There is a spectrum of neurologic conditions caused by high altitude, ranging from acute mountain sickness (AMS) to the more serious form, high-altitude cerebral edema (HACE) Clinicians may utilize various diagnostic tools to assess the level of cerebral impairment due to high altitude (visual analog scale [VAS] score, Acute Mountain Sickness-Cerebral [AMS-C] score, clinical functional score [CFS], Lake Louise Questionnaire Score [LLQS]).
AMS includes symptoms such as headache (most severe and persistent symptom), lassitude, drowsiness, dizziness, chilliness, nausea and vomiting, and difficulty sleeping. Later symptoms include irritability, difficulty concentrating, anorexia, insomnia, and increased headaches.
HACE includes the severe symptoms of AMS and results from cerebral vasogenic edema and cerebral cellular hypoxia. It usually occurs at elevations above 2500 meters (8202 feet) but may occur at lower elevations. It is more common in unacclimatized individuals. Hallmarks are altered mental status, ataxia, severe lassitude, and encephalopathy. The patient appears “mildly drunk.” Examination findings may include confusion, ataxia, urinary retention or incontinence, focal neurologic deficits, papilledema, and seizures. Symptoms may progress to obtundation, coma, and death. High-altitude retinopathy is a separate but related effect of altitude. It can include dilated vessels, retinal hemorrhage, vitreous hemorrhage, and papilledema.
Definitive treatment is immediate descent of at least 610 meters (2001 feet), and descent must continue until symptoms improve. Descent is essential if the symptoms are persistent, severe, or worsening, or if HACE or HAPE is present. If immediate descent is not possible, portable hyperbaric chambers can provide symptomatic relief, but this must not delay descent.
Initial treatment involves oxygen administration to keep the pulse oximetry SpO2 to greater than 90%.
Acetazolamide (250 mg orally twice daily) is an effective medication for both prophylaxis and treatment of mild symptoms of AMS. This is a sulfonamide drug and must be used with caution or avoided in persons with past reactions to this class of drug. Adverse reactions include peripheral paresthesias, altered taste of carbonated beverages, polyuria, nausea, drowsiness, erectile dysfunction, and myopia.
Dexamethasone is given for moderate to severe AMS (4 mg orally every 6 hours). Dexamethasone is the primary treatment for HACE (8 mg once then 4 mg orally every 6 hours). Acetazolamide can be added as an adjunct in severe HACE cases. In most individuals, symptoms clear within 24–48 hours. Dexamethasone does not facilitate acclimatization, so the patient needs to complete dexamethasone therapy and be asymptomatic before they can ascend any further. HACE treatment must continue until 24 hours after resolution of symptoms or until descent is completed. Dexamethasone should not be given for longer than 7 days.
It is imperative that the clinician also assess for other conditions that may mimic or coexist with AMS and HACE (eg, dehydration, exhaustion, hypoglycemia, hypothermia, hyponatremia, trauma, infection).
If HAPE symptoms and signs are present along with HACE, nifedipine or a selective phosphodiesterase inhibitor may be added for pulmonary vasodilation. The clinician must be cautious when using combinations of vasodilators. These medications lower the mean arterial pressure, and in combination, these may result in lowering the cerebral perfusion pressure and thereby increasing the risk of cerebral ischemia.