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Prognostic factors in avalanche resuscitation: A systematic review
Resuscitation 81 (2010) 645–652
Contents lists available at ScienceDirect
Resuscitation journal homepage: www.elsevier.com/locate/resuscitation
Review
Prognostic factors in avalanche resuscitation: A systematic review夽 Jeff Boyd a,b,∗ , Hermann Brugger c,d , Michael Shuster a a
Department of Emergency Medicine, Mineral Springs Hospital, Banff, AB, Canada International Federation of Mountain Guides, Banff, Alberta, Canada EURAC Institute of Mountain Emergency Medicine, Bozen/Bolzano, Italy d Innsbruck Medical University, Innsbruck, Austria b c
a r t i c l e
i n f o
Article history: Received 30 November 2009 Received in revised form 12 January 2010 Accepted 18 January 2010 Keywords: Avalanche Snow Asphyxia Hypothermia Airway Temperature Potassium Resuscitation Rescue
a b s t r a c t Objective: Avalanche resuscitation will save lives if focussed on victims that have the potential to survive. The purpose of this systematic review was to examine 4 critical prognostic factors for burial victims in cardiac arrest. Methods: Time of burial, airway patency, core temperature and serum potassium level were analyzed as PICO (Patient/population, Intervention, Comparator, Outcome) questions within the 2010 Consensus on Science process of the International Liaison Committee on Resuscitation. The electronic databases of Medline via PubMed, EMBASE via OVID and the Cochrane Database of Systematic Reviews were searched using combinations of the search terms “avalanche”, “air pocket”, “hypothermia” and “serum potassium”. Results: Of 1910 publications that were identified 30 were found relevant. The predictive value for survival of a short time of burial or a patent airway after 35 min of burial is supported by 10 retrospective case–control studies, 4 case series and 2 experimental studies, while no studies are neutral or opposed. A core temperature of less than 32 ◦ C with a patent airway is supported by 2 retrospective case–control studies and 3 case series, while 10 studies are neutral. Serum potassium level is supported by 6 retrospective case–control studies and 3 case reports, while 3 retrospective case–control studies and 1 animal model are neutral. Conclusion: After 35 min of burial, or where the core temperature is less than 32 ◦ C, a patent airway is associated with survival to hospital discharge. A serum potassium of less than 7 mmol/L may be a valuable indicator for survival when other indicators are unclear. These findings should modify the current avalanche resuscitation scheme. © 2010 Elsevier Ireland Ltd. All rights reserved.
Contents 1. 2.
3.
4.
Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.1. Prognostic factors as PICO questions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.2. Search strategy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.3. Evidence appraisal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.1. Time of burial and airway patency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.2. Core temperature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.3. Serum potassium . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.1. Interpretation of evidencea and recommendations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
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夽 “A Spanish translated version of the abstract of this article appears as Appendix in the final online version at doi:10.1016/j.resuscitation.2010.01.037”. ∗ Corresponding author at: Department of Emergency Medicine, Mineral Springs Hospital, Banff, AB, Canada. Tel.: +1 403 762 4974; fax: +1 403 762 4193. E-mail address: [email protected] (J. Boyd). a Our interpretation of the evidence incorporates the findings of the Consensus on Science developed by the Advanced Life Support Task Force during a web conference on January 5th, 2009. 0300-9572/$ – see front matter © 2010 Elsevier Ireland Ltd. All rights reserved. doi:10.1016/j.resuscitation.2010.01.037
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5.
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4.1.1. Time of burial and airway patency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.1.2. Core temperature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.1.3. Serum potassium . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.2. The ICAR MedCom avalanche resuscitation algorithm. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.3. Limitations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.4. Future research . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Authors conclusions and recommendations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Disclaimer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Conflict of interest . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Source of support . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Acknowledgement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
650 650 651 651 651 651 651 651 651 651 651 651
1. Background
2.1. Prognostic factors as PICO questions
Avalanches kill healthy people, most commonly in their twenties.1,2 Asphyxia causes most deaths3–5 although trauma is also a common cause of death.2 Mortality is 70% when there is complete burial and rescue depends on organized teams.6 Victims who are in cardiac arrest are often under- or over-resuscitated. The authors of a study examining potential prognostic factors observed that resuscitation was “grossly insufficient” for some victims.7 Another report describes a case in which standard Basic Life Support (BLS) was withheld from a young burial victim during transport, yet cardiopulmonary bypass after 150 min of cardiac arrest resulted in discharge from hospital without neurological impairment.8 Conversely, exhaustive resuscitation of victims of prolonged asphyxia leads to generally poor outcomes.7,9–11 As the median number of victims per incident is four12 and the environment is resource-poor,11 an evidence-based management tool is critical for on-scene triage. These factors prompted the Medical Commission of the International Commission for Alpine Rescue (ICAR MedCom) to develop an avalanche resuscitation algorithm (Fig. 1), which they based on a narrative review of 49 publications and consensus among the mountain rescue physicians.13 The algorithm is designed for buried victims and incorporates 4 critical prognostic factors—time of burial, air pocket with patent airway, core temperature and serum potassium level. Application of this algorithm has been reported to prompt appropriate resuscitation8 and to prevent futile resuscitation efforts in victims with no likelihood of recovery.14,15 The aim of our study is to perform a systematic review of the literature in order to examine the scientific basis of prognostic factors in the avalanche resuscitation algorithm and to identify improvements.
2.1.1. “For avalanche victims in cardiac arrest (P), does a shorter time of burial (I), compared to longer time of burial (C), predict survival to hospital discharge (O)?” 2.1.2. “For avalanche victims in cardiac arrest who have been buried longer than 35 min (P), does the presence of a patent airway (I), compared to absence of a patent airway (C), predict survival to hospital discharge (O)?” 2.1.3. “For avalanche victims in cardiac arrest who are found with a core temperature of less than 32 ◦ C (P), does the presence of a patent airway (I), compared to absence of a patent airway (C), predict survival to hospital discharge (O)?” 2.1.4. “For avalanche victims in cardiac arrest (P), do lower levels of serum potassium (I), compared to higher levels of serum potassium (C), predict survival to hospital discharge (O)?”
2. Methods Time of burial, airway patency,b core temperature and serum potassium were examined as Population Intervention Comparator Outcome (PICO) questions within the 2010 Consensus on Science evidence evaluation process of the International Liaison Committee on Resuscitation (ILCOR).16 Search strategy and evidence appraisal were subjected to critical evaluation by the ILCOR reviewing expert, and draft Consensus on Science and Treatment Recommendations were reviewed by the Advanced Life Support (ALS) Task Force.
b A patent airway is defined as an airway not obstructed by avalanche debris or other means. The “air pocket” has been defined as “any space surrounding the mouth and nose, no matter how small, with a patent airway”.11 A patent airway is therefore the necessary component of the definition of the “air pocket”. Air spaces “can easily be overlooked”.11 “Patent airway” is therefore used as the prognostic factor throughout this review in place of “air pocket” because “patent airway” is more reliably identified by a rescuer.
