NEW YORK (Reuters Health) – The hypoxia-altitude simulation test (HAST) can be used to identify patients with COPD in need of supplemental oxygen in flight, but not precisely how much they may require, Norwegian researchers report in the July issue of Chest.

As Dr. Aina Akero told Reuters Health by email, “We wanted to test patients who, according to the guidelines, should travel with supplemental oxygen. Our main objective was to evaluate if HAST can be used to titrate the optimal dose of oxygen required for air travel. Secondly, if the use of different oxygen equipment give different PaO2.”

Dr. Akero of Oslo University Hospital Ulleval and colleagues note that passengers with respiratory disease may develop severe hypoxemia during air travel because of the lowered cabin oxygen pressure. Compared to more than 20% at sea level, the oxygen content at altitude is 15.1%, equivalent to that at 8000 feet.

To determine the utility of the HAST in identifying those who might have need of supplemental oxygen, the team conducted a randomized crossover study involving 16 patients with COPD. All had been prescreened by HAST and had a mean PaO2 of less than 50 mm Hg.

They were exposed to alveolar hypoxia in a hypobaric chamber and by means of the HAST using a tight fitting face mask. During both tests, supplemental oxygen was given by nasal cannula via compressed gaseous oxygen with a continuous flow, an oxygen-conserving device, and a portable oxygen concentrator (POC).

Each subject was tested with each type of oxygen equipment in random order during exposure to both the HAST and the hyperbaric chamber.

With supplemental oxygen at a nominal 1 and 2 L/minute, the researchers found that titration via a nasal cannula during a HAST results in accumulation of oxygen within the facemask, giving falsely high PaO2 values.

The definitive hypobaric chamber experiments, continued Dr. Akero, “show that use of an oxygen-conserving-device gives similar PaO2 as oxygen with continuous flow, and is therefore preferable in order to reduce the number of cylinders needed during the flight. A portable oxygen concentrator gives a lower PaO2 and, thus, the oxygen flow has to be increased.”

The HAST test, she added, “cannot be used to titrate the oxygen dose required.”

However, all patients needing supplemental oxygen during air travel were identified by the HAST, say the investigators “and in clinical practice the HAST may be regarded as a reliable test for assessing whether oxygen during air travel is required.”

Chest 2011.