Hiking is one of the simplest and most rewarding outdoor activities. All you need is a decent pair of shoes, some water, and a snack, and you’re off. 
But, just because an activity doesn’t require specialized equipment or training doesn’t mean it can’t be dangerous. It’s easy to imagine and prepare for common hiking injuries such as twisted ankles, scratched skin, and poison ivy, but it can be more difficult to recognize and prepare for an invisible threat like altitude sickness.
Altitude sickness, also know as acute mountain sickness (AMS), altitude illness, hypobaropathy, or soroche, is caused by the reduction of air pressure as altitude increases. With each breath you take, you’re getting less oxygen than you would at lower altitudes.
The altitude at which you might begin to experience symptoms of altitude sickness can vary depending on your lung capacity, level of fitness, and general health. About 20 percent of people will experience a mild altitude sickness at 6300 to 9700 feet. At 14,000 feet, most people will experience mild altitude sickness, and some can experience severe altitude sickness in the form of a pulmonary or cerebral edema. Altitude sickness is most likely to affect the nervous system, lungs, and heart.
If you are climbing at higher altitudes, there are many warning signs you can look for. Symptoms of mild altitude sickness include shortness of breath during exertion, rapid heart beat, nausea or vomiting, headache, dizziness, fatigue, swelling of the hands and feet, and insomnia. More acute altitude sickness can lead to pulmonary or cerebral edema. A fever, dry cough, and shortness of breath even while at rest could indicate pulmonary edema, or fluid collecting in the lungs. A headache that won’t respond to medication, confusion, continued vomiting, loss of coordination, and loss of consciousness could indicate cerebral edema, or a swelling of the brain. Cyanosis, a bluish discoloration of the skin, may also develop, indicating low blood oxygen levels.
The easiest way to alleviate mild altitude sickness is to descend as rapidly and safely as possible. If there is a medical facility nearby, supplemental oxygen may help resolve symptoms more quickly. Acetazolamide (Diamox) can also help reduce symptoms of mild altitude sickness. Increased fluid intake can also help, as many people also experience mild dehydration at higher altitudes, where moisture evaporates from the lungs more quickly. Avoid alcohol for at least 24 hours after experiencing symptoms, as alcohol will only dehydrate you further.
More severe cases of altitude sickness require immediate action. At higher elevations, time is of the essence, because people experiencing severe altitude sickness will quickly loose consciousness. At 20,000 feet it may only take five to 15 minutes for a person to loose consciousness. At these altitudes, prevention has more impact. It is best to hike with an experienced guide, and to ascend slowly, over a period of days, so that the body has a chance to acclimate itself. If acute altitude sickness does occur, descent as rapidly as possible, and seek medical attention as soon as possible. Oxygen can be administered, and steroids can reduce any inflammation in the lungs and brain.
If rapid descent is impossible, a Gamwow bag, a portable plastic hyperbaric chamber, can be used to help stabilize a patient before medical evacuation.
While mild altitude sickness is easily treated, acute altitude sickness is life threatening. It is always better to prevent, rather than have to treat, altitude sickness. Prevention methods include adequate training before you attempt a high altitude hike, hiking at high altitudes only with a trained guide who can recognize the first signs of altitude sickness, allowing the body time to acclimate to the altitude, descending at the first sign of symptoms of altitude sickness, and staying well hydrated.
Be safe and enjoy the air.