A-Life - Increasing Survival Chances in Avalanches by Wearable Sensors

Avalanches are one of the major threats to life in high mountain terrain. Once buried by an avalanche, survival chances dramatically drop from 92% after 15 minutes to only 30% after 35 minutes mostly due to the lack of oxygen. It is therefore extremely important to rescue any victims as fast as possible in order to maximize survival chances. Today’s technology, so called electronic avalanche beacons, only allow to localize buried victims. In this paper we propose a novel avalanche rescue system enhanced with wearable sensors. Those sensors provide information about the vital state of buried victims such as heart rate, respiration activity, and blood oxygen saturation, as well as the orientation of the victim. We believe that this knowledge can empower non-professional companion rescuers with a tool to perform triage, i.e. sorting victims into categories of priority for treatment. Better allocation of resources can help to maximize survival chances of avalanche victims. 1. About Avalanches and Avalanche Rescue In the 17 European and North-American countries of the International Commission for Alpine Rescue (ICAR) on average 146 avalanche fatalities have been registered per year between 1975 and 1995 [23]. In 90% of all avalanche accidents, the victim or someone in the victim’s party triggers the slide [14]. Recreationists go beyond their limits, underestimate the danger of avalanches and risk their lives without the appropriate awareness of avalanche risks [16]. Accordingly, non-profit organizations and mountain clubs, such as the Swiss Alpine Club or the Canadian Mountain Rescue Association, put enormous efforts into educational programs on avalanche awareness and companion rescue operations. The key element of companion rescue is the so-called avalanche beacon. Worn by mountaineers, this electronic device allows to localize avalanche victims. In this paper we propose to enhance existing avalanche beacons with wearable sensors. Thus, rescuers obtain quick and early access to valuable information on the avalanche victims, such as vital sign functions. The aim is to enable rescuers to better allocate resources to the most urgent victims. It could also be used as a blackbox device, that records the sequence of events during an avalanche release for accident analysis or even legal actions. The two next subsections highlight two significant issues for avalanche rescue: importance of time and need for companion rescue. Section 2 shows how sensing technology can improve avalanche rescue. In Section 3, ways of interpreting sensor measurements are given. Section 4 poses constraints for a user interface of an enhanced avalanche beacon and section 5 summarizes technical challenges. Section 6 reviews our A-Life prototype. Finally in section 7, we summarize our ideas and provide an outlook on further improvements of our approach. 1.1. Importance of Time Avalanche statistics show that time is the most critical issue during rescue [13]. Figure 1 shows that the chances for finding a buried victim alive decrease rapidly with time: 92% of avalanche victims survive the first 15 minutes, from 15 to 35 minutes survival chances decline from 92% to 30%, the majority dies by asphyxiation. So-called “air pockets”, closed air bubbles in the snow in front of mouth and nose, can save lives until 90 minutes. After 130 minutes only 3% survive with big air pockets or air channels to the outside. Consequently, successful avalanche rescue has to aim at rescuing victims within the first 15 minutes. It is noteworthy that three quarters of all avalanche victims die from asphyxiation, only one quarter is killed from trauma. Whereas the latter group usually has no chances for recovery, air-pockets and fast companion rescue provide the best chances for surviving an avalanche accident. 1.2. Companion Rescue The standard companion rescue procedure as it is advertised today comprises three steps. First, the victims have to be localized in the avalanche. With avalanche beacons search should take no longer than 3 to 5 minutes. As Figure 1. Survival function (taken from [13]) a second step, extricating a localized victim with shovels should not take more than 10 to 15 minutes. Extrication has not only to be quick, but also to be performed with care: victims could be injured by the shovels, and air-pockets, victims’ protection against asphyxiation, could be destroyed. Rescuers today do not know how victims are oriented in the snow. The third step is to execute first aid: opening respiratory tracts and avoiding hypothermia. At this point professional aid should take over. The entire rescue process has to be as fast as possible in order to maximize survival chances. This puts rescuers under immense pressure, as in practice rescue resources are always limited. However, if immediate search of buried victims is performed properly by survivors or witnesses of an avalanche, survival chances are 4 times as high as in case of organized rescue [22]. 2. How sensors may improve the rescue process This section starts with a review of today’s avalanche beacon technology. Thereupon, phenomena and indicators are derived, which determine the rescue process but are not available today. Finally, it is shown how sensing technology can reveal those phenomena. 