Altitude sicknessAltitude sickness, also known as acute mountain sickness (AMS), altitude illness,hypobaropathy, or soroche, is a pathological effect of high altitude on humans, caused by acuteexposure to low air pressure (usually outdoors at high altitudes). It commonly occurs above2,400 metres (approximately 8,000 feet). Acute mountain sickness can progress to highaltitude pulmonary edema (HAPE) or high altitude cerebral edema (HACE).The cause of altitude sickness is still not understood. It occurs in low atmospheric pressureconditions but not necessarily in low oxygen conditions at sea level pressure. Although treatableto some extent by the administration of oxygen, most of the symptoms do not appear to becaused by low oxygen, but rather by the low CO2 levels causing a rise in blood pH, alkalosis.The percentage of oxygen in air remains essentially constant with altitude at 21% up until 70,000feet (21,330 m) but the air pressure (and therefore the number of oxygen molecules) drops asaltitude increases - consequently, the available amount of oxygen to sustain mental and physicalalertness decreases above 10,000 feet (3,050 m) . Altitude sickness usually does not affectpersons traveling in aircraft because modern aircraft passenger compartments are pressurized atan air pressure equivalent to an altitude of 8,000 feet (2,440 m).A related condition, occurring only after prolonged exposure to high altitude, is chronicmountain sickness, also known as Monges disease. An unrelated condition, although often confused with altitude sickness, is dehydration, due to the higher rate of water vapor lost from the lungs at higher altitudes.IntroductionHigh altitude or mountain sickness is defined when someone feels sick at high altitudes, such asin the mountains or any other altitude-related sicknesses. It is hard to determine who will beaffected by altitude-sickness as there are no specific factors that compare with this susceptibilityto altitude sickness. However, most people can climb up to 2500 meters (8000 ft) normally.Generally, different people have different susceptibilities to altitude sickness. For someotherwise healthy people, Acute Mountain Sickness (AMS) can begin to appear at around 2000meters (6,500 ft) above sea level, such as at many mountain ski resorts, equivalent to a pressureof 80 kPa. AMS is the most frequent type of altitude sickness encountered. Symptoms oftenmanifest themselves 6-10 hours after ascent and generally subside in 1 to 2 days, but theyoccasionally develop into the more serious conditions. Symptoms include headache, fatigue,stomach illness, dizziness, and sleep disturbance. Exertion aggravates the symptoms.
High altitude pulmonary edema (HAPE) and cerebral edema (HACE) are the most ominous ofthese symptoms, while AMS, retinal hemorrhage, and peripheral edema are less severe forms ofthe disease. The rate of ascent, altitude attained, amount of physical activity at high altitude, aswell as individual susceptibility, are contributing factors to the onset and severity of high-altitudeillness.Altitude sickness usually occurs following a rapid ascent and can usually be prevented byascending slowly. In most of these cases, the symptoms are temporary and usually abate asaltitude 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.Signs and symptoms1. Headache is a primary symptom used to diagnose altitude sickness, although headache is alsoa symptom of dehydration. A headache occurring at an altitude above 2,400 meters (8000 feet =76 kPa), combined with any one or more of the following symptoms, can indicate altitudesickness: Lack of appetite, nausea, or vomiting Fatigue or weakness Dizziness or light-headedness Insomnia Pins and needles Shortness of breath upon exertion Persistent rapid pulse Drowsiness General malaise Peripheral edema (swelling of hands, feet, and face).Symptoms that may indicate life-threatening altitude sickness include: pulmonary edema (fluid in the lungs): o persistent dry cough o fever o shortness of breath even when resting cerebral edema (swelling of the brain): o headache that does not respond to analgesics o unsteady gait o increased vomiting o gradual loss of consciousness.
