Effects of different dialysate calcium concentrations on intradialysis hemodynamic stability

The interplay of correct solute mass balances, such as those of sodium (Na+), potassium (K+) and total calcium (tCa) (Na+MB, K+MB and tCaMB, respectively) with adequate ultrafiltration volumes (VUF) is crucial to achieving hemodynamic stability during hemodialysis (HD).

Twenty-two stable anuric uremic patients underwent three 4-hour bicarbonate HD sessions, each with a different dialysate tCa concentration (1.25, 1.375 and 1.50 mmol/L). The GENIUS dialysis system (Fresenius Medical Care, Germany) was used. Volumes of blood and dialysate processed, VUF and dialysate Na+ and K+ concentrations were prescribed to be the same. Hourly measurements of plasma water ionized Ca (Ca++), Na+ and K+ were made, and their trends analyzed. tCaMBs, Na+MBs and K+MBs were determined. Systolic (SBP), diastolic (DBP) blood pressure, mean arterial pressure (MAP) and heart rate (HR) trends during dialysis were analyzed.

Mean hourly plasma water Ca++ concentrations were statistically significantly higher with a dialysate tCa concentration of 1.50 mmol/L. Mean tCaMBs were positive (diffusion gradient from the dialysate to the patient), increasing with increasing dialysate tCa concentrations (+75 ± 122 mg, +182 ± 125 mg, +293 ± 228 mg, respectively). Their difference was statistically significant (p<0.0005). Mean Na+MBs and K+MBs were not statistically significantly different. SBP, DBP, MAP and HR were not statistically significantly different among the 3 treatments.

These highly controlled experiments showed that hemodynamic stability does not appear to be statistically significantly influenced by any specific dialysate tCa concentration in this peculiar subset of patients.