Is Extracorporeal Rewarming Indicated in Avalanche Victims with Unwitnessed Hypothermic Cardiorespiratory Arrest?

Abstract

Mair, Peter, Hermann Brugger, Birgit Mair, Luca Moroder, and Elfriede Ruttmann. Is extracorporeal rewarming indicated in avalanche victims with unwitnessed hypothermic cardiorespiratory arrest? High Alt Med Biol 15:500–503, 2014.—International guidelines recommend using extracorporeal rewarming in all hypothermic avalanche victims with prolonged cardiac arrest if they have patent airways and a plasma potassium level ≤12 mmol/L. The aim of this study was to evaluate outcome data to determine if available experience with extracorporeal rewarming of avalanche victims supports this recommendation. At Innsbruck Medical University Hospital, 28 patients with hypothermic cardiac arrest following an avalanche accident were resuscitated using extracorporeal circulation. Of these patients, 25 were extricated from the snow masses with no vital signs and did not survive to hospital discharge. Three patients had witnessed cardiac arrest after extrication and a core temperature of 21.7°C, 22°C, and 24.0°C, two of whom survived long-term with full neurological recovery. A search of the literature revealed only one asystolic avalanche victim with unwitnessed hypothermic cardiac arrest (core temperature 19°C) surviving long-term. All other avalanche victims in the medical literature surviving prolonged hypothermic cardiac arrest suffered witnessed arrest after extrication with a core temperature below 24°C. Our results suggest that prognosis of hypothermic avalanche victims with unwitnessed asystolic cardiac arrest and a core temperature >24°C is extremely poor. Available outcome data do not support the use of extracorporeal rewarming in these patients.

Introduction

Hypothermia may protect avalanche victims from hypoxic tissue injury during prolonged cardiac arrest. Therefore, international guidelines (Brugger et al., 2013) recommend prolonged resuscitation and the use of extracorporeal support in all arrested avalanche victims with a core temperature below 32°C, a patent airway free of snow and a plasma potassium level <12 mmol/L. These recommendations are based predominantly on the possibility of rapid cooling during snow burial in selected cases (Oberhammer et al., 2008; Putzer et al., 2010) and a few reports of successful resuscitation of avalanche victims with hypothermic cardiac arrest (Althaus et al, 1982; Oberhammer et al., 2008; Boyd et al., 2010). Cases of successful resuscitation of hypothermic avalanche victims have not been analyzed concerning the circumstances of cardiac arrest (witnessed or unwitnessed) or the underlying rhythm (Boyd et al., 2010). It is assumed that hypothermia sufficient to protect from hypoxic tissue injury may already be present after 35 minutes of snow burial (Brugger et al., 2011; 2013).

The aim of this study was to evaluate if outcome data support recommendations for the routine use of extracorporeal rewarming in all hypothermic avalanche victims, also those with unwitnessed cardiac arrest and prolonged asystole. For this purpose, we retrospectively evaluated our own experience at Innsbruck Medical University Hospital and searched the literature for outcome data on resuscitation efforts in arrested hypothermic avalanche victims.

Materials and Methods

The hypothermia database of Innsbruck Medical University Hospital was searched for patients rewarmed with extracorporeal circulation after an avalanche accident. Data on the circumstances of cardiac arrest (witnessed/unwitnessed), body core temperature, plasma potassium, and patient outcome (died, survived to hospital discharge, survived long-term with full neurological recovery) were retrieved from the database for all avalanche victims identified.

Furthermore, Medline was searched for relevant studies, case series, and case reports using the terms “avalanche and resuscitation,” “avalanche and outcome,” and “avalanche and extracorporeal.” In addition, text books, reference texts, reference lists, and conference proceedings were hand-searched to identify further relevant studies and case reports. Finally experts in the field of extracorporeal rewarming were contacted to retrieve additional relevant information on the topic and to check for completeness of data collection.

Results

Experience at Innsbruck Medical University Hospital

At Innsbruck Medical University Hospital between 1987 and 2013, a total of 28 patients with prolonged hypothermic cardiac arrest after an avalanche accident were resuscitated using extracorporeal circulation. Mean core temperature was 25.7°C (range from 17.9°C to 30.8°C). Twenty-five of these patients had no vital signs at extrication (unwitnessed cardiac arrest); none survived to hospital discharge. Three patients suffered witnessed cardiac arrest due to ventricular fibrillation shortly after extrication. Core temperature was 21.7°C, 22°C, and 24°C. Two of these three patients with witnessed cardiac arrest survived long-term with full neurological recovery. The third patient sustained concomitant major trauma and died from intractable bleeding shortly after successful rewarming. Plasma potassium values ≥12 mmol/L were found in only five (18%) of the 28 arrested hypothermic avalanche victims (Table 1). Less than one-third of all avalanche victims resuscitated with extracorporeal circulation were profoundly hypothermic with a core temperature ≤24°C (Table 1).

