Central Venous Blood Gas Analysis: An Alternative to Arterial Blood Gas Analysis for pH, PCO2, Bicarbonate, Sodium, Potassium and Chloride in the Intensive Care Unit Patients

Aims: Arterial blood gas (ABG) analysis is a frequently ordered test in intensive care unit (ICU) and can analyze electrolyte in addition to pH and blood gases. Venous blood gas (VBG) analysis is a safer procedure and may be an alternative for ABG. Electrolyte estimation by auto analyzer usually takes 20-30 minutes. This study was aimed to investigate the correlation of pH, PCO2, bicarbonate, sodium, potassium, and chloride (electrolytes) between ABG and central VBG in ICU patients. Materials and methods: This was a prospective observational study conducted in medical college hospital ICU. Adult patients requiring ABG and electrolyte estimation as a part of their clinical care were consecutively included in the study. Patients having any intravenous infusion or who were pregnant were excluded. Venous samples were taken within 2 minutes of arterial sampling from in situ central line. Data were analyzed using Bland-Altman methods. Results: A total of 110 patient's paired blood samples were analyzed. The mean difference between arterial and central venous values of pH, PCO2, bicarbonate, sodium, potassium, and chloride was 0.04 units, -5.84 mm Hg, 0.89 mmol/L, -1.8 mEq/L, -0.04 mEq/L, and -0.89 mEq/L, respectively. The correlation coefficients for pH, PCO2, HCO3-, sodium, potassium, and chloride were 0.799, 0.831, 0.892, 0.652, 0.599 and 0.730, respectively. Limits of agreement (95%) were within acceptable limits. Conclusion: Central venous pH, PCO2, and bicarbonate may be an acceptable substitute for ABG in patients admitted in the ICU. However caution should be exercised while applying electrolyte measurements.