(19) United States
`(12) Patent Application Publication
`Utterberg et al.
`
`(10) Pub. No.: US 2002/0007137 Al
`Jan. 17, 2002
`( 43) Pub. Date:
`
`I lllll llllllll II llllll lllll lllll lllll lllll 1111111111111111111111111111111111
`US 20020007137 Al
`
`(54) DIALYSIS PRESSURE MONITORING WITH
`CLOT SUPPRESSION
`
`(76)
`
`Inventors: David S. Utterberg, Seattle, WA (US);
`William J. Schnell, Libertyville, IL
`(US)
`
`Correspondence Address:
`Garrettson Ellis
`SEYFARTH SHAW
`55 East Monroe Street
`Chicago, IL 60603 (US)
`
`(21) Appl. No.:
`
`09/957,990
`
`(22) Filed:
`
`Sep.21,2001
`
`Related U.S. Application Data
`
`(63) Continuation-in-part of application No. 09/203,274,
`filed on Dec. 1, 1998.
`
`Publication Classification
`
`(51)
`
`Int. Cl.7 .................................................... A61M 37/00
`
`(52) U.S. Cl. ............................................................ 604/4.01
`
`(57)
`
`ABSTRACT
`
`Pressure is sensed in blood flow tubing by placing an
`aqueous, preferably isotonic, substantially cell-free solution
`into branch connection tubing (branch tube) that connects in
`branching relation with the blood flow tubing at one end.
`The branch connection tubing may also connect in use with
`a pressure transducer unit at its other end, or pressure may
`be mechanically indicated. An air volume is maintained,
`occupying a portion of the branch connection tubing which
`is adjacent to the other end. One flows positively or nega(cid:173)
`tively pressurized blood through the blood flow tubing, with
`the result that the pressure of the blood is communicated
`through the aqueous solution and the air volume in the
`branch connection tubing to the pressure transducer unit,
`with the blood being spaced from the air volume. Preferably,
`substantially all of the branch connection tubing containing
`the aqueous solution and air volume has an inner diameter
`of substantially no more than 5 mm. This facilitates the
`continued separation of blood and solution when pressurized
`blood enters the branch connection tubing through the one
`end.
`
`DIALYSIS MACHINE
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`Patent Application Publication
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`Jan. 17, 2002 Sheet 1 of S
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`US 2002/0007137 Al
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`54
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`FIG. 1
`
`DIALYSIS MACHINE
`
`44
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`58~
`\
`I
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`37
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`34
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`·---10
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`24
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`26
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`p
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`14
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`Patent Application Publication
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`Jan. 17, 2002 Sheet 2 of 5
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`US 2002/0007137 Al
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`54
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`52
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`50
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`48
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`FIG. 1A
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`DIALYSIS MACHINE
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`44
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`Patent Application Publication
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`Jan. 17, 2002 Sheet 3 of 5
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`US 2002/0007137 Al
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`FIG. 2
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`DIALYSIS MACHINE
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`44.a
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`54a
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`52a
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`46a
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`48a
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`38a
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`29a
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`27a__/
`28a
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`24a
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`Patent Application Publication
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`Jan. 17, 2002 Sheet 4 of 5
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`US 2002/0007137 Al
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`FIG. 3
`
`DIALYSIS MACHINE
`44c
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`45c
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`43c
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`42c
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`88
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`80
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`37c
`56d
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`92
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`94
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`59c
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`84
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`10c
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`Patent Application Publication
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`Jan. 17, 2002 Sheet 5 of 5
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`US 2002/0007137 Al
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`FIG. 4
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`(Oe
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`I 02
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`US 2002/0007137 Al
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`Jan. 17,2002
`
`1
`
`DIALYSIS PRESSURE MONITORING WITH CLOT
`SUPPRESSION
`
`CROSS REFERENCE TO RELATED
`APPLICATION
`
`[0001] This is a continuation-in-part of Utterberg et al.
`application Ser. No. 09/203,274, filed Dec. 1, 1998.
`
`BACKGROUND OF THE INVENTION
`
`[0002] Arterial and venous blood pressures in hemodialy(cid:173)
`sis and other extracorporeal tube sets have traditionally been
`measured indirectly via a blood/air interface and air column
`communicating with a pressure measuring transducer. Such
`interface is typically located in an air trap chamber. The air
`column typically is contained within and communicates
`between various components: the top of a chamber, a
`pressure monitor tube (PMT), a dialysis machine tubing and
`a pressure measuring transducer housing within the dialysis
`machine. Also known are blood/air interfaces without a
`chamber where a PMT communicates with a blood tube at
`a "T" connection.