2.2. Search strategy The electronic database of Medline was searched via PubMed with the search terms (avalanche [All Fields]), (((hypothermia)) AND ((air pocket))) and (((“Hypothermia”[Mesh])) AND ((potassium)) AND survival) and the database of EMBASE via OVID with (avalanche {Including Related Terms}) and (hypothermia {Including Related Terms}). The Cochrane Database of Systematic Reviews was searched with the terms (avalanche in Title, Abstract or Keywords) and (hypothermia in Title, Abstract or Keywords). Additional hand searching of review articles, reference texts, reference lists and conference proceedings for relevant studies was performed. All articles describing studies on the 4 prognostic factors in relation to snow avalanches and hypothermia that were published in peer-reviewed journals were considered eligible for further review. 2.3. Evidence appraisal As airway patency does not become significant until after extended burial the prognostic factors of time of burial and airway patency were reviewed in combination. Core temperature and serum potassium were reviewed separately giving 3 review streams. Eligible studies were reviewed in detail and classified by level of evidence (LOE) (Table 1) and methodological quality as defined by ILCOR.16,17 The evidence was further categorized as supportive, neutral or opposed to the relevant question(s). 3. Results Our search identified 1910 articles. After excluding duplicate listings and studies not dealing with snow avalanches, we identified 149 articles that appeared pertinent and we subjected these
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Fig. 1. Avalanche resuscitation algorithm.13 Pre-hospital management of persons buried in an avalanche. *In all cases: core temperature + ECG monitoring, gentle extrication, oxygen, airway warming, insulation, hot packs on trunk; 0.9% NaCl and/or 5% glucose only if an intravenous line can be established within a few minutes; trauma treatment if indicated. **Transport to the nearest hospital for serum potassium measurement if hospitalisation in a specialist unit with cardiopulmonary bypass facilities is not logistically possible. If K+ exceeds 12 mmol/L, stop resuscitation and pronounce death by asphyxiation; if K+ is lower than, or equals, 12 mmol/L, continue cardiopulmonary resuscitation and transport the patient as soon as possible to a specialist hospital for extracorporeal rewarming. ACLS—advanced cardiac life support, CPR—cardiopulmonary resuscitation. Staging of hypothermia according to Swiss Society of Mountain Medicine guidelines. Source: Reprinted from Resuscitation, 2001;51:7–15, Brugger H, Durrer B, Adler-Kastner L, Falk M, Tschirky F. Field management of avalanche victims, with permission from Elsevier.
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Table 1 ILCORa levels of evidence for prognostic studies16,17 . LOE P1 LOE P2 LOE P3 LOE P4 LOE P5 a
Inception (prospective) cohort studies (or meta-analyses of inception cohort studies), or validation studies of a clinical decision rule (CDR) Follow-up of untreated control groups in randomized controlled trials (or meta-analyses of follow-up studies), or derivation studies of a CDR, or validation studies of a CDR using a split-sample Retrospective cohort studies Case series Studies not directly related to the specific patient/population (e.g. different patient/population, animal and mechanical models)
International Liaison Committee on Resuscitation.
Table 2 Summary of levels of evidence, quality of studies and outcome measuresa supporting time of burial and airway patency predicting survivalb . Level of evidence
LOE P1
Quality of study Good
Fair
a b c
LOE P2
LOE P3
LOE P4
LOE P5
Brugger and Falk18 BCc Brugger et al.13 BCc Burtscher21 BC Buser22 et al. BCc Falk et al.23 BCc Hohlrieder et al.12 BE Locher et al.9,24 AC Mair et al.7 ADc
Kornberger and Mair19 BC
Brugger et al.20 E
Grosse et al.25 BCD Stalsberg et al.27 BCD
Oberhammer et al.8 CD Radwin and Grissom28 BCD Sumann15 E
Grissom et al.26 E
Outcome measures: A = return of spontaneous circulation; B = survival of event; C = survival to hospital discharge; D = intact neurological survival; E = other end point. No studies were neutral or opposed to time of burial and airway patency predicting survival. Overlapping patients.
to abstract review. We then discarded 119 articles as not relevant, leaving 30 articles for full review.
3.1. Time of burial and airway patency Ten LOE P3 retrospective case–control studies, four LOE P4 case series and two LOE P5 studies of simulated air pockets in human volunteers are supportive of the hypotheses that a shorter time of burial and the presence of a patent airway after 35 min of burial predict survival, while no studies are neutral or opposed (Table 2). Four of these studies described survival to hospital discharge in victims buried for longer than 60 min when found with a patent airway.8,25,27,28 In four studies that examined the pattern of survival over time of burial, there was no survivor when burial was longer than 35 min and the victim had an obstructed airway (Table 3). Nor was survival with an obstructed airway described in any of the remaining studies. In a retrospective observational study, Falk et al.23 established a non-linear relationship between time of burial and survival. The relationship, labelled the “survival curve”, demonstrated a rate of survival over 90% in the first 15 min of burial but that plummeted to 30% over the next 20 min (Fig. 2). The authors concluded that asphyxia is the cause of this steep decline. They went on to hypothesize that survival beyond 35 min would be possible only with continued breathing via a patent airway. This small survivor group would then remain alive through a plateau phase of the survival curve but would eventually succumb to lethal hypothermia after approximately 90 min of burial, despite a patent airway. A prospective randomized crossover study found that, when breathing from a simulated air pocket, subjects achieved a steady state of hypoxia for at least 20 min in 11 of 28 (39%) uninterrupted tests, at a level adequate to support life.20 The authors concluded that prolonged survival after snow burial is possible in the presence of an air pocket of even small dimensions.
3.2. Core temperature Two LOE P3 retrospective case–control studies and three LOE P4 case series support the hypothesis that victims in cardiac arrest with a core temperature of less than 32 ◦ C may survive if they have a patent airway. Ten studies are neutral (Table 4). The Multicentre Hypothermia Survey29 examined 401 cases of hypothermia from various causes and found that 15 of 41 (37%) who had CPR survived while 5 of 16 (31%) who had extracorporeal rewarming survived. In a study of 234 severely hypothermic victims Walpoth et al.30 described 15 survivors out of 36 (42%) cardiac arrest victims who were rewarmed with cardiopulmonary bypass. Core temperatures in patients with cardiac arrest were all below 28 ◦ C. One avalanche burial victim with the core temperature of 19.6 ◦ C made a full recovery. The authors ascribed good outcomes to the protective effect of deep hypothermia, good rescue organization and young healthy victims. In a study of 32 hypothermic avalanche victims, 19 of whom were in cardiac arrest, Locher and Walpoth24 found the maximum cooling rate under the snow was 8 ◦ C/h. Subsequent cooling between the accident site and the hospital averaged 3 (range 0.75–5.8) ◦ C/h. In a case report8 of a hypothermic avalanche victim buried at 3 m depth for 100 min, the victim was unconscious but spontaneously breathing on extrication. His core temperature was 22 ◦ C for a cooling rate of 9 ◦ C/h. The victim then experienced cardiac arrest which was untreated during pre-hospital helicopter evacuation. The attending physician at the receiving hospital found the serum potassium to be 4.3 mmol/L, initiated CPR and re-directed the patient to a trauma centre for cardiopulmonary bypass, resulting in complete recovery despite 150 min of cardiac arrest. Return of spontaneous circulation (ROSC) and survival to hospital discharge of hypothermic avalanche victims rewarmed with extracorporeal circulation, either cardiopulmonary bypass or extracorporeal membrane oxygenation (ECMO), has been described in 6 other studies (Table 5).
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Table 3 Studies of survival patterns compared to time of burial and airway patency. Series 18 , b
Brugger and Falk Buser et al.22 , c Falk et al.23 , b Brugger et al.13 , b a b c
Total number
Survivors n (%)
Pattern survival curvea
Time of 30% survival (min)
Survival after 35 min with obstructed airway
332 332 442 638
150 (45) 150 (45) 181 (43) 334 (48)
Yes Yes Yes Yes
40 40 35 40
No No No No
Demonstrated a similar non-linear survival curve pattern to the key study of Falk et al.23 with a steep drop in survival to a plateau at 30% survival. Incremental overlapping populations. Same population as above but analyzed independently by different investigators.
Table 4 Summary of levels of evidence, quality of studies and outcome measuresa that are supportive or neutral to the hypothesis that victims in cardiac arrest with a core temperature of less than 32 ◦ C may survive if they have a patent airway. Level of evidence
LOE P1
LOE P2
Studies supportive of prognostic factor Good
LOE P3
LOE P4
Danzl et al.29 ABC Locher and Walpoth24 ACb
Walpoth et al.30 CDb Althaus et al.31 CD Oberhammer et al.8 CD
Fair
Studies neutral to prognostic factor Good
Brugger et al.13 BCc Brugger and Falk18 BCc Locher et al.9 ACb Mair et al.7 AD Farstad et al.33 CD Ruttman et al.14 ACD Stalsberg et al.27 BCD
Fair
a b c
LOE P5
Grissom et al.32 E
Kornberger and Mair19 BC
Grissom et al.34 E
Outcome measures: A = return of spontaneous circulation; B = survival of event; C = survival to hospital discharge; D = intact neurological survival; E = other end point. Overlapping patients. Overlapping patients.
