High Altitude Pulmonary Edema

High Altitude Pulmonary Edema (HAPE) is a life threatening medical condition which can occur in the mountains, typically above 8,000 or 10,000 feet elevation. The onset can be sudden, but usually takes 24-48 hours before symptoms become critical. Note that in some cases, the victim may be incapacitated in half of this time. Current research is attempting to answer the question of whether pulmonary edema is caused by "leaky" capillaries or by high blood pressure in the lungs.

What can we do to prevent HAPE?

Ascend into high elevations at a careful pace. Recommendations vary, but ascend no more than 1,000 or 2,000 feet per day. This allows the alveolar membrane to slowly adapt to the change in pressure. Optionally ascend higher than this for short periods during a day, but return to a sleeping camp no more than 1,000 or 2,000 feet higher than the previous camp. Oxygen saturation of the blood is lowest during sleep, and if it gets too low, initial symptoms are likely to begin. Remain well hydrated. If blood hematocrit levels stay normal, blood clumping is unlikely to occur so easily. Preparation by extensive physical conditioning does not prevent HAPE from occurring, however, anecdotal evidence suggests that well conditioned athletes are not so physically stressed during heavy climbing. If those athletes are not stressed and remain well hydrated, there may be less likelihood of rapid onset symptoms. Additionally, they may have enough reserve strength to evacuate themselves to a safer altitude without total commitment from a travel group.

What if HAPE symptoms already show?

Descend immediately. If symptoms are mild, perhaps an unforced descent of 2,000 feet will eliminate them. Sometimes the climber will be able to rejoin the group after a few days, with no ill effects. If symptoms are severe, and immediate assisted evacuation of at least 2,000 to 4,000 feet is necessary. With severe symptoms, the victim is likely to be incapacitated, and helicopter rescue may be required. If no helicopter is available due to weather or remote location, a litter rescue to lower altitude is necessary. Free flow oxygen should be administered if at all possible. There are new innovations, such as a Hyperbaric Bag, which are experimental. The victim is placed into a partially air-tight body bag and the bag is mechanically pumped with air. The increased air pressure in the bag simulates a lower altitude for the victim's breathing. Often, one night's sleep in the bag reduces symptoms at least on a temporary basis.

Further Suggestions

Pre-adolescent children seem to have a higher incidence of HAPE compared to adults. Low altitude residents who have never experienced high elevation tend to have a higher incidence of HAPE compared to others who have previous successful high altitude experience. Subjects with previous unsuccessful high altitude experience (suffering symptoms of HAPE) have higher incidence of recurring symptoms upon return to high altitudes. These subjects may consider asking a physician for prescription medication, acetazolamide (Diamox). In many subjects, this reduces or eliminates symptoms, however, there are potential side effects. This drug therapy should not be considered routine for all high altitude climbers.

This information is based on the 1994 Mountain Medicine Lecture Series, provided by the Mountain Medicine Institute.

Diamox (R)

The red blood cell is a versatile carrier. It has little need for oxygen for its own life and thus its hemoglobin is mostly used to carry oxygen to other tissues. But hemoglobin has two other roles which are of particular importance at high altitude: the transportation of carbon dioxide and the regulation of acid-base balance, both of which are crucial.

Carbon dioxide diffuses through capillary walls (both in lungs and tissues) more rapidly and completely than does oxygen, and most of it dissolves in the liquid portion of blood - the plasma - forming a weak acid. Only 10% of the carbon dioxide is carried within the red cell, loosely attached to hemoglobin, but even this is important in the pick-up and release of oxygen as noted above. When carbon dioxide is lowered by over-breathing (a normal response to altitude), oxygen transport is impaired - or would be if it were not for other compensatory changes. One of these is the leftward shift (of arterial oxygen saturation with respect to arterial oxygen pressure) caused by the increased alkalinity of blood which has been caused by the fall in carbon dioxide.

