Smooth bore double lumen catheter

A double-current catheter having an elongated cylindrical tube for injection and removal of fluid is provided with a smooth conical tapered tip that smoothly merges with the cylindrical surface of the tube so that insertion trauma and the possibility of kinking are minimized. To provide improved dilator characteristics, preferably the tip includes a relative concentration of material for rigidity, the conical taper is gradual and the apex of the conical tip is substantially centered on the axis of the cylindrical tube. To promote fluid flow, the cylindrical tube preferably includes an internal planar divider defining two "D" shaped lumens. A first lumen extends from the proximal end of the cylindrical tube to a first opening at the distal end, and the second lumen extends from the proximal end to a side opening in the cylindrical surface of the tube. Preferably additional side holes for the lumens are provided to enhance fluid flow.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to surgical instruments for withdrawing 
fluids from or introducing fluids into a cavity of the body. 
2. Description of the Related Art 
As is well known, a catheter is a tubular, flexible, surgical instrument 
for withdrawing fluids from (or introducing fluids into) a cavity of the 
body. A double-current catheter is a catheter having two channels; one for 
injection and one for removal of fluid. Dorlan's Illustrated Medical 
Dictionary Twenty-Fifth Edition (W. B. Saunders, Philadelphia 1974), p. 
274. As is well known, a double-current catheter is used for removing 
blood from a fistula or vein for processing in a dialysis machine and 
returning the processed blood back to the fistula or vein. A 
double-current catheter suitable for this purpose is disclosed in 
Mahurkar, U.S. Pat. No. 4,134,402 issued Jan. 16, 1979. Mahurkar U.S. Pat. 
No. 4,134,402 discloses a double lumen continuous flow hemodialysis needle 
and cannula having contiguous lumens of different lengths formed by 
dividing a unitary straight tube, the shorter lumen acting as a blood 
intake lumen and the longer acting as a blood return lumen. Semi-circular 
lumens provide a minimal resistance to blood flow resulting in a smaller 
but highly efficient catheter in comparison to a coaxial double-current 
catheter. Hemodialysis requires, for example, a blood flow rate of about 
200 ml/min or more and flow resistance less than about 100 mm of mercury. 
There are numerous other United States Patents disclosing double-current 
catheters for hemodialysis and evidencing a long-felt need for a small, 
functionally efficient catheter having a minimum of insertion trauma and 
potential for clotting. McLaughlin, U.S. Pat. No. 4,096,860 issued June 
27, 1978 discloses a coaxial hemodialysis catheter said to allow a step 
enlargement of the opening of a blood vessel to avoid tearing and rupture 
of the side walls. A simultaneous flow device incorporates a hub with an 
extension conduit and a valve therein for receipt of a needle 
therethrough. The extension conduit is of sufficient size to allow the 
passage of the needle therethrough adjacent the interior side walls 
thereof with an attendent extension thereof from its opening. The needle 
with the extension conduit is adapted for combined insertion within a 
blood vessel, after which it can be withdrawn while the valve prevents the 
backflow of blood through the axial passage of the hub. A coaxial flow 
device can then be inserted within the hub conduit. 
Sorenson et al., U.S. Pat. No. 4,099,528 issued July 11, 1978 discloses a 
coaxial double lumen cannula mounted upon a hub and having a central 
stylet needle for penetrating a patient's vein and which is retractable 
after penetration. 
Grimsrud, U.S. Pat. No. 4,203,436 issued May 20, 1980 discloses a hollow 
hypodermic needle with a divider for providing a first channel for removal 
of blood for treatment from a punctured blood vessel and a second channel 
for returning the treated blood to the blood vessel. 
Uthmann, U.S. Pat. No. 4,385,631 issued May 31, 1983 discloses a 
hemodialysis catheter for puncturing blood vessels which includes a 
section insertable through a puncture opening into a blood vessel and a 
hose line following thereafter. 
Jacobson et al., U.S. Pat. No. 4,180,068 issued Dec. 25, 1979 discloses a 
double-current hemodialysis catheter comprising a primary tube and an 
internal divider which also functions as a trocar and valve. The primary 
tube has a side opening for receiving blood and a central opening at the 
distal end of the primary tube. The internal divider includes a cutting 
end which protrudes from the distal opening when the divider is 
longitudinally moved to an insert position. In the insert position, blood 
flow is blocked. 
Mahurkar, U.S. Pat. No. Des. 272,651 issued Feb. 14, 1984 discloses a 
double lumen catheter having an outlet lumen which has an opening at the 
tip of the catheter and a shorter inlet lumen which terminates in a bevel 
substantially displaced from the tip. 
SUMMARY OF THE INVENTION 
The primary object of the invention is to provide an efficient dual lumen 
catheter having minimal insertion trauma and a minimal potential for 
clotting. 
Another object of the invention is to provide a dual lumen catheter which 
is an effective dilator for soft tissue and veins. 
In accordance with the invention, a dual lumen catheter has a smooth 
conical tapered tip that smoothly merges with the catheter body so that 
insertion of the catheter is facilitated. The tip guidance point is 
located at the center of the conical tip for uniform distribution of 
frictional resistance and minimization of insertion trauma and kinking. 
The conical tapered tip comprises a relative concentration of material to 
impart relative rigidity so that the tip functions as an effective dilator 
for soft tissue and veins. Semicircular lumens insure non-static laminar 
flow and prevent clotting. The smooth bore double lumen catheter is 
particularly advantageous when a tunneling procedure or blind technique 
must be used, for example, to reach a vein under the collar bone or neck.

