Skip to main content
Symptom
dx.
Menu
Clinical Reference
Approaches
I have a symptom
Management
I know the diagnosis
Orthopedic Injuries
Fractures & dislocations
Calculators
Clinical calculators
Practical Skills
ECG
Interpretation guide
POCUS
Bedside ultrasound
Procedures
Step-by-step guides
Resuscitation
ACLS / PALS / NRP
Learn
Blog
Articles & updates
Deep Dive
In-depth clinical reviews
About
Our mission
Symptom
dx.
Clinical Reference
Approaches
I have a symptom
Management
I know the diagnosis
Orthopedic Injuries
Fractures & dislocations
Calculators
Clinical calculators
Practical Skills
ECG
Interpretation guide
POCUS
Bedside ultrasound
Procedures
Step-by-step guides
Resuscitation
ACLS / PALS / NRP
Learn
Blog
Articles & updates
Deep Dive
In-depth clinical reviews
About
Our mission
Get Started
Menu
Clinical Reference
Approaches
I have a symptom
Management
I know the diagnosis
Orthopedic Injuries
Fractures & dislocations
Calculators
Clinical calculators
Practical Skills
ECG
Interpretation guide
POCUS
Bedside ultrasound
Procedures
Step-by-step guides
Resuscitation
ACLS / PALS / NRP
Learn
Blog
Articles & updates
Deep Dive
In-depth clinical reviews
About
Our mission
Loading...
Acute Mountain Sickness
Cardiovascular Presentations
Abdominal aortic aneurysm
Acute coronary syndrome (NSTEMI)
Acute coronary syndrome (STEMI)
Acute decompensated heart failure
Acute limb ischemia
Acute mesenteric ischemia
Aortic dissection
Aortic stenosis
Atrial fibrillation and flutter
Bradyarrhythmia and heart block
Cardiac arrest
Deep vein thrombosis
Myocarditis
Pericarditis
Pulmonary embolism
Stable angina
Superficial thrombophlebitis
Superior vena cava syndrome
Supraventricular tachycardia
Syncope (cardiogenic)
Unstable angina
Ventricular tachycardia
Respiratory Presentations
Acute bronchitis
Acute respiratory failure
Aspiration pneumonia
Asthma exacerbation
Bronchiolitis
Community-acquired pneumonia
COVID-19 pneumonia
COPD exacerbation
Croup
Croup (laryngotracheobronchitis)
Epiglottitis
Hemothorax
Hospital-acquired pneumonia
Pleural effusion
Pneumothorax (traumatic)
Pulmonary contusion
Spontaneous pneumothorax
Neurological Presentations
Bell's palsy
Benign paroxysmal positional vertigo
Brain abscess
Cauda equina syndrome
Cervical radiculopathy
Concussion (mild traumatic brain injury)
Encephalitis
Guillain-Barré syndrome
Hemorrhagic stroke (intracerebral)
Ischemic stroke
Lumbar radiculopathy
Malignant spinal cord compression
Migraine
Peripheral neuropathy (acute)
Retropharyngeal abscess
Schizophrenia (acute exacerbation)
Seizure (breakthrough:known epilepsy)
Seizure (first-time)
Spinal cord injury
Status epilepticus
Subarachnoid hemorrhage
Tension headache
Transient ischemic attack
Traumatic brain injury (moderate-severe)
Vestibular neuritis
Viral meningitis
Gastrointestinal Presentations
Acute appendicitis
Acute cholecystitis
Acute diverticulitis
Acute pancreatitis
Anal fissure
Choledocholithiasis and cholangitis
Clostridioides difficile colitis
Gastritis
Gastroenteritis (viral and bacterial)
Gastroesophageal reflux disease
Incarcerated or strangulated hernia
Inflammatory bowel disease flare
Large bowel obstruction
Lower GI hemorrhage
Peptic ulcer disease
Perforated viscus
Small bowel obstruction
Upper GI hemorrhage
Genitourinary and Reproductive Presentations
Acute prostatitis
Acute urinary retention
Ectopic pregnancy
Epididymitis
Orchitis
Ovarian torsion
Paraphimosis
Pelvic inflammatory disease
Priapism
Pyelonephritis
Renal laceration
