Health guide on altitude sickness prevention

The recent reports by the media on two Singaporeans - a 66-year-old man and a 61-year-old woman who died of altitude sickness at Mt Kailash - have generated tremendous interest and awareness of this condition.

This is important as there are more people taking adventurous tours such as scaling or trekking high mountains.

If diagnosed early, altitude sickness will not lead to life-threatening situations

This article hopes to put in perspective the condition of high altitude sickness, as well as information on the prevention of altitude sickness and how to look out for its onset.

1. What is altitude sickness and which parts of the body does it affect?

Altitude sickness is also known in the medical world as High Altitude Sickness/Illness.

This is the result of a series of pathophysiologic responses (maladaptation) in the human body that is triggered off by the acute exposure to high altitude atmosphere comprising of ambient hypoxia (lack of oxygen due to low partial pressure of oxygen at high altitudes), low air density and low air flow resistance.

High altitude sickness consists of 3 distinct conditions of maladaptation of the human body to high altitude exposure. They are :

i. Acute mountain sickness (AMS) - the earliest, most common and often benign presentation of high altitude sickness.

If not recognized, diagnosed and treated early will lead to the more serious and potentially life-threatening conditions including :

ii. High Altitude Cerebral Edema (HACE)

iii. High Altitude Pulmonary Edema (HAPE)

The main organs of the body that are involved in high altitude sickness are the following:

i. Lungs (respiratory)
ii. Heart (cardiovascular)
iii. Brain (neuro-endocrine)
iv. Kidneys (renal)

2) How can a person get altitude sickness?

i. As the altitude increases, the barometric pressures fall.

A fall in the barometric pressure causes a corresponding drop in the partial pressure of the oxygen (usually 21 per cent of the barometric pressure) resulting in a condition called hypobaric hypoxia i.e. lack of oxygen in the air.

The lack of oxygen at high altitude triggers a series of physiological response that affects the organs of the body including the lungs, heart, brain and the kidneys.

ii. The decreased partial pressure of oxygen affects the entire oxygen transport system in the body including ventilation, lung-gas exchange, cardiac output and tissue-oxygen uptake and utilization.

These changes begin within minutes of exposure to high altitude and require several days for both ventilatory and metabolic compensation.

iii. To understand further the degree and severity of altitude sickness, a classification of the degree of altitude is required:

- High altitude = 1500 to 3500 metres
- Very high altitude = 3500 to 5500 metres 
- Extreme altitude ≥ 5500 metres

Most people can ascend to 2,400 metres without difficulty. Altitude sickness (acute mountain sickness) usually occurs above 2500 metres (8200 feet).

At this level, the mountain sickness incidence ranges between 50 to 65 per cent depending on the individual susceptibility.

iv. Altitude sickness is likely to occur with higher altitudes, more rapid ascents, greater exertion levels on reaching the altitude and a history of mountain sickness.

Hence the extent of the acute mountain sickness as well as the prevalence and severity is dependent on several major factors which include:

a. The rate of ascent
b. The altitude reached/obtained
c. The length of time spent at altitude
d. Degree of physical exertion
e. Individual physiological susceptibility when the ascent to higher altitude outpaces the ability to acclimatise (most people ascending very rapidly to high altitude will get AMS)

3. Does it affect everybody or just people who have certain conditions or within a certain age group?

Altitude sickness can affect both the young and elderly, the healthy and those with underlying medical conditions. The following categories of people are more prone to altitude sickness :

High altitude illness especially AMS can affect up to 25 per cent of otherwise healthy individuals especially ascending to ≥ 2500 metres (8200 feet) above sea levels.

The elderly men and women between the ages of 59 to 83 years may be prone to AMS with potential risks of developing HAPE and HACE above 2500 metres (8200 feet).

This is especially so if they have associated coronary heart disease, high blood pressure or underlying chronic lung disease (due to chronic smoking, history of asthma or chronic bronchitis or lung infection).

A study showed that up to 2/3 of elderly men and women may have (at least) 1 of the above conditions.

In addition women and obese people are also susceptible to altitude sickness.

Interestingly young people are somewhat more predisposed to the development of AMS especially when they scale high altitudes with more rapid ascent and have greater exertional levels on reaching the altitude as they are fit and are able to perform greater physical activities upon reaching the altitude.

Newcomers to high altitudes are often surprised that sea level aerobic fitness is not protective for altitude sickness. They also feel that there is less need for acclimatisation.

4) What are the symptoms of altitude sickness? Altitude sickness comprise of 3 different syndromes:

i. First and most common and reversible is Acute Mountain Sickness (AMS) . This condition is characterized by:

a) Headaches, initially quite incapacitating (also called high altitude headaches [HAH]) 
b) Inability to sleep (insomnia) and poor sleep
c) Fatigue and increased lassitude.
d) Dizziness/light-headedness
e) Poor appetite (anorexia)
f) Nausea/vomiting
g) Pins and needles
h) Nose bleed
i) Persistent rapid pulse
j) Swelling of legs
k) Retinal hemorrhage (bleeding)

The best way for an individual to assess for AMS is by the Lake Louise Self-assessment Scoring System when the individual fulfill the following criteria (See table below, published in Acute Mountain Sickness : Pathophysiology, Prevention and Treatment.):

a) Recent ascent in altitude
b) Have a headache and
c) Have a total symptom score above 3




