What is altitude sickness?
Altitude sickness refers to various forms of undesirable health effects caused by the low air pressure and lack of oxygen when at altitude. If people who live in the lowlands climb rapidly to over 2,000 meters above sea level, acute altitude sickness can be distinguished. Chronic altitude sickness can occur in people living in highland regions above 3,000 m in South America and Asia.
Frequency of acute altitude sickness
Over half of mountain hikers are affected when climbing rapidly to over 3,000 m. The most common form of acute altitude sickness is acute mountain sickness. It affects around 50% of people who ascend from the lowlands to over 3,000 m within a few hours. High altitude cerebral edema and high altitude pulmonary edema are much rarer.
Causes and risk factors
The cause of altitude sickness is the low oxygen content (oxygen partial pressure) in the mountain air. The higher you climb, the lower it is, and the less oxygen can be absorbed into the blood by breathing. This results in hypoxemia, a lack of oxygen in the blood. The lungs and heart try to compensate for the deficiency by increasing the respiratory and heart rate. Not everyone gets altitude sick when climbing.
Risk factors for acute altitude sickness are:
- Fast ascent: Rapid ascent to over 3,000 m and more than 300 meters per day from an altitude of over 4,000 meters
- Known individual susceptibility to altitude sickness
- Lack of fluids, overexertion and unhealed infections
- Women and young adults are more susceptible
- You suffer from migraines or have previously suffered from altitude sickness
Symptoms: Altitude sickness
Typically, the mild form of acute mountain sickness begins with a headache around four to six hours after the ascent. Other symptoms include dizziness, reduced performance, nausea and vomiting, palpitations, slight shortness of breath, loss of appetite and insomnia. This clinical picture is also known as AMS (“acute mountain sickness”). If these symptoms are ignored, risky complications can occur: high altitude cerebral edema.
High altitude cerebral edema
There is a risk of cerebral edema if you continue to stay at 4,000 meters or higher despite the first mild symptoms of altitude sickness. The prolonged and pronounced lack of oxygen in the blood leads to increased blood flow in the brain, so that the intracranial pressure rises. An accumulation of water forms in the brain tissue, which is known as cerebral edema. High altitude cerebral edema manifests itself through:
- Insecurity when standing and sitting,
- Coordination and movement disorders,
- Disturbances of consciousness,
- Lack of motivation, sharp drop in performance.
Without medical treatment, high altitude cerebral edema leads to coma and death.
High altitude pulmonary edema
People who are sensitive to oxygen deficiency can develop high-altitude pulmonary edema at altitudes above 3,500 m. This leads to vasoconstriction and an increase in blood pressure in the lungs. Eventually, fluid leaks into the lung tissue and alveoli, which severely impairs oxygen uptake. After 48 to 72 hours, high-altitude pulmonary edema manifests itself as
- Shortness of breath, first during physical activity and then also at rest
- increasing decline in performance,
- Cough, first dry, then also with possibly bloody sputum,
- Rattling noises when breathing,
- Palpitations and
- Cyanosis, a bluish discoloration of the skin, mucous membranes, lips and fingernails.
Chronic altitude sickness
Chronic altitude sickness can occur in people living in highland regions above 3,000 m in South America and Asia. In Europe, the risk of suffering from chronic altitude sickness is minimal because even the highest permanent settlements and places of residence are below 3,000 meters.
Diagnosis of altitude sickness
The Lake Louise Scoring System (LLSS) is helpful in diagnosing altitude sickness. It was developed for the assessment of symptoms in adults with acute altitude sickness. During the stay on the mountain, a self-assessment can be carried out with the help of the questionnaire. In addition, arterial oxygen saturation can be measured with a pulse oximeter.
