The In-Vitro and In-Vivo Carbon Dioxide Dissociation Curves of True Plasma A Theoretical Analysis

Abstract

Dissociation curves were derived by calculation at a variety of normal and pathologic blood and body fluid compositions and volumes. The nature of the difference between in-vitro and in-vivo curves was analyzed. The difference between the course of mixed venous and of arterial plasma composition during in-vivo CO2 titration was stressed; and it was pointed out that only mixed venous sampling can be expected to yield accurate in-vivo CO2 titration curves. It was shown that, when blood CO2 tension is changed in-vivo, the conventionally derived "true plasma standard bicarbonate" and "blood buffer base" do not remain unchanged, in contrast with their behavior in in-vitro CO2 titration. Methods were given to correct these 2 indices, so that they become invariant with the CO2 tension at which the sample is withdrawn, and thus can serve their function as measures of fixed acid excess or deficit.