Abstract:
A system for preparing autologous plasma comprises a single use filter unit having two inlets in fluid communication with each other, an outlet, and a filtration membrane selectively permeable to blood plasma separating the inlets from the outlet. Manually operable, single use pumps, preferably syringes, connect to the inlets. A flow path is defined along the membrane between the pumps, whereby, whole blood can be repeatedly exchanged between the two pumps, past the membrane, to cause plasma to flow across the membrane and out of the outlet. A syringe can collect plasma from the outlet. Plasma thus collected can be simultaneously applied with a thrombin solution to a site on the body, thereby forming a fibrin gel.

Description:
This application is a divisional of prior application Ser. No. 08/410,028, filed Mar. 24, 1995, U.S. Pat. No. 5,674,394, and a continuation of prior application Ser. No. 08/935,831 filed Sep. 23, 1997, U.S. Pat. No. 6,001,259, which is a divisional of prior application Ser. No. 08/410,028 filed Mar. 24, 1995, U.S. Pat. No. 5,674,394; the contents of each of these prior applications are incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a system for obtaining autologous plasma from a patient during surgery. The invention further relates to a method for preparing fibrin gel and other hemostat or tissue sealant preparations from the autologous plasma. 
     2. Background Information 
     Preparations of human coagulation factors including fibrinogen and thrombin, have been used extensively in surgery over the last ten years. These biological fibrin sealants (also known as fibrin glue, fibrin adhesive, or fibrin tissue sealant) promote hemostasis and wound healing by sealing leakage from tissues, sutures, staples, and prostheses and are particularly useful during open heart surgery in heparinized patients. The sealants also have limited use as an adhesive for the bonding of tissues and they reduce the amount of blood required for transfusions by controlling intraoperative bleeding. Their effectiveness is reflected in the extensive range of surgical applications for which they have been used, including cardiovascular surgery, plastic surgery, orthopedics, urology, obstetrics and gynecology, dentistry, maxillofacial and ophthalmic surgery. 
     Fibrin sealant products can be prepared from pooled human plasma. However, such preparations potentially risk transmission of HIV, hepatitis B and other serologically transmitted illnesses. Also, in some instances these preparations could cause immunologic reactions. 
     As an alternative, some hospitals are preparing fibrin sealant in-house using the patient&#39;s own blood (autologous) or single-donor (homologous) plasma as a source of fibrinogen and Factor XIII. The components are typically prepared by freezing plasma at temperatures below −20 7  C. overnight, slowly thawing the material at 0-4 7  C., centrifuging, and transferring the cryoprecipitate to a syringe or spray container. The procedure usually requires several hours, making the product unavailable for emergency cases. The lengthy manipulations currently required to generate fibrin sealant also introduce the risk of contaminating the product and transmitting viral infections to the technicians involved. 
     The thrombin, usually purified from bovine plasma, can be obtained commercially and is typically prepared in a separate syringe or spray container. The two solutions are delivered simultaneously or alternately to generate fibrin sealant at the site of the wound. 
     The hemostatic efficacy of fibrin glue has been well established. Autologous fibrin gel, made from plasma rather than a fibrinogen-containing precipitate, appears to have comparable hemostatic properties to traditional fibrin glue as well as valuable sealant properties. For instance, fibrin gel is useful in sealing air leaks in pulmonary procedures. 
     In preparing fibrin gel, plasma is typically obtained from autologous blood following centrifugation for about ten minutes to separate blood cells from anticoagulated blood, followed by removal of the plasma. Centrifugation in the operating room, however, may be inconvenient because of the required instrumentation, potential for aerosolization with its concomitant contamination risks, and difficulty in decontaminating instrumentation between procedures. If centrifugation takes place external to the OR, aseptic transport of the plasma fraction to the operative site is required. 
     Hollow fiber devices permitting separation of plasma from blood without the need for centrifugation have been used for plasma exchange therapy (PET). In PET, the separated plasma is eliminated and the separated blood cells with replacement fluids are returned to the patient. 
