Article, Geriatrics

Considerations for resuscitation at high altitude in elderly and untrained populations and rescuers

a b s t r a c t

With the development of transportation technologies, Elderly people with chronic diseases are increasingly enjoying trekking and tours of nature resorts that include mountain highlands. Because of problems related to circulation, respiration, metabolism, and/or the musculoskeletal system in this population, the impact of High altitude on cardiopulmonary function is increased. alpine accidents, therefore, tend to be more common in this population, and cases of cardiopulmonary arrest (CPA) at high altitudes seem to be increasing. However, relatively few studies have described cardiopulmonary resuscitation (CPR) at high altitudes. Although insufficient studies are available to standardize CPR guidelines at high altitude at this time, the aim of this review is to summarize previous studies relevant to physiologic changes after exposure to high-altitude environments and exercise, which may be a risk factor for CPA in elderly trekkers. In addition, we summarize our previous studies that described the effect of CPR procedures on cardiopulmonary function in Untrained rescuers. The available data suggest that prolonged CPR at high altitudes requires strenuous work from rescuers and negatively affects their cardiopulmonary physics and subjectively measured fatigue. Alpine rescue teams should therefore be well prepared for their increased physical burden and difficult conditions. Elderly travelers should be made aware of their increased risk of CPA in alpine settings. The use of mechanical devices to assist CPR should be considered wherever possible.

(C) 2014

Introduction

The development of transportation technologies has provided tourists easy access to high-altitude (1500-3500 m above sea level) and very-high-altitude (3500-5500 m) environments, for example, by automobile, train, airplane, helicopter, or ropeway; however, high altitude has a negative effect on human cardiopulmonary function. In particular, it is now particularly easy for elderly people with decreased functional organ reserves and coexisting diseases to visit high-altitude environments. Consequently, the incidence of cardiopulmonary arrest (CPA) seems to be increasing. However, few studies have described the CPA risk of elderly trekkers at high altitude relative to that at sea level. Similarly, relatively few studies have addressed cardiopulmo- nary resuscitation (CPR) procedures in mountain settings. Therefore, the standardization of CPR procedures in high-altitude environment remains challenging for rescuers and clinicians. In this article, we

? Financial support: This work was funded by the Japanese Ministry of Education, Culture, Sports, Science, and Technology with a JSPS grant (no. 20659242) to Shigeru Saito.

?? No conflict of interest.

? This article has not been presented.

* Corresponding author. Department of Anesthesiology, Pain Mechanism Lab, Wake Forest University School of Medicine, Winston-Salem, NC 27157-1009, USA. Tel.: +1 336 716 2743; fax: +1 336 716 6744.

E-mail addresses: [email protected], [email protected] (T. Suto).

summarize our work on the alteration of physiologic parameters occurring after exposure to high-altitude environments, which are possible risk factors for CPA in elderly and untrained trekkers, and on the effects of CPR activity on rescuers. We propose provisional conclusions on the practice of CPR at high altitude from our own work combined with studies from other groups.

Increasing need for rescue activity at high altitude in elderly and untrained populations

In recent years, mountains have attracted an increasing number of visitors all over the world. Each year, 35 million Americans travel to altitudes more than 2400 m [1]. The number of hikers and skiers exposed every year to moderately high altitude may exceed 40 million for the entire region of the European Alps [2]. Therefore, there are assumed to be approximately 100 million mountain tourists world- wide every year.

Faulhaber et al [3] reported an increasing number of elderly trekkers with preexisting cardiovascular diseases. Approximately 58% of mountain hikers and 43% of downhill skiers in European Alps area are older than 40 years, and 15.3% to 28.0% of them have preexisting cardiovascular diseases. We also reported that an increasing number of elderly people enjoyed trekking in 2002 and 2012 [4,5] and that 70% of the trekkers were older than 50 years. The aged trekkers in these studies presented better physical performance than comparable

0735-6757/$ - see front matter (C) 2014 http://dx.doi.org/10.1016/j.ajem.2013.11.007

individuals in the general aged nontrekker population, and it is therefore possible that aged trekkers who enjoy exercise in mountainous areas are physically and biologically younger than their chronological age. However, the incidence of diabetes or hypertension in the trekkers was 40%. In addition, 75% of trekkers older than 70 years complained of conditions such as hypertension or diabetes, with most (68%) reporting multiple diseases, and the number of diseases significantly increased with age.

The number of accidents in highlands has increased markedly over the past 5 years [6,7], and many of these accidents involve aged trekkers. For example, in Japan, more than 75% of trekkers involved in such incidents are older than 40 years, and some experience a stroke or myocardial infarction while trekking at altitude (http://www.npa. go.jp/safetylife/chiiki28/sangakusounan.pdf.). Many of the accidents observed, such as those involving slipping, falling, or disorientation, likely originated from a preexisting physical problem. In contrast, classical serious high-altitude disorders, such as high-altitude pul- monary edema or cerebral edema, seem to be rare at altitudes of 1500 to 5500 m, where nature tours are popular.

older people are therefore advised to be particularly cautious when preparing for trekking activity [8]. Although exceptionally unprepared individuals do exist, most aged trekkers appear to take appropriate precautions and perform preliminary exercises before starting their treks. However, the physical stress involved in trekking may have a greater impact in this population, possibly because of the age-related decline in the functional reserve of their organs [9]. For example, in our previous study of physical performance [5], the general health condition, including balance performance, worsened in older individuals after trekking.

Impact of high altitude on the physiology of elderly and untrained trekkers: possible CPA risk

Burtscher et al [10] reported that sudden cardiac death comprises approximately 30% of all deaths involving mountain sports. The high- altitude environment itself and exercise at high altitude have general impacts on human physiology that may result in excessive cardiac and respiratory workload. acute exposure to high altitude induces abrupt physiologic changes in untrained humans. In our study at 2700 m and 3700 m, we observed alterations in heart rate, respiratory rate, oxygen saturation (SpO2), concentration of end-tidal carbon dioxide, Heart rate variability , and regional oxygen saturation in the brain even at the resting state [11-13]. These alterations indicate a possible risk of CPA in trekkers with decreased physical function and/or comorbid diseases.

