Department of Anesthesiology and Critical Care Medicine, The Johns Hopkins University School of Medicine, Baltimore, Maryland 21287, USA.
Anesth Analg. 2010 Feb 1;110(2):321-8. doi: 10.1213/ANE.0b013e3181c6fd12. Epub 2009 Dec 11.
Patient rewarming after hypothermic cardiopulmonary bypass (CPB) has been linked to brain injury after cardiac surgery. In this study, we evaluated whether cooling and then rewarming of body temperature during CPB in adult patients is associated with alterations in cerebral blood flow (CBF)-blood pressure autoregulation.
One hundred twenty-seven adult patients undergoing CPB during cardiac surgery had transcranial Doppler monitoring of the right and left middle cerebral artery blood flow velocity. Eleven patients undergoing CPB who had arterial inflow maintained at >35 degrees C served as controls. The mean velocity index (Mx) was calculated as a moving, linear correlation coefficient between slow waves of middle cerebral artery blood flow velocity and mean arterial blood pressure. Intact CBF-blood pressure autoregulation is associated with an Mx that approaches 0. Impaired autoregulation results in an increasing Mx approaching 1.0. Comparisons of time-averaged Mx values were made between the following periods: before CPB (baseline), during the cooling and rewarming phases of CPB, and after CPB. The number of patients in each phase of CPB with an Mx >4.0, indicative of impaired CBF autoregulation, was determined.
During cooling, Mx (left, 0.29 +/- 0.18; right, 0.28 +/- 0.18 [mean +/- SD]) was greater than that at baseline (left, 0.17 +/- 0.21; right, 0.17 +/- 0.20; P <or= 0.0001). Mx increased during the rewarming phase of CPB (left, 0.40 +/- 0.19; right, 0.39 +/- 0.19) compared with baseline (P <or= 0.001) and the cooling phase (P <or= 0.0001), indicating impaired CBF autoregulation. After CPB, Mx (left, 0.27 +/- 0.20; right, 0.28 +/- 0.21) was higher than at baseline (left, P = 0.0004; right, P = 0.0003), no different than during the cooling phase, but lower than during rewarming (left, P <or= 0.0001; right, P <or= 0.0005). Forty-three patients (34%) had an Mx >or=0.4 during the cooling phase of CPB and 68 (53%) had an average Mx >or=0.4 during rewarming. Nine of the 11 warm controls had an average Mx >or=0.4 during the entire CPB period. There were 7 strokes and 1 TIA after surgery. All strokes were in patients with Mx >or= 0.4 during rewarming (P = 0.015). The unadjusted odds ratio for any neurologic event (stroke or transient ischemic attack) for patients with Mx >or= 0.4 during rewarming was 6.57 (95% confidence interval, 0.79 to 55.0, P < 0.08).
Hypothermic CPB is associated with abnormal CBF-blood pressure autoregulation that is worsened with rewarming. We found a high rate of strokes in patients with evidence of impaired CBF autoregulation. Whether a pressure-passive CBF state during rewarming is associated with risk for ischemic brain injury requires further investigation.
低温体外循环（CPB）后患者复温与心脏手术后的脑损伤有关。在这项研究中，我们评估了在 CPB 过程中冷却和复温体温是否与脑血流（CBF）-血压自动调节的改变有关。
127 例在心脏手术中接受 CPB 的成年患者进行了右和左大脑中动脉血流速度的经颅多普勒监测。11 例接受 CPB 且动脉流入维持在>35°C 的患者作为对照。平均速度指数（Mx）被计算为大脑中动脉血流速度慢波与平均动脉血压之间的移动线性相关系数。完整的 CBF-血压自动调节与接近 0 的 Mx 相关。受损的自动调节导致接近 1.0 的 Mx 增加。在以下期间比较时间平均 Mx 值：CPB 前（基线）、CPB 冷却和复温阶段以及 CPB 后。确定在每个 CPB 阶段中 Mx>4.0 的患者数量，表明 CBF 自动调节受损。
在冷却过程中，Mx（左侧，0.29 +/- 0.18；右侧，0.28 +/- 0.18[平均值 +/- SD]）大于基线时（左侧，0.17 +/- 0.21；右侧，0.17 +/- 0.20；P<or=0.0001）。CPB 复温阶段 Mx（左侧，0.40 +/- 0.19；右侧，0.39 +/- 0.19）较基线增加（P<or=0.001）和冷却阶段（P<or=0.0001），表明 CBF 自动调节受损。CPB 后，Mx（左侧，0.27 +/- 0.20；右侧，0.28 +/- 0.21）高于基线（左侧，P=0.0004；右侧，P=0.0003），与冷却阶段无差异，但低于复温阶段（左侧，P<or=0.0001；右侧，P<or=0.0005）。43 例（34%）患者在 CPB 冷却阶段 Mx>or=0.4，68 例（53%）患者在复温期间平均 Mx>or=0.4。11 例温暖对照中有 9 例在整个 CPB 期间平均 Mx>or=0.4。手术后有 7 例中风和 1 例 TIA。所有中风均发生在复温时 Mx>or=0.4 的患者中（P=0.015）。复温时 Mx>or=0.4 的患者任何神经事件（中风或短暂性脑缺血发作）的未调整优势比为 6.57（95%置信区间，0.79 至 55.0，P<0.08）。
低温 CPB 与 CBF-血压自动调节异常有关，复温时会加重。我们发现有自动调节受损证据的患者中风发生率较高。复温期间是否存在被动 CBF 状态与缺血性脑损伤的风险有关，需要进一步研究。
