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| author = J.K. Baillie
| author = J.K. Baillie
| title = Living in Thin Air
| title = Living in Thin Air
| url = http://www.altitude.org/why_less_oxygen_at_altitude.htm
| url = http://www.altitude.org/why_less_oxygen.php
| publisher = Apex
| publisher = Apex
| accessdate = 2007-12-17
| accessdate = 2007-12-17
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[[Image:Altitude sickness warning.jpg|thumb|275px|This sign near the peak of [[Mount Evans]] (elev. 14264 ft or 4,350 meters) in [[Colorado]], USA, warns of altitude sickness symptoms.]]
[[Image:Altitude sickness warning.jpg|thumb|275px|This sign near the peak of [[Mount Evans]] (elev. 14264 ft or 4,350 meters) in [[Colorado]], USA, warns of altitude sickness symptoms.]]


People have different susceptibilities to altitude sickness; for some otherwise healthy people, acute mountain sickness (AMS) 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<ref>{{cite web | author=K. Baillie and A. Simpson | title=Acute mountain sickness| url=http://www.altitude.org/calculators/altitudefacts/altitudefacts.htm | publisher=Apex (Altitude Physiology Expeditions) | accessdate=2007-08-08}}&nbsp;— High altitude information for laypeople</ref>. AMS 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<ref name=Thompson/>. Exertion aggravates the symptoms.
People have different susceptibilities to altitude sickness; for some otherwise healthy people, acute mountain sickness (AMS) 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<ref>{{cite web | author=K. Baillie and A. Simpson | title=Acute mountain sickness| url=http://www.altitude.org/high_altitude.php | publisher=Apex (Altitude Physiology Expeditions) | accessdate=2007-08-08}}&nbsp;— High altitude information for laypeople</ref>. AMS 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<ref name=Thompson/>. 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.<ref>{{cite journal |last1=Savourey |first1=G |last2=Guinet |first2=A, |last3=Besnard |first3=Y |last4=Garcia |first4=N |last5=Hanniquet |first5=AM |last6=Bittel |first6=J |date=October 1995 |title=Evaluation of the Lake Louise acute mountain sickness scoring system in a hypobaric chamber |journal=Aviation, Space, and Environmental Medicine |publisher=Aerospace Medical Association |location=Alexandria, VA |volume=66 |issue=10 |pages=963–7 |pmid=8526833 }}</ref>
The Lake Louise assessment system of AMS is based on a self-report questionnaire as well as a quick clinical assessment.<ref>{{cite journal |last1=Savourey |first1=G |last2=Guinet |first2=A, |last3=Besnard |first3=Y |last4=Garcia |first4=N |last5=Hanniquet |first5=AM |last6=Bittel |first6=J |date=October 1995 |title=Evaluation of the Lake Louise acute mountain sickness scoring system in a hypobaric chamber |journal=Aviation, Space, and Environmental Medicine |publisher=Aerospace Medical Association |location=Alexandria, VA |volume=66 |issue=10 |pages=963–7 |pmid=8526833 }}</ref>
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== External links ==
== External links ==
* [http://medex.org.uk//medex_book/about_book.php A free booklet about travel at high altitude for laypeople.]
* [http://medex.org.uk//medex_book/about_book.php A free booklet about travel at high altitude for laypeople.]
* [http://www.altitude.org/altitude_sickness.php What every climber should know about altitude sickness. ]
* [http://www.ismmed.org/np_altitude_tutorial.htm The tutorial on altitude illness from the International Society for Mountain Medicine]
* [http://www.ismmed.org/np_altitude_tutorial.htm The tutorial on altitude illness from the International Society for Mountain Medicine]
* [http://www.merck.com/pubs/mmanual/section20/chapter281/281a.htm Merck Manual entry on altitude sickness]
* [http://www.merck.com/pubs/mmanual/section20/chapter281/281a.htm Merck Manual entry on altitude sickness]
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* [http://www.high-altitude-medicine.com/AMS-medical.html Altitude Illness Clinical Guide for Physicians]
* [http://www.high-altitude-medicine.com/AMS-medical.html Altitude Illness Clinical Guide for Physicians]
* [http://www.itg.be/itg/Uploads/MedServ/ealtitude.pdf General information about Altitude sickness by the Prince Leopold Institute of Tropical Medicine]
* [http://www.itg.be/itg/Uploads/MedServ/ealtitude.pdf General information about Altitude sickness by the Prince Leopold Institute of Tropical Medicine]
* [http://www.altitude.org/calculators/oxygencalculator/oxygencalculator.htm An online calculator to show the effects of high altitude on oxygen delivery]
* [http://www.altitude.org/oxygen_levels.php An online calculator to show the effects of high altitude on oxygen delivery]
* [http://www.csgnetwork.com/pressurealtcalc.html An online calculator to compute altitude from air pressure]
* [http://www.csgnetwork.com/pressurealtcalc.html An online calculator to compute altitude from air pressure]