`
`[0003] Each air column typically comprises a sterile cham(cid:173)
`ber/PMT portion and an unsterile machine portion. A steril(cid:173)
`ity barrier (or transducer protector), capable of transmitting
`air pressure while maintaining sterility, separates the sterile
`chamber/PMT portion from each unsterile machine portion.
`Typically the sterility barrier is a hydrophobic membrane
`permeable to air flow but not to aqueous liquids. Typically,
`the air column has an large cross section in the air trap
`chamber (10-35 mm ID) and a narrow cross section in the
`PMT (0.5-3.5 mm ID).
`
`[0004] Such blood/air interfaces have numerous problems.
`First, blood exposed to air activates a clotting cascade,
`usually in direct proportion to the blood/air interface surface
`area and to the degree of stagnation of the blood at the
`interface. Anticoagulants such as heparin are required to
`counteract such clotting tendency. Anticoagulants are costly
`and have numerous side effects for the patient.
`
`[0005] Second, air in conventional air trap chambers can
`escape and enter the patient, even if no air enters the
`chamber in the incoming blood flow. That is, if and when the
`blood/air interface falls below the blood inlet (e.g., a down(cid:173)
`spout) the incoming blood flow causes cavitation at the
`interface and entrains air emboli in the downward blood
`flow, such that the air may escape the air trap chamber.
`
`[0006] Third, air trap chambers often comprise over 20
`percent of the size, weight and cost of the entire blood tubing
`set.
`
`[0007] The fourth problem relates to blood/air interface
`level changes in the chamber due to pressure reductions
`(where liquid level goes down) and pressure increases
`(where liquid level goes up). Such level changes promote a
`risk of inhibiting accurate pressure measurements and may
`promote air emboli passing to the patient. The degree of
`blood/air interface level change is in direct proportion to the
`total volume of air in both the tube set and pressure machine
`portions according to Boyle's law. Machine air volumes
`typically vary from 0.5 cc to more than 10 cc, depending on
`manufacturer and model. PMT air volumes typically range
`from 0.5 cc to 6 cc. Chamber air volumes depend on the
`blood level chosen by the clinician, but typically range from
`
`3 cc to 20 cc. With the blood pump off, blood pressures are
`zero, and the arterial and venous blood/air interfaces are at
`the level in the chamber initially chosen by the clinician. But
`when blood flows increase to typical speeds (e.g. 450
`ml/min with 15 G AVF needles), pre-pump pressures drop as
`much as -400 mmHg or more and post-pump pressures
`increase as much as +500 mmHg.
`
`[0008]
`In the positive pressure case, the air volume may be
`compressed as much as 40 percent or more ((1160 mmHg-
`760 mmHg)/760 mmHg). If the chamber/PMT air volume is
`less than 40 percent of the total air volume, the blood/air
`interface level can rise into the PMT until it is stopped by the
`transducer protector. Blood is thus trapped in the transducer
`protector and typically clots, and the machine transducer is
`no longer able to accurately measure pressure. This is a
`highly dangerous situation. In the negative pressure case, the
`air volume may be expanded as much as 65 percent or more
`(760 mmHg/(760 mmHg-300 mmHg)). If the chamber
`blood volume is less than the expansion air volume, the
`blood/air interface may fall until it empties the chamber and
`passes air to the patient, causing air emboli, an even more
`dangerous situation.
`
`[0009] A fifth problem relates to dialysis tube sets and
`dialyzers requiring priming with physiologic fluid to elimi(cid:173)
`nate unwanted air prior to processing blood through the
`circuit. In typical prior art chambers, an initial saline prime
`creates a saline/air interface in an upper portion of the
`chamber at a position chosen by the physician. When blood
`flow starts, however, saline is completely displaced by blood
`due to the excellent mixing in these chambers. Typically, the
`blood inlet is close to the saline/air interface or points at the
`saline/air interface. Thus, the saline/air interface quickly
`becomes a blood/air interface.
