Altitude Sickness

Altitude sickness

Haste is the biggest risk factor

by Ulrike Wagner, Eschborn

More and more tourists are conquering the Himalayas. Trekking trips are in, and the roof of the world is the most attractive destination. Few people think about altitude sickness, even though the symptoms can appear as early as 2,500 meters. Numerous crosses already line some popular trekking routes. However, careful behavior and a slow ascent can prevent this often life-threatening illness.

The cause of acute altitude sickness is the lower air pressure and the associated lower partial pressure of oxygen at high altitudes. The human body tries to compensate for the lack of oxygen with a higher respiratory rate and a higher resting heart rate. In addition, the number of red blood cells increases. At an altitude of 4,500 meters, for example, this increases by around 10 percent after just two days. While this improves the body’s oxygen supply, the larger number of cells in the blood increases the risk of circulatory disorders, edema, and thrombosis. Many scientists consider high-altitude cerebral edema (HACE) and acute mountain sickness to be manifestations of the same disease process of varying severity.

Strictly speaking, it is not edema, but rather brain swelling, ie, a general enlargement of the brain, including an increase in cerebral blood volume and cerebrospinal fluid. The theory is that the cause is likely changes in the blood-brain barrier, which becomes leaky due to oxygen deprivation.
In
high-altitude pulmonary edema (HAPE), increased fluid leaks from the pulmonary vessels into the lung tissue and alveoli. This further impairs gas exchange and exacerbates the oxygen deprivation in the body.

Signs of mild acute mountain sickness (see box) often appear at altitudes between 2,000 and 2,500 meters. It is not possible to determine in advance which healthy adults are susceptible to it. Physically fit people suffer from the symptoms just as frequently as those who are less fit. Smoking is also not a risk factor. Older people are no more at risk than young people. Only children and infants are at higher risk.

First signs of acute altitude sickness

• Headache
• nausea
• Vomit
• Visual disturbances
• dizziness
• Resting heart rate increased by more than 20 percent
• Cough
• shortness of breath
• Facial or lower leg edema
• Loss of appetite
• Sleep disorders
• Performance decline
• Psychologically abnormal behavior such as lack of criticism, hyperactivity, euphoria, irrational behavior

One parameter frequently observed in people susceptible to altitude sickness is a slight increase in breathing under oxygen deprivation. However, a high respiratory drive under hypoxia does not automatically protect against the illness.
The main trigger
of altitude sickness is ascending too quickly. Other factors that can contribute to this include overexertion, alcohol consumption, fluid and mineral deficiencies due to increased excretion at altitude (high-altitude diuresis), infections, and sleeping pills.

Rest day or descent

: If the first symptoms of acute altitude sickness appear, you should not ascend any further but take a rest day. The symptoms often disappear completely within one to two days. Headaches can be treated with 600 mg of ibuprofen (lower doses are usually ineffective). If you are only relieved of pain with continued physical therapy, you should not climb but rest until you are free of symptoms without painkillers.
Since
freedom from symptoms means you have acclimatized, you can slowly resume the ascent. Mountaineers should not take even mild symptoms lightly. Even mild altitude sickness can cause brief loss of consciousness, dramatically increasing the risk of accidents. If symptoms worsen by the next morning, the affected person should immediately descend under supervision.

If warning signs (see box) appear, the patient must immediately descend at least 500 meters, and preferably even below 2500 meters. Other guidelines are less strict and stipulate descending to the altitude at which the patient previously spent a night without symptoms. Even a nighttime descent should be considered, as waiting at the same altitude is dangerous in this condition. When in doubt, always go down is one of the guiding principles for treating altitude sickness. The rule of thumb is: Never descend alone.
If
the descent is severe in cases of severe acute altitude sickness and at the first signs of pulmonary and high-altitude cerebral edema, the patient should always be transported, as physical activity can dangerously aggravate the symptoms

Warning signs

• Persistent, severe headache
• Persistent, severe nausea with vomiting
• Severe cough, even without sputum
• Heart palpitations and rapid pulse
• insomnia
• Rapid breathing
• Shortness of breath during exertion
• Nocturnal shortness of breath at rest
• Rapid performance decline
• Light sensitivity
• Dizziness, unsteady gait
• Dizziness
• Reduced urine output below 0.5 liters
• Excretion of dark urine
• Pressure on the chest

Always accompanied.

