Mountain mortality: a review of deaths that occur during recreational activities in the mountains

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1 1 UCL Centre for Altitude, Spae and Extreme Environment Mediine, Institute of Human Health and Performane, University College London, London, UK; 2 Department of Anesthesia and Critial Care, Massahusetts General Hospital, Boston, Massahusetts, USA; 3 University of Utah, College of Nursing and Shool of Mediine, Salt Lake City, Utah, USA Correspondene to: Dr J S Windsor, UCL Centre for Altitude, Spae and Extreme Environment Mediine, Institute of Human Health and Performane, University College London, Charterhouse Building, Arhway Campus, Highgate Hill, London N19 5LW, UK; jswindsor@dotors.org.uk Reeived 9 January 2009 Aepted 6 February 2009 Mountain mortality: a review of deaths that our during rereational ativities in the mountains J S Windsor, 1 P G Firth, 2 M P Groott, 1 G W Rodway, 1,3 H E Montgomery 1 ABSTRACT The growing popularity of ativities suh as hiking, limbing, skiing and snowboarding has ensured that the number of visitors to mountain environments ontinues to inrease. Sine suh areas plae enormous physial demands on individuals, it is inevitable that deaths will our. Differenes in the ativities, onditions and methods of alulation make meaningful mortality rates diffiult to obtain. However, it is lear that the mortality rate for some mountain ativities is omparable to hang gliding, parahuting, boxing and other pastimes that are traditionally viewed as dangerous. Deaths in the mountains are most ommonly due to trauma, high altitude illness, old injury, avalanhe burial and sudden ardia death. This review desribes the mortality rates of those who undertake rereational ativities in the mountains and examines the aetiology that lies behind them. The highest of mountains is apable of severity, a severity so awful and so fatal that the wiser sorts of men do well to think and tremble even on the threshold of their high endeavour George L Mallory 1 Mountainous regions oupy 40 million km 2 and aount for approximately 27% of the Earth s surfae. 2 It is estimated that 38 million people live permanently above 8000 feet (2439 m), with an additional 100 million visitors travelling to mountain regions for work and rereation eah year. 3 4 The inreasing popularity of ativities suh as trekking and limbing has ensured that these numbers ontinue to grow. The number of trekkers in Nepal has risen by 330% from 1982 to 1994, and by 450% from 1994 to A similar inrease has also been seen at above 6000 m: in the 40 years between 1950 and 1990, limbers attempted the highest peaks in Nepal ompared with between 1990 and Mountains are inherently dangerous. The ombination of falling barometri pressure, temperature and humidity, together with inreases in solar radiation and wind speed, mean that those heading to the mountains often enounter an extraordinary set of physial hallenges. 7 Clearly, managing these hallenges an prove enormously satisfying, however in some ases these fators an ontribute to serious injury or even death. This review identifies the mortality rates of those who undertake rereational ativities in the mountains and examines the aetiology that lies behind them. CALCULATING THE MORTALITY RATE IN A MOUNTAINOUS ENVIRONMENT Obtaining a meaningful and aurate piture of mortality in the mountains is not a straightforward task. While the number of deaths for any given ativity provides a basi level of fatual information, this does little to identify the degree of risk that an individual is exposed to. Although 58 more deaths were attributed to swimming than mountaineering in England and Wales between 1982 and 1988, this does not neessarily imply that swimming is more dangerous. 8 Instead it may simply reflet the fat that more individuals partiipate in swimming than mountaineering ativities. In a similar way, the inrease seen in mountaineering fatalities in the USA over the last 50 years does not neessarily suggest that mountaineering has beome more hazardous, but may instead reflet the growing number of partiipants. 