`
`[0010] Other prior art chambers have long blood inlet
`downspouts or other arrangements to enter the chamber well
`below the fluid level in the chamber and pointed away from
`the fluid level. For example, Fresenius AG has an air trap
`chamber designed to promote a blood/saline or plasma/air
`interface with the blood inlet directed transversely and
`located well below the interface of the chamber. In these
`chambers, the initial saline/air interface may be set well
`above the blood inlet to the chamber. Blood is slightly
`heavier than saline (the cellular elements more so than
`plasma), so when blood enters the chamber (especially at
`low or moderate flow common in Europe and Japan), blood
`tends not to invade the stagnant (saline) area above the inlet
`level. This is often sufficient to stratify into a blood/saline/air
`interface or even stratify into a blood/plasma/air interface
`since plasma is almost the density of saline and will rise
`above blood's cellular elements if relatively undisturbed. As
`saline-to-air contact
`initiates no clotting-cascade, and
`plasma-to-air contact has few if any initiators for clotting,
`this design is thought to provide clotting protection over a
`normal blood/air interface.
`
`[0011]
`In practice, however, this approach has had little
`practical value. Dialysis has many events that cause abrupt
`pressure changes: peristaltic pump action at high flows (a
`large pressure pulse where flow instantaneously slows, stops
`or even reverses with each roller stroke); pump stoppages
`due to alarms; patient movements, patient coughing, line
`kinking, inadvertent clamping, etc. These pressure changes
`cause the fluid level to rise or fall rapidly. In those chambers
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`which have large cross sectional areas, "plug flow" does not
`occur. Instead, blood "burps" up into the stagnant plasma or
`saline layers, and displaces some or all of the plasma and/or
`saline. Now blood is in a stagnant area of the chamber with
`a blood/air interface, and significant clotting is created.
`"Plug flow" is the movement of two fluids in a tube as
`separate but intact bodies, such that an interface separating
`the two fluids is maintained. Plug flow is easier with
`relatively small ID tubes than larger tubes.
`
`[0012] Sixth, a greater destroyer of a stable blood/plasma
`or saline interface in air trap chambers is air bubbles
`entrained in the incoming blood flow. These bubbles rise to
`the surface, passing through any saline or plasma layers
`because the cross sectional area of these chambers is much
`larger than the diameter of these bubbles. If bubbles enter a
`tube small enough that the bubble bridges from wall to wall,
`frictional forces stop the bubble from rising further, unless
`convective forces push on the fluid column. The bubble
`locks the fluid above the bubble from mixing with the fluid
`below the bubble (as artfully employed by clinical analyz(cid:173)
`ers). Bubbles of less diameter than the tube they are carried
`in, however, will freely rise. Due to the non-airfoil shape of
`these bubbles, they drag up blood in their wake into the
`plasma/saline layers. It takes relatively few bubbles to
`completely displace essentially all plasma or saline with
`blood creating a stagnant blood/air interface. As above, this
`blood is now subject to the stagnation clotting cascade
`mechanism.
`
`[0013] The prior art also includes Cabe machines that
`mate with a sterile cassette tube set with a non-porous,
`diaphragmatic sterility barrier mounted directly in an air trap
`chamber side wall, which eliminates the need for a pressure
`monitor tube. This set does, however, comprise a blood/air
`interface in the air trap chamber. Brugger et al U.S. Pat. No.
`5,693,008 shows an arrangement of machine and tube set
`which eliminates the blood/air interface. Zanger U.S. Pat.
`No. 5,392,653 discloses blood pressure measurement with(cid:173)
`out an blood/air interface, using a diaphragm in direct
`connection with a force transducer.
`
`[0014] Another prior art of a Japanese company seeks to
`overcome the blood/air problem by interposing a low weight
`fat between the blood and air phases. It discloses injecting
`a low weight fat into each chamber. Because this fat's
`density is significantly below that of blood or plasma, it
`floats on top and prevent a blood/air interface, and if the
`layer is disrupted by bubbles or pressure pulses, the fat again
`rises to become the air interface. It also claims that fat does
`not initiate any clotting cascade mechanism. The expense
`and pharmaceutical regulatory approval required of this
`approach has apparently prevented its use.
