The most appropriate next step is a hypoxia altitude simulation test (HAST). Initial evaluation of patients with lung disease who are not on long-term oxygen therapy and are planning air travel is usually with pulse oximetry at sea level. If the oxygen saturation is greater than 95%, it is unlikely that the patient will have significant desaturation at higher altitudes, and further testing or supplemental oxygen is not usually indicated. For patients with an oxygen saturation of less than 92%, in-flight supplemental oxygen is usually recommended. In patients with sea-level oxygen saturation between 92% and 95%, simulators that mimic altitude hypoxia, available at some centers, can be used to determine the need for oxygen supplementation during flight. Patients at high risk for in-flight hypoxia and its complications are those with COPD with hypercapnia, a recent exacerbation of chronic lung disease, pulmonary hypertension, and restrictive lung disease, in addition to those who have had previous in-flight symptoms. This patient, who has a resting oxyhemoglobin saturation of 93% breathing ambient air, has risk factors for altitude-related hypoxia, which include an FEV1 less than 50% of predicted and cardiac disease. The HAST predicts the in-flight arterial partial pressure of oxygen and whether supplemental oxygen is needed, accounting for the pressurization of airline cabins that simulate an altitude of less than 2440 meters (8000 feet).
In patients with COPD and a sea-level oxygen saturation between 92% and 95%, an alternative approach in locations where HAST testing is not available is to perform a 6-minute walk test. An oxygen saturation less than 84% suggests likely significant desaturation with altitude, and supplemental oxygen is usually prescribed without additional testing. Those with a walk test saturation greater than or equal to 84% should be referred for HAST testing.
Arterial blood gas studies alone are unlikely to provide important information beyond what is already known about this patient's oxygenation status. It is possible that this patient has chronic hypercapnia due to underlying lung disease, a finding that would support further testing in the form of HAST.
Similarly, echocardiographic evidence of pulmonary hypertension would represent a risk factor for in-flight hypoxia and would require further evaluation, but it does not have adequate predictive value alone in determining the need for in-flight oxygen.
With a proper pre-travel evaluation, it is unlikely that this patient with stable chronic lung disease would have an in-flight problem. Unless the patient declines further testing, recommending against travel is premature.