While the invention will be described in connection with a certain 
preferred embodiment, it will be understood that it is not intended to 
limit the invention to that particular embodiment. On the contrary, it is 
intended to cover all alternatives, modifications, and equivalents as may 
be included within the spirit and scope of the invention as defined by the 
appended claims. 
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
Turning now to the drawings, FIGS. 1-5 show the various external views of a 
smooth bore double lumen catheter, generally designated 10, in accordance 
with the present invention. As is conventional for a double-current 
catheter, the double lumen catheter 10 has a elongated hollow tube 11 
which is inserted into a cavity of the body such as a fistula or vein. The 
tube 11 is circular in cross section, as specifically shown in FIG. 6, and 
has an internal divider 12 defining a return lumen 13 and an inlet lumen 
14 within the interior of the hollow tube 11. The lumens 13 and 14 are 
semicircular or "D" shaped which minimizes resistance to fluid flow. As is 
conventional for this type of dual lumen construction, the divider 12 
extends axially along the tube 11 from a branching connector 15. The 
branching connector 15 connects the distal end portions of the return 
lumen 13 and the inlet lumen 14 to respective fluid return and inlet lines 
16 and 17 which are, for example, respective venous and arterial lines of 
a dialysis circuit. This preferred direction of fluid circulation is 
indicated by heavy arrows in FIGS. 1 and 3. The branching connector 15 
includes a coaxial sleeve 15' at the junction of the tube 11 and the 
connector 15. The sleeve 15' acts as a strain relief and also prevents 
kinking of the tube 11 at the junction. 
The hollow tube 11 includes openings or apertures at the distal end 
portions of the lumens 13, 14 to permit the flow of fluid between a body 
cavity (not shown) and the lumens. The return lumen 13 extends along the 
entire length of the tube 11 to an aperture or opening 18 at the distal 
end or tip of the tube 11 as is more clearly shown in FIG. 7. The inlet 
lumen 14 is shorter than the return lumen 13 and terminates at its distal 
end at an aperture or opening 19 that is in the side of the tube 11 and is 
substantially displaced from the aperture 18 at the distal end of the tube 
11. 
In accordance with the invention, the distal end portion of the tube 11 has 
a conical tip generally designated 20 which smoothly merges with the 
cylindrical body of the tube 11. Preferably the apex of the conical tip 20 
is centered on the axis of the cylindrical body of the tube 11 thus 
serving as a guidance point to uniformly distribute the frictional 
resistance encountered by the conical tip 20 when the tube 11 is inserted 
into the body cavity (not shown). As shown in FIGS. 1-4 and FIG. 7, the 
outer diameter of the tube 11 converges smoothly at the distal end portion 
of the tube defining a truncated cone 20 and the return lumen 13 opens at 
the truncated apex of the cone 18. Preferably, the conical tip 20 has a 
gradual taper. The conical tip 20, for example, has a length of at least 
approximately two diameters of the tube 11. Since the frictional 
resistance is uniformly distributed and the conical tip 20 smoothly merges 
with the body of the tube 11, insertion trauma and kinking are minimized. 
The relatively small size of the return and inlet apertures 18, 19 further 
reduce insertion trauma, but they also impede fluid flow. Therefore, an 
additional group of holes or apertures generally designated 21 connect the 
return lumen 13 to the outer surface of the tube 11, and an additional 
group of holes or apertures 22 connect the inlet lumen 14 to the outer 
surface of the tube 11. Viewed from the side, the holes 21, 22 are seen to 
have scaphoid margins. In particular the return holes or apertures 21 are 
axially disposed between the base of the conical tip 20 and the inlet 
aperture 19 at the distal end of the inlet lumen 14. The additional inlet 
holes or apertures 22 are axially disposed between the inlet aperture 19 
and the proximal end of the tube 11. The return holes 21 and the inlet 
holes 22 are further disposed circumferentially on opposite sides of the 
divider 12. Thus, there is axial as well as circumferential separation of 
the inlets and outlets for fluid circulation. 
In accordance with another aspect of the invention specifically shown in 
FIG. 7, the conical tip generally designated 20 is formed with a relative 
concentration of material 23 to stiffen the tip 20. This stiffening aids 
penetration of the tip 20 into the body cavity (not shown) and also aids 
the dilation of soft tissue such as veins. As shown in FIG. 7, the inlet 
lumen 14 terminates at the inlet aperture 19 and in place of the inlet 
lumen the relative concentration of material 23 extends axially from the 
aperture 19 to the distal end of the tube 11 at the truncated apex of the 
conical tip 20. Also, the wall thickness of the conical tip 20, the reurn 
lumen 13 and the aperture 18 are all eccentric to the axis of the conical 
tip. 
It is readily apparent to persons of ordinary skill in the art that the tip 
20 as shown in FIG. 7 is easily formed from thermo-plastic material. The 
tip 20 including the relative concentration of material 23 is easily 
molded and bonded or is integrally formed from the cylindrical tube 11 by 
the use of internal and external mandrels and the application of heat by 
any number of conventional means such as RF forming, thermal forming, or 
infrared forming. 
For use in hemodialysis, the smooth bore double lumen catheter 10 is 
introduced in the direction of blood flow in a large vein over a hypodemic 
needle or Seldinger's guide wire, or through a sheath as is conventional. 
The side holes 19 and 22 on the blood inlet lumen 14 draw the blood for 
processing and the processed blood is returned through the return lumen 13 
and out through the holes 18, 21 to return the blood upstream into 
circulation. As was described above, the geometrical properties of the 
smooth bore double lumen catheter as shown in the drawing figures insure 
that insertion trauma, kinking, and the possibility of clotting are 
minimized during hemodialysis.