Evaluation of adjusted central venous blood gases versus arterial blood gases of patients in post-operative paediatric cardiac surgical intensive care unit

BACKGROUND AND AIMS: Central venous catheters are in situ in most of the intensive care unit (ICU) patients, which may be an alternative for determining acid-base status and can reduce complications from prolonged arterial cannulation. The aim of this study was to examine the reliability between adjusted central venous blood gas (aVBG) and arterial blood gas (ABG) samples for pH, partial pressure of carbon-di-oxide (pCO2), bicarbonate (HCO3 (-)), base excess (BE) and lactates in paediatric cardiac surgical ICU. METHODS: We applied blood gas adjustment rule, that is aVBG pH = venous blood gas (VBG) pH +0.05, aVBG CO2 = VBG pCO2 - 5 mm Hg from the prior studies. In this study, we validated this relationship with simultaneous arterial and central venous blood obtained from 30 patients with four blood sample pairs each in paediatric cardiac surgical ICU patients. RESULTS: There was a strong correlation (R i.e., Pearson's correlation) between ABG and aVBG for pH = 0.9544, pCO2 = 0.8738, lactate = 0.9741, HCO3 (-) = 0.9650 and BE = 0.9778. Intraclass correlation co-efficients (ICCs) for agreement improved after applying the adjustment rule to venous pH (0.7505 to 0.9454) and pCO2 (0.4354 to 0.741). Bland Altman showed bias (and limits of agreement) for pH: 0.008 (-0.04 to + 0.057), pCO2: -3.52 (-9.68 to +2.65), lactate: -0.10 (-0.51 to +0.30), HCO3 (-): -2.3 (-5.11 to +0.50) and BE: -0.80 (-3.09 to +1.49). CONCLUSION: ABG and aVBG samples showed strong correlation, acceptable mean differences and improved agreement (high ICC) after adjusting the VBG. Hence, it can be promising to use trend values of VBG instead of ABG in conjunction with a correction factor under stable haemodynamic conditions.