9 In order to determine the mortality rate of different mountain ativities, researhers have adopted two methods of alulation, and these are desribed below. The number of deaths divided by the total number of individuals exposed In 1988, Pollard and Clarke published a short report in the Lanet that identified 23 fatalities that had ourred on 83 expeditions to mountains above 7000 m. 10 Sine these expeditions had 533 members, a mortality rate of 4.3 per 100 mountaineers was ited. However, sine many of these expeditions were foused upon dangerous and tehnially hallenging objetives like K2, this rate was somewhat higher than that found in subsequent studies. For many years the historian Elizabeth Hawley and her olleagues in Kathmandu have diligently assembled a omprehensive database ontaining information on the vast majority of mountaineering expeditions undertaken in the Nepali Himalaya. 6 Between 1990 and 2006, Hawley and her olleague Rihard Salisbury identified mortality rates of between 0 and 1.26 deaths for every 100 mountaineers limbing above 6000 m (table 1). On Mt Everest the mortality rate among those who asend above base amp is 1.3%, with the majority of deaths (82.3%) ourring during or following the day of a summit attempt. 11 The mortality rate among trekkers in Nepal is signifiantly lower. Between 1984 and 1987 only 23 deaths were reported. Sine approximately individuals were issued with trekking permits from the Nepali Ministry of Tourism, the mortality rates during two periods between 1984 and 1991 have been alulated as and per 100 Postgrad Med J: first published as /pgmj on 15 June Downloaded from on 17 July 2018 by guest. Proteted by opyright. 316 Postgrad Med J 2009;85: doi: /pgmj

2 Table 1 The mortality rate for mountaineers limbing above 6000 m in the Nepali Himalaya between 1990 and Peak altitude range Individuals above base amp Deaths above base amp Total Mortality rate (/100 individuals above base amp) The mortality rate is alulated by dividing the number of deaths by the total number of individuals who have limbed above a designated base amp and multiplying by 100. trekkers Mountaineering mortality rates in North Ameria lie between these figures. On Denali, the highest mountain in Alaska, deaths have been reported for every 100 mountaineers who register with the National Park Servie. 14 Meanwhile on Mt Rainier, a popular 4392 m peak in the north west state of Washington, 50 deaths were reported between 1977 and Sine approximately 8000 attempts are made on this mountain eah year, an estimated mortality rate of approximately per 100 mountaineers an be alulated. In reent years the mortality rate alulated in this way has appeared to deline. Aording to Hawley and Salisbury, the mortality rate between 1950 and 1989 in the Nepali Himalaya was 2.3 ompared to just 1.1 per 100 mountaineers for the period of 1990 to This redution has also been seen on Denali, with a 4% fall being reported for eah year sine 1932 and a 53% redution following the introdution of new safety measures in Nevertheless the mortality rate assoiated with mountaineering remains high. Not only is it greater than that of other mountain ativities, but it is also higher than sports suh as hang gliding, parahuting and boxing that are traditionally viewed as dangerous (table 2). Although this mortality rate allows omparisons to be made, it does not take into aount the impat of different amounts of exposure. To take an extreme example: do professional boxers who fight on a daily or weekly basis for several years have a lower mortality than the mountaineers who undertake a solitary expedition and turn bak after a few hours above base amp? In order to aknowledge the impat of the duration of exposure, a different method of alulating mortality rate is required. Table 2 The mortality rate for speifi ativities undertaken in the USA that were alulated by dividing the number of deaths by the total number of individuals exposed Ativity Mountaineering Hang gliding Parahuting Boxing Mountain hiking Suba diving Amerian football Skiing Mortality rate (/100 partiipants) The number of deaths for every days of exposure to a speifi mountain ativity Among skiers and snowboarders, the mortality rate alulated by this method ranges from 0.11 in long distane ross ountry ski raes in Sweden to 2.46 deaths per million exposure days in the downhill ski resorts of Utah, USA The mortality rates of trekkers and mountaineers is greater, with 11 deaths ourring during trekking in Nepal and 1870 deaths per exposure days of mountaineering on Mt Cook (table 3). While the mortality rate of trekkers in Nepal is similar to that found in other ativities suh as marathon running and motoryling, the mortality rate of mountaineers is signifiantly higher. 26 This is underlined by a reent follow-up study onduted on 46 experiened mountaineers in New Zealand: in just years, four (9%) had died during mountaineering and seven (15%) had retired from the sport. 