High Altitude Cerebral Edema (HACE)MANAGEMENT

ENVIRONMENTAL AND EXPOSURE PRESENTATIONS · 12 SECTIONS

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677 items

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Cardiovascular Presentations71▾

Respiratory Presentations52▾

Neurological Presentations83▾

Gastrointestinal Presentations74▾

Genitourinary and Reproductive Presentations48▾

Infectious Disease Presentations148▾

Trauma Presentations89▾

Toxicologic Presentations80▾

Psychiatric Presentations26▾

Musculoskeletal and Rheumatologic Presentations96▾

Dermatology Presentations23▾

Environmental and Exposure Presentations27▾

Acute Mountain Sickness Arterial Gas Embolism Bee-Wasp Sting (Anaphylaxis)Chilblains Ciguatera Fish Poisoning Coral Cut Decompression Sickness Electrical Burn Injury Envenomation (snake, spider, insect)High Altitude Cerebral Edema (HACE)High Altitude Pulmonary Edema (HAPE)High-altitude illness Hypothermia Hypothermia (Mild)Hypothermia (Severe)Immersion Foot Lightning Strike Injury Scombroid Fish Poisoning Scorpion Envenomation Sea Urchin Injury Shark Bite Snake Envenomation Spider Bite (Black Widow)Spider Bite (Brown Recluse)Stingray Spine Injury Tick paralysis White Phosphorus Burn