The diagnosis of acute altitude sickness is based on the following criteria:
- Recent ascent and stay at an altitude of at least 2,500 m (within the last four days)
- Presence of headaches
- Presence of at least one other symptom
- An overall score of 3 or more from the LLSS assessment questionnaire
LLSS evaluation questionnaire
- Headache:
- No = 0
- Mild = 1
- Moderate = 2
- Serious = 3
- Gastrointestinal symptoms:
- No = 0
- Loss of appetite or nausea = 1
- Moderate nausea or vomiting = 2
- Serious nausea or vomiting = 3
- Tiredness and weakness:
- No = 0
- Mild = 1
- Moderate = 2
- Serious = 3
- Dizziness and drowsiness:
- No = 0
- Mild = 1
- Moderate = 2
- Serious = 3
- Insomnia:
- No = 0
- Mild = 1
- Slept badly = 2
- Did not sleep at all = 3
Sleep disorders are common during a stay at altitude but are usually harmless and are no longer considered part of acute mountain sickness. A total score of three to five on the Lake Louise questionnaire indicates mild acute mountain sickness. A score of six or more indicates a severe acute mountain sickness.
Prevention, early detection, prognosis
The best way to avoid altitude sickness is to ascend slowly. This allows the body to gradually adapt to the lack of oxygen, which is called acclimatization. From 3,000 meters you should not climb more than 300 to 500 additional meters per day. Choose the lowest possible sleeping position and take time to get a good night’s sleep. Sufficient rest is important for the body at these altitudes. You should not exert yourself too much during the adaptation phase. Drink plenty of water and avoid alcohol if possible.
Some training before the main ascent will also help you to adapt to the high altitude air: Short tours at medium altitudes spread over three months will make it easier for your body to cope with the subsequent exertion at high altitudes.
You should be careful with altitudes above 3,000 meters:
- for diseases of the lungs, heart or circulation and other diseases that are not stable
- in the case of an infection that has not yet completely healed,
- for long-term medication. In this case, you should ask us whether you can take the tour.
If you have ever had altitude sickness or are susceptible to it, we may prescribe medication that you can take as a preventative measure.
Prophylactic medication may also be advisable if you are unable to ascend slowly or acclimatize sufficiently to the altitude. The following active ingredients are suitable:
- Acetazolamide: This is a drug that leads to an acidification of the blood and thus stimulates breathing. This improves the oxygen content of the blood and reduces the incidence of altitude sickness. Side effects include taste disturbances, unpleasant tingling around the mouth, in the hands and feet and allergic reactions.
- Steroids (for example dexamethasone): They have an anti-inflammatory effect and can be used for the prophylaxis of acute mountain sickness if there is an intolerance to acetazolamide.
- Pulmonary antihypertensives (e.g. nifedipine): They lower the blood pressure in the pulmonary vessels and are used to prevent high-altitude pulmonary edema in people who are known to be susceptible.
Course and prognosis
The prognosis for mild altitude sickness is very good, especially if you start descending again in good time. However, the severe forms and complications can be life-threatening!
Years of research and experience at the USZ
At the Clinic for Pneumology, we have been studying the effects of altitude exposure on healthy people and patients with pre-existing cardiopulmonary conditions for years. We have also conducted many scientific studies in this field and cared for patients. We have close research and clinical cooperation in this area with Kyrgyzstan and other research groups worldwide. We will be happy to advise you!
Treatment
The most important measure for treating acute altitude sickness is to descend at least 1,000 meters immediately – this applies in particular to people with severe symptoms. This descent can be life-saving! If this is not possible, for example because the weather is bad or there are other logistical problems, treatment must be carried out on site. The primary aim is to improve the oxygen supply by administering oxygen or by increasing the atmospheric pressure in special pressure bags.
The following medications are helpful in the treatment of acute mountain sickness:
- Non-steroidal anti-inflammatory drugs: for example ibuprofen, paracetamol or aspirin.
- Steroids: The drug has an anti-inflammatory effect in severe acute mountain sickness and high-altitude cerebral edema.
- Pulmonary antihypertensives (e.g. nifedipine): They lower the blood pressure in the pulmonary vessels and are effective against high-altitude pulmonary edema.
What you can do yourself
If you have chronic illnesses and are taking long-term medication, please discuss with us whether we can recommend the trip to you. We can assess poor performance with the help of spiroergometry. Among other things, this diagnostic procedure measures respiratory gases and respiratory rate during physical exertion. This allows the reaction of the heart, circulation, lungs and metabolism to be assessed.
Find out about the symptoms of altitude sickness and pay attention to the corresponding symptoms during the trip. If you are traveling to a place that is over 3,000 metres above sea level for the first time, also find out about
- the special features of the location
- the region’s medical infrastructure.
