Correlation of central venous and arterial blood gas measurements in mechanically ventilated trauma patients

Hypothesis: Central venous blood gas (VBG) measurements of pH, PCO ₂, and base excess can be substituted for the same values obtained from an arterial blood gas (ABG) analysis in mechanically ventilated trauma patients, obviating the need for arterial puncture. Design and Setting: Prospective comparison of 99 sets of VBGs and ABGs at a level 1 academic trauma center. Patients: A consecutive sample of 25 trauma patients admitted to the intensive care unit who required mechanical ventilation and had both central venous and arterial catheters. Main Outcome Measures: Pearson correlations and Bland-Altman limits of agreement (LOAs) for pH, PCO₂, and base excess values from each set of VBGs and ABGs. Results: When VBG and ABG values were compared, pH had R=0.92, P<.001, and 95% LOAs of -0.09 to 0.03; PCO ₂, R=0.88, P<.001, and 95% LOAs of -2.2 to 10.9; and base excess, R=0.96, P<.001, and 95% LOAs of -2.2 to 1.8. A receiver operating characteristic curve showed that a central venous PCO₂ of 50 mm Hg had 100% sensitivity and 84% specificity for determining significant hypercarbia (arterial PCO₂>50 mm Hg). Conclusions: Central venous and arterial PCO₂, pH, and base excess values correlate well, but their LOAs represent clinically significant ranges that could affect management. Although VBGs cannot be substituted for ABGs in mechanically ventilated trauma patients during the initial phases of resuscitation, clinically reliable conclusions can be reached with VBG analysis.