title: Does the rate of rewarming from profound hypothermic arrest influence the outcome in a swine model of lethal hemorrhage?
abstract: BACKGROUND
  Rapid induction of profound hypothermic arrest (suspended animation) can provide valuable time for the repair of complex injuries and improve survival. The optimal rate for re-warming from a state of profound hypothermia is unknown. This experiment was designed to test the impact of different warming rates on outcome in a swine model of lethal hemorrhage from complex vascular injuries.
  
  
  METHODS
  Uncontrolled lethal hemorrhage was induced in 40 swine (80-120 lbs) by creating an iliac artery and vein injury, followed 30 minutes later (simulating transport time) by laceration of the descending thoracic aorta. Through a thoracotomy approach, a catheter was placed in the aorta and hyperkalemic organ preservation solution was infused on cardiopulmonary bypass to rapidly (2 degrees C/min) induce profound (10 degrees C) hypothermia. Vascular injuries were repaired during 60 minutes of hypothermic arrest. The 4 groups (n = 10/group) included normothermic controls (NC) where core temperature was maintained between 36 to 37 degrees C, and re-warming from profound hypothermia at rates of: 0.25 degrees C/min (slow), 0.5 degrees C/min (medium), or 1 degrees C/min (fast). Hyperkalemia was reversed during the hypothermic arrest period, and blood was infused for resuscitation during re-warming. After discontinuation of cardiopulmonary bypass, the animals were recovered and monitored for 6 weeks for neurologic deficits, cognitive function (learning new skills), and organ dysfunction. Detailed examination of brains was performed at 6 weeks.
  
  
  RESULTS
  All the normothermic animals died, whereas survival rates for slow, medium and fast re-warming from hypothermic arrest were 50, 90, and 30%, respectively (p < 0.05 slow and medium warming versus normothermic control, p < 0.05 medium versus fast re-warming). All the surviving animals were neurologically intact, displayed normal learning capacity, and had no long-term organ dysfunction.
  
  
  CONCLUSIONS
  Rapid induction of hypothermic arrest maintains viability of brain during repair of lethal vascular injuries. Long-term survival is influenced by the rate of reversal of hypothermia.
authors.affiliation: Trauma Research and Readiness Institute for Surgery, Uniformed Services University of the Health Sciences, Bethesda, MD, USA. hbalam@partners.org
authors.forename: Hasan B
authors.initials: HB
authors.lastname: Alam
authors.forename: Peter
authors.initials: P
authors.lastname: Rhee
authors.forename: Kaneatsu
authors.initials: K
authors.lastname: Honma
authors.forename: Huazhen
authors.initials: H
authors.lastname: Chen
authors.forename: Eduardo C
authors.initials: EC
authors.lastname: Ayuste
authors.forename: Tom
authors.initials: T
authors.lastname: Lin
authors.forename: Kevin
authors.initials: K
authors.lastname: Toruno
authors.forename: Tina
authors.initials: T
authors.lastname: Mehrani
authors.forename: Caroline
authors.initials: C
authors.lastname: Engel
authors.forename: Zheng
authors.initials: Z
authors.lastname: Chen
mesh_terms: D000818:Animals; D015415:Biomarkers / Q000097:blood; D050792:Circulatory Arrest, Deep Hypothermia Induced; D003072:Cognition Disorders / Q000097:blood / Q000209:etiology; D016207:Cytokines / Q000097:blood; D004195:Disease Models, Animal; D005260:Female; D017694:Rewarming / Q000379:methods* / Q000523:psychology; D012771:Shock, Hemorrhagic / Q000097:blood / Q000209:etiology / Q000517:prevention & control*; D017695:Soft Tissue Injuries / Q000097:blood / Q000150:complications / Q000601:surgery*; D013552:Swine; D013997:Time Factors; D016896:Treatment Outcome
chemical_list: D015415:Biomarkers; D016207:Cytokines