Effects of physical work load on oxygen supply

Ward et al [14] reported that higher altitude is associated with a higher heart rate, both at rest and for a given level of exercise. In our previous study, where the effects of altitude on the resting values of cardiovascular parameters were minimal, a physiologic effect of altitude was observed only when exercise was performed [15,16]. Because the heart rate and blood pressure both increased after exercise, the rate pressure product (RPP, which is the product of the heart rate and systolic blood pressure and is expressed as beats per minute * millimeter of mercury) also increased at every altitude. The increase in RPP was greater and of a longer duration at high altitudes. Because RPP is considered to represent an index of the oxygen supply- demand balance of the heart [17], this lingering RPP elevation suggests a high risk of heart ischemia.

At high altitudes, the hemoglobin P50 (partial pressure of oxygen required to achieve 50% hemoglobin saturation) value and alveolar carbon dioxide tension are known to deviate from normal values [8]. However, these parameters may remain normal among nonacclima- tized individuals at moderate altitudes. The change in SpO2 immedi-

ately after exercise relative to the resting value is altered at high altitude; in particular, we previously demonstrated that exercise reduced SpO2 by 11.2% and 9.4% in nonacclimatized subjects at 2700 m and 3700 m, respectively, but had no effect at 1350 m and sea level [12]. This decrease in arterial hemoglobin saturation after simple exercise may underlie the fatigue commonly observed at high altitudes. Sutton et al [18] reported that, at high altitude, SpO2 decreased severely after exercise because of limited oxygen diffusion in the lungs. Because the hemoglobin concentration in blood cannot be altered rapidly, this reduction in SpO2 indicates a decrease in the O2 content in circulating blood. In a previous study, although the lactate accumulation observed after exercise at 2700 m was almost identical to that observed at sea level, significantly increased lactate accumu- lation was observed at 3700 m, which indicates that the oxygen demand during exercise far exceeds the supply at this altitude [12]. Therefore, a threshold for adequate oxygen supply may exist between 2700 and 3700 m. Mazzeo et al [19] recently obtained similar findings for lactate accumulation at 4300 m.

The observed acute elevation in RPP and reduction in SpO2 indicate that the oxygen supply-demand ratio in the heart is compromised after exercise at high altitudes. In our previous study, several subjects who showed no abnormality at sea level showed Abnormal changes on electrocardiography, that is, monofocal premature ventricular constriction, at high altitude, which indicates that physical activity and hypobaric hypoxia can induce heart dysfunction in subjects who appear to be completely healthy at sea level [13].

We previously measured Cerebral regional oxygen saturation (rSO2) in untrained trekkers by using a near-infrared oxymeter to evaluate the oxygen supply-demand balance in the brain at high altitudes [12]. The resting values of rSO2 were nearly identical at sea level, 2700 m, and 3700 m and were not reduced by exercise at sea level. In contrast, we observed a decrease of 26.9% and 48.1% in rSO2 after subjects exercised at 2700 m and 3700 m, respectively. Such an acute reduction in cerebral rSO2 may produce cognitive deterioration in older trekkers at high altitudes.

Blood pressure change and arrhythmia

In our study described above [4,5], systolic and diastolic blood pressures after a resting period were both decreased at the summit hut relative to the corresponding values at the starting gate, particularly in trekkers older than 70 years. This finding is consistent with a report by Schobersberger et al [20], who found that patients with systemic hypertension who moved to locations at moderate altitude (1500-2500 m) showed a reduction in blood pressure. Possible explanations include dehydration during exercise or vascular relaxation via ?-adrenergic stimulation induced by the increased workload. Both dehydration and excessively increased ?-adrenergic stimulation are possible risk factors for cardiac arrest.

Arrhythmia is also common among high-altitude trekkers, as noted by Alexander, who warned of the possibility of cardiac arrhythmia in the elderly population during trekking [21]. Further- more, SpO2 values have been found to decrease as age increases, which may reflect the well-known, age-dependent reduction of PaO2 [22]. Elderly trekkers, therefore, need to be aware of this increased risk of hypoperfusion of organs, hypoxemia, and related disorders when trekking at high altitude.

Alteration of autonomic balance

The autonomic nervous system plays an important role in the survival of victims under hypobaric Hypoxic conditions [8]. Previous studies implied that the activity of the autonomic nervous system was blunted and that Sympathetic activity was relatively dominant under high-altitude conditions [23-25]. Heart rate variability, which indicates the activity of the autonomic nervous system based on

beat-to-beat alteration of the R-R intervals on electrocardiography, is also altered by exposure to high altitudes [8,11,15]. Hughson et al [23] demonstrated changes in HRV in subjects exposed to an altitude higher than 4000 m for more than 10 days. Farinelli et al

[24] and Perini et al [25] independently reported changes in the autonomic regulation of heart rate among trekkers exposed to an altitude of 5050 m for almost a month. We previously assessed the autonomic control of the heart in untrained office workers with no habitual physical exercise regimen during short-term, high-altitude traveling and found that HRV was reduced in both high-(HF) and low-frequency domains (LF), whereas the LF/HF ratio was increased acutely at 3700 m (atmospheric pressure of 480 mm Hg) [11]. We found a correlation between SpO2 and HRV, especially in entropy (ENT%), thereby identifying a relationship between hypoxia and Autonomic dysfunction [15]. The ENT% describes the degree of fluctuation of the R-R interval; a completely random signal registers as 100%, and a regular signal, as 0%.

Although several previous studies implied that the low respon- siveness of the autonomic nervous system at high altitudes could be advantageous in protecting organs from excessive and continuous sympathetic stimulation during a long-term stay at a high altitude [26], the reduced responsiveness of the autonomic nervous system actually indicates an inability of the body to adapt to challenging conditions, such as acute exposure to a hypobaric hypoxic environ- ment or trauma [26,27]. Because decreased responsiveness of the autonomic nervous system has significant prognostic value for cardiac mortality [27,28], the blunted autonomic function observed under hypobaric conditions may reduce the possibility of survival for victims with preexisting medical problems [23-25].

