Conductivity pulses needed for Diascan® measurements: does it cause sodium burden?

Sir,

Recent, New techniques based on conductivity measurement enable physicians to evaluate the adequacy of haemodialysis dose (HDD) on all haemodialysis treatments by on-line monitoring of Kt/V. Ionic dialysance (Diascan® Hospal-Gambro, Mirandola, Italy) is a parameter calculated from the dialysate conductivity at the dialyser inlet and outlet. Every half hour, the inlet dialysate conductivity increases by 1 ms/cm during 5 min, while the outlet dialysate conductivity-cell measures the effect of this increase. The calculated ion transfer across the membrane (largely sodium) is almost equivalent to urea transfer and therefore ionic dialysance reflects the urea clearance. This method has been shown to have a good correlation with Kt/V measured by the mathematical urea equations in several studies [1-4].

However, some investigators suggest that during the conductivity pulse of 5 min, significant amounts of sodium may be transferred into the patient [5]. In our centre, we studied that effect. Diascan® also measures ionic mass balance (IMB) and plasma conductivity (PC) that are likely to represent sodium balance and plasma sodium, respectively (plasma sodium in mmol/l ≈ plasma conductivity in ms/ cm × 10). This is performed by constant measurements of the conductivity in the dialysate inlet and outlet, according to the formulas where Qdin and Qdout are dialysate flow at, respectively, inlet and outlet, Cdin and Cdout are dialysate conductivity at, respectively, inlet and outlet and D is ionic dialysance, and

A positive IMB means sodium removal from the patient. A negative IMB means sodium transport to the patient.

In patients with zero inter-diaytic weight gain, IMB was measured in 200 isovolaemic haemodialysis sessions by Diascan®, 137 sessions were performed with four to eight conductivity pulses. A total of 63 sessions was performed with only one conductivity pulse.

The results showed a highly significant correlation between pre-dialytic plasma conductivity and IMB (Spearman rank rs = 0.902, P < 0.005), in agreement with previous studies [6]. There was no correlation between IMB and the number of conductivity pulses (Spearman rank rs = 0.02, P = 0.328) (Figure 1).

Fig. 1

Correlation between IMB during isovolaemic haemodialysis and number of conductivity pulses.

In conclusion, Diascan® is a useful tool to assess HDD without evidence of an increased sodium load related to the conductivity pulses during haemodialysis treatment.

Conflict of interest statement. None declared.