Hematologic and Oncologic Presentations36▾

Pediatric-Specific Presentations19▾

Endocrine and Metabolic Presentations45▾

ENT and Maxillofacial Presentations27▾

Ophthalmologic Presentations19▾

Obstetric Presentations23▾

Systemic and Miscellaneous Presentations17▾

01Approach to the Critical Patient/attcp49

Immediate priorities

›Neurologic emergency recognition

›Altered mental status at altitude = HACE until proven otherwise

›Confusion, disorientation, drowsiness

›Inability to follow commands

›Truncal ataxia — earliest neurologic sign

›Tandem gait failure at bedside

›Inability to stand unsupported

›Coma risk within 12–24 hours of onset without intervention

›Brain herniation as end-stage complication

›Death if untreated

Descent and oxygen

›Immediate descent — most critical intervention

›Descend at least 300–1,000 m without delay

›Do not wait for daylight if clinically deteriorating

›Delay only if descent impossible due to terrain or weather

›Supplemental oxygen initiation

›Target SpO2 >90%

›2–4 L/min via nasal cannula

›Portable hyperbaric chamber if descent not immediately feasible

›Gamow bag pressurization simulates descent of 1,500–2,500 m

›Pressurize for 2–4 hours

›Not a substitute for definitive descent

Pharmacologic stabilization

›Dexamethasone loading dose

›8 mg IV/IM/PO immediately

›Followed by 4 mg every 6 hours

›Continue until descent achieved and symptoms resolve

02History/hx67

Ascent profile

›Altitude and rate of ascent

›Maximum altitude reached

›HACE rare below 3,500 m

›Prevalence 0.5–1.0% at 4,000–5,000 m

›Sleeping altitude changes

›Sleeping altitude increasing >500 m/night above 3,000 m is primary risk

›Number of acclimatization rest days taken

›Time course since ascent

›Onset typically 2–5 days after ascending above 4,000 m

›Earlier onset possible with concurrent HAPE

Symptom progression

›Preceding AMS symptoms

›Headache — onset, severity, NSAID responsiveness

›NSAID-refractory headache signals progression toward HACE

›Worsening despite acetaminophen or ibuprofen

›Nausea and vomiting

›Persistent vomiting with worsening headache

›Inability to tolerate oral fluids

›Fatigue, dizziness, sleep disturbance

›Lassitude and apathy

›Irritability and behavioral change

›Neurologic deterioration

›Gait instability

›Stumbling, inability to walk a straight line

›Often first noticed by climbing partners

›Confusion and disorientation

›Resembling alcohol intoxication

03Physical Exam/exam66

Vital signs

›Hemodynamic and respiratory assessment

›SpO2

›Expected to be low at altitude even in healthy individuals

›Markedly low values suggest concurrent HAPE or severe illness

›Target SpO2 >90% with supplemental O2

›Heart rate

›Tachycardia common with hypoxemia and HAPE

›Bradycardia with hypothermia

›Respiratory rate

›Tachypnea with concurrent HAPE

›Cheyne-Stokes breathing common at altitude during sleep

›Temperature

›Mild fever can occur in HACE

›Hypothermia as concurrent diagnosis

Neurologic exam

›Gait and cerebellar testing

›Tandem gait (heel-to-toe walking) — most practical bedside test

›Inability to complete 10 steps without stumbling = positive

›Most useful and reproducible field assessment for ataxia

›Romberg test

›Eyes closed stance instability

›Truncal instability noted

›Coordination

›Finger-nose-finger testing

›Rapid alternating movements

›Mental status

›GCS scoring

04Differential Diagnosis/ddx50

Life-threatening mimics

›Must-exclude diagnoses at altitude with altered mental status

›Carbon monoxide poisoning

›ICD-10: T58.01XA

›Stoves and heaters in enclosed shelters

›Multiple group members simultaneously affected

›Hypothermia

›ICD-10: T68.XXXA

›Ataxia and altered mentation overlap with HACE

›Core temperature <35 C

›Hypoglycemia

›ICD-10: E16.0

›Point-of-care glucose diagnostic

›Exertion and poor intake at altitude

›Hyponatremia

›ICD-10: E87.1

›Forced overhydration at altitude

›Na <125 mmol/l may cause seizures and encephalopathy

›Stroke or intracranial hemorrhage

›ICD-10: I64 (stroke), I62.9 (intracranial hemorrhage)

›Focal neurologic deficits distinguish from HACE

›CT head required if focal signs present

Neurologic mimics

›Conditions producing encephalopathy and ataxia

›Toxic ingestion or drug intoxication

›ICD-10: T40-T50 range

›Opioids, benzodiazepines, alcohol

›History from companions critical

05Laboratory Tests/lt38

Point-of-care testing

›Immediate bedside tests to exclude mimics

›Blood glucose

›Hypoglycemia excluded at <3.9 mmol/l

›Critical in exhausted, poorly nourished climbers

›Treat with oral glucose if alert; IV dextrose if altered

›Pulse oximetry SpO2

›Low at all altitudes above 3,000 m in healthy individuals

›Target >90% with supplemental oxygen

›Markedly low (<80%) suggests HAPE or severe illness

Serum electrolytes and metabolic panel

›Electrolytes

›Sodium

›Hyponatremia (<130 mmol/l) causes encephalopathy

›Risk with forced overhydration (SIADH-like at altitude)

›Distinguishing from HACE requires clinical context

›Potassium, creatinine, urea

›Dehydration assessment

›Renal function relevant before acetazolamide

›Bicarbonate

›Respiratory alkalosis expected at altitude (compensatory)

