Editing Altitude sickness (section)

== Signs and symptoms ==
[[File:Peripheral edema of a woman's face, before and after; Annapurna Base Camp, 2015.JPG|thumb|upright=1.3|Left: A woman at normal altitude. Right: The same woman with a swollen face while trekking at high altitude ([[Annapurna]] Base Camp, Nepal; {{convert|4130|m|ft|abbr=on}}).]]
People have different susceptibilities to altitude sickness; for some otherwise healthy people, acute altitude sickness can begin to appear at around {{convert|2000|m}} above sea level, such as at many mountain ski resorts, equivalent to a pressure of {{convert|80|kPa|atm|lk=on}}.<ref>{{Cite web |first1=K. |last1=Baillie |first2=A. |last2=Simpson |title=Acute mountain sickness |url=http://www.altitude.org/high_altitude.php |publisher=Apex (Altitude Physiology Expeditions) |access-date=8 August 2007 |archive-url=https://web.archive.org/web/20100201060010/http://www.altitude.org/high_altitude.php |archive-date=1 February 2010 |url-status=dead}}&nbsp;— High altitude information for laypeople</ref> 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.<ref name=Thompson>{{Cite web |first=A. A. R. |last=Thompson |title=Altitude Sickness |url=http://www.altitude.org/altitude_sickness.php |publisher=Apex |access-date=8 May 2007}}</ref> Exertion may aggravate the symptoms.{{citation needed|date=September 2022}}

Those individuals with the lowest initial [[Capnography|partial pressure of end-tidal pCO<sub>2</sub>]] (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 pCO<sub>2</sub> and low oxygen saturation levels.<ref>{{cite journal |vauthors=Douglas DJ, Schoene RB |title=End-tidal partial pressure of carbon dioxide and acute mountain sickness in the first 24 hours upon ascent to Cusco Peru (3326 meters) |journal=[[Wilderness & Environmental Medicine]] |volume=21 |issue=2 |pages=109–13 |date=June 2010 |pmid=20591371 |doi=10.1016/j.wem.2010.01.003 |doi-access=free}}</ref>

=== Primary symptoms ===
[[Headache]]s are the primary symptom used to diagnose altitude sickness, although a headache is also a symptom of [[dehydration]].{{citation needed|date=September 2022}} A headache occurring at an altitude above {{convert|2400|m}}{{snd}}a pressure of {{convert|76|kPa|atm}}{{snd}}combined with any one or more of the following symptoms, may indicate altitude sickness:
{|
|- style="vertical-align:bottom;text-align:left;"
! Disordered system
! Symptoms
|- style="vertical-align:top;"
| Gastrointestinal
| Loss of appetite, [[nausea]], vomiting, [[high-altitude flatus expulsion|excessive flatulation]]<ref name="Auerbach 2007" />
|- style="vertical-align:top;"
| Nervous
| [[Fatigue]] or weakness, headache with or without [[dizziness]] or [[lightheadedness]], [[insomnia]], [[Paraesthesia|"pins and needles" sensation]]
|- style="vertical-align:top;"
| Locomotory
| [[Peripheral edema]] (swelling of hands, feet, and face)
|- style="vertical-align:top;"
| Respiratory
| Nose bleeding, shortness of breath upon exertion
|- style="vertical-align:top;"
| Cardiovascular
| Persistent rapid pulse
|- style="vertical-align:top;"
| 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 (medical)|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.{{citation needed|date=September 2022}}

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.