A dual-lumen blood-treatment catheter has inner and outer lumina open towards the patient end. The catheter has expandable portions in the outer lumen located near the patient end for atraumatically preventing collapse of the blood vessel to ensure free flow of blood into and out of the catheter, In one embodiment, the outer lumen has a plurality of slits around its circumference which form slats therebetween. Withdrawal of the inner lumen relative to the outer lumen causes the slits to open, thereby bowing the slats to expand the outer lumen.

The present invention relates to a dual-lumen catheter. The dual-lumen 
catheter of the present invention has particular application for 
haemodialysis. 
Dual-lumen catheters have been proposed for use in haemodialysis and are 
inserted into a vein, usually the jugular, subclavian or femoral vein. 
Such dual-lumen catheters have a first, arterial lumen through which blood 
is withdrawn from the vein. The blood is pumped round a dialysis 
filtration circuit and returned to the vein through a second, venous lumen 
of the catheter. 
A dual-lumen haemodialysis catheter is usually fixed in situ on the patient 
for about two weeks, although in some instances the catheter may be in 
situ for up to eight months. The catheter is normally only removed when 
treatment is no longer required or in case of infection at the insertion 
site or due to catheter malfunction. 
With such catheters, particularly when used in children, who have 
relatively narrower and weaker veins than adults, and/or when the catheter 
is in situ for a relatively long period, collapse of the vein in which the 
catheter is inserted is a real problem, particularly because it can cause 
the catheter to be blocked and in any event reduces the efficiency of the 
catheter and may prevent the catheter from working altogether. 
According to the present invention, there is provided a dual-lumen catheter 
comprising an outer lumen and an inner lumen which are joined at an 
insertion end of the catheter, the inner lumen lying within the outer 
lumen, the outer lumen being expandable for atraumatically preventing 
collapse of a vessel into which the catheter is inserted. 
The outer lumen provides a support which prevents collapse of the vessel 
into which the catheter is inserted. The outer lumen need not necessarily 
be expanded so far that it contacts the vessel; rather, it will usually be 
sufficient that the outer lumen be expanded slightly so that it will keep 
the vessel open should the vessel begin to collapse. 
Preferably, the outer lumen has a plurality of slits around its 
circumference which forms slats therebetween, withdrawal of the inner 
lumen relative to the outer lumen causing the slits to open thereby bowing 
the slats to expand the outer lumen. 
The use of slits provides a simple mechanism for allowing the outer lumen 
to be expanded. The slits may also provide an opening through which blood 
can enter the outer (arterial) lumen. 
Means are preferably provided for controllably withdrawing the inner lumen 
relative to the outer lumen. 
The withdrawing means may comprise a linear mechanism, which may be a 
ratchet mechanism. Alternatively, the withdrawing means may comprise a 
rotary mechanism. The rotary withdrawing mechanism may comprise a screw 
thread on the inner lumen and a nut threaded on said inner lumen 
screw-thread, the nut being rotatable on said screw thread to withdraw and 
to advance the inner lumen relative to the outer lumen. 
As an alternative to providing slits in the outer lumen, the outer lumen 
may include at least one sac which may be pressurised to expand the outer 
lumen.

In FIG. 1 to FIG. 4, a catheter 1 includes a blade 2, which consists of the 
portion of the catheter which is inserted into the body of the patient, 
and a hub 3. 
The blade 2 includes an outer (arterial) lumen 4 and a substantially 
concentric inner (venous) lumen 5 within the outer lumen 4. The outer and 
inner lumina 4,5 are joined at the insertion end 6 of the catheter 1. At 
their other ends, the outer and inner lumina 4,5 enter and are fixed to 
the hub 3 as will be described in more detail below. 
In the first example shown in FIGS. 1 to 4, the outer lumen 4 is provided 
with a plurality of substantially parallel slits 7. In the example shown, 
there are six slits 7 around the circumference of the outer lumen 4. The 
slits 7 in the example shown are parallel to the longitudinal axis of the 
blade 2, thereby forming six slats 8 which are substantially parallel to 
the longitudinal axis of the blade 2. 
It is to be understood that, in some applications, the slits 7 may spiral 
around the circumference of the outer lumen 4. Furthermore, more or less 
than the six slits 7 shown in the example may be used according to 
particular requirements. 
Because the outer lumen 4 is joined to the inner lumen 5 at the insertion 
end 6 of the blade 2, withdrawal of the inner lumen 5 with respect to the 
outer lumen 4 causes the slats 8 to buckle and bow outwards as shown in 
FIGS. 1 and 2. This bowing of the slats 8 may be facilitated by thinning a 
portion of one or more of the slats 8 at or towards its centre, for 
example, which will increase the flexibility of the slat 8 in that region. 
