High Altitude Sickness problem during a high trek in Nepal
November 25, 2024
nepalguide
Altitude sickness, also known as acute mountain sickness (AMS), is a negative health effect of high altitude, caused by acute exposure to low amounts of oxygen at high altitude.
Although minor symptoms such as breathlessness may occur at altitudes of 1,500 metres (5,000 ft), AMS commonly occurs above 2,400 metres (8,000 ft) 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”. It is hard to determine who will be affected by altitude sickness, as there are no specific factors that correlate with a susceptibility to altitude sickness. However, most people can ascend to 2,400 metres (8,000 ft) without difficulty.
Acute mountain sickness can progress to high altitude pulmonary edema (HAPE) or high altitude cerebral edema (HACE), both of which are potentially fatal, and can only be cured by immediate descent to lower altitude or oxygen administration
Chronic mountain sickness is a different condition that only occurs after long term exposure to high altitude.
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). 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.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.
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 kilo pascals (0.79 atm).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 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.
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:
Gastrointestinal disorder: Loss of appetite, nausea, or vomiting, excessive flatulation
Nervous system disorder: Fatigue or weakness, headache with or without dizziness or pigheadedness, insomnia
Locomotory system disorder: Peripheral edema (swelling of hands, feet, and face)
Respiratory system disorder: Nose bleeding, shortness of breath upon exertion
Cardiovascular system disorder: Persistent rapid pulse
Others: Pins and needles, general malaise
Severe symptoms[edit]
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 vasodilatace 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, dextromethorfane 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.
Cause
Climbers on Mount Everest often experience altitude sickness.
Altitude sickness can first occur at 1,500 metres, with the effects becoming severe at extreme altitudes (greater than 5,500 metres). Only brief trips above 6,000 metres are possible and supplemental oxygen is needed to avert sickness.
As altitude increases, the available amount of oxygen to sustain mental and physical alertness decreases with the overall air pressure, though the relative percentage of oxygen in air, at about 21%, remains practically unchanged up to 21,000 metres (70,000 ft).[9] The RMS velocities of diatomic nitrogen and oxygen are very similar and thus no change occurs in the ratio of oxygen to nitrogen until stratospheric heights.
Dehydration due to the higher rate of water vapor lost from the lungs at higher altitudes may contribute to the symptoms of altitude sickness.
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 acclimatization occurs. However, in extreme cases, altitude sickness can be fatal.
High altitude
At high altitude, 1,500 to 3,500 metres (4,900 to 11,500 ft), the onset of physiological effects of diminished inspiratory oxygen pressure (PiO2) includes decreased exercise performance and increased ventilation (lower arterial partial pressure of carbon dioxide- PCO2). While arterial oxygen transport may be only slightly impaired the arterial oxygen saturation, SaO2, generally stays above 90%. Altitude sickness is common between 2,400 and 4,000m because of the large number of people who ascend rapidly to these altitudes.
Very high altitude
At very high altitude, 3,500 to 5,500 metres (11,500 to 18,000 ft), maximum SaO2 falls below 90% as the arterial PO2 falls below 60 mmHg. Extreme hypoxemia may occur during exercise, during sleep, and in the presence of high altitude pulmonary edema or other acute lung conditions. Severe altitude illness occurs most commonly in this range.
Extreme altitude
Above 5,500 metres (18,000 ft), marked hypoxemia, hypocapnia, and alkalosis are characteristic of extreme altitudes. Progressive deterioration of physiologic function eventually outstrips acclimatization. As a result, no permanent human habitation occurs above 6,000 metres (20,000 ft). A period of acclimatization is necessary when ascending to extreme altitude; abrupt ascent without supplemental oxygen for other than brief exposures invites severe altitude sickness.
Mechanism
The physiology of altitude sickness centres around the alveolar gas equation; the atmospheric pressure is low, but there is still 20.9% Oxygen, water vapour still occupies the same pressure too, this means that there is less oxygen pressure available in the lungs and blood. Compare these two equations comparing the amount of oxygen in blood at altitude
Altitude sickness is the reaction of the body adjusting to decreasing amounts of oxygen. Normally, the higher the altitude, the less oxygen available for the body to carry on normal functions. Altitude sickness most commonly occurs from above 2,800 metres (9,200 ft) but this is different for everyone – there is simply no way of knowing your own susceptibility prior to being at altitude thus it is vital you monitor your own health. Symptoms may be mild and subside/go away after a day’s rest, or if it is ignored it could lead to death.
