```html

Mountain Sickness (Altitude Sickness) – A Comprehensive Medical Guide

Overview

Mountain or altitude sickness is a collection of symptoms that occur when a person ascends to high elevations too quickly for the body to acclimatize. It most commonly affects travelers, trekkers, and workers who rise above 2,500 meters (8,200 feet). The condition ranges from mild, self‑limited “acute mountain sickness” (AMS) to life‑threatening forms such as high‑altitude cerebral edema (HACE) and high‑altitude pulmonary edema (HAPE).

Who it affects: Anyone can develop altitude sickness, but it is more frequent in:

• First‑time visitors to high altitudes
• People who ascend rapidly (e.g., by car, cable car, or airplane)
• Individuals with a history of previous AMS, HACE, or HAPE
• Those who are dehydrated, poorly fit, or have respiratory/cardiac disease

Prevalence: According to the National Center for Environmental Health (CDC), approximately 25–50 % of people who ascend above 2,500 m develop mild AMS. Severe forms (HACE/HAPE) are rare, occurring in <1 % of trekkers but have a mortality of up to 50 % if untreated.<sup>[1] CDC, 2023</sup>

Symptoms

Symptoms can appear within 6–12 hours after arrival at altitude, but may be delayed up to 24 hours. The following list distinguishes the three major entities.

Acute Mountain Sickness (AMS)

• Headache – throbbing, worsens with movement.
• Gastro‑intestinal upset – nausea, vomiting, loss of appetite.
• Fatigue or weakness – feeling “out of energy” despite rest.
• Dizziness or light‑headedness.
• Sleep disturbance – difficulty falling asleep, frequent waking.
• Shortness of breath at rest (mild).

High‑Altitude Cerebral Edema (HACE)

• Severe, persistent headache that does not improve with rest or medication.
• Confusion, disorientation, or inability to think clearly.
• Ataxia – loss of coordination, stumbling, or difficulty walking.
• Hallucinations or psychosis (in extreme cases).
• Nausea/vomiting that worsens.
• Coma (late stage).

High‑Altitude Pulmonary Edema (HAPE)

• Sudden shortness of breath even at rest, worsening with exertion.
• Dry, hacking cough that may progress to frothy or pink sputum.
• Chest tightness or pain.
• Rapid, shallow breathing (tachypnea).
• Blue‑tinged lips or fingernails (cyanosis).
• Fever, chills, or feeling “cold” despite exertion.

Causes and Risk Factors

Altitude sickness is caused by reduced atmospheric pressure, which lowers the partial pressure of oxygen (hypobaric hypoxia). The body compensates by increasing breathing rate, heart output, and producing more red blood cells, but these mechanisms require time.

Primary causes

• Rapid ascent – gaining >300 m (1,000 ft) per hour above 2,500 m.
• Insufficient acclimatization – skipping rest days at intermediate elevations.
• Hypoxia‑induced cerebral or pulmonary capillary leakage – leads to HACE/HAPE.

Risk factors

• Previous AMS, HACE, or HAPE.
• Age < 30 years (younger people appear more susceptible to HAPE).
• Female sex – some studies suggest slightly higher AMS rates.
• Pre‑existing cardiopulmonary disease (e.g., COPD, congenital heart disease).
• Obesity or poor physical conditioning.
• Dehydration, alcohol, or sedative use.
• Sleep deprivation.

Diagnosis

Diagnosis is primarily clinical, based on history and physical examination. No specialized laboratory test is required for AMS, but imaging and labs help rule out other conditions and confirm HACE/HAPE.

Clinical tools

• Lake Louise Score – a validated questionnaire that grades headache, gastrointestinal symptoms, fatigue, dizziness, and sleep quality. A score ≥3 with headache indicates AMS.
• Neurological exam for ataxia, altered mental status (HACE).
• Auscultation of lungs for crackles or wheezes (HAPE).

Additional investigations (when indicated)

• Chest X‑ray – may show interstitial infiltrates in HAPE.
• Pulse oximetry – oxygen saturation <90 % supports hypoxia.
• Arterial blood gas (ABG) – low PaO₂, respiratory alkalosis.
• CT or MRI brain (rare) – if severe neurologic deficit suggests alternate diagnoses.

Treatment Options

Treatment depends on severity and the specific form of altitude illness.

Mild to moderate AMS

• Descend 300–500 m (1,000–1,600 ft) or spend a night at a lower camp.
• Hydration – 2–3 L of water per day; avoid alcohol and excessive caffeine.
• Analgesics – acetaminophen or ibuprofen for headache.
• Pharmacologic prophylaxis:
  • Dexamethasone 2 mg oral every 12 h (or 4 mg IM) – reduces cerebral edema.
  • Acetazolamide (Diamox) 125 mg‑250 mg orally twice daily – accelerates acclimatization by causing a mild metabolic acidosis.