If the warning signs (see box) appear

Under no circumstances one should wait for outside rescue. “Several people suffering from HACE or HAPE have already died while waiting for days for a requested helicopter and could have been saved by rapid ground transport to lower altitudes,” writes Professor Dr. Franz Berghold of the Austrian Society for Alpine and High-Altitude Medicine.
Often
, especially in larger groups, those affected conceal their symptoms. They do not want to lose contact or delay the group. This explains why 80 percent of fatal incidents occur in organized groups, which only account for 40 percent of trekking trips.

Alarm signs

• Severely ill, unconscious or confused patient
• Shortness of breath at rest
• Severe cough with brown sputum
• Lack of urine production

Emergency therapy

The measures that, in addition to descent, are best suited for emergency treatment of severe acute mountain sickness, high-altitude pulmonary edema, and high-altitude cerebral edema, involve considerable effort. For example, hikers should always have oxygen cylinders ready when trekking at higher altitudes, but this is often overlooked. Oxygen is considered the treatment of choice for severe acute mountain sickness, high-altitude pulmonary edema, and high-altitude cerebral edema.

An alternative to oxygen ventilation is a hyperbaric backpack. One to two hours in a hyperbaric mobile chamber often reduces the symptoms of high-altitude pulmonary edema and high-altitude cerebral edema, but does not replace evacuation, which must take place immediately afterwards. However, such a chamber is usually not available in an emergency. Experts are not yet in agreement as to whether it is actually advisable to take the cumbersome hyperbaric backpack on every trekking tour. In addition, rescuers must constantly pump to maintain the pressure in the hyperbaric chamber – a significant strain at high altitudes.

Medications

The calcium antagonist nifedipine (eg, Adalat®) is used to

Dexamethasone is considered the drug of choice for severe acute mountain sickness and the onset of high-altitude cerebral edema. It is believed to stabilize the blood-brain barrier and thus improve symptoms (dosage: 8 mg initially, then 4 mg every six hours in tablet form). However, it is completely ineffective in high-altitude pulmonary edema. Early and abrupt discontinuation can lead to severe rebound. If evacuation is initially impossible, the combination of dexamethasone and hyperbaric therapy has proven beneficial in patients with high-altitude cerebral edema. For unclear severe forms, Berghold recommends triple therapy consisting of dexamethasone, nifedipine, and oxygen or hyperbaric bag.

Although acetazolamide (Diamox®) is still recommended by some for the treatment of acute mountain sickness, other medical experts advise against it. This is because taking the drug is not really necessary for milder forms, and dexamethasone is more effective for moderate to severe mountain sickness. Acetazolamide is not only largely ineffective for high-altitude pulmonary edema, it can even worsen symptoms. Other medications, such as theophylline, ginkgo biloba preparations, and montelukast, are currently being tested. PreventionYou can protect yourself from altitude sickness. The simplest and safest prophylaxis is a slow ascent. However, very few mountain hikers put this into practice, writes the Federal Foreign Office. The rules are simple: At altitudes above 2,500 meters, you should climb a maximum of 300 to 500 meters per day, and above 3,000 meters, a maximum of 250 to 300 meters (each calculated from your sleeping place). Ascending to higher altitudes during the day is safe if the sleeping altitude is lowered accordingly in the evening. After about 1000 meters, you should take a two-day acclimatization and rest period. You also need to adjust your fluid levels. An additional 1.5 liters of fluid are recommended for every 1000 meters. You should not sleep at altitudes above 3000 meters for the first three days. A stay of several days at 3000 meters is usually enough to acclimatize to higher altitudes. The prevalence of altitude sickness is higher the fewer days the mountaineer has previously spent above 3000 meters.
Some high-altitude doctors recommend acetazolamide for the prophylaxis of acute altitude sickness – especially if it has already been determined from previous tours that the affected person is sensitive to being at high altitudes or if a rapid ascent to high altitudes is unavoidable, for example, during rescue operations. The sulfur-containing carbonic anhydrase inhibitor increases ventilation at rest and during exercise, improves gas exchange, lowers intracranial pressure, and improves oxygen supply to tissues. This may prevent the symptoms of acute altitude sickness. However, increased diuresis is often cited as a counterargument. This can, however, be quite desirable because it reduces cerebral pressure, according to Berghold. However, repeated and indiscriminate use of acetazolamide can cause thrombosis. Critics of the prophylactic use of the drug fear that it masks the initial symptoms of acute altitude sickness, thereby increasing the risk of fatal incidents.