Vasoconstriction and dehydration

Relative Sympathetic hyperactivity at high altitudes may compro- mise the peripheral circulation. In our previous study where subjects underwent ascent exercises to 1000 m, hypobaric hypoxia itself induced a low peripheral body temperature [29]. High-altitude environments also easily induce dehydration through increased water loss caused by hyperventilation [8] in addition to nausea and vomiting as symptoms of high-altitude environment exposure, combined with the restriction of fluid intake resulting from the difficulty in obtaining water. Trekkers who experience additional water loss through heavy perspiration during physical exercise are particularly susceptible to high-altitude dehydration. Notably, in our study, at approximately 2000 m above sea level, body weight loss was greater in older subjects than in their younger counterparts [5], which suggests that older individuals are more susceptible to dehydration and that they do not consume sufficient liquids during trekking [30].

Increased risk of thrombosis

Dehydration induces hyperviscosity in the circulating blood. Cerebral sinus thrombosis, which is a consequence of high-altitude dehydration, is not frequently observed but is another serious complication of a stay at high altitude that must be considered [31,32], as a previous case report suggested that sinus thrombosis at high altitude may not be as rare as typically considered [33]. When a traveler has a procoagulation disorder (such as protein C deficiency, fibrinolytic enzyme deficiency, or antiphospholipid antibody syn- drome) or atherosclerosis, sinus thrombosis can develop even at a moderate altitude [31]. Jha et al [34] analyzed cases of cerebral infarction at high altitudes and proposed that hemoconcentration and hypercoagulability are major risk factors.

Travelers staying at high altitudes for weeks have additional risk factors for thrombosis. Notably, the Red blood cell count and hemoglobin concentration increase to maintain oxygen transport in the hypobaric environment [8], and cerebral edema induced by

vasodilatation under hypoxic conditions elevates intracranial pres- sure and compromises cerebral blood flow, which may then easily interrupt the venous low-pressure circulation. Thus, high-altitude pulmonary edema and high-altitude cerebral edema are well-known Serious diseases that can develop during high-altitude climbing [8].

Problems in rescue activities at high altitude

High-altitude environments induce unfavorable changes in phys- iologic function even in rescuers who are not acclimatized to the environment. These effects result in excessive exertion by the rescuers to perform rescue activities relative to the effort required at sea level. Rescuers need to consider factors that may reduce the quality of rescue activities at high altitude, such as low oxygen pressure, Low Temperature, difficult access to hospitals, and limited rescue gear.

Effects of CPR on rescuers’ SpO2

Performing cardiac compression and artificial respiration (CPR) is considered to be relatively hard physical work even at sea level. It has been demonstrated that CPR performed for approximately 10 minutes induces fatigue in rescuers [35], and frequent switching is therefore recommended among rescuers performing chest compressions. This physical exertion is further increased at high altitudes.

We have shown that CPR affects the cardioPulmonary system of the rescuer at 2700 and 3700 m [36] (Fig.). In particular, the SpO2 of rescuers at rest decreased along with the decrease in barometric pressure associated with increasing altitude. Physical exercise, that is, CPR, at high altitude induced further SpO2 reduction, and exercise at

Fig. Typical alteration of SpO2 (A) and heart rate (B) after exercise at high altitudes. Subjects performed a 3-minute Master II-equivalent stair up-down exercise at each altitude (adapted from Narahara et al [36]).

high altitudes augmented circulation. The relatively broad deviation of SpO2 among subjects was comparable with that observed in other studies, as it is well known that SpO2 values among highland travelers are variable at any given altitude [37]. Although the effects of the hypobaric environment on resting circulatory variables, such as Blood pressure and heart rate, were minor in our study at 2700 and 3700 m, we speculate that much higher altitudes may produce obvious changes in these variables in subjects who are not acclimatized.

Cardiopulmonary resuscitation has several unique features as a physical exercise. In our previous study in which subjects performed repeated ascents and descents in 2 steps (Master II test) at 2700 m, SpO2 was 82% +- 6% after the exercise [19]. However, SpO2 was only slightly reduced after CPR at 2700 m (89% +- 4%) [36]. During CPR, the rescuer inhales a larger-than-usual amount of air before providing a breath to the victim. In addition, while blowing into the victim’s lungs, the rescuer exhales against the victim’s airway and chest resistance, and the resistance to exhalation provides positive expiratory pressure for the rescuer. Thus, the positive end-expiratory pressure and relatively large tidal volumes incurred during CPR could increase the rescuer’s blood oxygenation and improve SpO2 values. In case of “mouth-to-mouth” ventilation, the reduction of the rescuer’s SpO2 is minor, and the amount of oxygen exhaled by the rescuer may not decrease dramatically, although CPR may have to be discontinued relatively quickly because of rapid exhaustion of the rescuer. It should be noted, however, that the recent shift toward Hands-only CPR may result in different effects on the rescuer’s physiology.

The use of other equipment such as portable automated external defibrillators, chest balloon pressure devices, and mechanical Chest compression devices should be considered to reduce the CPR-related workload of rescuers working at high altitudes [38]. However, most of these devices are designed for use at low altitudes; therefore, before deployment, operators should carefully evaluate the durability and ease of use of rescue equipment under severe conditions.

Difficult acclimatization

It is well documented that shortly after arrival at high altitudes, even healthy subjects suffer from severe fatigue or dyspnea after light work or exercise [37]. Although knowledge of the CPR technique and previous physical training of the rescuer obviously affect the energy expenditure and outcome associated with CPR, acclimatization to the environment where the rescue action is performed is another important contributing factor. Therefore, rescuers should ideally have a long resting period before they perform CPR. However, any rest period is inconsistent with the situations in which CPR is actually required. Thus, a pressing issue in high-altitude rescue operations is how much high-altitude acclimatization is necessary before provision of effective CPR. It is known that physical performance is improved after long periods of several months to years at high altitude [37,39]. Because muscle exercise induces alterations in blood O2 and CO2 levels, resetting of the hypoxic ventilatory response or CO2 ventilatory response during high-altitude acclimatization likely underlies the observed improvement [40].

