Patel R L, Turtle M R, Chambers D J, James D N, Newman S, Venn G E
Department of Cardiothoracic Surgery, The Rayne Institute, St. Thomas' Hospital, London, United Kingdom.
J Thorac Cardiovasc Surg. 1996 Jun;111(6):1267-79. doi: 10.1016/s0022-5223(96)70230-1.
Neuropsychologic impairment in patients undergoing cardiopulmonary bypass may be associated with cerebral blood flow changes arising from different management protocols for carbon dioxide tension during bypass. Seventy patients having coronary artery bypass grafting were randomized to either pH-stat or alpha-stat acid-base management during cardiopulmonary bypass with a membrane oxygenator. In each patient, cerebral blood flow (xenon 133 clearance), middle cerebral artery blood flow velocity (transcranial Doppler sonography), and cerebral oxygen metabolism (cerebral metabolic rate and cerebral extraction ratio) were measured during four phases of the operation: before bypass, during bypass (at hypothermia and at normothermia), and after bypass. A battery, of neuropsychologic tests were also conducted before and 6 weeks after the operation. During hypothermic (28 degrees C) bypass, cerebral blood flow was significantly (p < 0.001) greater in the pH-stat group (41 mlx100 gm(-1)xmin(-1); 95% confidence interval 39 to 43 mlx100 gm(-1)xmin(-1)) than in the alpha-stat group (24 mlx100 gm(-1)xmin(-1); confidence interval 22 to 26 mlx100 gm(-1)xmin(-1)) at constant pressure and How. Arterial carbon dioxide tensions were 41 mm Hg (40 to 41 mm Hg) and 26 mm Hg (25 to 27 mm Hg), respectively; pH was 7.36 (7.34 to 7.38) and 7.53 (7.51 to 7.55), respectively. Middle cerebral artery flow velocity was significantly (p < 0.05) reduced in the alpha-stat group to 87% (77% to 96%) of the prebypass value, whereas it was significantly (p < 0.05) increased (152%; 141% to 162%) in the pH-stat group. Cerebral extraction ratio for oxygen demonstrated relative cerebral hyperemia during hypothermic (28 degrees C) bypass in both the pH-stat and alpha-stat groups (0.12 [0.11 to 0.14] and 0.25 [0.22 to 0.28], respectively); however, hyperemia was significantly more pronounced in the pH-stat group, indicating greater disruption in cerebral autoregulation. Neuropsychologic impairment criteria of deterioration in results of three or more tests revealed that a significantly (Fisher's exact test, p = 0.02) higher proportion of patients in the pH-stat group fared poorly than in the alpha-stat group at 6 weeks (17/35, 48.6% [32% to 65.1%], and 7/35, 20% [6.7% to 33.2.2%], respectively). In conclusion, patients receiving alpha-stat management had less disruption of cerebral autoregulation during cardiopulmonary bypass, accompanied by a reduced incidence of postoperative cerebral dysfunction.
接受体外循环的患者出现神经心理损伤，可能与体外循环期间因不同二氧化碳张力管理方案引起的脑血流变化有关。七十例行冠状动脉搭桥术的患者在使用膜式氧合器进行体外循环期间，被随机分配至pH稳态或α稳态酸碱管理组。在每位患者手术的四个阶段：体外循环前、体外循环期间（低温期和常温期）以及体外循环后，均测量了脑血流（氙133清除率）、大脑中动脉血流速度（经颅多普勒超声检查）以及脑氧代谢（脑代谢率和脑摄取率）。术前及术后6周还进行了一系列神经心理测试。在低温（28℃）体外循环期间，pH稳态组的脑血流（41 ml×100 gm⁻¹×min⁻¹；95%置信区间39至43 ml×100 gm⁻¹×min⁻¹）在恒压和恒流条件下显著高于α稳态组（24 ml×100 gm⁻¹×min⁻¹；置信区间22至26 ml×100 gm⁻¹×min⁻¹）（p < 0.001）。动脉二氧化碳张力分别为41 mmHg（40至41 mmHg）和26 mmHg（25至27 mmHg）；pH值分别为7.36（7.34至7.38）和7.53（7.51至7.55）。α稳态组大脑中动脉血流速度显著降低（p < 0.05）至体外循环前值的87%（77%至96%），而pH稳态组则显著升高（p < 0.05）（152%；141%至162%）。在低温（28℃）体外循环期间，pH稳态组和α稳态组的脑氧摄取率均显示相对脑充血（分别为0.12 [0.11至0.14]和0.25 [0.22至0.28]）；然而，pH稳态组的充血更为显著，表明脑自动调节功能受到更大干扰。三项或更多测试结果恶化的神经心理损伤标准显示，在6周时，pH稳态组患者表现不佳的比例显著高于α稳态组（Fisher精确检验，p = 0.02）（分别为17/35，48.6% [32%至65.1%]和7/35，20% [6.7%至33.2%]）。总之，接受α稳态管理的患者在体外循环期间脑自动调节功能的干扰较小，术后脑功能障碍的发生率也较低。