Ruptured ovarian cyst
Testicular torsion
Tubo-ovarian abscess
Urinary tract infection (uncomplicated)
Urolithiasis (renal colic)
Vaginal bleeding (non-pregnant)
Infectious Disease Presentations
Acute sinusitis
Acute tonsillitis
Acute upper respiratory infection
Animal bite
Bacterial meningitis
Cellulitis
Conjunctivitis (bacterial)
Dental abscess
Endocarditis
Febrile neutropenia
Fournier gangrene
Hand-foot-mouth disease
Hepatitis (acute)
Herpes zoster
HIV-related illness
Human bite
Impetigo
Infected diabetic foot ulcer
Infectious mononucleosis
Influenza
Necrotizing fasciitis
Osteomyelitis
Otitis externa
Parasitic infection
Periorbital cellulitis
Peritonsillar abscess
Scabies
Sepsis
Septic arthritis
Spontaneous bacterial peritonitis
Tick-borne illness (Lyme disease)
Tinea infection
Tuberculosis
Viral exanthem
Wound infection
Trauma Presentations
Achilles tendon rupture
ACL and mceniscus tear
Ankle fracture
Ankle sprain
Burn
Calcaneus fracture
Cervical spine fracture
Clavicle fracture
Dental avulsion
Distal radius fracture
Drowning
Elbow fracture and dislocation
Electrical injury
Facial bone fracture
Facial laceration
Femur fracture
Fingertip amputation
Forearm fracture (radius and ulna)
Frostbite
Hand:finger laceration
Heat exhaustion
Heat stroke
Hip fracture
Humeral shaft fracture
Knee dislocation
Knee sprain
Lightning injury
Mandible fracture
Metacarpal fracture
Metatarsal fracture
Muscle strain
Nasal fracture
Non-accidental trauma
Orbital fracture
Patella fracture
Phalanx fracture (finger)
Proximal humerus fracture
Pulmonary contusion
Rib fracture
Rotator cuff tear (acute traumatic)
Scalp laceration
Scaphoid fracture
Shoulder dislocation
Skull fracture
Splenic laceration
Sternal fracture
Supracondylar pediatric fracture
Tendon laceration (hand:wrist)
Thoracic and lumbar spine fracture
Tibia:fibula fracture
Tibial plateau fracture
Toe fracture
Traumatic epistaxis
Traumatic hyphema
Toxicologic Presentations
Acetaminophen toxicity
Alcohol intoxication
Alcohol withdrawal
Anticholinergic toxicity
Anticoagulant overdose
Benzodiazepine overdose
Benzodiazepine:sedative overdose
Beta-blocker and calcium channel blocker toxicity
Carbon monoxide poisoning
Caustic ingestion
Digoxin toxicity
Drug eruption
Foreign body ingestion
Opioid intoxication
Opioid overdose
Opioid withdrawal
Organophosphate
Salicylate toxicity
Serotonin syndrome
Stimulant intoxication (cocaine, methamphetamine)
Tricyclic antidepressant overdose
Psychiatric Presentations
Acute anxiety
Acute psychosis
Agitation:behavioral emergency
Bipolar disorder
Conversion disorder
Major depressive episode
Neuroleptic malignant syndrome
Suicidal ideation and attempt
Musculoskeletal and Rheumatologic Presentations
Acute low back pain (mechanical)
Bursitis
Cervical radiculopathy
Costochondritis
Gout (acute)
Lumbar radiculopathy
Pseudogout
Tendinitis
Dermatology Presentations
Acute eczema (Eczema acute flare)
Allergic contact dermatitis
Erythema multiforme
Henoch-Schönlein purpura
Pressure injury
Psoriasis (acute flare)
Stevens-Johnson syndrome
Toxic epidermal necrolysis
Urticaria (acute)
Environmental and Exposure Presentations
Envenomation (snake, spider, insect)
High-altitude illness
Hypothermia
Hematologic and Oncologic Presentations
Acute chest syndrome
Coagulopathy
Hyperviscosity syndrome
Sickle cell crisis (vaso-occlusive)
Symptomatic anemia
Thrombocytopenia (severe)
Tumor lysis syndrome
Pediatric-Specific Presentations
Bronchiolitis
Croup
Emergency delivery