Table 1.

Plasma Potassium Values and Body Core Temperature in 28 Patients with Hypothermic Cardiac Arrest after Avalanche Accidents

Parameter	Unwitnessed arrest (%)	Witnessed arrest (%)	Total (%)
plasma potassium <6 mmol/L	n=8 (32%)	n=3 (100%)	n=11 (39%)
plasma potassium 6–8 mmol/L	n=10 (40%)	none	n=10 (36%)
plasma potassium 8–12 mmol/L	n=2 (8%)	none	n=2 (7%)
plasma potassium ≥12 mmol/L	n=5 (20%)	none	n=5 (18%)
core temperature ≤24°C	n=5 (20%)	n=3 (100%)	n=8 (28.5%)
core temperature 24°C–28°C	n=15 (60%)	none	n=15 (53.5%)
core temperature 28°C–32°C	n=5 (20%)	none	n=5 (18%)

Published case series and case reports in the medical literature

Medline search identified three larger case series including more than five avalanche victims with prolonged hypothermic cardiac arrest (Schaller et al., 1990; Locher et al., 1991; Hilmo et al., 2014). An additional larger case series was accessible by Internet only (I Moustapha. Factors associated with survival in patients with severe accidental hypothermia. Thesis. Faculté de Médecine Grenoble, Université Joseph Fourier). These four case series reported a total of 51 avalanche victims with prolonged hypothermic cardiac arrest. Four patients survived, all of whom had suffered witnessed cardiac arrest after extrication. None of the remaining 47 avalanche victims survived long-term (28 of 47 had unwitnessed cardiac arrest, in 19 no information on the arrest could be retrieved from the literature) (Schaller et al., 1990; Locher et al., 1991; Hilmo et al., 2014).

Medline search revealed additional case series including only one or two hypothermic avalanche victims (Althaus et al., 1982; Farstad et al., 2001; Swamato et al., 2014; Walpoth et al., 1990, 1997) and one case report (Oberhammer et al., 2008). These publications reporting a total of eight avalanche victims identified one hypothermic avalanche victim who survived unwitnessed asystolic cardiac arrest (Althaus et al., 1982). This patient was profoundly hypothermic with a core temperature of 19°C and was swept into a crevasse by a snow avalanche. Other than this patient, Medline search revealed reports of successful resuscitation following hypothermic cardiac arrest (Althaus et al., 1982; Locher et al., 1991; Mair et al., 1994; Oberhammer et al., 2008; Ruttmann et al., 2007; Walpoth et al., 1997) only in avalanche victims with witnessed cardiac arrest caused by ventricular fibrillation and a core temperature below 24°C (Table 2).

Table 2.

Survivors of Hypothermic Cardiac Arrest after Avalanche Accidents Identified Through Medline Search

Reference	Arrest witnessed	Rhythm	Core temperature
Althaus et al., 1982¹
victim 1	yes	VF	22°C
victim 2	no	A	19°C
Locher et al., 1991¹
victim 1	yes	no data	no data
victim 2	yes	no data	no data
Mair et al., 1994²	yes	VF	24°C
Oberhammer et al., 2008²	yes	VF	21.7°C
Ruttmann et al., 2007²
victim 1	Yes	VF	24°C
victim 2	yes	VF	21.7°C
Walpoth et al., 1997¹	yes	no data	19.6°C

Cross references, refer partly to the same patients from three Swiss centers; ²cross references, refer to the same two patients from Innsbruck Medical University Hospital.

Discussion

Our own experience and data from the literature demonstrate an extremely poor prognosis for asystolic hypothermic avalanche victims with unwitnessed cardiac arrest undergoing prolonged resuscitation efforts. We found only one published report of a long-term survivor following prolonged unwitnessed cardiac arrest (Althaus et al., 1982). This survivor was remarkable for his low body core temperature of 19°C (Althaus et al., 1982). Asystole in a hypothermic patient occurs at a core temperature of 22°C to 20°C (Mair et al., 2007). Consequently, asystole at a core temperature above 24°C indicates major concomitant pathology such as asphyxia, trauma, or prolonged cardiac arrest (Mair et al., 2007).

