Altitude sickness overview

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Epidemiology and Demographics
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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). Acute mountain sickness can progress to high altitude pulmonary edema (HAPE) or high altitude cerebral edema (HACE). 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.

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

Altitude sickness may be classified according to clinical symptoms and the pathological changes of principally encroached organs into 2 groups acute and chronic.

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

The incidence of altitude sickness is approximately 53,000 per 100,000 individuals worldwide. The prevalence and mortality rate of altitude sickness depends on altitude. Patients of all age groups may develop altitude sickness. The incidence of altitude sickness increases with age; the median age at diagnosis is 26-45 years. There is no racial predilection to altitude sickness. The majority of altitude sickness cases are reported in Kilimanjaro, Everest region of Nepal.

Epidemiology and Demographics

The incidence of altitude sickness is approximately 53,000 per 100,000 individuals worldwide. The prevalence and mortality rate of altitude sickness depends on altitude. Patients of all age groups may develop altitude sickness. The incidence of altitude sickness increases with age; the median age at diagnosis is 26-45 years. There is no racial predilection to altitude sickness. The majority of altitude sickness cases are reported in Kilimanjaro, Everest region of Nepal.

Risk Factors

Common risk factors in the development of altitude sickness include underlying lung disease, substances or conditions that interfere with acclimatization, previous history of high altitude sickness, lack of acclimatization.

Screening

There is insufficient evidence to recommend routine screening for altitude sickness which include cold pressor test, heart rate variability, pulmonary function test.

Natural History, Complications, and Prognosis

The important complications of altitude sickness are high altitude pulmonary edema and cerebral edema. Prognosis is generally good, and the 5 year mortality rate of patients with altitude sickness is approximately 12%.

Diagnosis

History and Symptoms

Patients with altitude sickness may have a positive history of underlying lung disease and substances or conditions that interfere with acclimatization. Common symptoms of altitude sickness include headache, dizziness, fatigue, cyanosis.

Physical Examination

Physical examination of patients with altitude sickness is usually remarkable for headache, nausea, vomiting and lightheadedness.

Laboratory Findings

Laboratory findings consistent with the diagnosis of altitude sickness include increased the level of hemoglobin, hematocrit and blood urea nitrogen and decreased level of bicarbonate, creatinine and PCO2.

EKG

An ECG may be helpful in the diagnosis of altitude sickness. Findings on an ECG suggestive of altitude sickness include shortening of R-R interval, shortening of the lengthening of Q-T and in particular for the ST-T flattening and Increase of P wave.

X Ray

X-ray may be helpful in the diagnosis of complications of altitude sickness which include patchy alveolar infiltrates, predominantly in the right central hemithorax, asymmetric pattern of airspace consolidation.

CT

CT scan may be helpful in the diagnosis of complications of altitude sickness pulmonary edema and it shows patchy alveolar infiltrates, predominantly in the right central hemithorax.

MRI

[MRI]] may be helpful in the diagnosis of complications of high altitude pulmonary edema and it shows increased T2 signal in the white matter of the splenium of the corpus callosum.

Treatment

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.

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. Individuals who have previously suffered from HAPE can register with this confidential database in order to help researchers study the condition.