Altitude Illness
Tenzing Norgay on the summit of Mount Everest, 11.30 a.m, May 29, 1953. Photo: Edmund Hillary. On 29 May 1953 at the age of 33, New Zealander Edmond Hillary and Nepalese Sherpa, Tenzing Norgay, became the first human beings known to have reached the summit of the world’s tallest mountain, Mount Everest.
“They must be getting to camp VI”, the watchers said. “They are hidden behind that serac (ice pinnacle) with the vertical crack in it – you know the one. “Two of them are sitting down; now they are up again”. “Only another hour to wait. What are the odds?” At last, soon after 1.30, just as the radio was announcing the reported failure of the assault, the party emerged above a rise in the ground 300 yards or so above the camp, their blue windproof jackets sharp and cheerful against the glistening snow. Hillary and Tenzing were leading. All at once it was through the camp by the magic wireless of excitement that Everest had been climbed”
James Morris,
Times Correspondent with the Hillary Everest Expedition, May 1953.
“I had carried my camera, loaded with colour film, inside my shirt to keep it warm, so I now produced it and got Tenzing to pose for me on the top, waving his ice-axe on which was a string of flags - British, Nepalese, United Nations, and Indian. Then I turned my attention to the great stretch of country lying below us.”
Sir Edmond Hillary
Edmond Hillary and Tenzing Norgay, on Mount Everest, May 1953
Altitude Illness
Introduction
The stresses of high-altitude environments include:
●Hypoxia, (by far the most important)
●Reduced ambient pressures
●Hypothermia
●Reduced humidity
●Increased ultraviolet (UV) radiation
Prevention strategies are important
The most important high altitude illness includes:
●Acute mountain sickness (AMS)
●High-altitude cerebral edema (HACE)
●High-altitude pulmonary edema (HAPE)
HAPE and HACE are both life threatening medical emergencies.
Definitive treatment of serious high altitude illness involves descent.
Pathophysiology
Altitude illness can occur on exposure to elevations greater than 3000 meters.1
(By comparison, commercial airliners fly with a cabin pressure equal to 2500 metres).
Theseverity of altitude illness will be related to:
1.Inherent susceptibility of the individual
●Genetic traits
●Pre-existing co-morbidities, (cardiovascular disease).
2.The rate of ascent
3.The maximum height achieved.
4.Duration of exposure
Hypoxia at altitude
The hypoxia experienced at high altitude leads to:
●Cerebral vasodilatation
●Cerebral oedema
●Hypoxic pulmonary vasoconstriction and pulmonary oedema.
At 3,000 meters, (10,000 feet) for example, the inspired PO2 is only 69% of the sea-level value.
Sleeping at high altitude produces the greatest hypoxia; day trips to high altitude with return to low altitude are much less stressful on the body.
Risk factors for high altitude illness2
Inadequate acclimatization may lead to altitude illness in any traveler going to 8,000 ft (2,500 m) or higher.
Susceptibility and resistance to altitude illness are related to:
1.Genetic traits, (no screening tests are available to predict risk).
2.Risk is not affected directly by training or physical fitness.
3.Children are equally susceptible as adults
4.Persons greater than 50 years of age, surprisingly, have slightly lower risk
5.How a traveler has responded to high altitude previously is the most reliable guide for future trips but is not infallible. However, given certain baseline susceptibility, risk is greatly influenced by rate of ascent and exertion.
Clinical features
There are three important clinical syndromes that are associated with altitude illness:
1.Acute mountain sickness (AMS)
2.High-altitude cerebral edema (HACE)
3.High-altitude pulmonary edema (HAPE)
High altitude cerebral oedema is usually preceded by unrecognized or undertreated acute mountain sickness, while high altitude pulmonary oedema may occur independently or with the other syndromes.
Acute mountain sickness (AMS)
AMS is the most common form of altitude illness, affecting for example, 25% of all visitors sleeping above 2,500 meters (8000 feet) in the Colorado Mountains.
The predominant clinical features of AMS include:
1.Headache
2.Nausea
3.Lassitude
AMS generally develops6 to 24 hours after ascent to altitude
High-altitude cerebral edema (HACE)
Similarinitial symptoms to acute mountain sickness, but rapidly progress to:
1.Severe headache
2.Vomiting
3.Changes in mental state
●Acute delirium
3.Ataxia
●This can be prominent.