27 Despite the widespread use of this alulation, obtaining the mortality rate in this way an be problemati. In small regional studies, information on the number of deaths is usually obtained from loal soures. Although these give a highly aurate summary of the deaths that our within these areas, they an sometimes overlook those who die later following a suessful evauation. Larger studies are also limited, sine they often rely upon oroners reports and assume that the loation and ativity of the vitim before the fatal event is aurately reorded. Calulating the total number of exposure days is also problemati. In studies that alulate skiing and snowboarding mortality, the denominator for the alulation is obtained from either an estimate obtained from a loal soure suh as a park servie or from the numbers of admission tikets sold for a given year. These figures tend to ignore those who either work in the region, loal residents who possess season tikets, or those who hoose to ski off piste and away from designated downhill runs. Despite inluding the deaths of 100 ross ountry skiers in their analysis, Xiang et al aknowledged that it was impossible to measure aurately the amount of exposure these individuals had enountered. 25 Studies that have foused upon trekking and mountaineering have also enountered methodologial diffiulties. Avery et al used the data from the national ensus in order to identify the amount of time the population of England and Wales spent mountaineering. 8 Clearly, this relies upon an individual s own estimate and an therefore be prone to some degree of inauray. Other studies have either used the number of days spent on the mountain or the nights spent in a hut to estimate the amount of exposure. Malolm, in his study of deaths among mountaineers on Mt Cook, assumed that for every day of mountaineering three nights were spent in one of seven huts on the mountain. 21 While this may have been a lose approximation to the degree of mountaineering exposure, Malolm foused upon a period of time when the mountaineer was faed with the greatest danger. It was therefore inevitable that the results from Mt Cook should appear so striking. In ontrast, MIntosh et al in their reent study of mortality on Denali inluded the total amount of time spent on the mountain. 14 This not only inluded time spent on the dangerous upper slopes, but also the approah to the mountain from the base amp at 2100 m. Clearly, mortality rates will vary depending upon the loations investigators wish to inlude. Inevitably this makes omparisons between different studies diffiult to make. Both of the methods desribed here have signifiant flaws. However, both an be useful and provide answers to a number of questions. Future studies should onsider using both Postgrad Med J: first published as /pgmj on 15 June Downloaded from on 17 July 2018 by guest. Proteted by opyright. Postgrad Med J 2009;85: doi: /pgmj

3 Table 3 A summary of those studies that have alulated mortality rate per exposure days for speifi mountain ativities Authors Loation Era Ativity Deaths approahes in order to provide the most omprehensive analysis. MECHANISMS OF MOUNTAIN MORTALITY While no single method of measuring mortality rate is ideal, it is lear that a onsiderable number of deaths our in mountain regions. How do they die? Trauma It is perhaps not surprising to learn that skiers, snowboarders, trekkers and mountaineers die in different ways. Fatalities in downhill skiing and ski jumping tend to our as a result of a fall or a ollision with either a tree, post or other skiers (table 4). In these ases deaths tend to be due to multiple blunt trauma to the head, hest and abdomen Deaths among trekkers and mountaineers are largely due to falls and tend to result in a similar pattern of injury In a study of mountaineering and rok limbing injuries in the USA, Addiss and olleagues were able to demonstrate that the median distane of a fatal fall was 91 m ompared to a non-fatal fall of just 9 m (p,0.001). The risk of death was influened by the angle of the slope, the landing surfae and the efforts made by the vitim and limbing partner to arrest the fall. 32 The pattern of deaths among mountaineers is also related to the time spent in ertain areas. Sherpa mountaineers working Age (years) % Male Mortality rate (/ exposure days) Avery et al (1990) 8 England and Wales Mountaineering Corra et al (2004) 22 South Tyrol, Italy Skiing and