Effects of Permissive Hypercapnia Versus Normocapnia on Cerebral Oxygenation and Postoperative Outcomes in Adult Surgical Patients: A Systematic Review and Meta‐Analysis
Areej Riaz, Amna Khan, Fatima Nawaz, Amna Shafaqat, Hadia Sheraz, Mohammed M. AlTelbany, Nauroze Khan, Adeel Ahmed Khan, Bismah Rafique Malik, Hermann YokoloBackground
Evidence suggests that intraoperative cerebral hypoxia is the main contributor of postoperative neurological complications, particularly postoperative cognitive dysfunction (POCD) and postoperative delirium (POD) in surgical patients. Permissive hypercapnia may improve cerebral oxygenation by increasing cerebral blood flow, but its perioperative benefits remain uncertain.
Research Question
In adult surgical patients, is permissive hypercapnia associated with improved cerebral oxygenation and perioperative outcomes compared with normocapnia?
Method
PubMed, Embase, Cochrane CENTRAL, and ClinicalTrials.gov were searched from inception to April 2026 for randomized controlled trials (RCTs) and cohort studies of adult surgical patients receiving permissive hypercapnia. Primary outcome included was intraoperative regional cerebral oxygen saturation (rSO 2 ). Secondary outcomes were POCD, POD, all‐cause mortality, respiratory parameters, arterial blood gas variables, and hemodynamic outcomes.
Results
Seven studies comprising 824 patients were included. Permissive hypercapnia significantly improved intraoperative rSO 2 (MD = 6.65%; 95% Cl: [4.93, 8.37]; p < 0.00001), PaCO 2 (MD = 10.21 mmHg (95% CI: [8.81, 11.60]; p < 0.00001), and end‐tidal CO 2 (MD = 10.83 mmHg; 95% CI [7.91, 13.76]; p < 0.00001), and significantly reduced dead space fraction (MD = −6.38%; 95% CI: [–9.26, −3.50], p < 0.00001), and arterial pH (MD = −0.08; 95% CI: [‐0.09, −0.07]; p < 0.00001). Hypercapnia had no significant effect on PaO 2 , mean arterial pressure, and heart rate. Qualitative analysis suggested reduced incidence of POCD with no significant effect on POD.
Conclusion
Permissive hypercapnia improves intraoperative cerebral oxygenation while maintaining hemodynamic stability. However, the available evidence for POCD and POD is limited and heterogeneous. Larger RCTs and observational studies are needed to confirm its effects on clinical outcomes before routine implementation.