Technical Field

The present disclosure relates to extracorporeal blood cir ^¬ cuits used for gas exchange in blood, in particular cir ^¬ cuits for cardiopulmonary bypass.

Description of the Related Art

Cardiopulmonary bypass (CPB) is commonly used in various surgical procedures performed on the heart or the lung of a patient. Examples include coronary artery bypass surgery, cardiac valve repair and/or replacement, repair of large septal defects, repair and/or palliation of congenital heart defects, transplantation, pulmonary thromboendarter- ectomy, or pulmonary thrombectomy. A machine pumps the blood, and, using an oxygenator, allows red blood cells to pick up oxygen, as well as allowing carbon dioxide levels to decrease. This mimics the function of the heart and the lungs, respectively. CPB mechanically circulates and oxy ^¬ genates blood for the body while bypassing the heart and lungs. It uses a heart-lung machine (HLM) to maintain perfusion to other body organs and tissues while the surgeon works in a bloodless surgical field.

During the surgical procedure, excessive water has to be removed from the patient, e.g., by ultrafiltration. Hemo- filters are commonly used for this purpose on heart-lung machines . Extracorporeal membrane oxygenation (ECMO) , also known as extracorporeal life support (ECLS) , is an extracorporeal technique of providing both cardiac and respiratory support to persons whose heart and lungs are unable to provide an adequate amount of gas exchange to sustain life. ECMO works by removing blood from the person's body and artificially removing the carbon dioxide and oxygenating red blood cells. In veno-arterial (VA) ECMO, this blood is returned to the arterial system and in veno-venous (VV) ECMO the blood is returned to the venous system.

During extracorporeal blood circulation, inflammatory mediators such as cytokines and endotoxins are produced that can lead to a systemic inflammatory response. Multiple measures have been developed over the years to reduce in ^¬ flammatory release. More recently, it has been proposed to integrate an adsorptive column capturing cytokines into the extracorporeal circuit.

Summary

The present disclosure provides an extracorporeal circuit in which ultrafiltration and the adsorption of inflammatory mediators is combined in a single device.

Detailed Description

An extracorporeal blood circuit is provided which comprises a gas exchange device and a diffusion- and/or filtration device. The diffusion- and/or filtration device comprises semipermeable membranes comprising i) a copolymer of acry- lonitrile and sodium methallyl sulfonate, ii) a polyethy- leneimine, and iii) heparin. In one embodiment of the ex ^¬ tracorporeal circuit of the present disclosure, the diffu- sion- and/or filtration device is a capillary dialyzer comprising a plurality of semipermeable hollow fiber mem ^¬ branes, the membranes comprising i) a copolymer of acrylo- nitrile and sodium methallyl sulfonate; ii) a polyethylene- imine; and iii) heparin.

The blood compartment of the capillary dialyzer, which comprises the lumen of the hollow fiber membranes, is connect ^¬ ed to the extracorporeal blood circuit. In other words, during operation of the extracorporeal blood circuit, the blood flow in the extracorporeal blood circuit passes through the blood compartment of the capillary dialyzer and thus through the lumen of the hollow fiber membranes, as is the customary setup for a dialyzer.

Diffusion- and/or filtration devices comprising semipermeable membranes comprising i) a copolymer of acrylonitrile and sodium methallyl sulfonate, ii) a polyethyleneimine, and iii) heparin are known in the art.

US 2003/0021826 Al discloses binding an anticoagulation agent in a stable manner to the surface of semi-permeable membranes essentially comprised of a copolymer of acryloni ^¬ trile and at least one anionic and anionizable monomer. A semi-permeable composite membrane is disclosed which com ^¬ prises a semi-permeable support membrane and an anticoagu ^¬ lation agent suitable for the treatment of blood or plasma by extracorporeal circulation, said semi-permeable support membrane being essentially constituted by a polyacryloni- trile carrying anionic or anionizable groups; the surface of the semipermeable support membrane intended to be brought into contact with the blood or plasma is coated in succession with a cationic polymer carrying cationic groups which can form an ionic bond with anionic or anionizable groups of polyacrylonitrile, the cationic polymer (for ex- ample polyethyleneimine, PEI) comprising chains of a size which is sufficient not to traverse the semi-permeable sup ^¬ port membrane, and an anticoagulation agent carrying anionic groups which are capable of forming an ionic bond with cationic groups of said cationic polymer (for example hepa ^¬ rin) .

WO 2007/148147 Al describes the use, on a membrane prefera ^¬ bly based on a copolymer of acrylonitrile and sodium me- thallyl sulfonate, of a solution of a polymer carrying anionic or anionizable groups in the colloidal form and in an acidic medium, in particular by mixing, for example, a solution of polymer carrying anionic or anionizable groups with a solution of organic polyacid in a specific propor ^¬ tion with respect to said polymer, which results in an increase in both the quantity of polymer grafted to the sur ^¬ face of the membrane and the availability of free cationic or cationizable groups at the surface of this membrane coating. The membrane described allows a large quantity of compounds carrying anionic or anionizable groups to be bound. It is suggested for the treatment of septic syn ^¬ drome, in particular for adsorbing endotoxins contained in the biological fluid, for purifying certain molecules con ^¬ tained in the blood or the plasma by extracorporeal circu ^¬ lation and for reducing systemic anticoagulation in a patient during an extracorporeal blood or plasma treatment. A method for preparing the membrane is also described in WO 2007/148147 Al .

