Background: 

Cerebral autoregulation (CA) continuously adjusts cerebrovascular resistance to maintain cerebral blood flow (CBF) constant despite changes in blood pressure. Also, CBF is proportional to changes in arterial carbon dioxide (CO₂) (cerebrovascular CO₂ reactivity). Hypercapnia elicits cerebral vasodilation that attenuates CA efficacy, while hypocapnia produces cerebral vasoconstriction that enhances CA efficacy. In this study, we quantified the influence of sevoflurane anesthesia on CO₂ reactivity and the CA-CO₂ relationship.

Methods: 

We studied patients with type 2 diabetes mellitus (DM), prone to cerebrovascular disease, and compared them to control subjects. In 33 patients (19 DM, 14 control), end-tidal CO₂, blood pressure, and CBF velocity were monitored awake and during sevoflurane-based anesthesia. CA, calculated with transfer function analysis assessing phase lead (degrees) between low-frequency oscillations in CBF velocity and mean arterial blood pressure, was quantified during hypocapnia, normocapnia, and hypercapnia.

Results: 

In both control and DM patients, awake CO₂ reactivity was smaller (2.8%/mm Hg CO₂) than during sevoflurane anesthesia (3.9%/mm Hg; P<0.005). Hyperventilation increased CA efficacy more (3 deg./mm Hg CO₂) in controls than in DM patients (1.8 deg./mm Hg CO₂; P<0.001) in both awake and sevoflurane-anesthetized states.

Conclusions: 

The CA-CO₂ relationship is impaired in awake patients with type 2 DM. Sevoflurane-based anesthesia does not further impair this relationship. In patients with DM, hypocapnia induces cerebral vasoconstriction, but CA efficacy does not improve as observed in healthy subjects.

中文翻译：

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二氧化碳对 2 型糖尿病患者七氟醚麻醉期间脑自动调节的影响

背景： 

尽管血压发生变化，但脑自动调节 (CA) 会不断调整脑血管阻力以维持脑血流量 (CBF) 恒定。此外，CBF 与动脉二氧化碳 (CO ₂ ) 的变化（脑血管 CO ₂反应性）成正比。高碳酸血症引起脑血管舒张，减弱 CA 疗效，而低碳酸血症引起脑血管收缩，增强 CA 疗效。在本研究中，我们量化了七氟烷麻醉对 CO ₂反应性和 CA-CO ₂关系的影响。

方法： 

我们研究了易患脑血管疾病的 2 型糖尿病 (DM) 患者，并将他们与对照组进行了比较。在 33 名患者（19 名糖尿病患者，14 名对照组）中，在清醒时和基于七氟醚的麻醉期间监测呼气末 CO ₂、血压和 CBF 速度。在低碳酸血症、正常碳酸血症和高碳酸血症期间量化 CA，通过传递函数分析评估 CBF 速度低频振荡与平均动脉血压之间的相位超前（度）。

结果： 

在对照组和 DM 患者中，清醒时的 CO ₂反应性 (2.8%/mm Hg CO ₂ ) 低于七氟烷麻醉期间的反应性 (3.9%/mm Hg；P <0.005)。在清醒状态和七氟醚麻醉状态下，过度通气增加 CA 疗效（3 deg./mm Hg CO ₂）比 DM 患者（1.8 deg./mm Hg CO ₂；P <0.001）更多。

结论： 

清醒的 2 型糖尿病患者的 CA-CO _{2关系受损。}基于七氟醚的麻醉不会进一步削弱这种关系。在 DM 患者中，低碳酸血症会引起脑血管收缩，但 CA 疗效并没有像在健康受试者中观察到的那样得到改善。