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Travel At High Altitude, a booklet that can be freely download by clicking this link - a guide to staying healthy in the mountains.
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Travel At High Altitude, a booklet that can be freely download by clicking this link - a guide to staying healthy in the mountains. |
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article first appeared in Doctor and is reproduced with their permission An Overview of High Altitude Illness Dr Paul Richards Travellers are becoming increasingly adventurous and are moving from the traditional beach holiday to more exciting activities such as trekking, rafting, climbing, mountain biking and skiing; sports which are often placed in high altitude areas. It is estimated that over a 100 million tourists visit high altitude destinations each year. At elevations above 2500m, acute arrival by those used to living in lowlands (which means all of the UK) can cause a syndrome of unpleasant symptoms known as acute mountain sickness (AMS). Some holiday flights deposit tourists directly to altitude, such as the airport at La Plaz, Bolivia at 4200m - but much of the epidemiolological research has been conducted in the ski resorts of Colorado. Here, at valley floor altitudes up to 3000m the incidence of AMS is 25 to 28% in acute arrivals. This is much higher than that usual travel worry of Traveller’s Diarrhoea but altitude is often overlooked in travel consultations for those going to such ‘normal’ holiday destinations. In tourists flying to 3700m in Nepal the incidence of AMS can reach 84%! It is useful to classify altitude according to the physiological effects: Intermediate altitude: 1500 - 2500m Oxygen saturations usually >90% AMS unlikely High Altitude: 2500- 3500m AMS common with rapid ascent >2500m Very High Altitude 3500-5800m Oxygen saturations<90%, AMS common, marked hypoxaemia with exercise Extreme Altitude >5800m Limit to acclimatisation. Progressive deterioration. Marked hypoxaemia even at rest The predominant symptom of AMS is Headache and this is often accompanied by one or more of: anorexia, nausea/vomiting, fatigue, dizziness and difficulty sleeping. The latter is particularly common at altitude and the typical AMS sufferer will have a headache, be off his or her food and have problems sleeping. Physical Signs and Symptoms Headache is often throbbing, occipital or bi-temporal, worse at night or in the morning, with bending forwards or valsalva manoeuvres, and can be prostrating. Physical signs are often unhelpful especially in mild cases. There may be a slight tachycardia and occasionally a slight increase in temperature. Peripheral and periorbital oedema are common at altitude but may be worse in those with AMS. A dry cough is also common at altitude with unknown aetiology but perhaps related to cold air or reduced humidity. Although breathlessness occurs instantly on arrival at altitude, AMS usually takes a few hours to develop, typically 6 to 10 though it can be as short as one and as long as 36. Symptoms may be worse on the second day, but if no further ascent is made, AMS usually settles over 1-3 days as acclimatisation occurs. After this time further ascent can result in a recurrence till acclimatisation to the new altitude occurs. As these symptoms are common they are often attributed by the tourist to travel fatigue, dehydration, jet lag or hangover, all of which may, of course, co-exist Risk Groups and Prevention The most important factors in the aetiology of AMS are the rate of ascent and altitude attained. Preferably altitude should be gained slowly, perhaps by breaking the journey with an overnight at a lower elevation. If an unacclimatised individual arrives acutely at 3000m, no further increase in sleeping altitude should occur until he or she is acclimatised. Above 3000m, the sleeping altitude should not be incremented by more than 300m per day and a rest day should be taken every third day or 1000m of height increase. Daytime journeys may climb higher provided sleep altitude approximates to the above schedule. There appear to be no appreciable gender differences in susceptibility to AMS. Menstruation, smoking, hypertension, coronary artery disease, diabetes, pregnancy or mild COPD do not appear to be factors. Children are not at greater risk and some studies suggest those over 60 years may have slightly less AMS incidence. Fitness is not protective, but may be a risk factor if the athletic types forge on ahead ascending quicker! Exertion soon after arrival at altitude may increase AMS. Predictive Tests It is thought that respiratory tract infections may predispose to AMS. Lack of the usual diuresis which occurs at altitude may indicate poor acclimatisation and potential development of AMS. There are, unfortunately, no predictive tests of who will develop AMS, the only real guide, but not guarantee being previous past performance at altitude. Bad acclimatisers tend to repeatedly