Most hunters (and most people generally) don’t realize how cheap “high altitude” actually is, and how often we access it. In the relatively new field of wilderness medicine, high altitude is defined as beginning at 1,500 meters, or approximately 4,900 feet above sea level, and extending to 3,500 meters, or 11,200 feet. Above that comes “very high altitude,” and above 18,000 feet, “extreme height.” As hunters, our primary concern is with the first zone, which for convenience can be thought of as about 5,000 feet and up. Many of us are frequent visitors to these heights. Think of elk and mule deer hunting in the Rockies, or mountain goat and Dali sheep hunts in Alaska, to name just a couple of examples. Because this altitude zone is so quickly and often accessed by a variety of recreationists, it is also where high-altitude illnesses are most common.
- You might also like: Do You Know What To Do If Someone In Your Hunting Party Is Injured?
All of the altitudes caused maladies I’ll discuss here arise from the same fundamental cause: the higher you go, the more difficult it is to get the necessary amount of oxygen into your system. This is not because there is less oxygen in the air at high altitude, as is often believed. The percentage of oxygen stays relatively constant at about 20 percent. The difference up great is that there is less available oxygen from a physiologic perspective. This, interestingly enough, is a result of lower barometric pressure.
Barometric pressure decreases with gains in elevation, and when the barometer drops too low, we can suffer from what physicians call “diminished inspiratory oxygen pressure.” In simplified terms, when we inhale (inspire) at altitude, less oxygen than normal is transported through our lungs and into our arterial bloodstream. We breathe harder in an attempt to compensate, but take in less oxygen than our bodies are accustomed to. The result is a minor or major level of hypoxia, which is a condition of stress or disease due to inadequate oxygen intake. For example, at 18,000 feet there is only half the barometric pressure found at sea level and only half the available oxygen. A person transported suddenly from sea level to 18K would most likely lose consciousness fairly quickly if not given supplemental oxygen. This, of course, is why high-flying airplanes pressurize their cabins; and it is also why people with oxygen-depleted conditions are sometimes put in hyperbaric (extreme high pressure) chambers, where oxygen is essentially forced into their bloodstreams at a higher-than-normal level.
The main thing to understand is that the higher you go, the more difficult it is for your body to get the oxygen required for normal functioning, especially during exertion. This problem can occur at elevations as low as 4,900 feet, depending where you start from and how quickly you ascend to altitude. The minimal consequence of altitude dysfunction is diminished exercise performance and the need to breathe harder and faster than usual. The more bad result is that you might suffer one or more of the following altitude-related illnesses.
HAH. This is not an exclamation of levity, but the acronym for High Altitude Headache, a relatively common (and sometimes miserable) affliction for those who ascend too high too quickly. This type of a headache can range from mild to severe, and often occurs within 24 hours of arriving at altitude. It is usually exacerbated by exertion or movement and often occurs at night. A headache can respond well to ibuprofen, aspirin, or acetaminophen. These drugs can also be taken preventively, to reduce the risk of onset. When available, bottled oxygen can be immediately effective for HAH, sometimes relieving distress in as little as ten minutes. However, if a headache worsens or is accompanied by other key symptoms, it might indicate a progression to the more severe:
AMS, or acute mountain sickness. According to Dr. Paul Auerbach, a leading authority on wilderness medicine, AMS “is the most common altitude-related disorder.” Symptoms, which may be quite subtle in the beginning, include two or more of the following: a headache, insomnia, fatigue, loss of appetite, nausea, dizziness, drowsiness, weakness, and apathy.
Treatment for AMS includes rest, fluid intake to avoid dehydration and one of the pain medications noted above for a headache. Oxygen therapy (on low flow, set to 0.5 to 1 liter per minute, using a face mask or nasal tube) is especially effective when used before or during sleep, and will sometimes slow or halt mild AMS. Those with AMS symptoms should not exert themselves at altitude or attempt to ascend to a higher elevation. Sometimes rest and oxygen therapy will allow the AMS sufferer to improve gradually as his or her body acclimates to the altitude. When the symptoms disappear, the activity can be resumed. But if the symptoms don’t improve, or worsen, the person should be evacuated to a lower altitude (preferably 1,650 feet lower than where the symptoms began). If AMS symptoms worsen, it could mean a progression to:
HACE, or high-altitude cerebral edema. Typically, the victim wants to be left alone, and begins to show signs of confusion, impaired judgment and ataxia (staggering, imbalance, lack of regular coordination.) Coma can occur within twenty-four hours of onset. HACE is a relatively uncommon but life-threatening disorder. The treatment is immediate descent to lower altitude and oxygen treatment at a flow rate of 5 to 10 liters per minute via face mask or nasal tube while en route to emergency medical help. HACE usually shows up above 9,800 feet, but has been reported as low as 6,900 feet. It sometimes appears concurrently with:
HAPE, or high-altitude pulmonary edema. This is “the most common cause of death related to high altitude,” according to Drs. Peter H. Hackett and Robert C. Roach, authorities on the subject. However, “HAPE is entirely and quickly reversed if recognized early and treated appropriately.” Interestingly, victims are frequently young, fit men who ascend rapidly to 8,000 feet or above. Pulmonary edema refers to excess fluid in the lung tissues or the spaces needed for oxygen/carbon-dioxide exchange.
All of the maladies I’ve described are the result of a too-sudden ascent to high places. Rapid ascent is easy these days because modern air travel can take us so quickly from sea level to high elevation. A person can leave L.A. or New York in the morning, arrive in mile-high Denver a few hours later, drive or fly to a 7,000-foot elk camp, and be climbing or horse packing to 8,000 feet or more the next morning. No surprise then, if in the next day or three that person begins experiencing headache or mountain sickness–or worse.
To avoid altitude illness is to “acclimatize” to elevation more gradually. Note that “high altitude” in this particular usage is where you begin your travels. Sea level to 5,000 feet is a significant jump; 3,600 feet (my home elevation in Montana) to 6,000 feet is not. Above 8,000 feet I stay alert for altitude symptoms, especially if heavy exertion is involved so that I can treat them promptly while they are still in the early and easily reversible onset stage.
People who have suffered an altitude illness once are more likely than average to experience it again. If you are traveling to a high elevation and want some protection just in case, consult a doctor (preferably one versed in travel or wilderness medicine) for an acetazolamide (Diamox) prescription. This drug stimulates breathing and has proven effective as both a preventative and treatment for altitude illness. Another drug to consider is Compazine, taken either by mouth or suppository, to help control nausea and vomiting that commonly accompany high-altitude problems. Note that alcohol is a respiratory depressant, and should not be consumed in large quantities at high altitude, or at all if you are experiencing any symptoms of illness.
How common are high-altitude illnesses?
One Colorado study showed that, out of 3,158 visitors to the mountains, 25 percent experienced symptoms of AMS, at elevations as low as 6,300 feet. However, not everyone is susceptible to sickness. Medical researchers aren’t sure why except to suspect unknown genetic components. Pre-existing health condition, for the most part, isn’t a factor, nor is advancing age. In fact, young people are more likely to suffer high-altitude illness than are those over fifty. (Perhaps because the over-fifty types tend to acclimate gradually and are less liable to go hard-charging around the high country immediately after arrival.) The best advice is to know the symptoms, from HAH to HAPE, so you can recognize them as soon as they begin to appear.