Early deaths from trauma are often caused by exsanguinating hemorrhage from injuries that appear "irreparable." We explored the limits of deep hypothermic circulatory arrest induced during hemorrhagic shock to enable repair of these injuries in a bloodless field. In 15 dogs, after 30 minutes of hemorrhagic shock (mean arterial pressure, 40 mm Hg), cardiopulmonary bypass (CPB) was used to cool to 15 degrees C in 13-37 minutes. After circulatory arrest of 60 (Group 1), 90 (Group 2), or 120 (Group 3) minutes, reperfusion and rewarming were accomplished by CPB. All dogs survived greater than 72 hours. Best neurologic deficit scores (ND) (0% = normal, 100% = brain death) were 0 +/- 0% (normal) in Group 1, 10 +/- 8% (mild disability) in Group 2, and 27 +/- 24% in Group 3. Outcome in Group 3 dogs ranged from near-normal to comatose. After perfusion-fixation sacrifice, brain histopathologic damage scores correlated with insult time, as did ND scores. Deep hypothermia can allow 60-90 min of circulatory arrest with good neurologic recovery, even after a period of severe hemorrhagic shock. This technique may allow repair of otherwise lethal injuries and survival without brain damage.