Relatively low dialysate conductivity (D cond.) is desirable as it is associated with lower interdialytic weight gains, and improved BP control. Excess sodium removal can, however, lead to hemodynamic instability. We performed a randomised controlled trial of empirical reduction of dialysate conductivity.
This study was approved by the Local Regional ethics Committee, and all patients gave written informed consent. Sodium removal as ionic mass balance (IMB), as well as plasma conductivity, was measured by conductivity monitoring, and routine clinical measurements were used to assess the clinical impact. 28 patients were recruited, and randomised to either maintenance of D cond at 13.6 mS/cm (equivalent to 140 mmol/l of Na+), or serial reduction of D cond in steps of 0.2 mS/cm. Reduction was guided by symptoms and BP. Of the 16 patients randomized to reduction of D cond., 6 achieved D cond 13.4 mS/cm, 6 achieved 13.2 mS/cm, and 4 achieved 13.0 mS/cm (13.0 mS/cm was pre-specified as the lowest acceptable D cond). No episodes of dysequilibrium occurred. Results are expressed as those achieved at minimum D cond once this was established, compared with baseline at 13.6 mS/cm (shown as mean ± S.E.M., significance calculated using paired t test).
Interdialytic weight gain was reduced from 2.34 ± 0.10 kg to 1.57 ± 0.11 kg P < 0.0001. Both pre and post dialysis BPs were significantly reduced (pre-dialysis systolic BP fell from 144 ± 3 mmHg to 137 ± 4 mmHg P < 0.05). The reduction in convective sodium removal due to reduced weight gains was matched by an increase in the amount of sodium removed by diffusion (91 ± 12 mmol cf. 158 ± 12 mmol P < 0.0001). Finally pre-dialysis plasma conductivity also fell, from 14.23 ± 0.04 mS/cm to 14.02 ± 0.05 mS/cm, suggesting a significant reduction in the overall sodium load, given that the target weight did not change.
In summary, we have demonstrated that reduction in D cond monitored by IMB is safe and practical, and leads to improvement in interdialytic weight gains, and BP control while avoiding excessive sodium removal.