High Altitude Simulation Test (HAST)

High Altitude Simulation Test (HAST) is a test that can determine the need for supplemental oxygen in patients who are going to be traveling by air or at higher altitude. If you have a chronic lung disease (COPD, emphysema, chronic bronchitis, severe asthma), and you are considering a trip by airplane, or a trip to a higher elevation, you may need this test. 

 If you are already on supplemental oxygen, you may still need testing. 

This is simply the safest and most accurate way to determine if you will need oxygen at higher altitudes, and exactly what level of oxygen keeps your oxygen saturation in the safe range. The FAA regulates that airplanes maintain a cabin pressure of between 8,000 to 10,000 feet above sea level. Rather than get into barometric pressure and partial pressure of gasses, this simply means that available oxygen has just dropped by about 6% compared to sea level. The air we breathe at sea level contains 21% oxygen, but when flying, or at elevations of 8,000 feet above sea level, the air now has about 15-16% oxygen (compared to sea level). 

In the past, we would simply guess based on a patient's oxygen saturation. If a person had an oxygen saturation above 95%, they were good to go, if not, they may need some supplemental oxygen in-flight. Many hospitals and pulmonary function labs now offer HAST to accurately determine the need for high altitude oxygen, as well as the exact amount that will keep patient's safe when flying or traveling at higher altitudes. 

If you are already on home oxygen, testing can determine what level you will need in-flight. The test can be done several different ways, but basically, a mixture of nitrogen and oxygen is delivered to the patient to simulate the available oxygen at high altitudes. During this time, the patients vital signs are closely monitored, as is the oxygen saturation. If the saturation drops below a set point, usually 85-88%, supplemental oxygen is titrated to keep the saturation in a predetermined range (usually 88-90%). 

Some guidelines recommend other screening, such as a 6 minute walk, arterial blood gasses, and other testing to determine the need for HAST, but the bottom line is there is a better way than simply guessing and estimating the need and the amount of oxygen needed for lung patients who travel by air, or those who plan to travel to higher elevations.