Continuous pH and HCO3 monitoring during hemodiafiltration without blood sampling

The correction of acid-base balance during hemodialysis, especially in high-efficiency techniques, could present some problem related to the lack of an adequate monitoring of pH and blood gases. During hemodiafiltration (HDF), performed with the two-chamber technique (paired filtration dialysis, PFD), the ultrafiltrate (Uf) is continuously available, unmixed with the dialysate. Connecting a pH electrode (as Ag/C1Ag) to the Uf circuit, the authors made 40 determinations on 16 different PFD patients, and they correlated the Uf values obtained with those measured on arterial blood with standard methods. The one sample analysis gave a t = 10.145 (p = 0.0), and the linear regression analysis an r = 0.931 (p = 0.0). At 30 min, in 8 PFD patients, the HCO3 values obtained from Uf, pH and transcutaneous PCO2, gave a t = 6.37 (p = 0.0004), and an r = 0.939 (p = 0.00052). In conclusion, during HDF performed with PFD, continuous pH monitoring of the patient is possible without blood sampling. Moreover, correlation with the transcutaneous PCO2 measurement could provide HCO3 values in real time.