• Acute mountain sickness (AMS)
  • Failure to adapt to the hypoxic demands of altitude
• Mild Mountain Sickness
  • Headache in morning and on exertion, anorexia, nausea, dizziness, vomiting, shortness of breath on exertion, insomnia, irritability, periodic breathing, poor performance
• Moderate Mountain Sickness
  • Severe headache, lassitude, weakness, anorexia, nausea, ataxia, decreased urine output, diminished judgment and coordination
  • Capable of activities with difficulty
• Severe Mountain Sickness
  • Insidious or acute onset, usually 2 to 4 days after ascent
  • Can progress to life-threatening within hours
• High-Altitude Cerebral Edema (HACE)
  • Headache, vomiting, lassitude, irritability, drowsiness, ataxia, slurred speech, cranial nerve paralysis, hypo or hyperreflexia, hemiparesis, hemiplegia, mental status changes (confusion, unreasonableness, depression, disorientation, amnesia, hallucinations, severe nightmares), decreased urine output, seizures, papilledema, coma, death
• High-Altitude Pulmonary Edema (HAPE)
  • Initially with dyspnea on exertion, then at rest, decreased exercise capability, dry cough, fatigue, tachypnea, low grade temperature (<38.5°C)
  • Develop pink frothy sputum, cyanosis, wheezing, rales, tachycardia, low-grade fever, orthopnea
• Other altitude related issues
  • High-altitude syncope, edema (facial and extremity), retinopathy (hemorrhages), pharyngitis and bronchitis, flatus, immune suppression, thrombosis, coagulation abnormalities, platelet changes

• Hypoxia, hypoventilation, hypercapnia, fluid, and electrolyte balance
  • Fluid shifts
  • Latent period of 12 to 72 hours between altitude exposure and symptoms
  • Usual remission period of 3 to 4 days coincides with fluid changes
  • Increased sympathetic nervous system activity

• Excellent if recognized quickly, ascent stopped, and/or descent and treatment begun
• Can be poor if symptoms not recognized or appreciated and appropriate descent and therapy not initiated
• Symptoms insidious or acute onset, usually 2 to 4 days after ascent
  • Can progress to life-threatening within hours

• Ophthalmologic
  • Retinal vessel engorgement
  • Retinal hemorrhages
    • Usually resolves in 7 to 10 days without symptoms
    • 100% of people at 6500 m (>21,000 ft)
  • Macular hemorrhages
    • More severe
    • Associated with visual changes
    • Ultraviolet keratitis
• Other
  • Pharyngitis
  • Bronchitis
  • Productive cough
  • Immunosuppression

• Alcohol toxicity
• Hangover
• Drug effects
• Hypothermia
• Carbon monoxide poisoning

• Dehydration

• Exhaustion
• Personality traits (irritability)
• Insomnia

Question: Previous altitude illness?
Significance: Suggests symptoms in future with ascent to similar altitude.

Question: Location (altitude) where symptoms occurred, how did the patient arrive at that altitude, and what was the rate of ascent?
Significance: Rapid ascent minimizes time for natural acclimatization and increases risk of developing altitude illness.

Question: Exertion level?
Significance: Increased exertion on ascent may increase speed of symptom development.

Question: Medication, drug or alcohol use, predisposing medical illness (asthma, restrictive lung disease)?
Significance: Underlying medical conditions may predispose one to development of altitude illness. Medication use or presumed medical illness may mask signs and symptoms of altitude illness.

Question: Symptom complex (variable)?
Significance: Altitude illness is a variable and progressive disease. Recognition of the early signs and symptoms can alert one to seek care prior to disease intensification.

Question: Morning headache, progressive with ascent?
Significance: Suggests HACE.

Question: Insomnia, difficulty falling asleep, frequent waking?
Significance: Suggests hypoxia and development of altitude illness.

Question: Periodic breathing (hyperpnea to apnea)?
Significance: Suggests moderate to more advanced altitude illness.

Question: Gastrointestinal: anorexia, nausea, vomiting, abdominal cramps, flatus?
Significance: Potentially related to ascent.

Question: Pulmonary: dry cough, shortness of breath, sore throat, dyspnea on exertion and at rest, decreased exercise capability?
Significance: Potential progression to HAPE.

Question: Neurologic: lassitude, weariness, indifference, fatigue, irritability, dizziness, ataxia, weakness?
Significance: Progression to HACE.

Question: Decreased urine output, fluid retention?
Significance: Indicative of fluid shifts, fluid losses, inadequate replacement, and dehydration.

Question: Peripheral edema: eyes, face, hands, ankles, feet (greater incidence in females)?
Significance: Suggests fluid shifts/retention with ascent. Should alert one to potential development of more significant altitude illness.

Finding: Normal in early AMS
Significance: Physical examinations are non-descript early in development.

Finding: Abnormalities usually occur after 12 to 24 hours at altitude (range 2 to 96 hours)
Significance: Tachycardia, tachypnea, dry cough, wheezing, rales, pink frothy sputum, cyanosis, low-grade fever, vomiting, ataxia, slurred speech, cranial nerve paralysis, hypo or hyperreflexia, hemiparesis, hemiplegia, mental status changes (confusion, lassitude, unreasonableness, drowsiness, depression, disorientation, amnesia, hallucinations), decreased urine output, retinal hemorrhage, seizures, papil-ledema and/or coma.

