Concordance of CO2 gaps measured using peripheral and central venous blood in patients diagnosed with septic shock

Erdem Yalcinkaya, Department of Pulmonary and Critical Care Medicine, Marmara University School of Medicine, Istanbul, Turkiye
Umut Sabri Kasapoglu, Department of Pulmonary and Critical Care Medicine, Marmara University School of Medicine, Istanbul, Turkiye
Huseyin Arikan, Department of Pulmonary and Critical Care Medicine, Marmara University School of Medicine, Istanbul, Turkiye
Nazım Onur Sahin, Department of Pulmonary and Critical Care Medicine, Marmara University School of Medicine, Istanbul, Turkiye
Betul Yildiz, Department of Pulmonary and Critical Care Medicine, Marmara University School of Medicine, Istanbul, Turkiye
Esra Tekin, Department of Critical Care Medicine, Marmara University Hospital, Istanbul, Turkiye
Aybuke Selcuk, Department of Pulmonary and Critical Care Medicine, Marmara University School of Medicine, Istanbul, Turkiye
Emel Eryuksel, Department of Pulmonary and Critical Care Medicine, Marmara University School of Medicine, Istanbul, Turkiye
Sait Karakurt, Department of Pulmonary and Critical Care Medicine, Marmara University School of Medicine, Istanbul, Turkiye

Objective: This study evaluates the venous-arterial CO₂ difference (Pv-aCO₂) from peripheral venous blood (Pv-aCO₂p) as a less invasive alternative to central venous Pv-aCO₂ for assessing tissue perfusion in septic shock. Methods: A prospective, single-center study included 54 septic shock patients with central venous catheters placed within 24 h of intensive care unit admission. Blood samples from arterial, central venous, and peripheral venous sources were analyzed. Correlation analyses and Bland-Altman plots were used to assess agreement between Pv-aCO₂p and central Pv-aCO₂. Results: Patients had a mean age of 70 years, and 51.9% were male. The median SOFA score was 8.5, and the mean APACHE-II score was 22.7. The Pv-aCO₂p gap was 8 mmHg, whereas the central Pv-aCO₂ gap was 6 mmHg. A moderate correlation was found between Pv-aCO₂p and central Pv-aCO₂ (r = 0.593, p < 0.001), with stronger correlations observed in patients with arterial lactate ≥2 mmol/L (r = 0.673) and hemoglobin <8 g/dL (r = 0.625). Bland-Altman analysis revealed a mean difference of 8.278 mmHg between arterial and peripheral pCO₂. Conclusions: Peripheral Pv-aCO₂p correlates well with central Pv-aCO₂ and can serve as a less invasive alternative for assessing tissue perfusion in septic shock patients. It offers practical utility when central venous access is not available, aiding in early clinical decisions.

Keywords: Pv-aCO2. Tissue perfusion. Septic shock. Veno-arterial CO2 difference. Hemodynamic monitoring.