In our modern era, people seek more adventure during their summer vacations and beyond. They engage in activities such as hiking in mountains, canoeing, mountaineering, skiing, and other sports that often take place at high altitudes. It is estimated that over 100 million tourists visit high-altitude destinations each year. At altitudes above 2,500 meters, sudden arrival of individuals who usually reside in lower areas or at sea level can lead to a syndrome of discomfort known as:
Acute Mountain Sickness - AMS or High Altitude Cerebral Edema - HACE
It is useful to classify altitude according to its effects on the physiology of individuals:
Intermediate altitude, 1500 - 2500m: Normal blood oxygen saturation usually >90%. Unlikely presence of AMS.
High altitude, 2500 - 3500m: Frequent presence of AMS with rapid ascent above 2500 meters.
Very high altitude, 3500 - 5800m: Decreased blood oxygen saturation <90%, frequent presence of AMS, accompanied by hypoxemia during exercise.
Excessive altitude, >5800m: Limited acclimatisation. Progressive deterioration. Presence of hypoxemia (low oxygen levels) even at rest.
The main symptom of AMS is headache, often accompanied by one or more symptoms such as loss of appetite, nausea/vomiting, fatigue, dizziness, and difficulty sleeping. The latter symptom is particularly common at high altitudes, and an individual who typically suffers from AMS will experience a headache, have poor appetite, and encounter sleep problems.
Signs and Symptoms in Physiology: A headache that is extremely intense, throbbing, or frontal, worsens at night or in the morning, and aggravates when bending forward or performing the Valsalva manoeuvre (breath-holding with a closed nose). It may also be accompanied by tachycardia and, in some cases, a slight increase in body temperature. Peripheral and periorbital edema are common features at high altitude but may worsen in individuals with AMS. The presence of a dry cough of unknown aetiology at high altitude is also common and may be related to cold air or reduced humidity.
Although shortness of breath occurs automatically upon arrival at high altitude, it usually takes several hours for AMS to develop, typically 6 to 10 hours, although it can occur earlier or later, up to 36 hours. Symptoms may worsen on the second day, but if there is no further increase in altitude, AMS usually subsides within 1-3 days as acclimatization is completed. After this time period, further ascent to higher altitudes may result in its reappearance until acclimatization is completed at the new altitude. As these symptoms are common, tourists and many climbers attribute them to fatigue from travel, dehydration, jet lag, or the consequences of alcohol consumption, all of which may coexist.
Regarding the Pathophysiology of AMS: The most important factors in the aetiology of AMS are the ascent rate and the total altitude gain. It is preferable to ascend gradually, possibly interrupting the journey with an overnight stay at a lower altitude first.
If an unacclimatised individual reaches 3000 meters at a fast pace, they should not increase their sleeping altitude until the acclimatization stage is completed. Above 3000 meters, the sleeping altitude should not increase by more than 300 meters per day, and one rest day should be taken every third day or every 1000 meters of ascent. Daytime excursions may reach higher altitudes, provided that the aforementioned schedule is approximately maintained.
There seems to be no differentiation between the sexes regarding their susceptibility to AMS. Menstruation, smoking, hypertension, heart disease, diabetes, pregnancy, or mild chronic obstructive pulmonary disease do not appear to be risk factors. Children do not have a higher vulnerability, and some studies suggest that individuals over 60 years of age may have a lower tendency for AMS. Being fit does not protect against AMS, but it may be a risk factor if athletic individuals ascend at a faster pace. Exercise immediately after arrival at high altitude can increase susceptibility to AMS.
Unfortunately, there are no preventive tests to determine who will develop AMS, and the only real guide, but not a guarantee, is previous performance at altitude. Individuals with poor acclimatisation tend to have recurrent relatively poor responses, and vice versa.
Additional Complications in Physiology: Ascent to high altitude may make one susceptible to AMS, however the two most potential conditions for developing altitude sickness is High Altitude Pulmonary Edema (HAPE) and High Altitude Cerebral Edema (HACE). Although they are considered separate entities, they share many common clinical characteristics but represent different degrees of severity of a common, albeit undocumented, pathophysiological mechanism.
While AMS is usually mild and self-limiting, it is considered to represent the benign end of a spectrum of mild cerebral edema, with HACE being a serious and potentially fatal consequence. Confusion is often the first and last sign in urgent treatment. If a patient exhibits this symptom, a change in behaviour, or even hallucinations, descent is mandatory.
HAPE has a distinct aetiology, although it often accompanies AMS, and can occur with or without the presence of HACE. Exertional dyspnoea at rest is a crucial sign. Initially, the cough is dry, gradually producing frothy yellow-white sputum with signs of blood. At high altitudes, a milder respiratory infection can easily be misinterpreted as HAPE, and descent would be the first action.
Treatment: The most effective treatment for any altitude-related illness is undoubtedly descent. However, mild AMS usually requires rest, relaxation, ensuring good hydration, and the use of simple analgesic medications despite stopping the ascent. The use of paracetamol, aspirin, and codeine is recommended. Severe AMS should prompt descent and can be treated with acetazolamide. In severe cases, dexamethasone and oxygen may be required.
HACE and HAPE can be life-threatening and require immediate and rapid descent, even at night. Oxygen, dexamethasone, and acetazolamide are adjunct treatments for HACE. Oxygen provides rapid relief for HAPE, and nifedipine can help. Mobile inflatable hyperbaric chambers, transported nowadays at increasing rates by mountaineering expeditions, can artificially "descend" a person by up to 2000 meters, providing temporary and satisfactory improvement to facilitate actual descent. Victims of HAPE will require support as the supine position is exhausting.
Recommendations: Despite the seriousness of all mountaineering illnesses due to high altitude, it is possible to prevent their adverse consequences, and with caution, climbing can present almost no problems. Currently, there are no available tests that can accurately predict altitude tolerance, and special care is needed when attempting to climb high mountains. The recommendations to be considered are as follows:
The ascent profile should be gradual, and above 3000 meters, the ascent rate should not exceed 300 meters per day, with one rest day every 3 days or 1000 meters. A safe ascent cannot be guaranteed as it usually varies between individuals.
Previous altitude illness history should be taken into account. Precautions should be taken to avoid future illness.
Medical support should be available within the group, and emergency evacuation plans should be in place at the campsite.
Flexibility in the itinerary to prevent inadequate acclimatisation and to allow for the treatment of any medical problems.
Knowing how to recognize the symptoms of AMS and when to terminate the ascent is important.
CONCLUDING REMARKS Altitude illness occurs not only at specific and specialised mountaineering altitudes but also at common tourist altitudes. It tends to be mild and self-limiting, but it can be a precursor to cerebral or pulmonary edema, which can threaten life. Mild AMS can be managed with rest, fluids, and simple analgesics, but those with more severe symptoms MUST start descending immediately. Prior to arrival at altitude, if there is a reason to address any issues, medical advice is important.