Now it’s called “high altitude illness” (HAI) and we know it’s caused by the reduced amount of oxygen in the air as density altitude and barometric pressure decrease with increasing altitude. We left off talking about the two most dangerous aspects of HAI. The first one is high-altitude cerebral edema (HACE), caused by the accumulation of abnormal fluid in the brain. The swelling elevates pressure inside the skull that initially stops the brain from working properly and if untreated eventually stops blood flow altogether, leading to coma and death. The brain is particularly susceptible to hypoxia (low oxygen levels) since it already accounts for 20% of total body oxygen consumption and has no adequate compensatory mechanisms to make up for low oxygen delivery. Its function is obviously critical as any compromise can lead to loss of cognition, coordination, and problem-solving skills, and that’s a deadly combination for us in the cockpit. The second symptom is high-altitude pulmonary edema (HAPE), caused by abnormal fluid collecting in the lungs preventing oxygen exchange. Combine that with the already low amount of O2 in the atmosphere at high altitudes and you can literally suffocate even while taking deep breaths!
The cardiovascular response to high altitude is also profound. For healthy hikers and pilots it’s a strain on the system, but for anyone with cardiovascular disease, altitude problems pile up very quickly. We know that coronary artery disease (CAD) is a basic supply/demand mismatch that we’ve talked about in these pages a while ago. Heart muscle, like everything else in our body, needs oxygen to function. At rest, a patient with narrowed atherosclerotic coronary arteries is usually compensated and the arteries can supply muscle needs. But add on top of CAD any exertion and decreased oxygen availability, the restricted vessels can’t keep up with the increased demand. It’s the most common consequence of CAD and it’s also the basis of an exercise stress test docs use to screen for the disease. You can give yourself the same kind of stress test by increasing demand while decreasing the amount of oxygen to your heart. That’s exactly what happens as altitude increases. Exercise capacity decreases with an increased risk of angina (chest pain) and myocardial infarction (heart attack).
The magnitude and consequences of the hypoxic stresses to the body depend on the balance of four factors—altitude, rate of ascent, and duration up high, along with genetic factors that predispose you to altitude illness. It’s the same whether you hike or fly up to altitude, but in general aviation, the time climbing to a high altitude is fast although we usually don’t stay up there all that long. Additionally, pilots breathe supplemental oxygen. Symptoms can start within a few hours of reaching altitude but generally take about ten hours to really set in. That brings us to the two final topics: how to avoid HAI and how to treat it if it strikes. The first thing to do, even before you go, is to be certain that if you have any existing medical conditions like heart problems, respiratory concerns (asthma, bronchitis), history of migraines or severe headaches, stroke, or diabetes, talk to your doctor as part of your pre-flight planning. Prevention is always the best treatment and thoughtful pre-planning can mitigate the risks of altitude illness.
There are a number of other things you can do if you’re climbing up the “Great Headache Mountain” to reduce your risks of HAI. Hikers know that in the mountains, the best way to avoid HAI is to climb slowly—but that’s not an option for us in GA. One thing we can do to decrease our risk of HAI as pilots is to get acclimated to high altitudes by spending increasing amounts of time up there. The process of acclimation is slow—a week or so. During that time your body will make adaptive biochemical changes and also you’ll produce more red blood cells that increase your ability to carry oxygen to the tissues. But even short repetitive exposures to high altitude will add up and help you adapt. Another way to cut the risk of altitude sickness is to drink plenty of water before and during your time up in the sky. Not only does altitude cause you to reposition fluid into your tissues, but the low humidity further dehydrates you and both combined will decrease your circulating blood volume, leading to a buildup of acid in the blood. An acid environment decreases the oxygen-carrying capacity of red blood cells by lowering the cells’ affinity for 02, and that’s exactly what you don’t want in a low oxygen environment. Extra water intake will help your body compensate for fluid shifts and loss of water vapor into the atmosphere due to lower density altitude.
