Correlation between Arterial and Central Venous Blood Gas Values in Critically Ill Patients

Arterial blood gas (ABG) analysis is a commonly and golden standard performed procedure that is often used to assess the acid-base status along with adequacy of ventilation and oxygenation among predominantly critically/acutely ill patients. Unfortunately, prolonged arterial catheterization or repeated direct blood sampling from the artery is associated with rare, but serious, complications to the patient as well as the health care providers. Patients who require frequent blood gas testing often have indwelling central venous catheters for the administration of intravenous medications or the monitoring of central vascular pressures, allowing for repeated central venous blood gas (VBG) analysis. Venous blood gas analysis requires fewer punctures, is a relatively safer procedure for both the patient and health care provider, and may be alternative to ABG analysis (Walkey et al., 2010), (Lorente et al., 2006), Scheer et al., 2002), (Valentine et al., 2005).This study was aimed to determine the correlation between arterial and central venous blood gas measurements for monitoring of acid-base balance & oxygenation in the critically ill patients. Prospective comparative study of 90 samples from 45 patients with diverse medical& surgical conditions was conducted. Arterial and venous values for pressure of hydrogen (pH), partial pressure of carbon dioxide (PCO2), bicarbonate (HCO3), partial pressure of oxygen (PO2), and oxygen saturation (SO2)were obtained simultaneously from each patient. Identity plot was used to check the perfect agreement between the paired measurements. The strength of the relationship between the arterial and venous gas values was assessed with the Pearson product–moment correlation coefficient test. Arterial pH and venous pH were found to be correlated significantly (Pearson correlation coefficient r = 0.93, 95% confidence limits of r = 0.90 to 0.96, P < 0.001). There was a strong correlation between the arterial and venous PCO2(r = 0.85, 95% confidence limits of r = 0.79 to 0.90, P < 0.0001), HCO3 (r = 0.96, 95% confidence limits 0.93 to 0.97, P = 0.0001). The correlation between the arterial and venous PO2 and SO2 were not statistically significant PO2 levels (r = - 0.38, 95% confidence limits of r = 0.19 - 0.55, P>0.05) &(r = -0.08, 95% confidence limits of r = -0.28 - 0.13, P >0.05) respectively. Conclusion: there was a perfect correlation between the arterial and central venous measurements of acid – base (pH, PCO2, HCO3-) in the critically ill patients. While, it is difficult to conclude at least a basic agreement between the arterial and central venous measurements of oxygenation (PO2 & SO2).