Extreme Cooling Rates in Avalanche Victims: Case Report and Narrative Review

Background

Aperson buried by an avalanche will typically die of hypoxia within the first 35 minutes (Falk et al., 1994; Haegeli et al., 2011). Surviving prolonged burial (≥60 minutes) is only possible if an air pocket exists, that is, patent airway and any space in front of nose and mouth. Chances of survival with favorable outcome of an avalanche victim are higher if the buried subject rapidly cooled to <30°C and arrested only thereafter (Frei et al., 2019; Podsiadlo et al., 2021). A low core temperature reduces oxygen metabolism in the body and protects the most oxygen-dependent organs, the brain and heart, from any hypoxia-induced damage longer than in normothermia (McCullough et al., 1999). In the European Resuscitation Guidelines 2015 and 2020, avalanche burial has been divided into <60 minutes and ≥60 minutes (Truhlar et al., 2015; Lott et al., 2021). This division was made on the basis that <60 minutes buried subjects do not cool sufficiently to suffer hypothermic cardiac arrest (core temperature <30°C in young and healthy subjects), with avalanche burial ≥60 minutes hypothermia-induced cardiac arrest is possible.

We report the case of a young female backcountry skier who cooled extremely fast following an avalanche burial of 25 minutes and review the literature with regard to similarly extreme cooling rates in persons rescued from an avalanche burial, defined as cooling >5°C/h. Reasons for extreme cooling in avalanche victims are discussed and guidance to rescuers is given.

Methods

A case report according to the CARE guidelines is presented. The patient has given informed written consent to the publication of this case report. A literature search with the keywords “avalanche” AND “hypothermia” was performed and yielded 96 results. The last update was on October 25, 2020. A narrative review complements our case report.

Results

The literature search revealed four avalanche patients with extreme cooling rates. References of included articles were searched for further relevant studies. Twenty-eight additional pertinent articles were found. Overall, 32 studies were included in this work.

Case Report

A 25-year-old athletic female backcountry skier (170 cm, 59 kg) was buried by an avalanche in the Tyrolean Alps, Austria. The incident occurred at 14:10 during the ascent at ∼1,650 m above sea level, on a sunny warm day at the end of March 2017. She wore one thin layer of functional long sleeve clothes (Dynafit, Munich, Germany). Later, she reported that she had “moderately” sweated before the incident. The avalanche buried her at a depth of 2–3 m. Initially, she was fully conscious and noticed that she was breathing into a small air pocket. Soon thereafter, she had difficulties in breathing and lost consciousness. Her two companions extricated her after ∼25 minutes, and she regained consciousness quickly. She was airlifted to the closest hospital (<20 km distance) in <10 minutes flight time. There, at 15:30 in the trauma department, she was sedated. An esophageal temperature probe was inserted, revealing a core temperature of 25.7°C (1 hour and 20 minutes after the avalanche accident) (Pasquier et al., 2020). Vital signs remained stable. An abdominal ultrasound was unremarkable. Blood tests were normal besides serum potassium of 5.1 mmol/l and creatine kinase of 500 U/l. Minimally invasive rewarming with forced air blankets was commenced, and, probably less effective, warmed infusions were administered immediately after arrival at the emergency room and continued in the intensive care unit.

The core temperature measured in the emergency room was 26.8°C at 15:45, 28°C at 16:00, and 29.7°C at 16:15. She was transferred to the intensive care unit at 16:30, and the measured core temperature was 35.7°C at 17:00 and 36.8°C at 18:00 thereafter (Fig. 1). The patient was rewarmed within 2.5 hours from 25.7°C to 36.8°C, resulting in a rewarming rate of 4.4°C/h. This fast rewarming rate for active noninvasive rewarming (Paal et al., 2016) can be explained by the slender physique of the patient, which besides her thin garment at the time of burial may also be a major reason of the rapid cooling. The patient was discharged from the hospital the next day. She resumed her job and has conducted a normal private and professional life ever since without any impairment. Three years later, she gave birth to healthy twins.

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FIG. 1.

Core temperature of avalanche victims related to time after burial. Grey lines denote time of burial, and black lines denote postburial exposure. Gray numbers indicate core temperature (°C), and black numbers indicate cooling rates (°C/h). *Esophageal, **epitympanic temperature measurement. Partial burial (Strohle et al., 2015). Complete burial (Putzer et al., 2010). Complete burial (Pasquier et al., 2015). Complete burial (Present case report). Complete burial (Oberhammer et al., 2008).