In general, the hypothermic heart does not respond to standard advanced cardiac life support at a core temperature below 28°C to 30°C (Mair et al., 2007, Walpoth et al., 1997). Therefore, cardiac surgery centers normally use extracorporeal support only in hypothermic patients with a core temperature below 28°C (Walpoth et al., 1997; Brodmann Maeder et al., 2011). Very rapid cooling may occur in a few occasional avalanche victims (Oberhammer et al., 2008; Putzer et al., 2010). However, in the majority, hypothermia sufficient to protect from hypoxic tissue injury will develop only after 90 to 120 minutes of snow burial (Locher et al., 1991; Brugger et al., 2011). Current guidelines (Brugger et al., 2013) recommend 35 minutes of snow burial and 32°C of core temperature as triage criteria for extracorporeal rewarming in asystolic avalanche victims with unwitnessed cardiac arrest. As our data clearly demonstrate, this inevitably results in a large number of avalanche victims with prolonged cardiac arrest and irreversible hypoxic injury being placed on extracorporeal support. Obviously, unwitnessed cardiac arrest is normally found in avalanche victims dying from asphyxia before cooling, in particular when presenting with asystole and a core temperature >24°C. By contrast, witnessed cardiac arrest is typically observed in avalanche victims with hypothermia associated ventricular fibrillation and therefore has a far better prognosis (Boyd et al., 2010; Brugger et al, 2011; Brown et al., 2012).

In a systematic review, Boyd et al. (2010) identified a total of eight avalanche victims with hypothermic cardiac arrest surviving long-term after extracorporeal rewarming. These long-term survivors were used as an argument to support the routine use of extracorporeal rewarming in all avalanche victims with cardiac arrest and a core temperature below 32°C (Boyd et al., 2010; Brugger et al., 2013). However, all victims referred to by Boyd and coworkers had a core temperature ≤24°C and, except for one with asystole, all also suffered witnessed cardiac arrest due to ventricular fibrillation after extrication (Table 2).

Obviously only profound hypothermia with a core temperature below 24°C offers sufficient protection from ischemic tissue injury to enable successful resuscitation. With such a low core temperature, asystole may be solely the consequence of hypothermia and extracorporeal rewarming is justified even in the presence of persistent asystole.

Current guidelines give a plasma potassium level ≥12 mmol/L as one of the key criteria for termination of CPR during in-hospital triage of arrested hypothermic avalanche victims (Brown et al., 2012; Brugger et al., 2013). In our experience at Innsbruck Medical University Hospital, only one of five avalanche victims with irreversible hypoxic injury had a plasma potassium ≥12 mmol/L. Although a reliable marker of irreversible cardiac arrest in all patients where it is present (Brown et al., 2012; Brugger et al., 2013), a plasma potassium level ≥12 mmol/L is of limited value in clinical practice due to its low sensitivity in detecting irreversible asphyxia in hypothermic avalanche victims. In our data, 70% of nonsurvivors had a plasma potassium concentration ≤8 mmol/L, clearly indicating that a normal or slightly elevated plasma potassium concentration cannot be used as a laboratory marker to exclude death from asphyxia. A plasma potassium concentration <12 mmol/L alone is no reason to use extracorporeal rewarming in a hypothermic avalanche victim with unwitnessed cardiac arrest.

This study has some limitations. Case series analyzed also include patients treated before the first publication of triage guidelines by IKAR MEDCOM 1996. Therefore, some of the patients studied would nowadays not have been rewarmed with extracorporeal circulation. Furthermore, triage decisions at the avalanche scene do not always follow the published recommendations. Thus, some avalanche victims benefitting from extracorporeal rewarming may not have been resuscitated until hospital admission. Due to these limitations and the small number of patients analyzed, we cannot definitively exclude that selected avalanche victims with asystole will survive unwitnessed hypothermic cardiac arrest, although our data clearly indicate an overall dismal prognosis.

Conclusion

In summary, we did not find outcome data that clearly support the routine use of extracorporeal rewarming in an asystolic avalanche victim with prolonged, unwitnessed cardiac arrest and a core temperature >24°C. Our results support a restrictive use of the expansive and limited resource of extracorporeal rewarming in avalanche victims with asystole when core temperature is below 24°C. By contrast, prognosis of hypothermic avalanche victims with witnessed cardiac arrest seems to be far better and extracorporeal rewarming is clearly warranted in the majority of cases.

Footnotes

Acknowledgments

We would like to thank perfusionist Anton Jeller for his support in data collection.