`
`[0015] Worldwide, all hemodialysis machines in use today
`are designed for blood/air interface
`tube sets. These
`machines provide over 120 million dialyses per year for over
`800,000 end stage renal disease patients. Recent disclosures
`of airless blood tubing sets will require new machines and
`many years to bring their benefits to a substantial number of
`patients. It is an objective of this invention to create tube sets
`and methods for all presently existing machines, and new
`machines, that eliminate the blood/air interface. It is also a
`preferred objective of this invention to reduce the amount of
`anticoagulant required to perform dialysis. It is a preferred
`objective of this invention to reduce clotting in the tube sets,
`
`putting the saline column at least partially in a tube that has
`an inner diameter that substantially promotes "plug flow"
`and keeps the saline in between the blood phase and the air
`phase. It is a preferred objective of this invention that no
`modification of the existing machines is required to use
`these tube sets and methods. Also by this invention, the
`number of tube set components can be reduced in number,
`size and cost.
`
`DESCRIPTION OF THE INVENTION
`
`[0016] By this invention, the blood/air interface can be
`eliminated while sensing pressure in blood flow tubing. The
`method comprises: placing an aqueous, typically physiologi(cid:173)
`cal, isotonic, substantially cell-free solution, (typically nor(cid:173)
`mal medical saline solution or the like) into branch connec(cid:173)
`tion tubing that connects in branching relation with the
`blood flow tubing at one end, and connecting with a pressure
`transducer unit at its other end. An air volume is maintained
`to occupy a portion of the branch connection tubing which
`is adjacent to the other end near the pressure transducer unit.
`One then flows positively or negatively pressurized blood
`through the blood flow tubing. Thus, the pressure of the
`blood is communicated through the aqueous solution and
`then the air volume in the branch connection tubing to the
`pressure transducer unit, with the blood being spaced from
`the air volume.
`
`[0017] Typically, substantially all of the branch connec(cid:173)
`tion tubing containing the aqueous solution and air volume
`has an inner diameter of substantially no more than 5 mm.
`One purpose of this is to facilitate continued separation of
`blood and the solution described above, when pressurized
`blood enters the branch connection tubing through the one
`end. Preferably, the inner diameter of the tubing will be
`substantially no more than 3.5 mm.
`
`[0018] While the above facilitates the continued separa(cid:173)
`tion of blood and solution, a certain amount of mixing may
`take place in the branch connection tubing so that the
`aqueous, cell-free solution can become pink in the area
`adjacent to the blood-solution interface. For this and other
`reasons, it is preferred for a priming solution tube, which is
`connected to a source of priming solution, to be connected
`in branching relation with the branch connection tube. Thus,
`added portions of priming solution can be periodically added
`to push downwardly the aqueous solution in the branch
`connection tubing, which has become mixed with a small
`amount of blood, into the blood flow tubing during opera(cid:173)
`tion, so that the aqueous solution in the branch connection
`tubing can remain substantially blood cell-free.
`
`[0019]
`In this invention, the blood/air interface of the prior
`art is thus replaced on a continuing basis by a blood/saline/
`air interface. A saline column (or other appropriate solution)
`is interposed during the priming procedure between the
`blood phase and the air phase. The saline column, saline/air
`interface and air column are located within the branch
`connection tubing communicating with a main blood flow
`tube, optionally with an enlarged chamber of the main blood
`flow tube. Preferably, such a blood chamber is filled com(cid:173)
`pletely (eliminating any blood/air interface), and is well
`mixed. Preferably, the branch connection tubing is sized to
`promote plug flow (so as to prevent the blood/saline inter(cid:173)
`face from rapidly degrading with pressure pulses, alarms,
`patient movements and changes in blood pressure from
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`atmospheric to operating pressures) and to resist free flow of
`air bubbles. Its inlet to the blood flow tubing may be
`positioned below the highest point in the chamber so as to
`resist entry of air bubbles.
`[0020] The ratio of the saline volume in the chamber/PMT
`to the air volume in the system is sufficient to prevent
`transducer protectors of the pressure transducer unit from
`being wetted out in a positive pressure situation, or air being
`dumped into the main blood tube in a negative pressure
`situation. An in-line chamber maybe added to the branch
`connection tubing to help accomplish this.
`[0021] This invention may use a variety of designs and
`methods, with and without air trap chambers in the blood
`tubing or in branch saline or air tubing.
`[0022] The aqueous solution may be formulated to be
`compatible with blood to suppress clotting, for example, by
`the addition of heparin or the like. The heparin line which is
`conventionally found in extracorporeal blood sets may be
`connected in another branching connection to the branch
`connection tubing, typically at a connection downstream of
`a branch connection with the source of added aqueous
`solution, for priming and patient fluid maintenance.