fair poorly and vice versa. Chemoprophylaxis Acetazolamide is a carbonic anhydrase inhibitor which produces an alkaline diuresis and consequent metabolic acidosis to counter the respiratory alkalosis produced by rapid breathing stimulated by hypoxia. It therefore promotes the normal renal method of acclimatisation which would normally take two or more days. It is therefore used by some on rapid itineraries to promote acclimatisation. A dose of 125-250mg appears to be effective but has side effects of peripheral paraesthesia, diuresis, and fizzy drinks tasting flat. A sulphur drug, it should not be prescribed to those potentially allergic though case reports of allergy are rare. It is no substitute for proper slow graded ascent allowing sufficient time for acclimatisation but can be very helpful for sleep disturbance at altitude. It is licensed in the UK for use in glaucoma, diuresis and epilepsy, so use for prophylaxis of AMS is off-lable. Dexamethasone is also effective in AMS prevention but does not promote acclimatisation - hence acute withdrawal, such as in tablet loss can precipitate AMS. Its use is generally discouraged unless in exceptional circumstances such as rapid mountain rescue. Again, its use is off-lable. Complications Although AMS is usually mild and self limiting, it is thought to represent the benign end of a spectrum of mild cerebral oedema with High Altitude Cerebral Oedema (HACE) a severe and potentially fatal consequence. Ataxia is often an early sign and the last to recover. Should a patient exhibit this, behavioural change, confusion, hallucinations or altered consciousness, then immediate descent is mandatory. High Altitude Pulmonary Oedema (HAPE) has a separate aetiology, though is often preceded by AMS, and may occur with or without HACE. Breathlessness at rest is a cardinal sign - cough, initially dry becomes bubbly, with frothy blood stained sputum. At altitude a lower respiratory infection is easily confused with HAPE and descent should be the first course of action. Treatment The most effective treatment of all altitude illness is undoubtedly descent but mild AMS usually requires no more than cessation of ascent, rest, ensuring of good hydration and use of simple analgesics. Paracetamol aspirin, ibuprofen and codeine are all effective.. More severe AMS should prompt descent and can be treated with acetazolamide 250mg po tds. In severe cases dexamethasone 4mg qds po/iv and oxygen may also be required. HACE and HAPE are life threatening and require immediate and prompt descent even at night. For HACE, oxygen, dexamethasone 8mg then 4mg qds, acetazolamide 250mg tds are adjuncts. In HAPE, oxygen gives rapid relief and nifedipine, initially 10mg s/l then 20mg M/R qds is helpful. Portable inflatable hyperbaric chambers are increasingly carried by high altitude trekking groups and can artificially descend the occupant by 2000m or so affording temporary improvement sufficient to facilitate real decent. HAPE victims will require propping up as a supine posture is distressing. Pre-Existing Diseases Asthma is often improved at altitude (less allergens, less dense air) but may be worse if precipitated by cold or exercise. Those with stable ischaemic heart disease and reasonable exercise ability at sea level appear to cope well with moderate altitudes but may become symptomatic. Those with symptomatic sea-level angina are likely to worsen at altitude. COPD symptoms will worsen at altitude with additional increased risk of infections. Those with interstitial lung disease such as pulmonary fibrosis are likely to deteriorate. Diabetes is not worsened by altitude per se but glucose test meters using oxygen reactions are likely to read inaccurately and hypoglycaemia can be confused with HACE. Altitude does not appear to increase the risk of fits in a well controlled epileptic but a fit in a remote environment may pose additional risks. Those with a history of LASIK eye surgery may suffer blurring and impaired vision due to hypoxic corneal swelling. Other Altitude Related Problems The sun is stronger at altitude due to a thinner atmosphere and less pollution to absorb light, so protection against sunburn is important. Good sunglasses should be worn, especially on reflective surfaces such as snow to prevent snowblindness (ultraviolet conjunctivitis). The high altitude atmosphere tends to be dry accelerating dehydration and sore membranes. Summary Altitude sickness occurs not only at mountaineering altitudes but at the commonly frequented tourist elevations. It tends to be mild and self limiting but can be the prodrome for life threatening cerebral or pulmonary oedema. Mild AMS can be managed by rest, fluids and simple analgesia but those with more severe symptoms should descend. Acetazolamide is an effective prophylactic but should not be a substitute for a sensible graded ascent profile. Paul Richards MBChB. MRCGP. MSc. (Trav Med) Director Medical Expeditions
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