Cannula and method for bidirectional blood flow

A cannula and method for bidirectional blood flow, the cannula being constructed so as to provide a bifurcated flow path, each branch of the flow path independently communicating through telescoping cannulae and a venipuncture needle initially projecting beyond the exterior cannula to facilitate venipuncture and thereafter being displaceable away from the venipuncture site to permit unobstructed simultaneous fluid flow in opposite directions through each of the bifurcated flow paths.

FIELD OF THE INVENTION 
The present invention relates to a cannula for medical use and more 
particularly to a double lumen cannula for independently conducting fluids 
into and out of a venipuncture site through two separate passageways. 
THE PRIOR ART 
Double lumen cannulae are well known in the art. The best known advantage 
offered by double lumen cannulae is the ability to separately withdraw 
blood from a blood vessel and inject blood back into the same blood vessel 
through a single venipuncture or fistula. The most common double lumen 
cannulae consist of a single tube with a horizontal division of the tube 
which places the lumen of the cannulae in immediate juxtaposition. 
Unfortunately, however, the construction of such double lumen cannulae is 
expensive, time consuming and unreliable. 
The least expensive and most reliable construction of the double lumen 
cannulae is in the form of concentric lumen disposed telescopically one 
within the other. Particularly when using cannulae for single needle 
dialysis, it is preferred to have one cannula lumen project substantially 
beyond the other. Attention is directed particularly to the common use of 
cannulae for single needle dialysis such as that disclosed and described 
in U.S. Pat. No. 3,756,234. In single needle dialysis, it is highly 
desirable to withdraw blood from a patient, treat the blood with a 
hemodialyzer (artificial kidney) and return the blood to the patient 
through the same fistula in which the blood was withdrawn. Under such 
circumstances, it is desirable to return the blood a significant distance 
upstream from where the blood is aspirated so as to minimize the problem 
of admixing. 
The problems with such telescopic construction are apparent when it is 
observed that both cannula must be used to penetrate the skin during 
venipuncture. Unless there is a smooth contour between the interior and 
exterior cannula, the venipuncture is both difficult and painful. On the 
other hand, if the telescoping cannulae present an exteriorly smooth 
surface for venipuncture, there is insufficient passageway for fluid to 
flow easily between the lumen. The structure of a double lumen cannula 
lends itself admirably to the ability to aspirate blood from a downstream 
location and to return blood at an upstream location all through the same 
fistula. However, until this present invention, structure and method for 
introducing a double lumen cannula into the bloodstream and for 
maintaining separate flow paths through a single fistula has not been 
known. 
BRIEF SUMMARY AND OBJECTS OF THE INVENTION 
The present invention, including method and apparatus, provides bifurcated 
flow paths through coextensive cannulae, the cannulae being introduced 
into the blood vessel initially by a needle which is thereafter removed to 
facilitate unobstructed flow through the independent flow paths 
established at a single fistula. 
It is, therefore, a primary object of the present invention to provide an 
improved double lumen cannula. 
It is another primary object of the present invention to provide a method 
of aspirating blood and returning blood through separate flow paths and 
through a single fistula. 
It is another primary object of the present invention to provide a novel 
double lumen cannula and method in which the needle is removed from the 
puncture site after venipuncture without adversely interfering with the 
blood flow paths. 
Another important object of the present invention is the provision for an 
elongated diametrally reduced portion of the inner cannula lumen over a 
predetermined portion of its length to provide for maximum flow between 
the lumen at minimum resistance. 
These and other objects and features of the present invention will become 
more fully apparent from the following description and appended claims 
taken in conjunction with the accompanying drawing.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Attention is now directed to the figures wherein like parts are designated 
with like numerals throughout. 
One presently preferred cannula assembly embodiment generally designated 80 
is illustrated best in FIGS. 1-3. The duplex cannula illustrated in FIGS. 
1-4 is intended to be used in any medical service and which bidirectional 
blood flow through a single fistula is desirable. One such medical service 
includes the creation of a single fistula for blood hemodialysis. In the 
description which follows, it will become apparent that the single fistula 
created by proper insertion of the duplex cannula 80 will permit blood to 
be withdrawn from and returned to a patient without creating an additional 
fistula and without otherwise modifying the structure of the assembly 80. 