Revision as of 22:58, 6 July 2010

Altitude sickness
SpecialtyEmergency medicine Edit this on Wikidata
Look up altitude sickness in Wiktionary, the free dictionary.

Altitude sickness, also known as acute mountain sickness (AMS), altitude illness, hypobaropathy, 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).[1][2] 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.[3]. It is hard to determine who will be affected by altitude-sickness, as there are no specific factors that compare with this susceptibility to altitude sickness. However, most people can climb up to 2500 meters (8000 ft) normally.

Acute mountain sickness can progress to high altitude pulmonary edema (HAPE) or high altitude cerebral edema (HACE), which are potentially fatal.[1][4]

Chronic mountain sickness, also known as Monge's disease, is a different condition that only occurs after very prolonged exposure to high altitude.[5]

Causes

The causes of altitude sickness are not fully understood.[1][6] The percentage of oxygen in air, at 21%, remains almost unchanged up to 7,000 feet (2,100 m). The RMS velocities of diatomic nitrogen and oxygen are very similar and thus no change occurs in the ratio of oxygen to nitrogen. However, it is the air pressure itself, the number of molecules (of both oxygen and nitrogen) per given volume, which drops as altitude increases. Consequently, the available amount of oxygen to sustain mental and physical alertness decreases above 10,000 feet (3,000 m).[7] Although the cabin altitude in modern passenger aircraft is kept to 8,000 feet (2,400 m) or lower, a large proportion of passengers on long-haul flights may experience some symptoms of altitude sickness.[8]

Dehydration due to the higher rate of water vapor lost from the lungs at higher altitudes may contribute to the symptoms of altitude sickness.[9]

The rate of ascent, altitude attained, amount of physical activity at high altitude, as well as individual susceptibility, are contributing factors to the onset and severity of high-altitude illness.

Altitude sickness usually occurs following a rapid ascent and can usually be prevented by ascending slowly.[4] In most of these cases, the symptoms are temporary and usually abate as altitude acclimatisation occurs. However, in extreme cases, altitude sickness can be fatal.

The word "soroche" came from South America and originally meant "ore", because of an old, incorrect belief that it was caused by toxic emanations of ores in the Andes mountains. [1]

Signs and symptoms

File:Altitude sickness warning.jpg
This sign near the peak of Mount Evans (elev. 14264 ft or 4,350 meters) in Colorado, USA, warns of altitude sickness symptoms.

People have different susceptibilities to altitude sickness; for some otherwise healthy people, acute mountain sickness (AMS) 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[10]. AMS 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[4]. 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.[11]

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 (8000 feet = 76 kPa), combined with any one or more of the following symptoms, may indicate altitude sickness:

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
    • Retinal hemorrhage
  • Increased nausea

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 occurs in about 2%[citation needed] of those who are adjusting to altitudes of about 3000 m (10,000 feet = 70 kPa) or more. It 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. It occurs in about 1%[citation needed] of people adjusting to altitudes above 2,700 m (9,000 feet = 73 kPa). 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.