snowboarding 1.6 Farahmand et al (2007) 19 Vasaloppet, Sweden Skiing MIntosh et al (2008) 14 Mt MKinley National Park, Mountaineering USA Malolm (2001) 21 Mt Cook National Park, New Mountaineering Zealand Morrow (1988) 23 Vermont, USA Skiing Shlim and Gallie (1992) 13 Nepal Trekking 23 11{ Sherry and Clout (1988) 24 Snowy Mountains, Australia Skiing Weston et al (1977) 20 Utah, USA Skiing Xiang et al (2003) 25 Colorado, USA Skiing and snowboarding * *The range of annual mortality rates obtained per skier visits to Colorado between 1980 and {Calulated by MIntosh et al. 14 on the Nepali side of Mt Everest spend onsiderable amounts of time arrying equipment through the dangerous Khumbu Iefall and other avalanhe prone areas in the Western Cwm. This leads to a onsiderable number of deaths aused by falling snow, ie and rok on lower setions of the route. 11 Cross ountry skiers and mountaineers are at a muh greater risk from the dangers of rokfall, iefall and avalanhes than those who prefer to stay within the onfines of onventional ski runs. Between 1994 and 2003, the median annual mortality from snow avalanhes in Europe and North Ameria was The majority of these vitims died from asphyxia rather than the result of traumati injuries that had ourred during snow burial. 34 In a reent analysis of 36 avalanhe fatalities, a team from the University of Innsbruk identified a traumati ause of death in only two vitims (5.6%). The remainder were found to have died from either hypothermia (2.8%) or asphyxia (91.6%). 34 Following a omplete snow burial, death from asphyxia is rapid with approximately 60% of those buried in an avalanhe dying within min. 35 Cold injury Sine ambient temperature falls by approximately 5.5uC for every 1000 m of altitude, it is inevitable that the old will ontribute to a number of deaths in the mountains. 2 Deaths aused by hypothermia tend to our as a result of an unexpeted event suh as a musuloskeletal injury or an episode Table 4 Summary of the auses of death found in studies of skiers and snowboarders Author Loation Ativity Deaths Collision Fall Avalanhe Hypothermia Medial Farahmand et al (2007) 19 Vasaloppet, Sweden Cross ountry skiing Morrow (1988) 23 Vermont, USA Skiing Sherry and Clout (1988) 24 Snowy Mountains, Skiing Australia Tough and Butt* (1993) 29 Alberta, Canada Cross ountry skiing Tough and Butt* (1993) 30 Alberta, Canada Skiing Weston et al (1977) 20 Utah, USA Skiing 10{ Wright (1988) 28 USA Nordi ski jumping Xiang et al (2003) 25 Colorado, USA Skiing and snow boarding 174{ NK 7 Xiang et al (2003) 25 Colorado, USA Cross ountry skiing 100{ NK 4 Total *Only deaths assoiated with traumati injuries or hypothermia were inluded. {One death was attributed to suiide following a single gunshot wound to the head. {Xiang et al s study was divided into deaths that ourred to either downhill skiing and snowboarding or ross ountry skiing. The remaining deaths in this study were attributed to either general skiing aidents or other/unknown. NK, not known. Postgrad Med J: first published as /pgmj on 15 June Downloaded from on 17 July 2018 by guest. Proteted by opyright. 318 Postgrad Med J 2009;85: doi: /pgmj

4 Key learning points Obtaining a meaningful and aurate piture of mortality in the mountains is not a straightforward task. In mountain ativities the mortality rate is alulated in two ways: the number of deaths divided by the total number of individuals exposed, or as the number of deaths for every days of exposure to a speifi mountain ativity. The reported mortality rate among skiers and snowboarders is 0.11 and 2.46 deaths for every million days of exposure, while the mortality rate among mountaineers is 2.3 to 1870 deaths for every million days of exposure. Deaths in the mountains are most ommonly due to trauma, high altitude illness, old injury, avalanhe burial, and sudden ardia death. of high altitude illness Alternatively, environmental fators suh as an avalanhe burial or deteriorating weather onditions an also be responsible. 