Acute Mountain Sickness (AMS) or high altitude illness (HAI) is a term used to describe a group of cerebral and pulmonary syndromes that can occur during travel to elevations above 2500 m (8200 ft.). The altitude is commonly classified as high – 1500 – 3500 m (4921- 11483 ft.), very high – 3500- 5500 m (11483 -18045 ft.) and extreme – above 5500 m (18045 ft.). HAI occurs in more than one-fourth of people traveling to above 3500 m (11 667 ft.) and more than one-half of people traveling to above 6000 m (20 000 ft.) (Flaherty GT, 2016) (Khodaee M, 2016). Symptoms usually occur on within 12 to 24 hours after reaching a higher elevation and include headache (a very common symptom at altitude), sleep disturbances, elevations of heart rate and increased depth and rate of breathing, fatigue, poor appetite, nausea and vomiting (Bailey DM, 2009) (Palmer, 2010). Because of the large number of people who ascend rapidly to between 2500 m and 3500 m, high altitude illness is common in this height range because of hypoxia (Davis C, 2017). The supply of oxygen to the tissues can be compromised because of the lower partial pressure of oxygen in the inspired air (Wilson MH, 2009). The physiological responses to hypoxia and acclimatization such as hyperventilation; elevation of systemic blood pressure; and tachycardia may be inadequate, so that the ascent to high altitude and the attendant hypoxia are complicated by HAI (Luks AM, 2017).
Well-known risk factors of experiencing HAI are the rate of ascent, the absolute change in altitude and individual physiology, such as anaemia, heart or lung disease, obstructive sleep apnoea, and past bouts of acute mountain sickness (Flaherty GT, 2016) (Leissner KB, 2009). Prevention tactics AMS include regular exposure to altitude (preacclimatization) and a gradual ascent, especially when it comes to sleeping altitude (aim for less than 400- 500 m (1333 -1640 ft.) difference between each night.
Three Cochrane Reviews published in the years 2017-2019 analyse the impact of interventions for preventing HAI (Molano Franco D, 2019, Gonzalez Garay A, 2018, Nieto Estrada VH, 2017). The results:
-Supplementation of antioxidants, medroxyprogesterone, and iron or Rhodiola crenulata might not improve the risk of HAI.
– The risk of HAI can be improved with the administration of erythropoietin.
– Sumatriptan showed a reduction of the risk of HAI when compared with a placebo.
– Data on acetazolamide versus placebo showed a reduction with acetazolamide. Acetazolamide compared with spironolactone showed a lower risk of HAI with the administration of acetazolamide.
– Data on budenoside showed a reduction in the incidence of HAI compared with placebo
– For dexamethasone, the data did not show benefits at any dosage.
Of course, the risk of adverse events for these interventions has to be individually evaluated.
In recent decades, the number of mountaineering athletes, alpinists, rock and ice climbers, ski mountaineers and high altitude travellers aged 60 years or older is increasing.
Recent in the Oxford Academic Journal of Travel Medicine published systematic analyse evaluates the impact of age at developing AMS. The review shows, that old age does not seem to be a contraindication for travelling at high altitude. (Gianfredi V, 2020)
Prevention tactics for HAI include regular exposure to altitude (preacclimatization) and a gradual (slow) ascent, especially when it comes to sleeping altitude (aim for less than 400 m (1333 ft.) difference between each night). People with a history of HAI or AMS should be especially careful. In case of a higher risk the prevention medication, such as acetazolamide before ascent hast to be considered. In severe cases of HAI oxygen supply and descent is recommended. In rare cases, symptoms can progress to a life-threatening condition – high altitude cerebral oedema (HACE), and high altitude pulmonary oedema (HAPE).