If you’re going to have some snacks in the cockpit, pass up the protein bars and eat a high-carb diet since carbohydrates require less oxygen to burn for energy than fats and proteins. Avoid drinking any alcohol if you’re planning a high-altitude flight; up there the effects hang around longer and it will not only add to risks of cognitive dysfunction but also add to dehydration. Don’t smoke since smoke contains carbon monoxide that further displaces the limited space for oxygen in the blood, something we’ve also talked about in these pages. Avoid any medications like sleeping meds or decongestant meds that also hang around and impair thinking. Take it easy at altitude since the more activity you do the more oxygen you will require. Another thing you can do is to try to sleep at low altitude while on high hops across the country to give your body a chance to recover.
Since HAI is a disease of low oxygen levels, get on, or increase, your supplemental O2 and switch from nasal cannulas to a mask since that’s a more effective oxygen delivery system. You can “pre-oxygenate” your system by starting to use supplemental oxygen early in the flight even before you get to altitude. This starts almost immediately when you breathe oxygen and it really works. We do it in the operating room all the time and we can see the results right on the OR monitors. If you’re lucky and fly a pressurized aircraft, keep the cabin pressure less than 8,000 ft MSL and also consider supplemental oxygen. It’s especially important if you fly high at night as your eyes are particularly sensitive to altitude from both the low O2 concentration and low water vapor content. Also don’t fly up high with contact lenses in your eyes since they block oxygen absorption by the corneas. We covered nighttime vision in detail in a previous post and combining that with high altitude makes it a more extreme problem.
There are a few medications that can help avoid HAI symptoms. Because it’s all about fluid buildup in body tissues of the brain and lungs it stands to reason that a medication to reduce fluid would be useful—“water pills” (diuretics) and the one that works best is called “Diamox” (acetazolamide). It’s not that strong a diuretic and it’s probably not only the diuretic function of the medication that helps but it’s the effect of Diamox on acid/base balance in your blood that works to avoid HAI. You need to start taking it at least two days before a trip, as there’s good evidence that Diamox can facilitate adaptation to altitude, and you need to continue taking it twice a day during your trip. You’ll need a prescription from your doctor to get it. It’s also important to know that you can still get altitude sickness even when taking acetazolamide. It’s not a treatment for HAI and once you start having symptoms, this medication won’t reduce them. Again, getting yourself to lower altitude is the only effective treatment. Tylenol (acetaminophen) and Motrin (ibuprofen) are pretty good treatments for headache at high altitudes but don’t work for any other symptoms of HAI and neither one treats the primary problem.
Treating HAI is another issue and that’s the biggest problem for us up in the sky. The first thing mountaineering rescuers will do is get victims to lower altitudes, so if you or any passengers feel symptoms of HAI coming on while flying up high, descend as quickly and safely as possible. In severe cases, hikers are placed in hyperbaric chambers—there are portable devices for mountain rescuers—that force more oxygen into the body tissues. Obviously it’s not something available to us in the air. In addition to administering supplemental oxygen, patients with acute onset of symptoms are usually given a high dose of steroids (dexamethasone) that decreases general inflammation and swelling and intravenous diuretics to cut down on lung edema. Obviously these options are also limited in the air so it’s imperative if you have a sick passenger to land and get them immediate medical attention. Declare an emergency with ATC if you have to—it’s that important.
Last month, we started with a quote from Jon Krakauer so it’s only fitting to end with one too. He wrote in his book Into Thin Air, “When I went to Everest, I underestimated things, I just didn’t know what altitude could do.” It’s a good warning for all of us. If you plan to climb up the “Great Headache Mountain,” be smart and do everything you can to avoid HAI. The risk in GA isn’t huge but it’s real, so take preventative measures in advance. If any of those symptoms I talked about set in, get lower, get there quickly, and get medical attention as soon as possible. Trust Krakauer, don’t underestimate the effects of high altitude, and no matter how cool it looks from the top—I’m still not climbing Mt. Everest!