Altitude sickness overview
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]
Overview
Every year, thousands of trekkers, skiers, climbers, security forces, rescuers, and others ascend to high altitudes with little or no time for acclimatization. The unacclimatized traveler ascending at such high rate are at risk for developing high altitude illness. Altitude sickness, also known as acute mountain sickness (AMS) or altitude illness is a pathological condition that is caused by acute exposure to low air pressure (usually outdoors on high altitudes). It commonly occurs above 2,400 metres (approximately 8,000 feet)[1]. Acute mountain sickness can progress to high altitude pulmonary edema (HAPE) or high altitude cerebral edema (HACE).[2] Altitude sickness does not typically affect persons traveling in aircraft, as the cabins of modern airplanes are pressurized. Another rarer type of altitude sickness caused by prolonged exposure to high altitude is chronic mountain sickness (CMS), also known as Monge's disease. It may develop after many years of living at high altitude. In medicine, high altitude is defined as over 2500 metres, but most cases of CMS occur at over 3000 m. HAFE or High Altitude Flatus Expulsion is a gastrointestinal syndrome which involves the spontaneous passage of increased quantities of rectal gases at high altitudes.[3]
High altitude pulmonary edema (HAPE) and High altitude cerebral edema (HACE) are the most ominous of these symptoms, while acute mountain sickness, retinal haemorrhages, and peripheral edema are the less severe forms of the disease. The rate of ascent, the altitude attained, the amount of physical activity at high altitude, as well as individual susceptibility, are contributing factors to the incidence and severity of high-altitude illness. HAPE is a life-threatening form of non-cardiogenic pulmonary edema that occurs in otherwise healthy mountaineers at altitudes above Template:M to ft. Some cases have however been reported also at lower altitudes (between 1500 and 2500 m in highly vulnerable subjects), although what makes some people susceptible to HAPE is not currently known. HAPE remains the major cause of death related to high altitude exposure with a high mortality in absence of emergency treatment. HACE is the result of swelling of brain tissue from fluid leakage.
Altitude sickness usually occurs following a rapid ascent and can usually be prevented by ascending slowly. In most of these cases, the symptoms are only temporary and usually abate with time as altitude acclimatisation occurs. However, in more extreme cases symptoms can be fatal.
Historical Perspective
Chronic mountain sickness (CMS) is also known as Monge's disease, after its first description in 1925 by Carlos Monge. High Altitude Flatus Expulsion was first described by Joseph Hamel in c. 1820. It was rediscovered in 1981 by Paul Auerbach and York Miller.
Classification
Pathophysiology
Causes
Altitude sickness is brought on by the combination of reduced air pressure and lower oxygen concentration that occur at high altitudes.
Epidemiology and Demographics
With a rapid ascension to high altitudes in 1 to 3 days, more than 50% of people develop altitude sickness. The incidence of clinical HAPE in unacclimatized travelers exposed to high altitude (~ 4,000 m) appears to be less than 1%. In over 30 years of research experience, the U.S. Army Pike's Peak Research Laboratory, utilizing about 300 sea-level resident volunteers (and more than 100 staff members) rapidly and directly exposed to high altitude, only 3 were evacuated with suspected HAPE.
Differentiating Altitude Sickness from Other Diseases
Epidemiology and Demographics
Risk Factors
The chance of getting altitude sickness increases the faster a person climbs to a high altitude. How severe the symptoms are also depends on this factor, as well as how hard the person pushes (exerts) himself or herself. People who normally live at or near sea level are more prone to altitude sickness. Individual susceptibility to high altitude pulmonary edema (HAPE) is difficult to predict. The most reliable risk factor is previous susceptibility to HAPE, and there is likely to be a genetic basis to this condition, perhaps involving the gene for angiotensin converting enzyme (ACE).
Screening
Natural History, Complications, and Prognosis
Diagnosis
History and Symptoms
Generally, different people have different susceptibilities to altitude sickness. For some otherwise healthy people Acute mountain sickness (AMS) can begin to appear at around 2000 meters (6,500 feet) above sea level such as at many mountain ski resorts. AMS is the most frequent type of altitude sickness encountered. Symptoms often manifest themselves 6 to 10 hours after ascent and generally subside in 1 to 2 days, but they occasionally develop into the more serious conditions. Symptoms are described as headache with fatigue, stomach sickness, dizziness, and sleep disturbance as additional possible symptoms. Exertion aggravates the symptoms.
Physical Examination
During physical examination, a clinician may find that a patient presenting with altitude sickness experiences temporary signs that usually abate with time as altitude acclimitisation occurs. High altitude pulmonary edema (HAPE) and cerebral edema (HACE) are the most ominous signs that may manifestation during physical examiantion.
Laboratory Findings
Chronic mountain sickness (CMS) is characterized by polycythemia (increased hematocrit) and hypoxemia which both decrease on descent from altitude. CMS is believed to arise because of an excessive production of red blood cells, which increases the oxygen carrying capacity of the blood but may cause increased blood viscosity and uneven blood flow through the lungs (V/Q mismatch). However, CMS is also considered an adaptation of pulmonary and heart disease to life under chronic hypoxia at altitude.[4] Clinical diagnosis by laboratory indicators have ranges of: Hb > 200 g/L, Hct > 65%, and arterial oxygen saturation (SaO2) <85% in both genders.[5]
EKG
X Ray
CT
MRI
Other imaging findings
Other diagnostic studies
Treatment
Medical Therapy
Surgery
Primary Prevention
Altitude sickness is largely preventable. Potential factors that influence altitude sickness prevention include: avoiding alcohol ingestion and strenuous activity within 24 hours of traveling to a different altitude and actively preparing for altitude acclimatization.
Secondary Prevention
Future or Investigational Therapies
In order to help understand the factors that make some individuals susceptible to high altitude pulmonary edema (HAPE), the International HAPE Database was set up in 2004.[6] Individuals who have previously suffered from HAPE can register with this confidential database in order to help researchers study the condition.
References
- ↑ K Baillie and A Simpson. "Acute mountain sickness". Apex (Altitude Physiology Expeditions). Retrieved 2007-08-08. - High altitude information for laypeople
- ↑ AAR Thompson. "Altitude-Sickness.org". Apex. Retrieved 2007-05-08.
- ↑ Medicine For the Outdoors by Paul S. Auerbach, M.D. © 1999 by Paul S. Auerbach, M.D.
- ↑ Zubieta-Castillo G, Zubieta-Calleja GR, Zubieta-Calleja L (2006). "Chronic mountain sickness: the reaction of physical disorders to chronic hypoxia". J Physiol Pharmacol. 57 Suppl 4: 431–42. PMID 17072074.
- ↑ West JB (2010). "English translation of "Nomenclature, classification, and diagnostic criteria of high altitude disease in China"". High Alt Med Biol. 11 (2): 169–72. doi:10.1089/ham.2010.1014. PMID 20586602.
- ↑ "International HAPE database". Apex (Altitude Physiology EXpeditions). Retrieved 2006-08-10.