One of the most common mistakes is continuing to climb when symptoms of mild altitude sickness occur despite prophylactic use. This is because the substance cannot prevent the development of high-altitude pulmonary edema. Only those who are completely symptom-free while taking acetazolamide may safely climb higher. A low dose is recommended for prophylactic purposes: twice a day, 125 mg, starting 24 hours before crossing the 3,000-meter line for two to three days, but for at least 24 hours after reaching the final altitude. This medication should not be taken if you are allergic to sulfonamides

When acetazolamide prevents altitude sickness

Geneva – The carbonic anhydrase inhibitor acetazolamide is a popular medication for preventing altitude sickness among alpine climbers. However, according to a meta-analysis in High Altitude Medicine & Biology (2012, 13: 82-92), the most pronounced effect is achieved in tourists and workers who travel to high altitudes in a short period of time by vehicle.

Ten to 20 percent of all non-acclimatized people develop acute altitude sickness after ascending to 2,500 to 3,000 meters above sea level. For stays above 4,000 meters, the incidence can rise to as much as 80 percent. The main symptom is headaches accompanied by non-specific general complaints. In severe cases, life-threatening cerebral edema with treatment-resistant headaches, ataxia, and impaired consciousness can occur, and/or pulmonary edema, which is also often fatal, with bronchial symptoms, cough, fever, and shortness of breath.

Many alpine climbers are aware of the danger. According to Bengt Kayser of the University of Geneva, the proportion of Himalayan tourists who (attempt to) protect themselves against altitude sickness with acetazolamide has increased from one percent in 1986 to 25 percent in 2010. The physiologist evaluated 24 studies with 1,011 subjects that examined the effects of acetazolamide at daily doses of 250, 500, or 750 mg.

Perhaps the most surprising result was that dosage had only a minor influence on the effect. At just 250 mg/day, the incidence of acute mountain sickness was reduced by 45 percent (risk ratio RR 0.55; 95 percent confidence interval 0.42-0.74), at 500 mg/day the risk was reduced by 50 percent (RR 0.50; 0.40-0.63), and at 750 mg/day the incidence was 55 percent lower (RR 0.45; 0.34-0.61).
Kayser
recommends a sufficiently high dosage, as long as it is tolerated. The most important side effects of acetazolamide are polyuria and taste disturbances. According to the study results, both occur more frequently at the higher doses of 500 and 750 mg/day, while paresthesia is not dose-dependent.

Kayser evaluates the preventive effect using the number needed to treat. This is the number of people who need to take acetazolamide to prevent one person from experiencing altitude sickness. This number is particularly high among mountaineers who ascend the mountain on foot, at 5.3 (at the highest dosage). This means that the fewest cases of altitude sickness are prevented in this group.

The reason, however, is not the weak effect of acetazolamide in this group, but rather the low initial risk of 34 percent due to the slow ascent of 14 meters/hour. When tourists in a study traveled 491 meters up the mountain by bus or car, 60 percent developed altitude sickness without acetazolamide. The number needed to treat was correspondingly lower at 3.0 (at the highest dosage).

Incidentally, mountaineers who arrived by bus and then continued climbing on foot, overcoming a total elevation difference of only 133 meters/hour, had the same risk. The initial risk was highest in experiments in the hypobaric pressure chamber: When an ascent of 4,438 meters/hour was simulated, 86 percent of the participants became ill. The number needed to treat here was only 2.1.