Prevention

Ascending slowly is the best way to avoid altitude sickness.[4] Avoiding strenuous activity such as skiing, hiking, etc. in the first 24 hours at high altitude reduces the symptoms of AMS. As alcohol tends to cause dehydration, which exacerbates AMS, avoiding alcohol consumption in the first 24-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.[12] Once above approximately 3,000 metres (10,000 feet = 70 kPa), most climbers and high-altitude trekkers take the "climb-high, sleep-low" approach. For high-altitude climbers, a typical acclimatization regime might be to stay a few days at a base camp, climb up to a higher camp (slowly), and then return to base camp. A subsequent climb to the higher camp then includes an overnight stay. This process is then repeated a few times, each time extending the time spent at higher altitudes to let the body adjust to the oxygen level there, a process that involves the production of additional red blood cells [citation needed]. Once the climber has acclimatised to a given altitude, the process is repeated with camps placed at progressively higher elevations. The general rule of thumb is to not ascend more than 300 metres (1,000 ft) per day to sleep. That is, one can climb from 3,000 (10,000 feet = 70 kPa) to 4,500 metres(15,000 feet = 58 kPa) in one day, but one should then descend back to 3,300 metres (11,000 feet = 67.5 kPa) to sleep. This process cannot safely be rushed, and this is why climbers need to spend days (or even weeks at times) acclimatising before attempting to climb a high peak. Simulated altitude equipment that produces hypoxic (reduced oxygen) air can be used to acclimate to high altitude, reducing the total time required on the mountain itself [citation needed].

Altitude acclimatization is necessary for some people who move rapidly from lower altitudes to intermediate altitudes, e.g. by aircraft and ground transportation over a few hours, such as from sea level to 8,000 feet (2,400 m) of many Colorado, USA mountain resorts. Stopping at an intermediate altitude overnight can reduce or eliminate a reoccurrence of AMS.

Medical treatment

The drug acetazolamide may help some people making a rapid ascent to sleeping altitude above 2750 metres, and it may also be effective if started early in the course of AMS.[13] The Everest Base Camp Medical Centre cautions against its routine use as a substitute for a reasonable ascent schedule, except where rapid ascent is forced by flying into high altitude locations or due to terrain considerations.[14] The Centre suggests a dosage of 125-250 mg twice daily for prophylaxis, starting from 24 hours before ascending until a few days at the highest altitude or on descending;[14] with 250 mg twice daily recommended for treatment of AMS.[15] The Centers for Disease Control and Prevention suggest a lower dose for prevention of 125 mg acetazolamide every 12 hours.[16] The CDC advises that Dexamethasone be reserved for treatment of AMS and HACE during descents, and notes that Nifedipine may prevent HAPE.[16]

A single randomized controlled trial found that sumatriptan may help prevent altitude sickness.[17]. Despite their popularity, antioxidant treatments have not been found to be effective medications for prevention of AMS.[18] Interest in phosphodiesterase inhibitors such as sildenafil has been limited by the possibility that these drugs might worsen the headache of mountain sickness.[19]

For centuries, indigenous peoples of the Americas such as the Aymaras of the Altiplano, have chewed coca leaves to try to alleviate the symptoms of mild altitude sickness.

Oxygen enrichment

In high-altitude conditions, oxygen enrichment can counteract the effects of altitude sickness, or hypoxia. A small amount of supplemental oxygen reduces the equivalent altitude in climate-controlled rooms. At 3,400 m (67 kPa), raising the oxygen concentration level by 5 percent via an oxygen concentrator and an existing ventilation system provides an effective altitude of 3,000 m (70 kPa), which is more tolerable for surface-dwellers.[20].

Other methods

Drinking plenty of water will also help in acclimatisation[21] to replace the fluids lost through heavier breathing in the thin, dry air found at altitude, although consuming excessive quantities ("over-hydration") has no benefits and may cause dangerous hyponatremia.

Oxygen from gas bottles or liquid containers can be applied directly via a nasal cannula or mask. Oxygen concentrators based upon pressure swing adsorption (PSA), VSA, or vacuum-pressure swing adsorption (VPSA) can be used to generate the oxygen if electricity is available. Stationary oxygen concentrators typically use PSA technology, which has performance degradations at the lower barometric pressures at high altitudes. One way to compensate for the performance degradation is to utilize a concentrator with more flow capacity. There are also portable oxygen concentrators that can be used on vehicular DC power or on internal batteries, and at least one system commercially available measures and compensates for the altitude effect on its performance up to 4,000 meters (13,000 ft). The application of high-purity oxygen from one of these methods increases the partial pressure of oxygen by raising the FIO2 (fraction of inspired oxygen).

