Correlation and agreement between arterial and central venous blood pH, PO2, PCO2 and HCO3− values of mechanically ventilated patients in intensive care unit: A prospective observational study

Background The procedure for arterial blood sampling can be technically difficult with limitations and complications. Aims To evaluate the correlation and agreement between arterial and central venous blood pH, PO2, PCO2 and HCO3− values and infer whether central venous blood gas (CVBG) values could replace arterial blood gas (ABG) values. Design Prospective observational study. Methods and Material A total of 100 samples were collected from 50 adult normotensive and normothermic patients requiring mechanical ventilation. Arterial blood was collected from radial artery and within 2 minutes central venous blood was withdrawn from the same patient. Correlation and agreement was tested using Pearson's Correlation and Bland Altman Analysis. Results The pH, PO2, PCO2 and HCO3− of CVBG correlated significantly with arterial values (rpH = 0.88, p < 0.001; rPO2=0.358rPO2=0.358, p < 0.05; rPCO2=0.470rPCO2=0.470, p < 0.001 and rHCO3=0.714rHCO3=0.714, p < 0.001). Regression equations were derived to predict AVG values from CVBG values as follows: Arterial pH = 0.879 × central venous pH + 0.9422 (constant), arterial PO2 = 0.421 × central venous PO2 + 114.4 (constant), R2 = 0.128, arterial PCO2 = 0.429 × central venous PCO2 + 24.627 (constant), R2 = 0.2205 and arterial HCO3 = 1.045 × central venous HCO3 + 3.402 (constant), R2 = 0.5101.The mean arterial minus venous difference for pH, PO2, PCO2, and bicarbonate was 0.053 ± 0.014, 56.04 ± 15.74, 2.20 ± 4.4 and 4.30 ± 1.64 respectively. Bland-Altman plots for agreement of pH, PO2, PCO2, and bicarbonate showed 95% limits of agreement of −0.04 to 0.146, −52.51 to 164.59, −26.61 to 31.01 and −7.0 to 15.6, respectively. Conclusions The arterial pH, PO2, PCO2 and HCO3− values correlated well with central venous values. However, only the arterial pH value can replace the central venous pH value.