Avalanche burial has a high mortality and yet in some cases there have been some amazing saves despite prolonged cardiac arrest. An international working group undertook a systematic review to examine 4 critical prognostic factors for burial victims in cardiac arrest. You have a better chance of surviving a prolonged burial if you have a patent airway and a pocket of air (even a very small one), are hypothermic, and preferably not hyperkalaemic.
Prognostic factors in avalanche resuscitation: A systematic review
Resuscitation. 2010 Jun;81(6):645-52