Comparative Analysis of alpha-STAT and pH-STAT Strategies During Deep Hypothermic Circulatory Arrest in the Young Pig

Kim, Won Gon; Lim, Chung; Moon, Hyun Jong; Won, Tae Hee; Kim, Yong Jin

Abstract

INTRODUCTION: The most dramatic application of hypothermia in cardiac surgery is in deep hypothermic circulatory arrest (DHCA). Because man in natural circumstances is never exposed to this extreme hypothermic condition, one of the controversial aspects of clinical hypothermia is appropriate acid-base management (alpha-stat versus pH-stat). This study aims to compare alpha-stat with pH-stat for: (1) brain cooling and re-warming speed during hypothermia induction and re-warming by cardiopulmonary bypass (CPB); (2) cerebral perfusion, metabolism, and their coupling; and (3) the extent of development of cerebral edema after circulatory arrest, in young pigs. MATERIALS AND METHODS: Fourteen young pigs were assigned to one of two strategies of gas manipulation. Cerebral blood flow was measured with a cerebral venous outflow technique. After a median sternotomy, CPB was established. Core cooling was initiated and continued until nasopHaryngeal temperature fell below 20degree C. The flow rate was set at 2,500 ml/min. Once their temperatures were below 20degree C, the animals were subjected to DHCA for 40 mins. During cooling, acid-base balance was maintained according to either alpha-STAT or pH-STAT strategies. After DHCA, the body was re-warmed to normal body temperature. The animals were then sacrificed, and their brains measured for edema. Cerebral perfusion and metabolism were measured before the onset of CPB, before cooling, before DHCA, 15 mins after re-warming, and upon completion of re-warming. RESULTS AND CONCLUSION: Cooling time was significantly shorter with alpha-stat than with pH-stat strategy, while there were no significant differences in rewarming time between the two groups. Nosignificant differences were found in cerebral blood flow, metabolic rate, or flow/ metabolic rate ratio between two groups. Temperature-related differences were significant in cerebral blood flow, metabolic rate, and flow/metabolic rate ratio within each group. Brain water content showed no significant differences between two groups.