Classification and assessment of altitude illness

Hackett, 1992

Altitude illness presents as three clinical syndromes, which can occur alone or in combination:

acute mountain sickness (AMS) (the most common form of altitude illness)
high-altitude cerebral oedema (HACE)
high-altitude pulmonary oedema (HAPE).

Altitude illness syndromes describes each of these illnesses and the associated symptoms. Symptoms of any altitude illness can present at any time from 1 to 5 days following gain in altitude.

Table 1. Altitude illness syndromes
[NB1] [NB2]
Acute mountain sickness (AMS)
General information	Marked cerebral vasodilation and increased capillary fluid leakage. The most common altitude illness; mild AMS is a normal physiological response to altitude.
Clinical features and diagnosis [NB3]	Diagnosed clinically based on headache, plus at least one of the following: gastrointestinal symptoms (anorexia, nausea or vomiting) fatigue or weakness dizziness or lightheadedness.
High-altitude cerebral oedema (HACE)
General information	Marked cerebral vasodilation and increased capillary fluid leakage. Usually a progression from AMS, but can occur without warning or prior symptoms. Can be considered ‘end stage’ or severe AMS. Rare below 4000 metres, but should not be discounted at lower altitudesLuks, 2017. Medical emergency.
Clinical features and diagnosis [NB3]	Diagnosed clinically based on: mental status changes or ataxia (co-ordination difficulties) in a person with AMS mental status changes and ataxia in a person without AMS.
High-altitude pulmonary oedema (HAPE)
General information	Marked pulmonary vasoconstriction and capillary fluid leakage, causing accumulation of fluid in the lungs. About half of all cases develop without preceding symptoms of AMS, but HAPE can present at the same time as AMS or HACELuks, 2017. Medical emergency.
Clinical features and diagnosis [NB3]	Diagnosed clinically based on at least 2 of the following symptoms: dyspnoea at rest cough weakness or decreased exercise performance chest tightness or congestion PLUS at least 2 of the following signs: crackles or wheezing in at least one lung field central cyanosis tachypnoea tachycardia. Signs of advanced HAPE are worsening cough and dyspnoea, followed by orthopnoea and frothy sputum (sometimes blood-stained).
Note: NB1: These definitions were adopted at the 1991 International Hypoxia Symposium, held at Lake Louise in Alberta, CanadaHackett, 1992. The definition of AMS was revised in 2018 to exclude the symptom of difficulty sleepingRoach, 2018. NB2: Symptoms can present at any time from 1 to 5 days following ascent. NB3: Features are assumed to have occurred in the setting of a recent gain in altitude.

The self-reported Lake Louise Score (see Lake Louise Score for acute mountain sickness (AMS) in adults (2018)) can estimate the severity of symptoms of acute mountain sickness (AMS) in adults, noting that headache must be present to fulfil these diagnostic criteria. The severity of AMS is graded as:

mild: score of 3 to 5
moderate: score of 6 to 9
severe: score of 10 to 12Roach, 2018.

The Lake Louise Score is most useful for serial measurements to determine the response to therapeutic interventions (rather than an absolute score). An increasing or constant score despite treatment signals progression towards high-altitude cerebral oedema.

Table 2. Lake Louise Score for acute mountain sickness (AMS) in adults (2018)
Printable table

[NB1][NB2]
Headache (this is the cardinal symptom)
None (excludes diagnosis of AMS using this score) [NB3]) Mild headache Moderate headache Severe headache that is incapacitating	0 1 2 3
Gastrointestinal symptoms
Good appetite Poor appetite or nausea Moderate nausea or vomiting Severe nausea and vomiting that is incapacitating	0 1 2 3
Fatigue and/or weakness
Not tired or weak Mild fatigue/weakness Moderate fatigue/weakness Severe fatigue/weakness that is incapacitating	0 1 2 3
Dizziness/light-headedness
No dizziness/light-headedness Mild dizziness/ light-headedness Moderate dizziness/light-headedness Severe dizziness/light-headedness that is incapacitating	0 1 2 3
Total symptom score [NB3]
Mild acute mountain sickness = 3 to 5 Moderate acute mountain sickness = 6 to 9 Severe acute mountain sickness = 10 to 12
Note: AMS= acute mountain sickness NB1: This scoring system was developed for use in research, but many now use it as a guide in clinical settings. Do not measure the score earlier than 6 hours after gain in altitude (earlier measures may reflect symptoms from travel or acute hypoxia). NB2: Serial scores are important in assessing whether the trend is deteriorating. NB3: Headache (together with at least one other symptom) is required to meet these diagnostic criteria for AMSLuks, 2017. Source: Adapted from Roach RC, Hackett PH, Oelz O, et al. The 2018 Lake Louise Acute Mountain Sickness Score High Altitude Medicine and Biology. Mar 2018.4-6. This is an open access article distributed under the terms of the Creative Commons Attribution Noncommercial 4.0 International License (CC BY).