altitude sickness altitude sickness altitude sickness, the mildest form being acute mountain sickness (ams), is the harmful effect of high altitude, caused by rapid exposure to low amounts of oxygen at high elevation. people can respond to high altitude in different ways. symptoms may include headaches, vomiting, tiredness, confusion, trouble sleeping, and dizziness. 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. chronic mountain sickness may occur after long-term exposure to high altitude. altitude sicknessother nameshigh-altitude sickness, altitude illness, hypobaropathy, altitude bends, sorochealtitude sickness warning – indian armyspecialtyemergency medicinesymptomsheadache, vomiting, feeling tired, trouble sleeping, dizzinesscomplicationshigh-altitude pulmonary edema (hape),high-altitude cerebral edema (hace)usual onsetwithin 24 hourstypesacute mountain sickness, high-altitude pulmonary edema, high-altitude cerebral edema, chronic mountain sicknesscauseslow amounts of oxygen at high elevationrisk factorsprior episode, high degree of activity, rapid increase in elevationdiagnostic methodbased on symptomsdifferential diagnosisexhaustion, viral infection, hangover, dehydration, carbon monoxide poisoningpreventiongradual ascenttreatmentdescent to lower altitude, sufficient fluidsmedicationibuprofen, acetazolamide, dexamethasone, oxygen therapyfrequency20% at 2,500 metres (8,000 ft)40% at 3,000 metres (10,000 ft) altitude sickness typically occurs only above 2,500 metres (8,000 ft), though some are affected at lower altitudes. risk factors include a prior episode of altitude sickness, a high degree of activity, and a rapid increase in elevation. diagnosis is based on symptoms and is supported in those who have more than a minor reduction in activities. it is recommended that at high altitude any symptoms of headache, nausea, shortness of breath, or vomiting be assumed to be altitude sickness. sickness is prevented by gradually increasing elevation by no more than 300 metres (1,000 ft) per day. being physically fit does not decrease the risk. generally, descent and sufficient fluid intake can treat symptoms. mild cases may be helped by ibuprofen, acetazolamide, or dexamethasone. severe cases may benefit from oxygen therapy and a portable hyperbaric bag may be used if descent is not possible. treatment efforts, however, have not been well studied. 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). while ams and hace occurs equally frequently in males and females, hape occurs more often in males. 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. signs and symptoms left: a woman at normal altitude. right: the same woman with a swollen face while trekking at high altitude (annapurna base camp, nepal; 4,130 m (13,550 ft)). 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). this is the most frequent type of altitude sickness encountered. symptoms often manifest within ten hours of ascent and generally subside within two days, though they occasionally develop into the more serious conditions. symptoms include headache, confusion, fatigue, stomach illness, dizziness, and sleep disturbance. exertion may aggravate 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. 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, vomiting, excessive flatulation 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 with 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 affected by hace. cause