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Emergency And Acute Medicine – High-Altitude Illness
Basics
Description
High-altitude illness occurs due to hypobaric hypoxia following rapid ascent to higher elevations, typically above 8,000 ft (≈2,500 m), without adequate acclimatization. The incidence depends on the rate of ascent, final altitude reached, sleeping altitude, and duration of exposure.
Acute mountain sickness (AMS) occurs in up to 67% of individuals who ascend rapidly (1–2 days) to elevations above 14,000 ft. Among skiers sleeping at altitude, AMS occurs in approximately 22% at 7,000–9,000 ft and 40% at 10,000 ft.
High-altitude pulmonary edema (HAPE) occurs in fewer than 1–2% of exposed individuals, and high-altitude cerebral edema (HACE) occurs in less than 1%. HAPE and HACE are uncommon below 13,000 ft (≈4,000 m).
Risk Factors
Risk factors for AMS include a prior history of high-altitude illness, rapid ascent, physical exertion, younger age (<50 yr), obesity, and preexisting lung disease. physical fitness does not confer protection.< />pan>
Pregnancy Considerations
The relationship between pregnancy and high-altitude illness is not well defined. Pregnancy-induced hypertension, proteinuria, and peripheral edema are more common at altitude, likely related to maternal hypoxemia. There is no evidence of increased risk of spontaneous abortion or placental complications at moderate altitude. Travel above 13,000 ft should be approached cautiously, especially in complicated pregnancies.
Geriatric Considerations
Although older adults often have comorbidities such as hypertension, COPD, or coronary artery disease, individuals older than 55 years appear to have a lower risk of AMS than younger adults.
Etiology
The primary cause of high-altitude illness is rapid ascent without acclimatization. Susceptibility varies between individuals, and illness is influenced by ascent rate, altitude attained, sleeping altitude, and physiologic response to hypoxia.
Diagnosis
Signs and Symptoms
Acute Mountain Sickness (AMS)
AMS is defined by headache plus at least one of the following: nausea or vomiting, fatigue or lassitude, dizziness, or difficulty sleeping. Symptoms typically begin 4–12 hours after ascent and are usually self-limited but may become debilitating.
High-Altitude Pulmonary Edema (HAPE)
HAPE usually develops 2–4 days after ascent, often on the second night. It is potentially life-threatening and presents with dry cough progressing to productive cough, dyspnea at rest, and decreased exercise tolerance.
High-Altitude Cerebral Edema (HACE)
HACE is life-threatening and typically occurs in patients with AMS and/or HAPE. Onset usually requires 2–4 days but may occur as early as 12 hours after AMS symptoms. Findings include severe headache, nausea and vomiting, altered mental status, and ataxia.
Pediatric Considerations
In infants and young children, AMS may present as irritability, decreased playfulness, reduced appetite, vomiting, and sleep disturbances. HAPE occurs more frequently in individuals younger than 20 years, and cases have not been reported in children younger than 4 years.
Physical Examination
Essential Workup
Diagnosis is primarily clinical in the setting of recent altitude gain.
Diagnostic Tests and Interpretation
Differential Diagnosis
Treatment
Prehospital Care
Severe cases require immediate descent. Further ascent is contraindicated in symptomatic individuals. Supplemental oxygen or simulated descent using a portable hyperbaric chamber (e.g., Gamow bag) may be lifesaving when evacuation is delayed.
Initial Stabilization and Therapy
For HAPE and HACE, prioritize airway, breathing, and circulation. Provide supplemental oxygen, establish IV access, and monitor closely. Endotracheal intubation may be required for respiratory failure or airway protection. CPAP may be beneficial in HAPE.
Emergency Department Treatment and Procedures
AMS
Mild cases are usually self-limited. Management includes halting ascent, symptomatic treatment, acetazolamide for moderate to severe symptoms, analgesics for headache, antiemetics for nausea, and oxygen for severe cases. Descent is required if symptoms persist or worsen.
HAPE
Immediate descent is mandatory for moderate to severe disease. Mild cases may be managed at altitude only if oxygen and close monitoring are available. Bed rest, high-flow supplemental oxygen, and avoidance of exertion are critical. Nifedipine may be used when oxygen or descent is unavailable. Hyperbaric therapy may be used when descent is impossible.