›Metabolic acidosis from tissue hypoxia in severe illness

Blood gas and oxygen assessment

›Arterial or venous blood gas

›Severe hypoxemia assessment if ABG available

›PaO2 markedly reduced at altitude

›PaCO2 low (respiratory alkalosis) from hyperventilation

›Lactate

06Diagnostic Tests/dt63

Scoring Systems

›Lake Louise AMS Score

›Components: headache, GI symptoms, fatigue, dizziness, sleep disturbance

›Score 3–5: mild AMS

›Score 6–12: moderate to severe AMS

›Limitation: does not diagnose HACE directly

›HACE diagnosis requires ataxia or altered mental status regardless of AMS score

›AMS score contextualizes the clinical spectrum

›Tandem Gait Test

›Field diagnostic for cerebellar ataxia

›Heel-to-toe walking of 10 steps in straight line

›Inability to complete = positive; supports HACE

›Most practical reproducible bedside assessment available in remote setting

›No equipment required

›Can be re-tested to track clinical trajectory

MRI

›MRI indications

›Gold standard neuroimaging for HACE when available post-evacuation

›Not required for diagnosis in the field

›Performed after patient reaches definitive medical facility

›Acute MRI findings

›T2/FLAIR hyperintensity in white matter

›Splenium of corpus callosum — characteristic early finding

›Centrum semiovale involvement

›Diffusion restriction on DWI

›Vasogenic edema pattern

›No gray matter abnormalities typical

›MRI special sequences

07Disposition/dispo40

Evacuation and admission

›All HACE patients require evacuation to lower altitude

›Immediate descent remains primary treatment

›All other interventions are temporizing

›Descent of ≥300–1,000 m typically sufficient

›Ground evacuation, helicopter, or litter carry depending on terrain

›Prioritize evacuation even at night if patient deteriorating

›Supplemental oxygen during all transport

Level of care criteria

›ICU admission indications

›GCS ≤8 or rapidly declining

›Intubation and mechanical ventilation required

›Continuous neuro monitoring

›Concurrent severe HAPE with respiratory failure

›High-flow oxygen or mechanical ventilation

›Hemodynamic monitoring

›Hemodynamic instability

›MAP <65 mmHg

›Vasopressor consideration

›General ward or observation admission

›Improving mental status after descent and dexamethasone

›Ataxia resolving but not fully cleared

›Monitoring at lower altitude facility

›Concurrent mild-to-moderate HAPE

›Oxygen therapy and nifedipine

›Serial SpO2 monitoring

Discharge criteria

›Safe discharge requirements

08Treatment/t84

Descent and oxygen — first-line

›Immediate descent

›Priority action — supersedes all other interventions

›Do not delay for weather if patient is deteriorating

›Descent of 300–1,000 m is typically sufficient to improve symptoms

›Supplemental oxygen

›2–4 L/min by nasal cannula

›Target SpO2 >90%

›Titrate to response

›High-flow oxygen if concurrent HAPE or SpO2 <80%

›10–15 L/min via non-rebreather mask

›Consider CPAP if HAPE-dominant

Dexamethasone

›Dexamethasone (glucocorticoid — reduces vasogenic cerebral edema)

›Loading dose: 8 mg IV/IM/PO

›Route: IV preferred if accessible, IM if no IV access, PO if able to swallow

›Onset within 1–6 hours of administration

›Maintenance: 4 mg every 6 hours

›Continue until descent achieved and symptoms resolve

›Taper before discontinuing if prolonged use

›Mechanism

›Reduces vasogenic edema via anti-inflammatory effects

›Does not promote acclimatization

›Symptoms may recur if dexamethasone discontinued at altitude without true acclimatization

›Pediatric dosing

›0.15 mg/kg per dose every 6 hours

›Maximum 4 mg per dose

Portable hyperbaric therapy

›Gamow bag (portable hyperbaric chamber)

›Indication: Descent impossible due to terrain, weather, or patient condition

›Adjunct to dexamethasone and oxygen, not a replacement for descent

›Simulates descent of 1,500–2,500 m

›Protocol

›Inflate to 2 psi (104 mmHg) above ambient pressure

›Requires continuous pumping (foot pump)

›Duration 2–4 hours per session

›Exit patient every 20–30 minutes for reassessment

›Re-administer medications during exits

›Symptoms may recur after removal from bag

Acetazolamide

›Acetazolamide (carbonic anhydrase inhibitor)

›Role in HACE: Adjunct only; does not directly treat HACE

›250 mg orally every 12 hours

›Facilitates acclimatization by accelerating respiratory alkalosis

›Contraindications

›Sulfonamide allergy (anaphylaxis risk; Stevens-Johnson syndrome risk)

›Severe renal impairment

›Pediatric dosing: 2.5 mg/kg every 12 hours (maximum 250 mg per dose)

Concurrent HAPE treatment

›Nifedipine for HAPE component

›Nifedipine 30 mg extended-release every 12 hours

›Reduces pulmonary artery pressure

›First-line pharmacotherapy for HAPE when descent impossible

›Alternative: Tadalafil 10 mg every 12 hours or sildenafil 50 mg every 8 hours

›Phosphodiesterase-5 inhibitors reduce pulmonary vascular resistance

›Use if nifedipine unavailable

›Medications to avoid in HACE

›Opioids

›Respiratory depression at altitude

›Worsen hypoxemia and mask neurologic deterioration

›Sedatives and hypnotics

›Mask neurologic deterioration

›Exacerbate respiratory depression

›Diuretics (furosemide)

