Agreement between central venous and arterial blood gas measurements in the intensive care unit.

BACKGROUND AND OBJECTIVES Venous blood gas (VBG) analysis is a safer procedure than arterial blood gas (ABG) analysis and may be an alternative for determining acid-base status. The objective of this study was to examine the agreement between ABG and central VBG samples for all commonly used parameters in a medical intensive care unit (ICU) population. DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS We performed a single-center, prospective trial to assess the agreement between arterial and central VBG measurements in a medical ICU. Adult patients who were admitted to the ICU and required both a central venous line and an arterial line were enrolled. When an ABG was performed, a central venous sample was obtained to examine the agreement among the pH, Pco(2), and bicarbonate. Data comparing central and peripheral VBG values were also obtained. RESULTS The mean arterial minus venous difference for pH, Pco(2), and bicarbonate was 0.027, -3.8, and -0.80, respectively. Bland-Altman plots for agreement of pH, Pco(2), and bicarbonate showed 95% limits of agreement of -0.028 to 0.081, -12.3 to 4.8, and -4.0 to 2.4, respectively. Regression equations were derived to predict arterial values from venous values as follows: Arterial pH = -0.307 + 1.05 x venous pH, arterial Pco(2) = 0.805 + 0.936 x venous Pco(2), and arterial bicarbonate = 0.513 + 0.945 x venous bicarbonate. The mean central minus peripheral differences for pH, Pco(2), and bicarbonate were not clinically important. CONCLUSIONS Peripheral or central venous pH, Pco(2), and bicarbonate can replace their arterial equivalents in many clinical contexts encountered in the ICU.