Impact of Permissive Hypercapnia on Postoperative Early Plasma Neurofilament Light Chain in Elderly Patients Undergoing Laparoscopic Surgery: A Prospective, Randomized Controlled Trial

Background: The effects of intraoperative permissive hypercapnia (PaCO2 of 45- 55 mmHg) on the central nervous system remain unclear. Neurofilament light chain (NfL, a protein found in the axons and nerve fibers of neurons) has been associated with central nervous system disorders. This study investigated the effect of intraoperative permissive hypercapnia on plasma NfL concentration 1 day postoperatively, and in turn on the central nervous system, during laparoscopic surgery.<br /> Methods: This investigation was a prospective, single-blind randomized controlled trial. Eighty-four individuals aged above 60 years were randomly allocated to either the normocapnia group with an PaCO2 of 35- 45 mmHg (n=42) or the hypercapnia group with a PaCO2 of 45- 55 mmHg (n=42). The primary outcome was the 1-day postoperative plasma NfL concentration. Secondary outcomes included the area under the curve (AUC) values for PaCO2 and regional cerebral oxygen saturation (rSO(2)). The Mann-Whitney U-test was mainly used to analyze the outcomes.<br /> Results: The final analysis included 38 and 40 patients in the normocapnia and hypercapnia groups, respectively. There was no statistically significant difference observed between the groups regarding the preoperative and 1-day postoperative plasma NfL concentration (14.0 [11.1, 19.9] vs 16.3 [9.06, 19.9] pg/mL, P> 0.05; 23.4 [16.8, 32.3] vs 21.5 [15.6, 29.9] pg/mL, P> 0.05, respectively). However, in both groups, the postoperative plasma concentration of NfL showed a significant increase when compared with the preoperative levels (both P < 0.001). The AUCs of PaCO2 and rSO(2) from the beginning to the end of the pneumoperitoneum were significantly higher in the hypercapnia group compared with the normocapnia group (both P< 0.05).<br /> Conclusion: Our results indicate that intraoperative permissive hypercapnia targeting a PaCO2 of 45- 55 mmHg does not significantly influence postoperative early plasma NfL elevation levels in elderly patients undergoing laparoscopic surgery. During general anesthesia, intraoperative permissive hypercapnia might not significantly impact the central nervous system.