Febrile seizure
Kawasaki disease
Neonatal jaundice
Neonatal sepsis
Nursemaid's elbow
Pediatric fever 0 to 28 days
Pediatric fever 29 to 60 days
Pediatric fever 61 to 90 days
Pyloric stenosis
Slipped capital femoral epiphysis
Intussusception
Endocrine and Metabolic Presentations
Adrenal crisis
Diabetic ketoacidosis
Hypercalcemia
Hyperosmolar hyperglycemic state
Hypertensive emergency
Hypertensive urgency
Hypoglycemia
Myasthenia gravis crisis
Myxedema coma
Severe hyperkalemia
Severe hyponatremia
Thyroid storm
ENT and Maxillofacial Presentations
Acute laryngitis
Acute otitis media
Acute pharyngitis
Cerumen impaction
Epistaxis (anterior)
Nasal foreign body
Otitis externa
Tympanic membrane perforation
Ophthalmologic Presentations
Acute angle-closure glaucoma
Central retinal artery occlusion
Chemical eye injury
Corneal abrasion
Corneal ulcer
Globe rupture
Ocular foreign body
Orbital cellulitis
Retinal detachment
Obstetric Presentations
Hyperemesis gravidarum
Painful vaginal bleeding in pregnancy
Placenta previa
Placental abruption
Preeclampsia:eclampsia
Preterm labor
Threatened:inevitable:incomplete abortion
Systemic and Miscellaneous Presentations
Anaphylaxis
Angioedema
Cannabis-induced hyperemesis
Acute Mountain Sickness
POCUS
Procedures
Calculators
Resuscitation
ECG Guide
Back
Clinical Assessment Checklist
Browse categories and answer follow-up questions to refine your symptom profile.
Approach to the Critical Patient
Immediate priorities
Distinguish benign AMS from life threats
▶
High altitude cerebral edema concern
▶
Ataxia on heel-to-toe walking
Altered mental status or drowsiness
Coma may ensue within 12 to 24 hours of ataxia onset if untreated
High altitude pulmonary edema concern
▶
Dyspnea at rest
Cough with pink frothy sputum
Cyanosis
If any HACE or HAPE sign, immediate descent and oxygen
▶
Descent is definitive treatment
Do not delay for imaging or labs
Time-critical airway and breathing
▶
Oxygenation failure at altitude
▶
SpO2 lower than expected for altitude
Target SpO2 above 90% with supplemental oxygen
Mental status threat to airway
▶
Obtunded patient from HACE
Aspiration risk with vomiting
If unable to protect airway, definitive airway control
▶
Rapid sequence intubation preparation
Continue descent and oxygen during transfer
Early branching decision
▶
Uncomplicated AMS pattern
▶
Headache plus nausea, fatigue, or dizziness with normal neuro exam
Self-limited course over 12 to 48 hours without further ascent
Complicated altitude illness pattern
▶
Neurologic signs suggest HACE
Pulmonary signs suggest HAPE
If diagnosis uncertain, treat as more severe illness and arrange descent
▶
Golden rule: never ascend with AMS symptoms
Rapid improvement with descent is diagnostically confirmatory
Monitoring and targets
Monitoring bundle
▶
Pulse oximetry
▶
Trend SpO2 to gauge acclimatization
High SpO2 for altitude appears protective
Serial neurologic checks
▶
Heel-to-toe walk for ataxia
Mental status trend
Respiratory reassessment
▶
Rest dyspnea trend
Cough character change
Escalation triggers
▶
Worsening symptoms despite rest and treatment at current altitude
▶
Initiate descent
Add dexamethasone
New ataxia or confusion
▶
Treat as HACE
Immediate descent and oxygen
New rest dyspnea or cough
▶
Treat as HAPE
Oxygen and nifedipine if descent not feasible
Immediate consults
Coordination triggers
▶
Evacuation logistics in wilderness setting
▶
Search and rescue activation
Portable hyperbaric chamber availability
