Chapter 122. High-Altitude Medical Problems

High-altitude syndromes are due primarily to hypoxia; the rapidity and height of ascent influence the risk of occurrence.

Clinical Features

Acute mountain sickness (AMS) is usually seen in nonacclimated people making a rapid ascent to higher than 2000 m (6560 ft) above sea level. Symptoms resembling a hangover may develop within 6 hours after arrival at altitude but may be delayed as long as 1 day. Typical symptoms include bifrontal headache, anorexia, nausea, weakness, and fatigue. Worsening headache, vomiting, oliguria, dyspnea, and weakness indicate progression of AMS. Physical examination findings in early AMS are limited. Postural hypotension and peripheral and facial edema may occur. Localized rales are noted in 20% of cases. Funduscopy shows tortuous and dilated veins; retinal hemorrhages are common at altitudes higher than 5000 m (16,500 ft). Resting SaO2 is typically normal for altitude and correlates poorly with the diagnosis of AMS.

Diagnosis and Differential

The differential diagnosis includes hypothermia, carbon monoxide poisoning, pulmonary or central nervous system infections, migraine, dehydration, and exhaustion. The diagnosis is based largely on history of rapid ascent and symptoms.

Emergency Department Care and Disposition

The goals of treatment are to prevent progression, abort the illness and improve acclimatization.

1. Terminate further ascent until symptoms resolve. For mild AMS, symptomatic therapy includes an analgesic, such acetaminophen or an NSAID, and an antiemetic, such as ondansetron, 4 milligrams every 4 to 6 hours po, disintegrating tablet. Mild AMS usually improves or resolves in 12 to 36 hours if ascent is stopped.

2. A decrease in altitude of 300 to 1000 m should provide prompt relief of symptoms. Immediate descent and treatment are indicated for patients with moderate AMS or if there is a change in the level of consciousness, ataxia, or pulmonary edema.

3. Low flow oxygen also relieves symptoms.

4. Consider hyperbaric therapy for moderate AMS if descent is not possible.

5. Pharmacologic therapy for moderate AMS includes acetazolamide, 125 to 250 milligrams PO twice daily (in children 2.5 milligrams/kilogram twice daily), until symptoms resolve and dexamethasone 4 milligrams po, IM, or IV every 6 hours with a taper over several days.

   1. Indications for acetazolamide are (a) history of altitude illness, (b) abrupt ascent higher than 3000 m (9840 ft), (c) AMS, and (d) symptomatic periodic breathing during sleep at high altitude.

   2. Acetazolamide pharmacologically produces an acclimatization response by inducing a bicarbonate diuresis and metabolic acidosis. Acetazolamide is effective for both prophylaxis and treatment.

   3. Acetazolamide is contraindicated in sulfa-allergic patients.

6. Patients who respond well to treatment may be discharged. Provide counseling on preventing future episodes: graded ascent, avoidance of overexertion, alcohol, and respiratory depressants and prophylaxis using acetazolamide (start a day before ascent and continue for at least 2 days after reaching high altitude).

Risk factors for high-altitude pulmonary edema (HAPE) include rapid ascent, heavy exertion, cold, pulmonary hypertension, and use of a sleep medication. Children with acute respiratory infections may be more susceptible to HAPE. HAPE may be fatal if not recognized and treated early.

Clinical Features

HAPE usually begins on the second to fourth night at a new altitude and may progress quickly from dry cough and impaired exercise capacity to resting dyspnea, productive cough, severe weakness and cyanosis. Physical examination findings include tachycardia, tachypnea, localized or generalized rales, and signs of pulmonary hypertension, such as a prominent P2 and right ventricular heave. Resting SaO2 is low for altitude and drops significantly with exertion. CXR abnormalities progress from interstitial to localized to generalized alveolar infiltrates. Right axis deviation and a right ventricular strain pattern are seen on EKG with progressive disease.

Diagnosis and Differential

The differential diagnosis includes pneumonia, acute asthma, congestive heart failure, myocardial ischemia, and pulmonary embolism. Decreased exercise performance and dry cough are enough to suspect early HAPE. A key to diagnosis is response to treatment.

Emergency Department Care and Disposition

Early recognition of HAPE is essential to prevent progression. General measures include rest and keeping patients warm.

1. Initiate supplemental oxygen and titrate to SaO2 ≥90%.

2. Immediate descent is the treatment of choice. Hyperbaric treatment may be used if descent is not an option. Patients with very mild cases of HAPE may be managed with bedrest and oxygen alone.

3. Pharmacologic treatment is usually unnecessary if descent and oxygen are available. In such cases (field conditions), options include nifedipine 20 to 30 milligrams extended release PO every 12 hours, sildenafil 50 milligrams PO 3 times daily or tadalafil 10 milligrams PO twice daily. Sildenafil and tadalafil blunt hypoxic pulmonary vasoconstriction. Nifedipine, sildenafil, or tadalafil may also be used for HAPE prophylaxis in persons with prior episodes. Inhaled albuterol 2 to 4 puffs every 4 to 6 hours may be used for both prophylaxis and treatment but is not well studied.

4. Patients may be discharged if clinical improvement is noted and room air SaO2 remains >90%.

Clinical Features

High-altitude cerebral edema (HACE) is defined as progressive neurologic deterioration of AMS or HAPE. Patients present with altered mental status, ataxia, stupor, and progress to coma if untreated. Focal neurologic signs such as third and sixth cranial nerve palsies may be present.

Diagnosis and Differential

The differential diagnosis includes stroke or transient ischemic attack, tumor, meningitis, encephalitis, or metabolic disturbance. Increased T2 signaling in the splenium of the corpus callosum is seen on MRI. Laboratory testing to rule out other diagnoses is warranted but should not delay treatment.

Emergency Department Care and Disposition

1. Initiate supplemental oxygen and titrate to SaO2 ≥90%. Comatose patients require intubation and ventilation.

2. Immediate descent is needed. Initiate hyperbaric therapy if descent is not possible.

3. Administer dexamethasone 8 milligrams po, IM or IV, followed by 4 milligrams po, IM, IV every 6 hours.

4. In intubated patients, monitor arterial blood gases, taking care to avoid lowering Paco2 below 30 mm Hg. Monitor intracranial pressures and cerebral blood velocities by transcranial Doppler US, if possible.

5. Patients remaining ataxic or confused after descent require admission.