Double lumen catheter

A double lumened catheter defined by inner and outer cannulas having spaced apart walls defining a fluid passageway therebetween. The outer cannula is sharpened at its outer end for ease in puncturing a blood vessel. The inner cannula is extendible past the sharpened end of the outer cannula and is bent at an angle toward the inner wall of the outer cannula. Engagement of the bent portion of the inner cannula with the sharpened front end of the outer cannula's inner wall prevents damage to the blood vessel after insertion of the double lumened catheter thereinto. After insertion, blood may be dialyzed by with-drawing blood through the space between the cannulas and returned via the inner cannula.

The invention concerns a double lumen catheter, in particular for providing 
blood vessel access in extra-corporal hemodialysis, and having separate 
ducts for blood streams flowing into and out of the body. 
Extra-corporal hemodialysis is a process for treating chronic kidney 
failure in its final stage, which because of its life-saving effectiveness 
has gained general acceptance. In this process, the patient's blood is 
passed over a dialysing membrane for several hours during treatment at a 
rate of about 150 to 250 ml/per min., and is thereafter immediately 
returned to the patient. Exchange of uremic poisons from the blood takes 
place across the membrane into a dialysing solution flowing on the other 
side of the dialysing membrane. In order to maintain life, it is necessary 
that the extra-corporal hemodialysis be carried out about two or three 
times weekly, each time for an average period of six hours. One problem of 
extra-corporal hemodialysis is the problem of access to the blood vessel. 
For this, the so-called Scribner-shunt has become known. In this case, an 
operation is performed to interconnect an artery and a nearby vein 
(generally in the lower arm of the patient) by a plastic tube. The plastic 
tube is inserted through the skin after tying of the blood vessels. The 
outer portion of the tube is divided and connected by a coupling part. The 
blood rushes constantly at a high speed through this artificial short 
circuit (arterial-venous shunt) during the treatment intermissions, 
because of the considerable pressure difference between the artery and the 
vein. In order to accomplish extra-corporal hemodialysis, the arterial and 
venous parts are disconnected and connected to the artificial kidney, that 
is the arterial part is connected to the entry and the venous part is 
connected to the output of the dialyzer. The tubes are disconnected from 
the artificial kidney after treatment and remain coupled to each other 
until the next treatment. 
In this type of vessel access there exists the drawback that new parts of 
the blood vessel must be continuously opened up, since the operational 
life of this type of blood vessel connection is limited due to typical 
complications, such as the formation of coagulation at the connection of 
the plastic tubes and in the blood vessels into which they are connected, 
as well as the life-endangering general and local infections caused by 
bacteria entering into the body through the skin at the point where the 
plastic tubes pass through the skin. 
In providing access to a blood vessel, it has further become known to 
directly join together an artery and a vein usually in the lower arm, by 
sewing together an artery and vein in an operation. Because of the 
considerably higher blood pressure in the artery relative to that in the 
vein, the wall structure of the substantially weaker vein will expand 
considerably so that its cross section assumes a multiple of its original 
size until the vein wall becomes adapted to the higher pressure and the 
far larger blood quantity flowing through it per time unit. Such an 
"arterialized" vein can then, in favorable instances over some years be 
punctured by a larger lumen cannula (about 1.6 to 2 mm inside diameter) 
for the blood inflow and the blood return. The cannula is removed after 
treatment. The punctures heal in natural fashion. This type of vessel 
access has the drawback that the optimum anatomical and biological 
development of the so-called "cimino-bresciafistula" requires a time 
period of several weeks to some months. Moreover, the anatomical and 
functional develpment is not always good, and each scar formed after a 
puncture leads to a weakening of the blood vessel wall. It is therefore 
more advantageous if the connection between the patient and the artificial 
kidney is made by a single catheter only. 
It has already been suggested to connect an ancillary device having a valve 
function in series with a single cannula. This arrangement works in such a 
way that the blood is alternately aspirated through the cannula, then the 
valve being switched, and the blood returning through the same cannula. 
The so-called single needle technique requires a considerable additional 
equipment and increased cost. 