›No role in HACE; worsen dehydration

›Mannitol or hypertonic saline

›No established role in HACE management

›Not recommended by Wilderness Medical Society guidelines

Seizure management

›Active seizure at altitude

›Benzodiazepine first-line

›Midazolam 5–10 mg IM if no IV access

›Onset within 5 minutes IM

›Repeat once if no response after 5 minutes

›Lorazepam 0.1 mg/kg IV if access available

›Maximum 4 mg per dose

›Respiratory monitoring after administration

›Seizures in HACE should prompt search for alternative cause

›Hyponatremia

›Hypoglycemia

›Intracranial hemorrhage

Prophylaxis for future ascents

›Acetazolamide prophylaxis

›125 mg orally every 12 hours starting 1–2 days before ascent

›Continue for 2 days after reaching target altitude

›Wilderness Medical Society Grade 1A recommendation for high-risk individuals

›250 mg every 12 hours for those with prior HACE or HAPE

›Dexamethasone prophylaxis (sulfonamide-allergic or acetazolamide-intolerant)

›2 mg every 6 hours or 4 mg every 12 hours

›Start day before ascent

›Does not promote acclimatization

09Special Populations/sp64

Pregnancy

›Physiologic considerations

›Physiologic hyperventilation of pregnancy

›Baseline respiratory alkalosis (PaCO2 27–32 mmHg at term)

›May attenuate hypoxic ventilatory response at altitude

›Uteroplacental blood flow sensitivity to hypoxemia

›Fetal SpO2 reduced at maternal SpO2 <90%

›Placental vasoconstriction with severe hypoxemia

›Risk and recommendations

›No reliable data on HACE prevalence in pregnancy

›High altitude generally not recommended >3,500 m in pregnancy

›Wilderness Medical Society advises caution above 2,500–3,000 m in pregnancy

›Medication considerations in pregnancy

›Dexamethasone: Category C; use if HACE life-threatening

›Risk to fetus substantially lower than maternal death from untreated HACE

›Neonatal adrenal suppression risk with prolonged use

›Acetazolamide: Category C (potential teratogen in animal studies)

›Avoid in pregnancy if possible; weigh risk vs. benefit

›Nifedipine: Commonly used in obstetric settings; generally acceptable

›Immediate descent priority unchanged in pregnancy

›Descent takes precedence over all other considerations

›Supplemental oxygen to maintain maternal SpO2 >95% in pregnancy

Geriatric

›Age-related considerations

›Baseline cognitive impairment may obscure mental status change

›Collateral history from companions essential

›Baseline cognitive screening at departure recommended for elderly trekkers

›Blunted hypoxic ventilatory response

10Background/b67

Epidemiology

›Altitude illness spectrum

›HACE is the end-stage of the AMS-HACE continuum

›Prevalence of HACE approximately 0.5–1.0% at 4,000–5,000 m

›Rare below 3,500–4,300 m (approximately 11,500–14,000 ft)

›Population affected

›Trekkers, mountaineers, skiers at high altitude

›Military personnel on rapid deployment to altitude

›Helicopter crew, mountain rescue workers

›Mortality

›Fatal if untreated; brain herniation within 12–24 hours of coma onset

›Excellent prognosis with prompt recognition, descent, and dexamethasone

›Geographic distribution

›Himalaya, Andes, Kilimanjaro, and Rocky Mountains most commonly affected regions

›Nepal Himalaya: HACE cases reported frequently among trekkers above 4,000 m

›Prevalence increases with ascent rate and absolute altitude

›Risk is not altitude-dependent alone

›Individual susceptibility varies markedly

›"Tight fit" hypothesis: small CSF reserve volume increases risk

Pathophysiology

›Hypoxia-driven cascade

›Hypobaric hypoxia at high altitude triggers cascade

›Reduced alveolar PO2 from decreased barometric pressure

›At 5,000 m, barometric pressure approximately 404 mmHg vs 760 mmHg at sea level

›Cerebral vasodilation response

›Hypoxemia causes cerebrovascular dilation

›Increased cerebral blood flow raises intracranial pressure

›Blood-brain barrier disruption

›Oxidative stress and hypoxia-inducible factor (HIF-1alpha) activation

›VEGF upregulation increases vascular permeability

›Vasogenic edema accumulates in white matter

›Microhemorrhage mechanism

›Mechanical disruption of small vessels

›Raised intravascular pressure in dilated cerebral vessels

›Diapedesis of red blood cells through disrupted BBB

›Hemosiderin deposits persist long after edema resolves

›Detectable on SWI-MRI for months to years

›Long-term cognitive implications under investigation

›Interstitial and vasogenic edema predominance

›HACE is predominantly vasogenic (not cytotoxic) edema

›MRI DWI shows facilitated diffusion (vasogenic pattern)