Treatment

The only reliable treatment and in many cases the only option available is to descend. Attempts to treat or stabilise the patient in situ at altitude is dangerous unless highly controlled and with good medical facilities. However, the following treatments have been used when the patient's location and circumstances permit:

  • Oxygen may be used for mild to moderate AMS below 12,000 feet (3,700 m) and is commonly provided by physicians at mountain resorts. Symptoms abate in 12-36 hours without the need to descend.
  • For more serious cases of AMS, or where rapid descent is impractical, a Gamow bag, a portable plastic hyperbaric chamber inflated with a foot pump, can be used to reduce the effective altitude by as much as 1,500 meters (5,000 ft). A Gamow bag is generally used only as an aid to evacuate severe AMS patients, not to treat them at altitude.
  • Acetazolamide may assist in altitude aclimatisation but is not a reliable treatment for established cases of even mild altitude sickness.[22][23]
  • Some claim that mild altitude sickness can be controlled by consciously taking 10-12 large, rapid breaths every 5 minutes, (hyperventilation) but this claim lacks both empirical evidence and a plausible medical reason as to why this should be effective.[citation needed] If overdone, this can remove too much carbon dioxide causing hypocapnia.
  • The folk remedy for altitude sickness in Ecuador, Peru and Bolivia is a tea made from the coca plant. See mate de coca.
  • Other treatments include injectable steroids to reduce pulmonary edema, this may buy time to descend but treats a symptom, it does not treat the underlying AMS.