In our previous study in which exhaustion was observed after provision of CPR, the rescuers were healthy young volunteers [36]. However, they were nonacclimatized and relatively unfit. Because there are no specially trained high-altitude rangers or rescuers in our area, we enrolled regular office workers who may visit popular tourist areas as participants in sightseeing tours. At moderate altitudes, acclimatized rescuers may be able to perform CPR without difficulty. However, at higher altitudes or among older rescuers, CPR could have negative effects on the physical condition of the rescuer. This is an important consideration because, in reality, more than half of the trekkers in industrially advanced countries are older than 40 years [5]. Therefore, in the event that CPR is required, the person performing CPR is increasingly likely to be elderly.

In our previous study at 4000 m, we were unable to detect any improvement in SpO2 after exercise in a sequential trekking expedition, probably because a 1-night stay at an altitude greater than 4000 m is not sufficient to induce the appropriate ventilatory response to exercise [16]. Preliminary short-term trekking to high altitudes does not appear sufficient to induce full acclimatization. In another study in which the subjects stayed above 4000 m for more than 100 days, we showed that the SpO2 reduction during and after a squatting exercise became minor after a 2-week stay [16]. Katayama et al [41] and Townsend et al [42] also examined carry-over acclimatization at high altitudes, and they suggested that the effect of acclimatization probably decreases exponentially over 2 to 3 weeks. Considering these previous data, personnel who may be involved in high-altitude rescue activity should routinely be prepared for physical exercise in a low-oxygen environment.

Rathat et al [43] reported that the simultaneous adaptation of hypoxia and exercise before high-altitude trekking is of value for detecting subjects at high risk for high-altitude disease. Such a procedure may be effective to identify personnel who may not be suitable for emergency duties including CPR at high altitudes.

Effects of unfavorable conditions

In addition to the exertion of the procedure itself, CPR performed under unfavorable conditions presents further difficulties to rescuers. In a case we experienced, a CPA victim was transported by a “crawler,” which is a diesel-powered tractor adapted for steep slopes [36]. The victim was laid supine on the back seat, which was transversely set in the crawler. A rescuer who continued resuscitation during transpor- tation was subsequently exhausted, as CPR in the lopsided, narrow carriage was very difficult. Because the only available medical equipment, including an automated external defibrillator, was in a mountain hut approximately 1 km away from the accident site, another rescuer had to fetch the device on foot. Under such circumstances, unfavorable weather, low temperature, strong wind, and rain or snow may present additional obstacles.

Difficulty in transportation

Determining when to transport the patients during and/or after CPR is a difficult question even in a sea-level procedure. Interruption of CPR by transportation can decrease the Quality of CPR. In a high- altitude environment, many factors make transportation difficult, such as distance to the hospital, steep slope, poor foothold, and lack of visibility. It is thought that the quality of on-site CPR is better than that of CPR applied during transportation. However, in such cases, the rescuers need to contend with the unfavorable conditions of the high- altitude environment as described above.

Eisenburger et al [44] reported that transport with ongoing CPR may not be futile. Transportation of the patient can deteriorate the quality of CPR, but Odegaard et al [45] also reported that the CPR quality before transport was not different from that in patients in which CPR was terminated on site. They also suggested that CPR has higher quality when performed on site. In a high-altitude environ- ment, decision making can be affected by the weather, difficult access to the hospital, available gear for CPR, and transportation options. Transportation by helicopter may be useful if appropriate criteria are used to determine the most appropriate utilization [46,47]. The decision between transport and on-site CPR is still a pressing issue that requires further research and discussion.

It is unlikely that a highland traveler who experiences a life- threatening health problem will be transported to an appropriate hospital immediately after the onset of symptoms [36]. Public announcement of the risks involved and the establishment of prophylaxis may be important [39]. Untrained travelers and workers should be made aware that cardiovascular parameters become altered

even after routine exercise at high altitudes and that they are therefore at risk for heart problems in high-altitude environments, especially during and after exercise.

Interruption of CPR in severe environments

Performing prolonged CPR on a patient with a suspected cardiac or neurologic event in an out-of-hospital setting, especially a remote outdoor environment, is generally futile [48]. Inability to revive the patient despite prolonged CPR under unfavorable environmental conditions may reasonably cause the rescuers to decide to abandon the procedure [49]. Rescuers should be allowed to declare the patient dead after a relatively short period of CPR, regardless of urging by the patient’s companions. Withholding CPR from the beginning should also be considered as an option under certain conditions.

Some meta-analyses have focused on the termination of CPR in the out-of-hospital setting [50-52], and they listed 3 criteria for CPR termination based on the predictors of survival in out-of-hospital cardiac arrest: (1) event not witnessed by emergency medical services personnel, (2) no automated external defibrillator used or manual shock applied in an out-of-hospital setting, and (3) no return of spontaneous circulation in out-of-hospital setting. Although patients receiving CPR at high altitude may have a different physiology from patients at sea level, these criteria may help rescuers to determine when to start and when to terminate CPR in high-altitude environ- ments. Further discussion on this topic is needed.

Resuscitation-related gear available at high altitudes: effective use of oxygen

Regardless of the site of an accident, oxygen is essential for emergency treatment including resuscitation [53]. Although several types of medication, such as acetazolamide, steroids, and herbal compositions from Traditional Chinese Medicine, have been proposed as effective therapies for mild high-altitude disorders, oxygen supplementation and descent from the low-oxygen environment are still the most effective and fundamental treatments for patients at high altitudes [8]. Oxygen is normally supplied in cylinders that are heavy and bulky to transport, which is a serious problem when emergency action is necessary at high altitudes or in remote areas that are difficult to access by motor vehicles. Lightweight cylinders and portable Oxygen concentrators that extract oxygen from the ambient atmosphere seem to be effective in such circumstances [54].

