What are the symptoms of acute altitude sickness and what is the recommended treatment?

Symptoms and Treatment of Altitude Sickness

For rapid ascents above 3,500 m, acetazolamide 500-750 mg daily started within 24 hours of exposure is most effective for preventing acute mountain sickness, while immediate descent plus oxygen and dexamethasone are the primary treatments for severe cases.

Clinical Presentation

Altitude sickness encompasses three distinct syndromes that occur at elevations typically above 2,500 m 1, 2:

Acute Mountain Sickness (AMS)

• Onset: 6-12 hours after ascent, affecting >50% of unacclimatized individuals above 4,500 m 3, 4
• Cardinal symptoms:
  • Headache (required for diagnosis)
  • Nausea/vomiting
  • Dizziness
  • Fatigue/lassitude
  • Loss of appetite
  • Sleep disturbances 1, 5
• Course: Usually benign and self-limiting, resolving within 1-2 days without further ascent 4, 6

High-Altitude Cerebral Edema (HACE)

• Represents progression of AMS with life-threatening complications (50% mortality if untreated) 3
• Key features:
  • Severe headache unresponsive to acetaminophen
  • Ataxia (loss of movement coordination)
  • Altered mental status/decreased consciousness
  • Neurological deficits progressing to coma 6, 7

High-Altitude Pulmonary Edema (HAPE)

• Non-cardiogenic pulmonary edema from excessive hypoxic pulmonary vasoconstriction 2, 7
• Symptoms:
  • Dyspnea (initially on exertion, progressing to rest)
  • Incapacitating fatigue
  • Chest tightness
  • Dry cough progressing to pink frothy sputum
  • Cyanosis and crackles on examination 6, 8
• May occur with or without AMS symptoms (20% present without AMS) 6

Treatment Algorithm

Mild AMS

1. Stop ascent and allow acclimatization at current altitude
2. Acetazolamide 500 mg/day for symptom relief 6
3. Symptomatic treatment: Rest, hydration, analgesics for headache
4. Reassess: If symptoms persist or worsen after 24 hours, descend

Severe AMS/HACE

This is a medical emergency requiring immediate action:

1. Immediate descent (most critical intervention) 4, 7
2. Supplemental oxygen to maintain SpO₂ >90% 7, 8
3. Dexamethasone as first-line pharmacotherapy 4, 6, 7
4. If descent impossible: portable hyperbaric chamber while arranging evacuation

HAPE

1. Immediate descent (priority treatment) 4, 7
2. Supplemental oxygen 7, 8
3. Nifedipine (pulmonary vasodilator) or PDE-5 inhibitors 4, 6, 7
4. Minimize exertion during descent
5. Keep patient warm (avoid hypothermia)

Prevention Strategies

Non-Pharmacological (Primary Prevention)

• Slow ascent rate: Maximum 300 m/day above 2,500 m 4, 6
• Acclimatization days: Rest day every 1,000 m of elevation gain
• Avoid overexertion during initial days at altitude 5

Pharmacological Prevention

For rapid ascents >3,500 m (military/emergency personnel):

• Acetazolamide 500-750 mg/day started within 24 hours of exposure shows enhanced effectiveness at higher doses 9

For standard trekking ascents:

• Acetazolamide 500 mg/day for AMS prevention 6
• Dexamethasone as alternative if acetazolamide contraindicated 4, 7
• Nifedipine specifically for HAPE prevention in susceptible individuals 4, 6

Critical Pitfalls to Avoid

1. Never continue ascending with AMS symptoms - this risks progression to HACE/HAPE
2. Do not mistake HACE for simple AMS - ataxia or altered mental status mandates immediate descent
3. HAPE can occur without preceding AMS - maintain high suspicion with isolated respiratory symptoms 6
4. Acetazolamide is NOT effective for treating established HACE - dexamethasone is required 4, 7
5. Nifedipine is ineffective for AMS/HACE - only use for HAPE 4, 6

Special Considerations

Acetazolamide mechanism: Induces metabolic acidosis, stimulating ventilation and improving oxygenation while reducing cerebral blood volume 10. It also lowers blood pressure at altitude and reduces periodic breathing 10.

Cardiovascular patients: Should continue baseline medications at altitude, with acetazolamide potentially reducing subendocardial ischemia risk 10. However, patients with severe uncontrolled hypertension should avoid high-altitude exposure 10.

The evidence strongly supports that both HACE and HAPE progress rapidly and are fatal if untreated 7, making early recognition and aggressive intervention with descent and oxygen non-negotiable priorities over pharmacological management alone.