Differences Found between Prescribed and Delivered Dialysate Sodium Concentrations

In a project conducted recently by Ambreen Gul, MD, and colleagues, there were significant differences between concentrations of prescribed and measured dialysate sodium. That was among the findings of the cross-sectional quality improvement project reported in the American Journal of Kidney Diseases [2016;67 (3):439-445].

To achieve a zero sodium predialysis gradient between dialysate and serum, some investigators suggest the use of individualized dialysate sodium prescriptions. The chief medical officers of 14 dialysis providers in the United States recently suggested that dialysate sodium prescriptions should range from 134 to 138 mEq/L, staying that thirst, interdialytic weight gain, and systolic blood pressure may be reduced with the use of those dialysate sodium concentrations.

Conversely, DOPPS (Dialysis Outcomes and Practice Patterns Study) and other investigators have reported only modest increases in interdialytic weight gain and blood pressure with higher prescribed concentrations of dialysate sodium. Further, there was an association between lower dialysate sodium concentration and increased incidence of hospitalization and mortality. Based on those findings, the investigators have questioned the recommendations of the chief medical officers and urged caution in recommending the use of lower dialysate sodium concentrations.

According to the investigators of the reported project, none of the studies cited included the consideration that there might be significant differences between prescribed and measured dialysate sodium concentrations. The quality improvement project reported was designed to explore how closely the delivered dialysate sodium concentration matched the prescribed  dialysate sodium concentration ordered by the physician.

The investigators examined the difference between prescribed and delivered dialysate sodium concentrations in 333 maintenance hemodialysis patients receiving dialysis three times a week at four outpatient dialysis facilities owned by Dialysis Clinic, Inc., in the United States. The project aimed to test the hypothesis that prescribed dialysate sodium concentrations would be within ±2 mEq/L of measured dialysate sodium concentrations.

Clinics 1 and 2 used more individualized prescriptions than clinics 3 and 4. Clinic 1 used eight different prescriptions for dialysate sodium concentrations and clinic 2 used seven different prescriptions. At clinic 3, 99% of patients were dialyzed with a dialysate sodium concentration of 134 mEq/L; 96% of patients at clinic 3 received a dialysate sodium concentration of 140 mEq/L.

Differences in measured dialysate sodium concentrations from samples obtained predialysis versus in the last 10 minutes of treatment, despite some scatter, were centered around zero (with the exception of the highest dialysate sodium values).

Mean and median differences between prescribed and delivered dialysate sodium concentrations were less than zero in each clinic, which indicated that the measured dialysate sodium concentration was usually higher that the prescribed dialysate sodium concentration. There were significant variations in the magnitude of the differences by clinic (P<.001); the greatest differences between prescribed and measured dialysate sodium concentrations were seen in clinics 1 and 2.

Clinics 1 and 2 used Fresenius machines, mixed concentrates on site, and had a large variety of prescriptions for dialysate sodium concentrations. Least squares mean differences were larger at clinics 1 and 2 (-3.27; 95% confidence interval [CI], -4.02 to -2.53 and -3.77; 95% CI, -4.49 to -3.05, mEq/L, respectively) compared with clinics 3 and 4 (-1.44; 95% CI, -2.10 to -0.78 and -1.78; 95% CI, -2.4 to -1.10 mEq/L, respectively.

The magnitude of the differences ranged from -13 mEq/L to +6 mEq/L. At clinics 1, 2, 3, and 4, measured dialysate sodium concentrations were within 2 mEq/L of prescribed dialysate sodium concentrations in 47%, 25%, 71%, and 77% of treatments, respectively.

Limitations cited by the authors included studying only four dialysis centers, all operated by the same provider, and the inability to quantitate the contribution of each of the multiple factors that differed across the four facilities to the observed disparities. Strengths highlighted included the four facilities using dialysate delivery machines and dialysate concentrations obtained from varying manufacturers and measuring all dialysate sodium concentrations at a central laboratory.

The researchers summarized their findings by saying, “The present study demonstrated that there were often significant differences between prescribed and measured dialysate sodium concentrations. There was a positive bias, with measured dialysate sodium concentration often higher than that prescribed. The magnitude of these errors varied by clinic. It will be difficult to resolve the ongoing controversy regarding the optimal dialysate sodium concentration for hemodialysis patients unless we put in place the requisite quality control processes necessary to minimize differences between prescribed and delivered dialysate sodium concentrations. Therefore, consideration should be given to monitoring differences between prescribed and measured dialysate sodium concentrations as part of routine practice. Further research is needed to identify system processes that will minimize these differences.”


Takeaway Points

  1. This quality improvement project was designed to explore how closely the delivered dialysate sodium concentration matched prescribed dialysate sodium concentration ordered by the physician.
  2. The project was conducted in four dialysis clinics in the United States. Clinics 1 and 2 used more individualized prescriptions than clinics 3 and 4.
  3. Mean and median differences between prescribed and delivered dialysate sodium concentrations were less than zero in each clinic, indicating that the measured dialysate sodium concentration was usually higher that the prescribed dialysate sodium concentration.