Lightweight cylinders

Several types of lightweight oxygen cylinder are available, most which are designed for patients with chronic obstructive pulmonary disorder who need oxygen supplementation when they go outside [55]. Aluminum alloys and carbon fiber are used to decrease the weight of these cylinders; titanium cannot be used because of its possible chemical reaction with oxygen [56]. Liquid oxygen is also used to facilitate ambulation [57]. Alpinists also use special cylinders for oxygen supplementation, some of which were originally designed for military jet pilots and can be recharged many times. Among climbers, light weight has the highest priority, and safety may be of lesser concern.

Concentrators

In contrast to Oxygen cylinders, oxygen concentrators that concentrate ambient oxygen are unlimited with regard to their oxygen supply [58]. However, concentrators require electricity to power their compressors, and the efficacy (oxygen concentration and output flow) of these devices is limited by the power of the compressor. Onsite oxygen concentration from ambient air originally

became possible nearly 30 years ago through the use of either an oxygen-enriching membrane or zeolite molecular sieve technology [59]. Although the efficacy of concentrators is rapidly improving, the membrane type can still only produce 40% oxygen, whereas the molecular sieve type can produce up to 95% oxygen depending on compression power. Synthetic zeolite consists of a rigid framework of silica and aluminum; the lifespan of the zeolite crystal is reported to be at least 20000 hours, and maintenance of the unit is relatively simple.

Regular type for chronic obstructive pulmonary disorder patients Oxygen concentrators are now widely used among patients with chronic respiratory disease who need oxygen supplementation for daily life. Market expansion has also refined the technology of oxygen concentrating systems, which has made the units more reliable and compact [60]. Litch and Bishop [61] previously reported the use of an oxygen concentrator in a high-altitude area, and Shrestha et al [62] reported the use of an oxygen concentrator in a remote hospital in Nepal. In particular, Shrestha et al noted that altitude had no effect on the concentration of oxygen produced, and they concluded that the use of the oxygen concentrator was reliable and satisfactory. Our study at 3700 m further confirmed that molecular sieving by zeolite or an oxygen enrichment membrane is not affected by the ambient pressure where the machine is used [54]; a high-performance oxygen concentrator (TO-90-3 N; Teijin, Inc, Chiyoda, Tokyo, Japan) provided oxygen to subjects at a concentration of nearly 90% and a flow rate of 3 L/min, which produced an Arterial oxygen saturation of 95% +- 1% at 3700 m without the use of other devices. Assuming that an electrical energy supply is available and the weight of 33 kg is not a concern, this high-performance system seems to be highly suitable for medical treatment. However, decreases in ambient atmospheric pressure typically trigger alarms in oxygen concentrators designed for use at sea level. Therefore, readjustment of the system is required when

these machines are used at high altitudes.

Transportable type

Although they have relatively limited performance, membrane concentrators are light and require little energy for activation; the machine that we used in a previous study was easily transportable and could be powered by its internal battery for 30 minutes [54].

In that study, we reported for the first time the use of a compact oxygen concentrator at high altitude. The weight of the machine used in the study was only 3.8 kg, and it required no external energy sources to output 30% oxygen at 3 L/min. Because the oxygen-concentrating performance of the machine was relatively low, we also used a semiclosed respiratory circuit containing soda lime. The semiclosed circuit allowed oxygen contained in the receptacle for expired gas to be efficiently reused, and expired carbon dioxide was absorbed by the soda lime [63]. The inspiratory oxygen concentration measured by a gas monitor placed at the inspiratory port ahead of the face mask was 22% to 26%. Further improvement of the circuit together with improvement of the oxygen enrichment membrane and compressor will make the system more potent and reliable for emergency use.

On-site descent using a pressurizing tank

Following successful recovery of the heartbeat and/or spontaneous respiration, evacuation from the hypoxic environment is mandatory. Repressurization in a Hyperbaric chamber is not ideal, but it is an effective alternative to descent if pressurization facilities are available. The Gamow bag, which is a foldable and transportable hyperbaric chamber devised in 1988, is occasionally used by high-altitude rescuers [64-66], particularly for climbers who experience high- altitude disorders only after an ascent to altitudes higher than 4000 m. At these high altitudes, the pressurization in the Gamow bag (ie, 2 psi) is equivalent to a descent of more than 1500 m. Similar devices have

been released by several manufacturers [8]. A problem associated with such chambers is the strenuous workload of the operators who perform pressurization and ventilation. However, soda lime with a semiclosed respiratory circuit can be applied to reduce the workload to approximately 10% of the original value [63].

Another type of portable hyperbaric chamber called the Cham- berlite is durable up to 15 psi [67]. Improvement of the hardware to make the bag capable of withstanding higher pressures has made it possible to perform on-site standard hyperbaric oxygen therapy. This chamber was originally designed for the treatment of decompression sickness after problematic diving. In cases of severe, acute decom- pression sickness, that is, air embolization in major vessels, immediate application of hyperbaric oxygen therapy on site is highly useful [68]. Furthermore, we [67] and Jay et al [69] reported the usefulness of the Chamberlite chamber treatment for carbon monoxide intoxication, and we reported that this device can be used for emergencies at high altitudes [70]. Compressed air is used for inflation of the Chamberlite chamber [67], which is convenient in the original Intended use of the device because cylinders of compressed air are usually available where scuba diving is performed. However, as described above, compressed air tanks are typically inconvenient to carry and use in remote high-altitude environments. Furthermore, although the device is transportable, it weighs 35 kg, which makes it inconvenient to carry by the limited number of people in a rescue team.