Critical care for severe illness
▶
Refractory hypoxemia
Encephalopathy
Neurology or stroke service if focal deficit
▶
Focal signs argue against HACE
Consider stroke, mass, or hyponatremia
History
Presentation pattern
Cardinal symptom
▶
Headache
▶
Dull bifrontal or temporal quality
Worsened by movement or Valsalva
Required associated symptom
▶
Nausea or anorexia
Fatigue or lassitude
Dizziness or lightheadedness
Sleep disturbance
▶
Insomnia with frequent awakenings
Central sleep apnea common at altitude
Ascent and exposure context
▶
Altitude reached and sleeping elevation
▶
Prevalence rises about 13% per 1000 m above 2500 m
Onset usually 2 to 12 hours after arrival
Rate of ascent
▶
Gain above 400 m per day in sleeping elevation increases risk
Lack of preacclimatization in prior 1 to 2 months
Timing relative to arrival
▶
Symptoms starting beyond 3 days without further ascent argue against AMS
Symptom onset relative to peak exertion
Risk factors
Strong predictors
▶
Prior AMS history
▶
Strongest individual risk factor
Recurrence odds ratio up to 12
Rapid ascent rate
▶
Odds ratio 4.69 for AMS
Higher sleeping elevation gain per day
Younger age below 50 years
▶
Risk about two-fold higher
Greater exertion tendency
Possible contributors
▶
Migraine history
▶
Lower threshold for altitude headache
Aura distinguishes primary migraine
Obesity and anxiety
▶
May increase susceptibility
Variable evidence strength
Exertion at altitude
▶
Increases risk
Physical fitness does not reduce risk
Factors not increasing risk
▶
Smoking
▶
Does not appear to increase AMS risk
Counsel separately for other harms
Physical fitness level
▶
Fit travelers remain susceptible
False reassurance pitfall
Important negatives and clues
Features arguing against AMS
▶
No fever, coryza, chills, or myalgia
▶
These suggest viral illness
Reassess for alternative diagnosis
No focal neurologic deficit
▶
Focal signs suggest stroke or mass
Hyponatremia consideration
No ataxia or altered mental status
▶
Presence indicates HACE
Earliest HACE sign is gait ataxia
Collateral history value
▶
Companions report gait or behavior change
▶
Patient may not recognize ataxia
Confusion may be subtle
Prior altitude outcomes
▶
Tolerance at similar elevations
Response to prior prophylaxis
Physical Exam
Vitals and general
Altitude-adjusted vitals
▶
Tachycardia
▶
Expected physiologic response at altitude
Palpitations usually benign
Mild tachypnea
▶
Hypoxic ventilatory response
Rest dyspnea is abnormal and suggests HAPE
Oxygen saturation
▶
Lower than sea level and varies by altitude
Notably low SpO2 for altitude suggests severe illness
General appearance
▶
Hydration status
▶
Dry mucosa from respiratory water loss
Reduced thirst drive
Pallor or cyanosis
▶
Cyanosis suggests HAPE
Functional impairment marker
Neurologic exam
HACE screening
▶
Heel-to-toe walk test
▶
Earliest sign is gait ataxia
Inability indicates HACE
Mental status
▶
Must be normal in AMS
Confusion or drowsiness indicates HACE
Funduscopic exam
▶
Papilledema confirms cerebral edema
Retinal hemorrhages may occur at altitude
Focal exam
▶
Cranial nerve testing
▶
Focal deficit argues against HACE
Consider stroke or mass
Motor and coordination
▶
Symmetric findings expected
Asymmetry prompts alternative workup
Pulmonary and PITFALLS
Lung exam
▶
Auscultation
▶
Clear in uncomplicated AMS
Crackles or rales suggest HAPE
Work of breathing
▶
Accessory muscle use abnormal
Cough character assessment
Diagnostic pitfalls
▶
No physical finding is specific for AMS
