The recent reports by the media on 2 Singaporeans – 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. This article hopes to put in perspective the condition of high altitude sickness and information with regards to the prevention of altitude sickness as well as the look-out for the development of altitude sickness because if diagnosed early will not lead to life-threatening situations.

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 :

1. 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 :
2. High Altitude Cerebral Edema (HACE)
3. High Altitude Pulmonary Edema (HAPE)

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

1. Lungs (respiratory)
2. Heart (cardiovascular)
3. Brain (neuro-endocrine)
4. Kidneys (renal)

2. How can a person get altitude sickness?

Altitude sickness occurs in the following settings :

1. 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% 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.
2. 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.
3. 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% depending on the individual susceptibility. (See figure 1).

Figure 1. Neurological consequences of increasing altitude : The Relation among altitude (classified as high [1500-3500m], very high [3500-5500m] and extreme [>5500 m]), the partial pressure of oxygen and the neurological consequences of acute and gradual exposure to these pressure chnges. Neurological consequences will vary greatly from person to person and with rate of ascent. HACE is far more common at higher altitudes, although there are case reports of HACE at 2500m. PO2 partial pressure of oxygen, FTT – finger-tapping test. Ref : Acute Mountain Sickness : Pathophysiology, Prevention and Treatment. Chris Imray et al. Progress in Cardiovascular Disease 2010;52:467-484
iv.

1. 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 :
   1. The rate of ascent
   2. The altitude reached/obtained
   3. The length of time spent at altitude
   4. Degree of physical exertion
   5. 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)

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% 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) especially 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.

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

1. First and most common and reversible is Acute Mountain Sickness (AMS). This condition is characterized by :
   1. Headaches, initially quite incapacitating (also called high altitude headaches [HAH]).
   2. Inability to sleep (insomnia) and poor sleep
   3. Fatigue and increased lassitude.
   4. Dizziness/light-headedness
   5. Poor appetite (anorexia)
   6. Nausea/vomiting
   7. Pins and needles
   8. Nose bleed
   9. Persistent rapid pulse
   10. Swelling of legs
   11. 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 1):

1. Recent ascent in altitude
2. Have a headache and
3. Have a total symptom score above 3

Table 1.  Lake Louise self-assessment scoring system.  Ref : Acute Mountain Sickness : Pathophysiology, Prevention and Treatment.  Chris Imray et al.  Progress in Cardiovascular Disease 2010;52:467-484

High Altitude Cerebral Edema (HACE)

1. Altered mental state
2. Gait disturbances (ataxia)
   • Inability to walk heel to toe in a straight line and maintain balance
3. Drowsiness leading to coma

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

High Altitude Pulmonary Edema (HAPE)

1. Palpitations
2. Increasing shortness of breath (acute breathlessness)
3. Initially dry cough then followed by cough with frothy and blood-stained sputum

4. What should people do if they suspect that they are experiencing altitude sickness?

• Stop ascent/rest
• Descend 300 – 500 metres
• Oxygen supplementation ( 1 – 2 litres/min)
• Consider portable hyperbaric chamber (193 m bar/hr)
• Medications :
  1. Paracetamol 1gm 6-hourly (for headaches)
  2. Ibuprofen 400 mg 8-hourly
  3. Acetazolamide 125 – 250 mg 2 times daily (Acetazolamide is a respiratory stimulant at altitude and improves oxygenation. It causes diuresis (increase urine output) and increases arterial partial pressure of oxygen.
     Dose : 125 – 250 mg oral 12-hourly 24 hours before ascent (prophylaxis) and continue for 2 days after reaching the highest point. Acute treatment of AMS – 250 mg 12-hourly.
  4. Dexamethasone : 8 mg stat (AMS)
     4 mg 6-hourly (oral, intramuscular or intravenous injection) (HACE)

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

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

Altitude acclimatization is the process of adjusting to decreasing oxygen levels at higher elevations, in order to avoid altitude sickness. Once above approximately 3,000 metres (10,000 feet = 70 kPa), most climbers and high-altitude trekkers take the “climb-high, sleep-low” approach.  For high-altitude climbers, a typical acclimatization regimen might be to stay a few days at a base camp,  climb up to a higher camp (slowly), and then return to base camp. A subsequent climb to the higher camp then includes an overnight stay. This process is then repeated a few times, each time extending the time spent at higher altitudes to let the body adjust to the oxygen level there, a process that involves the production of additional red blood cells.  Once the climber has acclimatised to a given altitude, the process is repeated with camps placed at progressively higher elevations. The general rule of thumb is to not ascend more than 300 metres (1,000 ft) per day to sleep. That is, one can climb from 3,000 (10,000 feet = 70 kPa) to 4,500 metres (15,000 feet = 58 kPa) in one day, but one should then descend back to 3,300 metres (11,000 feet = 67.5 kPa) to sleep. This process cannot safely be rushed, and this is why climbers need to spend days (or even weeks at times) acclimatising before attempting to climb a high peak.  Ref : http://en.wikipedia.org/wiki/Altitude_sickness

The process of acclimatization involves a series of adjustments by the body to meet the changes of hypoxemia.  Table 2 summarises the recommendations for travel to high altitudes.

Ref :  High Altitude by Andrew F Gaffney.  Cardiac Responses to Environmental Stress

There are also several medical conditions that are absolutely contraindicated for high altitude exposure.  See table 3.

Ref : High-Altitude Exposure in Patients with Cardiovascular Disease : Risk Assessment and Practical Recommendations.  Stefano F Rimoldi et al.  Progress in Cardiovascular Disease 2010;52:512-524