1) Headache :


No headache


Mild headache


Moderate headache


Severe, incapacitating


2) GI symptoms


No GI symptoms


Poor appetite or nausea


Moderate nausea or vomiting


Severe nausea and vomiting incapacitating


3) Fatigue / weak :


Not tired or weak


Mild fatigue / weakness


Moderate fatigue / weakness


Severe fatigue / weakness, incapacitating


4) Dizzy / lightheadedness :


Not dizzy


Mild dizziness


Moderate dizziness


Severe, incapacitating


5) Difficulty in sleeping :


Slept well as usual


Did not sleep as well as usual


Woke many times, poor night’s sleep


Could not sleep at all


Total symptom score :






6) Change in mental status :


No change


Lethargy / lassitude


Disoriented / confused


Stupor / semiconsciousness


7) Ataxia (heel to toe walking) :


No ataxia


Maneuvers to maintain balance


Steps off line


Falls down


Can’t stand


8) Peripheral edema :


No edema


One location


Two or more locations


Clinical assessment score :





ii. High Altitude Cerebral Edema (HACE)

High Altitude Cerebral Edema (HACE) symptoms include:

i. Altered mental state 
ii. Gait disturbances (ataxia) - Inability to walk heel to toe in a straight line and maintain balance
iii. Drowsiness leading to coma

Coma may occur rapidly within the 24 hours after onset of mental changes and gait disturbances

iii. High Altitude Pulmonary Edema (HAPE)

High Altitude Pulmonary Edema (HAPE) consists of

i. Palpitations 
ii. Increasing shortness of breath (acute breathlessness) 
iii. Initially dry cough then followed by cough with frothy and blood-stained sputum

5) How can it be avoided if you are going to a place with a high altitude?

Altitude acclimatisation is the key and only way to avoid AMS, HACE and HAPE.

This basically involves allowing your body to adjust to the decreasing oxygen levels at higher altitudes.

The human body is very adaptable. With enough time, the body can get used to the decrease in oxygen molecules at a specific altitude.

Experienced climbers usually take the "climb-high, sleep-low" approach, where they set up a base camp at a safe altitude, and move up to a higher altitude slowly, then down again.

This allows their bodies to get used to the reduced oxygen content of the air and is undertaken when climbers reach approximately 3,000 metres (10,000 feet = 70 kPa).

Higher camps are set up, and the climber then ascends to the next higher camp for an overnight stay.

This process is repeated a few times, with progressively higher camps once he or she acclimatises. Each session spent at higher altitudes is extended.

The general rule of thumb is to not to sleep in an altitude more than 300 metres higher than the starting point. For example, a climber at 3,000 metres altitude can ascend to 4,500 metres in a day. However, he or she should then return to 3,300 metres for the overnight stay.

The whole process results in the additional production of red blood cells.

Acclimatisation may be slow and tedious, often lasting days or even weeks, but climbers must not try to rush the process, as it is dangerous.

Summary of recommendations

• Begin below 3000 metres if transported to altitude ( i.e. avoid direct transportation to an altitude > 3000 metres)
• Avoid exertion for the first 24 hours
• Avoid alcohol consumption for the first 1-2 days
• At very high altitudes, maintain ascent rate below 300 m/day
• "Climb high, sleep low" (ascent at a slow rate 1500-200 metres but increase sleep altitude by < 300m/day)
• Begin acetazolamide 250 mg a12h or q8h, at least the day before ascent and continue it for 3 -4 days at altitude
• Avoid sedatives
• Seek medical attention immediately if symptoms of HAPE, HACE or retinal hemorrhage occur; delay in descent may be fatal

Information above attributed to High Altitude by Andrew F Gaffney. Cardiac Responses to Environmental Stress

DO NOT expose yourself to high altitudes if you have:

• Unstable clinical condition, i.e.
- Unstable angina
- Symptoms or signs of ischemia during exercise testing at low to moderate workload (< 80 W or <5 metabolic equivalents)
- Decompensated heart failure
- Uncontrolled atrial or ventricular arrhythmia

• Myocardial infarction and/or coronary revascularization in the past 3 - 6 months
• Decompensated heart failure during the past 3 months
• Poorly controlled arterial hypertension (blood pressure ≥ 160/100 mmHg at rest, > 220 mmHg systolic blood pressure during exercise)
• Marked pulmonary hypertension (mean pulmonary artery pressure > 30 mmhg, RV-RA gradient > 40 mmHg) and/or any pulmonary hypertension associated with functional class ≥ II and/or presence of markers of poor prognosis
• Severe valvular heart disease, even if asymptomatic
• Thromboembolic event during the past 3 months
• Cyanotic or severe acyanotic congenital heart disease
• ICD implantation or ICD intervention for ventricular arrhythmias in the past 3 - 6 months
• Stroke, transient ischemic attack or cerebral hemorrhage during the past 3 - 6 months

Information above attributed to High-Altitude Exposure in Patients with Cardiovascular Disease : Risk Assessment and Practical Recommendations.

Dr Peter Yan This article was contributed by Dr Peter Yan, Medical Director of Parkway Heart and Vascular Centre, and Consultant Cardiologist at Gleneagles, Mt Elizabeth and Mt E Novena Hospitals.