▶
Diagnosis remains clinical
Avoid over-reliance on single sign
Optic nerve sheath ultrasound
▶
Not reliable for AMS or HACE diagnosis
Do not exclude HACE based on POCUS
Differential Diagnosis
Life threats and altitude spectrum
Altitude illness spectrum
▶
Acute mountain sickness
▶
ICD-10 T70.20XA effects of high altitude
Headache plus one associated symptom
High altitude cerebral edema
▶
Ataxia and encephalopathy
End stage of AMS continuum
High altitude pulmonary edema
▶
Rest dyspnea and cough
Patchy infiltrates on imaging
Immediate non-altitude threats
▶
Carbon monoxide poisoning
▶
Enclosed shelters or tents with stoves
Elevated carboxyhemoglobin
Ischemic stroke or mass lesion
▶
Focal neurologic deficits
Seizure activity
Hyponatremia
▶
Excessive water intake during exertion
Altered mentation and headache
Common mimics
Constitutional and toxic mimics
▶
Alcohol hangover
▶
Symptoms closely mimic AMS
Recent heavy intake history
Dehydration and exhaustion
▶
Common at altitude
Overlapping fatigue and headache
Viral illness
▶
Fever, coryza, and myalgia present
Distinguishes from AMS
Metabolic and primary headache mimics
▶
Hypoglycemia
▶
Diabetics or prolonged exertion
Point-of-care glucose
Hypothermia
▶
Altered mentation in cold setting
Core temperature measurement
Migraine
▶
Triggered by altitude
Prior history and aura distinguish
Laboratory Tests
Diagnostic role
Diagnosis is clinical
▶
No lab establishes AMS
▶
Lake Louise scoring drives diagnosis
Labs reserved for excluding mimics
Pulse oximetry adjunct
▶
Monitors acclimatization
High SpO2 for altitude protective
Rule-out studies
Metabolic panel
▶
Basic metabolic panel
▶
Hyponatremia from water intoxication
Renal function assessment
Point-of-care glucose
▶
Hypoglycemia if altered mentation
Rapid bedside result
Targeted studies
▶
Complete blood count
▶
If infection suspected
Leukocytosis supports alternative diagnosis
Carboxyhemoglobin
▶
If CO exposure in enclosed shelter
Co-oximetry required, standard SpO2 misleading
Gas exchange and severity markers
Oxygenation assessment
▶
SpO2 trend
▶
Disproportionately low value suggests HAPE
Useful for gauging acclimatization
Arterial or venous blood gas
▶
Respiratory alkalosis expected at altitude
PaO2 in mmHg lower than sea level
Severity correlates
▶
Worsening hypoxemia
▶
Suggests progression to HAPE
Trigger for descent and oxygen
Acidosis
▶
Suggests severe illness
Prompts broader evaluation
Diagnostic Tests
Scoring Systems
Lake Louise AMS Score 2018 revision
▶
Scored domains
▶
Headache on 0 to 3 scale
Gastrointestinal symptoms on 0 to 3 scale
Fatigue on 0 to 3 scale
Dizziness on 0 to 3 scale
Interpretation
▶
Score 3 or more with headache defines AMS
Mild AMS score 3 to 5
Moderate to severe AMS score 6 to 12
Revision note
▶
Sleep disturbance removed in 2018 revision
Used in clinical and research settings
Clinical Functional Score
▶
Single question on activity impact
▶
Scored 0 to 3
Simplest bedside tool
Performance
▶
Score 2 or more positive LR 3.2 for severe AMS
Complements Lake Louise Score
AMS-Cerebral score
▶
Research-oriented measure
▶
Threshold 0.70 or more indicates AMS
Used primarily in studies
Limitations
▶
Not practical for rapid bedside use
Clinical trajectory supersedes score
MRI
Brain MRI role
▶
Limited acute utility
▶
Generally unnecessary for straightforward AMS
Availability constraints in field settings
HACE findings if obtained
▶
T2 and FLAIR white matter edema
Splenium of corpus callosum involvement