The diffusion- and/or filtration device removes excessive water from the patient by ultrafiltration and also adsorbs inflammatory mediators from the blood of the patient. Exam ^¬ ples of suitable diffusion- and/or filtration devices include commercial capillary dialyzers available from Gambro Lundia AB under the trade names oXiris ^® and Evodial ^® . One example for a current product comprising a AN69 type membrane is the Evodial dialyzer, which is a hemodialyzer equipped with a heparin-grafted acrylonitrile based mem ^¬ brane such as described in the aforementioned WO 2007/148147 Al (the so-called HeprAN membrane) . The Evodial membrane is characterized also in that the charged surface, originating from anionic sulfonate groups, is neutralized by the polycationic biopolymer polyethyleneimine. The sur ^¬ face treatment also allows the almost irreversible fixing of said heparin through very strong ionic binding between the negative charges of heparin and the free positive charges of the cationic polymer. Membranes having the abil ^¬ ity to immobilize heparin are highly desirable as it fur ^¬ ther reduces the need of systemic doses of heparin.

In one embodiment of the extracorporeal blood circuit, the membranes of the diffusion- and/or filtration device comprise polyethyleneimine in an amount of from 10 to 100 mg, for instance, from 25 to 50 mg per m ² of membrane surface area, and from 1,500 to 10,000 UI, for instance, 3,000 to 6,000 UI, e.g. 4,50011,500 UI, of heparin per m ² of mem ^¬ brane surface area.

In one embodiment, the diffusion- and/or filtration device comprises hollow fiber membranes having an inner diameter in the range of from 180 to 260 ym, e.g. 210 ym, or 240 ym. In one embodiment, the wall strength of the hollow fiber membranes is in the range of from 30 to 60 ym, e.g., 40 to 50 ym. In one embodiment, the overall surface area of the membranes in the diffusion- and/or filtration device is in the range of from 1 to 3 m ² , for instance, 1.0 to 2.2 m ² .

In one embodiment, the hollow fiber membranes in the diffu ^¬ sion- and/or filtration device show sieving coefficients, measured at 37°C in bovine plasma having a protein content of 60 g/1, of > 0.95 for inulin; > 0.55 for myoglobin; and < 0.01 for albumin.

The membranes in the diffusion- and/or filtration device have a remarkable ability to immobilize inflammatory media ^¬ tors and endotoxins to their surface by adsorption. In one embodiment, the clearance rate for IL-6 in HDF mode with Q _B =400ml/min, Q _D =700ml/min and UF= 100 ml/min is in the range of from 20 to 40 ml/min.

The extracorporeal blood circuit of the present disclosure also comprises a gas exchange device. The gas exchange de ^¬ vice performs gas exchange in the blood of the patient, i.e., it removes carbon dioxide from the blood and/or oxy ^¬ genates the blood. In one embodiment of the extracorporeal circuit, the gas exchange device is a membrane oxygenator. Membrane oxygenators are known in the art, and a large va ^¬ riety of devices is commercially available. The membrane oxygenator comprises semipermeable polymer membranes. Exam ^¬ ples of suitable polymers include polypropylene, polyeth ^¬ ylene, poly-4-methylpentene (PMP) , polyvinylidene fluoride (PVDF) , and polytetrafluoroethylene (PTFE) . In another em ^¬ bodiment, the gas exchange device is a bubble oxygenator. Bubble oxygenators also are known in the art, and commer ^¬ cially available.

In one embodiment, the extracorporeal blood circuit of the present disclosure is a cardiopulmonary bypass (CPB) . In one embodiment, the cardiopulmonary bypass is a veno ^¬ arterial bypass. In another embodiment, the cardiopulmonary bypass is a veno-venous bypass. In one embodiment, the ex ^¬ tracorporeal blood circuit comprises a heart-lung machine (HLM) . In another embodiment, the extracorporeal blood cir ^¬ cuit is configured for extracorporeal membrane oxygenation (ECMO) . In one embodiment, the extracorporeal blood circuit is configured for veno-arterial (VA) ECMO. In another em ^¬ bodiment, the extracorporeal blood circuit is configured for veno-venous (VV) ECMO.

The present disclosure also concerns the use of a diffu ^¬ sion- and/or filtration device comprising semipermeable membranes in cardiopulmonary bypass or ECMO. The membranes comprise i) a copolymer of acrylonitrile and sodium methai- lyl sulfonate; ii) a polyethyleneimine ; and iii) heparin. In one embodiment, the diffusion- and/or filtration device is a capillary dialyzer comprising a plurality of semipermeable hollow fiber membranes. In one embodiment, the car ^¬ diopulmonary bypass comprises a membrane oxygenator. In a further embodiment, the cardiopulmonary bypass comprises a heart-lung machine.

