A healthy kidney removes toxic wastes and excess water from the blood. In End Stage Renal Disease (“ESRD”), or chronic kidney failure, the kidneys progressively stop performing these essential functions over a long period of time. When the kidneys fail, a patient dies within a short period of time unless that patient receives dialysis treatment for the rest of that patient's life or undergoes transplantation of a healthy, normal kidney. Since relatively few kidneys are currently available for transplantation, the overwhelming majority of patients with ESRD receive dialysis treatment.
Hemodialysis therapy is an extracorporeal (i.e., outside the body) process which removes toxins and water from a patient's blood. A hemodialysis machine pumps blood from the patient, through a dialyzer, and then back into the patient. The dialyzer removes the toxins and water from the blood by a membrane diffusion process. Typically, a patient with chronic kidney disease requires hemodialysis treatments three times per week, for 3-6 hours per session.
Thus, hemodialysis treatments require repetitive access to the vascular system of the patient.
One common method for repetitively accessing the vascular system of a patient for hemodialysis involves the use of a percutaneous catheter. The percutaneous catheter is inserted into a major vein, such as a femoral, subclavian or jugular vein. For long term maintenance dialysis, a jugular vein is generally the preferred insertion site. The catheter is percutaneous, with one end external to the body and the other end dwelling in either the superior vena cava or the right atrium of the heart. The external portion of the catheter has connectors permitting attachment of blood lines leading to and from the hemodialysis machine.
FIGS. 1 and 2 show a typical prior art hemodialysis catheter 5 disposed in the body of a patient. More particularly, hemodialysis catheter 5 generally comprises a catheter portion 10 comprising a dual-lumen catheter element 15, and a connector portion 20 comprising an extracorporeal connector element 25. The catheter's extracorporeal connector element 25 is disposed against the chest 30 of the patient, with the distal end 35 of catheter element 15 extending down the patient's jugular vein 40 and into the patient's superior vena cava 45. More particularly, the distal end 35 of dual-lumen catheter element 15 is positioned within the patient's superior vena cava 45 such that the mouth 50 of the suction line (i.e., lumen) 55, and the mouth 60 of the return line (i.e., lumen) 65, are both located between the patient's right atrium 70 and the patient's left subclavia vein 75 and right subclavia vein 80. Alternatively, the distal end 35 of dual-lumen catheter element 15 may be positioned so that mouth 50 of suction line 55, and mouth 60 of return line 65, are located within the patient's right atrium 70. The hemodialysis catheter 5 is then left in this position relative to the body, waiting to be used during an active dialysis session.
When hemodialysis is to be performed on a patient, the catheter's extracorporeal connector element 25 is appropriately connected to a dialysis machine (not shown), i.e., suction line 55 is connected to the suction port of the dialysis machine, and return line 65 is connected to the return port of the dialysis machine. The dialysis machine is then activated (i.e., the dialysis machine's blood pump is turned on and the flow rate set), whereupon the dialysis machine will withdraw relatively “dirty” blood from the patient through suction line 55 and return relatively “clean” blood to the patient through return line 65.
In order to minimize clotting within the hemodialysis catheter between dialysis sessions, the lumens of the hemodialysis catheter are typically filled with a diluted heparin solution (i.e., a “lock solution”) between the dialysis sessions. More particularly, after a dialysis session has been completed, a diluted heparin solution (i.e., the “lock solution”) is loaded into the lumens of the hemodialysis catheter and clamps set at the proximal end of the hemodialysis catheter (i.e., at the catheter's extracorporeal connector element 25). These clamps prevent the lock solution from draining out of the distal end of the catheter into systemic circulation. At the start of a hemodialysis session, the clamps are released and the lock solution is withdrawn from the hemodialysis catheter, whereupon the hemodialysis catheter is ready for use in a dialysis procedure.
It will be appreciated that the efficiency of a hemodialysis procedure will be reduced if there is recirculation of the dialyzed blood flow, i.e., if the cleansed blood returning to the body through the return line 65 is immediately drawn back into the suction line 55. To avoid this problem, hemodialysis catheters have traditionally staggered the openings 50, 60 of the lines 55, 65, respectively, in the manner shown in FIG. 2, i.e., so that mouth 60 of return line 65 is disposed distal to mouth 50 of suction line 55. With this arrangement, given the direction of the blood flow in superior vena cava 45, mouth 60 of return line 65 is always disposed “downstream” of mouth 50 of suction line 55. As a result, there is a reduced possibility that the cleansed blood returning to the body through return line 65 will be immediately drawn back into suction line 55, and hence any undesirable recirculation of the cleansed blood flow is minimized.
