Influence of solutes in plasma on the total CO2 content determination: implications for clinical disorders

The purpose of these experiments was to determine the effect of non-aqueous solids on the total CO2 content of plasma. Two major groups of compounds were explored; those which reduced the total CO2 content, such as saline, and those which did not, such as albumin. To assess the former, sufficient sodium chloride was added to a bicarbonate solution gassed with 5% CO2 to increase the total volume by 10%. The total CO2 content fell the predicted 10% from 27.2 to 24.5 mmol/L when sodium chloride was added. In contrast, when the aqueous volume of a bicarbonate solution gassed with 5% CO2 was decreased by isohydric albumin, the total CO2 content was not reduced. We hypothesize that carbamino-compounds were formed with albumin and this raised the volume of CO2 released by an excess of acid. Therefore, the calculated pK' for the bicarbonate buffer system, which is derived from solutions lacking proteins, is not solely determined by the concentrations of bicarbonate, dissolved CO2, carbonate and carbonic acid when albumin is present. The clinical implications of these results will be discussed.