›Explains reversibility with treatment

›AMS may represent early BBB disruption without frank edema

›AMS-HACE continuum supported by MRI evidence

›Not all AMS progresses to HACE

Therapeutic Considerations

›Evidence base for treatments

›Dexamethasone evidence

›Reduces vasogenic edema via multiple anti-inflammatory mechanisms

›Wilderness Medical Society Grade 1C recommendation for HACE treatment

›Does not facilitate acclimatization (symptoms recur without true acclimatization)

›Descent evidence

›Gold standard treatment across all altitude illness guidelines

›Every 300 m descent raises barometric pressure and alveolar PO2

›Grade 1A recommendation in all society guidelines

›Acetazolamide mechanism

›Carbonic anhydrase inhibition

›Produces bicarbonate diuresis and mild metabolic acidosis

›Stimulates respiratory drive (corrects central sleep apnea at altitude)

›Accelerates ventilatory acclimatization

›Prophylactic efficacy established; therapeutic role in HACE limited

›Primarily prevents AMS from progressing to HACE

›Does not reverse established HACE

›Gamow bag mechanism

›Increases ambient pressure surrounding patient

›Raises partial pressure of inspired oxygen

›Equivalent to descent of 1,500–2,500 m physiologically

›Limitation: symptoms recur on removal at same altitude

›Temporizing measure only

›Must be combined with pharmacologic therapy

11Patient Discharge Instructions/pdi42

copy discharge instructions

›Diagnosis explanation

›You were treated for High Altitude Cerebral Edema (HACE)

›HACE is a life-threatening brain swelling caused by traveling to high altitude too quickly

›Your brain did not have enough time to adjust to lower oxygen levels at altitude

›You received dexamethasone (a steroid) and oxygen to reduce brain swelling

›You have been moved to a lower altitude where you can recover safely

›Medication instructions

›Continue prescribed dexamethasone exactly as directed

›Do not stop the steroid suddenly without physician guidance

›Take with food to reduce stomach irritation

›Acetazolamide if prescribed

›Take with plenty of water

›May cause increased urination and tingling in fingers and toes

›Activity restrictions

›No further ascent to high altitude until fully cleared by a physician

›Do not attempt to return to altitude while still on dexamethasone

›Minimum 2–3 days fully symptom-free before any future altitude attempt

›Avoid strenuous physical activity for 1–2 weeks

›Rest until all neurologic symptoms fully resolved

›Follow-up instructions

›Neurology follow-up within 1–2 weeks

›MRI of the brain may be recommended to confirm full recovery

›Cognitive assessment if experiencing memory or concentration problems

›Primary care within 1 week for steroid taper management

›Future altitude safety

›Future ascents require slower ascent profile

›Sleep altitude increase no more than 300–500 m per night above 3,000 m

12References/r47

Guidelines and key sources

›Wilderness Medical Society Clinical Practice Guidelines 2024

›Luks AM, Beidleman BA, Freer L, et al.

›Wilderness Medical Society Clinical Practice Guidelines for the Prevention, Diagnosis, and Treatment of Acute Altitude Illness: 2024 Update

›Wilderness and Environmental Medicine 2024

›Provides Grade 1A recommendation for descent in HACE

›Grade 1C recommendation for dexamethasone in HACE

›Acetazolamide 125–250 mg q12h for prophylaxis

›Wilderness Medical Society Clinical Practice Guidelines 2019

›Luks AM, Auerbach PS, Freer L, et al.

›Wilderness and Environmental Medicine 2019

›Microhemorrhage documentation and long-term HACE sequelae

›CDC Yellow Book 2025

›Hackett PH and Shlim DR

›High-Altitude Travel and Altitude Illness

›2025 edition; comprehensive traveler guidance

Landmark clinical studies

›Bärtsch P, Swenson ER

›Acute High-Altitude Illnesses

›New England Journal of Medicine 2013

›Comprehensive review of AMS, HACE, and HAPE pathophysiology and management

›Hackett PH, Roach RC

›High-Altitude Illness

›New England Journal of Medicine 2001

›Foundational pharmacologic treatment evidence

›Hackett PH, Yarnell PR, Hill R, et al.

›High-Altitude Cerebral Edema Evaluated With MRI: Clinical Correlation and Pathophysiology

›JAMA 1998

Learn More: High Altitude Cerebral Edema (HACE)→

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Reviewed by SymptomDx Medical Team · Last reviewed August 18, 2026

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