See also

References

  1. ^ a b c Roach, Robert; Stepanek, Jan; and Hackett, Peter. (2002). "24". Acute Mountain Sickness and High-Altitude Cerebral Edema. In: Medical Aspects of Harsh Environments. Vol. 2. Washington, DC. Retrieved 2009-01-05. {{cite book}}: More than one of |location= and |place= specified (help)CS1 maint: location missing publisher (link) CS1 maint: multiple names: authors list (link)
  2. ^ Baillie, Kenneth; Simpson, Alistair. "Altitude Tutorials - Altitude Sickness". Apex (Altitude Physiology Expeditions). Retrieved 2010-01-26.
  3. ^ The Mountaineers. Mountaineering: The Freedom of the Hills, 7th Edition. Seattle, WA: Mountaineers Books, 2003
  4. ^ a b c d A.A.R. Thompson. "Altitude Sickness". Apex. Retrieved 2007-05-08.
  5. ^ A.J. Giannini, H.R. Black, R.L. Goettsche. The Psychiatric, Psychogenic and Somatopsychic Disorders Handbook. New Hyde Park, NY. Medical Examination Publishing Co.,1978. pp.190,192. ISBN 0-87488-596-5.
  6. ^ The High Altitude Medicine Handbook, 3rd Edition, Andrew J. Pollard and David R. Murdoch.
  7. ^ J.K. Baillie. "Living in Thin Air". Apex. Retrieved 2007-12-17.
  8. ^ Muhm, J. Michael (2007-07-05). "Effect of Aircraft-Cabin Altitude on Passenger Discomfort". N Engl J Med. 357 (1): 18–27. doi:10.1056/NEJMoa062770. PMID 17611205. Retrieved 2009-12-23. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)
  9. ^ Hackett, P H (2001-07-12). "High-altitude illness". The New England Journal of Medicine. 345 (2): 107–14. doi:10.1056/NEJM200107123450206. ISSN 0028-4793. PMID 11450659. Retrieved 2009-03-25. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)
  10. ^ K. Baillie and A. Simpson. "Acute mountain sickness". Apex (Altitude Physiology Expeditions). Retrieved 2007-08-08. — High altitude information for laypeople
  11. ^ Savourey, G; Guinet, A,; Besnard, Y; Garcia, N; Hanniquet, AM; Bittel, J (October 1995). "Evaluation of the Lake Louise acute mountain sickness scoring system in a hypobaric chamber". Aviation, Space, and Environmental Medicine. 66 (10). Alexandria, VA: Aerospace Medical Association: 963–7. PMID 8526833.{{cite journal}}: CS1 maint: extra punctuation (link) CS1 maint: multiple names: authors list (link)
  12. ^ Muza, S.R.; Fulco, C.S.; Cymerman, A. (2004). "Altitude Acclimatization Guide". U.S. Army Research Inst. of Environmental Medicine Thermal and Mountain Medicine Division Technical Report (USARIEM-TN-04-05). Retrieved 2009-03-05.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  13. ^ World Health Organization (1 January 2007). "CHAPTER 3 Environmental health risks". International travel and health. p. 31. {{cite book}}: |access-date= requires |url= (help); |format= requires |url= (help); External link in |chapterurl= (help); Unknown parameter |chapterurl= ignored (|chapter-url= suggested) (help)
  14. ^ a b Himalayan Rescue Association - Everest Medicial Clinic. "Prophylaxis". ExplorersWeb. Retrieved 2009-11-21.
  15. ^ Himalayan Rescue Association - Everest Medicial Clinic. "Treating AMS". ExplorersWeb. Retrieved 2009-11-21.
  16. ^ a b Hackett P, Shlim D (2009). "Chapter 2 The Pre-Travel Consultation - Self-Treatable Diseases - Altitude Illness". In Turell D, Brunette G, Kozarsky P, Lefor A (ed.). CDC Health Information for International Travel 2010 "The Yellow Book". St. Louis: Mosby. ISBN 0-7020-3481-9. {{cite book}}: |access-date= requires |url= (help); External link in |chapterurl= (help); Unknown parameter |chapterurl= ignored (|chapter-url= suggested) (help)CS1 maint: multiple names: editors list (link)
  17. ^ Jafarian S., Gorouhi F., Salimi S., Lotfi J. (2007). "Sumatriptan for prevention of acute mountain sickness: randomized clinical trial". Ann. Neurol. 62 (3): 273–7. doi:10.1002/ana.21162. PMID 17557349.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  18. ^ Baillie JK, Thompson AA, Irving JB, Bates MG, Sutherland AI, Macnee W, Maxwell SR, Webb DJ (2009). "Oral antioxidant supplementation does not prevent acute mountain sickness: double blind, randomized placebo-controlled trial". QJM. 102 (5): 341–8. doi:10.1093/qjmed/hcp026. PMID 19273551. {{cite journal}}: Unknown parameter |month= ignored (help)CS1 maint: multiple names: authors list (link)
  19. ^ Bates MG, Thompson AA, Baillie JK (2007). "Phosphodiesterase type 5 inhibitors in the treatment and prevention of high altitude pulmonary edema". Curr Opin Investig Drugs. 8 (3): 226–31. PMID 17408118. {{cite journal}}: Unknown parameter |month= ignored (help)CS1 maint: multiple names: authors list (link)
  20. ^ West JB (1995). "Oxygen enrichment of room air to relieve the hypoxia of high altitude". Respir Physiol. 99 (2): 225–32. doi:10.1016/0034-5687(94)00094-G. PMID 7777705. {{cite journal}}: Unknown parameter |month= ignored (help)
  21. ^ Dannen, Kent (2002). Rocky Mountain National Park. anywere: Globe Pequot. p. 9. ISBN 0762722452. Visitors unaccustomed to high elevations may experience symptoms of Acute Mountain Sickness (AMS)[...s]uggestions for alleviating symptoms include drinking plenty of water[.] {{cite book}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)
  22. ^ Cain SM, Dunn JE (1966). "Low doses of acetazolamide to aid accommodation of men to altitude". J Appl Physiol. 21 (4): 1195–200. PMID 5916650. {{cite journal}}: Unknown parameter |month= ignored (help)
  23. ^ Grissom CK, Roach RC, Sarnquist FH, Hackett PH (1992). "Acetazolamide in the treatment of acute mountain sickness: clinical efficacy and effect on gas exchange". Ann. Intern. Med. 116 (6): 461–5. PMID 1739236. {{cite journal}}: Unknown parameter |month= ignored (help)CS1 maint: multiple names: authors list (link)

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