In use, the inner lumen 5 is advanced relative to the outer lumen 4 so that 
the slats 8 are preferably flush with the surface of the remainder of the 
outer lumen 4. For haemodialysis, the blade 2 of the catheter 1 is then 
inserted conventionally into the vessel, which is usually one of a 
jugular, subclavian, or femoral vein. This insertion of the blade 2 is 
facilitated by the tapered, generally frustoconical shape of the insertion 
end 6. 
Once the blade 2 has been inserted sufficiently far, the inner lumen 5 is 
withdrawn relative to the outer lumen 4 which causes the slats 8 to bow 
outwards. It will not normally be necessary for the slats 8 to be bowed 
outwards so far that they actually exert an outwards force on the vein 
wall as their primary purpose is not necessarily to expand the vein wall, 
rather it is to prevent collapse of the vein wall. Accordingly, the 
overall diameter of the expanded slats 8 will normally be less than the 
diameter of the vein into which the blade 2 is inserted. Where the 
diameter of the expanded slats 8 exceeds that of the vein, it is not so 
large as to cause expansion of the vein beyond its elastic limit, thereby 
allowing the vein to relax to its natural size when the slats 8 are 
flattened. 
The blade 2 can be formed by extruding the outer and inner lumina 4,5 as 
tubes. Suitable materials include a thermosoftening polymer such as 
polyurethane, although other materials such as PTFE may be used. The 
preferred material is radio-opaque "Teco-Flex" (trade mark) medical grade 
polyurethane. The outer and inner lumina 4,5 are then joined at the tip 9 
of the insertion end 6. 
It is preferred that the outer lumen 4 be blocked at the end of the slits 7 
proximate the insertion end 6 to prevent blood stagnating in the space 
otherwise formed between the outer and inner lumina 4,5 at the insertion 
end 6, thereby preventing infection or clotting of the blood. This can be 
achieved by putting the tip ends of the outer and inner lumina 4,5 into a 
mould which is frustoconically shaped to provide the shaped insertion end 
6 and injecting material so that it travels up the outer lumen 4 until it 
reaches the slits 7. The material of the tip 9 of the blade 2 is generally 
similar to that of the blade 2, but may be a softer grade to produce an 
atraumatic tip 9 which reduces the risk of tissue damage on insertion of 
the blade 2. 
As an alternative to injecting material up the outer lumen 4, the inner 
lumen 5 may be provided with a relatively wider section so that, when the 
inner lumen 5 is inserted into the outer lumen 4, the wider section forms 
a blockage at the correct location adjacent the ends of the slits 7 
proximate the tip 9. A thermoforming process may be used to make this 
wider section integral with the outer lumen 4. 
When the blade 2 is inserted into or withdrawn from a vein, the arrangement 
is preferably such that the slats 8 are substantially flush with the outer 
surface of the outer lumen 4 so as to minimise the risk of tissue damage. 
During dialysis, the slits are opened to allow blood to flow from the vein 
into the outer lumen 4 through the gaps created by the slits 7 between the 
slats 8. The degree of opening of the slits 7 can be varied as will be 
described further below. 
The slits 7 may be formed simply by cutting into the outer lumen 4, without 
removing any material from the outer lumen 4. This would have the 
advantage that the slits 7 would be completely closed when the inner lumen 
5 is fully advanced relative to the outer lumen 4, creating a seal around 
the expansion area of the outer lumen 4. This may be helpful in preserving 
the effectiveness of operation of any anti-coagulant injected into the 
lumina 4,5 between dialysis to prevent thrombosis within the blade 2. 
Alternatively, the slits 7 may be formed by removing slithers of material 
which would leave an opening in the outer lumen 4 even in the unexpanded 
state. This may help in avoiding tissue damage as the slits 7 are being 
closed prior to removal of the blade 2 from the vein. 
Blood removed from the outer lumen 4 is returned, after dialysis, via the 
inner lumen 5 and returned to the vein through an opening 10 provided in 
the end of the tip 9. Further openings may be provided in or close to the 
tip 9 through the side of the blade 2 to facilitate transfer of blood from 
the catheter 1. 
A guidewire may be used when inserting the catheter, the guidewire being 
inserted into the vein and the catheter then being passed along this 
guidewire with the wire passing up the centre of the inner lumen 5. The 
guidewire is then removed from the vein through the inner lumen 5 once the 
catheter 1 is in position. 
Two examples of mechanisms for moving the inner lumen 5 relative to the 
outer lumen 4 are shown in FIGS. 3 and 4 respectively. 
In FIG. 3, the hub 3 has a generally triangular shape and is hollow along 
two joined arms 31,32 to form a generally Y-shaped channel. The inner 
lumen 5 passes through one of the hollow arms 32 to a rotary withdrawing 
mechanism 20. A screw thread 21 is formed on the end of the inner lumen 5. 
This screw thread 21 may be cut into or otherwise formed directly on the 
end of the inner lumen 5 or, alternatively, may be formed on a separate 
hollow component which is then rigidly fixed to the end of the inner lumen 
5. A nut 22 is threaded on the screw thread 21, the nut 22 projecting 
through the sides of the hub 3. 