Microhemorrhages on susceptibility sequences
Problem-solving indications
▶
Focal deficits suggesting stroke or mass
Atypical or persistent encephalopathy
CT
Head CT indications
▶
When to image
▶
Focal neurologic deficits
Seizures
Concern for intracranial pathology other than HACE
Expected findings
▶
Often normal early in HACE
Diffuse cerebral edema in severe HACE
Limitations
▶
Less sensitive than MRI for early edema
Do not delay descent for imaging
Imaging not routine
▶
Straightforward AMS
▶
Imaging generally unnecessary
Diagnosis is clinical
Resource stewardship
▶
Reserve for red-flag features
ACEP Level C guidance for selective imaging
Ultrasound
Lung ultrasound
▶
B-line assessment
▶
B-lines suggest subclinical pulmonary edema at altitude
Clinical significance debated
HAPE evaluation
▶
Bilateral B-lines support HAPE
Correlate with rest dyspnea and SpO2
Limitations
▶
Operator dependent
Not diagnostic of AMS itself
Optic nerve sheath ultrasound
▶
Diameter measurement
▶
Proposed surrogate for raised intracranial pressure
Not reliable for AMS or HACE diagnosis
Practical caution
▶
Do not exclude HACE based on normal measurement
Clinical exam remains primary
Disposition
Level of care selection
May remain at altitude
▶
Mild AMS improving on treatment
▶
Normal neuro exam
Functional and tolerating oral intake
Close observation conditions
▶
Companion monitoring available
No further ascent until symptoms resolve
Descent indicated
▶
Moderate to severe AMS not improving
▶
No improvement after 1 to 3 days of treatment
Descend 300 to 1000 m
Any HACE sign
▶
Ataxia or altered mental status
Immediate descent is definitive
Any HAPE sign
▶
Rest dyspnea or cyanosis
Productive cough
Admission or higher-level care
▶
HACE or HAPE
▶
Require monitoring and supplemental oxygen
Pharmacotherapy and possible critical care
Instability
▶
Altered mental status
Hemodynamic instability
Resuming ascent and follow up
Copy
Reascent criteria
▶
Complete symptom resolution required
▶
Further ascent contraindicated with any symptoms
Golden rule reinforcement
Prophylaxis on reascent
▶
Acetazolamide 125 mg PO every 12 hours
Slower ascent profile
Follow up planning
▶
Counsel on future trips
▶
Prior AMS does not preclude high-altitude travel
Requires better planning and slower ascent
Return precautions provided
▶
HACE and HAPE red flags
Threshold for descent
Treatment
Initial stabilization
Stop further ascent
▶
Rest at current elevation
▶
Do not ascend until symptoms resolve
Reassess for HACE and HAPE features
Supportive measures
▶
Maintain hydration
Avoid alcohol and sedative-hypnotics
Oxygen and descent thresholds
▶
Supplemental oxygen
▶
1 to 2 L/min for symptomatic relief
Target SpO2 above 90% in severe illness
If symptoms worsen, descend
▶
Descent 300 to 1000 m
Descent of even 300 m is therapeutic
Mild AMS
Symptomatic therapy
▶
Analgesia
▶
Ibuprofen 600 mg PO every 8 hours
Acetaminophen 500 mg PO every 8 hours alternative
Antiemetic
▶
Ondansetron 4 mg orally disintegrating tablet as needed
Avoid sedating antiemetics where possible
Acclimatization aid
▶
Acetazolamide 250 mg PO every 12 hours to speed acclimatization
Remain at current altitude until resolution
Avoidances
▶
Opioid analgesics
▶
Respiratory depression risk at altitude
Use non-opioid analgesia
Sedative-hypnotics
▶
Avoid unless combined with acetazolamide
Risk of nocturnal hypoventilation
Moderate to severe AMS
Corticosteroid therapy
▶
Dexamethasone
▶
4 mg PO, IV, or IM every 6 hours for 24 hours
