Recommendation on the Use of the HOPE Score at the Hospital for Outcome Prediction in Critically Buried Hypothermic Avalanche Victims Considered for ECLS Rewarming

To the Editor:

We read with great interest the article on the 2024 update of the Wilderness Medical Society clinical practice guidelines for the prevention and management of avalanche and nonavalanche snow burial accidents. ¹ We would like to comment on the recommendation regarding the use of the HOPE (hypothermia outcome prediction after ECLS rewarming) score for outcome prediction in hypothermic avalanche victims.

We agree that the HOPE score should be used, at hospital, for outcome prediction in critically buried hypothermic avalanche victims in cardiac arrest being considered for ECLS rewarming. The authors, however, recommend using the asphyxia scenario to calculate the HOPE score when circumstances are not clear, to guide decisions on whether to rewarm victims in hypothermic cardiac arrest (CA). The recommendation should indeed be to use the nonasphyxia scenario rather than the asphyxia one and most probably reflects a writing mistake rather than the expert's actual recommendation.

The HOPE score variable “asphyxia” corresponds to mechanisms for hypothermia classified as asphyxia-related (ie, submersion, avalanche with burial of the head under the snow), whereas non-asphyxia-related includes immersion or outdoor or indoor exposure to cold. ² Most avalanche deaths are caused by asphyxia from critical burial.^3,4 Avalanche burials with CA and hypothermia have, therefore, a much poorer prognosis compared to nonasphyxia mechanisms of hypothermia, independently of the serum potassium measured at hospital admission. Indeed, according to the HOPE score, as estimated in a derivation study ² and confirmed in a validation study, ⁵ the odds of survival after ECLS are reduced by a factor of about 7 for a patient with an asphyxia-related mechanism. A small proportion of patients may, however, survive the asphyxia and suffer from CA secondary to hypothermia, notably in the presence of an air pocket, which has been associated with increased survival, ³ although this information is challenging to assess during victim extrication and rarely available.

In this context, consider the case of a critically buried victim caught in an avalanche, with a long burial duration, a patent airway, and a significant air pocket. Cardiac arrest could therefore be attributed to pure hypothermia (without an asphyxia component) and have a potentially excellent outcome after ECLS rewarming. In such a situation, as well as in any situation where there may be a possibility that an avalanche victim may not have been asphyxiated despite full burial, it is certainly better to be over-optimistic than over-pessimistic and use the nonasphyxia scenario to calculate the HOPE score.

The International Commission for Mountain Emergency Medicine (ICAR MedCom) specifically addressed this situation by stating the 2023 recommendations on the management of avalanche victims that if there is a possibility that an avalanche victim may not have been asphyxiated despite full burial, calculating the HOPE score using the nonasphyxia scenario will decrease the risk of underestimating the probability of survival after rewarming and prevent ECLS from not being performed despite the possibility of survival. ²