HACE
Immediate evacuation to lower altitude is essential. Administer oxygen and dexamethasone. Maintain bed rest with head elevation and manage elevated intracranial pressure aggressively in severe cases.
Medications
First-Line Therapy
Acetazolamide for AMS, nifedipine for HAPE
Second-Line Therapy
Dexamethasone
Use of multiple medications concurrently is not supported by current evidence.
Follow-Up and Disposition
Admission Criteria
HAPE, HACE, or persistent symptoms after descent and observation require admission.
Discharge Criteria
Patients may be discharged after clinical improvement with oxygen saturation >95% on room air at sea level or appropriate baseline saturation at altitude.
Issues for Referral
Patients with recurrent AMS may benefit from acetazolamide prophylaxis for future ascents. Those with prior HAPE may benefit from nifedipine prophylaxis.
Clinical Pearls and Pitfalls
High-altitude illness often mimics viral syndromes, leading to missed diagnosis. Once symptoms develop, further ascent is contraindicated until complete resolution. Ataxia and dyspnea at rest are early warning signs of HACE and HAPE, respectively. When descent is not possible, hyperbaric therapy and adjunctive medications should be considered promptly.
Basics
Description
High-altitude illness occurs due to hypobaric hypoxia following rapid ascent to higher elevations, typically above 8,000 ft (≈2,500 m), without adequate acclimatization. The incidence depends on the rate of ascent, final altitude reached, sleeping altitude, and duration of exposure.
Acute mountain sickness (AMS) occurs in up to 67% of individuals who ascend rapidly (1–2 days) to elevations above 14,000 ft. Among skiers sleeping at altitude, AMS occurs in approximately 22% at 7,000–9,000 ft and 40% at 10,000 ft.
High-altitude pulmonary edema (HAPE) occurs in fewer than 1–2% of exposed individuals, and high-altitude cerebral edema (HACE) occurs in less than 1%. HAPE and HACE are uncommon below 13,000 ft (≈4,000 m).
Risk Factors
Risk factors for AMS include a prior history of high-altitude illness, rapid ascent, physical exertion, younger age (<50 yr), obesity, and preexisting lung disease. physical fitness does not confer protection.< />pan>
Pregnancy Considerations
The relationship between pregnancy and high-altitude illness is not well defined. Pregnancy-induced hypertension, proteinuria, and peripheral edema are more common at altitude, likely related to maternal hypoxemia. There is no evidence of increased risk of spontaneous abortion or placental complications at moderate altitude. Travel above 13,000 ft should be approached cautiously, especially in complicated pregnancies.
Geriatric Considerations
Although older adults often have comorbidities such as hypertension, COPD, or coronary artery disease, individuals older than 55 years appear to have a lower risk of AMS than younger adults.
Etiology
The primary cause of high-altitude illness is rapid ascent without acclimatization. Susceptibility varies between individuals, and illness is influenced by ascent rate, altitude attained, sleeping altitude, and physiologic response to hypoxia.
Diagnosis
Signs and Symptoms
Acute Mountain Sickness (AMS)
AMS is defined by headache plus at least one of the following: nausea or vomiting, fatigue or lassitude, dizziness, or difficulty sleeping. Symptoms typically begin 4–12 hours after ascent and are usually self-limited but may become debilitating.
High-Altitude Pulmonary Edema (HAPE)
HAPE usually develops 2–4 days after ascent, often on the second night. It is potentially life-threatening and presents with dry cough progressing to productive cough, dyspnea at rest, and decreased exercise tolerance.
High-Altitude Cerebral Edema (HACE)
HACE is life-threatening and typically occurs in patients with AMS and/or HAPE. Onset usually requires 2–4 days but may occur as early as 12 hours after AMS symptoms. Findings include severe headache, nausea and vomiting, altered mental status, and ataxia.
Pediatric Considerations
In infants and young children, AMS may present as irritability, decreased playfulness, reduced appetite, vomiting, and sleep disturbances. HAPE occurs more frequently in individuals younger than 20 years, and cases have not been reported in children younger than 4 years.
