Pulmonology · Environmental Medicine
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Acute Mountain Sickness (AMS) presents with headache accompanied by fatigue, gastrointestinal distress, or dizziness following rapid ascent to altitudes typically above 2,500 meters.
Acetazolamide is the first-line pharmacologic agent for the prevention of AMS by inducing a metabolic acidosis that stimulates ventilation; for treatment of moderate-severe AMS, dexamethasone is preferred, with acetazolamide used as an adjunct or when dexamethasone is unavailable.
High-Altitude Pulmonary Edema (HAPE) is a life-threatening condition characterized by non-cardiogenic pulmonary edema caused by exaggerated pulmonary hypertension in response to hypoxia.
Descent is the definitive and most effective treatment for all forms of severe high-altitude illness, including HAPE and High-Altitude Cerebral Edema (HACE).
High-Altitude Cerebral Edema (HACE) is the most severe form of altitude illness, defined by ataxia and altered mental status in a person with AMS or HAPE; papilledema and retinal hemorrhages may be seen but are not required for diagnosis.
Nifedipine is used for HAPE only when descent is impossible or delayed and supplemental oxygen or portable hyperbaric therapy is unavailable; it lowers pulmonary artery pressure but is an adjunct — as are phosphodiesterase-5 inhibitors such as tadalafil or sildenafil — not a substitute for descent or oxygen.
Dexamethasone is the mandatory adjunctive treatment for HACE to reduce vasogenic edema while facilitating immediate descent.
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A 32-year-old hiker is brought to the base camp after ascending to 4,000 meters over the last 24 hours. He complains of a severe, throbbing headache, nausea, and persistent vomiting. On physical examination, he is noted to have truncal ataxia and confusion. His oxygen saturation is 78% on room air, and lung auscultation reveals clear breath sounds without crackles.
What is the most appropriate next step in management?
Immediate descent and administration of dexamethasone
The patient's presentation of ataxia and altered mental status is diagnostic of HACE, which requires immediate descent and high-dose dexamethasone to reduce cerebral edema.
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Etiology / Epidemiology
Occurs due to rapid ascent to altitudes >2,500m. Hypobaric hypoxia is the primary trigger.
Clinical Manifestations
AMS presents as hangover-like headache. HACE shows ataxia; HAPE shows crackles.
Diagnosis
Clinical diagnosis. Lake Louise Score for AMS. Pulse oximetry shows low SpO2.
Treatment
Acetazolamide is first-line for prevention; dexamethasone is preferred for treating moderate-severe AMS/HACE. Avoid in prior severe reaction to acetazolamide or a sulfonamide (e.g., SJS/TEN, anaphylaxis); a history of ordinary sulfonamide-antibiotic allergy is not an absolute contraindication.
Prognosis
Descent is curative. Pulmonary edema is the leading cause of death.
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Epidemiology & Etiology
Risk is determined by rate of ascent and final altitude rather than physical fitness. Individuals with a history of altitude illness are at highest risk for recurrence. Rapid transit to altitudes exceeding 2,500 meters triggers the physiological maladaptation.
Pertinent Anatomy
The primary anatomical impact involves the pulmonary vasculature and cerebral microvasculature. Hypoxia-induced pulmonary vasoconstriction leads to increased pulmonary artery pressure. Cerebral capillary leakage results from impaired blood-brain barrier integrity.
Pathophysiology
Low partial pressure of oxygen triggers hyperventilation, causing respiratory alkalosis. Failure to acclimatize leads to fluid retention and cerebral edema (HACE) or pulmonary edema (HAPE). HAPE is specifically driven by uneven hypoxic pulmonary vasoconstriction causing capillary stress failure.
Clinical Manifestations
AMS manifests as headache, nausea, and fatigue. HACE is defined by ataxia and altered mental status, representing a neurological emergency. HAPE presents with dyspnea at rest, tachycardia, and pink frothy sputum. Altered mental status or ataxia mandates immediate descent.
Diagnosis
Diagnosis is strictly clinical. The Lake Louise Score is used for AMS assessment. Pulse oximetry is useful but not diagnostic; values are typically lower than predicted for altitude. Chest X-ray in HAPE shows patchy alveolar infiltrates.
Treatment
Acetazolamide is the gold standard for prophylaxis; dexamethasone is preferred for treating moderate-severe AMS and is mandatory in HACE. In HAPE, supplemental oxygen or portable hyperbaric therapy follows descent; nifedipine is added only when descent, oxygen, and hyperbaric therapy are all unavailable. Avoid respiratory depressants in HACE or altered mental status; short-acting hypnotics (zolpidem 5 mg, zaleplon 5 mg) are considered safe for sleep in acclimatizing individuals without altitude illness. Supplemental oxygen and immediate descent are the definitive treatments.
Prognosis
Most cases resolve within 24-48 hours with rest or descent. HAPE and HACE carry high mortality if untreated, with cerebral herniation being the primary cause of death in HACE. Patients must be monitored for hypoxemia until symptoms resolve.
Differential Diagnosis
Dehydration: absence of neurological deficits
Carbon monoxide poisoning: history of enclosed space exposure
Pneumonia: presence of fever and purulent sputum
Congestive heart failure: history of cardiac disease
Migraine: lack of altitude exposure history