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Haemodialysis recirculation detected by the three-sample method is an artefact
J E Tattersall1, K Farrington, P D Raniga
1Renal Unit, Lister Hospital, Stevenage, UK.
Summary
The common three-sample method for detecting haemodialysis recirculation may be flawed, indicating high rates in all patients. Direct saline dilution testing showed no recirculation, suggesting the three-sample method should be abandoned.
Area of Science:
- Nephrology
- Medical Devices
- Clinical Diagnostics
Background:
- Haemodialysis efficiency can be compromised by blood recirculation between venous and arterial needles.
- Recirculation is typically assessed using direct saline dilution or indirect urea-based three-sample methods.
- Discrepancies exist in recirculation rates detected by these different methods.
Purpose of the Study:
- To investigate whether saline dilution and three-sample methods detect different recirculation phenomena.
- To evaluate the reliability of the three-sample method in assessing haemodialysis recirculation.
Main Methods:
- Simultaneous testing of saline dilution and three-sample methods in 16 haemodialysis patients.
- Measurements were taken at varying extracorporeal blood flow rates (Qb).
Main Results:
- The saline dilution method detected no recirculation in any patient.
- The three-sample method indicated recirculation in all patients, with a mean fraction of 12.5% (SD 6.1).
- Recirculation rates from the three-sample method were independent of blood flow rates (Qb), suggesting it does not measure fistula recirculation.
Conclusions:
- The three-sample method likely detects a solute disequilibrium between central and peripheral blood pools, not true fistula recirculation.
- The findings suggest the three-sample method for detecting haemodialysis recirculation is unreliable and should be discontinued.