More reliable than acetazolamide for treatment
Rebound caution
▶
Does not facilitate acclimatization
Rebound symptoms if stopped at altitude before acclimatizing
Adjuncts and descent
▶
Acetazolamide adjunct
▶
250 mg PO every 12 hours
Aids underlying acclimatization
Oxygen and descent
▶
Supplemental oxygen 1 to 2 L/min if available
Descend 300 to 1000 m if symptoms persist
HACE and HAPE management
HACE treatment
▶
Immediate descent
▶
Definitive treatment
Do not delay for testing
Dexamethasone
▶
8 mg loading dose PO, IV, or IM
Then 4 mg every 6 hours
Oxygen and chamber
▶
Supplemental oxygen to SpO2 above 90%
Portable hyperbaric chamber simulates about 2000 m descent at 2 psi
HAPE treatment
▶
Descent and oxygen
▶
Descent plus supplemental oxygen
Minimize exertion during descent
Pulmonary vasodilator
▶
Nifedipine SR 30 mg PO every 12 hours if oxygen unavailable and descent not feasible
Monitor for hypotension
Avoid diuretics
▶
No role in HAPE
Risk of hypovolemia
Prevention and evidence
Pharmacologic prophylaxis
▶
Acetazolamide
▶
125 mg PO every 12 hours starting day before ascent
Continue 2 to 4 days at target altitude
Contraindicated with anaphylaxis or Stevens-Johnson to sulfonamides
Dexamethasone
▶
2 mg PO every 6 hours or 4 mg every 12 hours
Alternative if acetazolamide intolerant
Does not aid acclimatization
Ibuprofen
▶
600 mg PO every 8 hours
Alternative when other agents contraindicated
Guideline basis
▶
Wilderness Medical Society 2024 update
▶
Severity stratification and treatment recommendations
Acetazolamide for prevention and acclimatization
Nonpharmacologic prevention
▶
Gradual ascent below 500 m per day in sleeping elevation above 3000 m
Rest days every 3 to 4 days
Special Populations
Pregnancy
Pregnancy considerations
▶
Travel counseling
▶
Limited data on high-altitude exposure
Avoid sleeping above 3000 m where feasible
Medication safety
▶
Acetazolamide generally avoided in pregnancy
Dexamethasone reserved for severe illness only
Management priorities
▶
Descent and oxygen are mainstays
Maintain maternal SpO2 above 95% when feasible
Monitoring
▶
Fetal assessment when viable gestation
Low threshold for descent
Geriatric
Older adult features
▶
Susceptibility nuance
▶
Age above 50 years not protective against severe outcomes
Comorbidities increase risk
Comorbidity interactions
▶
Chronic lung disease raises HAPE risk
Cardiac disease affects travel tolerance
Medication caution
▶
Renal dosing of acetazolamide
Polypharmacy and sedation burden review
Disposition bias
▶
Lower threshold for descent
Closer monitoring
Pediatrics
Pediatric differences
▶
Atypical presentation
▶
Preverbal children show irritability and poor feeding
Pallor and fussiness as clues
Diagnostic challenge
▶
Cannot self-report headache
Lower threshold for descent
Weight-based dosing
▶
Acetazolamide 2.5 mg/kg PO every 12 hours, maximum 125 mg per dose
Dexamethasone 0.15 mg/kg PO, IV, or IM every 6 hours
Prevention emphasis
▶
Gradual ascent profiles
Avoid rapid gain in sleeping elevation
Background
Epidemiology
Incidence and burden
▶
Prevalence among ascenders
▶
Affects 25% to 43% of travelers above 2500 m
Most common form of altitude illness
Altitude dependence
▶
Prevalence rises about 13% per 1000 m above 2500 m
Higher sleeping elevation increases risk
Progression and recurrence
▶
Progression to HACE in under 1% of AMS cases
Recurrence up to 60% with similar ascent profiles
Natural history
▶
Self-limited course
▶