Death from HACE can ensue within 24 hours of developing ataxia if the person fails to descend.2
High-altitude pulmonary edema (HAPE)
Typically HAPE develops on the second or third day after ascent.
Clinical features of HAPE include:
1.Initial dry cough.
2.Followed by increasingly severe dyspnoea:
With signs of increasing respiratory distress:
●Tachycardia
●Tachypnea
●Increased ventilatory effort, (tracheal tug, intercostal recession)
3.Frothy type sputum production.
4.Frank acute non-cardiogenic pulmonary oedema.
●Lung crepitations
●Cyanosis
●Altered conscious state
●Diaphoresis
●Exhaustion
HAPE can be even more rapidly fatal than HACE.
Investigations
Investigation is obviously not immediately possible in most high altitude illness situations.
Once the patient has been stabilized and in a medical facility, investigations to consider will then include:
Blood tests
1.FBE
2.U&Es/ glucose
3.Cardiac enzymes
4.AGBs
ECG
This is routine for any seriously ill patient, but especially in those who have pre-existing cardiovascular disease.
CXR
In those suspected of having HACE
There will be typical bilateral alveolar infiltrates.
CT Scan
This should be done in any case of an altered conscious state when the diagnosis is unclear.
Confused patients with presumed HACE whose symptoms resolve with treatment, will not require a CT, but if symptoms fail to completely resolve a CT will be needed.
MRI Scan
MRI will be needed in those whose symptoms of HACE have not resolved with treatment and where a cerebral CT scan has not provided a clear diagnosis.
MRI is better able than CT scan to show evidence of hypoxic brain injury.
Management
Prevention
Prevention is a vital strategy for any one ascending to high altitude.
The main point of instructing travelers about altitude illness is not to prevent any possibility of altitude illness, but to prevent death from altitude illness.
The onset of symptoms and clinical course is usually sufficiently slow and predictable that there is little reason for someone to die from altitude illness unless trapped by weather or geography in a situation in which descent is impossible.
The three rules that travelers should be made aware of to prevent death from altitude illness are: 2
●Know the early symptoms of altitude illness and be willing to acknowledge when they are present.
●Never ascend to sleep at a higher altitude when experiencing symptoms of altitude illness, no matter how minor they seem.
●Descend if the symptoms become worse while resting at the same altitude
The best preventive strategies for altitude illness are acclimatization and drug therapy.
Acclimatization
Gradual ascent to allow for physiological acclimatisation:
●Sleeping no more than 500 meters higher per day. 1
The human body adjusts very well to moderate hypoxia, but requires time to do so (for strategies see below).
The process of acute acclimatization to high altitude takes 3–5 days; therefore, acclimatizing for a few days at 8,000–9,000 ft before proceeding to higher altitude is ideal.
Acclimatization prevents altitude illness, improves sleep, and increases comfort and well-being, although exercise performance will always be reduced compared with low altitude.
Increase in ventilation is the most important factor in acute acclimatization; therefore, respiratory depressants must be avoided.
Increased red-cell production does not play a role in acute acclimatization.
The following are useful general tips recommended by the CDC for people traveling to high altitude destinations.
●Ascend gradually, if possible.
●Try not to go directly from low altitude to >9,000 ft (2,750 m) sleeping altitude in one day.
●Avoid alcohol for the first 48 hours.
●Participate in only mild exercise for the first 48 hours.
●Having a high-altitude exposure at >9,000 ft (2,750 m), for 2 nights or more within 30 days prior to the trip is useful.
●Treat an altitude headache with simple analgesics
Preventive drug therapies
Drug therapies are effective in the prevention of altitude illness in susceptible individuals.
The best evidence is for acetazolamide and dexamethasone in preventing acute mountain sickness andhigh altitude cerebral oedema.
Acetazolamide:
●Acetazolamide 125 mg orally, twice daily commencing on the day of ascent and usually continuing until acclimatisation occurs (approximately 3 days)1
Dexamethasone:
●Dexamethasone 4 mg orally, 3 times daily commencing at the time of ascent and usually continuing until acclimatisation occurs (approximately 3 days).1
Nifedipine:
●Nifedipine prevents and ameliorates HAPE in persons who are particularly susceptible to the condition. The adult dosage is 20 mg of extended release every 8–12 hours.2
See also latest edition of Emergency Medicine Therapeutic Guidelines for further prescribing details.
