Progress on the Effects of Permissive Hypercapnia on the CNS During the Intraoperative Period: A Narrative Review

Previous experimental findings and clinical evidence have shown the important role of carbon dioxide (CO₂) in regulating cerebral vascular tension. CO₂ can affect the CNS through various mechanisms. With factors such as patient physiology or surgical interventions potentially causing increased arterial partial pressure of carbon dioxide (PaCO₂) levels during mechanical ventilation in general anesthesia, it is important to explore the potential risks or benefits of intraoperative permissive hypercapnia on brain function. In November 2023, we conducted a thorough review of PubMed to establish the article outline. Articles that were non-English or repetitive were eliminated. We collected information on the year, topic, key findings, and opinions of each article. This review not only comprehensively summarizes the factors that contribute to the elevation of intraoperative PaCO₂, but also explores the impact of fluctuations in PaCO₂ levels on the CNS and the underlying mechanisms involved. At the same time, this article provides our understanding of the potential clinical significance of actively regulating PaCO₂ levels. In addition, we propose that the aspects of permissive hypercapnia can be further studied to provide a reliable basis for clinical decision-making. The effects of permissive hypercapnia on the CNS remain a topic of debate. Further prospective randomized controlled studies are needed to determine if permissive hypercapnia can be safely promoted during mechanical ventilation in general anesthesia.