Lake Louise Consensus on the Definition of Altitude Sickness

Frozen Lake

The Definition of Altitude Illness

The three main forms of altitude sickness are:

  • AMS = Acute Mountain Sickness
  • HACE = High Altitude Cerebral Edema
  • HAPE = High Altitude Pulmonary Edema

In 1991, an international symposium on hypoxia was held at Lake Louise in Alberta, Canada, and produced the following definitions for the diagnosis of altitude sickness. 


In the setting of a recent gain in altitude, the presence of headache and at least one of the following symptoms:

  • gastrointestinal (anorexia, nausea or vomiting)
  • fatigue or weakness
  • dizziness or lightheadedness
  • difficulty sleeping


Can be considered “end stage” or severe AMS. In the setting of a recent gain in altitude, either:

  • the presence of a change in mental status and/or ataxia in a person with AMS
  • or, the presence of both mental status changes and ataxia in a person without AMS


In the setting of a recent gain in altitude, the presence of the following:

Symptoms: at least two of:

  • dyspnea at rest
  • cough
  • weakness or decreased exercise performance
  • chest tightness or congestion

Signs: at least two of:

  • crackles or wheezing in at least one lung field
  • central cyanosis
  • tachypnea
  • tachycardia

Learn more in the YoWangdu Series on Altitude Sickness:

Reference for the information in the table: The Lake Louise Consensus on the Definition and Quantification of Altitude Illness in Sutton JR, Coates G, Houston CS (eds), Hypoxia and Mountain Medicine. Queen City Printers, Burlington, Vermont, 1992.

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Updated on February 11, 2020. First published on December 20, 2015.

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