3.3. Serum potassium Six LOE P3 retrospective case–control studies and three LOE P4 case reports support the hypothesis that serum potassium levels predict survival in avalanche victims in cardiac arrest, and three LOE P3 retrospective case–control studies and one LOE P5 animal model are neutral (Table 6). In a retrospective case–control study of 32 hypothermic avalanche victims Locher and Walpoth24 found the serum potassium at hospital admission to be 4.25 ± 0.9 (range 3.1–6.4) mmol/L in survivors compared to 9.95 ± 4.9 (range 2.0–18) mmol/L in non-survivors (P = 0.003). The authors identified asphyxia as the cause of hyperkalaemia and cardiac arrest in the non-survivors. A retrospective case–control study by Mair et al.7 examined for prognostic markers in patients with severe hypothermia and cardiac arrest who were rewarmed with cardiopulmonary bypass (12 of the 22 victims were from avalanche accidents). Patients who had
ROSC had a median serum potassium of 5 (range 3.4–8) mmol/L while those without ROSC had a median serum potassium of 8.7 (range 3.4-over 20) mmol/L. Autopsy in 8 of the avalanche victims without ROSC, who had admission serum potassium levels rang-
Table 5 Hypothermic avalanche victims in cardiac arrest treated with extracorporeal circulation rewarminga . Series
Return of spontaneous circulationb
Survival to hospital discharge
Althaus et al.31 Locher and Walpoth24 Mair et al.7 Oberhammer et al.8 Ruttman et al.14 Schaller et al.10 Walpoth et al.30
1 5 4 1 10 1 1
1 2 1 1 1 1 1
Total
23
a b
8 ◦
Core temperatures were all lower than 32 C. Includes victims that survived to discharge.
Fig. 2. Survival probability for completely-buried avalanche victims.13 Survival probability for completely-buried avalanche victims in Switzerland 1981–1998 (n = 735) in relation to time (min) buried under the snow, contrasting victims buried in open areas (black curve, n = 638) with those buried in buildings or on roads (grey curve, n = 97). Median extrication times were 37 min (open areas) and 56 min (buildings, roads) (P = 0.17, Mann–Whitney U-test). In open areas only 16.6% of all survivors are extricated after the cut-off point of 35 min, as compared with 32.7% in buildings and on roads (P = 0.008; Pearson’s chi-square). The respective findings for the cut-off point of 130 min are 1.7% (open areas) and 16.3% (buildings, roads) (P = 0.001; Pearson’s chi-square). The dotted curve represents the survival function for completely-buried avalanche victims in open areas (n = 422) based on the Swiss data for 1981–1991, calculated by Falk et al.23 Source: Reprinted from Resuscitation, 2001;51:7–15, Brugger H, Durrer B, Adler-Kastner L, Falk M, Tschirky F. Field management of avalanche victims, with permission from Elsevier.
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Table 6 Summary of levels of evidence, quality of studies and outcome measuresa that are supportive or neutral to the hypothesis that for victims in cardiac arrest the serum potassium predicts survival to discharge. Level of evidence
LOE P1
LOE P2
Studies supportive of prognostic factor Good
LOE P3
LOE P4
Danzl et al.29 ABC Hauty et al.35 C Locher et al.9 ACb Locher and Walpoth24 ACb Mair et al.7 AD Schaller et al.10 AC Dobson et al.36 CD Oberhammer et al.8 CD von Segesser et al.37 CD
Fair
Studies neutral to prognostic factor Good
LOE P5
Farstad et al.33 CD Ruttman et al.14 ACD Silvfast and Pettila39 AC
Bender et al.38 E
a Outcome measures: A = return of spontaneous circulation; B = survival of event; C = survival to hospital discharge; D = intact neurological survival; E = other end point; Italics = animal study. b Overlapping patients.
ing from 5.9 to over 20 mmol/L, established the cause of death was asphyxia in 6 and trauma in 2. One long-term avalanche survivor with the serum potassium on admission of 3.8 mmol/L was in cardiac arrest for 210 min with a core temperature of 24 ◦ C. The authors concluded that, although “a decision to continue or terminate resuscitation in a hypothermic arrest victim cannot be made based on laboratory parameters”, “they can be used to confirm or question the decision to terminate resuscitation based on clinical judgment”. A retrospective case–control study of 24 hypothermic victims by Schaller et al.10 found a median serum potassium of 3.5 (range 2.7–5.3) mmol/L in survivors (not avalanche victims) compared to 14.5 (6.8–24.5) mmol/L in non-survivors (all avalanche victims). They then described an avalanche victim in cardiac arrest for 205 min after burial for 60 min at a depth of 2 m. The victim’s serum potassium was 4.5 mmol/L and they survived to hospital discharge after rewarming with cardiopulmonary bypass. The authors concluded that the normal serum potassium “might be used to select those patients in whom heroic resuscitation efforts can be useful”. The highest admission serum potassium in an avalanche victim in cardiac arrest who survived to hospital discharge was 6.4 mmol/L24 while in all-cause hypothermia it was 11.8 mmol/L, in a child exposed to freezing weather.36 4. Discussion It is critical that we find prognostic indicators that will reliably identify avalanche victims who have the potential to survive, so that we may effectively focus resuscitation resources. This review finds evidence that time of burial, airway patency, body temperature and serum potassium can provide valuable prognostic input to determine who may benefit from aggressive resuscitation and advanced rewarming. 4.1. Interpretation of evidencec and recommendations 4.1.1. Time of burial and airway patency Cardiac arrest from avalanche involvement is more commonly due to asphyxia than hypothermia11 but may also occur due to trauma2 or as a combination of these 3 factors. Asphyxia in a buried
c Our interpretation of the evidence incorporates the findings of the Consensus on Science developed by the Advanced Life Support Task Force during a web conference on January 5th, 2009.
victim results from airway obstruction by avalanche debris or vomitus, airway malalignment, mechanical compression of the chest27 or hypoxia with hypercapnia due to poor gas diffusion through avalanche debris.20,26,32,34 Mortality after the first 15 min of burial is approximately 10%, then increases until it is 70% at 35 min of burial as demonstrated by the “survival curve” (Fig. 2) (Table 3). All avalanche victims found in cardiac arrest within this first 35 min should be actively resuscitated following BLS and ALS guidelines unless they have suffered lethal trauma or when other factors such as concern for rescuer safety prevail. After 35 min of burial the only survivors are those with a patent airway and the ability to continue breathing.7,8,13,18,19,22,23,25,27,28 The presence of an air pocket may be difficult to confirm as it is often destroyed during rescue. The 30% of victims that have survived beyond the first 35 min of burial often remain alive while becoming progressively more hypothermic until the onset of lethal hypothermia after approximately 90 min of burial (Fig. 2) (Table 3). Therefore, all victims buried longer than 35 min that exhibit a patent or unknown airway should be actively resuscitated while resuscitation may be terminated in victims who have been buried for more than 35 min and are found in asystolic cardiac arrest with an obstructed airway. 4.1.2. Core temperature When time of burial is not known precisely, core temperature may serve as a reasonable proxy. Considering that the maximum rate of cooling while buried has been observed to be 9 ◦ C/h,8,24 it follows that a victim with a core temperature of less than 32 ◦ C would have been buried longer than 35 min. If this victim with a core temperature of less than 32 ◦ C is to have any possibility of survival, the victim must exhibit a patent airway. However, if the core temperature is above 32 ◦ C, the duration of burial may be either more or less than 35 min. Therefore, a victim with an unknown time of burial that is found with a core temperature greater than 32 ◦ C should be actively resuscitated regardless of airway patency. Avalanche victims in cardiac arrest with a core temperature of less than 32 ◦ C, have achieved ROSC and survival to hospital discharge with extracorporeal rewarming using cardiopulmonary bypass or ECMO where asphyxia has not predominated.7,8,10,14,19,24,30,31 Therefore, victims in cardiac arrest with a core temperature less than 32 ◦ C with a patent or unknown airway should be actively resuscitated and transported for extracorporeal rewarming when practical. Resuscitation may be terminated when a victim with a core temperature of less than 32 ◦ C is found in asystolic cardiac arrest with an obstructed airway.
