BackgroundSystemic blood flow in patients on extracorporeal assist devices is frequently not or only minimally pulsatile. Loss of pulsatile brain perfusion, however, has been implicated in neurological complications. Furthermore, the adverse effects of absent pulsatility on the cerebral microcirculation are modulated similarly as CO2 vasoreactivity in resistance vessels. During support with an extracorporeal assist device swings in arterial carbon dioxide partial pressures (PaCO2) that determine cerebral oxygen delivery are not uncommon—especially when CO2 is eliminated by the respirator as well as via the gas exchanger of an extracorporeal membrane oxygenation machine. We, therefore, investigated whether non-pulsatile flow affects cerebrovascular CO2 reactivity (CVR) and regional brain oxygenation (rSO2).MethodsIn this prospective, single-centre case-control trial, we studied 32 patients undergoing elective cardiac surgery. Blood flow velocity in the middle cerebral artery (MCAv) as well as rSO2 was determined during step changes of PaCO2 between 30, 40, and 50 mmHg. Measurements were conducted on cardiopulmonary bypass during non-pulsatile and postoperatively under pulsatile blood flow at comparable test conditions. Corresponding changes of CVR and concomitant rSO2 alterations were determined for each flow mode. Each patient served as her own control.ResultsMCAv was generally lower during hypocapnia than during normocapnia and hypercapnia (p < 0.0001). However, the MCAv/PaCO2 slope during non-pulsatile flow was 14.4 cm/s/mmHg [CI 11.8–16.9] and 10.4 cm/s/mmHg [CI 7.9–13.0] after return of pulsatility (p = 0.03). During hypocapnia, non-pulsatile CVR (4.3 ± 1.7%/mmHg) was higher than pulsatile CVR (3.1 ± 1.3%/mmHg, p = 0.01). Independent of the flow mode, we observed a decline in rSO2 during hypocapnia and a corresponding rise during hypercapnia (p < 0.0001). However, the relationship between ΔrSO2 and ΔMCAv was less pronounced during non-pulsatile flow.ConclusionsNon-pulsatile perfusion is associated with enhanced cerebrovascular CVR resulting in greater relative decreases of cerebral blood flow during hypocapnia. Heterogenic microvascular perfusion may account for the attenuated ΔrSO2/ΔMCAv slope. Potential hazards related to this altered regulation of cerebral perfusion still need to be assessed.Trial registrationThe study was retrospectively registered on October 30, 2018, with Clinical Trial.gov (NCT03732651).

中文翻译：

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非搏动血流与脑血管二氧化碳反应性增强以及脑血流与局部脑氧合之间的减弱相关

背景 使用体外辅助装置的患者的全身血流通常没有脉动或仅有最低限度的脉动。然而，搏动性脑灌注的丧失与神经系统并发症有关。此外，缺乏搏动对脑微循环的不利影响与阻力血管中的 CO2 血管反应性类似。在使用体外辅助设备支持期间，决定大脑供氧量的动脉二氧化碳分压 (PaCO2) 的波动并不少见——尤其是当 CO2 被呼吸器以及体外膜氧合机的气体交换器清除时。因此，我们研究了非脉动血流是否影响脑血管 CO2 反应性 (CVR) 和局部脑氧合 (rSO2)。在单中心病例对照试验中，我们研究了 32 名接受择期心脏手术的患者。在 PaCO2 在 30、40 和 50 mmHg 之间的阶跃变化期间，确定了大脑中动脉 (MCAv) 中的血流速度以及 rSO2。在可比较的测试条件下，在非脉动和术后脉动血流下对体外循环进行测量。确定每种流动模式的 CVR 的相应变化和伴随的 rSO2 变化。每个患者作为她自己的对照。结果 低碳酸血症期间的 MCAv 通常低于正常碳酸血症和高碳酸血症期间 (p < 0.0001)。然而，非脉动血流期间的 MCAv/PaCO2 斜率是 14.4 cm/s/mmHg [CI 11.8-16.9] 和 10.4 cm/s/mmHg [CI 7.9-13.0] 在脉动恢复后 (p = 0.03)。低碳酸血症期间，非搏动性 CVR (4.3 ± 1. 7%/mmHg) 高于脉动 CVR (3.1 ± 1.3%/mmHg, p = 0.01)。独立于流量模式，我们观察到低碳酸血症期间 rSO2 下降，而高碳酸血症期间相应升高（p < 0.0001）。然而，在非脉动血流期间，ΔrSO2 和 ΔMCAv 之间的关系不太明显。结论非脉动灌注与增强的脑血管 CVR 相关，导致低碳酸血症期间脑血流的更大相对减少。异源微血管灌注可以解释衰减的 ΔrSO2/ΔMCAv 斜率。与这种脑灌注调节改变相关的潜在危害仍需评估。 试验注册 该研究于 2018 年 10 月 30 日在 Clinical Trial.gov (NCT03732651) 进行了回顾性注册。我们观察到低碳酸血症期间 rSO2 下降，而高碳酸血症期间 rSO2 相应升高（p < 0.0001）。然而，在非脉动血流期间，ΔrSO2 和 ΔMCAv 之间的关系不太明显。结论非脉动灌注与增强的脑血管 CVR 相关，导致低碳酸血症期间脑血流量的更大相对减少。异源微血管灌注可以解释衰减的 ΔrSO2/ΔMCAv 斜率。与这种脑灌注调节改变相关的潜在危害仍然需要评估。 试验注册 该研究于 2018 年 10 月 30 日在 Clinical Trial.gov (NCT03732651) 进行了回顾性注册。我们观察到低碳酸血症期间 rSO2 下降，而高碳酸血症期间 rSO2 相应升高（p < 0.0001）。然而，在非脉动血流期间，ΔrSO2 和 ΔMCAv 之间的关系不太明显。结论非脉动灌注与增强的脑血管 CVR 相关，导致低碳酸血症期间脑血流的更大相对减少。异源微血管灌注可以解释衰减的 ΔrSO2/ΔMCAv 斜率。与这种脑灌注调节改变相关的潜在危害仍需评估。 试验注册 该研究于 2018 年 10 月 30 日在 Clinical Trial.gov (NCT03732651) 进行了回顾性注册。ΔrSO2 和 ΔMCAv 之间的关系在非搏动性血流期间不太明显。结论非搏动性灌注与增强的脑血管 CVR 相关，导致低碳酸血症期间脑血流的相对减少更大。异源微血管灌注可以解释衰减的 ΔrSO2/ΔMCAv 斜率。与这种脑灌注调节改变相关的潜在危害仍需评估。 试验注册 该研究于 2018 年 10 月 30 日在 Clinical Trial.gov (NCT03732651) 进行了回顾性注册。ΔrSO2 和 ΔMCAv 之间的关系在非搏动性血流期间不太明显。结论非搏动性灌注与增强的脑血管 CVR 相关，导致低碳酸血症期间脑血流的相对减少更大。异源微血管灌注可能是衰减 ΔrSO2/ΔMCAv 斜率的原因。与这种脑灌注调节改变相关的潜在危害仍需评估。 试验注册 该研究于 2018 年 10 月 30 日在 Clinical Trial.gov (NCT03732651) 进行了回顾性注册。