When blood from a patient passes through the extracorporeal circuit of the present disclosure, the gas exchange device removes carbon dioxide from the blood and/or oxygenates it, i.e., replenishes it with oxygen. Inflammatory mediators and endotoxins are adsorbed by the diffusion- and/or fil ^¬ tration device; and water is withdrawn from the bloodstream by ultrafiltration. It is an advantage of the extracorpore ^¬ al circuit of the present disclosure that removal of in ^¬ flammatory mediators and endotoxins as well as removal of excess water from the patient are accomplished using a sin ^¬ gle diffusion- and/or filtration device. This greatly simplifies the assembly and operation of the extracorporeal circuit. It is hypothesized that in comparison to a cardio ^¬ pulmonary bypass which only features a hemofilter for removing excess water, the additional removal of inflammatory mediators and endotoxins positively affects the outcome of surgical procedures requiring CPB. It will be readily apparent to one skilled in the art that various substitutions and modifications may be made to the invention disclosed herein without departing from the scope and spirit of the invention.

The present invention is illustrated by way of non-limiting examples which are further detailed in the Figures accompa ^¬ nying them in order to further facilitate the understanding of the invention.

Examples

Removal of inflammatory mediators and endotoxins by a ca ^¬ pillary dialyzer having an effective surface area of 1.5 m ²

(oXiris ^® , Gambro Lundia AB) was tested. The dialyzer com ^¬ prises hollow fiber membranes comprising a copolymer of ac- rylonitrile and sodium methallyl sulfonate. The surface of the fibers comprises 30 mg/m ² of high MW polyethyleneimine

(PEI) and is grafted with 4,500 ± 1,500 UI/m ² of heparin. The fibers have an inner diameter of 240 ym and a wall strength of 40 ym.

Interleukin-10 (IL-10; MW=18 kDa) , Interleukin 6 (IL-6; MW=26 kDa), High-mobility group box 1 (HMGB-1; MW=30 kDa) and Tumor necrosis factor alpha (TNF-a; MW=51 kDa) were used as cytokines. Lipopolysaccharide (LPS; MW>100 kDa) was used as endotoxin.

The in vitro experiments were conducted using a pool of 500 ml of frozen human plasma with a protein content of 60±5 g/1 from healthy volunteers stabilized with a LPS theoreti ^¬ cal concentration of [25 — 75] EU/mL. Spiking of IL-10, IL- 6, HMGB-1 and TNF-a cytokines at a respective concentration of 500 pg/mL, 1,500 pg/mL, 30 ng/mL and 250 pg/mL was performed prior to the start of circulation.

A number of n=3 samples was selected (including n=3 multi ^¬ ple batches) , which has been found adequate to demonstrate a systematic removal mechanism and considering that clinical outcomes related to endotoxin/cytokine removal may sig ^¬ nificantly differ depending on the patient pathological conditions (no direct clinical correlation between the foreseen cytokine adsorbed quantity and the plasma final circulating cytokine level) . The circulation conditions are representative of standard CRRT practices.

Prior to circulation of the plasma pool, the blood compart ^¬ ment of the dialyzer was washed with 1.5 L of heparinized (5 UI/mL) saline solution at 150 ml/min. Additional 500 ml of the solution were used to rinse the dialysate compart ^¬ ment by ultrafiltration.

The plasma pool was circulated in a closed loop for 120 min at 150 ml/min. Sampling was performed during the circula ^¬ tion at baseline and after t=5, t=10, t=30, t=60 and t=120 min directly from the plasma pool.

Concentration of cytokines was measured in duplicate by en ^¬ zyme-linked immunosorbent assay (ELISA) utilizing matched antibody pairs and recombinant (Quantikine R&D system, France; and IBL international, Germany for human HMGB-1) . LPS concentration was measured in duplicate by limulus amoebocyte lysate (LAL) chromogenic method (K-QCL Lonza as ^¬ say) .

Removal Rate specifications at the end of the circulation (t=120 min) are calculated for each mediator using: RR(t=120 min) ^— min) ] X 100 with

C (t=0 min) · initial concentration in the plasma pool

(baseline sample)

min) : final concentration in the plasma pool at

t=120 min

The results are summarized in Table 1.

Tab .1 Mean calculated removal rate at t=120 min for IL-10, IL-6, HMGB-1, TNF-a cytokines and LPS

The in vitro experiments confirm the high affinity of the oXiris ^® membrane to the different cytokines challenged (IL- 10 / IL-6 / HMGB-1 and TNF-a) as well as to the endotoxin LPS. Those observations appear consistent with available clinical evidence, suggesting the capability of the device for selective elimination of inflammatory mediators and as ^¬ sociated improved patient condition (improved SOFA score and cardiovascular function) .