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4.1.3. Serum potassium In some hypothermic avalanche victims the serum potassium may assist when details of other prognostic factors are unknown or a decision needs to be made for prolonged resuscitation or evacuation to a major centre for extracorporeal rewarming. The highest admission serum potassium in an avalanche victim in cardiac arrest who survived to hospital discharge was 6.4 mmol/L.24 There is, however, a single case report of survival in a hypothermic child with an initial potassium of 11.8 mmol/L.36 Therefore, a victim in cardiac arrest with a core temperature of less than 32 ◦ C with a patent or unknown airway and a serum potassium of less than 7 mmol/L should be actively resuscitated and transported for extracorporeal rewarming. A serum potassium of greater than 7 mmol/L in an adult avalanche victim in asystolic cardiac arrest may, in combination with other factors, assist in the decision to terminate resuscitation. Resuscitation should be terminated when initial serum potassium is greater than 12 mmol/L. 4.2. The ICAR MedCom avalanche resuscitation algorithm Our analysis of prognostic elements confirms the soundness of the ICAR MedCom avalanche resuscitation algorithm. However, because an “air pocket” may be so small as to be overlooked, and because a patent airway is the necessary condition for an air pocket, we recommend substituting “patent airway” for “air pocket” in the algorithm. Standard trauma precautions such as spinal immobilization should be emphasized. Treatment interventions such as defibrillation and hypothermia management need to be modified to comply with the 2010 BLS and ALS guidelines. 4.3. Limitations All the studies on avalanche victims are retrospective observational in nature. Many have extracted information from avalanche databases that are subject to reporting deficiencies and may not have consistently identified prognostic factors such as an air pocket or patent airway. Some studies may have followed the avalanche resuscitation algorithm after its publication and therefore been biased. However, 13 of the avalanche studies considered in this systematic review contained data collected prior to the publication of the algorithm.7,9,10,13,18,19,21–24,27,30,31,37 This systematic review is confined to full text peer-reviewed publications in internationally indexed journals, consistent with ILCOR standards, and may have missed pertinent publications in the other literature. However, the algorithm has been published in its current form on 5 occasions in peer-reviewed journals with no subsequent negative comment.8,13,40–42
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temperature of less than 32 ◦ C contributes dependable prognostic input to an avalanche resuscitation scheme. A serum potassium less than 7 mmol/L is associated with survival to hospital discharge and may be a valuable tool when other indicators are unclear or evacuation to extracorporeal rewarming is contemplated. Extracorporeal rewarming techniques are recommended for victims with a core temperature of less than 32 ◦ C when prognostic indicators are consistent with survival and where these modalities are available. Disclaimer This review includes information on resuscitation questions developed through the C2010 Consensus on Science and Treatment Recommendations process, managed by the International Liaison Committee on Resuscitation (http://www. americanheart.org/ILCOR). The questions were developed by ILCOR Task Forces, using strict conflict of interest guidelines. In general, each question was assigned to two experts to complete a detailed structured review of the literature, and complete a detailed worksheet. Worksheets are discussed at ILCOR meetings to reach consensus and will be published in 2010 as the Consensus on Science and Treatment Recommendations (CoSTR). The conclusions published in the final CoSTR consensus document may differ from the conclusions of in this review because the CoSTR consensus will reflect input from other worksheet authors and discussants at the conference, and will take into consideration implementation and feasibility issues as well as new relevant research. Conflict of interest None of the authors has a commercial or industrial conflict of interest. HB has published studies on avalanche resuscitation examining time of burial and airway patency. Neither JB or MS have published on prognostic factors. Source of support Hermann Brugger receives support as the head of the EURAC Institute of Mountain Emergency Medicine. Neither JB or MS receive funding for avalanche research. Acknowledgement We thank Shelley Mardiros for manuscript review. References
4.4. Future research Databases should be prospectively designed to obtain data on prognostic factors such as airway patency, core temperature and serum potassium. Core temperatures should be documented upon extrication to allow the calculation of accurate cooling rates for avalanche burial. Outcome data should include measures of neurological function. Further research on the pathophysiology of avalanche burial, including air pocket physiology, should be done. Prospective validation studies on the algorithm should compare outcomes between resuscitation complying with the algorithm and not. 5. Authors conclusions and recommendations Our review has found evidence that, for victims in cardiac arrest, the patency of the airway after 35 min of burial or with a core
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8. Oberhammer R, Beikircher W, Hormann C, et al. Full recovery of an avalanche victim with profound hypothermia and prolonged cardiac arrest treated by extracorporeal re-warming. Resuscitation 2008;76:474–80. 9. Locher T, Walpoth B, Pfluger D, Althaus U. Accidental hypothermia in Switzerland (1980–1987)—case reports and prognostic factors. Schweiz Med Wochenschr 1991;121:1020–8. 10. Schaller MD, Fischer AP, Perret CH. Hyperkalemia. A prognostic factor during acute severe hypothermia. JAMA 1990;264:1842–5. 11. Brugger H, Durrer B, Adler-Kastner L. On-site triage of avalanche victims with asystole by the emergency doctor. Resuscitation 1996;31:11–6. 12. Hohlrieder M, Mair P, Wuertl W, Brugger H. The impact of avalanche transceivers on mortality from avalanche accidents. High Alt Med Biol 2005;6:72–7. 13. Brugger H, Durrer B, Adler-Kastner L, Falk M, Tschirky F. Field management of avalanche victims. Resuscitation 2001;51:7–15. 14. Ruttmann E, Weissenbacher A, Ulmer H, et al. Prolonged extracorporeal membrane oxygenation-assisted support provides improved survival in hypothermic patients with cardiocirculatory arrest. J Thorac Cardiovasc Surg 2007;134:594–600. 15. Sumann G. Pre-hospital triage and therapy of avalanche victims. Intensivmedizin 2002;39:315–20. 16. Morley PT. Evidence evaluation worksheets: the systematic reviews for the evidence evaluation process for the 2010 International Consensus on Resuscitation Science. Resuscitation 2009;80:719–21. 17. International Liaison Committee on Resuscitation. Defining Quality of Evidence.doc. Accessed 26 October 2009, at http://www.mc.manuscriptcentral. com:80/societyimages/ilcor/Defining%20Quality%20of%20Evidence.doc. 18. Brugger H, Falk M. New perspectives of avalanche disasters. Phase classification using pathophysiologic considerations. Wien Klin Wochenschr 1992;104:167–73. 19. Kornberger E, Mair P. Important aspects in the treatment of severe accidental hypothermia: the Innsbruck experience. J Neurosurg Anesthesiol 1996;8:83–7. 20. Brugger H, Sumann G, Meister R, et al. Hypoxia and hypercapnia during respiration into an artificial air pocket in snow: implications for avalanche survival. Resuscitation 2003;58:81–8. 21. Burtscher M. Avalanche survival chances. Nature 1994;371:482. 22. Buser O, Etter HJ, Jaccard C. Probability of dying in an avalanche. Z Unfallchir Versicherungsmed 1993;(Suppl. 1):263–71. 23. Falk M, Brugger H, Adler-Kastner L. Avalanche survival chances. Nature 1994;368:21. 24. Locher T, Walpoth BH. Differential diagnosis of circulatory failure in hypothermic avalanche victims: retrospective analysis of 32 avalanche accidents. Schweiz Rundsch Med Prax 1996;85:1275–82. 25. Grosse AB, Grosse CA, Steinbach LS, Zimmermann H, Anderson S. Imaging findings of avalanche victims. Skeletal Radiol 2007;36:515–21.