`[0023] The branch connection tubing may, if desired,
`define an in-line chamber that preferably extends for no
`more than 10 percent (and typically less than 7 percent) of
`the length of the branch connection tubing. The purpose of
`this is to provide an increased volume to the branch con(cid:173)
`nection tubing, to reduce the movement of particularly the
`interface between blood and the aqueous solution as blood
`pressure changes.
`[0024] Also, it may be desirable for the branch connection
`tubing to comprise a flow-resisting constriction to slow
`movement of the interface boundary between the blood and
`aqueous solution upon pressure changes. Particularly, the
`flow-resisting constriction is preferably positioned at a por(cid:173)
`tion of the branch connection tubing that carries the aqueous
`solution, farther up the tubing than blood would be expected
`to travel. Thus, the movement of the interface boundary
`between the blood and the aqueous solution maybe slowed
`in a manner to reduce mixing of blood and solution at their
`interface in the event of large, sudden pressure changes.
`Preferably, the flow-resisting constriction is positioned at a
`portion of the branch connection tubing that carries the
`aqueous solution, to spare the blood from the stresses that
`might be encountered by passing through such restriction.
`[0025]
`In another embodiment, the main blood flow tubing
`may comprise an enlarged chamber portion. The branch
`connection tube connects in branching relation with the
`blood flow tubing through a wall of the enlarged chamber
`portion. The enlarged chamber portion is preferably com(cid:173)
`pletely filled with aqueous solution at the end of priming of
`the set for use, and then it becomes completely filled with
`blood, except for air bubbles that may be trapped in the
`chamber during the use, and are periodically drawn away by
`a syringe through an injection site or branch tube, or through
`a hydrophobic vent, in conventional manner.
`[0026]
`In this embodiment, the branch connection tube
`may have a proximal end portion which extends for a
`substantial distance into the enlarged chamber portion
`inwardly through its wall. In use, the interface boundary
`between the blood and aqueous fluid may occupy the
`proximal end portion.
`
`[0027] The branch connection tube may be integral and
`nonseparable along its length from its connection to the
`main blood flow tubing, to the connector at its other end
`through which it connects with the pressure transducer unit.
`Alternatively, the branch connection tube may be separable
`into two or more serial components by means of a pair or
`pairs of engaging connectors in various ways as maybe
`desired. For example, the branch connection tube maybe
`separable by a pair of adjoining connectors positioned
`between a T- or Y-junction where a line to a source of
`priming solution connects with the branching tubing, and to
`the main blood tube, so that most of the branch connection
`tubing and its connected priming solution tube can be a
`separate set. Alternatively, the tube that connects between
`the priming solution and the branch connection tubing
`maybe a separate set, while the branch connection tubing is
`integral with the main blood tube. As another alternative, the
`branch connection tubing may carry an in-line chamber
`comprising preferably less than ten percent of the length of
`the branch connection tubing, and the line connected to the
`source of aqueous, cell-free solution (priming solution) can
`connect to that chamber in a form of a branch connection.
`[0028] Branch connection tubings may connect to the
`blood tube both upstream (negative pressure) and down(cid:173)
`stream (positive pressure) of roller pump tubing, or other
`tubing which engages another type of pump for pumping
`through the tubing. Each of these branch connection tubings
`may communicate with a pressure transducer so that
`upstream and/or downstream pressure from the pump can be
`measured. The tubings will each have an air filled section
`adjacent the transducer protector and an aqueous solution(cid:173)
`filled section adjacent the blood tube in accordance with this
`invention. Also, if desired, tubing may connect to each of
`these tubings in branching connection to provide access to a
`source of aqueous, isotonic, substantially cell-free solution
`(such as normal saline solution) so that such solution may be
`applied to the branch connection tubing. This solution may
`also be added back to the blood after treatment by hemo(cid:173)
`filtration for example, to give the patient a desired hemat(cid:173)
`ocrit in the blood before returning the blood to the patient.
`[0029] The invention of this application may be utilized in
`the particular sets and the process of automatic priming
`thereof that fall under the scope of the invention as described
`in Utterberg U.S. patent application Ser. No. 08/954,804,
`filed Oct. 21, 1997, entitled "Automatic Priming of Blood
`Sets", now U.S. Pat. No. 5,951,870.
