(a) The Invention
The invention relates to a catheter assembly and a method for inserting a cannula useful for the introduction of nutrients or medication, or the extraction of fluids from a living subject. The catheter assembly more particularly comprises a cannula, needle and catheter inserter which allows the selection of the desired length of cannula to be inserted. The method particularly relates to a method of inserting a cannula into a living subject to a desired length.
(b) Background Information
A number of catheter assemblies are known for introduction of a polymeric cannula into a vein, artery or cavity of a living subject for infusion or extraction of fluids.
In one method, a steel needle is sized to fit within the duct of a cannula and is inserted from the proximal end of the cannula so that the needle exits the distal end. The needle is then inserted into the living subject after which the needle is removed from the cannula, leaving the cannula behind with at least its distal end in the subject. Additional tubing can be attached thereto or medicaments or nutrients can be caused to flow through the cannula into the subject.
In order to prevent the needle from sliding relative to the cannula on insertion, several catheter inserters have been developed which aid the person inserting the cannula to prevent such sliding. This also provides a way to control the cannula without contaminating it. Inserters of a type comprising a positionally fixed device having a pair of winged members which when folded up will pinch the needle and prevent motion of the needle relative to the cannula and catheter inserter are known. Generally a relatively stiff cannula of a material to be inserted into the subject such as TEFLON (from DuPONT) is fixed to the distal end of the inserter, while a flexible tubing (e.g. polyvinyl chloride) is attached to the proximal end of the inserter in flow communication with the cannula.
For example, in U.S. Pat. No. 4,194,504 a winged catheter inserter fixed to a cannula is described comprising a resilient tubular body having a lumen and a pair of wings having substantially uniform thickness such that on folding up of the wings, the lumen changes shape to capture the needle within for easier insertion. See also U.S. Pat. Nos. 4,198,973; 4,192,304; 4,192,305; 4,300,553; 4,388,074; 4,445,893; 4,353,369; and 4,326,519.
A difficulty with this type of winged inserter is that the length of cannula to be inserted is limited. The length is predetermined by the position that the inserter has been fixed on the cannula material. The winged inserters of the prior art have been attached to the cannula for a number of reasons including the need to secure cannula at one end of the inserter and flexible tubing at the other end and to prevent the relative movement of the inserter after use. Relatively long lengths of cannula cannot be used with this type of inserter because the inserter must be affixed relatively close to the distal end for accurate control of the cannula and only that portion extending from the distal end of the inserter may be used. Another difficulty with the fixed wing inserter is the desirability of being able to differ the length of the needle and the cannula for ease of insertion into the subject. A person inserting such cannulae, such as a nurse or doctor, will have varying preferences as to the positioning of the inserter relative to the needle and cannula end. This requires stocking several different sizes of cannula fabricated with differing distal end lengths.
One method of overcoming the difficulty of inserting a variable or relatively long length of cannula (greater than about 50 mm) has been to select a needle with an inner diameter greater than the outer diameter of the cannula. The needle is inserted into the subject and the cannula is fed through the needle into the subject to the desired length. This technique has several difficulties. First, the cannula for insertion must be stiff and/or have a wire running through its duct during insertion. Also, when inserting such a device into an area such as a blood vessel, removal of the needle allows blood to escape around the insertion site or possible infection to enter through the insertion site which is larger than the cannula. After the cannula is in the desired position, the needle is generally removed. There is difficulty in removing the needle without further escape of blood or chance of infection. This is especially true when the cannula is attached to a hub portion which prevents sliding the needle off of the cannula's proximal end. If the needle is allowed to remain on the cannula there can be difficulty in preventing the sharpened edge of the needle from further piercing the subject or piercing the cannula. Bulky containment mechanisms are used to minimize but not eliminate this danger. The alternative to this type of method is direct surgical implantation of a cannula in the desired area which is both traumatic and costly.
In summary the prior art to date has encountered great long standing difficulty in inserting a desired length of cannula initially or relatively long lengths of cannula after insertion of the distal end of a cannula. The present invention is directed to overcoming one or more of the problems as set forth above.