Severe casesThe most serious symptoms of altitude sickness are due to edema (fluid accumulation in thetissues 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-inducededema is not conclusively established. It is currently believed, however, that HACE is caused bylocal vasodilation of cerebral blood vessels in response to hypoxia, resulting in greater bloodflow and, consequently, greater capillary pressures. On the other hand, HAPE may be due togeneral vasoconstriction in the pulmonary circulation (normally a response to regionalventilation-perfusion mismatches) which, with constant or increased cardiac output, also leads toincreases in capillary pressures. For those suffering HACE, dexamethasone may providetemporary relief from symptoms in order to keep descending under their own power.HAPE occurs in ~2% of those who are adjusting to altitudes of ~3000 m (10,000 feet = 70 kPa)or more. It can progress rapidly and is often fatal. Symptoms include fatigue, severe dyspnea atrest, and cough that is initially dry but may progress to produce pink, frothy sputum. Descent tolower altitudes alleviates the symptoms of HAPE.HACE is a life threatening condition that can lead to coma or death. It occurs in about 1% ofpeople adjusting to altitudes above ~2700 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 thoseafflicted with HACE.A person suffering from serious symptoms of altitude sickness has a relatively short period oftime of useful consciousness in which corrective action can be taken. The following is acorrelation of altitude to the amount of time that a person will have useful consciousness: ~20,000 ft / 6,100 m = 5-12 minutes (peak of Mount McKinley or Mount Kilimanjaro) ~25,000 ft / 7,620 m = 3-5 minutes; ~29,000 ft / 8,840 m = 1-2 minutes; (peak of Mount Everest) ~40,000 ft / 12,200 m = 9-15 seconds (represents the oxygen that was in a persons system before the exposure)Prevention1. Avoiding alcohol ingestionAs alcohol tends to dehydrate, avoidance in the first 24 hours at a higher altitude is optimal.
2. Strenuous activityPeople with recurrent AMS note that by avoiding strenuous activity such as skiing, hiking, etc inthe first 24 hours at altitude reduces their problems.3. Altitude acclimatizationAltitude acclimatization is the process of adjusting to decreasing oxygen levels at higherelevations, in order to avoid altitude sickness. Once above approximately 3,000 metres (10,000feet = 70 kPa), most climbers and high altitude trekkers follow the "golden rule" - climb high,sleep low. For high altitude climbers, a typical acclimatization regime might be to stay a fewdays at a base camp, climb up to a higher camp (slowly), then return to base camp. A subsequentclimb to the higher camp would then include an overnight stay. This process is then repeated afew times, each time extending the time spent at higher altitudes to let the body adjust to theoxygen level there, a process that involves the production of additional red blood cells. Once theclimber has acclimatised to a given altitude, the process is repeated with camps placed atprogressively 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 4,500metres(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 explains whyclimbers need to spend days (or even weeks at times) acclimatising before attempting to climb ahigh peak. Simulated altitude equipment that produce hypoxic (reduced oxygen) air can be usedto acclimate to altitude, reducing the total time required on the mountain itself.Altitude acclimatization is necessary for some people who rapidly move from lower altitudes tomore moderate altitudes, usually by aircraft and ground transportation over a few hours, such asfrom sea level to 8,000 feet (2,400 m) of many Colorado, USA mountain resorts. Stopping at anintermediate altitude overnight can reduce or eliminate a repeat episode of AMS.4. DrugsAcetazolamide may help some people to speed up the acclimatisation process when taken beforearriving at altitude, and can treat mild cases of altitude sickness. A typical dose is 250 mg twicedaily starting the day before moving to altitude.A single randomized controlled trial found that sumatriptan may help prevent altitudesickness.For centuries, indigenous cultures of the Altiplano, such as the Aymaras, have used coca leavesto treat mild altitude sickness.
5. Oxygen enrichmentIn high-altitude conditions, oxygen enrichment can counteract the effects of altitude sickness, orhypoxia. 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 viaan oxygen concentrator and an existing ventilation system provides an effective altitude of 3,000m (70 kPa), which is more tolerable for surface-dwellers. The most effective source ofsupplemental oxygen at high altitude are oxygen concentrators that use vacuum swing absorption(VSA) technology.[neutrality disputed] As opposed to generators that use pressure swing absorption(PSA), VSA technology does not suffer from performance degradation at increased altitude. Thelower air density actually facilitates the vacuum step process.6. Other methodsDrinking plenty of water will also help in acclimatisation to replace the fluids lost throughheavier breathing in the thin, dry air found at altitude, although consuming excessive quantities("over-hydration") has no benefits and may lead to hyponatremia.Oxygen from gas bottles or liquid containers can be applied directly via a nasal cannula or mask.Oxygen concentrators based upon PSA, VSA, or VPSA can be used to generate the oxygen ifelectricity is available. Stationary oxygen concentrators typically use PSA technology, which hasperformance degradations at the lower barometric pressures at high altitudes. One way tocompensate for the performance degradation is to utilize a concentrator with more flow capacity.There are also portable oxygen concentrators that can be used on vehicle DC power or oninternal batteries, and at least one system commercially available measures and compensates forthe 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 theFIO2 (fraction of inspired oxygen).
TreatmentThe only reliable treatment and in many cases the only option available is to descend.Attempts to treat or stabilize the patient in situ at altitude is dangerous unless highly controlledand with good medical facilities. However, the following treatments have been used when thepatients 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 pressure bag 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. 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 .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. . 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.