The withdrawal and return of blood may occur simultaneously or serially, 
as desired. Moreover, the needle which is used to create the fistula 
through the surface of the skin can be easily and safely withdrawn from 
the fistula and concealed safely within the needle hub so as to prevent 
injury to patient or to the catheter without any auxiliary structure or 
needle protection devices. 
More particularly, the assembly 80 comprises an exterior cannula 82 which 
is mounted at the forward end 84 of a cannula hub 86. Preferably, the 
exterior cannula 82 is forwardly tapered at 88 and defines an interior 
bore 90 (see FIG. 3). The bore 90 of the cannula 82 communicates directly 
with a recess 91 in the hub 86. The recess 91 opens at the trailing end 94 
of the hub 86. Rubber sleeve 87 is nested within recess 91 and defines a 
throughbore 92 which tightly circumscribes needle 126 to form an air-tight 
seal as will hereinafter be more fully described. 
An interior catheter or cannula 98 traverses the entire throughbore 92 and 
the bore 90 of exterior cannula 82. The leading end 100 of the catheter 98 
projects beyond the leading end 88 of cannula 82 as shown in both FIGS. 2 
and 3. The trailing end of catheter 98 is mounted within coupling member 
102, the coupling member 102 having a male Luer fitting 104 which is in 
direct alignment with the throughbore 92. The interior catheter 98 is 
hollow and opens directly into the female Luer coupling 106. The coupling 
member 102 is maintained in direct alignment and fixed axial spacial 
relationship with the hub 86 by a strut 108. It can be seen, therefore, 
that there is a discrete passageway from the leading tip 100 of the 
catheter 98 through the entire length of the catheter 98 to the coupling 
member 102. 
The cannula hub 86 is bifurcated at 110 to form a branch 112. The branch 
112 has a female Luer fitting 114 at its trailing end 116 into which a 
suitable coupling 120 from a conventional extracorporeal fluid circuit is 
press-fit. The branch 112 has a hollow interior 122 which communicates 
directly with the bore 90 of exterior cannula 82. Accordingly, a discrete 
passageway exists through the bore 90 and hollow 122 to the coupling 120. 
In addition, a separate and discrete passageway exists through the hollow 
of interior catheter 98 to the trailing end of coupling member 102 and to 
a male coupling 124 press-fit therein. Significantly, the structure of the 
cannula assembly 80 permits the extracorporeal fluid circuit at 120 and 
124 to be attached prior to venipuncture and to remain attached during and 
after venipuncture. Thus, the assembly 80 can be flushed with sterile 
fluid and introduced into the patient without break in sterile technique. 
In order to facilitate introduction of the coextensive cannulae 82 and 98, 
a venipuncture needle 126 is provided. The venipuncture needle 126 has a 
sharp beveled end 128 which, in the initial position illustrated in FIG. 
1, projects through the interior of cannula 82 and telescopically around 
and beyond catheter 98. With reference to FIG. 3, it can be appreciated 
that the needle 126 is reciprocably displaceable within the bore 92 of the 
sleeve 87. The sleeve 87 forms an air-tight seal with needle 126 so that 
negative pressure within the hub 86 and branch 112 will not draw air 
around the needle 126 into the blood within the hub. The trailing end 128 
of the needle 126 is firmly mounted to a shuttle 130, the shuttle having a 
rearwardly facing female fitting 132 which is selectively press-fit upon 
the male fitting 104 of the coupling member 102 as illustrated in FIG. 3. 
Clearly, the location of the male fitting 104 and female fitting 132 could 
be reversed without adverse consequence. This press-fit coupling minimizes 
blood leakage around the needle 126 after venipuncture and forms an air 
seal for preventing air from entering the hub 86 when the interior of hub 
86 is subjected to negative internal pressure. 
The method of using the embodiment of FIGS. 1-3 is apparent from the 
drawing. Initially, the shuttle 130 is advanced forwardly until the needle 
126 projects beyond the leading end 88 of the cannula 82 and substantially 
circumscribes and confines the interior catheter 98. By restraining the 
shuttle 130 in place with the fingers, the venipuncture can easily be 
made. It is observed, however, that the needle 126 will substantially fill 
the passageway in the throughbore 90 between the cannula 82 and the 
catheter 98. Accordingly, blood will not flow through the bore 90 and 
hollow 122 in the branch 112 while the needle is in the forward position 
illustrated in FIG. 1. 
