Acute mountain sickness
(Redirected from Acute altitude sickness)
Background
- Also referred to as AMS
- Usually only occurs with altitude >7,000-8,000ft (2,000 m)
- May occur at lower altitudes in patients who are particularly susceptible (COPD, CHF, obesity, history of AMS)
- Development of symptoms based on: rate of ascent, sleeping altitude, strength of hypoxic ventilatory response, alcohol intake, obesity
- NOT based on physical fitness, age, sex, smoking, previous high-altitude experience
- Tend to have recurrence of symptoms whenever they return to the symptomatic altitude
- Low partial pressure of O2 leads to decreased diffusion of O2 across alveolar spaces -> hypoxemia results in tachypnea and cerebral vasodilation (↓ CO2) -> increased ICP
Clinical Features
Onset
- Symptoms usually develop 1-6hr after arrival at elevation
- May be delayed for 1-2d
- Especially common after the 1st or 2nd night's sleep
Duration
- Average duration of symptoms at 10,000ft = 15hr
- At higher elevations symptoms may last weeks / more likely to progress to headache
Differential Diagnosis
- Dehydration
- AMS is not improved by fluid administration alone
- Body hydration does not influence susceptibility to AMS
- Exhaustion
- Viral syndrome
- Alcohol hangover
- Substance abuse
- Caffeine withdrawal
- Hypothermia
- CO poisoning
- CNS infection: Meningitis, Encephalitis
- Cerebral venous sinus thrombosis
- Migraine
- Whereas supplemental O2 helps headache due to AMS in 10-15min, O2 has no effect on migraines
- TIA
- Hypoglycemia
High Altitude Illnesses
- Acute mountain sickness
- Chronic mountain sickness
- High altitude cerebral edema
- High altitude pulmonary edema
- High altitude peripheral edema
- High altitude retinopathy
- High altitude pharyngitis and bronchitis
- Ultraviolet keratitis
Evaluation
- Clinical diagnosis
- Mental status, cerebellar exam - rule out HACE
- Lung exam - rule out HAPE
- Lake Louise Scoring System: Sum of symptoms 0-3 (none, mild, moderate, severe/incapacitating). Mild corresponds to score 3-4, Moderate-severe corresponds to score ≥5
- Headache
- Gastrointestinal symptoms
- Fatigue/weakness
- Lightheadedness
- Difficulty Sleeping
Expected SpO2 and PaO2 levels at altitude[2]
| Altitude | SpO2 | PaO2 (mm Hg) |
|---|---|---|
| 1,500 to 3,500 m (4,900 to 11,500 ft) | about 90% | 55-75 |
| 3,500 to 5,500 m (11,500 to 18,000 ft) | 75-85% | 40-60 |
| 5,500 to 8,850 m (18,000 to 29,000 ft) | 58-75% | 28-40 |
Management
Mild
- Terminate ascent and/or descend [3]
- Descend to lower altitude of 300-500m (1000-3000ft) OR acclimatize for 12-36hr at same altitude
- Acetazolamide
- Mechanism: speeds acclimatization by promoting bicarb diuresis -> metabolic acidosis -> ↑ ventilation
- Indications:
- History of altitude illness
- Abrupt ascent to >9800ft
- AMS requiring treatment
- Bothersome periodic breathing during sleep
- 125-250mg PO BID until symptoms resolve
- Side-effects
- Allergic reaction (if patient allergic to sulfa), paresthesias, polyuria, carbonated beverages taste bitter
- Can also worsen dehydration by promoting bicarb diuresis
- Symptomatic treatment as necessary with analgesics (NSAIDs) and antiemetics (ondansetron)
- Sleep-agents
- Benzos are only safe if given in conjunction with acetazolamide
- Nonbenzodiazepines are safe (zolpidem, diphenhydramine)
Moderate-Severe
- Immediate descent of 500 m (~ 1500 ft) for worsening symptoms
- Low-flow 0.5-1 L/min O2 if available (especially nocturnal administration)
- Acetazolamide 250mg PO BID
- Dexamethasone 4mg PO q6hr
- Symptom-improvement only; unlike acetazolamide does not aid acclimatization
- Hyperbaric therapy
Prevention
- Graded ascent with adequate time for acclimatization is the best prevention
- Acetazolamide prophylaxis
- Indicated for patients with history of altitude illness or forced rapid ascent to altitude
- Start 125 mg PO BID 24hr before ascent and continue for the first 48hrs at peak altitude
- Can be restarted if illness develops
- Reduces symptoms of AMS by 75% in patients ascending rapidly to altitudes >8200ft
- Dexamethasone[4]
- Start day of ascent and continue for first 2 days at altitude
- 4mg PO q12hr
- Prevents and treats cerebral edema
- Combination acetazolamide and dexamethasone
- Small study showed combination of both (500mg SR daily of acetazolamide and 4 mg BID dexamethasone) was more effective at preventing AMS than acetazolamide alone for rapid ascent [5]
- Ginkgo biloba
- Controversial if effective; safe
- Ibuprofen
- Prevention - less effective than acetazolamide, better than placebo
- Treatment of headache (however, important to consider that taking ibuprofen may mask symptoms)
Disposition
- Most patients are treated symptomatically and managed as outpatients
- If other high altitude illnesses are considered, consider further work-up and/or observation
See Also
References
- ↑ Maggiorini M, Müller A, Hofstetter D, Bärtsch P, Oelz O. Assessment of acute mountain sickness by different score protocols in the Swiss Alps. Aviat Space Environ Med. 1998;69(12):1186-1192.
- ↑ Gallagher, MD, Scott A.; Hackett, MD, Peter (August 28, 2018). "High altitude pulmonary edema". UpToDate. Retrieved May 2, 2019.
- ↑ Luks A, McIntosh S, Grissom C, Auerbach P, Rodway G, Schoene R, Zafren K, Hackett P. Wilderness Medical Society Practice Guidelines for the Prevention and Treatment of Acute Altitude Illness: 2014 Update. Wilderness Environ Med. 2014; S4-S14.
- ↑ Luks AM, McIntosh SE, Grissom CK, et al. Wilderness Medical Society Practice Guidelines for the Prevention and Treatment of Acute Altitude Illness: 2014 Update. Wilderness & Environmental Medicine. 2014(25): S4–S14)
- ↑ Bernhard WN, Schalick LM, Delaney PA, Bernhard TM, Barnas GM. Acetazolamide plus low-dose dexamethasone is better than acetazolamide alone to ameliorate symptoms of acute mountain sickness. Aviat Space Environ Med. 1998;69(9):883-886.