Much of the carbon dioxide in blood is carried as bicarbonate, a combination controlled by a special enzyme - carbonic anhydrase - of which there is a high concentration in red cells and in kidneys. The equilibrium between carbon dioxide (in solution as carbonic acid) and bicarbonate is dependent on carbonic anhydrase, and disturbed by an agent which inhibits that enzyme - acetazolamide or Diamox. This medication which has been used clinically for almost thirty years, impedes the release of carbon dioxide by increasing loss of bicarbonate in the kidney. This not only permits a slight increase in breathing without too much loss of carbon dioxide, but also increases the carriage of oxygen. Action of this drug is not completely understood and the small increase in breathing which it causes is not enough to fully explain the increase in arterial oxygen saturation which usually follows use of Diamox. This medication is being used more and more widely.

The acidity or alkalinity of blood - like any solution - depends on the amount of hydrogen (H+) or hydroxyl (OH-) ions in solution; strong acids have an excess of hydrogen ions. The degree of acidity is indicated by the symbol pH, which is the negative logarithm of the concentration of hydrogen ions. The lower the pH the stronger the acid, and the higher the pH the more alkaline the solution. Neutrality is at pH 7.0, at which point the hydrogen and hydroxyl ions are exactly balanced.

Body metabolism produces many substances that threaten the stability of blood pH, normally very close to 7.43: carbon dioxide is formed, lactic acid generated by exertion, proteins break down to amino acids, fats are metabolized into fatty acids, and nucleoproteins give rise to phosphoric and uric acids. Nitrogenous foods and tissue breakdown yield ammonia - the only alkaline substance formed.

With so many strong and weak acids and only one alkaline substance entering and leaving the blood unpredictably, it is remarkable that its pH remains so stable. This is due to the buffers in the blood (which reduce the inpact of the ions), to the lungs (which permit rapid loss or retention of weakly acid carbon dioxide through change in ventilation) and to the kidneys (which are able to eliminate either acids or alkalis as needed).

There are six of these buffer pairs in the blood - six combinations of a weak acid with a strong base, and each can resist change in ion concentration by absorbing the strong or releasing the weak acid radical. Hemoglobin has three buffer pairs, and the shift from oxygenated to reduced hemoglobin helps to minimize the change in pH. Many efforts have been made to manipulate these intricate and intimately interrelated systems. Some are remarkably successful in clinical conditions such as diabetic acidosis or liver failure. To date only Diamox is effective in hypoxia, but it seems likely that as knowledge increases, other effective interventions will be found.

[excerpt from Going Higher, The Story of Man and Altitude by Charles S. Houston, M.D.]

So, basically, Diamox does not make you immune to altitude illnesses, it just speeds up the altitude adaptation process in your biochemistry.

Diamox is a prescription member of a family called sulfonamides ("sulfa drugs"). Some people are allergic to sulfa drugs. There are side effects, like increased urination and tingling in the extremites, that may vary with dosage.

Personal Comment

I only took Diamox once for a period of about ten days (we were going above 20,000 feet). I began with a half dose the day before we started hiking from 9,000 feet. I shifted to full dose at 14,000 feet. I would say that the drug was effective, and the side effects never got too bothersome. I never had any altitude problems. Others on the same expedition who were not taking the drug could not consistently make the same claim. But that was not a big sample.

On a previous occasion in Nepal, some trekkers in my group were taking Diamox. We were going up very cautiously, though (1000 or 2000 feet per day) up to Kala Pattar (18,200') near Everest. I did not see any necessity of Diamox. Everybody made it up and down, so this does not prove anything. On the most recent trek there, I took it along but did not use it.

During a Kilimanjaro climb in 2000, all of the other trekkers were taking Diamox in preparation for the summit elevation of 19,340 feet). I checked my rest pulse each morning as we moved up the mountain, and it never increased except very slightly, so I assumed that I was not under stress. Therefore, I did not take the Diamox. When we camped at 18,800 feet and there was a water shortage, there was a big demand for Diamox and Ibuprofen. Somehow I stayed fine with nothing.

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