2.1. Today’s Avalanche Beacons Today, beacon technology only assists during search. Beacon devices operate on 457 kHz long wave frequency, which has become an international standard. Microprocessors on the devices can calculate distance and direction to a single victim from the emitted dipole flux pattern [17]. By that, the devices can guide the rescuer to the victim either through arrows on a display or sounds with rising volume as the rescuer approaches the victim. Usually, a range of 80m can be achieved. Batteries last up to 300h. By default, devices operate in sending mode and can be switched to receive mode to initiate rescue operations. 2.2. Phenomena of Interest to sense Our vision is to provide rescuers and mountaineers with information that goes far beyond location by including valuable information on the victim’s state of emergency. Accordingly, in the following we outline important phenomena and indicators pertinent to efficient and successful rescue. Direction and a rough estimation of the distance is all beacons provide today. However, more support would be desirable: • knowledge about the state of the victims, survival chances, urgency, vital sign functions • support for rescuing multiple people • orientation of the victim in the snow • burial depth of the victim Knowledge about a victim’s physical situation is a rich source of information for rescuers. Vital sign functions, such as heart rate, respiration activity, consciousness and core temperature are the key elements for initial assessment and provision of basic life support [1]: Missing heart rate requires manual chest compression, absence of respiration activity demands rescue breathing, unconsciousness has to be treated by anti-shock therapy, and low temperature requires treating hypothermia [15]. As rescue operations differ in rescue resources, e.g. chest compression requires two trained rescuers, anti-shock therapy only one low-skilled rescuer, knowledge on victims’ vital sign functions enables rescuers to foresee upcoming rescue procedures and allocate rescuers among victims more properly. Evidence of life signs may also motivate rescuers and drive rescue of remaining victims even under harsh conditions. Last but not least, vital sign functions of victims can also be communicated to professional rescue service already before having access to victims. As discussed in section 1 the existence of an air pocket can help buried victims to survive under snow up to 90 minutes. Victims with air pockets can be considered less urgent than others without. Rescuers can be instructed to focus on those victims first, as their survival time will be much shorter. Equally, rescuers can be reminded not to destroy this life saving source. Finally, air pockets are a very good indication of working respiration tracts, which is important to know for emergency physicians. Currently, air pocket detection is very difficult; rescuers do not know whether a victim has or does not have an air pocket. Orientation of an avalanche victim in snow determines from which direction rescuers should approach the victim, so that they do not step on top and destroy an air pocket. For extrication today’s rescuers are instructed to drive a channel sidewards in direction to the victim. As rescuers today only can localize a victim without knowing the orientation, a starting point for digging is hard to define. Awareness of orientation could help to preserve air pockets, speed up access to the victim’s head for first aid. Giving rescuers access to different relevant sources of information can lead to a more efficient and better scheduled rescue. 2.3. Available Sensing Technology This section shows, how sensors worn by mountaineers can give rescuers access to valuable information, that is beyond the human senses. Oximeters, which have a firm place in everyday clinical practice, offer an unobtrusive way of measuring heart rate and blood oxygen saturation. Attached to one’s finger, toe, or forehead, the ratio of the fluctuation of red and infrared light caused by hemoglobin – the oxygen carrier in human blood – is used to calculate the heart rate and oxygen blood saturation (%SpO2). Body core temperature is another valid vital sign function describing a victim’s physical state. Skin temperature is easy to measure, but it’s significance is rather low, as skin temperature and body core temperature are not well correlated. However, [9] reports a pill-sized thermometer, which can be swallowed and then transmit measurements wirelessly through the body to another device worn outside the body. The existence of air pockets can be indicated by oxygen sensors (e.g. [3]), that measure the oxygen concentration of the environment. Distance sensors, operating on infra-red or ultra sound, can be used for detecting convexity in the snow covering a buried victim. Combining results of oxygen sensors and oximeter can give a good indication for a person’s respiration activity. Finally, 3D accelerometers can reveal a victims’ body orientation in the snow. As pointed out earlier, our vision is to augment today’s avalanche beacons mountaineers are wearing anyway: collected data from the various sensor distributed around the body is communicated through long wave to rescuers in emergency cases. We discussed how existing sensing technology can add value to today’s avalanche rescue and increase survival chances. 