15 In some ases equipment failure has also been blamed. Damage to skis and their bindings an leave ross ountry skiers stranded in remote areas, while loss of rampons or ie axes an slow a mountaineer s desent and inrease the time spent exposed to the old. High altitude illness An asent to altitude results in a fall in barometri pressure and a subsequent redution in the partial pressure of inspired oxygen. In order to ope with this hange the human body undergoes a proess of alimatisation. In those who asend rapidly, this an be inomplete and result in the development of life threatening onditions suh as high altitude pulmonary oedema (HAPE) and high altitude erebral oedema (HACE). In a study of Indian soldiers, 5.7% of those who were flown to altitudes of 3500 m ontrated HAPE ompared to just 0.3% who ompleted the same journey by road. 36 The inidene of these onditions also inreases with altitude. On arrival at 3063 m, 0.1% of lowland residents had evidene of HAPE ompared to 5.3% at 4486 m. 37 In a number of ases, HAPE and HACE oexist. Up to 20% of those who present with HAPE also demonstrate signs of HACE, while up to 50% of those who died from HAPE also had evidene of HACE on autopsy. Historially, HAPE and HACE have been thought to be responsible for the majority of deaths that our at altitude. While evidene olleted in this review would suggest that this is not the ase, it is possible that HAPE and HACE ontribute in some part to those deaths attributed to trauma or hypothermia. In the early stages of HACE, hanges in onsiousness, abnormalities in motor funtion and the presene of visual disturbanes an our, while in HAPE, lethargy, malaise and breathlessness are ommonly seen. 11 Clearly these symptoms an have an adverse effet on anyone undertaking physial ativities at altitude and have the potential to inrease the risk of a fatal fall or prolong a period of old exposure that subsequently results in hypothermia. Sudden ardia death While HAPE and HACE tend to figure highly among nontraumati deaths on the highest peaks, at lower altitudes sudden ardia death (SCD) appears to be more prevalent. SCD is defined as an unexpeted, non-traumati death that ours within one hour of the onset of symptoms, and aounts for up to 52% of deaths during downhill skiing and Current researh questions How do differenes in ativities and environmental fators impat upon mortality rates in the mountain environment? How an deaths from trauma, old injury, high altitude illness and sudden ardia death be redued in the mountain environment? 30% of mountain hiking fatalities The reported inidene of SCD in mountain regions ranges from approximately 1 to 10 i per million person days ativity in the mountains In adults, vigorous exerise, suh as that seen in mountain ativities, is assoiated with an inrease in the inidene of SCD. 42 Vigorous physial exertion has been reported to have ourred within 1 h of myoardial infartion in 4 10% of ases. 43 Studies of long distane skiers and runners demonstrate that the inidene of SCD in adults is between 5 50 times greater during exerise than during sedentary ativities In most ases SCD is due to oronary artery disease and is refleted by the sex and age distribution of those who die from the ondition. 47 In studies undertaken in the European Alps between 90 95% of SCDs ourred in males, while the frequeny of SCD has been shown to inrease dramatially in those aged over 34 years. Importantly, only those who undertake regular exerise are afforded signifiant protetion from the risk of SCD during vigorous ativity. The relative risk of a life threatening ardia event has been shown to be 150 in sedentary individuals and just 5 in those individuals who undertake regular exerise. 48 Among the 38 SCDs identified in the Tyrolean Alps between 1999 and 2002, 86% did not take regular physial ativity. 41 Rigorous exerise has a profound effet upon the autonomi nervous system, prompting hanges in myoardial eletrial stability and inreases in an individual s suseptibility to fatal arrhythmias. 49 Fortunately, regular exerise not only inreases basal vagal tone and enhanes eletrial stability, but also prevents the development of oronary artery disease and the formation of vulnerable plaques that are prone to rupture during surges in sympatheti ativity. Unfortunately, many heading to the mountains are sedentary and prone to oronary artery disease. In a study of hikers and skiers in the Tyrolean Alps, up to 21.7% undertook less than 1 h of exerise per week and 12.7% had a history of ardiovasular disease. 52 It therefore seems inevitable that a signifiant number of SCDs will our in the mountains. CONCLUSION Although only a small number of deaths our in the mountain environment, their unexpeted nature raises a onsiderable amount of onern in wider soiety. In order to devise strategies to prevent these deaths, it is important that mortality rates an be alulated. However, differenes in the ativities, environmental onditions and methods of alulation often make these results diffiult to interpret. Nevertheless, a number of onlusions an be drawn. Firstly, the mortality rate among skiers and snowboarders oupies a narrow range: between deaths for every million days of exposure. Seondly, the mortality rate for mountaineering is greater and varies enormously: 2.3 to 1870 deaths for every million days of i This was alulated from Burtsher et al s results that showed one SCD for every hiking hours. 