Skaryak L A, Chai P J, Kern F H, Greeley W J, Ungerleider R M
Department of Surgery, Duke University Medical Center, Durham, NC 27710, USA.
J Thorac Cardiovasc Surg. 1995 Dec;110(6):1649-57. doi: 10.1016/S0022-5223(95)70026-9.
This study investigated the effects of different cooling strategies on cerebral metabolic response to circulatory arrest. In particular, it examined the impact of blood gas management and degree of cooling on cerebral metabolism before and after deep hypothermic circulatory arrest. Sixty-nine 1-week-old piglets (2 to 3 kg) were placed on cardiopulmonary bypass (37 degrees C) at 100 ml/kg per minute. Animals were cooled to 18 degrees or 14 degrees C as follows: alpha-stat strategy to 18 degrees C (n = 9) or 14 degrees C (n = 6), pH-stat strategy to 18 degrees C (n = 12) or 14 degrees C (n = 10). Animals underwent 60 minutes of circulator arrest followed by rewarming with alpha-stat strategy to 36 degrees C. Control animals were cooled with alpha-stat strategy to 18 degrees C (n = 10) or 14 degrees C (n = 3) and then maintained on cold cardiopulmonary bypass (100 ml/kg per minute) for 60 minutes. Three animals were excluded (see text). With the use of xenon 133 clearance methods, cerebral blood flow was measured at the following points: point I, cardiopulmonary bypass (37 degrees C); point II, cardiopulmonary bypass before circulatory arrest or control flow (18 degrees or 14 degrees C); and point III, cardiopulmonary bypass after rewarming (36 degrees C). Cerebral metabolic rate of oxygen consumption was calculated for each point. At point II, cerebral metabolism was more suppressed at 14 degrees C compared with that at 18 degrees C. At any given temperature (18 degrees or 14 degrees C), pH-stat strategy provided the greatest suppression of of cerebral metabolism. In control animals, cerebral metabolic oxygen consumption of point III returned to baseline values after 60 minutes of cold bypass. Sixty minutes of circulatory arrest resulted in a significant reduction in cerebral metabolic oxygen consumption at point III compared with that at point I regardless of cooling temperature or blood gas strategy. The amount of cerebral metabolic recovery was significantly reduced in the pH-stat 14 degrees C group compared with that in the pH-stat 18 degrees C group at point III. The use of pH-stat strategy followed by a switch to alpha-stat at 14 degrees C provided better cerebral metabolic recovery compared with either strategy used alone. The use of pH-stat strategy during initial cooling may provide the animal with maximal cerebral metabolic suppression. The cerebral acidosis produced with pH-stat cooling may worsen cerebral metabolic injury from circulatory arrest, but this affect is eliminated with the use of alpha-stat just before the period of circulatory arrest.
本研究调查了不同降温策略对大脑对循环停止的代谢反应的影响。具体而言，研究了血气管理和降温程度对深低温循环停止前后大脑代谢的影响。69只1周龄仔猪（2至3千克）以每分钟100毫升/千克的流量进行体外循环（37摄氏度）。动物按如下方式冷却至18摄氏度或14摄氏度：采用α-stat策略冷却至18摄氏度（n = 9）或14摄氏度（n = 6），采用pH-stat策略冷却至18摄氏度（n = 12）或14摄氏度（n = 10）。动物经历60分钟的循环停止，然后采用α-stat策略复温至36摄氏度。对照动物采用α-stat策略冷却至18摄氏度（n = 10）或14摄氏度（n = 3），然后在冷体外循环（每分钟100毫升/千克）下维持60分钟。排除3只动物（见正文）。使用氙133清除法在以下时间点测量脑血流量：时间点I，体外循环（37摄氏度）；时间点II，循环停止前的体外循环或对照流量（18摄氏度或14摄氏度）；时间点III，复温后的体外循环（36摄氏度）。计算每个时间点的大脑氧消耗代谢率。在时间点II，与18摄氏度相比，14摄氏度时大脑代谢受抑制更明显。在任何给定温度（18摄氏度或14摄氏度）下，pH-stat策略对大脑代谢的抑制作用最大。在对照动物中，冷旁路60分钟后，时间点III的大脑代谢氧消耗恢复到基线值。无论降温温度或血气策略如何，60分钟的循环停止导致时间点III的大脑代谢氧消耗与时间点I相比显著降低。在时间点III，pH-stat 14摄氏度组的大脑代谢恢复量与pH-stat 18摄氏度组相比显著减少。在14摄氏度时先采用pH-stat策略然后切换至α-stat策略比单独使用任何一种策略能提供更好的大脑代谢恢复。在初始冷却期间使用pH-stat策略可能为动物提供最大程度的大脑代谢抑制。pH-stat冷却产生的脑酸中毒可能会加重循环停止导致的大脑代谢损伤，但在循环停止前使用α-stat策略可消除这种影响。
