Method and apparatus for detecting access recirculation
A switch valve for use in an extracorporeal blood flow circuit comprises a valve housing having a chamber, four openings communicating with the chamber, and a valve member located in the valve chamber. A first opening is to be connected to a patient via an arterial cannula, a second opening is to be connected to a patient via an venous cannula, a third opening is to be connected to a first inlet/outlet of a blood treatment device, and a fourth opening is to be connected to a second inlet/outlet of a blood treatment device. The valve member is movable within the valve housing to fluidly connect the first opening to either the third or the fourth opening and to fluidly connect the second opening to either the third or the fourth opening. The width of the valve member is smaller than a peripheral dimension of the openings.
1. A method of detecting access recirculation, comprising: removing a first fluid flow at a first fluid flow rate from a fluid flow access at a removal position to an external flow circuit comprising a dialyzer having a dialysis fluid inlet and a dialysis fluid outlet and having a semipermeable membrane, said first fluid flow passing along said membrane at one side thereof and a dialysis fluid being emitted from the other side thereof, and returning said first fluid flow from said external flow circuit to said access at a return position downstream of said removal position; measuring a first variable which is essentially proportional to a concentration of a substance in said dialysis fluid emitted from the dialyzer; changing the first fluid flow rate; monitoring the concentration of said substance in the dialysis fluid emitted from the dialyzer; and detecting a possible access recirculation by correlating a change in said concentration to said change of the first fluid flow rate.
2. The method of claim 1 , wherein said first fluid flow is blood flow.
3. The method of claim 2 , wherein the blood flow rate is decreased and change in a urea concentration is monitored, and wherein the absence of an expected decrease in the urea concentration is indicative of access recirculation.
4. The method of claim 2 , wherein said substance is selected from the group consisting of: urea, creatinine, vitamin B12, beta-two-microglobuline and glucose.
5. The method of claim 2 , wherein said substance is an ion selected from the group consisting of: Na+, Cl—, K+, Mg++, Ca++, HCO3—, acetate ion, or any combination thereof; and said concentration is measured as the concentration difference between the outlet and the inlet of the dialyzer.
6. The method of claim 2 , wherein said concentration of said substance is measured as the conductivity difference between the dialysis fluid at the outlet of the dialyzer and the dialysis fluid at the inlet of the dialyzer.
7. The method of claim 1 , wherein said substance is selected from the group consisting of: urea, creatinine, vitamin B12, beta-two-microglobuline and glucose.
8. The method of claim 1 , wherein said substance is an ion selected from the group consisting of: Na+, Cl—, K+, Mg++, Ca++, HCO3—, acetate ion, or any combination thereof; and said concentration is measured as the concentration difference between the outlet and the inlet of the dialyzer.
9. The method of claim 1 , wherein said concentration of said substance is measured as the conductivity difference between the dialysis fluid at the outlet of the dialyzer and the dialysis fluid at the inlet of the dialyzer.
10. An apparatus for detecting access recirculation comprising: means for removing a first fluid flow at a first fluid flow rate from a fluid flow access at a removal position to an external flow circuit comprising a dialyzer having a dialysis fluid inlet and a dialysis fluid outlet and having a semipermeable membrane; means for passing said first fluid flow along said membrane at one side thereof and means for emitting dialysis fluid from the other side thereof; means for returning said first fluid flow from said external flow circuit to said access at a return position downstream of said removal position; means for measuring a first variable which is essentially proportional to a concentration of a substance in said dialysis fluid emitted from the dialyzer; means for changing the first fluid flow rate; means for monitoring the concentration of said substance in the dialysis fluid emitted from the dialyzer; and means for detecting a possible access recirculation by correlating a change in said concentration to said change of the first fluid flow rate.
11. The apparatus of claim 10 , wherein said first fluid flow is blood flow.
12. The apparatus of claim 11 , wherein said substance is selected from the group consisting of: urea, creatinine, vitamin B12, beta-two-microglobuline and glucose.
13. The apparatus of claim 11 , wherein said substance is an ion selected from the group consisting of: Na+, Cl—, K+, Mg++, Ca++, HCO3—, acetate ion, or any combination thereof; and said concentration is measured as the concentration difference between the outlet and the inlet of the dialyzer.
14. The apparatus of claim 11 , wherein said concentration of said substance is measured as the conductivity difference between the dialysis fluid at the outlet of the dialyzer and the dialysis fluid at the inlet of the dialyzer.