Because the availability of oxygen is limited in high-altitude emergencies, in addition to air tanks and oxygen concentrators, several devices have been proposed to allow more efficient utilization of available oxygen. For example, rebreathing bags are often used to decrease oxygen loss in the expiration phase, and they have been successfully used by high-altitude climbers [71]. Although such bags are relatively small (commonly 1 L), they are durable in extreme conditions, such as extremely low temperature and high wind.

Demand valves

Demand valves are also used to increase the efficiency of oxygen utilization when oxygen supplies are limited. Patients receiving home oxygen therapy widely use demand valves together with ultralight oxygen cylinders [60], and some oxygen supply systems designed for high-altitude climbers have used a similar system. However, demand valves use conventional batteries, and they are relatively fragile and sensitive to low temperatures; therefore, they are still unsuitable for use under extreme outdoor conditions. Further improvement of the durability of demand valves is therefore necessary before they can be routinely used in high-altitude emergencies.

Conclusion

The high-altitude environment affects human cardiac and Respiratory physiology not only in elderly and untrained trekkers, but also in rescuers. We have the following recommendations for trekkers and rescuers:

  • Trekkers should be aware of the increased health risk and potential need for rescue activity.
  • Rescuers should use gear such as oxygen supply devices, Mechanical chest compression devices, and automated defibril- lators if available to reduce their workload and increase the quality of CPR.
  • Rescuers should be aware that rescue activity on mountain trails is associated with the combined difficulties of high-altitude environment and out-of-hospital setting.
  • Rescuers should carefully consider the environmental condi- tions, which may decrease the quality of CPR and make transportation difficult, to determine when to start and when to terminate CPR.

Acknowledgment

We would like to dedicate this article to the memory of Mr Yuji Futamata, Mr Ryusi Hoshino, Mr Masasi Fukumoto, and Mr Shuji Nazuka, who were energetic alpinists who cooperated fully in our previous studies and were victimized in an avalanche at 8000 m in the Himalayan mountains. In addition, the authors thank Dr Devang Thakor of Anioplex, LLC, for the English editing of this manuscript and critical review of the contents.

