Determination of total carbon dioxide in blood and plasma by means of the cediometer. Theory and experimental verification

Abstract

The cediometer, an instrument for the determination of total carbon dioxide in blood and plasma samples, consists of a closed system incorporating an electrode chamber filled with a NaHCO 3 solution, a sample chamber in which the CO 2 of injected blood or plasma is set free with an acid reagent and a roller pump which circulates the CO 2-containing gas until the P CO 2 , has become uniform throughout the system and a stable pH in the electrode chamber solution has been reached. The relationship between this pH and the total carbon dioxide content of the sample has been formulated exactly. For an arbitrarily chosen standard system with constant volumes of the three parts of the circuit, constant volume of the sample injected and constant temperature as well as constant pre-injection pH of the electrode chamber solution, the relationship of final pH and total carbon dioxide of the samples was calculated and presented in a table. This table can be used with any cediometer to convert the final pH into total carbon dioxide content. A simple calibration procedure using Na 2CO 3 reference solutions can be used. The method is accurate within ± 1%, when the volumes of the various parts of the circuit do not differ by more than 10% from those of the standard system. The apparatus needs no special care and performs well under ordinary clinical conditions.