Altitude sickness

Altitude sickness—also known as acute mountain sickness (AMS), altitude illness, hypobaropathy, "the altitude bends", or soroche is a pathological effect of high altitude on humans, caused by acute exposure to low partial pressure of oxygen at high altitude. It commonly occurs above 2,400 metres (8,000 feet). It presents as a collection of nonspecific symptoms, acquired at high altitude or in low air pressure, resembling a case of "flu, carbon monoxide poisoning, or a hangover". It is hard to determine who will be affected by altitude sickness, as there are no specific factors that correlate with a susceptibility to altitude sickness. However, most people can ascend to 2,400 metres (8,000 ft) without difficulty.

Acute mountain sickness can progress to high altitude pulmonary edema (HAPE) or high altitude cerebral edema (HACE), which are potentially fatal.

Chronic mountain sickness, also known as Monge's disease, is a different condition that only occurs after very prolonged exposure to high altitude.

High altitude: 1,500 to 3,500 metres (4,900 to 11,500 ft) - The onset of physiological effects of diminished inspiratory oxygen pressure (PiO2) includes decreased exercise performance and increased ventilation (lower arterial PCO2). Minor impairment exists in arterial oxygen transport (arterial oxygen saturation (SaO2) at least 90%), but arterial PO2 is significantly diminished. Because of the large number of people who ascend rapidly to altitudes between 2,400 and 4,000 m, high-altitude illness is common in this range.

Very high altitude: 3,500 to 5,500 metres (11,500 to 18,000 ft) - Maximum SaO2 falls below 90% as the arterial PO2 falls below 60mmHg. Extreme hypoxemia may occur during exercise, during sleep, and in the presence of high altitude pulmonary edema or other acute lung conditions. Severe altitude illness occurs most commonly in this range.

Extreme altitude: above 5,500 metres (18,000 ft) - Marked hypoxemia, hypocapnia, and alkalosis are characteristic of extreme altitudes. Progressive deterioration of physiologic function eventually outstrips acclimatization. As a result, no permanent human habitation occurs above 6,000 m. A period of acclimatization is necessary when ascending to extreme altitude; abrupt ascent without supplemental oxygen for other than brief exposures invites severe altitude sickness.

Signs and symptomes
People have different susceptibilities to altitude sickness; for some otherwise healthy people, acute altitude sickness can begin to appear at around 2000 meters (6,500 ft) above sea level, such as at many mountain ski resorts, equivalent to a pressure of 80 kPa.This is the most frequent type of altitude sickness encountered. Symptoms often manifest themselves six to ten hours after ascent and generally subside in one to two days, but they occasionally develop into the more serious conditions. Symptoms include headache, fatigue, stomach illness, dizziness, and sleep disturbance. Exertion aggravates the symptoms.

The Lake Louise assessment system of AMS is based on a self-report questionnaire as well as a quick clinical assessment.

Those individuals with the lowest initial partial pressure of end-tidal pCO2 (the lowest concentration of carbon dioxide at the end of the respiratory cycle, a measure of a higher alveolar ventilation) and corresponding high oxygen saturation levels tend to have a lower incidence of acute mountain sickness than those with high end-tidal pCO2 and low oxygen saturation levels.

Signs and symptomes
Headaches are the primary symptom used to diagnose altitude sickness, although a headache is also a symptom of dehydration. A headache occurring at an altitude above 2,400 metres (8,000 feet = 76 kPa), combined with any one or more of the following symptoms, may indicate altitude sickness:

  • Lack of appetite, nausea, or vomiting

  • Fatigue or weakness

  • Dizziness or lightheadedness

  • Insomnia

  • Pins and needles

  • Shortness of breath upon exertion

  • Nosebleed

  • Persistent rapid pulse

  • Drowsiness

  • Excessive flatulation

  • General malaise

  • Peripheral edema (swelling of hands, feet, and face)

  • Severe symptomes

  • Symptoms that may indicate life-threatening altitude sickness include:

  • Pulmonary edema (fluid in the lungs)

  • Symptoms similar to bronchitis

  • Persistent dry cough

  • Fever

  • Shortness of breath even when resting

  • Cerebral edema (swelling of the brain)

  • Headache that does not respond to analgesics

  • Unsteady gait

  • Gradual loss of consciousness

  • Increased nausea

  • Retinal hemorrhage

The most serious symptoms of altitude sickness arise from edema (fluid accumulation in the tissues of the body). At very high altitude, humans can get either high altitude pulmonary edema (HAPE), or high altitude cerebral edema (HACE). The physiological cause of altitude-induced edema is not conclusively established. It is currently believed, however, that HACE is caused by local vasodilation of cerebral blood vessels in response to hypoxia, resulting in greater blood flow and, consequently, greater capillary pressures. On the other hand, HAPE may be due to general vasoconstriction in the pulmonary circulation (normally a response to regional ventilation-perfusion mismatches) which, with constant or increased cardiac output, also leads to increases in capillary pressures. For those suffering HACE, dexamethasone may provide temporary relief from symptoms in order to keep descending under their own power.

HAPE can progress rapidly and is often fatal. Symptoms include fatigue, severe dyspnea at rest, and cough that is initially dry but may progress to produce pink, frothy sputum. Descent to lower altitudes alleviates the symptoms of HAPE.

HACE is a life-threatening condition that can lead to coma or death. Symptoms include headache, fatigue, visual impairment, bladder dysfunction, bowel dysfunction, loss of coordination, paralysis on one side of the body, and confusion. Descent to lower altitudes may save those afflicted with HACE.

Ascending slowly is the best way to avoid altitude sickness. Avoiding strenuous activity in the first 24 hours at high altitude reduces the symptoms of AMS. Alcohol and sleeping pills are respiratory depressants, and thus slow down the acclimatization process and should be avoided. Alcohol also tends to cause dehydration and exacerbates AMS. Thus, avoiding alcohol consumption in the first 24–48 hours at a higher altitude is optimal.

Altitude acclimatization
Altitude acclimatization is the process of adjusting to decreasing oxygen levels at higher elevations, in order to avoid altitude sickness.

1. Drink plenty of Water: Stay away from alcohol 48 hours before heading up, walk slow


2. Take it easy, eat drink and rest.

3. RRHA guides will do all in their power to prevent mountain sickness.

Rwenzori Ranges Hikers Association, copyright 2018