2.4. Placement of Sensors In the following it is described how sensors can be unobtrusively placed on the mountaineers’ bodies, such that the mountaineers are minimally disturbed in their activities and the sensors are protected against loss during avalanches. We tested different placements of the oximeter: forehead, finger tips, and toe. Only the toe turned out to be appropriate in mountaineering. Today’s ski and hiking boots are well isolated and can shelter the sensor from damage and loss. Loss of boots in avalanches is very rare. Once wrapped around the toe the sensor is not noticed anymore and does not disturb at all. However, severe cold may cause retreat of blood from the extremities, such that measurements at the toe may get unreliable under harsh conditions. But victims under snow cover are very well isolated and hypothermia is not the dominant factor during the first hour after the avalanche [13]. The placement of an oxygen sensor detecting air pockets is more difficult: it has be worn very close to the mouth as air pocket usually are only a few centimeters wide [21]. We propose to integrate the oxygen sensor into the collar of the jacket. Notwithstanding the danger of loss in an avalanche, we prefer the collar, as other locations, such as glasses seem even weaker. The accelerometers for measuring orientation can be embedded directly into today’s avalanche beacons. As those beacons are fixed well on the human body, loss during avalanches is almost impossible. As mountaineers are used to wearing those devices, they do not feel disturbed. 3. Visualization of Sensor Readings Knowledge on victims’ physical state enables rescuers to foresee upcoming rescue procedures and to better plan on-going rescue. Today, triage [10] the principle of sorting casualties in disaster into categories of priority for treatment is reserved for professional aid, as triage is rather complex and requires medical experience. Automation of triage through sensors would also provide companion rescuers with a tool to support decision that helps to focus on most urgent victims first. 3.1. The Curse of Information Avalanche rescue is a cognitively demanding situation. Rescuers must not be flooded with sensor measurements, but data has to be pre-processed and presented in a concise way: translations to the rescuer’s language such as “upright”, “horizontal”, “upright down”, “air pocket”, “no air pocket” are more meaningful than the actual sensor measurements. Thresholds for oximeter values used in medical practice [19] are more tailored to rescuers’ understanding than the actual values. Further, sensor measurements should be double checked whenever possible, e.g. respiration activity should only be inferred if both an air pocket is detected and the oxygen blood saturation is over 80%. Only if those two conditions are satisfied, reasoning about respiratory activity is valid. Proper placement of the oximeter, can be detected by the sensor itself: it reports whether its measurements are valid or not. Putting all available sensor information of multiple victims at once is too much: We propose separation in location and urgency. First, visual presentation of the victims’ spatial distribution enables to select victims close-by to keep paths short. Secondly, separation in urgency provides rescuers with a global view on the emergency, automation of triage, which allows to rescue urgent victims first. Figure 2. Urgency Measure 3.2. Urgency Measure We developed a global measure that integrates all sensor readings, referred to as urgency measure. Figure 2 depicts the decision tree we use to assign an urgency measure to each victim. Motivated by triage, as performed by emergency physicists, we take heart rate as the primary criterion. If heart rate cannot be detected, we assume the highest urgency, as reactivation will have to take place immediately. On the other hand, rescuers could also reason that this victim has already died due to a fatal injury. We want to leave this decision with the rescuers, as they as witnesses still have additional knowledge about the accident they can integrate into their decision process. If heart rate can be detected, we take the existence of an air pocket as the secondary criterion for determining urgency. As outlined in section 1.1, air pockets may help to survive up to 90 minutes in contrast to only 15 minutes without. Accordingly, the latter group is in a more urgent state than the first. We use oxygen blood saturation as a third criterion of urgency determination. We adopt the categories from [19] for obtaining urgency from oximeter measurements. Finally, we take orientation as the fourth attribute of urgency. We assume that orientation can give hints about injuries occurred to the victim. Further, one can assume that different orientations may also constrain a victim’s self-rescue capabilities. We rate “upside down” as the worst case, “vertical” as intermediary and “upright” as the best condition. However, we do not judge orientation as a very strong criterion for urgency, so orientation has the lowest impact in the decision tree. This urgency measure provides rescuers with a global view of the emergency. Each victim can be described by one value, which allows to align multiple victims on a onedimensional scale. Multiple victims can thus be compared much easier. Hence, the urgency measure allows to reason about allocating resources to victims according to the severeness of their situation. Nevertheless, rescuers are not distracted from their rescue, as the system integrates all relevant sensor values into one view and takes away the cognitive load of interpreting too many sensor values. Another improvement over pure sensor values is observability over time and deriving predictions for future developments. Apart from only presenting the victims’ sensor values, a system can also derive tendencies and guide attention to critical parameters.