We determined the clinical efficacy of using the venous CO2 value, as obtained with routine "electrolytes," in acid-base management. Venipuncture samples for venous CO2 content and chloride concentrations were obtained in 336 patients with arterial blood pH, Pao2 Paco2, and oxygen saturation determinations. The linear correlation between actual calculated arterial HCO3and the measured venous CO2 was significant (P <.001). Using venous CO2, chloride, and arterial pH values, we present various prediction equations for estimating arterial HCO3-. We determined the effects of time delay, exposure to air, and acute changes in arterial blood pH and Paco2 on venous CO 1evels. Venous CO2 determinations should not be substituted for the arterial HCO3- value in the Henderson-Hasselbalch equation to calculate arterial blood pH or Paco2. Clinically, the venous CO2 value has little direct use, but when venous CO2 content is abnormal, it should alert the clinician to the need for obtaining arterial blood gas and pH values.
(Arch Intern Med 139:440-442, 1979).