Altitude Sickness - Symptoms, Causes, Treatment & Prevention

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Overview

Altitude sickness, also called acute mountain sickness (AMS) or high‑altitude illness, is a collection of symptoms that occur when a person ascends to elevations where the atmospheric pressure – and thus the amount of oxygen available to breathe – is lower than at sea level. The condition usually appears within the first 24 hours after arrival at > 2,500 m (8,200 ft) but can develop as low as 2,000 m in sensitive individuals.

• Who it affects: Anyone who rapidly gains altitude, regardless of age, fitness, or prior experience. However, people with a history of AMS, pre‑existing lung or heart disease, and those who ascend without proper acclimatization are at higher risk.
• Prevalence: Studies of trekkers in the Himalayas report that 25‑50 % develop AMS symptoms when climbing above 3,000 m, while severe forms such as high‑altitude cerebral edema (HACE) and high‑altitude pulmonary edema (HAPE) occur in ≤ 1 % of climbers (Mayo Clinic, 2023; WHO 2022).

Symptoms

Symptoms can be mild, moderate, or severe. They usually progress in a predictable pattern:

Mild to moderate (Acute Mountain Sickness)

• Headache: Throbbing, often described as “pressure” over the forehead.
• Dizziness or light‑headedness – feeling off‑balance.
• Nausea & vomiting – often accompanied by loss of appetite.
• Fatigue or weakness – an overwhelming sense of tiredness, even with minimal activity.
• Difficulty sleeping – frequent awakenings, often accompanied by a “cough” or shortness of breath.
• Shortness of breath on exertion – breathlessness that feels disproportionate to the level of activity.

Severe forms

• High‑Altitude Cerebral Edema (HACE) – confusion, inability to think clearly, ataxia (loss of coordination), slurred speech, or unconsciousness.
• High‑Altitude Pulmonary Edema (HAPE) – severe shortness of breath at rest, persistent cough producing frothy or pink sputum, rapid heartbeat, and a feeling of “tightness” in the chest.

Symptoms typically worsen with continued ascent and improve with descent or proper treatment.

Causes and Risk Factors

Pathophysiology

At high altitude the barometric pressure drops, reducing the partial pressure of oxygen. The body initially compensates by increasing breathing rate (hyperventilation) and heart rate. If ascent is too rapid, these mechanisms cannot keep tissue oxygenation adequate, leading to hypoxia and the cascade of symptoms.

Key Risk Factors

• Rate of ascent: Gaining > 300 m (1,000 ft) per day above 2,500 m dramatically raises risk.
• Altitude reached: The higher you go, the greater the likelihood of illness.
• Previous AMS or high‑altitude illness: History of AMS predicts recurrence.
• Age: Children and older adults (> 65 y) are more vulnerable.
• Pre‑existing cardiopulmonary disease: COPD, asthma, congenital heart disease, or anemia limit oxygen delivery.
• Exertion level: Very strenuous activity shortly after arrival increases oxygen demand.
• Dehydration and alcohol consumption: Both exacerbate hypoxia and impair acclimatization.
• Genetic susceptibility: Certain gene variants (e.g., EPAS1) affect hypoxia‑inducible factor pathways; research is ongoing (NIH, 2022).

Diagnosis

Diagnosis is primarily clinical, based on history and physical exam. No single laboratory test confirms AMS, but certain investigations help rule out other conditions and assess severity.

Clinical assessment tools

• Lake Louise Score (LLS): A validated questionnaire that grades headache, gastrointestinal symptoms, fatigue, dizziness, and sleep disturbance (0‑3 each). A total score ≥ 3 with headache indicates AMS.
• Pulse oximetry: Peripheral oxygen saturation (SpO₂) < 90 % at rest is concerning and may suggest HAPE or HACE.

Ancillary tests (used when severe disease is suspected)

• Chest X‑ray: Detects interstitial infiltrates in HAPE.
• Arterial blood gas (ABG): Shows hypoxemia (low PaO₂) and respiratory alkalosis in early AMS.
• CT brain (rare): Reserved for HACE to exclude intracranial bleed or mass.
• Echocardiogram: May reveal pulmonary artery hypertension in HAPE.

