• Acute Mountain Sickness (AMS), known also as attitude sickness, may occur when individuals rapidly ascend to elevations greater than 2500 metres (8202 feet) above sea level. Large and rapid increases in elevation are associated with increased incidence and severity of symptoms. Symptom onset typically occurs 6 to 12 hours after ascent.
• The incidence of AMS in Canada is limited by virtue of no Canadian highways or townsites exceeding the 2500m threshold. Lake Louise, Alberta, is the highest townsite at an elevation of 1600m; Highwood Pass is the highest mountain highway at an elevation of 2200m. However, it is possible for individuals recreating or working in the mountains of western Canada to encounter AMS as British Columbia’s tallest summit, Mt. Waddington, stands 4019m above sea level.
• AMS is characterized by headache accompanied by any of the following: nausea, vomiting, dizziness, fatigue or insomnia. The severity of symptoms may range from mild to incapacitating. AMS does not produce clinical signs, thus physical exam is expected to be unremarkable. Symptoms are expected to resolve with rest or descent to lower elevations.
• Critical diagnoses related to increased altitude include High-Altitude Cerebral Edema (HACE) and High-Altitude Pulmonary Edema (HAPE). Abnormal neurological exam with altered mental status, reduced level of consciousness, lassitude, truncal ataxia or mild fever should raise suspicion of HACE. Tachypnea, mild fever and excessively decreased arterial oxygen saturation should raise suspicion of HAPE.
• A differential for AMS should include carbon monoxide poisoning, dehydration, exhaustion, hypoglycemia, hyponatremia, and hypothermia.

For AMS patients presenting to the Emergency Department

• The most effective treatment for altitude-induced illnesses is descent to lower elevations. A patient with AMS who has already descended and is presenting in the emergency department can expect symptoms to resolve rapidly.

For AMS patients who remain at elevation

• For patients with mild to moderate AMS who remain at elevation, one rest day at altitude can be trialed. If a rest day does not resolve symptoms, or symptoms worsen, descending 500-1000m is recommended.
• Current guidelines consider dexamethasone the most effective treatment for AMS (8mg loading dose followed by 4mg doses every 6 hours). Ibuprofen has demonstrated effectiveness at relieving headaches associated with AMS. Acetazolamide (125-250mg/day) may also be considered.
• For severe AMS, dexamethasone, supplemental oxygen and portable hyperbaric bags are beneficial to stabilize patients until they can be brought to lower elevations. Patients with severe AMS should be treated with dexamethasone (8mg loading dose followed by 4mg doses every 6 hours) and given supplemental oxygen at a rate of 2-4 litres per minute.
• Portable hyperbaric bags require constant monitoring and may be challenging to use for vomiting or claustrophobic patients.

AMS is a self-limiting process that does not require hospital admission. If HACE or HAPE is suspected, the patient should be admitted for treatment.

AMS is self-limiting and does not require observation after descent below 2500m.

• Council the patient that a history of AMS is a risk factor for AMS in the future.
• Acclimatization immediately prior to climbing and limiting ascent to 500m per day will reduce the likelihood of recurrence of AMS.
• Prophylactic therapeutics to prevent AMS include:
  • Acetazolamide (125mg every 12 hours)
  • Dexamethasone (2mg every 6 hours or 4mg every 12 hours)
  • Ibuprofen (600mg every 8 hours)
• Acetazolamide is the preferred prophylactic therapeutic to prevent AMS, however, a trial of acetazolamide prior to ascent is necessary to assess whether it is well tolerated.

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2. Broome JR, Stoneham MD, Beeley JM, Milledge JS, Hughes AS. High Altitude Headache: Treatment with ibuprofen. Aviation, Space and Environmental Medicine 1994; 19-20.

   
   

3. Ferrazzini G, Maggiorini M, Kriemler S, Bartsch P, Oelz O. Successful treatment of acute mountain sickness with dexamethasone. Br Med J (Clin Res Ed) 1987;294:1380-1382.

   
   

4. Luks, AM, Auerbach PS, Freer L, Grissom CK, Keyes LE, McIntosh SE, Rodway GW, Schoene RB, Zafren K, Hackett PH. Wilderness Medical Society Clinical Practice Guidelines for the Prevention and Treatment of Acute Altitude Illness: 2019 Update. Wilderness & Environmental Medicine. 2019; 30(4S): S3-S18.