     Recently, hollow fiber filtration technology has been developed to meet the requirements of cell separation from cell cultures—including shear-sensitive mammalian cells—while allowing free passage of soluble proteins. This membrane technology offers an alternative to centrifugation, precipitation and conventional filtration techniques for bioseparations, eg. the processing of fermentation products, and is available for small volume applications. Sterilizable, disposable filtration modules are available from at least one manufacturer. 
     SUMMARY OF THE INVENTION 
     The described invention uses compact, small-volume disposable filtration technology to separate plasma from blood. In contrast to PET applications, the separated blood cells trapped by the filter are disposed of along with the filter. The separated plasma is used as a source of autologous material—eliminating the risk of cross-infection of immunological consequences. Preparation of the plasma requires no instrumentation and can be performed quickly and conveniently at the time and location of the surgical or medical procedure for which the material will be used. Specific uses for the autologous plasma obtained in this manner include preparation of fibrin gel and other hemostatic/tissue sealant formulations based on proteins and or clotting factors. 
     A single use system for obtaining autologous plasma according to the present invention comprises a plasma separator for separating plasma from whole blood. The plasma separator comprises a single use filter unit having a first inlet and a second inlet in fluid communication with each other, an outlet, and a filtration membrane separating the inlets from the outlet. The filtration membrane is selectively permeable to blood plasma. A manually operable, single use first pump comprises a receiving chamber connected to the first inlet. The receiving chamber has a manually moveable wall for altering the volume of its receiving chamber. A manually operable, single use second pump comprises a receiving chamber connected to the second inlet and a manually moveable wall for altering the volume of its receiving chamber. A flow path is defined along the membrane between the first and second pumps. Thereby, whole blood can be repeatedly exchanged between the receiving chambers in the first and second pumps, past the membrane, to cause plasma to flow across the membrane and out of the outlet. 
     Preferably, the membrane comprises one or more hollow fibers, each of the one or more fibers having a lumen therethrough, and the flow path extends through the lumens of the one or more fibers. Also preferably, the filter unit comprises an elongated housing having a first end and a second end with the one or more hollow fibers extending axially therethrough. Each of the one or more fibers has an outer surface, the housing has an inner surface and an interior space is thus formed between the outer surfaces of the fibers and the inner surface of the housing. Pottings at the first and second ends of the housing secure the fibers therein and separate the lumens from the interior space. The first pump connects to the housing first end and the second pump connects to the housing second end, each with its respective receiving chamber in fluid communication with the lumens of the hollow fibers. The outlet is in fluid communication with the interior space whereby when the blood is pumped through the lumens of the hollow fibers by the first and second pumps, the plasma flows through the membrane into the interior space of the housing and out of the outlet. Preferably, the first and second pumps comprise syringes. A collection syringe preferably connects to the outlet for receiving the plasma. 
     The system can further comprise an applicator for preparing and applying fibrin gel in a medical procedure. The applicator comprises a first injector containing a thrombin solution, a second injector containing the plasma, the plasma containing an amount of fibrinogen, and a manifold in communication with the first and second injectors for applying the thrombin solution and plasma simultaneously to a site on a body. Preferably, the first and second injectors comprise syringes. Also, the syringe forming the second injector is preferably the collection syringe. 
     The system can be provided in a sealed sterile package containing the plasma separator and the fibrin applicator; and instructions for obtaining whole blood from a patient in the first syringe, manually pumping the whole blood in alternating fashion between the first and second syringes and collecting plasma from the whole blood in the collection syringe, and simultaneously applying the plasma thus collected along with a solution of thrombin to a site on a body. 
     A method, according to the invention, for preparing fibrin gel from autologous plasma comprises the steps of: extracting a quantity of blood from a patient; providing a single use filter unit having first and second inlets and an outlet; providing first and second manually operable pumps, each having a receiving chamber with a manually moveable wall; placing the receiving chambers of the first and second pumps into fluid communication with the first and second inlets, respectively; disposing a membrane selectively permeable to blood plasma between the first and second inlets, thereby forming a flow path along the membrane between the first and second inlets and isolating them from the outlet; alternatingly and manually moving the moveable walls in the first and second pumps to provide an alternating flow between the first and second inlets along the membrane; passing the plasma through the membrane to an outlet of the filter unit; collecting the plasma; and disposing of the filter unit. 
