Some Numerical Methods of Estimating Acid-Base Variables in Normal Human Blood with a Haemoglobin Concentration of 5g/100 cm³

Abstract

Three methods are discussed for calculating pH_NR, i.e. pH at P_CO2=40 mm Hg, from measurements of arterial pH and P_CO2. In method I the manual procedure with the Siggaard-Andersen nomogram is transferred to a computer. In method II pH_NR is calculated on a desk calculator and in method III on a computer from analytical expressions derived in this paper. The estimated standard deviations, within the range -20 < BE < 20, between pH_NR obtained with method I and the pH_NR values obtained with methods II and III are 0.0017 and 0.0006 pH units, respectively. The largest differences are 0.005 and 0.003 pH units, respectively. These figures refer to a blood with a haemoglobin concentration of 5 g/100 cm³. An equation for calculating ‘buffer base’ (BB) from pH_NR is also given. Other methods of computing acid-base values are reviewed.

Key Words:

• Computer
• desk calculator
• empirical relationships
• point of intersection