Symptoms of altitude sickness…
Symptoms can appear within 1-2 hours although most often appear 6-10 hours after ascent and generally subside in 1-2 days as the body adjusts to altitude. They may reappear as you continue to go higher. Symptoms usually occur gradually & can be one or a combination of the following:
Headache
Loss of appetite
Disturbed sleep or drowsiness
Irritability
Fatigue
Nausea/vomiting
Dizziness
Swelling of hands, feet & face
How to Prevent Altitude Sickness for Trekkers
* The information on this page is the consensus among experienced trekkers but is not intended to replace the advice of a medical professional. Consult a doctor before trekking at high altitudes or using any medications.
1. Drink 5 Liters of Water Per Day
Quite simply, drink a minimum of five liters of water per day, no matter what. This is easier at lower elevations when it’s hot, but becomes more burdensome when temperatures cool off and you perspire less. After a few liters you may feel properly hydrated, but your body is doing extra work with less oxygen and needs the water. Force down five liters per day, without exceptions.
2. Avoid Dramatic Gains in Elevation
Treks at altitude should avoid big single-day gains in elevation (more than 1,500 vertical feet). A common misconception about trekking at high altitude is that physical condition dictates the body’s ability to fend off altitude sickness. This causes many people who are “in good shape” to ignore the rules of acclimatization, go too high too fast, and have problems. Your itinerary should factor in altitude gains and consequently some hiking days will end early. Embrace the pace, rest your legs, and hydrate.
3. Climb High, Sleep Low
Altitude Sickness and High Altitude Trekking
Thorong La Pass (5,416 m) on the Annapurna Circuit | Credit: Ali Beittoei
You will acclimatize better if you expose yourself to higher altitudes but return to a lower altitude to sleep. After setting up camp, scramble up a nearby hill, scope out the scenery, and head back down for a better night’s rest. When you have a rest day, use the opportunity to hike to higher elevations and back down—even a few hundred vertical feet is worth the effort. At higher altitudes—around 10,000 feet and above—this rule becomes even more important as your body is learning to cope with considerably less oxygen.
4. Eat, Eat, Eat…
Your body is doing more work than usual so make sure to stay nourished and full of carbohydrates. For a dependable snack, Nepal has embraced the Snickers bar wholeheartedly and it can be found even in the tiniest villages (and for very cheap). Too much sugar, yes, but full of good things like nuts and chocolate. Do a good deed and buy some for your porters and guide whenever possible.
5. Listen to Your Body
By following the above rules, you will greatly increase your odds of staying healthy throughout your trek, but everybody reacts differently to altitude so pay close attention to how you feel. Every trek should have rest days built in and you shouldn’t be afraid to use them. Stay hydrated, wear sunscreen, and have layers available for protection from the powerful sun. Avoid alcohol and other substances. Monitor yourself and always communicate any health concerns to your group.
An estimated 75% of people feel some affects of altitude, mostly in the form of headaches, nausea, fatigue, and trouble sleeping. These are actually mild manifestations of Acute Mountain Sickness (AMS). Mild AMS should not interfere with normal activity and the symptoms should subside as acclimatization occurs. As long as the symptoms are mild, it’s generally okay to continue hiking up at a moderate rate. If feeling poorly persists or worsens, turn around.
Medications for Altitude Sickness
The only treatment for altitude sickness is descent, but medication can help with the symptoms. Consult a doctor before use.
Ibuprofen can be used to treat the symptoms of mild altitude sickness such as headaches and nausea.
Diamox (Acetazolamide) is a respiratory stimulant that helps the body metabolize more oxygen, especially at night, thereby accelerating the process of acclimatization. Diamox can be used as a prophylactic, particularly by those making unavoidably large ascents.
Severe Problems
In severe cases altitude sickness can be truly life-threatening. If a trekker ever gets an unusual or severe headache, or feels unusually short of breath, they should immediately descend 2,000 feet (600 meters), no matter the time of day. High Altitude Pulmonary Edema (HAPE), excess fluid in the lungs, and High Altitude Cerebral Edema (HACE), swelling of the brain, are rare but life threatening conditions that require immediate descent and medical attention.
Have Questions?
