Flexible tubes for fixed peripheral venous cannulas are used in the peripheral vascular system to deliver solutions for infusions and injections as well as for taking blood. Solutions or injections are delivered or blood taken from a vein in the peripheral vascular system, meaning far from the heart, by means of a flexible tube or plastic cannula. The materials used for this according to prior art are FEP or PUR in the form of single-material flexible tubes, with or without radiopaque strips.
Several important properties of flexible tubes of FEP or PUR for fixed venous cannulas are evaluated in the following Table 1.
Explanattions
As shown in the above Table, FEP primarily distinguishes itself through an extremely good advancing ability. However, it has the disadvantage of being subject to higher incidences of buckling, which lead to interference with or even a complete stop of the throughput, as well as the strongly increased risk of injury and/or inflammation of the vascular walls.
In contrast, PUR has an acceptable buckling resistance and good blood compatibility and the risk of inflammation or injury to the vessel walls is nearly zero.
The reason for the latter is that PUR becomes soft within a few minutes at body temperature, meaning that hardly any mechanical irritation of the vascular walls occurs.
However, PUR has the particular disadvantage of a noticeably higher “roll-up” risk for the cannula during the application.
It is therefore the object of the present invention to make available flexible tubes for fixed peripheral venous cannulas which combine the positive properties of FEP with those of the PUR without also taking over the respectively negative properties (see Table 1 for this).
Surprisingly, this object was solved with a flexible tube design for fixed peripheral venous cannulas, which uses a composite laminate, comprising an inside layer of polyamide and an outside layer of polyurethane.
The considerations that went into solving this problem are described in the following:
However, if the spectrum of properties for standard materials or self-formulated materials is not sufficient, composite laminates of materials having different properties are used. To be considered are cases where the inside surface of the flexible tube must have noticeably different properties than the outside surface, for example if the outside surface must have a good bonding ability and the inside surface a high chemical resistance.
The macroscopic properties of such conventional composite laminates, e.g. rigidity or bending resistance, are determined by the sum of the individual material property shares, for example as described in the following U.S. Pat. No. 4,385,632. Described in this reference is a composite laminate for an angiography catheter, provided with a soft, a-traumatic tip made exclusively from polyurethane, a transition region and a main flexible tube section consisting of an internal polyamide layer and an external layer of polyurethane with an approximate wall thickness ratio of 50:50.
It is the object of this embodiment in the form of a composite laminate is to meet the following requirements:
The present invention, on the other hand, is designed to achieve the above-described flexible tube properties for tubes used as fixed venous cannulas, wherein these properties must clearly exceed the sum of the individual material properties. Such combinations of material properties should be achievable only if the systems exhibit a certain synergic effect and the materials used are furthermore precisely adapted to the respective application case.
According to one important requirement, the flexible tube should be as rigid as possible during the insertion into the body and as flexible as possible while remaining in the body. These properties, which initially seem to be mutually exclusive, can surprisingly be achieved with the material combination according to our invention. This is due to the fact that PUR with a shore hardness of 60 D, for example, softens to 50 D at 37° C. within 5 minutes. In contrast, the flexibility of PA is primarily influenced by the absorption of moisture, wherein this action is insignificant as compared to PUR and requires a longer period of time.
These in part opposing and in part super-imposed effects not only make possible—depending on the relative wall thickness of PUR to PA and the respective shore hardness of the individual materials—to precisely adjust on the one hand the required rigidity for placing the flexible tube and, on the other hand, the required flexibility necessary for remaining inside the body. Rather, it was particularly surprising that other properties necessary for using the flexible tube could also be adjusted purposely, namely the rigidity, the buckling resistance, the advancing ability, and the roll-up behavior.
With this invention, the user therefore has many options to purposely and easily influence the flexible tube properties of fixed venous cannulas, meaning so-to-speak adjust them precisely to the requirements. That is not possible with the currently used single-material flexible tubes according to prior art.
The desired properties of flexible tubes for fixed peripheral venous cannulas furthermore can in most cases be guaranteed even with fluctuations in the raw-material quality by varying the respective layer thicknesses of the co-extruded flexible tube.
The sum of all properties of the composite-material flexible tube can furthermore be changed considerably, but in a simple manner, without requiring special formula mixtures by using different, commonly used standard raw materials with different mechanical properties.
However, such formula mixtures can additionally be used and can result in a further optimization and/or a precise adjustment of the flexible tube properties.
The following Table 2 provides a summary of the properties of the composite laminate according to the invention, comprising an external PA layer and an internal PUR layer for the flexible tube, as compared to tubes made from the starting substances PA and PUR and/or FEP:
+ = good
++ = very good
− = poor
−− = very poor
The following is intended to explain with the aid of an exemplary embodiment whether the invention is suitable for use as flexible tube for a fixed peripheral venous cannula. The tested flexible tube, used as fixed peripheral venous cannula, has an external diameter of 1.07 mm, an internal diameter of 0.79 mm and is provided with radiopaque strips.
If this flexible tube with PA internal layer and PUTR external layer is deflected by 180° around a pin with 4 mm diameter, it does not buckle in the temperature range between 23° C. and 37° C.
For a comparison:
Number | Date | Country | Kind |
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10220410.1 | May 2002 | DE | national |
Filing Document | Filing Date | Country | Kind |
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PCT/EP03/04515 | 4/30/2003 | WO |