Acute Mountain Sickness – Treatment
Environmental Injuries / Exposures
- 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.
Criteria For Hospital Admission
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.
Criteria For Close Observation And/or Consult
AMS is self-limiting and does not require observation after descent below 2500m.
Criteria For Safe Discharge Home
- 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.
Quality Of Evidence?
We are highly confident that the true effect lies close to that of the estimate of the effect. There is a wide range of studies included in the analyses with no major limitations, there is little variation between studies, and the summary estimate has a narrow confidence interval.
We consider that the true effect is likely to be close to the estimate of the effect, but there is a possibility that it is substantially different. There are only a few studies and some have limitations but not major flaws, there are some variations between studies, or the confidence interval of the summary estimate is wide.
When the true effect may be substantially different from the estimate of the effect. The studies have major flaws, there is important variations between studies, of the confidence interval of the summary estimate is very wide.
Descent to lower elevation for the treatment of AMS is regarded as the most effective treatment for AMS in current Wilderness Medicine Society guidelines.
Supplemental oxygen for the treatment of AMS is strongly recommended with high quality evidence (randomized controlled trials and observational studies) in current Wilderness Medicine Society guidelines.
Dexamethasone for treatment of AMS is strongly recommended with moderate quality evidence (observational studies and two double-blind randomized controlled trails with placebo groups) in current Wilderness Medicine Society guidelines.
Body-length hyperbaric bag treatment of AMS is strongly recommended with moderate quality evidence in current Wilderness Medicine Society guidelines.
Acetazolamide for treatment of AMS is strongly recommended with low quality evidence (a single randomized controlled trial limited to 12 participants) in current Wilderness Medicine Society guidelines.
Ibuprofen for the treatment of AMS-headache is strongly recommended with low quality evidence (a single double-blind randomized controlled trial with placebo group) in current Wilderness Medicine Society guidelines.
Bärtsch P and Swenson ER. Acute High-Altitude Illnesses. N Engl J Med 2013; 368:2294-2302.
Broome JR, Stoneham MD, Beeley JM, Milledge JS, Hughes AS. High Altitude Headache: Treatment with ibuprofen. Aviation, Space and Environmental Medicine 1994; 19-20.
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.
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.
The purpose of this document is to provide health care professionals with key facts and recommendations for the diagnosis and treatment of patients in the emergency department. This summary was produced by Emergency Care BC (formerly the BC Emergency Medicine Network) and uses the best available knowledge at the time of publication. However, healthcare professionals should continue to use their own judgment and take into consideration context, resources and other relevant factors. Emergency Care BC is not liable for any damages, claims, liabilities, costs or obligations arising from the use of this document including loss or damages arising from any claims made by a third party. Emergency Care BC also assumes no responsibility or liability for changes made to this document without its consent.
Last Updated Mar 10, 2021
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