DIAGNOSIS AND TREATMENT

Acute Mountain Sickness/ High-Altitude Cerebral Edema

The differential diagnosis of AMS/HACE is broad and includes dehydration, exhaustion, hypoglycemia, hypothermia, hyponatremia, carbon monoxide poisoning, infections, drug effects, and neurologic problems including migraine. Focal neurologic symptoms and seizures are rare in HACE and should lead to suspicion of an intracranial lesion or seizure disorder. Descending ≥300 m in elevation relieves HACE symptoms rapidly. Alternatively, supplemental oxygen at 2 L per minute relieves headache quickly and helps resolve AMS over hours, but it is rarely available. People with AMS can also safely remain at their current elevation and treat symptoms with nonopiate analgesics and antiemetics, such as ondansetron. They may also take acetazolamide, which speeds acclimatization and effectively treats AMS but is better for prophylaxis than treatment. Dexamethasone is more effective than acetazolamide at rapidly relieving the symptoms of moderate to severe AMS. If symptoms are getting worse while the traveler is resting at the same elevation, or in spite of medication, he or she must descend.

HACE is an extension of AMS characterized by neurologic findings, particularly ataxia, confusion, or altered mental status. HACE may also occur in the presence of HAPE. Initiate descent in any person suspected of having HACE. If descent is not feasible because of logistical issues, supplemental oxygen or a portable hyperbaric chamber in addition to dexamethasone can be lifesaving.

High-Altitude Pulmonary Edema

Although the progression of decreased exercise tolerance, increased breathlessness, and breathlessness at rest is almost always recognizable as HAPE, the differential diagnosis includes pneumonia, bronchospasm, myocardial infarction, or pulmonary embolism. Descent in this situation is urgent and mandatory, accomplished with as little exertion as is feasible for the patient. If descent is not immediately possible, supplemental oxygen or a portable hyperbaric chamber is critical. Patients with HAPE who have access to oxygen (at a hospital or high-altitude medical clinic, for example) may not need to descend to lower elevation and can be treated with oxygen at the current elevation. In the field setting, where resources are limited and there is a lower margin for error, nifedipine can be used as an adjunct to descent, oxygen, or portable hyperbaric therapy. A phosphodiesterase inhibitor may be used if nifedipine is not available, but concurrent use of multiple pulmonary vasodilators is not recommended.

MEDICATIONS

In addition to the discussion below, recommen­dations for the usage and dosing of medications to prevent and treat altitude illness are outlined in Table 3-06.

Acetazolamide

Acetazolamide prevents AMS when taken before ascent; it can also help speed recovery if taken after symptoms have developed. The drug works by acidifying the blood and reducing the respiratory alkalosis associated with high elevations, thus increasing respiration and arterial oxygenation and speeding acclimatization. An effective dose that minimizes the common side effects of increased urination and paresthesias of the fingers and toes is 125 mg every 12 hours, beginning the day before ascent and continuing the first 2 days at elevation, or longer if ascent continues.

Allergic reactions to acetazolamide are uncommon. As a nonantimicrobial sulfonamide, it does not cross-react with antimicrobial sulfonamides. However, it is best avoided by people with history of anaphylaxis to any sulfa. People with history of severe penicillin allergy have occasionally had allergic reactions to acetazolamide. The pediatric dose is 5 mg/kg/day in divided doses, up to 125 mg twice a day.

Dexamethasone

Dexamethasone is effective for preventing and treating AMS and HACE and prevents HAPE as well. Unlike acetazolamide, if the drug is discontinued at elevation before acclimatization, mild rebound can occur. Acetazolamide is preferable to prevent AMS while ascending, with dexamethasone reserved as an adjunct treatment for descent. The adult dose is 4 mg every 6 hours. An increasing trend is to use dexamethasone for “summit day” on high peaks such as Kilimanjaro and Aconcagua, in order to prevent abrupt altitude illness.

Nifedipine

Nifedipine both prevents and ameliorates HAPE. For prevention, it is generally reserved for people who are particularly susceptible to the condition. The adult dose for prevention or treatment is 30 mg of extended release every 12 hours or 20 mg every 8 hours.