References

  1. Moore LG. Altitude-aggravated illness: examples from pregnancy and prenatal life. Ann Emerg Med 1987;16(9):965-73.
  2. Burtscher M, Nachbauer W, Schrocksnadel P. Risk of traumatic death during downhill skiing compared with that during mountaineering. In: Johnson RJ, Mote CDJ, Ekeland A, editors. Skiing trauma and safety . 11th ed. West Conshohocken: ASTM International; 1997. p. 23-9.
  3. Faulhaber M, Flatz M, Gatterer H, Schobersberger W, Burtscher M. Prevalence of cardiovascular diseases among alpine skiers and hikers in the Austrian Alps. High Alt Med Biol 2007;8(3):245-52.
  4. Saito S, Tobe K, Harada N, Aso C, Nishihara F, Shimada H. Physical condition among middle altitude trekkers in an aging society. Am J Emerg Med 2002;20(4):291-4.
  5. Kimura M, Tobe M, Suto T, Narahara S, Yamada M, Aso C, et al. Balance of older trekkers: data on alpine accidents and performance as assessed using a video game machine. Am J Emerg Med 2012;30(7):1125-8.
  6. Heggie TW, Heggie TM. Search and rescue trends associated with recreational travel in US national parks. J Travel Med 2009;16(1):23-7.
  7. Yarwood R. Risk, rescue and emergency services: the changing spatialities of Mountain Rescue Teams in England and Wales. Geoforum 2010;41(2):257-70.
  8. Hackett PH, Roach RC. In: Auerbach Paul S, editor. Wilderness medicine. 5th ed. Philadelphia: Mosby; 2007. p. 2-36.
  9. Muravchick S. Geriatric patients. In: Longnecker DE, Murphy FL, editors. Introduction to Anesthesia. 9th ed. Philadelphia: WB Saunders; 1997. p. 364-76.
  10. Burtscher M, Philadelphy M, Likar R. Sudden cardiac death during mountain hiking and downhill skiing. N Engl J Med 1993;329(23):1738-9.
  11. Kanai M, Nishihara F, Shiga T, Shimada H, Saito S. Alterations in autonomic nervous control of heart rate among tourists at 2700 and 3700 m above sea level. Wilderness Environ Med 2001;12(1):5.
  12. Saito S, Nishihara F, Takazawa T, Kanai M, Aso C, Shiga T, et al. Exercise-induced cerebral deoxygenation among untrained trekkers at moderate altitudes. Arch Environ Health 1999;54(4):271-6.
  13. Nishihara F, Shimada H, Saito S. Rate pressure product and oxygen saturation in tourists at approximately 3000 m above sea level. Int Arch Occup Environ Health 1998;71(8):520-4.
  14. Ward MP, Milledge JS, West JB, editors. High altitude medicine and physiology. 2nd ed. London: Chapman Hall; 1995. p. 219-40.
  15. Saito S, Tanobe K, Yamada M, Nishihara F. Relationship between arterial oxygen saturation and heart rate variability at high altitudes. Am J Emerg Med 2005;23(1):8-12.
  16. Saito S, Shimada H, Imai T, Futamata Y, Yamamori K. Estimation of the degree of acclimatization to high altitude by a rapid and simple physiological examination. Int Arch Occup Environ Health 1995;67(5):347-51.
  17. Kodama Y, Yokota M, Miyahara T, Matsunami T, Sobue T, Saito H. Effect of antianginal agents on the relationship between rate-pressure product and myocardial oxygen uptake. Am Heart J 1993;126(3 Pt 1):587-93.
  18. Sutton JR, Reeves JT, Wagner PD, Groves BM, Cymerman A, Malconian MK, et al. Operation Everest II: oxygen transport during exercise at extreme simulated altitude. J Appl Physiol 1988;64(4):1309-21.
  19. Mazzeo RS, Brooks GA, Butterfield GE, Cymerman A, Roberts AC, Selland M, et al. Beta-adrenergic blockade does not prevent the lactate response to exercise after acclimatization to high altitude. J Appl Physiol 1994;76(2):610-5.
  20. Schobersberger W, Leichtfried V, Mueck-Weymann M, Humpeler E. Austrian Moderate Altitude Studies (AMAS): benefits of exposure to moderate altitudes (1,500-2,500 m). Sleep Breath 2010;14(3):201-7.
  21. Alexander JK. Cardiac arrhythmia at high altitude: the progressive effect of aging. Tex Heart Inst J 1999;26(4):258-63.
  22. Kronenberg RS, Drage CW. Attenuation of the ventilatory and heart rate responses to hypoxia and hypercapnia with aging in normal men. J Clin Invest 1973;52(8): 1812-9.
  23. Hughson RL, Yamamoto Y, McCullough RE, Sutton JR, Reeves JT. Sympathetic and parasympathetic indicators of heart Rate control at altitude studied by spectral analysis. J Appl Physiol 1994;77(6):2537-42.
  24. Farinelli CC, Kayser B, Binzoni T, Cerretelli P, Girardier L. Autonomic nervous control of heart rate at altitude (5050 m). Eur J Appl Physiol Occup Physiol 1994 Jan 1;69(6):502-7.
  25. Perini R, Milesi S, Biancardi L, Veicsteinas A. Effects of high altitude acclimatization on heart rate variability in resting humans. Eur J Appl Physiol Occup Physiol 1996;73(6):521-8.
  26. Voelkel NF, Hegstrand L, Reeves JT, McMurty IF, Molinoff PB. Effects of hypoxia on density of beta-adrenergic receptors. J Appl Physiol 1981;50(2):363-6.
  27. Barron HV, Viskin S. Autonomic markers and prediction of cardiac death after myocardial infarction. Lancet 1998;351(9101):461-2.
  28. Trimarco B, Chierchia S, Lembo G, De Luca N, Ricciardelli B, Condorelli G, et al. Prolonged duration of myocardial ischemia in patients with coronary heart disease and impaired cardiopulmonary baroreceptor sensitivity. Circulation 1990;81(6):1792-802.
  29. Fukuda-Matsuda E, Yamada M, Tanobe K, Shhigeru S. Peripheral circulation monitored by surface temperature and Autonomic nervous function in hypobaric hypoxic environment: effects of submaximal exercise. Int J Environ Health Res 2007;17(1):53-60.
  30. Saito S, Tanaka S-K. A case of cerebral sinus thrombosis developed during a high- altitude expedition to Gasherbrum I. Wilderness Environ Med 2003;14(4): 226-30.
  31. Phillips PA, Rolls BJ, Ledingham JG, Forsling ML, Morton JJ, Crowe MJ, et al. Reduced thirst after water deprivation in healthy elderly men. N Engl J Med 1984;311(12): 753-9.
  32. Fujimaki T, Matsutani M, Asai A, Kohno T, Koike M. Cerebral venous thrombosis due to high-altitude polycythemia. Case report. J Neurosurg 1986;64(1):148-50.
  33. Song SY, Asaji T, Tanizaki Y, Fujimaki T, Matsutani M, Okeda R. Cerebral thrombosis at altitude: its pathogenesis and the problems of prevention and treatment. Aviat Space Environ Med 1986;57(1):71-6.
  34. Jha SK, Anand AC, Sharma V, Kumar N, Adya CM. Stroke at high altitude: Indian experience. High Alt Med Biol 2002;3(1):21-7.
  35. Bridgewater FHG, Zeitz C, Field J, Inglis A, Poulish K. The impact of the ILCOR 2005 CPR guidelines on a physical fitness assessment: a comparison of old and new protocols. Resuscitation 2008;76(3):405-12.
  36. Narahara H, Kimura M, Suto T, Saito H, Tobe M, Aso C, et al. Effects of cardiopulmonary resuscitation at high altitudes on the physical condition of untrained and unacclimatized rescuers. Wilderness Environ Med 2012;23(2): 161-4.