A plug 23 is fitted in the rear of the hub 3 to retain the rotary 
withdrawing mechanism 20 within the hub 3. The plug 23 has an elongate 
guide groove 24 running generally parallel to the direction of travel of 
the inner lumen 5. A nib 25 is provided on the inner lumen 5 behind the 
screw thread 21, the nib 25 travelling in the groove 24 which therefore 
acts as a key-way to prevent rotation of the inner lumen 5 in the hub 3. 
As will be understood, the nut 22 can be rotated to withdraw or advance the 
inner lumen 5 in the hub 3 according to need. It will be seen that the nib 
25 has limited travel in the groove 24 defined by the ends of the groove 
24, which therefore acts to limit the extent of travel of the inner lumen 
5 and accordingly the degree of expansion of the slats 8. 
The outer lumen 4 is connected to the channel 33 formed in the other hollow 
arm 31. This channel 33 is separated from the channel in the first arm 32 
by a diaphragm 34 through which the inner lumen 5 passes. This diaphragm 
34 separates the concentric lumina 4,5 into two separate blood lines and 
prevents leakage of blood and aspiration of air as well as being a 
bacterial seal. The diaphragm 34 may be made of polyurethane produced by a 
dipping technique to bond the diaphragm between the hub 3 and the inner 
lumen 5. Alternatively, a natural rubber plug may be provided around the 
inner lumen 5 in the hollow arm 32 through which the inner lumen 5 passes. 
It will be seen that the degree of movement of the inner lumen 5 back and 
forth relative to the hub 3 can be monitored by determining the number of 
rotations of the nut 22, for example. Additionally or alternatively, a 
scale (not shown) may be provided on the back tube 40 which connects the 
inner lumen 5 to the dialysis machine so that the degree of movement back 
and forth of the inner lumen 5 can be readily seen. 
As an alternative to the rotary mechanism shown in FIG. 3, a linear 
withdrawing mechanism 50 is shown in FIG. 4. The shape of the hub 3 is 
generally similar to that of the hub 3 shown in FIG. 3 although in the 
figure 4 example, an elongate rubber seal 34a is shown. 
In this second example, the inner lumen 5 is rigidly fixed to a ratchet 
block 51 which is provided with a plurality of teeth 52 along one edge. 
The hub 3 is provided with a corresponding set of teeth 53 over which the 
teeth 52 on the ratchet block 51 ride. The ratchet block 51 can be 
retained in the hub 3 by elongate ribs (not shown) on the block 51 running 
in elongate grooves (not shown) in the hub 3, for example. 
To withdraw and advance the inner lumen 5, the ratchet block 51 is simply 
moved backwards and forwards as required, the teeth 52 on the block 51 
riding over the teeth 53 in the hub 3. 
In each of the examples shown in FIGS. 3 and 4, friction in the system is 
likely to be sufficient to prevent collapse of the expanded slats 8, 
particularly where a rubber seal 34a is used in the hub 3. If necessary, 
an extra lock can be provided so that the relative positions of the inner 
and outer lumina 4,5 can be maintained. 
As shown in FIG. 1, flanges 42,43 can be provided on the back tubes 40,41 
with which the inner and outer lumina 5,4 are respectively in fluid 
communication, the flanges 42,43 facilitating connection to a blood line. 
Each of the back tubes 40,41 is terminated with a conventional female luer 
connector 44. Clamps 45 may also be provided on the back tubes 40,41 and 
suture wings (not shown) may be provided on or near the hub 3 to allow the 
catheter to be stitched to a patient's skin. 
In the example of the catheter shown in FIGS. 5 and 6, the outer lumen 4 is 
provided with closed pockets or sacs 60. In the example shown, two 
diagonally opposite sacs 60 are shown, although more or less sacs may be 
provided. An opening 61 is provided in the outer lumen 4, the opening 61 
allowing withdrawal of blood from the vein 62 in which the catheter 1 is 
inserted. A similar opening 61 may be provided on the diagonally opposite 
side of the outer lumen 4. To expand the outer lumen 4, air or another 
fluid under pressure is introduced into the sacs 60. The material of the 
outer lumen 4 is elastic, or at least that portion around the hole or 
holes 61 is elastic, so that the outer lumen 4 expands in this region to 
prevent the vein 62 from collapsing. 
The blade 2 of the catheter 1 of the examples described above, i.e. the 
portion from the hub 3 to the insertion end 6, may be 120 to 200 mm long, 
although a paediatric catheter may be shorter. The diameter of the blade 2 
would be between about 3.33 to 4 mm; other sizes may be used. 
The ends of the slits 7 proximate the insertion end 6 of the catheter 2 may 
be approximately 30 mm from the insertion end 6 of the catheter 1 and the 
slits 8 may be 10 to 15 mm long.