Determination of the acid-base status in blood of patients on chronic haemodialysis and of bicarbonate in dialysate: comparison of three techniques and their mathematically derived values.

The study deals with the comparison of acid-base parameters in blood of patients on chronic haemodialysis and of bicarbonate dialysate determined by Gas-Check AVL 945, equilibration technique (ET), and a titrimetric method. The results show that an acceptable agreement exists between AVL and ET with respect to measurements of pH, pCO2, HCO3-, and base excess. However, the values obtained for total buffer base related to the actual haemoglobin concentration are significantly lower (P less than 0.001) when determined by AVL. A titrimetric method is proposed for routine measurement of HCO3- in bicarbonate dialysate. Values obtained using this method are 3-4 mmol/l higher than those determined by AVL and ET. However, when the values for pK1' and for the solubility coefficient used in the Henderson-Hasselbalch equation are replaced by those for saline-bicarbonate solutions, results obtained using the titrimetric determined values agree well with those obtained by AVL and ET.