Objective: We hypothesize that during severe normothermic hemorrhagic shock (HS), induction of profound hypothermic circulatory arrest (PHCA) of 60 minutes to allow repair of otherwise lethal injuries in a bloodless field, can be survived without brain damage. In previous dog studies, normothermic HS with mean arterial pressure (MAP) of 40 mm Hg for 30 minutes, followed by PHCA of 2 hours at brain (tympanic membrane) temperature of 5 to 10 degrees C and core temperature of 10 degrees C, induced and reversed with cardiopulmonary bypass, resulted in survival with mild histopathologic brain damage. This study was designed to determine the severity of HS that can safely allow 1 hour of PHCA. In pilot studies with HS at MAP 30 mm Hg for 90 minutes with or without subsequent PHCA of 60 minutes there were no survivors.
Methods: In the definitive study, outcomes in four groups of five dogs each were compared: group I, HS at MAP 30 mm Hg for 60 minutes and normothermic fluid resuscitation; group II, HS at MAP 30 mm Hg for 60 minutes, PHCA for 60 minutes, and resuscitation; group III, HS at MAP 40 mm Hg for 60 minutes and normothermic fluid resuscitation; and group IV, HS at MAP 40 mm Hg for 60 minutes, PHCA for 60 minutes, and resuscitation. Controlled ventilation was maintained for at least 20 hours and intensive care for 72 hours.
Results: In groups I and II, two of five dogs in each group survived to 72 hours. In groups III and IV, all ten dogs survived. All survivors were functionally normal, with neurologic deficit scores (0% = normal, 100% = brain dead) of < 10%. Light microscopic scoring of 18 brain regions revealed no ischemic changes. All nonsurvivors had a severe metabolic acidemia after HS and developed multiple organ failure, including pulmonary edema, pneumonia, and intestinal necrosis.
Conclusions: The critical level of hypotension during 60 minutes normothermic HS that is compatible with survival in dogs is a MAP of between 30 and 40 mm Hg. After otherwise survivable severe normothermic HS of 60 minutes, PHCA of 60 minutes does not add brain damage or mortality, and may allow survival from injuries that would otherwise be irreparable.