A proposal for analysing the acid-base balance at steady state in vivo

[H+] in plasma in vivo is composed of a PCO2-dependent component [H+]* and a PCO2-independent component delta [H+]. The correct equation for the calculation of [H+]* was found by referring to the slope of the regression line between the venous-arterial difference of delta [H+] and that of PCO2. Using [H+]*, the buffer value in vivo and the base excess were calculated. Since the base excess was hyperbolic against delta [H+] and dependent on PCO2, we concluded that it was better to use delta [H+] rather than the base excess to evaluate the metabolic change of [H+] in plasma.