26. Grissom CK, Radwin MI, Harmston CH, Hirshberg EL, Crowley TJ. Respiration during snow burial using an artificial air pocket. JAMA 2000;283:2266–71. 27. Stalsberg H, Albretsen C, Gilbert M, et al. Mechanism of death in avalanche victims. Virchows Arch A Pathol Anat Histopathol 1989;414:415–22. 28. Radwin MI, Grissom CK. Technological advances in avalanche survival. Wilderness Environ Med 2002;13:143–52. 29. Danzl DF, Robert SP, Paul SA, et al. Multicenter hypothermia survey. Ann Emerg Med 1987;16:1042–55. 30. Walpoth BH, Walpoth-Aslan BN, Mattle HP, et al. Outcome of survivors of accidental deep hypothermia and circulatory arrest treated with extracorporeal blood warming. N Engl J Med 1997;337:1500–5. 31. Althaus U, Aeberhard P, Schupbach P, Nachbur BH, Muhlemann W. Management of profound accidental hypothermia with cardiorespiratory arrest. Ann Surg 1982;195:492–5. 32. Grissom CK, McAlpine JC, Harmston CH, et al. Hypercapnia effect on core cooling and shivering threshold during snow burial. Aviat Space Environ Med 2008;79:735–42. 33. Farstad M, Andersen KS, Koller ME, Grong K, Segadal L, Husby P. Rewarming from accidental hypothermia by extracorporeal circulation. A retrospective study. Eur J Cardiothorac Surg 2001;20:58–64. 34. Grissom CK, Radwin MI, Scholand MB, Harmston CH, Muetterties MC, Bywater TJ. Hypercapnia increases core temperature cooling rate during snow burial. J Appl Physiol 2004;96:1365–70. 35. Hauty MG, Esrig BC, Hill JG, Long WB. Prognostic factors in severe accidental hypothermia: experience from the Mt. Hood tragedy. J Trauma 1987;27:1107–12. 36. Dobson JA, Burgess JJ. Resuscitation of Severe Hypothermia by Extracorporeal Rewarming in a Child. Journal of Trauma: Inj Infect Crit Care 1996;40: 483–5. 37. von Segesser LK, Garcia E, Turina M. Perfusion without systemic heparinization for rewarming in accidental hypothermia. Ann Thorac Surg 1991;52:560–1. 38. Bender PR, Debehnke DJ, Swart GL, Hall KN. Serum potassium concentration as a predictor of resuscitation outcome in hypothermic cardiac arrest. Wilderness Environ Med 1995;6:273–82. 39. Silfvast T, Pettila V. Outcome from severe accidental hypothermia in Southern Finland—a 10-year review. Resuscitation 2003;59:285–90. 40. Brugger H, Durrer B. On-site treatment of avalanche victims ICAR-MEDCOMrecommendation. High Alt Med Biol 2002;3:421–5. 41. Paal P, Beikircher W, Brugger H. Avalanche emergencies: review of the current situation. Anaesthesist 2006;55:314–24. 42. Strohm PC, Kostler W, Hammer T, Sudkamp NP. Avalanche emergency and accidental hypothermia. Unfallchirurg 2003;106:343–7.
Contents lists available at ScienceDirect
Resuscitation journal homepage: www.elsevier.com/locate/resuscitation
Review
Prognostic factors in avalanche resuscitation: A systematic review夽 Jeff Boyd a,b,∗ , Hermann Brugger c,d , Michael Shuster a a
Department of Emergency Medicine, Mineral Springs Hospital, Banff, AB, Canada International Federation of Mountain Guides, Banff, Alberta, Canada EURAC Institute of Mountain Emergency Medicine, Bozen/Bolzano, Italy d Innsbruck Medical University, Innsbruck, Austria b c
a r t i c l e
i n f o
Article history: Received 30 November 2009 Received in revised form 12 January 2010 Accepted 18 January 2010 Keywords: Avalanche Snow Asphyxia Hypothermia Airway Temperature Potassium Resuscitation Rescue
a b s t r a c t Objective: Avalanche resuscitation will save lives if focussed on victims that have the potential to survive. The purpose of this systematic review was to examine 4 critical prognostic factors for burial victims in cardiac arrest. Methods: Time of burial, airway patency, core temperature and serum potassium level were analyzed as PICO (Patient/population, Intervention, Comparator, Outcome) questions within the 2010 Consensus on Science process of the International Liaison Committee on Resuscitation. The electronic databases of Medline via PubMed, EMBASE via OVID and the Cochrane Database of Systematic Reviews were searched using combinations of the search terms “avalanche”, “air pocket”, “hypothermia” and “serum potassium”. Results: Of 1910 publications that were identified 30 were found relevant. The predictive value for survival of a short time of burial or a patent airway after 35 min of burial is supported by 10 retrospective case–control studies, 4 case series and 2 experimental studies, while no studies are neutral or opposed. A core temperature of less than 32 ◦ C with a patent airway is supported by 2 retrospective case–control studies and 3 case series, while 10 studies are neutral. Serum potassium level is supported by 6 retrospective case–control studies and 3 case reports, while 3 retrospective case–control studies and 1 animal model are neutral. Conclusion: After 35 min of burial, or where the core temperature is less than 32 ◦ C, a patent airway is associated with survival to hospital discharge. A serum potassium of less than 7 mmol/L may be a valuable indicator for survival when other indicators are unclear. These findings should modify the current avalanche resuscitation scheme. © 2010 Elsevier Ireland Ltd. All rights reserved.
Contents 1. 2.
3.
4.
Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.1. Prognostic factors as PICO questions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.2. Search strategy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.3. Evidence appraisal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.1. Time of burial and airway patency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.2. Core temperature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.3. Serum potassium . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.1. Interpretation of evidencea and recommendations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
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夽 “A Spanish translated version of the abstract of this article appears as Appendix in the final online version at doi:10.1016/j.resuscitation.2010.01.037”. ∗ Corresponding author at: Department of Emergency Medicine, Mineral Springs Hospital, Banff, AB, Canada. Tel.: +1 403 762 4974; fax: +1 403 762 4193. E-mail address: [email protected] (J. Boyd). a Our interpretation of the evidence incorporates the findings of the Consensus on Science developed by the Advanced Life Support Task Force during a web conference on January 5th, 2009. 0300-9572/$ – see front matter © 2010 Elsevier Ireland Ltd. All rights reserved. doi:10.1016/j.resuscitation.2010.01.037
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4.1.1. Time of burial and airway patency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.1.2. Core temperature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.1.3. Serum potassium . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.2. The ICAR MedCom avalanche resuscitation algorithm. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.3. Limitations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.4. Future research . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Authors conclusions and recommendations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Disclaimer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Conflict of interest . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Source of support . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Acknowledgement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
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1. Background
2.1. Prognostic factors as PICO questions
Avalanches kill healthy people, most commonly in their twenties.1,2 Asphyxia causes most deaths3–5 although trauma is also a common cause of death.2 Mortality is 70% when there is complete burial and rescue depends on organized teams.6 Victims who are in cardiac arrest are often under- or over-resuscitated. The authors of a study examining potential prognostic factors observed that resuscitation was “grossly insufficient” for some victims.7 Another report describes a case in which standard Basic Life Support (BLS) was withheld from a young burial victim during transport, yet cardiopulmonary bypass after 150 min of cardiac arrest resulted in discharge from hospital without neurological impairment.8 Conversely, exhaustive resuscitation of victims of prolonged asphyxia leads to generally poor outcomes.7,9–11 As the median number of victims per incident is four12 and the environment is resource-poor,11 an evidence-based management tool is critical for on-scene triage. These factors prompted the Medical Commission of the International Commission for Alpine Rescue (ICAR MedCom) to develop an avalanche resuscitation algorithm (Fig. 1), which they based on a narrative review of 49 publications and consensus among the mountain rescue physicians.13 The algorithm is designed for buried victims and incorporates 4 critical prognostic factors—time of burial, air pocket with patent airway, core temperature and serum potassium level. Application of this algorithm has been reported to prompt appropriate resuscitation8 and to prevent futile resuscitation efforts in victims with no likelihood of recovery.14,15 The aim of our study is to perform a systematic review of the literature in order to examine the scientific basis of prognostic factors in the avalanche resuscitation algorithm and to identify improvements.
