What is the best approach to preventing and treating altitude sickness?

Altitude Sickness Prevention and Treatment

Primary Prevention: Gradual Ascent is Key

The most effective prevention of altitude sickness is slow, gradual ascent at rates of 300-600 m/day above 2500m, with a rest day for every 600-1200m of elevation gained. 1

Ascent Strategy

• Limit ascent rate to 300-600 m/day above 2500m to allow proper acclimatization 1
• Include a mandatory rest day for every 600-1200m of elevation gained 1
• Avoid vigorous physical exertion before acclimatization occurs, as heavy physical activity on arrival significantly increases risk of serious complications 1, 2
• Stop ascending immediately if symptoms develop and do not proceed higher until symptoms resolve 1

Understanding the Risk

More than 50% of unacclimatized individuals develop acute mountain sickness (AMS) above 4500m with rapid ascent (>300 m/day), making gradual ascent critically important 1. The risk is particularly high with rapid ascent combined with immediate physical exertion like climbing or skiing 2.

Pharmacological Prophylaxis

First-Line: Acetazolamide

Acetazolamide is the first-line prophylactic medication, dosed at 250 mg twice daily or 500 mg once daily. 1

• Mechanism: Acts as a carbonic anhydrase inhibitor causing mild diuresis and metabolic acidosis, which stimulates ventilation and improves oxygenation 1
• Start before ascent and continue during the initial days at altitude 3
• Additional benefits: May reduce risk of subendocardial ischemia at high altitude in healthy subjects 1
• Caution in heart failure patients: Carefully evaluate when used with other diuretics due to dehydration and electrolyte imbalance risks 1

Alternative Prophylaxis Options

• Dexamethasone: Use when acetazolamide is contraindicated 1, 4
• Nifedipine: Specifically effective for preventing high-altitude pulmonary edema (HAPE), particularly in those with prior HAPE history (62% recurrence rate with rapid ascent) 1, 3
• Start nifedipine with ascent and continue 3-4 days after reaching terminal altitude in HAPE-susceptible individuals 1

Treatment Approach

Acute Mountain Sickness (Mild)

• Acetazolamide 500 mg/day is effective for mild AMS 3
• Stop further ascent until symptoms resolve 1
• Symptoms typically worsen on days 2-3 after arrival, then improve with acclimatization 2

High-Altitude Cerebral Edema (HACE)

Glucocorticoids (dexamethasone) are first-line treatment for the malignant form of AMS/HACE. 3

• Immediate descent is crucial - this is a life-threatening emergency 4, 5
• Supplemental high-flow oxygen while arranging descent 4, 2
• Symptoms include: Severe headache unrelieved by acetaminophen, ataxia, mental deterioration progressing to coma 3

High-Altitude Pulmonary Edema (HAPE)

Immediate descent to lower altitude and supplemental oxygen are primary therapies, with nifedipine as the medication of choice. 1

• HAPE is the leading cause of mortality from altitude sickness 6
• Nifedipine works by counteracting exaggerated hypoxic pulmonary vasoconstriction, the hallmark of HAPE 3
• Early recognition is critical: Incapacitating fatigue, chest tightness, dyspnea progressing from exertion to rest, dry cough advancing to pink frothy sputum 3
• Approximately 0.5-1.0% of visitors above 10,000 feet develop serious complications like HAPE or cerebral edema 2

Special Population Considerations

Women

• No clear evidence of greater vulnerability to AMS in women, though sex-dependent physiological reactions may contribute to increased vulnerability in some 1
• Respiratory muscle training prior to altitude exposure may be particularly valuable for women due to larger expiratory limitations 7, 1
• Higher risk of iron deficiency: Check iron profiles 6 weeks before altitude exposure; consider systematic supplementation (210 mg daily) 7
• Phases of menstrual cycle may affect acclimatization, with hypoxic ventilatory response higher during luteal phase 7, 1

Cardiovascular Disease Patients

• Continue pre-existing cardiac medications at high altitude 1
• Travel to intermediate altitude (~2000m) is safe for heart failure patients with good exercise tolerance (NYHA class I-II) 7
• NYHA class III patients should consider supplemental oxygen; NYHA class IV patients should avoid high altitude travel 8
• Hypertensive patients may benefit from acetazolamide, which can lower blood pressure at altitude while improving oxygen saturation 1

Pediatric Patients

• No randomized trials exist for HAPE prevention/treatment in children 1
• Apply same principles as adults: Slow ascent, proper acclimatization, similar medications with weight-adjusted dosing 1

Critical Pitfalls to Avoid

• Underestimating the importance of gradual ascent - this is more effective than any medication 1
• Inadequate hydration worsens symptoms - maintain fluid intake despite hypoxic diuresis 1
• Continuing ascent with symptoms - this can rapidly progress to life-threatening HACE or HAPE 1, 5
• Delaying descent in severe cases - rapid descent remains the most important treatment factor for HACE and HAPE 5, 2
• Failing to recognize that HAPE can present without AMS symptoms in roughly 20% of cases 3