Literature Review of Other Subjects Buried in Avalanches with Extreme Cooling Rates (>5°/h)

Discussion

The stunning feature of our case is the cooling rate of 8.5°C/h, assuming a preburial core temperature of 37.0°C. The core temperature of 25.7°C was measured esophageally 80 minutes after the avalanche incident. This is the fastest cooling rate ever reported in a patient rescued from a complete avalanche burial with persistent circulation and respiration. Faster cooling rates have only been reported in patients who suffered a hypothermic cardiac arrest or were partially buried.

The measured cooling rate in an avalanche patient is influenced by various factors. First, a subject buried in an avalanche cools in different phases, and every phase may have different cooling rates: (1) during burial, (2) during postburial environmental exposure on-site, and (3) during transport to hospital. In our case, burial lasted 25 minutes, postburial exposure 45 minutes, and air rescue another 10 minutes. Unfortunately, neither do most studies report these three phases separately nor do they uniformly report clothing and environmental conditions, which may influence cooling, for example, protection against cold on-site, air temperature, presence of sun, wind conditions, and conditions during transport. To increase comparability of cooling rates in subjects buried in avalanches, some authors suggested to exclude the postextrication time when reporting the cooling rate (Brugger et al., 2015). Unfortunately, for some of the presented cases, no prehospital temperature measurement has been reported, which again limits comparability.

Second, the measured cooling rate in avalanche patients is dependent on the location of core temperature measurement. Measurement in the esophagus is considered the gold standard (Strapazzon et al., 2014); thus, we consider the core temperature and cooling rate in our subject as correct. Three of the four cases above reported only tympanically measured core temperatures (Oberhammer et al., 2008; Putzer et al., 2010; Strohle et al., 2015). Tympanic measurement is prone to false low reading, especially in a cold out-of-hospital environment (Strapazzon et al., 2015).

Third, we hypothesize that cooling is considerably faster in patients whose clothing is moist from sweating and who have lost the ability to shiver, whose level of consciousness is impaired for any reason, or who have reached a state of low metabolism and endogenous heat production, either because energy stores are depleted due to exhaustion or they have suffered cardiac arrest. Evidence regarding the latter two factors is only anecdotal.

Another important parameter is the insulation characteristic of the clothing. For example, backcountry skiers during ascent dressed in a thin monolayer garment cool faster than downhill skiers with a thick multilayer ski-dress where head and hands are also covered. Cooling during snow burial can be as slow as 1°C/h, as demonstrated in an experimental study on volunteers wearing skiing dress, gloves, and a cap (Grissom et al., 2008). This is far less than the 6–9°C/h in the aforementioned cases of thinly dressed athletes (Oberhammer et al., 2008; Putzer et al., 2010; Pasquier et al., 2015; Strohle et al., 2015). One study elucidated another important factor that impacts on the cooling rate: carbon dioxide (CO₂). It reported faster cooling rates in hypercapnic subjects: 1.2°C/h in hypercapnic (39 ± 7 to 58 ± 9 mmHg) versus 0.7°C/h in normocapnic conditions (Grissom et al., 2004). Hypercapnia is a known vasodilator in the systemic circulation and may speed cooling by increasing heat loss through conduction. In a person buried by an avalanche and with the presence of an air pocket, CO₂ accumulates and may have an additional effect on the rate of cooling. In an experimental model, anesthetized and intubated pigs were breathing spontaneously into an air pocket of a simulated avalanche and cooled at an average rate of 4.6–4.7°C/h (Paal et al., 2013).

Finally, the quantity of adipose tissue in a given subject determines cooling. In cold conditions, slender persons cool faster, whereas adipose persons can keep the core temperature stable. The importance of adipose tissue to keep core temperature stable was impressively shown in a tragic accident when a ship capsized in March 1984 near the Icelandic coast. Three companions escaped the sinking boat into open water. Two disappeared from the water surface within 10 minutes, likely because of severe hypothermia and consecutive drowning. The third companion swam 5 to 6 hours in 5°C–6°C cold water 6 km to the next island, wearing only shirt, sweater, and jeans. Thereafter, he crossed 3 km of volcanic ground before reaching the first inhabited house. In the hospital, his core temperature was only <34°C (Keatinge, 1986; Edge, 2013). Several investigations confirmed that only his adipose tissue and the continuous physical efforts saved him from severe hypothermia and perishing like his companions.

