**3.2.4 Thirst**

Effect of dialysate sodium on thirst was quite variable. Thirst is probably most dependent on subjective patient factors than any other factor.

Sodium and Hemodialysis 53

examined the effect of lowering dialysate conductivity on blood pressure. One study showed improved control in blood pressure as conductivity was decreased (Farmer et al. 2000). Another study found improvement in blood pressure control and IDWG but worsening intradialytic hypotension with decreasing dialysate conductivity (Lambie et al., 2005). The study with the narrowest range of comparison did not show changes in any

(2000) 10 4 132.7, 137.7 no change improved N/A N/A

(2005) 16 8a 130,132,134,136 improved improved worsened N/A

(2007) 10 6 132, 134, 136 no change no change no change no change

Table 3. Three prospective studies showing the effect of lowering dialysate conductivity on interdialytic weight gain (IDWG), Blood Pressure (BP) Control, Intradialytic Hypotension, and Thirst. Estimated dry weight was not changed during these studies. n = number of patients in study. N/A = data not available. aExact duration not reported, but estimated from number of stepwise changes in conductivity and duration of dialysis for each step.

As demonstrated above, higher dialysate sodium provides questionable and inconsistent benefit for intradialytic hemodynamic stability at the cost of proven exacerbation of hypertension and interdialytic weight gain. "Lower" dialysate sodium should therefore be preferred, however, the exact definition of "lower" concentration is variable between studies. In the prospective studies, "lower" was defined from below 132 mEq/L to 145mEq/L while "higher" was defined from 137 to 155 or higher. Of the 165 patients in these studies, we could identify 131 patients where the exact high and low settings could be identified. The weighted average for the lower sodium was 137mEq/L and 143mEq/L for

Given the number of potential barriers to crafting an individualized approach the sodium prescription for each patient, implementing a facility-wide change to 137mEq/L may be safely recommended. Typically, each dialysis unit sets a 'usual' dialysate sodium concentration based on the decision of the medical director. The 'standard' sodium can serve as the default with each provider making individualized changes based on individual patient's needs. Therefore, the initial step is encouraging dialysis directors to choose a

Several questions must be answered when formulating an individualized dialysate sodium. Will changing dialysate sodium cause long-term changes in serum osmolality? Are serum

**Effect of Lower Dialysate Conductivity on** 

**Hypotension Thirst** 

**IDWG BP Control Intradialytic** 

parameters (Selby et al., 2007).

**t (weeks)**

bCalculated from dialysate conductivity.

**4.1 Facility-wide approach** 

the higher sodium settings.

**4.2 Individualized approach** 

**Approximate [Na+] (mEq/L)b**

**4. Recommendations for the dialysate sodium prescription** 

default dialysate sodium concentration at, or close to, 137mEq/L.

**Author (Year) <sup>n</sup>**

Farmer

Lambie

Selby


Table 2. Ten prospective studies examining the relationship of dialysate sodium prescription on interdialytic weight gain (IDWG), Blood Pressure (BP) Control, Intradialytic Hypotension, and Thirst. BP control is defined as improved pre-dialysis blood pressure measures and/or reduction in number of antihypertensives prescribed. Estimated dry weight was not changed during these studies. n = number of patients in study. N/A = data not available. aPatients on Sodium Profiling with [Na+] expressed as Time Averaged Concentration (TAC). bPatients placed on 135 if serum was below 137, and on 137 if serum was above 137 (not explained what they did if it WAS 137). No record of baseline Na+ Rx prior to the change. cImprovement was seen in the normotensive subset. dHalf of the participants had an unquantified improvement. eImprovement seen in patients with baseline IDWG greater than 1kg/day. f Improvement was seen in the 'previously hypertensive' subset. g138 & 140 groups were improved when compared to 147 group. hThere was a 'tendency' toward worsened intradialytic hypotension, data not reported.

