Agreement and Correlation between Arterial and Central Venous Blood Gas Following Coronary Artery Bypass Graft Surgery

Introduction: Arterial blood sampling, used to assess patients in acute conditions, may result in complications such as thrombosis and embolism. However, it can be replaced by venous blood sampling, but there is a dearth of information on this.

Aim: To assess the correlation and agreement between the arterial and central venous blood gases analyses in patients undergoing elective Coronary Artery Bypass Graft (CABG) surgery.

Materials and methods: In this cross-sectional study, 100 ICU patients undergoing elective CABG surgery were recruited. 2 mm arterial and a 2 mm venous blood samples were obtained from each patient's arterial and central venous lines, respectively. To predict Arterial Blood Gas (ABG) values based on central Venous Blood Gas (VBG) values, the linear regression analysis was used and for evaluating their agreement Bland-Altman method was used.

Results: In total of 200 samples were obtained. The mean and Standard Deviation (SD) of age was 58.9±9.1 years and 51% of the participants were female. There was a strong correlation between ABG and central VBG values regarding pH, partial Pressure of Carbon Dioxide (PCO₂), Bicarbonate (HCO₃) and Base Excess (BE) (r= 0.73, r=0.74, r=0.67 and r=0.71, respectively; p<0.001); however, the correlation between the arterial and venous Partial Pressure of Oxygen (PO₂) and Oxygen Saturation (SO₂) was moderate (r=0.29, p=0.005 and r=0.27, p=0.006, respectively). The Bland-Altman analysis showed an excellent agreement between all the variables (p<0.001).

Conclusion: Central VBG analysis cannot replace ABG analysis in measuring exact PO₂ status, necessitating arterial sampling in some matters, but with respect to the accuracy of pulse oximetry measurements in determining the exact PO₂ status, for the rest of the indices a central VBG rather than an ABG can be utilised for determining patient's acid-base status. Particularly in patients who are hospitalised for a long time and have a central venous catheter in place like patients who have undergone CABG, thus reducing the risk and need for invasive arterial sampling.