The effect of changing dialysate bicarbonate concentration on serum bicarbonate, body weight and normalized nitrogen...

Most hemodialysis machines deliver a fixed bicarbonate concentration. Higher concentrations may improve acidosis, but risk post-hemodialysis alkalosis, whereas lower concentrations potentially increase acidosis but reduce alkalosis. We reviewed the effects of lowering dialysate bicarbonate.

We reviewed peri-dialysis chemistries in patients switching to a lower bicarbonate dialysate at 4 time points over 19 months.

We studied 126 patients, mean age 63.7 ± 16.3 years, 57.9% males. Post-hemodialysis alkalosis fell from 1.6 to 0.3% sessions, but pre-hemodialysis acidosis increased from 11.9 to 23.8% sessions (p = 0.005) reducing dialysate bicarbonate from 32 to 28 mmol/L. After 3 months, pre-hemodialysis serum bicarbonate fell (21.1 ± 2.3 to 19.8 ± 2.2 mmol/L), and post-hemodialysis (24.9 ± 2.1 to 22.5 ± 2.0 mmol/L, p < 0.001) with a fall in pre-hemodialysis weight from 74.6 ± 20.7 to 71.7 ± 18.2 kg, normalized protein nitrogen accumulation rate 0.8 ± 0.28 to 0.77 ± 0.2 g/kg/day, p < 0.05, and serum albumin 39.7 ± 4.2 to 37.7 ± 4.9 g/L, p < 0.001. Thereafter, apart from pre- and post-hemodialysis serum bicarbonate, weight and normalized protein nitrogen accumulation stabilized, although albumin remained lower (37.6 ± 4.0 g/L, p < 0.001). On multivariate logistic analysis, serum bicarbonate increased more with lower pre-hemodialysis bicarbonate standardized coefficient β 0.5 (95% confidence interval -0.6 to -0.42), increased normalized protein nitrogen accumulation β 0.2 (0.96 to 2.38), p < 0.001, and session time β 0.09, (0.47 to 5.98), p < 0.022, and less with lower dialysate bicarbonate 0.0-0.23 (-1.54 to -0.74), p < 0.001.

Increases in SE-Bic with hemodialysis, depend on the bicarbonate gradient, session time and nPNA. Lower D-Bic reduces post-hemodialysis alkalosis but increases pre-hemodialysis acidosis and may initially have adverse effects on weight and normalized protein nitrogen accumulation.