Method and device for measuring access flow
AssigneeGambro AB
InventorsJan Peter Sternby, Gary Joel Mishkin, Perry Asbrink, Eddie Nilsson
Life of this patent
Estimating the term…
Abstract
An arterial needle removes blood from the access to an extracorporeal circuit comprising a dialyzer and a venous needle returns the blood to the access site. Blood passes along one side of the membrane of the dialyzer and dialysis fluid along the other side. The concentration (Cd norm and Cd rev) of urea in the dialysate emitted from the dialyzer is measured with the needles in the normal position and in a reversed position. The access flow rate before the arterial needle is calculated according to the formula: Cd norm/Cd rev=1+Keff/Qa in which Keff is the effective clearance of the dialyzer and Qa is the access flow rate.
Claims27
A method of estimating fluid flow rate (Qa) in a fluid flow access, comprising:
- removing a first fluid flow from said access at a removal position to an external flow circuit comprising a dialyzer 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 (Cd norm) of a substance in said dialysis fluid emitted from the dialyzer;
- reversing the removal position with the return position and measuring a second variable which is essentially proportional to the concentration (Cd rev) of said substance in said dialysis fluid in the reversed position;
- and
- calculating the fluid flow rate (Qa) in said flow access from said measured concentrations.
An apparatus for extracorporeal blood treatment comprising:
- a dialyzer having first and second compartments separated by a semi-permeable membrane;
- a blood circuit having;
- a blood removal line for connecting, in a normal condition, an inlet of the first chamber to a blood access of a patient at a first connecting point, and
- a blood return line for connecting, in the normal condition, an outlet of the first compartment to the blood access of the patient at a second connecting point;
- a reversal means for switching the connection of the blood removal line and blood return line to the blood access so that, in a reverse condition, the first connecting point is in fluid communication with the outlet of the first chamber and the second connecting point is in fluid communication with the inlet of the first chamber;
- a dialysis liquid circuit having:
- a dialysis liquid line for supplying a dialysis liquid to an inlet of the second compartment, and
- a dialysate line for draining a dialysate from an outlet of the second compartment;
- a sensor connected to the dialysate line for measuring, in the normal condition, a first variable in the dialysate, and for measuring, in the reverse condition, a second variable in the dialysate, the first variable being essentially proportional to a first concentration (Cd norm) of a substance in the dialysate and the second variable being essentially proportional to a second concentration (Cd rev) of the substance in the dialysate;
- a calculating means for calculating a fluid flow rate (Qa) in the blood access from the first and second variables and from a clearance of the dialyzer.
Dependencies are inferred from the claim text.