High-Altitude Cerebral Edema (HACE)

Epidemiology

  • Incidence: 0.5-1.0% in persons at 4000-5000 m altitude

Physiology

  • High Altitude with Inadequate Acclimatization
    • Acute Mountain Sickness and High-Altitude Cerebral Edema (HACE) Represent Different Points Along a Spectrum of Disease (see Acute Mountain Sickness, [[Acute Mountain Sickness]])

Diagnosis

  • Brain Magnetic Resonance Imaging (MRI) (see Brain Magnetic Resonance Imaging, [[Brain Magnetic Resonance Imaging]])
    • Microhemorrhages Located Predominantly in the Corpus Callosum
    • Vasogenic Edema

Clinical Manifestations

General Comments

  • Onset: usually develops after at least 2 days at altitudes >4000 m
  • Moderate-Severe Symptoms of Acute Mountain Sickness (see Acute Mountain Sickness, [[Acute Mountain Sickness]]): since acute mountain sickness and high-altitude cerebral edema represent different points along a spectrum of disease

Gastrointestinal Manifestations

Neurologic Manifestations

  • Altered Mental Status (see Obtundation-Coma, [[Obtundation-Coma]]): ranges from lethargy to coma
  • Headache (see Headache, [[Headache]]): usually poorly-responsive to analgesics
  • Increased Intracranial Pressure (see Increased Intracranial Pressure, [[Increased Intracranial Pressure]]): without proper treatment, breain herniation/death may occur within 24 hrs
  • Truncal Ataxia (see Ataxia, [[Ataxia]])

Other Manifestations

  • Mild Fever (see Fever, [[Fever]])

Prevention of High-Altitude Cerebral Edema (HACE)

General Measures

  • Avoid Ethanol and Respiratory Depressants (see Ethanol, [[Ethanol]])
  • Avoid Extreme Cold
  • Maintain Hydration
  • Graded Ascent (For Planned Final Altitude >3000 m): ascent rate of 300-500 m/day with rest q3-4 days
    • An ascent made after 1 wk at an altitude of at least 2000 m (as compared with an ascent from near sea level) reduces both the incidence and severity of acute mountain sickness at 4300 m by 50% [MEDLINE]

Risk Assessment [MEDLINE]

  • Low Risk
    • Slow Ascent <500 m/day above 2500 m)
    • No History of Acute Mountain Sickness/High-Altitude Cerebral Edema/High-Altitude Pulmonary Edema
    • Rapid Ascent (>500 m/day in Person Partially Acclimatized (At Altitude <3000 m in Preceding Weeks)
  • Medium Risk
    • Unknown History of Acute Mountain Sickness/High-Altitude Cerebral Edema/High-Altitude Pulmonary Edema and Fast Ascent (>500 m/day Above 3000 m)
    • Unknown History of Acute Mountain Sickness/High-Altitude Cerebral Edema/High-Altitude Pulmonary Edema and Rapid Ascent (Ascent to >3000 m in 1 Day)
  • High Risk
    • Unknown History of Acute Mountain Sickness/High-Altitude Cerebral Edema/High-Altitude Pulmonary Edema Very Rapid Ascent (Considerably >500 m/day), and High Final Altitude (>4000 m)
    • History of Acute Mountain Sickness/High-Altitude Cerebral Edema/High-Altitude Pulmonary Edema with Previous Exposure to High Altitude That is Similar to Planned Final Altitude

Acetazolamide (Diamox) (see Acetazolamide, [[Acetazolamide]])

  • Pharmacology: causes hyperchloremic metabolic acidosis, which stimulates ventilation, mimicking the acclimatization process
  • Indications: moderate-high risk
  • Administration: 125-250 mg PO BID beginning 1-2 days before ascent, discontinue after 2 days at final altitude
  • Clinical Efficacy: acetazolamide reduces the relative risk of severe high altitude-related illness by 44% [MEDLINE]

Dexamethasone (Decadron) (see Dexamethasone, [[Dexamethasone]])

  • Indications: moderate-high risk
  • Administration: 4 mg PO BID-TID
  • Clinical Efficacy: second-line agent, if acetazolamide is not tolerated

Graded Ascent

  • Recommended Rate of Ascent: 300-500 m/day above 3000 m altitude
    • Also recommended to rest q3-4 days

Treatment of High-Altitude Cerebral Edema (HACE)

  • Descent from Altitude: recommended
  • Oxygen (see Oxygen, [[Oxygen]])
  • Hyperbaric/Gamow Bag
  • Dexamethasone (Decadron) (see Dexamethasone, [[Dexamethasone]])
    • Administration: 8 mg, then 4 mg PO q6hrs (or IV/IM)
  • Re-Ascent: possible after complete recovery and discontinuation of dexemethasone
    • Consider acetazolamide 250 mg PO BID during re-ascent

References

  • Acute mountain sickness susceptibility, fitness and hypoxic ventilatory response. Eur Respir J 1991;4:1000-1003 [MEDLINE]
  • Acute mountain sickness: influence of susceptibility, pre-exposure and ascent rate. Med Sci Sports Exerc 2002;34:1886-1891 [MEDLINE]
  • Effect of six days of staging on physiologic adjustments and acute mountain sickness during ascent to 4300 meters. High Alt Med Biol 2009;10:253-60 [MEDLINE]
  • Physiologic risk factors of severe high altitude illness: a prospective cohort study. Am J Respir Crit Care Med 2012;185:192-198 [MEDLINE]
  • Acute high-altitude illnesses. N Engl J Med 2013;368:2294-2302 [MEDLINE]