2.1.1. “For avalanche victims in cardiac arrest (P), does a shorter time of burial (I), compared to longer time of burial (C), predict survival to hospital discharge (O)?” 2.1.2. “For avalanche victims in cardiac arrest who have been buried longer than 35 min (P), does the presence of a patent airway (I), compared to absence of a patent airway (C), predict survival to hospital discharge (O)?” 2.1.3. “For avalanche victims in cardiac arrest who are found with a core temperature of less than 32 ◦ C (P), does the presence of a patent airway (I), compared to absence of a patent airway (C), predict survival to hospital discharge (O)?” 2.1.4. “For avalanche victims in cardiac arrest (P), do lower levels of serum potassium (I), compared to higher levels of serum potassium (C), predict survival to hospital discharge (O)?”
2. Methods Time of burial, airway patency,b core temperature and serum potassium were examined as Population Intervention Comparator Outcome (PICO) questions within the 2010 Consensus on Science evidence evaluation process of the International Liaison Committee on Resuscitation (ILCOR).16 Search strategy and evidence appraisal were subjected to critical evaluation by the ILCOR reviewing expert, and draft Consensus on Science and Treatment Recommendations were reviewed by the Advanced Life Support (ALS) Task Force.
b A patent airway is defined as an airway not obstructed by avalanche debris or other means. The “air pocket” has been defined as “any space surrounding the mouth and nose, no matter how small, with a patent airway”.11 A patent airway is therefore the necessary component of the definition of the “air pocket”. Air spaces “can easily be overlooked”.11 “Patent airway” is therefore used as the prognostic factor throughout this review in place of “air pocket” because “patent airway” is more reliably identified by a rescuer.
2.2. Search strategy The electronic database of Medline was searched via PubMed with the search terms (avalanche [All Fields]), (((hypothermia)) AND ((air pocket))) and (((“Hypothermia”[Mesh])) AND ((potassium)) AND survival) and the database of EMBASE via OVID with (avalanche {Including Related Terms}) and (hypothermia {Including Related Terms}). The Cochrane Database of Systematic Reviews was searched with the terms (avalanche in Title, Abstract or Keywords) and (hypothermia in Title, Abstract or Keywords). Additional hand searching of review articles, reference texts, reference lists and conference proceedings for relevant studies was performed. All articles describing studies on the 4 prognostic factors in relation to snow avalanches and hypothermia that were published in peer-reviewed journals were considered eligible for further review. 2.3. Evidence appraisal As airway patency does not become significant until after extended burial the prognostic factors of time of burial and airway patency were reviewed in combination. Core temperature and serum potassium were reviewed separately giving 3 review streams. Eligible studies were reviewed in detail and classified by level of evidence (LOE) (Table 1) and methodological quality as defined by ILCOR.16,17 The evidence was further categorized as supportive, neutral or opposed to the relevant question(s). 3. Results Our search identified 1910 articles. After excluding duplicate listings and studies not dealing with snow avalanches, we identified 149 articles that appeared pertinent and we subjected these
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Fig. 1. Avalanche resuscitation algorithm.13 Pre-hospital management of persons buried in an avalanche. *In all cases: core temperature + ECG monitoring, gentle extrication, oxygen, airway warming, insulation, hot packs on trunk; 0.9% NaCl and/or 5% glucose only if an intravenous line can be established within a few minutes; trauma treatment if indicated. **Transport to the nearest hospital for serum potassium measurement if hospitalisation in a specialist unit with cardiopulmonary bypass facilities is not logistically possible. If K+ exceeds 12 mmol/L, stop resuscitation and pronounce death by asphyxiation; if K+ is lower than, or equals, 12 mmol/L, continue cardiopulmonary resuscitation and transport the patient as soon as possible to a specialist hospital for extracorporeal rewarming. ACLS—advanced cardiac life support, CPR—cardiopulmonary resuscitation. Staging of hypothermia according to Swiss Society of Mountain Medicine guidelines. Source: Reprinted from Resuscitation, 2001;51:7–15, Brugger H, Durrer B, Adler-Kastner L, Falk M, Tschirky F. Field management of avalanche victims, with permission from Elsevier.
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Table 1 ILCORa levels of evidence for prognostic studies16,17 . LOE P1 LOE P2 LOE P3 LOE P4 LOE P5 a
Inception (prospective) cohort studies (or meta-analyses of inception cohort studies), or validation studies of a clinical decision rule (CDR) Follow-up of untreated control groups in randomized controlled trials (or meta-analyses of follow-up studies), or derivation studies of a CDR, or validation studies of a CDR using a split-sample Retrospective cohort studies Case series Studies not directly related to the specific patient/population (e.g. different patient/population, animal and mechanical models)
International Liaison Committee on Resuscitation.
Table 2 Summary of levels of evidence, quality of studies and outcome measuresa supporting time of burial and airway patency predicting survivalb . Level of evidence
LOE P1
Quality of study Good
Fair
a b c
LOE P2
LOE P3
LOE P4
LOE P5
Brugger and Falk18 BCc Brugger et al.13 BCc Burtscher21 BC Buser22 et al. BCc Falk et al.23 BCc Hohlrieder et al.12 BE Locher et al.9,24 AC Mair et al.7 ADc
Kornberger and Mair19 BC
Brugger et al.20 E
Grosse et al.25 BCD Stalsberg et al.27 BCD
Oberhammer et al.8 CD Radwin and Grissom28 BCD Sumann15 E
Grissom et al.26 E
Outcome measures: A = return of spontaneous circulation; B = survival of event; C = survival to hospital discharge; D = intact neurological survival; E = other end point. No studies were neutral or opposed to time of burial and airway patency predicting survival. Overlapping patients.
to abstract review. We then discarded 119 articles as not relevant, leaving 30 articles for full review.
3.1. Time of burial and airway patency Ten LOE P3 retrospective case–control studies, four LOE P4 case series and two LOE P5 studies of simulated air pockets in human volunteers are supportive of the hypotheses that a shorter time of burial and the presence of a patent airway after 35 min of burial predict survival, while no studies are neutral or opposed (Table 2). Four of these studies described survival to hospital discharge in victims buried for longer than 60 min when found with a patent airway.8,25,27,28 In four studies that examined the pattern of survival over time of burial, there was no survivor when burial was longer than 35 min and the victim had an obstructed airway (Table 3). Nor was survival with an obstructed airway described in any of the remaining studies. In a retrospective observational study, Falk et al.23 established a non-linear relationship between time of burial and survival. The relationship, labelled the “survival curve”, demonstrated a rate of survival over 90% in the first 15 min of burial but that plummeted to 30% over the next 20 min (Fig. 2). The authors concluded that asphyxia is the cause of this steep decline. They went on to hypothesize that survival beyond 35 min would be possible only with continued breathing via a patent airway. This small survivor group would then remain alive through a plateau phase of the survival curve but would eventually succumb to lethal hypothermia after approximately 90 min of burial, despite a patent airway. A prospective randomized crossover study found that, when breathing from a simulated air pocket, subjects achieved a steady state of hypoxia for at least 20 min in 11 of 28 (39%) uninterrupted tests, at a level adequate to support life.20 The authors concluded that prolonged survival after snow burial is possible in the presence of an air pocket of even small dimensions.