## **3.3 Conductivity studies**

Electrical conductivity of solutions reflects the concentration of solute in solution. Substituting conductivity measurements for concentration measurements allows real-time estimations of solute concentrations. Modeling solute clearance, sodium mass transfer, and access recirculation by differences in pre/post dialyzer conductivity represent powerful applications of this technology (Polaschegg, 1993; Locatelli et al., 1995; Petitclerc, 1999). In its most straightforward application, dialysate conductivity can be used as a surrogate for dialysate sodium concentration with one mS/cm conductivity equivalent to 10meq/L sodium. Three short, prospective studies involving 36 patients were identified which

(1985) 16 52 133, 144 improvedc improvedf worsened no change

(1985) 7 12 135, 143, 160/133 model improved no change no change improved

(1988) 5 24 145, 150, 155 improved no change N/A variable

(1998) 8 24-30 135, 140 improvedd improved N/A N/A

(2000) 6 6 136, 140 N/A no change N/Ah N/A

(2002) 11 24 138, 140, 147a improved improvedg worsened N/A

(2004) 27 6 138, serum [Na+] x 0.95 improved improvedf improved improved

(2004) 15 8 132, 137 improvede N/A N/A worsened

(2007) 52 32 138, 141 no change improved no change N/A

(2007) 18 8 'higher' to 137 or 135b improved improved N/A N/A Table 2. Ten prospective studies examining the relationship of dialysate sodium prescription

Improvement was seen in the 'previously

Hypotension, and Thirst. BP control is defined as improved pre-dialysis blood pressure measures and/or reduction in number of antihypertensives prescribed. Estimated dry weight was not changed during these studies. n = number of patients in study. N/A = data not available. aPatients on Sodium Profiling with [Na+] expressed as Time Averaged Concentration (TAC). bPatients placed on 135 if serum was below 137, and on 137 if serum was above 137 (not explained what they did if it WAS 137). No record of baseline Na+ Rx prior to the change. cImprovement was seen in the normotensive subset. dHalf of the participants had an unquantified improvement. eImprovement seen in patients with

hypertensive' subset. g138 & 140 groups were improved when compared to 147 group. hThere was a 'tendency' toward worsened intradialytic hypotension, data not reported.

Electrical conductivity of solutions reflects the concentration of solute in solution. Substituting conductivity measurements for concentration measurements allows real-time estimations of solute concentrations. Modeling solute clearance, sodium mass transfer, and access recirculation by differences in pre/post dialyzer conductivity represent powerful applications of this technology (Polaschegg, 1993; Locatelli et al., 1995; Petitclerc, 1999). In its most straightforward application, dialysate conductivity can be used as a surrogate for dialysate sodium concentration with one mS/cm conductivity equivalent to 10meq/L sodium. Three short, prospective studies involving 36 patients were identified which

on interdialytic weight gain (IDWG), Blood Pressure (BP) Control, Intradialytic

**Effect of Lower Dialysate [Na+] on** 

**Hypotension Thirst** 

**IDWG BP Control Intradialytic** 

**Dialysate [Na+] (mEq/L)** 

**Author (Year)** 

Cybulsky

Daugirdas

Barré

Krautzig

Kooman

Song

de Paula

Oliver

Thein

Sayarlioglu

baseline IDWG greater than 1kg/day. f

**3.3 Conductivity studies** 

**n t (weeks)** examined the effect of lowering dialysate conductivity on blood pressure. One study showed improved control in blood pressure as conductivity was decreased (Farmer et al. 2000). Another study found improvement in blood pressure control and IDWG but worsening intradialytic hypotension with decreasing dialysate conductivity (Lambie et al., 2005). The study with the narrowest range of comparison did not show changes in any parameters (Selby et al., 2007).


Table 3. Three prospective studies showing the effect of lowering dialysate conductivity on interdialytic weight gain (IDWG), Blood Pressure (BP) Control, Intradialytic Hypotension, and Thirst. Estimated dry weight was not changed during these studies. n = number of patients in study. N/A = data not available. aExact duration not reported, but estimated from number of stepwise changes in conductivity and duration of dialysis for each step. bCalculated from dialysate conductivity.