One consequence of forming the hemodialysis catheter with the aforementioned “staggered tip” configuration (i.e., so that mouth 60 of return line 65 is disposed distal to mouth 50 of suction line 55) is that each lumen of the dual-lumen hemodialysis catheter is effectively dedicated to a particular function, i.e., line 65 is limited to use as a return line and line 55 is limited to use as a suction line. This point becomes clear if one considers the effect of reversing the use of each line, i.e., of using line 65 as a suction line and of using line 55 as a return line—in this reversed situation, the undesirable recirculation of the cleansed blood would tend to increase significantly, since the cleansed blood emerging from the mouth of the return line would be released just upstream of the mouth of the suction line, so that the cleansed blood would tend to be drawn back into the mouth of the suction line immediately after being returned to the body. As a result, there would be a significant reduction in the efficiency of a hemodialysis procedure (e.g., 15-30%, depending on the catheter tip design), and hence dialysis sessions would need to increase significantly in duration and/or frequency. Furthermore, if such a line reversal were to occur inadvertently and escape the attention of the attending medical personnel, the reduced hemodialysis efficiency might cause a patient to unknowingly receive inadequate dialysis during a treatment session, which could have serious health consequences for the patient.
The requirement that each line be dedicated to a particular function (i.e., suction or return, depending on whether its mouth is disposed proximal or distal to the mouth of its counterpart line) can be problematic in certain situations.
By way of example but not limitation, if a blood clot were to form in the suction line, it could be desirable to reverse flow through this line to see if the blood clot could be cleared from the catheter by forcing the blood clot out the distal end of the catheter. However, this approach requires the aforementioned line reversal, with the suction line being used as the return line and the return line being used as the suction line. As noted above, such line reversal is problematic where the hemodialysis catheter utilizes the aforementioned “staggered tip” construction.
By way of further example but not limitation, where the disposition of the hemodialysis catheter within the vascular system of the patient is such that suction from the suction line causes the hemodialysis catheter to repeatedly adhere to a vascular wall, it could be desirable to reverse flow through this line to avoid such recurrent adhesion. However, as noted above, such line reversal is problematic where the hemodialysis catheter utilizes the aforementioned “staggered tip” construction, since the mouth of the suction line should be disposed upstream of the mouth of the return line in order to minimize the recirculation of dialyzed blood.
The requirement that each line be dedicated to a particular function (i.e., suction or return, depending on whether its mouth is disposed proximal or distal to the mouth of its counterpart line) is eliminated if the two lines of the dialysis catheter co-terminate, i.e., if the mouths of the two lines are disposed in a side-by-side configuration, such as that shown in FIG. 3. This construction can be highly desirable, since it eliminates the need to dedicate a particular line to a particular function, and hence would greatly simplify dialysis setup and provide increased flexibility during catheter operation. However, in a conventional application of this side-by-side construction, hemodialysis efficiency is greatly reduced, since the mouth of the return line is no longer disposed distal to the mouth of the suction line, and hence there is a much higher likelihood that cleansed blood exiting the return line will be immediately drawn back into the suction line of the dialysis catheter, thereby resulting in the undesirable recirculation problem discussed above. Furthermore, where the mouths of the two lines are disposed in a side-by-side configuration such as that shown in FIG. 3, suction from the suction line may cause the distal tip of the hemodialysis catheter to adhere to a vascular wall (see, for example, FIG. 4), which can also greatly reduce catheter efficiency. In order to reduce the possibility of, and/or in order to reduce the effects of, such suction adhesion to an adjacent vascular wall, some hemodialysis catheters provide small holes in the sides of the catheter, proximal to the catheter tip. Such side holes can permit blood flow to continue even where suction causes the distal end of the catheter to adhere to an adjacent vascular wall. However, since these side holes are smaller in size than the mouth of the suction line, they are incapable of supporting normal catheter flow rates and hence catheter flow rates are still greatly reduced.
Prior art hemodialysis catheters also tend to suffer from various additional deficiencies. By way of example but not limitation, even with the use of catheter lock solutions between dialysis sessions, blood clots may form in the mouths of one or both lumens of the hemodialysis catheter, and at locations between the mouths of the two lumens. This is particularly true during the time between dialysis sessions, when the hemodialysis catheter is not in active use. This is because the distal end of the hemodialysis catheter is disposed in a turbulent blood environment, and some of the catheter lock solution inevitably leaks out of the distal end of the hemodialysis catheter and is replaced by blood, which can then clot at the distal end of the hemodialysis catheter. These blood clots can be difficult and/or time-consuming to remove, thereby slowing down dialysis set-up and/or reducing dialysis throughput. In this respect it should be appreciated that blood clot removal can be particularly difficult where side windows are formed adjacent to the distal ends of the lumens of the hemodialysis catheter, since portions of the blood clots may extend through the windows and thereby mechanically “lock” the blood clots to the hemodialysis catheter.
Therefore, it would be desirable to provide a new hemodialysis catheter which is configured to minimize the aforementioned undesirable recirculation of dialyzed blood, yet which allows its lumens to be interchangeably used for suction or return functions. It would also be desirable to provide a new hemodialysis catheter which minimizes the possibility of the catheter inadvertently adhering to vascular walls, and which simplifies removing any clots which might form adjacent to the distal end of the catheter. And it would be desirable to provide a new hemodialysis catheter which is easy to manufacture and inexpensive to produce.