3.2. Core temperature Two LOE P3 retrospective case–control studies and three LOE P4 case series support the hypothesis that victims in cardiac arrest with a core temperature of less than 32 ◦ C may survive if they have a patent airway. Ten studies are neutral (Table 4). The Multicentre Hypothermia Survey29 examined 401 cases of hypothermia from various causes and found that 15 of 41 (37%) who had CPR survived while 5 of 16 (31%) who had extracorporeal rewarming survived. In a study of 234 severely hypothermic victims Walpoth et al.30 described 15 survivors out of 36 (42%) cardiac arrest victims who were rewarmed with cardiopulmonary bypass. Core temperatures in patients with cardiac arrest were all below 28 ◦ C. One avalanche burial victim with the core temperature of 19.6 ◦ C made a full recovery. The authors ascribed good outcomes to the protective effect of deep hypothermia, good rescue organization and young healthy victims. In a study of 32 hypothermic avalanche victims, 19 of whom were in cardiac arrest, Locher and Walpoth24 found the maximum cooling rate under the snow was 8 ◦ C/h. Subsequent cooling between the accident site and the hospital averaged 3 (range 0.75–5.8) ◦ C/h. In a case report8 of a hypothermic avalanche victim buried at 3 m depth for 100 min, the victim was unconscious but spontaneously breathing on extrication. His core temperature was 22 ◦ C for a cooling rate of 9 ◦ C/h. The victim then experienced cardiac arrest which was untreated during pre-hospital helicopter evacuation. The attending physician at the receiving hospital found the serum potassium to be 4.3 mmol/L, initiated CPR and re-directed the patient to a trauma centre for cardiopulmonary bypass, resulting in complete recovery despite 150 min of cardiac arrest. Return of spontaneous circulation (ROSC) and survival to hospital discharge of hypothermic avalanche victims rewarmed with extracorporeal circulation, either cardiopulmonary bypass or extracorporeal membrane oxygenation (ECMO), has been described in 6 other studies (Table 5).
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Table 3 Studies of survival patterns compared to time of burial and airway patency. Series 18 , b
Brugger and Falk Buser et al.22 , c Falk et al.23 , b Brugger et al.13 , b a b c
Total number
Survivors n (%)
Pattern survival curvea
Time of 30% survival (min)
Survival after 35 min with obstructed airway
332 332 442 638
150 (45) 150 (45) 181 (43) 334 (48)
Yes Yes Yes Yes
40 40 35 40
No No No No
Demonstrated a similar non-linear survival curve pattern to the key study of Falk et al.23 with a steep drop in survival to a plateau at 30% survival. Incremental overlapping populations. Same population as above but analyzed independently by different investigators.
Table 4 Summary of levels of evidence, quality of studies and outcome measuresa that are supportive or neutral to the hypothesis that victims in cardiac arrest with a core temperature of less than 32 ◦ C may survive if they have a patent airway. Level of evidence
LOE P1
LOE P2
Studies supportive of prognostic factor Good
LOE P3
LOE P4
Danzl et al.29 ABC Locher and Walpoth24 ACb
Walpoth et al.30 CDb Althaus et al.31 CD Oberhammer et al.8 CD
Fair
Studies neutral to prognostic factor Good
Brugger et al.13 BCc Brugger and Falk18 BCc Locher et al.9 ACb Mair et al.7 AD Farstad et al.33 CD Ruttman et al.14 ACD Stalsberg et al.27 BCD
Fair
a b c
LOE P5
Grissom et al.32 E
Kornberger and Mair19 BC
Grissom et al.34 E
Outcome measures: A = return of spontaneous circulation; B = survival of event; C = survival to hospital discharge; D = intact neurological survival; E = other end point. Overlapping patients. Overlapping patients.
3.3. Serum potassium Six LOE P3 retrospective case–control studies and three LOE P4 case reports support the hypothesis that serum potassium levels predict survival in avalanche victims in cardiac arrest, and three LOE P3 retrospective case–control studies and one LOE P5 animal model are neutral (Table 6). In a retrospective case–control study of 32 hypothermic avalanche victims Locher and Walpoth24 found the serum potassium at hospital admission to be 4.25 ± 0.9 (range 3.1–6.4) mmol/L in survivors compared to 9.95 ± 4.9 (range 2.0–18) mmol/L in non-survivors (P = 0.003). The authors identified asphyxia as the cause of hyperkalaemia and cardiac arrest in the non-survivors. A retrospective case–control study by Mair et al.7 examined for prognostic markers in patients with severe hypothermia and cardiac arrest who were rewarmed with cardiopulmonary bypass (12 of the 22 victims were from avalanche accidents). Patients who had
ROSC had a median serum potassium of 5 (range 3.4–8) mmol/L while those without ROSC had a median serum potassium of 8.7 (range 3.4-over 20) mmol/L. Autopsy in 8 of the avalanche victims without ROSC, who had admission serum potassium levels rang-
Table 5 Hypothermic avalanche victims in cardiac arrest treated with extracorporeal circulation rewarminga . Series
Return of spontaneous circulationb
Survival to hospital discharge
Althaus et al.31 Locher and Walpoth24 Mair et al.7 Oberhammer et al.8 Ruttman et al.14 Schaller et al.10 Walpoth et al.30
1 5 4 1 10 1 1
1 2 1 1 1 1 1
Total
23
a b
8 ◦
Core temperatures were all lower than 32 C. Includes victims that survived to discharge.
Fig. 2. Survival probability for completely-buried avalanche victims.13 Survival probability for completely-buried avalanche victims in Switzerland 1981–1998 (n = 735) in relation to time (min) buried under the snow, contrasting victims buried in open areas (black curve, n = 638) with those buried in buildings or on roads (grey curve, n = 97). Median extrication times were 37 min (open areas) and 56 min (buildings, roads) (P = 0.17, Mann–Whitney U-test). In open areas only 16.6% of all survivors are extricated after the cut-off point of 35 min, as compared with 32.7% in buildings and on roads (P = 0.008; Pearson’s chi-square). The respective findings for the cut-off point of 130 min are 1.7% (open areas) and 16.3% (buildings, roads) (P = 0.001; Pearson’s chi-square). The dotted curve represents the survival function for completely-buried avalanche victims in open areas (n = 422) based on the Swiss data for 1981–1991, calculated by Falk et al.23 Source: Reprinted from Resuscitation, 2001;51:7–15, Brugger H, Durrer B, Adler-Kastner L, Falk M, Tschirky F. Field management of avalanche victims, with permission from Elsevier.
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Table 6 Summary of levels of evidence, quality of studies and outcome measuresa that are supportive or neutral to the hypothesis that for victims in cardiac arrest the serum potassium predicts survival to discharge. Level of evidence
LOE P1
LOE P2
Studies supportive of prognostic factor Good
LOE P3
LOE P4
Danzl et al.29 ABC Hauty et al.35 C Locher et al.9 ACb Locher and Walpoth24 ACb Mair et al.7 AD Schaller et al.10 AC Dobson et al.36 CD Oberhammer et al.8 CD von Segesser et al.37 CD
Fair
Studies neutral to prognostic factor Good
LOE P5
Farstad et al.33 CD Ruttman et al.14 ACD Silvfast and Pettila39 AC
Bender et al.38 E
a Outcome measures: A = return of spontaneous circulation; B = survival of event; C = survival to hospital discharge; D = intact neurological survival; E = other end point; Italics = animal study. b Overlapping patients.
