The AKsys uses Ultra Pure Dialysate (UPD) in place of saline. The machine makes someting like 50 liters of UPD during its preperation for treatment. When I begin treatment the lines are primed with UPD then when I hook up the lines and press ‘go’ the machine draws the UPD out through the F-80 kidney until my blood meets in the middle of the kidney (you could also set the machine to give the prime, I set my machine to discard the prime).
If you need fluid during treatment the machine infuses UPD through the F-80. And it uses UPD to rinse back the blood - again through the F-80 which is nice because there is no need to disconnect the lines until the treatment is over.
Here is a link to a good article on how the Aksys PHD works:
PHD®: the technological solution for daily haemodialysis?
by Zbylut J. Twardowski
here is Dr. Twardowski’s account of the Aksys PHD’s operation:
Preparation of dialysis solution for each dialysis
The system is filled with RO water, including the blood compartment of the dialyzer and the bloodlines. The dialysis solution is prepared by dissolving the powdered chemicals and diluting the concentrate in water in the main tank. The temperature of the dialysis solution is regulated by a thermistor, and the proper dissolution of chemicals is checked by the first conductivity meter (CM 1). The dialysis solution fills the dialysate and blood compartments of the dialyzer.
Discard prime and start of dialysis. The patient changes the transducer protector, attaches the arterial and venous lines to the blood access, injects heparin to the arterial line and touches the start button to activate the system. The blood and UF pumps are activated. Negative pressure in the dialysate compartment pulls dialysis solution from the blood compartment and blood enters the blood compartment of the dialyzer through both the arterial and venous lines. Once the compartment is filled with blood, the blood pump speed increases and the UF pump speed automatically adjusts to create appropriate transmembrane pressure for the desired UF. The dialysis solution is heated to 37°C, flows through the dialysate compartment of the dialyzer and returns to the top of the main tank (Figure 1).
Backflush and solute infusion
Every 15 min, if desired, the directions of blood and UF pumps are reversed to create negative pressure in the blood compartment and positive pressure in the dialysate compartment. The fluid from the UF tank flows to the dialysis solution line through the bypass. The reversed transmembrane pressure gradient filters dialysate through the membrane into the blood compartment dislodging proteins and other molecules embedded in the dialyzer membrane pores. After a bolus of fluid passes through the membrane, the direction of pumps is reversed and dialysis continues. Backflushes are intended to preserve the efficiency of dialyzers for up to 30 reuses.
If infusion of fluid is necessary, ultrapure dialysis solution may be infused during dialysis in the same way as during the backflush.
At the end of dialysis, the direction of the blood pump is reversed. Dialysate from the main tank flows through the heater and ultrafilter 1 to the dialysate compartment of the dialyzer, creating high pressure in the dialysate compartment. The blood is returned to the patient through both the arterial and venous lines, pushed by the dialysate transferred to the blood compartment due to the reversed transmembrane pressure gradient. This method allows for almost complete return of blood with minimal delivery of fluid to the patient. After the blood is returned, the patient disconnects lines from the blood access and attaches the lines to the connectors in the dialyzer module, changes bottles 1 and 2, tests the quality of pre-treated water and gives information through the touch screen that the machine may start preparation for the next dialysis.
Preparation of the machine for the next dialysis
The machine first determines the clearance of the dialyzer by measuring changes in conductivity. The blood pump pulls RO water to the blood compartment of the dialyzer through the ultrafilter 2 and the dialysis solution flows countercurrently through the dialysate compartment. Based on the changes in conductivity measured by the second conductivity meter (CM 2), the conductivity clearance is calculated by the machine’s computer. If clearance is within an appropriate range, the dialyzer is accepted and the machine continues with the heat disinfection and dialysis solution preparation for the next dialysis, as described above.