Altitude Illness

The protocol for Altitude Illness:

Altitude Illness


Let’s break it down!

Altitude illness is a unique problem that can affect soldiers in austere environments, particularly those training or engaging in mountain warfare.  It can be broken down into three primary conditions: Acute Mountain Sickness (AMS), High Altitude Cerebral Edema (HACE), and High Altitude Pulmonary Edema (HAPE):

Acute Mountain Sickness (AMS)

AMS is by far the most common of the three, with an incidence between 5%-68% beyond 8,000ft depending on how rapid the ascent.  It’s directly caused by a lack of oxygen in the air in elevated altitudes, making the patient hypoxic.  The modern theory is that this hypoxia makes the vessels in the brain “leaky“, causing mild inflammation in the brain.  For the most part, this only causes mild symptoms like headache, malaise, and anorexia.

High Altitude Cerebral Edema (HACE)

Rarely occurs below 11,500 ft (0.1%-0.2%) and only occurs in 1% of climbers at all altitudes.  Overall, HACE is uncommon.  HACE follows similar pathology as AMS, just more extreme. Inflammation and edema continue to build up until more extreme symptoms appear like altered mental status and ataxic gait (poor balance). HACE can be fatal.

High Altitude Pulmonary Edema (HAPE)

This occurs in 2% of people above 8,000ft and is the most common cause of death from altitude illness. The physiology of HAPE is characterized by vasoconstriction of the pulmonary vasculature and leaking of plasma from the vessels into the lungs, causing significant respiratory distress that can ultimately be life-threatening. 

The EMin5 video below does an excellent job summarizing these conditions:

Acute Mountain Sickness (AMS)

When you think AMS, think “Hangover“. The way you feel during AMS is very similar to that of a hangover: pounding headache with occasional nausea, vomiting, fatigue, and anorexia (unwillingness to eat). This is exactly how prior AMS patients have described it.

High Altitude Cerebral Edema (HACE)

When you think HACE, think “Drunk“. The patient will still likely have the same symptoms as AMS, but now they also can’t think straight (altered mental status) or walk straight (ataxia)… much like a drunk person.

High Altitude Pulmonary Edema (HAPE)

If you can imagine what it’s like to have water sitting in your lungs, you can probably imagine what it’s like to have HAPE. These patients will be struggling to breathe and may appear cyanotic (blue discoloration of the skin) due to hypoxia.  It’s important to note that everybody should have some degree of hypoxia being above 8,000ft, but these patients will be much worse (<90%) If you auscultate their lungs, you can hear the fluid at the bases (crackles or rales). It can begin subtly, often starting with only a mild, nonproductive cough or difficulty walking.  It’s often confused with bronchitis or pneumonia.

In patients with HACE and HAPE, immediately descending is happening without a question.  For mild cases of AMS, it may be enough just to halt the progression and allow the patient to acclimatize. Rates for acclimatization vary among individuals, but it generally only takes 24-48 hours for most.  Physiologically speaking, acclimatization refers to an increased heart rate, respiratory rate, and diuresis. 

Man descending from mountain by Marko - Stocksy United

Acetazolamide has a complex mechanism but ultimately works by increasing the patient’s respiratory rate while they sleep, thus improving oxygenation and speeding. In a way, you could say it accelerates acclimatization to the environment. There aren’t a lot of studies proving the effectiveness of Acetazolamide, but it is not considered harmful and it continues to be the standard treatment. Since Acetazolamide is a sulfa-based drug, be sure to avoid giving this to anybody with a sulfa allergy.  

Dexamethasone is a corticosteroid that works as an anti-inflammatory to reduce swelling in the brain.  For AMS, this would be a little overzealous unless the symptoms were progressively worsening or if the patient couldn’t take acetazolamide. Dexamethasone is not particularly helpful in aiding acclimatization, so it’s recommended that no further ascent should be made until the patient is asymptomatic for 24 hours after the last dose.

Acetazolamide: Glaucoma: Pharmaceuticals

Hypoxia is remarkably worse for those that have progressed into HACE, so supplemental oxygen is warranted. The goal is to bring the Sp02 back to 90%, which is around where everybody else should be at while at that altitude. A nasal cannula is usually adequate. This should be performed in adjunct with Acetazolamide and rapid descent.

Dexamethasone begins to play a stronger role in HACE. As you’ll notice, the dose for HACE is higher than it is in AMS and it’s given IV/IM for a more rapid result. Dexamethasone has been shown to work very well for HACE if given early. 

NOTE: Never leave a HACE patient alone! They can rapidly deteriorate into a coma and die.

Dexamethasone Sodium Phosphate Injection, USP | Emergency Medical ...

HAPE treatment starts to get a little tricky… 

Rapid descent is still needed. Oxygen definitely needs to be given. Acetazolamide and Dexamethasone may also yield some benefit as well, but we also need a way to manage the blood pressure, which will help prevent the leakage of fluid into the lungs…

Nifedipine is a calcium channel blocker that can help reduce blood pressure by relaxing the blood vessels so that the heart doesn’t have to pump as hard. Interestingly enough, if you don’t have this on hand then you can use erectile dysfunction medications like Viagra and Cialis to help initiate a dilation of blood vessels to reduce blood pressure.

And of course, special care should be taken to minimize the patient’s exertion as they make their descent.

Nifedipine Tablet, Hypertension And High Blood Pressure Drugs ...

5. Treat per Pain Management protocol, but avoid narcotics

NSAIDs (Ibuprofen, Meloxicam, etc.) and Tylenol are useful for managing the headaches from AMS and HACE.  Narcotics like morphine and fentanyl are generally avoided due to their potential for causing respiratory depression.

6. Treat per Nausea/Vomiting protocol

Nausea is a frequent symptom of AMS and HACE; Ondansetron appears to be a particularly useful antiemetic for these situations.

7. Treat per Dehydration protocol

Severe dehydration often accompanies altitude illness.  Oral rehydration should be initiated before any IV fluids.

A GAMOW bag is a novel portable recompression bag that can be used to create an artificial environment that simulates descent of about 3,000-9,000 feet.  This can be life-saving while awaiting a tactically feasible way to initiate descent, which is still far more effective. The video below is a demonstration of how it’s used:

AMS cases are typically self-resolving, especially when given the opportunity to properly acclimatize.  Those who get progressively worse despite medical interventions need a Priority evacuation before sliding into HAPE or HACE.  Since these things can decompensate quickly, HACE and HAPE should both warrant an Urgent evacuation.


Good luck out there!




Brandon Simpson, PA-C
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