Acid-base balance determination on ultrafiltrate in two-chamber technique hemodiafiltration (PFD)

Correction of the acid-base balance in uremic patients during hemodiafiltration (HFD) may be biased by an inadequate monitoring of pH and blood gases. HDF performed with the two-chamber technique (PFD) generates pure ultrafiltrate (uf) unmixed with dialysate. We carried out 84 determinations of HCO3- levels in 15 different PFD patients by measuring the pH and pCO2 of the uf, then correlated the values with those simultaneously evaluated on arterial blood with standard methods. The mean HCO3- levels (mmol/L) were 23.21 +/- 2.49 in blood samples and 25.54 +/- 3.07 in uf, with a mean difference of -2.33 +/- 1.46. Statistical analysis gave: t = 13.5 (p = O) (one-sample analysis), r = 0.86 (p = 0) (linear regression analysis) and a good agreement between the two clinical measurements (81 out of 84 data points fell within the 95% confidence interval) (Bland-Altman analysis). In conclusion, we suggest that during HDF performed with the two-chamber technique, the patient's HCO3- level can be monitored on the uf without blood sampling.