Correct Answer: C. IV digoxin
The clinical presentation of headache and breathlessness following rapid ascent above 3000 meters is acute mountain sickness (AMS), which can progress to life-threatening high altitude cerebral edema (HACE) or high altitude pulmonary edema (HAPE). The pathophysiology involves hypoxemia due to reduced atmospheric oxygen partial pressure, triggering hypoxic pulmonary vasoconstriction, increased pulmonary capillary pressure, and cerebral vasodilation with increased intracranial pressure.
IV digoxin has no role in AMS management. Digoxin is a cardiac glycoside used for heart failure and arrhythmias—conditions not present in uncomplicated AMS. While HAPE involves pulmonary edema, digoxin is contraindicated in high-altitude settings because: (1) it increases myocardial oxygen demand in an already hypoxic state, (2) it can precipitate arrhythmias in hypoxemia, and (3) the edema in HAPE is primarily hydrostatic/capillary leak, not cardiogenic failure. The standard treatment triad for AMS is oxygen supplementation, descent, and acetazolamide (a carbonic anhydrase inhibitor that increases renal bicarbonate excretion, promoting respiratory alkalosis and improving oxygenation). Dexamethasone is also used for severe AMS/HACE. Digoxin addresses none of these pathophysiological mechanisms and adds iatrogenic risk in hypoxia.
Why the other options are wrong
A. Administration of oxygen — Oxygen is the cornerstone of AMS management. It directly corrects hypoxemia by increasing alveolar and arterial oxygen partial pressure, reducing hypoxic pulmonary vasoconstriction and cerebral vasodilation. Supplemental oxygen is given immediately in symptomatic AMS and is non-negotiable in HAPE/HACE. This is a standard first-line intervention in Indian high-altitude medical protocols. B. Immediate descent — Descent is the definitive treatment for AMS because it restores atmospheric oxygen partial pressure to normal levels. Even a 500–1000 meter descent significantly improves symptoms. In severe AMS with signs of HACE (ataxia, altered mental status) or HAPE (orthopnea, crackles), immediate descent is life-saving and takes priority over all other interventions. This is emphasized in all trekking safety guidelines in India. D. Tablet acetazolamide — Acetazolamide is the pharmacological mainstay of AMS prevention and treatment. It inhibits carbonic anhydrase, increasing renal bicarbonate excretion and promoting metabolic acidosis, which stimulates respiration and improves oxygenation. Standard dosing is 250 mg twice daily. It reduces AMS incidence by ~50% when used prophylactically and accelerates symptom resolution. It is recommended by Indian mountaineering and medical societies for high-altitude expeditions.
High-Yield Facts
- AMS threshold: Symptoms typically appear above 2500–3000 meters, with incidence increasing with rapid ascent and individual susceptibility.
- Acetazolamide mechanism: Carbonic anhydrase inhibitor → ↑ renal HCO₃⁻ excretion → metabolic acidosis → ↑ respiratory drive → ↑ PaO₂.
- HAPE pathophysiology: Hypoxic pulmonary vasoconstriction → ↑ pulmonary capillary pressure → capillary leak (NOT cardiogenic edema) → digoxin ineffective.
- Digoxin contraindication in hypoxia: Increases myocardial O₂ demand, precipitates arrhythmias, and has no role in hypoxic or high-altitude pulmonary edema.
- AMS management triad: Oxygen + descent + acetazolamide; dexamethasone (4 mg QID) added for severe AMS/HACE.
Mnemonics
ODA for AMS Oxygen, Descend, Acetazolamide — the three pillars of acute mountain sickness management. Remember: oxygen works immediately, descent is definitive, acetazolamide prevents recurrence. NOT in AMS: Digoxin Digoxin is for cardiac failure, not pulmonary edema from hypoxia. HAPE is capillary leak (hypoxic vasoconstriction), not pump failure — digoxin worsens hypoxia and arrhythmia risk.
NBE Trap
NBE pairs "pulmonary edema" (HAPE) with "digoxin" to trap students who reflexively associate any edema with heart failure and diuretics/inotropes. The trap is forgetting that HAPE is hypoxic capillary leak, not cardiogenic, and that digoxin increases oxygen demand in an already hypoxic patient.
Clinical Pearl
In Indian trekking expeditions (Himalayas, Western Ghats), rapid ascent without acclimatization is the leading cause of AMS. A trekker with headache + dyspnea should descend immediately and receive oxygen; acetazolamide is given prophylactically before future climbs. Digoxin has no place—it is a red herring that tests whether students understand the pathophysiology of altitude-induced hypoxia versus cardiogenic failure.
_Reference: Guyton & Hall Textbook of Medical Physiology Ch. 42 (Respiration); Harrison Principles of Internal Medicine Ch. 297 (High Altitude Medicine); KD Tripathi Essentials of Medical Pharmacology Ch. 12 (Carbonic Anhydrase Inhibitors)_