  37. West JB, Schoene RB, Milledge JS. High altitude medicine & physiology (4th Ed.) WEST J.B.: Librairie Lavoisier. High altitude medicine & physiology. 4 ed. 2007.
  38. Wigginton JG, Miller AH, Benitez FL, Pepe PE. Mechanical devices for cardiopul- monary resuscitation. Curr Opin Crit Care 2005;11(3):219.
  39. Gautret P, Gaudart J, Leder K, Schwartz E, Castelli F, Lim PL, et al. Travel-associated illness in older adults (N60 y). J Travel Med 2012;19(3):169-77.
  40. Schoene RB, Lahiri S, Hackett PH, Peters RM, Milledge JS, Pizzo CJ, et al. Relationship of hypoxic ventilatory response to exercise performance on Mount Everest. J Appl Physiol 1984;56(6):1478-83.
  41. Katayama K, Sato Y, Morotome Y, Shima N, Ishida K, Mori S, et al. Intermittent hypoxia increases ventilation and SaO2 during hypoxic exercise and hypoxic chemosensitivity; 2001.
  42. Townsend NE, Gore CJ, Hahn AG, McKenna MJ, Aughey RJ, Clark SA, et al. Living high-training low increases hypoxic ventilatory response of well-trained endurance athletes. J Appl Physiol 2002;93(4):1498-505.
  43. Rathat C, Richalet JP, Herry JP, Larmignat P. Detection of high-risk subjects for high altitude diseases. Int J Sports Med 1992;13(Suppl 1):S76-8.
  44. Eisenburger P, Havel C, Sterz F, Uray T, Zeiner A, Haugk M, et al. Transport with ongoing cardiopulmonary resuscitation may not be futile. Br J Anaesth 2008;101(4):518-22.
  45. Odegaard S, Olasveengen T, Steen PA, Kramer-Johansen J. The effect of transport on Quality of cardiopulmonary resuscitation in out-of-hospital cardiac arrest. Resuscitation 2009;80(8):843-8.
  46. Tomazin I, Vegnuti M, Ellerton J, Reisten O, Sumann G, Kersnik J. Factors impacting on the activation and approach times of helicopter emergency medical services in four Alpine countries. Scand J Trauma Resusc Emerg Med 2012;20:56.
  47. Walcott BP, Coumans J-V, Mian MK, Nahed BV, Kahle KT. Interfacility helicopter Ambulance transport of neurosurgical patients: observations, utilization, and outcomes from a quaternary level care hospital. PLoS ONE 2011;6(10):e26216.
  48. Schmidt TA, Federiuk CS, Zechnich A, Forsythe M, Christie M, Andrews C. Advanced life support in the wilderness: 5-year experience of the Reach and Treat team. Wilderness Environ Med 1996;7(3):208-15.
  49. Langer CS. Medical liability and wilderness emergencies. In: Auerbach PS, editor. Wilderness medicine. 5 ed. Philaderlphia: Mosby Elsevier; 2007. p. 2163-70.
  50. Sasson C, Hegg AJ, Macy M, Park A, Kellermann A, McNally B, et al. Prehospital termination of resuscitation in cases of refractory out-of-hospital cardiac arrest. JAMA Am Med Assoc 2008;300(12):1432-8.
  51. Sasson C, Rogers MAM, Dahl J, Kellermann AL. Predictors of survival from out-of- hospital cardiac arrest: a systematic review and meta-analysis. Circ Cardiovasc Qual Outcomes 2010;3(1):63-81.
  52. Sherbino J, Keim SM, Davis DP, Best Evidence In Emergency Medicine (BEEM) Group. Evidence-based medicine. J Emerg Med [Internet]. Elsevier Inc; 2010 Jan 1;38(1):80-6. Available from: http://eutils.ncbi.nlm.nih.gov/entrez/eutils/elink. fcgi?dbfrom=pubmed&id=19800755&retmode=ref&cmd=prlinks.
  53. Maroko PR, Radvany P, Braunwald E, Hale SL. Reduction of infarct size by oxygen inhalation following acute coronary occlusion. Circulation 1975;52(3):360-8.
  54. Sakaue H, Suto T, Kimura M, Narahara S, Sato T, Tobe M, et al. Oxygen inhalation using an oxygen concentrator in a Low-pressure environment outside of a hospital. Am J Emerg Med 2008 Nov 1;26(9):4.
  55. Arnold E, Bruton A, Donovan-Hall M, Fenwick A, Dibb B, Walker E. Ambulatory oxygen: why do COPD patients not use their portable systems as prescribed? A qualitative study. BMC Pulm Med 2011;11:9.
  56. Gulbransen EA, Andrew KF. Reactions of zirconium, titanium, columbium, and tantalum with the gases, oxygen, nitrogen, and hydrogen at elevated tempera- tures. J Electrochem Soc 1949;96(6):364.
  57. Ram FS, Wedzicha JA. Ambulatory oxygen for chronic obstructive pulmonary disease. Cochrane Database Syst Rev 2002. http://dx.doi.org/10.1002/14651858.CD000238.
  58. Rathgeber J, Zuchner K, Kietzmann D, Kraus E. Efficiency of a mobile oxygen concentrator for mechanical ventilation in anesthesia. Studies with a metabolic lung model and early clinical results. Anaesthesist 1995;44(9):643-50.
  59. Gould GA, Scott W, Hayhurst MD, Flenley DC. Technical and clinical assessment of oxygen concentrators. Thorax 1985;40(11):811-6.
  60. Strickland SL, Hogan TM, Hogan RG, Sohal HS, McKenzie WN, Petroski GF. A randomized multi-arm repeated-measures prospective study of several modali- ties of portable oxygen delivery during assessment of functional exercise capacity. Respir Care 2009;54(3):344-9.
  61. Litch JA, Bishop RA. Oxygen concentrators for the delivery of supplemental oxygen in remote high-altitude areas. Wilderness Environ Med 2000;11(3):189-91.
  62. Shrestha BM, Singh BB, Gautam MP, Chand MB. The oxygen concentrator is a suitable alternative to oxygen cylinders in Nepal. Can J Anaesth 2002;49(1):8-12.
  63. Saito S, Shimada H, Yamamori K. A transportable hyperbaric chamber with soda lime for the treatment of high-altitude disorders. J Wilderness Med 1994;5(3):295-301.
  64. Gamow RI, Geer GD, Kasic JF, Smith HM. Methods of gas-balance control to be used with a portable hyperbaric chamber in the treatment of high altitude illness. J Wilderness Med 1990;1(3):165-80.
  65. Taber RL. Protocols for the use of a portable hyperbaric chamber for the treatment of high altitude disorders. J Wilderness Med 1990;1(3):181-92.
  66. King SJ, Greenlee RR. Successful use of the Gamow Hyperbaric Bag in the treatment of altitude illness at Mount Everest. J Wilderness Med 1990;1(3):193-202.
  67. Shimada H, Morita T, Kunimoto F, Saito S. Immediate application of hyperbaric oxygen therapy using a newly devised transportable chamber. Am J Emerg Med 1996;14(4):412-5.
  68. Karen B, Hoesen V. Hyperbaric medicine. In: Auerbach PS, editor. Wilderness medicine. 5 ed. Philaderlphia: Mosby Elsevier; 2007. p. 1638-54.
  69. Jay GD, Tetz DJ, Hartigan CF, Lane LL, Aghababian RV. Portable hyperbaric oxygen therapy in the emergency department with the modified Gamow bag. Ann Emerg Med 1995;26(6):5.
  70. Saito S, Aso C, Masaki K, Takazawa T, Tatsuya S, Shimada H. Experimental use of a transportable hyperbaric chamber durable for 15 psi at 3700 meters above sea level. Wilderness Environ Med 2000 Mar 1;11(1):21-4.
  71. Pattinson KTS, Somogyi RB, Fisher JA, Bradwell AR, Society the Birmingham Medical Research Expeditionary. Efficient breathing circuit for use at altitude. Wilderness Environ Med 2005;16(2):101-3.