     The method preferably further comprises the steps of mixing the plasma with thrombin to form fibrin gel and applying the fibrin gel to a site on a body. Preferably, the plasma and a solution containing the thrombin are simultaneously applied to the body site to form the fibrin gel. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of a filter for preparing autologous plasma according to the invention; 
     FIG. 2 is a sectional view taken along lines  2 — 2  of FIG. 1; 
     FIG. 3 is a sectional view taken along lines  3 — 3  of FIG. 1; and 
     FIG. 4 is a perspective view of a fibrin gel applicator according to the invention. 
    
    
     DETAILED DESCRIPTION 
     Turning now to the drawings, FIGS. 1 and 4 illustrate a system  10  for preparing fibrin gel from autologous plasma. The system  10  comprises in gross a plasma separator  12  (FIG. 1) and a fibrin gel applicator  14  (FIG.  4 ). 
     Concentrating on FIG. 1, the plasma separator comprises a filter unit  16 , a first retentate syringe  18  at a filter unit first end  20  and a second retentate syringe  22  at a filter unit second end  24 . A collection syringe  26  affixes to a central portion  28  of the filter unit  16 . Each of the syringes  18 ,  22  and  26  is of a type commonly used in the medical field and comprises a tubular body  30 , a plunger  32  with an elastomeric head  34 , and a Luer fitting  36  on the syringe body  30 . 
     Turning now to FIGS. 2 and 3, the filter unit  16  comprises an elongated tubular housing  38  having female luer fittings  40  at its first and second ends  20  and  24 . A right angle adapter  42  connects to each of the luer fittings  40  and provides a male luer fitting  44  for receiving the retentate syringes  18  and  22 . A central fitting  46  is provided in the filter unit central portion  28  and receives the collection syringe  26 . 
     One of skill in the art will appreciate that the retentate syringes  18  and  22  may attach to the housing  38  in various other fashions and orientations. For instance, appropriate mating luer fittings (not shown) may be provided at the filter unit first and second ends  20  and  24  for directly receiving the retentate syringes  18  and  22  without the need for separate adapters  42 , and of course the retentate syringes  18  and  22  may be axially oriented with respect to the housing  38 . 
     A plurality of hollow fiber filter membranes  48  extend axially through the housing  38 . As best seen in FIG. 3, each of the fibers  48  has an interior lumen  50  and outer surface  52 . The housing  38  has an interior surface  54  and an interior space  56  is defined between the fiber outer surfaces  52  and the housing inner surface  54 . A plug or potting  58  at each of the filter unit first and second ends  20  and  24  retains the fibers  48  within the housing  38  and separates the lumens  50  from the interior space  56 . 
     Preferably, the housing  38  is formed of polysulfone and the potting  58  is formed of polyurethane. of course, other materials suitable for use in medical devices may be substituted therefor. Preferably, the parts housing  38  is formed as a single unit, or if formed of separate parts is bonded using sonic welding to avoid the use of solvent bonding. The fibers  48  are preferably formed of a mixed cellulose ester membrane, polysulfone membrane, or other suitable material as is known in the art. 
     The pores (not shown) in the membrane fibers  48  are preferable sized to pass blood plasma without allowing erythrocytes or leukocytes to pass. The membrane pore size may or may not exclude blood platelets. For instance, the fibers  48  having a maximum pore size of 0.55 microns, a lumen diameter of 0.3 to 1.0 mm, a lumen length of 9.0 cm and a total membrane surface area of at least 4 square cm provides sufficient separation of plasma from whole blood without causing undo hemolysis. Preferably, flow through the fibers  48  is laminar. Sufficient surface area is important to achieving relatively quick separation of plasma from whole blood. Preferably, about 2 ml of plasma should be separable from 4 ml of whole blood in about 2 minutes. 
     Turning to FIG. 4, the fibrin gel applicator  14  may be of any type commonly know for simultaneously applying blood plasma along with a solution of thrombin. The Wolff et al. U.S. Pat. No. 5,104,375, issued Apr. 14, 1992, discloses a locking holder for a pair of syringes and a method for using the syringes to simultaneously apply blood plasma and a solution of thrombin to produce fibrin gel. The disclosure of this patent is incorporated by reference. 
