Patel R L, Turtle M R, Chambers D J, Venn G E
Department of Cardiothoracic Surgery, The Rayne Institute, St. Thomas' Hospital, London, UK.
Eur J Cardiothorac Surg. 1992;6(6):302-6; discussion 307. doi: 10.1016/1010-7940(92)90146-o.
Cerebral dysfunction following cardiopulmonary bypass may be aggravated by altered autoregulation of cerebral blood flow. We have used trans-cranial Doppler to measure middle cerebral artery blood flow velocity during cardiopulmonary bypass managed by either pH-stat or alpha-stat acid-base protocols. Fourteen patients were studied, 7 in each group. During bypass at 28 degrees C, patients underwent incremental alterations in mean arterial pressure from 20-90 mmHg, maintaining systemic perfusion flow at 1.75 L/min per m2. The cerebral extraction ratio of oxygen was measured to indicate matching of cerebral blood flow to demand. The pH-stat group showed a pressure passive cerebral circulation with significant (r = 0.999, P less than 0.05) increase in blood flow velocity with increasing arterial pressure. This also occurred in alpha-stat group during the pressure range of 20-50 mmHg (r = 0.951, P less than 0.05). During the pressure range of 50-90 mmHg in alpha-stat group the change in flow velocity (0.16 cm/sec per mmHg) was significantly (P less than 0.05) less than that in pH-stat group (0.58 cm/second per mmHg). The cerebral extraction ratio of oxygen was less depressed in the alpha-stat group than in the pH-stat group, indicating more appropriate matching of cerebral blood flow and tissue demand. These results suggest that, during alpha-stat managed cardiopulmonary bypass, cerebral blood flow velocity is less subject to wide pressure alteration than pH-stat.
体外循环后发生的脑功能障碍可能因脑血流自身调节改变而加重。我们已使用经颅多普勒测量在采用pH稳态或α稳态酸碱方案管理的体外循环期间大脑中动脉的血流速度。研究了14例患者，每组7例。在28℃体外循环期间，患者平均动脉压从20 - 90 mmHg逐步改变，全身灌注流量维持在每平方米1.75 L/min。测量氧的脑摄取率以表明脑血流与需求的匹配情况。pH稳态组显示脑循环呈压力被动状态，随着动脉压升高，血流速度显著增加（r = 0.999，P < 0.05）。在20 - 50 mmHg的压力范围内，α稳态组也出现这种情况（r = 0.951，P < 0.05）。在α稳态组50 - 90 mmHg的压力范围内，血流速度的变化（每mmHg 0.16 cm/秒）显著（P < 0.05）小于pH稳态组（每mmHg 0.58 cm/秒）。α稳态组氧的脑摄取率比pH稳态组降低得少，表明脑血流与组织需求的匹配更合适。这些结果表明，在α稳态管理的体外循环期间，脑血流速度比pH稳态时受压力大幅改变的影响小。
