Asthma, General | November 10, 2015 | Author: The Super Pharmacist
Altitude Sickness, also commonly referred to as Acute Mountain Sickness (AMS), is a medical condition that occurs when individuals climb to a high altitude too quickly. The decrease in atmospheric pressure makes breathing less efficient, and milder forms of the illness are characterised by exhaustion, feelings of nausea, headaches and dizziness. Generally it is a self-limiting condition that will improve with good self-care, although in its more severe forms altitude sickness can manifest as a high altitude pulmonary oedema (HAPE) or a high-altitude cerebral oedema (HACE). Both HAPE and HACE can lead to a coma and death if left untreated. Altitude sickness can occur in its mildest form when individuals travel to heights greater than 2500m. In its most severe form, it requires individuals to be at a height greater than 3600 metres (approximately 12,000ft). Its incidence generally increases with absolute height attained and rate of ascent, although it is not related to baseline levels of physical fitness and can affect even the most physically healthy individuals.
The standard assessment tool for altitude sickness is the Lake Louis AMS questionnaire. Any score greater than three is considered to be acute mountain sickness. There are a number of other diagnostic tests that can identify altitude sickness (CT/MRI Scan, arterial blood gases and CXR in HAPE), although for obvious reasons investigations at altitude are often severely limited and rely on the personal judgement of attending medical professionals.
Patients with cardiac or pulmonary disease are at greater risk of developing altitude sickness (1). Patients with coronary heart disease, asthma or hypertension can attain high altitudes, although patients with chronic obstructive pulmonary disorder (COPD) or pulmonary hypertension would be at significantly greater risk of altitude sickness if they were to ascend quickly (2).
If individuals begin to display symptoms of altitude sickness, the optimal management of the condition is descent from altitude (3). Where descent is not an immediate possibility the use of oxygen or hyperbaric bags can help alleviate the distress of altitude sickness (4) but they should not delay descent where possible and will only be of use for a limited time. Very mild symptomatic altitude sickness can be managed with a combination of analgesics and anti-emetics. Ibuprofen has been evidenced to be more effective than aspirin in the relief of high altitude related headaches (5). Simply resting and avoiding further ascent can also lessen the symptoms, although moderate to severe sickness may require supplementary oxygen therapy. If descent is not possible for a prolonged period of time, the administration of prophylactic acetazolomide (more frequently used to treat glaucoma) and/or dexamethasone has been evidenced to be effective (6). However, it is not specifically licensed for use in relation to altitude sickness and requires off label prescription from a qualified medical professional. Acetazolomide can be taken in advance of prolonged periods of time spent at altitude, although as it has some unpleasant side effects including numbness and tingling of the face, fingers and toes, medical professionals will often advise patients to take it several days prior to ascent to allow their body to become used to such symptoms. Similarly, nifedipine, most commonly used to treat hypertension, can also be used of label to treat high altitude pulmonary oedema. Nifedipine can cause a sudden drop in blood pressure so it is important to get up quickly from a laying or sitting position if taking this medication. There are a number of other practical measures that will reduce the onset of symptoms including abstaining from alcohol, taking very modest exercise on acclimatisation days, maintaining a high carbohydrate diet, and keeping warm and well hydrated. Individuals who know they will be spending a prolonged period at altitude can also use the Lake Louise questionnaire in a preventative capacity, keeping a close eye on their condition to determine if they require action to manage the early onset of acute sickness (7). A single study considering the effects of ginkgo bilboa extract found it to have no discernible benefit (8). There are no alternative medicines that have a positive impact on the ability of individuals to recover from altitude sickness.
Altitude sickness can be avoided through a measured process of acclimatisation to increased altitude. Gradual exposure to higher altitudes results in a number of physiological changes that improve individual capacity to cope. These are increased red blood cell production, increasing vascularity of the lungs and tissues, the suppression of antidiuretic hormone (ADH) and aldosterone, and increasing ventilation. Typical acclimatisation will consist of a gradual ascent to a position of greater altitude at a rate of around 500 metres per day for 3-4 days on large mountain climbs. Additionally, for at risk patients or patients with a history of AMS, the use of acetazolamide has been demonstrated to prevent the symptoms when taken in preparation of travel to such areas. Again this recommendation is an off-label use as the medication is typically used to treat glaucoma.