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 arre st. Here we have compared two temperatures of retrograde cerebral perfusion (15 degrees C and 25 degrees C) with hypothermic circulatory arrest at sys temic hypothermia of 25 degrees C to clarify whether the possible benefit o f retrograde cerebral perfusion may only be due to improved cooling effect. Methods: Eighteen pigs (23-27 kg) were randomly assigned to undergo 15 degr ees C retrograde cerebral perfusion at systemic hypothermia of 25 degrees C , 25 degrees C retrograde cerebral perfusion at 25 degrees C systemic hypot hermia, or hypothermic circulatory arrest at 25 degrees C for 40 minutes, F low 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 a nimals were killed on day 7. Histopathologic analysis of the brain was carr ied out on all animals. Results: Epidural temperatures were lower in the 15 degrees C retrograde ce rebral 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 cerebr al perfusion and hypothermic circulatory arrest groups. The median total hi stopathologic 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 th e major beneficial factor of retrograde cerebral perfusion when careful att ention is paid to its implementation.