40 It assumed that 8 h of hiking was equivalent to 1 day of ativity in the mountains. Postgrad Med J: first published as /pgmj on 15 June Downloaded from on 17 July 2018 by guest. Proteted by opyright. Postgrad Med J 2009;85: doi: /pgmj

5 Key referenes Firth PG, Zheng H, Windsor JS, et al. Mortality on Mt Everest : desriptive study. BMJ 2008;337:a2654. MIntosh SE, Campbell AD, Dow J, et al. Mountaineering fatalities on Denali. High Alt Med Biol 2008;9: Christensen ED, Lasina EQ. Mountaineering fatalities on Mt Rainier, Washington, : autopsy and investigative findings. Am J Foren Med Path 1999;20: Hakett PH, Roah RC. High altitude erebral edema. High Alt Med Biol 2004;5: Burtsher M, Philadelphy M, Likar R. Sudden ardia death during mountain hiking and downhill skiing. N Engl J Med 1993;329: exposure. Finally, the differene between the two groups may be explained by not only the ativity itself but also by the environment eah ativity operates in. The ski resort is likely to be a far safer plae than the remote mountain liff! Fortunately, there is now evidene demonstrating that in reent years mortality rates have begun to fall. Nevertheless, the mountain remains a dangerous plae and are must be taken by anyone who straps on skis or rampons and ventures into them. MULTIPLE CHOICE QUESTIONS (TRUE (T)/FALSE (F); ANSWERS AFTER THE REFERENCES) 1. Mountain regions: A. Oupy 40 million km 2 B. Aount for 2.7% of the earth s surfae C. Attrat 100 million visitors for work and rereation eah year D. Above 8000 feet (2667 m) are home to 0.38 million people E. In Nepal have seen the numbers of visitors fall over the last two deades 2. The mortality rate alulated by dividing the number of deaths by the total number of individuals exposed: A. Has inreased among US mountaineers over the last 50 years B. Is higher in swimmers than mountaineers C. Has been falling on Denali D. Ranges from 10 to 12.6 deaths for every 100 mountaineers limbing above 6000 m in the Himalayas E. Is 13% on Mt Everest 3. In the mountains: A. Deaths aused by avalanhes are normally due to trauma B. Deaths among sherpas on Mt Everest tend to our low on the mountain C. Cross ountry skiers and mountaineers are at a muh greater risk from the dangers of rokfall, iefall and avalanhes than those who prefer to stay within the onfines of onventional ski runs D. Ambient temperature falls by approximately 0.5uC for every 1000 m of altitude E. 60% of those buried in an avalanhe die within min 4. High altitude illnesses: A. Are the result of a fall in the partial pressure of inspired oxygen B. Are responsible for the majority of non-traumati deaths in the mountains C. Are more ommon following a slow asent D. Rarely oinide E. May ontribute to other mehanisms of death 5. Sudden ardia death: A. Has been defined as an unexpeted, non-traumati death that ours within 24 h of the onset of symptoms B. Has been shown to aount for up to 52% of deaths during downhill skiing and 30% of mountain hiking fatalities C. Is due to oronary artery disease in the majority of ases D. Risk is redued in those who exerise regularly E. In the mountain environment inreases dramatially in men aged over 34 years Competing interests: None. REFERENCES 1. Mallory GL. The reonnaissane of the mountain. In: Howard-Bury CK, ed. Mt Everest: the reonnaissane. London: Edward Arnold, 1921: World Health Organisation. Introdution to mountain regions. who.int/linkfiles/publiations_and_douments_healthimaptsc2.pdf (Aessed 1 Nov 2008). 3. Moore LG. Altitude-aggravated illness: examples from pregnany and prenatal life. Ann Emerg Med 1987;16: Burtsher M, Bahmann O, Hatzl T, et al. Cardiopulmonary and metaboli responses in healthy elderly humans during a 1-week hiking programme at high altitude. Eur J Appl Physiol 2001;84: Gaillard S, Dellasanta P, Loutan P, et al. Awareness, prevalene, mediation use and risk fators of aute mountain sikness in tourists trekking around the Annapurnas in Nepal: a 12 year follow up. High Alt Med Biol 2004;5: Salisbury R, Hawley E. 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