Surgery – Blood drawn and replaced or treated and returned to body – Constituent removed from blood and remainder returned to body
Reexamination Certificate
2001-06-08
2004-02-03
Bianco, Patricia M. (Department: 3762)
Surgery
Blood drawn and replaced or treated and returned to body
Constituent removed from blood and remainder returned to body
C604S005010, C604S004010, C604S006090, C604S006160, C604S272000, C210S646000, C210S650000, C210S321600, C422S044000
Reexamination Certificate
active
06685664
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to the extracorporeal treatment of blood, and more particularly to the blood access for Renal Replacement Therapy or treatments using an artificial kidney. It is also related to the treatment of congestive heart failure and fluid overload in a patient.
BACKGROUND OF THE INVENTION
Renal Replacement Therapy (RRT) is a class of medical treatments that artificially provide functions that would naturally be provided by the kidneys. Mechanical RRT generally involves an extracorporeal blood circuit that treats blood that is temporarily removed from and then returned to a patient. RRT performs two primary functions: (i) ultrafiltration (removal of water from blood plasma), and (ii) solute clearance (removal of different molecular weight substances from blood plasma). Devices used for RRT generally include: an extracorporeal blood circuit that extends from the patient through a filter and back to the patient; a pump acting on the blood circuit tube that moves the blood through the tube and filter, and a filter where the blood components are separated and where the solute exchange takes place. In addition, a RRT device may include a controller to regulate the pumps, which in turn control the flow rate of blood and other fluids through the circuit, and detect blockages and leaks in the blood circuit.
In operation, blood from a patient flows through the RRT blood circuit at a flow rate determined by the pump speed. As the blood flows through the filter, certain fluids, solutes or both from the blood pass through the filter membrane and are extracted from the blood plasma. The extracted fluids with solutes flow from the filter through a filtrate tube and are temporarily stored in a filtrate bag. The extraction of fluids and/or solutes by the RRT device replaces or supplements the natural functions of the kidneys. Fluids may be injected into the remaining blood plasma which then flows through the blood circuit tube and is infused into the patient.
The filter in an RRT device, also called hemofilter or “dialyzer”, can be set up to perform fluid removal, solute clearance, or both. The RRT device may also operate with or without fluid replacement. “Clearance” and “ultrafiltration” are common terms used in RRT. “Clearance” is the term used to describe the net removal of substances, both normal and waste product, from the blood. “Ultrafiltration” is the term used to describe the removal of plasma water, without significant affect on the concentration of small solutes in blood plasma, from the blood plasma. In mechanical terms “Ultrafiltration” is the convective transfer of fluid out of the plasma compartment of a filter through pores in the filter membrane and into a filtrate output compartment of the filter.
Blood filters generally have a blood compartment having input and output ports connected to the blood circuit, a filter membrane, and a filtrate compartment. The membrane separates the blood compartment and the filtrate compartment in the filter. In a filter used primarily for ultrafiltration, the pores of the filter membrane may be hollow fibers having blood passages of approximately 0.2 mm or less in diameter. The filter membrane pass fluids, electrolytes and small and middle sized molecules (typically up to 50,000 Daltons) from the blood plasma. The ultrafiltrate output from the filtration pores is similar to plasma, but without the plasma proteins or blood cells. In an ultrafiltration filter, the concentration of small solutes is the same in the ultrafiltrate as in the plasma, and, thus, no clearance or concentration change is obtained of small solutes in the blood plasma that is returned to the patient. However, the ultrafiltration does remove water from the blood and is useful for treating patients suffering from fluid overload. During the ultrafiltration treatment of a fluid overloaded patient the fluid that is mechanically “filtered” or removed from blood is typically immediately replaced by the access fluid that has been stored in the body. As a result the excess fluid or “edema” in the legs, the abdomen and the lungs of the patient is reduced and the patient's condition is relieved.
Dialysis is a different form of RRT. Dialysis is the transfer of small solutes out of a blood plasma compartment of a filter by diffusion across the filter membrane. Dialysis occurs as a result of a concentration gradient across the filter membrane. Diffusion of small solutes occurs from the filter compartment with a higher concentration (typically the blood compartment) to a compartment with lower concentration (typically the dialysate compartment). Since the concentration of solutes in the plasma decreases, clearance is obtained. Fluid removal does not necessarily occur during dialysis.
Ultrafiltration can be combined with dialysis to remove both fluid and small solutes from the blood plasma during RRT. Hemofiltration is the combination of ultrafiltration and fluid replacement. The volume of the replacement fluid is typically much larger than is needed just for fluid control. The replacement fluid generally contains electrolytes, but not other small molecules. There is some clearance because there is a net removal of small solutes due to both replacing fluids without small solutes and ultrafiltration of fluid with small solutes. A primary difference between the ultrafiltration and hemofiltration treatments is that during the former the plasma water removed from blood is replaced by the natural excess fluid internally stored in the patient's body. During the later the replacement solution is supplied by the treatment in a form of an artificial infusion.
Generally, all modes of Renal Replacement Therapy involve the removal of blood (typically venous) from a patient and passing the blood through a hollow fiber filter where there occurs fluid removal and, if desired, a solute removal or exchange. After passing through the filter, the blood is returned to the blood stream of the patient. So-called “batch” type RRT devices extract and return blood through the same single lumen IV catheter or “needle” and blood tube by reversing the direction of the blood pump. More common “continuous” type devices extract and return blood continuously using one double lumen catheter in the same vein or separate catheters in two separate veins. Catheter and needles used in RRT are generally known as “blood access”. Some RRT patients have permanently lost their kidney function and need to undergo dialysis several times a week. These patients typically have surgically implanted or modified sited for blood access such as arterial-venous shunts or fistulas.
Another large group of “renal” patients do not have permanent kidney damage. These renal patients have generally healthy kidneys that are not fully functioning, and the kidneys that have allowed the patient to become overloaded with fluids and toxic solutes. These patients require temporary support by an artificial kidney. Some of these patients suffer from Acute Renal Failure (ARF) in which their natural kidneys no longer have the ability to remove excess fluid and toxic solute from their blood stream for days or even weeks. These patients temperately require a RRT that removes both fluids and solutes from the blood stream.
Another large group of patients, who can benefit from fluid removal by ultrafiltration of blood, have functional kidneys, but suffer from fluid overload due to Congestive Heart Failure (CHF). The kidneys of CHF patients are generally healthy but are not fully functioning due to the failing heart and low blood pressure. Because the kidneys are not fully functioning, fluids build up in the patient and the fluid overload contributes to the stress on the already failing heart. However, the kidneys do make some urine that is usually sufficient for the kidneys to remove toxic solutes.
CHF patients need an RRT treatment that removes excess fluid from the body. These patients typically do not require solute removal or a long-term chronic treatment. The fluid can be removed from the patient relatively quick
Bernard Steve
Gelfand Mark
Levin Howard R.
Bianco Patricia M.
CHF Solutions Inc.
Nixon & Vanderhye P.C.
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