     The applicator  14  comprises a first injector syringe  60  for containing a solution of thrombin, and a second injector syringe  62  for containing blood plasma. Each of the first and second injector syringes  60  and  62  connects to a manifold  64  which directs the flow of thrombin solution and plasma to a distal outlet  66 . Proximal ends  68  of the first and second injector syringes  60  and  62  are connected by a brace  70  which holds the first and second injector syringes  60  and  62  in parallel relationship to one another. A bridge  72  interconnects plungers  74  in the first and second injector syringes  60  and  62 . A finger rest  76  extends laterally from the brace  70  for easy engagement by a user&#39;s index and middle finger and an upper surface  78  of the bridge  72  easily engages a user&#39;s thumb, whereby both the first and second injector syringes  60  and  62  may be easily actuated in a single-handed operation. 
     Each of the components of the system  10  which come into contact with whole blood or plasma should be treated with an anticoagulant such as sodium citrate, EDTA, or heparin to prevent premature clot formation. Thus, the syringes  18 ,  22  and  26 , the filter unit  16  and the fibrin applicator  14  should preferably be treated with an anticoagulant. 
     The plasma separator  12  and fibrin applicator  14  are most conveniently provided in a sterile condition within a sterile package (not shown) containing instruction for obtaining whole blood from a patient, separating plasma from the whole blood, and applying the plasma and the thrombin solution simultaneously to produce fibrin gel. In such an arrangement, the first retentate syringe  18  has a standard blood collection needle tip (not shown) and contains an anticoagulant. For instance, a 10 ml syringe preferably contains 0.1 ml of a 46.7% trisodium citrate anticoagulant. Also, the collection syringe  26  preferably serves as the first injector syringe  60 . Thrombin and a hemostatic agent to overcome the anticoagulant are provided for use in the second injector syringe  62 . Preferably, 1000 units of thrombin in 9 ml of normal saline plus 0.5 ml of a 10% calcium chloride solution are mixed and packaged within the second injector syringe  62 . 
     In use, a quantity of whole blood is withdrawn from a patient using the first retentate syringe  18  with the trisodium citrate therein. The needle is removed from the first retentate syringe  18  and its luer fitting  36  connected to the luer fitting  40  at the filter unit first end  20 . The second retentate syringe  22  is similarly affixed to the filter unit second end  24 . The collection syringe  26  is then affixed to the central fitting  46 . By alternatingly depressing the plungers  32  on the first and second retentate syringes  18  and  22 , the blood is forced to flow back and forth through the lumens  50  of the membrane fibers  48 . This flow and a resulting slightly elevated pressure within the lumens  50  causes the plasma in the blood to migrate across the fibers  48  and into the interior space  56 . The central fitting  46  is in fluid communication with the interior space  56  and thus receives the blood plasma. 
     After a sufficient amount of plasma has been accumulated in the collection syringe  26 , it is removed from the filter unit  16  and inserted into the manifold  64  of the fibrin applicator  14 . The solution of thrombin containing calcium chloride and the blood plasma are then simultaneously applied to a site on the body with the fibrin applicator  14 . As the plasma and thrombin solutions mix, they create a fibrin gel which can be used in any number of medical procedures. 
     In one test, disposable tangential flow filtration units such as the filter unit  24  were used to separate plasma from canine blood. The plasma was collected within a few minutes and when combined with thrombin, formed a cohesive gelatinous clot. Clot formation as measured in a fibrinometer occurred in less than one second. In a second test, a 0.2 micron filter was used, and 1.8 ml of plasma was easily separated from approximately 4.0 ml of whole citrated porcine blood in two minutes. Clotting characteristics were similar to the first experiment. 
     While the invention has been described with regard to a particular embodiment thereof, those skilled in the art will understand, of course, that the invention is not limited thereto since modifications can be made by those skilled in the art, particularly in light of the foregoing teachings. Reasonable variation and modification are possible within the foregoing disclosure of the invention without the departing from the spirit of the invention.