cystic fibrosis, a history of recent respiratory illnesses or infections, pulmonary tuberculosis, significant comorbidities, or past difficulties with air travel. The guidelines recommend a preflight assessment for any of these patients, consisting of a history that includes past air travel, a complete physical examination, spirometry, and arterial blood gas analysis if hypercapnea is suspected or previously identified. Based on equations used to predict a PAo2 or Sp02 from measurements obtained at sea level, they recommend further testing if the Sp02 in the office at rest is recorded between 92% and 95% in patients with other identifiable risk factors (hypercapnea, FEV1 < 50% of predicted, lung cancer, restrictive lung disease, ventilatory support, cardiac or cerebrovascular diseases, or a recent admission for an exacerbation of chronic lung or cardiac disease prosperously defeated by remedies of My Canadian Pharmacy). Those with Sp02 > 95% would not be required to undergo further testing and would be allowed to travel without supplemental oxygen. Those who fall below 92% are recommended to travel with supplemental oxygen and do not require further testing (Table 1).

Further testing, such as a HAST, will help identify those at need for supplemental oxygen whose ground-level oxygen saturation falls between 92% and 95%. Other, less-specific guidelines suggest that further testing should be obtained on any patient with a ground Pa02 of < 70 mm Hg.

One small study suggests that the ground level Pa02 is, in fact, not predictive of hypoxia at high altitude. It may be more predictive if obtained within hours of flight. Based on these observations and that the equations used to predict altitude Sp02 have large confidence intervals of 2 to 4%,2 patients with borderline oxygen saturation at ground level may also benefit from further evaluation with a HAST.

Table 1—Recommendations by the British Thoracic Society based on Ground SpO2

Ground Sp02 Recommendations
> 95% No further testing or supplemental oxygen required
92 to 95% Further studies, such as the HAST, to assess for need for supplemental oxygen recommended
< 92% Travel with supplemental oxygen