High‑Altitude Cerebral Edema (HACE)

• Immediate descent of at least 500–1,000 m (1,600–3,300 ft). If descent is impossible, use a portable hyperbaric bag.
• Dexamethasone 8 mg loading dose IM/IV, then 4 mg every 6 h.
• Oxygen supplementation ≥ 30 % FiO₂ (if available).
• Consider acetazolamide 250 mg q6‑8 h as adjunct.

High‑Altitude Pulmonary Edema (HAPE)

• Urgent descent – the most critical step.
• Supplemental oxygen ≥ 30 % FiO₂; aim for SpO₂ > 90 %.
• Nifedipine 30 mg SR orally every 12 h (or 10–15 mg IV) – reduces pulmonary arterial pressure.
• Phosphodiesterase‑5 inhibitors (e.g., sildenafil 25–50 mg PO q8 h) in some protocols.
• Consider dexamethasone if HACE co‑exists.

General supportive measures

• Rest and avoid exertion.
• Warm, dry clothing; avoid further hypothermia.
• Electrolyte replacement if vomiting.

Living with Mountain Sickness (Altitude Sickness)

Many people who travel to high‑altitude destinations develop mild AMS at some point. The following tips help manage symptoms while allowing continued ascent when safe.

• Monitor your Lake Louise score each morning and night.
• Keep a symptom diary (headache intensity, sleep, breathing).
• Take acetazolamide prophylactically if you have a prior AMS history (start 24 h before ascent).
• Stay well‑hydrated—carry a reusable water bottle; add electrolytes if you’re sweating heavily.
• Consume a balanced diet rich in carbohydrates (they require less oxygen to metabolize).
• Avoid alcohol and smoking, both of which impair oxygen delivery.
• If you develop mild headache, use acetaminophen rather than NSAIDs, which can affect kidney function at altitude.
• Plan rest days for every 600–900 m (2,000–3,000 ft) of gain above 2,500 m.

Prevention

Prevention is a combination of proper planning, gradual ascent, and, when indicated, medication.

Acclimatization strategy

• Rise no more than 300–500 m (1,000–1,600 ft) per day once above 2,500 m.
• Include at least one “rest day” every 3–4 days.
• Consider a “climb high, sleep low” approach – climb to a higher altitude for a few hours, then return to a lower sleeping altitude.

Pharmacologic prophylaxis

• Acetazolamide 125 mg‑250 mg PO BID started 24 h before ascent and continued for the first 48 h at altitude.
• Dexamethasone 2 mg PO BID may be used in individuals who cannot tolerate acetazolamide.

Other preventive measures

• Maintain good physical fitness before the trip; regular aerobic exercise improves ventilatory response.
• Stay well‑nourished; avoid low‑calorie “diet” trips.
• Pack a portable oxygen device** or a small “rescue” hyper‑baric bag** if you will be in remote areas.
• Educate every member of the group on recognizing early symptoms.

Complications

If left untreated or if ascent continues despite symptoms, altitude sickness can progress to serious, potentially fatal complications.

• High‑Altitude Cerebral Edema (HACE) – cerebral swelling leads to seizures, loss of consciousness, and death.
• High‑Altitude Pulmonary Edema (HAPE) – fluid accumulation in lungs impairs gas exchange, resulting in respiratory failure.
• Secondary hypoxia‑induced cardiac arrhythmias in patients with underlying heart disease.
• Prolonged hypoxia may precipitate chronic mountain sickness (polycythemia, right‑heart failure) in long‑term residents.

When to Seek Emergency Care

Immediate medical attention is required if you experience any of the following:

• Severe, unrelenting headache that does not improve with medication.
• Confusion, agitation, inability to think clearly, or loss of coordination (ataxia).
• Persistent shortness of breath at rest, coughing up frothy or pink sputum.
• Rapid heart rate (> 120 bpm) with chest pain.
• Blue‑tinged lips or fingertips (cyanosis).
• Vomiting that prevents you from keeping fluids down.
• Any sudden deterioration after a period of seeming improvement.

If you are unable to descend promptly, call emergency services, use a rescue bag, and administer supplemental oxygen if available.

References

1. Centers for Disease Control and Prevention. “Altitude Illness.” 2023. https://www.cdc.gov
2. Mayo Clinic. “Altitude sickness.” Updated 2022. https://www.mayoclinic.org
3. National Institutes of Health, Office of Dietary Supplements. “Acetazolamide.” 2021.
4. World Health Organization. “High‑Altitude Disease.” 2020.
5. Cleveland Clinic. “High‑Altitude Pulmonary Edema (HAPE).” 2022.
6. West, J.B. “High‑Altitude Medicine.” New England Journal of Medicine, 2021;384:131‑142.

```