Physical Examination
- AMS: Often normal examination; mild cases may mimic viral illness or alcohol hangover.
- HAPE: Tachypnea, rales, cyanosis, possible fever, and signs of respiratory distress.
- HACE: Ataxia, altered mental status, papilledema, retinal hemorrhages, seizures (rare), and coma in severe cases.
Essential Workup
Diagnosis is primarily clinical in the setting of recent altitude gain.
Diagnostic Tests and Interpretation
- AMS: No laboratory or imaging studies required.
- HAPE:
- Arterial blood gas: Hypoxemia (PaO₂ 30–50 mm Hg) with respiratory alkalosis
- Chest radiograph: Patchy alveolar infiltrates with areas of sparing; cardiomegaly and classic signs of cardiogenic pulmonary edema are typically absent
- ECG: Tachycardia, possible right-heart strain
- HACE:
- CT or MRI: Vasogenic edema of the cerebral white matter
Differential Diagnosis
- AMS: Viral syndrome, alcohol hangover, carbon monoxide poisoning, meningitis, encephalitis, exhaustion
- HAPE: Pneumonia, pulmonary embolism (typically more acute with pleuritic chest pain), high-altitude bronchitis
- HACE: Stroke or transient ischemic attack (focal deficits suggest vascular etiology)
Treatment
Prehospital Care
Severe cases require immediate descent. Further ascent is contraindicated in symptomatic individuals. Supplemental oxygen or simulated descent using a portable hyperbaric chamber (e.g., Gamow bag) may be lifesaving when evacuation is delayed.
Initial Stabilization and Therapy
For HAPE and HACE, prioritize airway, breathing, and circulation. Provide supplemental oxygen, establish IV access, and monitor closely. Endotracheal intubation may be required for respiratory failure or airway protection. CPAP may be beneficial in HAPE.
Emergency Department Treatment and Procedures
AMS
Mild cases are usually self-limited. Management includes halting ascent, symptomatic treatment, acetazolamide for moderate to severe symptoms, analgesics for headache, antiemetics for nausea, and oxygen for severe cases. Descent is required if symptoms persist or worsen.
HAPE
Immediate descent is mandatory for moderate to severe disease. Mild cases may be managed at altitude only if oxygen and close monitoring are available. Bed rest, high-flow supplemental oxygen, and avoidance of exertion are critical. Nifedipine may be used when oxygen or descent is unavailable. Hyperbaric therapy may be used when descent is impossible.
HACE
Immediate evacuation to lower altitude is essential. Administer oxygen and dexamethasone. Maintain bed rest with head elevation and manage elevated intracranial pressure aggressively in severe cases.
Medications
- Acetazolamide:
- AMS treatment: 250–500 mg PO BID (peds: 5 mg/kg PO BID)
- AMS prophylaxis: 250 mg PO BID starting 24 hr before ascent
- Dexamethasone: 8 mg IV, then 4 mg PO/IV QID
- Ibuprofen: 800 mg PO TID (peds: 5–10 mg/kg)
- Nifedipine: 10 mg PO, then 30 mg sustained release PO daily
- Promethazine: 12.5–25 mg PO/IM/PR q4–6h
First-Line Therapy
Acetazolamide for AMS, nifedipine for HAPE
Second-Line Therapy
Dexamethasone
Use of multiple medications concurrently is not supported by current evidence.
Follow-Up and Disposition
Admission Criteria
HAPE, HACE, or persistent symptoms after descent and observation require admission.
Discharge Criteria
Patients may be discharged after clinical improvement with oxygen saturation >95% on room air at sea level or appropriate baseline saturation at altitude.
Issues for Referral
Patients with recurrent AMS may benefit from acetazolamide prophylaxis for future ascents. Those with prior HAPE may benefit from nifedipine prophylaxis.
Clinical Pearls and Pitfalls
High-altitude illness often mimics viral syndromes, leading to missed diagnosis. Once symptoms develop, further ascent is contraindicated until complete resolution. Ataxia and dyspnea at rest are early warning signs of HACE and HAPE, respectively. When descent is not possible, hyperbaric therapy and adjunctive medications should be considered promptly.
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