`[0030]
`In another embodiment of this invention, an elec(cid:173)
`tronic transducer for pressure sensing can be dispensed with,
`and the pressure may be directly sensed by observing the
`behavior of a chamber or the interface between an aqueous
`solution-filled section and an air-filled section of the cham(cid:173)
`ber of branch connection tubing, as more specifically
`described below.
`DESCRIPTION OF THE DRAWINGS
`[0031] FIG. 1 is a partially schematic view of a hemodi(cid:173)
`alysis blood circuit system, showing one embodiment of the
`invention;
`[0032] FIG. lA shows the circuit system of FIG. 1 in its
`priming mode prior to adding blood;
`[0033] FIG. 2 is an elevational view of a portion of
`another hemodialysis blood circuit showing other embodi(cid:173)
`ments of the invention of this application;
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`[0034] FIG. 3 is an elevational view of a portion of a third
`hemodialysis blood circuit, showing another embodiment of
`this invention; and
`
`interface is formed because there is no venting outlet for
`tube 36 on its end connected with transducer protector 40
`and pressure transducer 42.
`
`[0035] FIG. 4 is an elevational view of a portion of a
`fourth hemodialysis blood circuit, showing another embodi(cid:173)
`ment of this invention.
`
`DESCRIPTION OF SPECIFIC EMBODIMENTS
`
`[0036] Referring to the drawings, FIG. 1 shows an
`embodiment of the invention for arterial pre-pump pressure
`monitoring, showing a partially schematic blood flow circuit
`for removing blood from patient P, passing the blood
`through blood flow tubing system 10 including arterial line
`24, and a generally conventional blood pumping system 12,
`passing blood through a hemodialyzer 14 or other blood
`processing device such as a hemofiltration device, and then
`via venous line 26 returning the blood to the patient. As is
`conventional, blood pump 12 may comprise a length of
`peristaltic pump tubing 16 having connectors 18, 20 at the
`respective ends thereof, which may connect with branch
`connection line or lines 22 in conventional manner. Branch
`connection line 22 may be used to add heparin, to remove
`blood samples, or the like.
`
`[0037] As shown in FIG. 1, a section 28 of branch
`connection tubing 27 is provided, being integral with arterial
`blood tubing 24, and connecting with a second section 30 of
`the branch connection tubing 27 by means of a conventional
`luer lock connector system 32 or the like. Branch connection
`tubing section 30 defines a flow path that extends through
`T-connector 34 and then through a third section 36 of branch
`connection tubing 27 that terminates in a female luer con(cid:173)
`nector 38.
`
`[0038] Connector 38 is shown to connect to a transducer
`protector 40 of known design, which carries an air perme(cid:173)
`able, liquid blocking barrier, to protect a conventional pres(cid:173)
`sure transducer 42, which is positioned within the housing of
`a conventional dialysis machine 44 of present commercial
`design, which machine controls the flow and dialysis con(cid:173)
`ditions through the system and monitors necessary param(cid:173)
`eters in known manner. Usually, dialyzer 14 is carried on the
`dialysis machine 44, although not so shown in this schematic
`view of FIG. 1.
`
`[0039] T-connector 34 has a third connection which com(cid:173)
`municates with priming solution tube 46, which carries a
`roller clamp 48, and terminates at its upper end in a
`conventional I.V. drip chamber 50. Drip chamber 50 has a
`conventional spike 52, which is shown to be in connection
`with a bag of medical saline solution 54.
`
`In accordance with this invention, referring to FIG.
`[0040]
`1 a, flow of liquid from saline bag 54 is opened after all
`connections are made so that saline solution fills the sections
`of branch connection tubing 27, and also flows into arterial
`blood flow tubing 24 to prime the respective arterial and
`venous tubing sets 24, 26 and the dialyzer 14, preferably via
`removable recirculation tube 99 prior to patient connection.
`Clamp 37 may be opened so that an amount of the solution
`from bag 54 passes into tube section 36 by venting out via
`temporarily unconnected transducer protector 40, stopping
`at some clinically chosen point along the tube such as point
`56, where a solution-air interface is formed after transducer
`protector 40 is sealed to the machine fitment 41. This
`
`[0041] Then, referring again to FIG. 1, roller clamp 48
`may be typically closed, patient P is connected, and roller
`pump 12 begins operation, drawing blood from patient P
`into arterial set 24, while returning first priming solution and
`then blood to the patient via dialyzer 14 and then venous set
`26 in a conventional dialysis circuit.