Treatment Options

Immediate measures

• Descent: The most effective treatment. Even a 300‑m (1,000‑ft) drop can markedly improve symptoms.
• Rest and reduced exertion: Allows the body to acclimatize.
• Hydration: 2–3 L of water per day; avoid alcohol and caffeine.

Medications

• Acetazolamide (Diamox): 125‑250 mg orally twice daily; accelerates acclimatization by creating a mild metabolic acidosis that stimulates breathing.
• Dexamethasone: 4 mg oral loading dose, then 2 mg q6h for severe AMS or HACE. Taper after symptoms improve.
• Nifedipine: 30 mg slow‑release tablet every 12 h for HAPE; reduces pulmonary artery pressure.
• Oxygen therapy: 2–4 L/min via mask; raises SpO₂ > 90 % and buys time for descent.
• Portable hyperbaric (airtight) chambers: Useful in remote settings when descent is delayed.

Supportive care

• Warm, calm environment for HACE patients.
• Positive‑pressure ventilation for severe HAPE (if available).

Living with Altitude Sickness

For people who live or work at elevation (e.g., miners, residents of high‑altitude cities), ongoing management focuses on symptom control and gradual adaptation.

• Gradual ascent: If travel involves further elevation, increase sleeping altitude by no more than 300–500 m per day.
• Medication schedule: Some chronic residents take low‑dose acetazolamide prophylactically (125 mg nightly).
• Regular monitoring: Check SpO₂ at rest and during exertion; seek care if it falls below 85 %.
• Fitness conditioning: Aerobic exercise at moderate altitude improves ventilatory response.
• Nutrition: Adequate carbohydrates (high‑glycemic foods) provide quick energy and may reduce breathlessness.
• Sleep hygiene: Use a sleeping mask, avoid heavy meals, and keep the sleeping area well‑ventilated.

Prevention

Prevention is centered on controlled exposure to altitude.

1. Plan a gradual ascent: Follow the “300 m per day” rule after 2,500 m; insert a “rest day” every 1,000 m.
2. Acclimatization trips: Spend 2–3 nights at intermediate elevations before attempting higher peaks.
3. Prophylactic acetazolamide: 125 mg once daily beginning 24 h before ascent and continuing for the first 48 h at altitude.
4. Stay hydrated and avoid alcohol: Aim for 2–3 L of fluid per day.
5. Maintain a moderate pace: Keep exertion at a level where you can hold a conversation.
6. Monitor symptoms daily: Use the Lake Louise questionnaire each morning.
7. Carry emergency medication: Dexamethasone and a portable O₂ source should be part of any high‑altitude kit.

Complications

If left untreated, mild AMS can progress to life‑threatening conditions.

• High‑Altitude Cerebral Edema (HACE): Cerebral swelling leads to ataxia, coma, and death within hours.
• High‑Altitude Pulmonary Edema (HAPE): Fluid accumulation in the lungs impairs gas exchange; mortality can reach 30 % without descent and oxygen.
• Chronic mountain sickness: Long‑term residents may develop polycythemia, right‑heart failure, or severe hypoxemia.
• Secondary infections: Fluid in the lungs predisposes to bacterial pneumonia.

When to Seek Emergency Care

References

• Mayo Clinic. “Altitude illness.” Updated 2023. https://www.mayoclinic.org
• World Health Organization. “High‑Altitude Disease.” 2022. https://www.who.int
• U.S. Centers for Disease Control and Prevention. “Travelers’ Health: High Altitude.” 2023. https://www.cdc.gov
• National Institutes of Health. “Acute Mountain Sickness.” 2022. https://www.nih.gov
• Cleveland Clinic. “High‑Altitude Pulmonary Edema (HAPE).” 2024. https://my.clevelandclinic.org
• Hackett PH, Roach RC. “High‑Altitude Illness.” The New England Journal of Medicine. 2021;384:2349‑2359.

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