I. Field of the Invention
This invention relates generally to artificial organs and in particular to a blood access system for the treatment of end stage kidney failure. The apparatus comprising a preferred embodiment includes a patient-wearable, extracorporeal system which accesses a patient's arterial/venous pressure differential and regulates the extracorporeal arteriovenous blood flow and proportionally with that blood flow, pumps and regulates dialysate flow in the case of hemodialysis (HD) for kidney failure. The externally wearable unit offers portable, continuous, HD for a patient. The HD unit of this invention also proportionally with the blood and dialysate, pumps and regulates anti-coagulant and CaMg additions.
II. Discussion of the Prior Art
Patients suffering from chronic end stage renal disease or acute traumatic kidney failure regularly undergo the process of HD in which chemical waste and water are removed from the blood using a system of semi-permeable membranes. Conventional chronic treatment requires the patient to remain sedentary for three sessions per week. Each treatment session constitutes approximately three to six hours at a treatment center or at home and additional hours for travel and recovery. It is an uncomfortable and tiring procedure, since patients must remain sedentary and because of the rapid rate at which their body fluids are adjusted toward normal. Approximately 100 times the usual daily intake of water, in the form of dialysate, passes by the artificial membranes opposite the blood during an average session. Consequently, failure of the dialysate preparation or membrane conduction systems may have severe consequences.
The process of HD becomes necessary when disease or trauma causes the kidneys to fail or become so impaired that they no longer adequately remove toxins and/or water from the blood. It involves mechanically and chemically assisted removal of toxins (largely urea) and water in a manner that restores a balance of fluids and electrolytes in the blood. The essential components for this process are a semi-permeable membrane and a dialysate solution that will absorb the unwanted blood components after they have passed through the membrane. A way of preventing clotting of blood in and around the dialyzer unit is required.
Interest in miniaturizing the equipment used in hemodialysis has resulted in the availability of small portable (as opposed to truly ambulatory) dialysis devices. Ash and Kessler in U.S. Pat. No. 4,071,444 provide an example of a portable dialysis machine. Semipermeable membranes separate alternating chambers of blood and dialysate. Varying the pressure within the dialysate chambers pumps blood and dialysate. Both blood and dialysate flow paths include one-way check valves, thus eliminating the need for any other mechanical pumping apparatus. The drawback of the lack of a second blood pump is that the process is generally slower. Although not ambulatory, this portable apparatus permits travel, making the longer hooked-up time more tolerable.
An ambulatory hemodialysis machine requires an ambulatory source of dialysate. This has been achieved experimentally and practically by miniaturizing commercially available, three times weekly, dialysate recycling urease and adsorbents containing cartridges. An ambulatory dialysate recycling cartridge must accommodate several factors. If dialysate flow rate is too slow, then blood toxin clearance rates are diminished and duration of dialysis must be increased proportionately. Also, the cartridges available.
As is pointed out in the Twardowski U.S. Pat. No. 5,336,165 there is a real need for equipment that will make at-home hemodialysis possible. There are nearly 500,000 patients on dialysis in the United States at any one time. Most of these patients must visit kidney dialysis centers three times a week and spend several hours on each of those days tied to a machine that includes an extracorporeal circuit for extracting blood, “cleaning” it, and returning it back into the patient. This not only exposes the patient or a third-party payer to very significant medical costs, but also adversely affects quality of life considerations. In an attempt to address this problem, Twardowski describes an at-home hemodialysis system that includes a dialyzer membrane and provision for passage of a dialysis solution along one side of the membrane and blood with uremic components along the other side.
The Beltz U.S. Pat. No. 5,284,470 describes a portable, artificial kidney in the form of a self-contained unit whose size and shape is such that it is lightweight and relatively small so that it can be worn by the patient who is able to go about routine daily activities. The Beltz system includes a blood plasma separator unit, a chemical treatment unit, and a water removal unit. It also includes a cannula inserted in an arteriovenous shunt for gaining access to the patient's blood stream. The toxic whole blood is routed to the artificial kidney and then returned in detoxified form back to the patient. The artificial kidney includes a separator packet for extracting a predetermined amount of plasma from the patient's blood and then a further packet containing a treatment chemical for cleansing the plasma is included in the flow path. Means are provided to remove water from the plasma before the cleansed plasma is returned to the patient's body. Blood flow through the unit is due primarily to the hydrostatic blood pressure of the patient, but it is recognized that a lightweight pump and battery may be needed to generate additional pressure for routing the cleansed plasma back into the patient.
A continuous-use ambulatory hemodialysis unit is described in U.S. Pat. No. 3,864,259 of Newhart. It features a harness that secures a dialysate reservoir to the patient's hip and a perfusion unit on the anterior thigh, connected to a femoral shunt. The perfusion unit has multiple dialysis tubules bathed in dialysate, enabling the removal of waste products from the blood in the tubules. The apparatus consists of seven exterior parts: harness, diaphragm pump, reservoir, perfusion unit, dialysate exchange unit, and femoral arterial and venous cannulae. The exchanger is smaller than the perfusion unit at approximately 8.5 cm×6 cm and 1 cm deep. It should be apparent that this apparatus is cumbersome and uncomfortable.