Deep and profound hypothermia in haemorrhagic shock, friend or foe? A systematic review.

INTRODUCTION: Survival in exsanguinating cardiac arrest patients is poor, as is neurological outcome in survivors. Hypothermia has traditionally been seen as harmful to trauma patients and associated with increased mortality; however, there has been speculation that cooling to very low temperatures ( ≤ 20°C) could be used to treat haemorrhagic trauma patients by the induction of a suspended animation period through extreme cooling, which improves survival and preserves neurological function. This has been termed emergency preservation and resuscitation (EPR).

METHODS: A systematic review of the literature was used to examine the evidence base behind the use of deep and profound hypothermia in haemorrhagic shock (HS). It included original research articles (human or animal) with cooling to ≤ 20°C after HS or an experimental model replicating it. Normovolaemic cardiac arrest, central nervous system injury and non-HS models were excluded.

RESULTS: Twenty articles using 456 animal subjects were included, in which 327 were cooled to ≤ 20°C. All studies describing good survival rates were possible using EPR and 19/20 demonstrated that EPR can preserve neurological function after prolonged periods of circulatory arrest or minimal circulatory flow. This additional period can be used for surgical intervention to arrest haemorrhage in HS that would otherwise be lethal.

CONCLUSIONS: The outcomes of this review have significant implications for application to human patients and the ongoing human clinical trial (EPR for Cardiac Arrest from Trauma). Current evidence suggests that hypothermia ≤ 20°C used in the form of EPR could be beneficial to the HS patient.