Author Disclosure Statement

None of the authors has financial or other relations that could be deemed a conflict of interest.

References

Althaus

, Aeberhard

, Schuepbach

, Nachbur

, and Muehlemann

. (1982). Management of profound accidental hypothermia with cardiorespiratory arrest. Ann Surg, 195:492–495.

Boyd

, Brugger

, and Shuster

. (2010). Prognostic factors in avalanche resuscitation: A systematic review. Resuscitation, 81:645–652.

Brodmann Maeder

, Duenser

, Eberle

, et al. (2011). The Bernese Hypothermia Algorithm: A consensus paper on in-hospital decision-making and treatment of patients in hypothermic cardiac arrest at an alpine level 1 trauma centre. Injury, 42:539–43.

Brown

, Brugger

, Boyd

, and Paal

. (2012). Accidental hypothermia. N Engl J Med, 367:1930–1938.

Brugger

, Durrer

, Elsensohn

, Paal

, Strapazzon

, Winterberger

, Zafren

, and Boyd

. (2013). Resuscitation of avalanche victims: Evidence-based guidelines of the international commission for mountain emergency medicine (ICAR MEDCOM): intended for physicians and other advanced life support personnel. Resuscitation, 84:539–546.

Brugger

, Paal

, and Boyd

. (2011). Prehospital resuscitation of the buried avalanche victim. High Alt Med Biol, 12:199–205.

Farstad

, Andersen

, Koller

, Grong

, Segadal

, and Husby

. (2001). Rewarming from accidental hypothermia by extracorporeal circulation. A retrospective study. Eur J Cardiothorac Surg, 20:58–64.

Hilmo

, Naesheim

, and Gilbert

. (2014). “Nobody is dead until warm and dead”: Optimistic and prolonged resuscitation is warranted in victims of accidental hypothermia with cardiac arrest in remote areas. A retrospective study from the High North. Resuscitation, 85:1204–1211.

Locher

, Walpoth

, Pfluger

, and Althaus

. (1991). Akzidentelle Hypothermie in der Schweiz (1980–1987). Scweiz Med Wschr, 121:1020–1028.

10.

Mair

, Schwarz

, Walpoth

, and Silfvast

. (2007). Cardiopulmonary resuscitation in hypothermic patients. In: Cardiac Arrest—The Science and Practice of Resuscitation Medicine. Paradis

, Halperin

, Kern

, Wenzel

, Da Chamberlain , eds. Cambridge University Press, Cambridge, pp. 1014–1027.

11.

Mair

, Kornberger

, Furtwaengler

, Balogh

, and Antretter

. (1994). Prognostic markers in patients with severe accidental hypothermia and cardiocirculatory arrest. Resuscitation, 27:47–54.

12.

Oberhammer

, Beikircher

, Hoermann

, Lorenz

, Pycha

, Adler-Kastner

, and Brugger

. (2008). Full recovery of an avalanche victim with profound hypothermia and prolonged cardiac arrest treated by extracorporeal re-warming. Resuscitation, 76:474–480.

13.

Putzer

, Schmid

, Braun

, Brugger

, and Paal

. (2010). Cooling of six centigrade in an hour during avalanche burial. Resuscitation, 81:1043–1044.

14.

Ruttmann

, Weissenbacher

, Ulmer

, et al. (2007). Prolonged extracorporeal membrane oxygenation-assisted support provides improved survival in hypothermic patients with cardiocirculatory arrest. J Thorac Cardiovasc Surg, 134:594–600.

15.

Schaller

, Fischer

, and Perret

. (1990). Hyperkalemia. A prognostic factor during acute severe hypothermia. JAMA, 264:1842–1845.

16.

Swamato

, Bird

, Katayama

, Maekawa

, Uemura

, Tanno

, and Narimatsu

. (2014). Outcome from severe accidental hypothermia with cardiac arrest resuscitated with extracorporeal cardiopulmonary resuscitation. Am J Emerg Med, 32:320–324.

17.

Walpoth

, Locher

, Leupi

, Schuepbach

, Muehlemann

, and Althaus

. (1990). Accidental deep hypothermia with cardiopulmonary arrest: Extracorporeal blood rewarming in 11 patients. Eur J Cardiothorac Surg, 4:390–393.

18.

Walpoth

, Walpoth-Aslan

, Mattle

, et al. (1997). Outcome of survivors of accidental deep hypothermia and circulatory arrest treated with extracorporeal blood warming. N Engl J Med, 337:1500–1505.