ing from 5.9 to over 20 mmol/L, established the cause of death was asphyxia in 6 and trauma in 2. One long-term avalanche survivor with the serum potassium on admission of 3.8 mmol/L was in cardiac arrest for 210 min with a core temperature of 24 ◦ C. The authors concluded that, although “a decision to continue or terminate resuscitation in a hypothermic arrest victim cannot be made based on laboratory parameters”, “they can be used to confirm or question the decision to terminate resuscitation based on clinical judgment”. A retrospective case–control study of 24 hypothermic victims by Schaller et al.10 found a median serum potassium of 3.5 (range 2.7–5.3) mmol/L in survivors (not avalanche victims) compared to 14.5 (6.8–24.5) mmol/L in non-survivors (all avalanche victims). They then described an avalanche victim in cardiac arrest for 205 min after burial for 60 min at a depth of 2 m. The victim’s serum potassium was 4.5 mmol/L and they survived to hospital discharge after rewarming with cardiopulmonary bypass. The authors concluded that the normal serum potassium “might be used to select those patients in whom heroic resuscitation efforts can be useful”. The highest admission serum potassium in an avalanche victim in cardiac arrest who survived to hospital discharge was 6.4 mmol/L24 while in all-cause hypothermia it was 11.8 mmol/L, in a child exposed to freezing weather.36 4. Discussion It is critical that we find prognostic indicators that will reliably identify avalanche victims who have the potential to survive, so that we may effectively focus resuscitation resources. This review finds evidence that time of burial, airway patency, body temperature and serum potassium can provide valuable prognostic input to determine who may benefit from aggressive resuscitation and advanced rewarming. 4.1. Interpretation of evidencec and recommendations 4.1.1. Time of burial and airway patency Cardiac arrest from avalanche involvement is more commonly due to asphyxia than hypothermia11 but may also occur due to trauma2 or as a combination of these 3 factors. Asphyxia in a buried
c Our interpretation of the evidence incorporates the findings of the Consensus on Science developed by the Advanced Life Support Task Force during a web conference on January 5th, 2009.
victim results from airway obstruction by avalanche debris or vomitus, airway malalignment, mechanical compression of the chest27 or hypoxia with hypercapnia due to poor gas diffusion through avalanche debris.20,26,32,34 Mortality after the first 15 min of burial is approximately 10%, then increases until it is 70% at 35 min of burial as demonstrated by the “survival curve” (Fig. 2) (Table 3). All avalanche victims found in cardiac arrest within this first 35 min should be actively resuscitated following BLS and ALS guidelines unless they have suffered lethal trauma or when other factors such as concern for rescuer safety prevail. After 35 min of burial the only survivors are those with a patent airway and the ability to continue breathing.7,8,13,18,19,22,23,25,27,28 The presence of an air pocket may be difficult to confirm as it is often destroyed during rescue. The 30% of victims that have survived beyond the first 35 min of burial often remain alive while becoming progressively more hypothermic until the onset of lethal hypothermia after approximately 90 min of burial (Fig. 2) (Table 3). Therefore, all victims buried longer than 35 min that exhibit a patent or unknown airway should be actively resuscitated while resuscitation may be terminated in victims who have been buried for more than 35 min and are found in asystolic cardiac arrest with an obstructed airway. 4.1.2. Core temperature When time of burial is not known precisely, core temperature may serve as a reasonable proxy. Considering that the maximum rate of cooling while buried has been observed to be 9 ◦ C/h,8,24 it follows that a victim with a core temperature of less than 32 ◦ C would have been buried longer than 35 min. If this victim with a core temperature of less than 32 ◦ C is to have any possibility of survival, the victim must exhibit a patent airway. However, if the core temperature is above 32 ◦ C, the duration of burial may be either more or less than 35 min. Therefore, a victim with an unknown time of burial that is found with a core temperature greater than 32 ◦ C should be actively resuscitated regardless of airway patency. Avalanche victims in cardiac arrest with a core temperature of less than 32 ◦ C, have achieved ROSC and survival to hospital discharge with extracorporeal rewarming using cardiopulmonary bypass or ECMO where asphyxia has not predominated.7,8,10,14,19,24,30,31 Therefore, victims in cardiac arrest with a core temperature less than 32 ◦ C with a patent or unknown airway should be actively resuscitated and transported for extracorporeal rewarming when practical. Resuscitation may be terminated when a victim with a core temperature of less than 32 ◦ C is found in asystolic cardiac arrest with an obstructed airway.
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4.1.3. Serum potassium In some hypothermic avalanche victims the serum potassium may assist when details of other prognostic factors are unknown or a decision needs to be made for prolonged resuscitation or evacuation to a major centre for extracorporeal rewarming. The highest admission serum potassium in an avalanche victim in cardiac arrest who survived to hospital discharge was 6.4 mmol/L.24 There is, however, a single case report of survival in a hypothermic child with an initial potassium of 11.8 mmol/L.36 Therefore, a victim in cardiac arrest with a core temperature of less than 32 ◦ C with a patent or unknown airway and a serum potassium of less than 7 mmol/L should be actively resuscitated and transported for extracorporeal rewarming. A serum potassium of greater than 7 mmol/L in an adult avalanche victim in asystolic cardiac arrest may, in combination with other factors, assist in the decision to terminate resuscitation. Resuscitation should be terminated when initial serum potassium is greater than 12 mmol/L. 4.2. The ICAR MedCom avalanche resuscitation algorithm Our analysis of prognostic elements confirms the soundness of the ICAR MedCom avalanche resuscitation algorithm. However, because an “air pocket” may be so small as to be overlooked, and because a patent airway is the necessary condition for an air pocket, we recommend substituting “patent airway” for “air pocket” in the algorithm. Standard trauma precautions such as spinal immobilization should be emphasized. Treatment interventions such as defibrillation and hypothermia management need to be modified to comply with the 2010 BLS and ALS guidelines. 4.3. Limitations All the studies on avalanche victims are retrospective observational in nature. Many have extracted information from avalanche databases that are subject to reporting deficiencies and may not have consistently identified prognostic factors such as an air pocket or patent airway. Some studies may have followed the avalanche resuscitation algorithm after its publication and therefore been biased. However, 13 of the avalanche studies considered in this systematic review contained data collected prior to the publication of the algorithm.7,9,10,13,18,19,21–24,27,30,31,37 This systematic review is confined to full text peer-reviewed publications in internationally indexed journals, consistent with ILCOR standards, and may have missed pertinent publications in the other literature. However, the algorithm has been published in its current form on 5 occasions in peer-reviewed journals with no subsequent negative comment.8,13,40–42
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temperature of less than 32 ◦ C contributes dependable prognostic input to an avalanche resuscitation scheme. A serum potassium less than 7 mmol/L is associated with survival to hospital discharge and may be a valuable tool when other indicators are unclear or evacuation to extracorporeal rewarming is contemplated. Extracorporeal rewarming techniques are recommended for victims with a core temperature of less than 32 ◦ C when prognostic indicators are consistent with survival and where these modalities are available. Disclaimer This review includes information on resuscitation questions developed through the C2010 Consensus on Science and Treatment Recommendations process, managed by the International Liaison Committee on Resuscitation (http://www. americanheart.org/ILCOR). The questions were developed by ILCOR Task Forces, using strict conflict of interest guidelines. In general, each question was assigned to two experts to complete a detailed structured review of the literature, and complete a detailed worksheet. Worksheets are discussed at ILCOR meetings to reach consensus and will be published in 2010 as the Consensus on Science and Treatment Recommendations (CoSTR). The conclusions published in the final CoSTR consensus document may differ from the conclusions of in this review because the CoSTR consensus will reflect input from other worksheet authors and discussants at the conference, and will take into consideration implementation and feasibility issues as well as new relevant research. Conflict of interest None of the authors has a commercial or industrial conflict of interest. HB has published studies on avalanche resuscitation examining time of burial and airway patency. Neither JB or MS have published on prognostic factors. Source of support Hermann Brugger receives support as the head of the EURAC Institute of Mountain Emergency Medicine. Neither JB or MS receive funding for avalanche research. Acknowledgement We thank Shelley Mardiros for manuscript review. References
4.4. Future research Databases should be prospectively designed to obtain data on prognostic factors such as airway patency, core temperature and serum potassium. Core temperatures should be documented upon extrication to allow the calculation of accurate cooling rates for avalanche burial. Outcome data should include measures of neurological function. Further research on the pathophysiology of avalanche burial, including air pocket physiology, should be done. Prospective validation studies on the algorithm should compare outcomes between resuscitation complying with the algorithm and not. 5. Authors conclusions and recommendations Our review has found evidence that, for victims in cardiac arrest, the patency of the airway after 35 min of burial or with a core
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