Resolves in 12 to 48 hours without further ascent
Rapid improvement with descent
Severity distribution
▶
Most cases mild
Moderate to severe minority
Pathophysiology
Hypoxia-driven mechanism
▶
Hypobaric hypoxia
▶
Reduced inspired oxygen partial pressure
Triggers hypoxic ventilatory response
Cerebral mechanisms
▶
Cerebral vasodilation and increased blood flow
Vasogenic edema in HACE
Pulmonary mechanisms
▶
Hypoxic pulmonary vasoconstriction
Uneven vasoconstriction and capillary stress in HAPE
Acclimatization physiology
▶
Compensatory responses
▶
Increased ventilation
Renal bicarbonate excretion
Acetazolamide effect
▶
Carbonic anhydrase inhibition induces metabolic acidosis
Stimulates ventilation to aid acclimatization
Individual variation
▶
Differences in respiratory drive
Genetic susceptibility suggested by animal studies
Therapeutic Considerations
Treatment principles
▶
Descent primacy
▶
Descent is the most effective intervention
Even 300 m descent is therapeutic
Pharmacologic roles
▶
Acetazolamide aids acclimatization
Dexamethasone treats symptoms without aiding acclimatization
Oxygen as bridge
▶
Relieves hypoxemia when descent delayed
Portable hyperbaric chamber simulates descent
Prevention strategy
▶
Graded ascent
▶
Below 500 m per day sleeping elevation gain above 3000 m
Rest days every 3 to 4 days
Risk-based prophylaxis
▶
Acetazolamide for moderate to high-risk profiles
History of AMS warrants prophylaxis
Behavioral measures
▶
Avoid alcohol and overexertion early
Maintain hydration
Patient Discharge Instructions
copy discharge instructions
Copy
Altitude illness home care
▶
Do not go any higher to sleep until you feel completely better
Rest at your current elevation
Drink plenty of fluids and avoid alcohol
Take medicines exactly as prescribed
Medication guidance
▶
Use acetaminophen or ibuprofen for headache
Take acetazolamide as directed to help you adjust
Do not use sleeping pills or strong pain medicines
Return to ER or descend immediately if
▶
Trouble walking straight or feeling clumsy
Confusion, severe drowsiness, or trouble waking
Shortness of breath at rest
Cough with pink or frothy spit
Blue lips or fingertips
Vomiting that prevents keeping fluids or medicines down
Future trip advice
▶
Climb slowly and allow rest days
Ask your clinician about preventive medicine if this has happened before
Prior altitude sickness does not mean you cannot travel high again
References
Guidelines and key sources
Society guidelines
▶
Wilderness Medical Society Clinical Practice Guidelines 2024 update
CDC Yellow Book High-Altitude Travel and Altitude Illness 2025
AAFP summary of Wilderness Medical Society altitude guidelines 2020
Landmark reviews
▶
Luks and Hackett Medical Conditions and High-Altitude Travel NEJM 2022
Bartsch and Swenson Acute High-Altitude Illnesses NEJM 2013
Gatterer et al Altitude Illnesses Nature Reviews Disease Primers 2024
Scoring and decision tools
▶
Roach et al 2018 Lake Louise Acute Mountain Sickness Score
Does This Patient Have Acute Mountain Sickness JAMA 2017 Rational Clinical Examination
Clinical Functional Score for bedside severity assessment
Coding standards
▶
ICD-10 T70.20XA effects of high altitude unspecified
SNOMED CT acute mountain sickness disorder concept
SymptomDx is an educational tool for medical professionals. It does not replace clinical judgment. Verify all clinical data and drug dosages with authoritative sources.
← Management Protocols
Home
Management Protocols
Acute Mountain Sickness