`
`[0042] Clamps 29 and 37 remain open, so that negative
`pressure in the blood flow tubing system 10 upstream of
`pump 12 is directly transmitted through the branch connec(cid:173)
`tion tubing sections 28, 30, 36 to the pressure transducer 42.
`This negative pressure can be read out and displayed
`through the electronics of dialysis machine 44, and auto(cid:173)
`matic shut off can occur when wrong pressures are sensed.
`
`[0043] As this negative pressure is monitored during the
`operation of roller pump 12 and the flow of blood through
`tubing system 10, dynamic pressure pulse variations may
`take place, and will be transmitted through tubing sections
`28, 30, 36 to the pressure transducer 42, for a moment-by(cid:173)
`moment readout of the pressure. As negative pressure
`increases, the saline/air interface will move down line 36 to
`position 56b, for example, in a "plug flow" type manner,
`forming a stable solution-air interface because there is little
`mixing between the priming solution in tubing 36 and the
`blood. This happens because branch connection tubing sec(cid:173)
`tions 28, 30, 36 each have an inner diameter of no more than
`about 5 mm, and typically less than 3.5 mm. The solution-air
`interface 56b will correspondingly move back and forth, and
`the air found in section 58 of tubing 36 will be relatively
`compressed and decompressed as the pressure in the system
`fluctuates, transferring the moment-by-moment pressures to
`pressure transducer 42.
`
`[0044] Branch connection tubing sections 28, 30, 36 can
`be of a sufficient length that the pressure fluctuations
`encountered fail to drive the liquid-air interface 56 into
`transducer protector 40 at maximum pressures encountered,
`while also preventing minimum pressures from causing
`liquid-air interface 56b to be driven down tubing sections
`28, 30 to cause air to enter blood flow tubing 10.
`
`[0045] During operation, it may be desirable to open roller
`clamp 48 to allow more normal saline priming solution to
`pass into the branch connection tubing 27, and particularly
`tubing sections 28, 30, if blood begins to mix with the
`cell-free aqueous solution in sections 28,30. The solution
`which has become pink due to admixing with blood can pass
`into blood flow tubing circuit 10, so that a discrete blood(cid:173)
`solution interface 59 can be easily recreated as needed. The
`pressure head of solution from the elevated bag 54 is
`generally sufficient to drive solution into the blood circuit
`10. Thus, stagnant blood residing in the branch tubing 27,
`and obscuring the blood-solution interface 59 by mixing
`with the solution, can be returned to the main circuit 10. The
`effect of this is to suppress clotting, as well as to maintain
`a clear blood-solution interface 59, since stagnant blood can
`be returned to the circuit 10 before the clotting process gets
`under way. This interface 59 also can move along branch
`connector tubing 27, 28 with varying pressures.
`
`[0046] Referring to FIG. 2, a similar dialysis blood flow
`circuit lOa is shown, with a similar branch connector tube
`
`Nipro Ex. 1033
`
`000010
`
`

`
`US 2002/0007137 Al
`
`Jan. 17,2002
`
`5
`
`27a for pre-pump arterial negative pressure measurement,
`the system having components of similar number to the
`reference numerals of FIG. 1, but with the added suffix "a."
`Branch connector tubing 28a represents an integral combi(cid:173)
`nation with the other sections of the branch connection
`tubing 27a, extending from a connector 18a at one end of
`roller pump tubing 16a to female luer 38a connecting with
`transducer protector 40a and transducer 42a in dialysis
`machine 44a. The integral connection of tubing 28a to the
`main blood flow tubing lOa may be made at connector 18a
`in conventional manner.
`
`[0047] As a further modification, a chamber 34a is sub(cid:173)
`stituted for the previous T-connector of similar number,
`which chamber provides the function of a T-connector with
`respect to priming solution tube 46a, which can connect
`through spike 52a to a saline bag 54a. In this embodiment,
`chamber 34a can comprise the typical site of the liquid-air
`interface 56a, being placed in the enlarged diameter cham(cid:173)
`ber 34a relative to the tubing 28a, 36a. This also eliminates
`the need for chamber 50 of the previous embodiment, since
`chamber 34a can serve both as a drip chamber and as an
`enlarged chamber to hold the priming solution-air interface
`56a. Thus, as the system is negatively pressurize