yogabook / pathologie / acute mountain sickness

Acute Mountain Sickness AMS / altitude sickness / D’Acosta-Krankheit, AMS

Definition of

The oxygen content of the air, and therefore the partial pressure, decreases with altitude. This leads to vasoconstriction of the lungs (Euler-Liljestrand), resulting in reduced oxygenation of the blood (hypoxia). Reflex hyperventilation leads to hypocapnia and thus to alkalosis of the blood. With good acclimatization, the kidneys can largely compensate for this up to approx. 7000 m, but dehydration, which increases with altitude, makes this increasingly difficult. In the brain, the low partial pressure of CO2 causes vasoconstriction, as does the low partial pressure of O2 in the lungs. This can lead to Cheye-Stokes respiration. Sympathetic activationincreases blood pressure, which results in a risk of edema of the brain and lungs. The following are some basic statements about staying and exercising at higher altitudes. The altitudes are divided into zones:

1. from 2500 m: critical zone, threshold height. Up to this point, the immediate adjustment is sufficient
2. From 3000 m to 5300 m: the sleeping altitude should not be increased by more than 300-400 m / d, take a day’s break every 3-4 d, if more ascent is necessary on one day, stay there for another day. Acclimatization obligatory.
3. from 5300 m: extreme altitude: only for short stays
4. From 7000 m: „death zone“ 1: here the partial pressure O2 drops to below 30 to 35 mm Hg, which makes adequate oxygenation and regeneration impossible even after long periods of rest.
5. From 8000 m: „death zone“ 2: survival of more than 48 h extremely unlikely

For an ascent up to 4500 m, a week’s stay at 2000 to 3000 m with day tours at higher altitudes should be planned, for one at 6000 m another week. This reduces the risk of altitude sickness by 50%. The adaptation to higher altitudes is largely genetically predisposed and less trainable, even genetically favorably equipped untrained people can double their erythrocyte population, while a comparable adaptation in many genetically less favorably equipped, but athletically trained people may be much lower even with a longer stay at altitude. The influence of medication taken on altitude and its possible masking of altitude symptoms should be clarified with a doctor beforehand. Already at an altitude of 1000 meters above sea level 3-5% of people show symptoms of AMS (Acute Mountain Sickness), at 2500 already 10 – 25%: headache, dizziness, nausea, drowsiness. No acclimatization is required for stays of up to 8 hours, but performance is lower than after acclimatization. Breathing becomes deeper and faster. Sleep at altitude is lighter and more restless, the dream phases are shortened, breathing interruptions occur more frequently. The resting pulse rate is increased – depending on altitude – often by 10-20 %. An immediate adaptation is increased diuresis, so that the hematocrit rises. To counteract the risks of an excessively high hematocrit, you must drink enough. The bone marrow will then produce more erythrocytes after about 2-3 weeks at altitude.

A doctor should be consulted beforehand if you have a known heart or lung condition. Acclimatization cannot be trained. However, more frequent stays at altitude lead to better adaptation of breathing. Performance decreases by approximately 10% per 1000 meters of altitude. So if you live in the lowlands, you will still have 2/3 of your performance capacity at 4000 meters and just over half at 6000 meters. Good fitness is essential for mountaineering, but only people over 55 years of age can demonstrate better altitude tolerance through a good level of training. When climbing and working at altitude, you should never use more than 50-60% of your maximum capacity, which corresponds to a maximum pulse rate of around 140 bpm, or 120 bpm for older people, and breathing through the nose should still be possible. Anaerobic performance at altitude is AI. The diet should be rich in carbohydrates, fats take longer to metabolize. Vitamins, minerals including salt must be supplied in sufficient quantities. As the air is drier at altitude, more fluid is needed at altitude, approx. 4-5 l / d. The excretion of urine should not fall below 1 l / d, it must not become too dark.

Asthma is generally not a problem at high altitudes; on the contrary, asthmatics benefit from the lower levels of harmful substances in the air. Hypohemoglobinemia can be an AI for staying at high altitudes. As a rule of thumb, any occurrence of symptoms above 2500 meters must be considered altitude sickness until proven otherwise. Symptoms contraindicate further ascent and, depending on the extent or worsening, indicate descent from altitude. People with symptoms of altitude sickness must not be left alone. Lack of fitness is not a risk factor for altitude sickness, but predisposes to excessive exhaustion. When assessing the resting heart rate, it must be seen relative to the known resting heart rate, not to normal values. The following known AIs exist for ascents and stays above 2000 meters:

1. up to 3 months after myocardial infarction
2. Thromboembolism
3. cerebrovascular insult (apoplexy)
4. ICD implantation (defibrillator implantation)
5. Unstable angina pectoris (stable CHD is not an AI)
6. planned coronary intervention
7. Heart failure
8. cyanotic and severe non-cyanotic vitia
9. pulmonary arterial hypertension
10. severe COPD (no AI for less severe COPD that is stable on medication)

ICD T70.2

Cause

1. Mainly: lack of oxygen at high altitude

Predisposing

1. Ascents of more than 625 meters per day from 2000 meters above sea level
2. lack of prior acclimatization with less than five days above 3000 meters in the previous two months
3. Female gender
4. Age under 46 years

Symptoms

In general, the spectrum of possible symptoms includes

1. Leading symptom: Headache: dull, throbbing, often at night and on waking, stress headache
2. Drowsiness to apathy
3. Dizziness, unsteady gait, unsteady stance
4. Tachypnea, dyspnea on exertion, also dyspnea at rest
5. Tachycardia (more than 20% above known resting heart rate)
6. Nausea
7. Loss of appetite
8. Vomiting
9. Sudden drop in performance with excessive tiredness
10. possibly unproductive cough
11. Sleep disorders
12. Confusion, misperceptions
13. Oliguria

Subdivided into early warning, warning and alarm signs:

1. Early signs: Headache, nausea, dizziness, resting pulse rate above 20 of the known, peripheral edema, loss of appetite, loss of performance, euphoria or irrational behavior
2. Warning signs: severe, persistent headache, severe, persistent nausea with vomiting, dry cough, tachycardia, resting dyspnea, insomnia, rapid drop in performance, dizziness, drowsiness, unsteady stance, unsteady gait, oliguria, dark urine
3. Alarm signs: Confusion, severe resting dyspnea, persistent productive cough with brown sputum, rales in breathing, cyanosis of the lips, anuria

Complications

1. High altitude cerebral edema (HACE) , acutely life-threatening
2. High-altitude pulmonary edema (HAPE), acutely life-threatening: increasing dyspnea, development of alveolar pulmonary edema, possibly foamy or bloody sputum (hemoptysis)

Therapy

1. Prophylactic medication (efficacy proven, but not approved for the indication of prophylaxis of altitude sickness): Acetazolamide, ASA, dexamethasone, salmeterol, ibuprofen 600, calcium carbasalate
2. If mild symptoms occur, pause ascent, NSAIDs for headache, antiemetic, acetazolamide (CAVE: clarify occurrence of NW beforehand) against formation of cerebral edema
3. In case of severe symptoms, immediate descent or transportation to lower altitudes, oxygen ventilation, Gamow bag (portable pressure chamber). Re-ascend only if no symptoms occur without medication.
4. Drug of choice: Nifedipine