Test: Chest x-ray study (CXR)
Significance: Vasocongestion, patchy or diffuse infiltrates; often worse than physical examination would suggest

Test: ECG
Significance: Rule out myocardial etiology of symptomatology or consequence of ascent.

Test: Toxicologic screen
Significance: Rule out medication effect for presenting symptomatology.

Test: Electrolytes
Significance: Assess hydration status and fluid shifts.

Test: Carbon monoxide level
Significance: Ensure carbon monoxide poisoning not a factor in presentation.

Test: CBC
Significance: Assess oxygen carrying capacity of blood. Look for anemia and platelet abnormalities.

Test: Ventilation and perfusion scan
Significance: Structural pulmonary assessment.

Test: Brain CT
Significance: Assess for structural abnormalities and cerebral edema.

• Suspect AMS
• Stop ascent
• Partial or full descent
• Oxygen if available
• Fluids
• Consider acetazolamide to hasten acclimatization
• Avoid alcohol, codeine, sedative-hypnotics
• Avoid respiratory depressants

• Mild AMS
  • Treatment may not be needed
  • Symptomatic headache relief with ibuprofen, acetaminophen, aspirin, prochlorperazine (Compazine)
  • Temporal artery massage
• Moderate to severe AMS
  • Oxygen (relieves hypoxia, reduces pulmonary hypertension)
  • Furosemide (be careful of volume depletion)
  • Acetazolamide
  • Consider dexamethasone (if allergic to Sulfa or cannot take acetazolamide)
  • Vasodilators (nifedipine, morphine)
• HACE
  • Descend immediately
  • Oxygen
  • Furosemide
  • Dexamethasone
  • Consider intubation and hyperventilation
• HAPE
  • Descend immediately
  • Oxygen
  • Furosemide
  • Acetazolamide
  • Vasodilators (nifedipine, morphine) may be useful
  • Consider antibiotics
  • Positive-pressure breathing
    • Pursed-lip breathing, mask, intubation
    • Knee-chest position with abdominal squeeze
    • Symptoms may recur when positive pressure removed

• Acetazolamide (Diamox) (a carbonic anhydrase inhibitor)
  • Hastens natural respiratory changes that occur during acclimatization
  • Can help prevent AMS
  • Effectiveness in treating established AMS not clear
  • General guidelines for use
    • Use in conjunction with (not in place of) gradual ascent, with passive transport to 3000 m (9850 ft) and rapid active transport
    • Prophylaxis if previous history of AMS, history of periodic breathing, insomnia
    • Treatment of early AMS
    • May be useful if sulfa allergy is present
    • Dosage: 5 to 10 mg/kg/day divided b.i.d. (maximum 250 mg/dose), 24 hours prior to ascent and 1 to 2 days at altitude
    • Side effects: polyuria, paresthesias, nausea, drowsiness, taste changes
• Dexamethasone (Decadron)
  • Helpful for AMS treatment and early cerebral edema
  • Dosage: 4 mg b.i.d. to q.i.d.
• Oxygen
  • Helpful at low flow at night (for headache, insomnia, cyanosis)
  • Increases PaO₂
• Nifedipine
  • Dosage: 20 mg sustained release q 8 hours may be useful for treatment and prevention of HAPE, 24 hours prior to ascent and for 2 to 3 days at altitude
• Diet
  • Increase fluid consumption with altitude and exertion
  • Carbohydrate diet

• Expect improvement with mild mountain sickness in 1 to 2 days
• Moderate mountain sickness clears with descent and acclimation
• Severe mountain sickness clears with descent and therapy

• Good if recognized and treated appropriately
• Poor if not recognized or treated appropriately

• Avoid rapid ascent
  • Do not go too high too fast
  • Do not fly or drive to heights >3000 m (>10,000 ft)
• Gradual acclimatization
  • Limit ascents to 300 m (1000 ft) per day above 3000 m (10,000 ft)
  • Allow at least 24 hours for each 1000 m (3300 ft) gained
  • Exercise is not a substitute for acclimatization
• Be aware and respectful of symptoms (even if minor)
  • Assume symptoms secondary to AMS unless proven otherwise
  • Go no higher until symptoms resolve
  • Descend if worsening
• Climb high, sleep low
• Avoid alcohol, codeine, sedative-hypnotics, respiratory depressants
• Exercise within individual capacity; avoid heavy exercise after passive ascent for at least 24 hours

Q: Can one develop AMS at moderate altitudes, such as during a ski vacation?
A: Yes, although the altitudes encountered rarely lead to the development of severe symptoms in this population.

Q: Will physical conditioning prior to ascent decrease the risk of developing altitude illness?
A: No, in fact better conditioning may inadvertently increase the risk of developing altitude illness as one may achieve higher altitudes more quickly.

Q: Should everyone in whom a headache develops when at a higher than usual altitude be treated (pretreated) with acetazolamide?
A: No. One must weigh other options and severity of illness prior to decision to treat or prophylax for AMS.

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Johnson TS, Rock PB. Acute mountain sickness. N Engl J Med 1988;319:841–845.

Richalet JP. High altitude pulmonary oedema: still a place for controversy? Thorax 1995;50:923–929.