Specific treatments
Once any of the syndromes of high altitude illness are recognized, ascent should be immediately halted.
In cases of high altitude cerebral oedema and high altitude pulmonary oedema, immediate descent, if possible, is the highest priority.
Acute mountain sickness (AMS)
1.Halt the ascent
2.Rest and gradual ascent, once symptoms settle, is appropriate for acute mountain sickness.
3.Dexamethasone:
For adults with severe acute mountain sickness (optimal dosing for children in this situation is unknown), use:
●Dexamethasone 8 mg IV or orally initially, then 4 mg every 6 hours. 1
High-altitude cerebral edema (HACE)
1.Halt the ascent
2.Immediate descent, if possible
3.Oxygen therapy:
●Temporary recovery for high altitude cerebral oedema and high altitude pulmonary oedema victims prior to evacuation can be achieved with the use of a portable hyperbaric chamber, which may be carried by larger parties. 1
●If oxygen is available, it can be given by nasal prongs at 2 to 3L/minute. 1
4.Dexamethasone:
For adults with high altitude cerebral oedema (optimal dosing for children in this situation is unknown), use:
●Dexamethasone 8 mg IV or orally initially, then 4 mg every 6 hours. 1
5.Further measures:
Once in a medical facility further measures may be required for the very ill:
●Mannitol
●Intubation and mechanical ventilation
High-altitude pulmonary edema (HAPE)
1.Halt the ascent
2.Immediate descent, if possible
3.Oxygen therapy:
●Temporary recovery for high altitude cerebral oedema and high altitude pulmonary oedema victims prior to evacuation can be achieved with the use of a portable hyperbaric chamber, which may be carried by larger parties. 1
●If oxygen is available, it can be given by nasal prongs at 2 to 3L/minute. 1
4.Nifedipine:
For adults with high altitude pulmonary oedema (optimal dosing for children in this situation is unknown), use:
●Nifedipine (immediate-release) 10 to 20 mg orally, every 6 hours. 1
5.Further measures:
Once in a medical facility further measures may be required for the very ill:
●Non-invasive ventilation
●Intubation and mechanical ventilation.
Appendix 1
Tallest Mountains in the World
Table of the 10 tallest mountains in the world:
Rank / Mountain / Height in meters and feet / Country1 / Mount Everest / 8,850m / 29,035 ft / Nepal
2 / Qogir (K2) / 8,611m / 28,250 ft / Pakistan
3 / Kangchenjunga / 8,586m / 28,169 ft / Nepal
4 / Lhotse / 8,501m / 27,920 ft / Nepal
5 / Makalu I / 8,462m / 27,765 ft / Nepal
6 / Cho Oyu / 8,201m / 26,906 ft / Nepal
7 / Dhaulagiri / 8,167m / 26,794 ft / Nepal
8 / Manaslu I / 8,156m / 26,758 ft / Nepal
9 / Nanga Parbat / 8,125m / 26,658 ft / Pakistan
10 / Annapurna I / 8,091m / 26,545 ft / Nepal
Highest Mountains by geographic location:
Highest Mountain in the Asia (and the world)
Everest, Nepal-China: 8850 meters (29,035 feet)
Highest Mountain in Africa
Kilimanjaro, Tanzania: 5895 meters (19,340 feet).
Highest Mountain in Antarctica
Vinson Massif: 4897 meters (16,066 feet).
Highest Mountain in Australia
Kosciusko: 2228 meters (7310 feet).
Highest Mountain in Eastern Europe
Elbrus, Russia (Caucasus): 5642 meters (18,510 feet).
Highest Mountain in Western Europe
Mont Blanc, France-Italy: 4807 meters (15,771 feet)
Highest Mountain in Oceania
Puncak Jaya, New Guinea: 5040 meters (16,535 feet)
Highest Mountain in North America
McKinley (Denali), Alaska: 6194 meters (20,320 feet)
Highest Mountain in the 48 Contiguous United States
Whitney, California: 4418 meters (14,494 feet).
Highest Mountain in South America
Aconcagua, Argentina: 6960 meters (22,834 feet)
Mount Everest
References
1.Emergency Medicine Therapeutic Guidelines 1st ed 2008
2.Peter H. Hackett, David R. Shlim: Altitude Illness, CDC Yellow Book, July 2009
Dr J. Hayes
April 2010