In addition to this, it is also known to couple an artificial kidney to a 
patient with only one puncture. In this double lumen catheter, the inner 
duct of the inner cannula is provided for the inflowing blood stream an 
annular duct between the inner cannula and an outer cannula surrounding 
the inner cannula is provided for the outflowing blood stream. The 
internal cannula of this double lumen catheter is sharply honed to 
facilitate puncture of the blood vessel. For this reason, the front end of 
the inner cannula projects considerably farther than the front end of the 
outer cannula. This leads to a relatively high resistance to flow in the 
inner duct of the inner cannula used for the blood return. The front end 
of the outer cannula tapers conically toward the outer wall of the inner 
cannula and has three apertures as aspiration openings directly behind 
this conical section. The drawback of this catheter is that the 
configuration of the aspiration openings leads to a high resistance to 
suction, a turbulent flow and dead spaces in the most forward portion of 
the annular duct between the inner and outer cannulue, so that this known 
cannula promotes coagulation and closure of the annular duct. Furthermore, 
the interrupted surface of the outer cannula is undesirable during 
insertion of the double lumen catheter into the blood vessel. 
The present invention has provided a double lumen catheter which avoids the 
drawbacks of the known double lumen catheter as well as the other 
techniques mentioned above. 
The present invention provides a double lumen catheter having an outer 
cannula that is sharply honed at its front end to facilitate puncture of 
the blood vessel. The double lumen catheter includes an inner cannula that 
is slidably mounted within the outer cannula, and the aspiration opening 
for the annular duct between the inner and outer cannulue is an annular 
passage at the front end of the annular duct. During puncturing of the 
blood vessel, in accordance with the present invention the inner cannula 
is retracted into the outer cannula. When the front end of the outer 
cannula is within the blood vessel the inner cannula is pushed forward. 
Since the aspiration opening has the form of an annular passage, the 
aspiration opening wil not increase the resistance to suction. In 
addition, there is no turbulent flow in the aspiration opening and there 
is no dead space in the most forward portion of the annular duct. 
In accordance with another aspect of the present invention, the rear end of 
the outer cannula may be provided with a Y or T shaped coupling device 
having a fixed step. The coupling device includes a guiding aperture 
tightly surrounding the inner cannula and a coupling end communicating 
with the annular duct, with tube being affixed to the coupling end to 
conduct the outflowing blood stream from the double lumen catheter. 
In accordance with yet another aspect of the present invention, the step of 
the coupling device is formed at its free end by a guide sleeve having an 
outwardly tapering conically shaped guide surface. The inner cannula is 
fixed to a coupling part having an externally tapered end slidably 
received within the guide sleeve of the coupling device. The taper on the 
end of the coupling part corresponds to the taper of the guide sleeve, and 
when the tapered surfaces are in engagement with one another, the front 
end of the inner cannula protrudes at least to the front face end of the 
outer cannula. With the tapered surfaces in engagement with one another, 
the position of the inner cannula is fixed with respect to the outer 
cannula and the possible aspiration of air is prevented. 
In accordance with still another aspect of the present invention, the 
coupling part is provided with a flange type protrusion to facilitate 
manual manupulation of the coupling part and inner cannula. 
In order to prevent the sharply honed point of the outer cannula from 
injuring the blood vessel in accordance with a further aspect of the 
present invention the front end range of the inner cannula is bent in the 
direction to the inner wall of the outer cannula. This has the inner wall 
of the sharply honed end of the outer cannula resting with a light 
pressure against the inner cannula, which prevents the sharply honed front 
face end of the outer cannula from cutting the vessel after the outer 
cannula has punctured the vessel and the inner cannula has been pushed 
forward. 
This invention will next be explained in greater detail by reference to the 
embodiment shown in the drawing.

