View source for Acute mountain 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==


*Lake Louise Consensus Definition <ref>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.</ref>
**An Individual is at or above 2500 m (~8000 ft) above sea level ''and''
**A [[headache]] is present ''and'':
**An Individual has any one of the following:
***GI Symptoms ([[nausea]], [[vomiting]], anorexia)
***Sleep symptoms ([[insomnia]], difficulty sleeping)
***[[Dizziness]] and/or lightheadedness 
*[[Ataxia]] and [[confusion]] heralds onset of [[headache]]

===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 DDX}}

==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 at altitude}}

==Management==
[[File:Altitude flow sheet.png|thumb|High altitude management algorithm.]]
===Mild===
*Terminate ascent and/or descend <ref> 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.</ref>
**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 
*Portable hyperbaric chamber
**Useful in conditions which do not allow descent (ie blizzard, avalanche)
**Simulate descent to 3000-8000ft


==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]]<ref>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)</ref>
**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 <ref>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.</ref>
*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)


==Medication Dosing==
{{MedicationDose
| drug = Acetazolamide
| dose = 125-250mg BID
| route = PO
| context = Mild AMS; speeds acclimatization via bicarb diuresis
| indication = Acute mountain sickness
| population = Adult
| notes = Continue until symptoms resolve; caution in sulfa allergy
}}
{{MedicationDose
| drug = Acetazolamide
| dose = 250mg BID
| route = PO
| context = Moderate-severe AMS
| indication = Acute mountain sickness
| population = Adult
}}
{{MedicationDose
| drug = Dexamethasone
| dose = 4mg q6hr
| route = PO
| context = Moderate-severe AMS; symptomatic relief only, does not aid acclimatization
| indication = Acute mountain sickness
| population = Adult
}}

==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==
*[[High Altitude Medicine]]

==References==
<References/>

[[Category:Environmental]]