Kho Eline, van den Dool Rokus E C, Mahes Sandjiv S, Corsmit Oskar T, Vlaar Alexander P J, Koolbergen Dave R, Veelo Denise P, Sperna Weiland Nicholaas H, Immink Rogier V
Department of Anaesthesiology, Amsterdam UMC, University of Amsterdam, Amsterdam Cardiovascular Sciences, Amsterdam, the Netherlands; Department of Intensive Care, Amsterdam UMC, University of Amsterdam, Amsterdam, the Netherlands.
Department of Anaesthesiology, Amsterdam UMC, University of Amsterdam, Amsterdam Cardiovascular Sciences, Amsterdam, the Netherlands.
Br J Anaesth. 2025 Apr;134(4):1009-1017. doi: 10.1016/j.bja.2024.12.037. Epub 2025 Feb 28.
To maintain adequate perfusion, cerebral blood flow (CBF) is preserved by changes in cerebrovascular resistance (CVR) inversely related to fluctuations in mean arterial blood pressure (MAP). It has been hypothesised that during progressive hypotension, a lower limit of cerebral autoregulation (LLCA) is reached beyond which cerebrovascular dilation becomes exhausted and CBF starts to decrease together with BP. We tested this hypothesis by assessing CVR above and below the LLCA.
Radial arterial pressure, thermodilution cardiac output (CO), and mean middle cerebral artery blood velocity (MCAV) were recorded during sustained intraoperative hypotension clinically needed for off-pump aortic root aneurysm surgery. For each participant, the individual LLCA was determined. Systemic vascular resistance (SVR) and CVR were calculated, and changes below and above the LLCA were assessed with a generalised linear effect models.
For 50 participants undergoing aortic root surgery who met inclusion criteria, LLCA was located at 58 (12) mm Hg, with a corresponding MCAV of 32 (8) cm s and CO of 5.1 (1.2) L min. Above the LLCA, the decline in CVR and SVR were similar, both with 19% per 10 mm Hg decrease in MAP (P<0.001). Below the LLCA, CVR declined at a lower rate (7% per 10 mm Hg), whereas the decrease in SVR was 13% per 10 mm Hg decrease in MAP (both P<0.001).
The continuing decline of CVR below the LLCA indicated that brain vasculature is still able to react on changing BP. This implies that LLCA should not be regarded as a fixed point but rather a transitional zone between exhausted and normally functioning autoregulation.
为维持充足灌注，脑血管阻力（CVR）会发生变化以维持脑血流量（CBF），CVR与平均动脉压（MAP）的波动呈负相关。据推测，在进行性低血压期间，会达到脑自动调节下限（LLCA），超过此限度，脑血管扩张能力耗尽，CBF开始随血压下降。我们通过评估LLCA上下的CVR来验证这一假设。
在非体外循环主动脉根部动脉瘤手术临床所需的持续性术中低血压期间，记录桡动脉压、热稀释法心输出量（CO）和大脑中动脉平均血流速度（MCAV）。为每位参与者确定其个体LLCA。计算全身血管阻力（SVR）和CVR，并使用广义线性效应模型评估LLCA上下的变化。
50名符合纳入标准的接受主动脉根部手术的参与者，LLCA为58（12）mmHg，相应的MCAV为32（8）cm/s，CO为5.1（1.2）L/min。在LLCA以上，CVR和SVR的下降相似，MAP每降低10 mmHg两者均下降19%（P<0.001）。在LLCA以下，CVR下降速率较低（每10 mmHg下降7%），而SVR每10 mmHg下降13%（两者P<0.001）。
LLCA以下CVR持续下降表明脑血管系统仍能对血压变化做出反应。这意味着不应将LLCA视为一个固定点，而应看作是自动调节耗尽与正常功能之间的过渡区域。
