Altitude sickness

Altitude sickness
Other namesHigh-altitude sickness,[1] altitude illness,[1] hypobaropathy, altitude bends, soroche
Sign displays "Caution! You are at 17586 ft (5360 m)"
Altitude sickness warning – Indian Army
SpecialtyEmergency medicine
SymptomsHeadache, vomiting, feeling tired, trouble sleeping, dizziness[1]
ComplicationsHigh altitude pulmonary edema (HAPE),
high altitude cerebral edema (HACE)[1]
Usual onsetWithin 24 hours[1]
TypesAcute mountain sickness, high altitude pulmonary edema, high altitude cerebral edema, chronic mountain sickness[2]
CausesLow amounts of oxygen at high elevation[1][2]
Risk factorsPrior episode, high degree of activity, rapid increase in elevation[2]
Diagnostic methodBased on symptoms[2]
Differential diagnosisExhaustion, viral infection, hangover, dehydration, carbon monoxide poisoning[1]
PreventionGradual ascent[1]
TreatmentDescent to lower altitude, sufficient fluids[1][2]
MedicationIbuprofen, acetazolamide, dexamethasone, oxygen therapy[2]
Frequency20% at 2,500 metres (8,000 ft)
40% at 3,000 metres (10,000 ft)[1][2]

Altitude sickness, the mildest form being acute mountain sickness (AMS), is the negative health effect of high altitude, caused by rapid exposure to low amounts of oxygen at high elevation.[1][2] Symptoms may include headaches, vomiting, tiredness, trouble sleeping, and dizziness.[1] Acute mountain sickness can progress to high altitude pulmonary edema (HAPE) with associated shortness of breath or high altitude cerebral edema (HACE) with associated confusion.[1][2] Chronic mountain sickness may occur after long term exposure to high altitude.[2]

Altitude sickness typically occurs only above 2,500 metres (8,000 ft), though some are affected at lower altitudes.[2][3] Risk factors include a prior episode of altitude sickness, a high degree of activity, and a rapid increase in elevation.[2] Diagnosis is based on symptoms and is supported in those who have more than a minor reduction in activities.[2][4] It is recommended that at high-altitude any symptoms of headache, nausea, shortness of breath, or vomiting be assumed to be altitude sickness.[5]

Prevention is by gradually increasing elevation by no more than 300 metres (1,000 ft) per day.[1] Being physically fit does not decrease the risk.[2] Treatment is generally by descending to a lower altitude and sufficient fluids.[1][2] Mild cases may be helped by ibuprofen, acetazolamide, or dexamethasone.[2] Severe cases may benefit from oxygen therapy and a portable hyperbaric bag may be used if descent is not possible.[1] Treatment efforts, however, have not been well studied.[3]

AMS occurs in about 20% of people after rapidly going to 2,500 metres (8,000 ft) and 40% of people going to 3,000 metres (10,000 ft).[1][2] While AMS and HACE occurs equally frequently in males and females, HAPE occurs more often in males.[1] The earliest description of altitude sickness is attributed to a Chinese text from around 30 BCE which describes "Big Headache Mountains" possibly referring to the Karakoram Mountains around Kilik Pass.[6]

Signs and symptoms

Right: A woman with a swollen face while trekking at high altitude (Annapurna Base Camp, Nepal; 4130 m). Left: The same woman at normal altitude.

People have different susceptibilities to altitude sickness; for some otherwise healthy people, acute altitude sickness can begin to appear at around 2,000 metres (6,600 ft) above sea level, such as at many mountain ski resorts, equivalent to a pressure of 80 kilopascals (0.79 atm).[7] 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.[8] Exertion aggravates the symptoms.

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.[9]

Primary symptoms

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 (7,900 ft) – a pressure of 76 kilopascals (0.75 atm) – combined with any one or more of the following symptoms, may indicate altitude sickness:

Disordered System Symptoms
Gastrointestinal Loss of appetite, nausea, or vomiting, excessive flatulation[10]
Nervous Fatigue or weakness, headache with or without dizziness or lightheadedness, insomnia, “pins and needles” sensation
Locomotory Peripheral edema (swelling of hands, feet, and face)
Respiratory Nose bleeding, shortness of breath upon exertion
Cardiovascular Persistent rapid pulse
Other General malaise

Severe symptoms

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 and vomiting
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.

Other Languages
Bân-lâm-gú: Ko-san-chèng
беларуская: Вышынная хвароба
català: Mal d'altura
dansk: Højdesyge
español: Mal de montaña
Esperanto: Altomalsano
Gaeilge: Galar airde
한국어: 고산병
italiano: Mal di montagna
Кыргызча: Түтөк
Bahasa Melayu: Mabuk gunung
Nederlands: Hoogteziekte
日本語: 高山病
oʻzbekcha/ўзбекча: Balandlik kasalligi
português: Mal da montanha
Runa Simi: Suruqch'i
српски / srpski: Висинска болест
srpskohrvatski / српскохрватски: Visinska bolest
svenska: Höjdsjuka
українська: Висотна хвороба
Tiếng Việt: Say độ cao
中文: 高山症