To effect infusion into a patient, an indwelling catheter connected with an infusion line is inserted into the blood vessel of the patient. This indwelling catheter is constructed of a hollow outer catheter and a hollow inner needle having a sloped edge face at its leading end that protrudes beyond the leading end of the outer catheter. The needle point of the inner needle is provided with an opening. The catheter is inserted into the blood vessel of the patient by first introducing the leading end of the needle into the blood vessel of the patient.
When the inner needle reaches the inside of the blood vessel, the blood enters the opening at the needle point and flows or flashes back into a transparent housing which is mounted at the root portion of the inner needle. This makes it possible to confirm that the inner needle has reached the blood vessel. At this time, the inner needle and the outer catheter are moved forward a slight distance to insert the leading end of the outer catheter into the blood vessel.
In known indwelling catheter assemblies, the inner circumference of the leading end of the outer catheter is closely fitted to the outer circumference of the inner needle so that the blood will not flow between the outer catheter and the inner needle. This makes it impossible to visually confirm by flashback of the blood whether or not the outer catheter has captured or been inserted into the blood vessel.
Thus, after confirming capture of the blood vessel by the inner needle, the inner needle and the outer catheter are delicately advanced by the operator based on the senses and experience of the operator. Because of this, the proper insertion of the outer catheter into the blood vessel is not always achieved, but may be too shallow or deep. This is partly because the spacing between the edge face of the inner needle and the leading end of the outer catheter is slightly different depending upon the kind and size of the indwelling catheter assembly, and the manufacturer of the indwelling catheter assembly. This is also due in part to the fact that the size of blood vessels in a patient(s) varies.
One proposal that attempts to address this problem is described in U.S. Pat. No. 5,279,572. This patent discloses an indwelling intravenous needle that includes a metallic internal needle, an external needle positioned over the internal needle so that the leading end of the external needle is set back from the leading end of the internal needle, and a plastic housing fitted to the rear end of the exterior needle. The patent describes providing a longitudinal groove on the surface of the inner needle. This groove extends from the leading edge face of the inner needle and terminates at a point within the housing. During use of the indwelling intravenous needle, the leading end of the internal needle is inserted into the vein cavity and the visual observation of blood flashback within the internal needle confirms that the internal needle has captured the vein cavity. Further advancement of the indwelling intravenous needle eventually causes the leading end of the external needle to capture the vein cavity and this capture can be observed as a result of blood flashback within the groove in the surface of the internal needle. The groove allows blood to flow between the inner surface of the exterior needle and the exterior surface of the internal needle.
The indwelling intravenous needle disclosed in the aforementioned patent is, however, susceptible of certain disadvantages and drawbacks. In one respect, the patent describes forming the groove on the surface of the internal needle by machining. The nature of this machining process causes a significant reduction in the wall thickness of the internal needle, thus resulting in a severe weakening of the needle wall. This weakened wall can cause problems during use of the needle, particularly given the rather thin nature of the needle. Further, the machining process results in a groove having relatively sharp or rough corners where the sides of the groove meet the outer surface of the needle. These roughened corners can cause damage to the external needle. Also, because the front portion of the internal needle is exposed beyond the leading end of the external needle, these sharp corners of the groove present the potential for scraping against and possibly causing damage to the vein during insertion of the indwelling intravenous needle into the vein. It is possible to attempt to round these sharp edges through use of a secondary working operation such as a polishing or deburring operation, but this undesirably complicates the manufacturing process and increases the manufacturing time.
In light of the foregoing, a need exists for an indwelling catheter assembly which permits visual confirmation that the indwelling catheter has captured a blood vessel, but which does not present the possibility of damaging the surrounding portion of the assembly or needlessly injuring the vein.