Surgery – Diagnostic testing – Flexible catheter guide
Reexamination Certificate
2000-02-01
2004-08-03
Hayes, Michael J. (Department: 3763)
Surgery
Diagnostic testing
Flexible catheter guide
C600S435000
Reexamination Certificate
active
06770038
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to the field of medical devices. In particular, this invention pertains to a stylet that helps increase the rigidity of a medical device, particularly when the medical device is being inserted.
2. Description of Related Art
Numerous types of catheters are well-known in the prior art; for example, peripherally inserted central catheters (PICCs) are commonly used in the prior art. Peripherally inserted central catheters are used to access the vascular system. In particular, PICCs are used when long-term-vascular access is required (e.g., more than two weeks indwelling time in a patient) to avoid multiple injections of the patient. A PICC is a long catheter that is often inserted mid-way on a patient's arm and the end of the catheter is often placed in the superior vena cava of the heart. PICCs often provide access to a patient's vascular system for chemotherapy or other types of intravenous medication. Because the PICC must often travel through many natural obstacles in the venous/vascular system, the catheter must be soft and pliable for ease of navigation and to avoid trauma to a blood vessel. In addition, the catheter must also be made of bio-compatible materials so that it will not irritate a patient's veins during the catheter's long dwelling time.
Unfortunately, PICC lines made of a soft bio-compatible material are very difficult to insert into a patient because its soft or pliable construction causes the PICC to often collapse and bend before entering the patient's veins. In order to more quickly and efficiently insert a PICC, a flexible metal stylet (or guidewire) is used as a stiffening member inside the catheter during insertion. Once the catheter is placed inside the patient, the guidewire is removed. Guidewires, however, cause several problems. There is increased friction between the guidewire and the inner wall of the catheter since the catheter often makes many turns and twists before reaching its final destination. As a result, it is often difficult to manipulate and then remove the guidewire. Second, the use of the guidewire also introduces the possibility that the guidewire may perforate a catheter when it is forced against the catheter.
One solution to these problems is to flush the catheter before using it, during the insertion process to aid manipulation of the guidewire, and/or after the insertion process to assist removal of the guidewire. These flushing solutions often contain heparin and saline. The need for a flushing system and a stiffening member, such as a stylet, becomes even more significant as catheters decrease in diameter. A smaller catheter is often more beneficial for patients with small or fragile veins since a smaller catheter causes less trauma to the patient's veins. The use of smaller catheters has also necessitated that the guidewire or stylet be smaller. Yet stylets have not decreased in size to the degree needed. Consequently, the fluid flow area for the flushing solution is decreasing at the same time the need for the flushing solution and a larger fluid flow area are increasing. This is counter-productive.
Referring to
FIG. 1
, a cross-section of a prior art guidewire
102
is shown in a small catheter
100
with minimal space for the fluid flow area
104
. In an exemplary catheter with a 0.035 inch diameter, a cross-sectional area of guidewire
102
occupies about 70% of the cross-sectional area of the lumen of catheter
100
. Consequently, only about 30% of the cross-sectional area of catheter's
100
lumen is available as the fluid flow area
104
. Another prior art embodiment of a guidewire
200
is shown in FIG.
2
A. The guidewire
200
is made of three elements: a flat ribbon of material
207
adjacent to a core
209
, both of which are disposed within a twisted-helical coil
205
. The resulting fluid flow area
203
between the guidewire
200
and the catheter
201
is minimal.
A side view of the guidewire
200
of
FIG. 2A
is illustrated in FIG.
2
B. The helical coil
205
is welded on both ends of the ribbon
207
at
211
a
and
211
b
. The twists of the helical coil
205
are often not visible to the naked eye, but for the sake of clarity, the space between each of the coils in coil
205
have been exaggerated in FIG.
2
B. The coil
205
often flexes as it twists and turns with the catheter
201
. This allows some fluid to flow in between the coils
205
and around the core
209
, which provides stiffness, and the flat ribbon
207
. In addition, the core
209
can also be welded to the flat ribbon
207
.
FIG. 3
illustrates a cross-section of another prior art embodiment in which the guidewire
301
is made of three separate wires
301
a-c
, which are braided together. Each wire may have a diameter of approximately 0.008 inches while the internal diameter of the catheter
300
may be 0.032 inch.
FIG. 3
illustrates one disadvantage of the prior art systems. The length of the guidewire cannot be changed without altering or compromising the structural integrity of the guidewire. For example, guidewire
301
of
FIG. 3
cannot be cut without compromising or destroying the structural integrity of the guidewire
301
as its three wires
301
a-c
will unravel and separate. The same is true for the guidewire
200
of FIG.
2
and its three components,
205
,
207
and
209
.
As is evident from
FIGS. 1
,
2
and
3
, the fluid flow area (
104
,
203
,
303
) around each respective guidewire (
102
,
200
,
301
) is severely restricted as the diameter of the guidewire approaches the internal diameter of the catheter. Many prior art guidewires are made of metal so that the guidewire may not be cut when adjustability of the catheter length is desired. As a result, in these prior art embodiments, the guidewire is adjusted by first withdrawing the guidewire from the proximal end of the catheter and then cutting the catheter. These catheters thus require extra-tedious manipulations before being able to use them.
Smaller fluid flow due to decreased area between the guidewire (or stylet) and the inner wall of the catheter is undesirable. Adequate fluid flow is necessary for the flushing solution to aid insertion and removal of the guidewire (or stylet) in the catheter. In addition, unhindered fluid flow helps prevent friction between the guidewire (or stylet) and the inner wall of the catheter. Thus, it is desirable that a guidewire (or stylet) serves as a stiffening member in a medical device, such as for example, a PICC catheter, during insertion of the medical device. It is also desirable that the shape of the stiffening member helps increase fluid flow around the guidewire (or stylet) disposed within the medical device.
SUMMARY
The present invention describes a stiffening member that allows an increase in the fluid flow area within a medical device, such as a catheter. In one embodiment, the stiffening member is an elongated, substantially rectangular stylet that is disposed within the catheter, such that the stylet can occupy less than half of the lumen area of the catheter. As a result, adequate fluid flow is allowed between the stylet and the inner wall of the catheter. This increases patient comfort. In a preferred embodiment, the stylet is made of substantially flat stock such that in cross-section, the longer dimension of the stylet closely approximates or is slightly smaller than the internal diameter of the catheter. Furthermore, in the preferred embodiment, the flat stock is twisted over the length of the stylet to achieve equal rigidity or bendability over the entire length of the stylet in any axis. Different pitches (i.e., number of twists or turns per inch) may be used to obtain stylets with different degrees of rigidity. Moreover, the pitch within a single stylet may be varied to create multiple stiffnesses within a single stylet. For example, the proximal end can have a greater pitch than the digital end of a stylet to create a softer proximal end. This is beneficial since the proximal
Balbierz Daniel J.
Bley Robert
Blakely , Sokoloff, Taylor & Zafman LLP
Hayes Michael J.
Johnson & Johnson
Sirmons K.
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