Fast cooling is key for neurologically intact survival after hypothermic cardiac arrest (Gilbert et al., 2000; Oberhammer et al., 2008; Mroczek et al., 2020). It is essential to cool to low temperatures, for example, <30°C, before hypoxia-induced cardiac arrest sets in Gordon et al. (2015). Specifically, persons who submerge require cold water conditions and large body surface to body volume ratio, as in children and small and slim adults, to allow for rapid cooling (Truhlar et al., 2015). Conditions, which predispose patients caught in avalanche to fast cooling, include sweating prior burial, early cessation of shivering, light clothing with uncovered hands and head, and a slender physique. In children and slim individuals (as in this case), a high body surface area/body mass ratio will accelerate cooling and, later, rewarming (Bolte et al., 1988; Romlin et al., 2015).

Recent studies have shown that most buried avalanche victims do not survive once they have arrested because they die from hypoxic cardiac arrest before they eventually cool. Very few succumb to severe hypothermia before they arrest and can be rescued neurologically intact (Moroder et al., 2015; Metrailler-Mermoud et al., 2019). Survival from hypothermic cardiac arrest is substantially higher than from normothermic cardiac arrest (Gordon and Paal, 2018). This was confirmed by two recent systematic reviews, which reported good chances of neurologically intact survival in patients with witnessed hypothermic cardiac arrest (73% survival to hospital discharge of whom 89% with favorable outcome) (Frei et al., 2019) and even unwitnessed hypothermic cardiac arrest (27% survivors of whom 83% with neurologically intact) (Podsiadlo et al., 2021). Data suggest that most avalanche victims with burial <60 minutes are normothermic when they go into cardiac arrest and neurologically intact survival therefore is rare (Boue et al., 2014; Debaty et al., 2015; Moroder et al., 2015). For instance, a single-center study reported no survivors out of all 66 avalanche victims included during a 12.5-year time frame (Metrailler-Mermoud et al., 2019). Another study compared outcome of long-term (defined as >35 minutes in this study, n = 11) and short-term buried persons (n = 9). No long-term buried patient survived, but two short-term buried persons survived neurologically intact; bystanders had started cardiopulmonary resuscitation immediately before arrival of professional help (Moroder et al., 2015).

Rescuers should be prepared to encounter severe hypothermia even after burials <60 minutes. Fast cooling of patients buried in an avalanche should be anticipated when patients are sweating prior burial, are wearing only light garment with uncovered hands and head, when they are slender, and are not shivering. Extrication should be performed as fast as possible. However, brusque movement of the patient should be avoided as this is potentially harmful by increasing the return of cold blood to the heart and lowering myocardial temperature, which may increase the risk of cardiac arrest. After extrication, the insulation and the prevention of further heat loss is crucial since it is almost impossible to rewarm the patient out-of-hospital. A severely hypothermic patient (<30°C) should be transported as fast as possible to the next hospital with the possibility of ECLS rewarming, if it is accessible within 6 hours (Lott et al., 2021).

We report the fastest cooling rate in a subject following avalanche burial without cardiac arrest. This case is also remarkable because the patient did not sustain a cardiac arrest despite the severe hypothermia of 25.7°C (Pasquier et al., 2014). A review showed that older and sicker subjects may suffer hypothermia-induced cardiac arrest <32°C, whereas younger and healthy subjects tend to arrest <30°C (Lott et al., 2021). In our patient, we attribute the persistent circulation to the young age, fitness, and good health. Another protective factor might be the professional treatment, which the patient received immediately after extrication on-site, during transfer, and in the hospital.

Some limitations of this study should be mentioned. First, only few cases with extreme cooling rates exist in the literature; this limits the strength and value of our conclusions. Second, most case reports and larger studies do not report all relevant parameters, which impact on cooling; this again limits the development of well-based statements.

Conclusions

In conclusion, we report the case of a 25-year-old athletic female backcountry skier who was completely buried by an avalanche during ascent. The cooling rate of 8.5°C/h is the fastest ever reported in a completely buried avalanche victim with persistent circulation. Rescuers should be prepared to encounter severe hypothermia (core temperature <30°C) even after burials <60 minutes. Subjects buried in avalanche may cool extremely fast the more contributing factors for rapid cooling are present. After prolonged avalanche burial (>60 minutes) and unwitnessed cardiac arrest, chances of neurologically intact survival are small and depend on rapid cooling and onset of severe hypothermia (<30°C) before hypoxia-induced cardiac arrest.

Consent for Publication

All participants gave written informed consent to publication of the data.