Introduction
An increasing number of skiers and snowboarders are caught in nonavalanche tree-well snow immersions. Given the lighter density of snow and inverted position of burial, this emerging injury pattern may have different victim physiology and associated rescue considerations compared with avalanche-related burials.
Objective
This study aimed to measure the differential effect of burial type (tree-well vs avalanche) on victim physiology related to survival.
Methods
Eleven volunteers participated in 2 paired 60-minute snow burials: avalanche and tree-well scenarios simulated by controlling burial position and snowpack densities. Minute-by-minute physiologic parameters were monitored for safety and recorded, including core temperature, respiratory rate, minute ventilation, end-tidal carbon dioxide, oxygen saturation, and heart rate.
Results
Using a quasi-Bayesian generalized linear mixed model, we found the subject-specific average rate of core temperature cooling in avalanche conditions was –0.017°C/min. (95% CI –0.023 to –0.011; P = .001); in tree-well conditions, it was –0.013°C/min. (95% CI –0.019 to –0.005; P < .001). The subject-level average expected time to hypothermia (35°C) was 185 minutes in avalanche and 250 minutes in tree-well conditions. Upon limiting the false discovery rate to 5%, secondary analyses revealed no statistically significant difference between burial types for respiratory rate, minute ventilation, end-tidal carbon dioxide, oxygen saturation, or pulse.
Conclusions
The lower density of snowpack in tree-well snow immersions is likely to result in the 24% slower rate of cooling observed and thus in longer expected time to hypothermia compared with higher snow density avalanche conditions. These implications may lead to allocating extended search and rescue efforts to accommodate for longer time to hypothermia when looking for tree-well burial victims compared to avalanche victims.