High-Altitude Illness	Elevation Level	Symptoms	Treatment	Prevention
Acute mountain sickness	2000-2500 m	Nonspecific; include headache, malaise, anorexia, nausea, vomiting	Oxygen, acetazolamide, dexamethasone, descent from altitude, aspirin or NSAID for headache	Gradual ascent (<500 m/d) at high altitude; prophylaxis with acetazolamide or dexamethasone in rapid ascent or patients at high risk
High-altitude cerebral edema	3000-4000 m	Confusion, irritability, ataxic gait, coma, death	Descent from altitude, supplemental oxygen, hyperbaric therapy	Gradual ascent; consider acetazolamide or dexamethasone in patients at high risk
High-altitude pulmonary edema	>2500 m	Cough, exertional intolerance, dyspnea at rest (2-4 d after arrival at new altitude)	Supplemental oxygen and descent from altitude; adjunctive therapy: nifedipine, PDE-5 inhibitors Diuretics and nitrates not recommended Intubation may be required	Gradual ascent; consider nifedipine in patients at high risk

Risk Factors

prior altitude related illness
rapid ascent more than 3500m in less than 2d, or more than 500m daily above altitudes of 3000m
medical comorbidities such as Interstitial Lung Disease, Chronic obstructive pulmonary disease (COPD), Pulmonary Hypertension

Acute Mountain Sickness

Nonspecific general symptoms such as nausea, vomiting, fatigue, and headache. Due to cerebral blood flow alterations and brain oxygenation changes associated with hypoxia and hypocapnia.

Affects 25% of people at altitude of 2000m. Worsened by heavy exertion and dehydration. Without further ascent, resolves within 1-2 days.

High-altitude periodic breathing is periods of apnea driven by a hypoxic breathing drive --> hypocapnia --> centra apnea --> interrupted sleep, insominia, and paroxysms of dyspnea at night. Worsened by alcohol.

High-Altitude Cerebral Edema

Cerebral edema can occur when the autoregulatory compensation is overwhelmed. This is a manifestation of acute mountain sickness that tends to occur at higher elevations (>3000m).

Definitive treatment is early descent from altitude. Consider prophylaxis with acetazolamide or steroids. See also Elevated ICP.

High-Altitude Pulmonary Edema

Hypoxia pulmonary vasoconstriction causes elevations in pulmonary vascular resistance which can lead to acute pulmonary edema. This can be life threatening.

Presents as respiratory distress, pulmonary congestion, and frothy sputum or frank hemoptysis. Treat with oxygen, rest, and consider descent from altitude. Nifedipine can theoretically help alleviate the pulmonary arterial hypertension.

Air Travel in Pulmonary Disease

Airline cabins are pressured to about 1500-2000m altitude, which means that the PAO2 is about 110-120 mmHg (70% of sea level) and PaO2 is usually 60 mmHg. In patients with underlying pulmonary disease (advanced Chronic obstructive pulmonary disease (COPD), pulmonary hypertension, restrictive lung disease recent AECOPD) this can predispose to significant hypoxemia during flight (see the Alveolar Gas Equation).

Pneumothorax: risk is low due to the pressurization. For a suspected pneumothorax, provide supplemental oxygen to aid with resorption of pleural air.

Post CV surgery: delay of 3-4 weeks post surgery is advisable. Existing pneumothorax is a contraindication to air travel due to risk of expansion and tension physiology.

Preflight Screening in Chronic Lung Disease:

Oxygen Saturation	Recommendation
<92%	In-flight oxygen (typically 2-3 L/min)
92%-95%	Hypoxia altitude simulation testing
Already receiving long-term oxygen	Double flow rate during flight

References

MKSAP 19