Is maintained cranial hypothermia the only factor leading to improved outcome after retrograde cerebral perfusion?: An experimental study with a chronic porcine model

Background: previous studies have shown that retrograde cerebral perfusion can improve neurologic outcome after prolonged hypothermic circulatory arrest. Here we have compared two temperatures of retrograde cerebral perfusion (15 degrees C and 25 degrees C) with hypothermic circulatory arrest at systemic hypothermia of 25 degrees C to clarify whether the possible benefit of retrograde cerebral perfusion may only be due to improved cooling effect. Methods: Eighteen pigs (23-27 kg) were randomly assigned to undergo 15 degrees C retrograde cerebral perfusion at systemic hypothermia of 25 degrees C, 25 degrees C retrograde cerebral perfusion at 25 degrees C systemic hypothermia, or hypothermic circulatory arrest at 25 degrees C for 40 minutes, Flow was adjusted to maintain superior vena cava pressure at 20 mm Hg during retrograde cerebral perfusion, Hemodynamic, electrophysiologic, metabolic, and temperature monitoring were performed until 4 hours after the start of rewarming, Daily behavioral assessment was done until death or until the animals were killed on day 7. Histopathologic analysis of the brain was carried out on all animals. Results: Epidural temperatures were lower in the 15 degrees C retrograde cerebral perfusion group during the intervention (P < .05), In the 15 degrees C retrograde cerebral perfusion group, 4 (67%) of 6 animals survived for 7 days compared with 3 (50%) of 6 in both the 25 degrees C retrograde cerebral perfusion and hypothermic circulatory arrest groups. The median total histopathologic score was 5 in the 15 degrees C retrograde cerebral perfusion group and 7 in the 25 degrees C retrograde cerebral perfusion group (P = .04). Conclusions: These findings suggest that enhanced cranial hypothermia is the major beneficial factor of retrograde cerebral perfusion when careful attention is paid to its implementation.