After venipuncture has been successfully accomplished and the fistula 
established, the shuttle 130 may be manually displaced rearwardly and 
telescopically over the exposed portion of the interior catheter 98 until 
the shuttle 130 mates with the coupling member 102. In this mode, blood 
will freely flow between the cannulae 82 and 98, through the branch 112 
and the extracorporeal blood circuit connected at 120. At the same time, 
blood may also flow through the hollow of the interior catheter 98 along 
the discrete flow path defined by the interior catheter 98 and through the 
coupling 124 to the extracorporeal fluid circuit. As described above, the 
assembly 80 may be coupled to the extracorporeal fluid circuit before 
venipuncture, if desired. Prior coupling may facilitate flushing of the 
assembly with sterile fluid for subsequent blood aspiration or fluid 
delivery into the blood stream. 
The length of the needle 126 and the strut 108 are selected so that when 
the shuttle 130 is in the rearmost position illustrated in FIGS. 2 and 3, 
the sharpened leading end 128 of the needle 126 will remain supported and 
protected by the cannula hub 86 but be fully retracted out of the pathway 
122 so as to avoid interfering with the blood flow. In this retracted 
position, the needle is safely preserved to avoid injury to patient or 
catheter. Clearly, the needle can be reciprocated without disconnection of 
the assembly 80 from the extracorporeal fluid circuit. 
Reference is now directed to the embodiment of FIG. 4 which differs from 
the embodiment of FIGS. 1-3 only in the structure of the interior catheter 
198. The interior catheter 198 is diametrally reduced in both inside and 
outside diameter from the intermediate point 200 to the proximal end 202 
of catheter 198. 
It has been well known for a number of years to slightly taper the proximal 
end of a catheter to facilitate insertion of the catheter into a blood 
vessel. The taper facilitating this purpose is illustrated at the proximal 
end 88 of the exterior catheter 82 illustrated in FIGS. 1 and 2. Clearly, 
an exterior taper to facilitate insertion is not necessary for the 
catheter 198 because catheter 198 is typically surrounded by the needle 
126 prior to venipuncture (see, for example, FIG. 1). 
In the embodiment of FIG. 4, it is contemplated that blood will be 
transferred from a high pressure system to the patient through the 
catheter 198. Conversely, blood will be withdrawn from the patient through 
the catheter 82 and the space 190 between the catheter 82 and the catheter 
198 into the patient through the branch 112. Because the blood displaced 
through the space 190 and the branch 112 is transported due to negative 
pressure caused by a blood pump or other suitable negative pressure 
producing device, resistance to flow in the space 190 is of critical 
importance. Accordingly, the interior catheter 198 has been reduced in 
inside and outside dimension so as to create a reduced resistance to flow 
in the space 190 between the leading end 88 of the cannula 82 and the 
sleeve 87 located at the trailing end of the branch 112. On the other 
hand, if the entire catheter 198 were reduced in dimension, it has been 
found that the pressure necessary to force the blood into the patient 
through the lumen of interior catheter 198 is too great. Accordingly, 
catheter 198 has an increased dimension at the proximal end beginning at 
the point 200. 
By way of example only, it has been found desirable to have the largest 
diametral dimensions of catheter 198 at about 0.57 inches ID and 0.61 
inches OD. The reduced dimension for catheter 198 may desirably be on the 
order of 0.66 inches ID and 0.71 inches OD. 
The aforedescribed catheter with an intermediately reduced dimension has 
been found surprisingly effective in permitting blood to flow easily 
through the space 190 responsive to the negative pressure transmitted 
through branch 112 and at the same time avoid the serious effects of 
materially increasing the pressure with which the blood would be forced to 
endure if the smallest dimension of catheter 198 extended the entire 
length thereof into the coupling member 102. 
Clearly, in the embodiments illustrated herein structure and method have 
been described which facilitates successful cannulation of a blood vessel 
and, after cannulation, the displacement and/or removal of the sharpened 
needle to permit essentially simultaneous aspiration of blood from the 
patient and delivery of blood back to the patient through two discrete 
flow paths in the assembly. 
The invention may be embodied in other specific forms without departing 
from its spirit or essential characteristics. The described embodiments 
are to be considered in all respects only as illustrative and not 
restrictive and the scope of the invention is, therefore, indicated by the 
appended claims rather than by the foregoing description. All changes 
which come within the meaning and range of equivalency of the claims are 
to be embraced within their scope.