DETAILED DESCRIPTION 
The double lumen catheter has a tubularly inner cannula 1 and a tubular 
outer cannula 2 coaxial with it. The inner cannula has an open front end 3 
disposed generally perpendicularly to the axis of the inner cannula. The 
rear end of the inner cannula 1 is connected to a plastic coupling part 4 
and is fixed to the coupling part by means of glue or another sealing 
material. The couplng part 4 has an inner duct 6 which communicates with 
the inner duct 7 of the inner cannula 1. A coupling tube 8 is fitted onto 
the rear end of the coupling part 4, and the inflowing blood stream passes 
through tube 8 and ducts 6 and 7 in the direction of arrow A. The forward 
end 10 of the coupling part 4 is externally tapered and generally 
frusto-conically shaped and in the position shown, is seated within a 
corresponding outwardly tapered conically shaped guide sleeve 9 of a 
coupling device 11. The outer cannula 2 is fitted within the forward end 
of coupling device 11, and affixed to it by means of glue or another 
sealing material 12. The coupling device 11 which is generally T-shaped as 
shown in the drawing, has a guiding aperture 13 tightly surrounding the 
inner cannula 1. An annular passage 14 is formed between the outer wall of 
the inner cannula 1 and the inner wall of the outer cannula 2 and 
communicates with a perpendicularly disposed inner duct 15 of the coupling 
device 11. A coupling tube 16 is fitted over the lower end of the coupling 
device, and the outflowing blood stream flows in the direction of arrow B 
through passage 14, duct 15 and tube 16. The outer cannula 2 has a slanted 
end 17 to permit an undisturbed passage of the blood from the annular 
passage 14 into the duct 15. The leading end 18 of the outer cannula is 
sharply honed to facilitate puncturing. 
In order to carry out the puncture, the inner cannula 1 is grasped manually 
by a flange type protrusion 19 on coupling part 4 and is moved to the 
right with respect to the outer cannula 2 from the position shown in the 
drawing until the front end 3 of the inner cannula 1 is positioned 
rearwardly of the eye 21 of the sharply honed point 18. In this position, 
the tapered surfaces 9 and 10 separate and the inner cannula 1 has slid to 
the right through the guiding aperture 13, whch effects a seal against the 
exit of blood and the entry of air because of its tight sealing engagement 
with the outer wall of the inner cannula. The catheter is then introduced 
into the blood vessel of the patient in the usual manner. Once the outer 
cannula 2 with its sharply honed point 18 is in the blood vessel, the 
inner cannula 1 is pushed forwardly into the position shown in the 
drawing. This causes a seating and sealing relationship by virtue of the 
tapered surfaces 9 and 10 engaging one another whereby the position of the 
inner cannula 1 is fixed with respect to the outer cannula 2 thereby 
preventing aspiration of air. 
As can be seen from the drawing, the free end portion of the inner cannula 
1 is bent at an angle in the direction of the inside wall of the outer 
cannula. In the position shown in the FIGURE the inside of the sharply 
honed point exerts a light pressure against the outer surface of the inner 
cannula. This prevents the sharply honed point 18 from causing injuries to 
the blood vessel after its introduction therein. The annular duct 14 is 
formed continuously right to the front end of the outer cannula 2, so that 
there is no need for a special formation of an aspiration opening, such as 
drilled holes or the like, and the aspiration opening of the annular duct 
14 is therefore a non-constricted gap, thus permitting unimpeded flow. 
In another embodiment of the invention not shown in the drawing, the bevel 
formed from honing the front face end of the outer cannula 2 is arranged 
with respect to the T-shaped coupling device 11 such that the top view of 
the bevel represents an oval when the part of the coupling device 11 
showing the inside duct 15 runs in the direction of the small diameter of 
the oval. Thus, since the double lumen catheter is generally introduced 
with the honed point of the outer cannula downward, this embodiment 
permits turning the catheter 180.degree. so that the end facing away from 
the beveled point protrudes farther into the blood vessel. This is of 
special importance when the inner and outer cannulue have been made as 
short as possible to reduce the resistance to flow, for instance. 
Numerous clinical tests have shown that the double lumen catheter in 
accordance with the present invention can be used on all patients without 
problems having no excessive and unbearable over or under pressures at 
comparable blood quantities per time unit in comparison to the customary 
two-cannula technique. Coagulation inside the cannulue, which would have 
led to a closure of the blood canal, could not be observed. Despite the 
relatively large diameter of the puncturing instrument, no after-bleeding 
was observed either fron the punctured vessel.