A CANNULA

Abstract: An intravenous cannula (1) with a bevelled point (2) is designed so as to make the cutting edge (3) of point (2) extend along the portion of the cannula (1) wall which is intended to lie furthest away from the skin (8) in use. The cutting edge (3) is preferably placed along the light opening (6) of cannula (5).

Description: A cannula . The present invention relates to a cannula, preferably an intravenous cannula of the kind that has a bevelled point forming a cutting edge. At present, there is a veriety of cannulae on the market, however, they only differ in details as regards connection with tubing, medicament wells, and the like. It is common to all these cannulae that the cutting edge of the cannula is provided along a portion of the cannula circumference and, also, along the portion of the cannula circumference which is intended to lie closest to the skin when in use. With correct use and correct equipment complications will generally be avoided when, especially peripheral venes are punctured and cannulated, however, some cases of complicat¬ ions or accidents will be unavoidable. If the cannula is inserted into the vene in a too steep or vigorous manner, there is a hazard of the opposite vene wall being punctured as well. Such a puncture may, in turn, cause blood to ooze from the vene to the tissue with a consequent haematoma. Also, medicaments may be injected into areas outside the vene in stead of into the blood stream, because the introd¬ uced plastic tube is provided adjacent to the unintended place of puncture. Furthermore, the inserted plastic tube may unintentionally be perforated by unintended movement of the cannula in the tube in connection with removal. Among known technology, we refer to EP 0 238 419 A3 and EP 0 271 775 A3, DE-OS 24 34 618, GP-PS 1 298 707, and US-PS 2 748 769 . All cited documents disclose straight cannulae or cannulae which are slightly arched at the point, with the cutting edge of the cannula extending along the periphery of the cannula tube, and with the cannula, additionally, being equipped with auxiliary openings or with a two-piece cannula opening, this to provide a certain turbulence when injecting. There are also cannulae on the market the cutting edge of which is displaced by grinding to a point between the periphery and the light opening. It is an object of the present invention to improve known technology, and the invention, thus, relates to a cannula with a bevelled point which forms a cutting edge, and the cannula is characterized by the fact that the cutting edge of the point extends along the light opening of the cannula in the portion which is placed furthest from the skin when the cannula is inserted. Experiments proved that the cannula according to the invention results in a smaller penetration or wound area than known cannulae. This was confimed in tests on patients, up to 0 of whom said on inquiry that piercing with the cannula according to the invention caused less discomfort than piercing with cannulae of known technology. The tests were made with masked cannulae, one of each kind and one on each arm of the same patient. Another advantage which is achieved with the cannula according to the invention is that the cannula opening will face the stream when inserted into the vene, which will provide a more rapid "backflow" and, thus, confirmation that the cannula is in place. Other advantages of the invention will appear from th following disclosure with reference to the accompanyin drawings, in which: Figure 1 shows a conventional cannula with a cannula tub 1 and a point 2; Figure 2 shows an enlarged portion of the point area o Figure 1; Figure 3 shows a conventional cannula in a position fo penetration; Figure 4 shows the situation in case of unintentional penetration of the opposite vene wall; Figure 5 shows the unintended situation occurring when the cannula tube is wrongly placed; Figure 6 shows an unintentional perforation of the cannula tube by the pont of the cannula; Figure 7 shows the general position of the point of the cannula according to the invention (compare with Figure 2) ; Figure 8 corresponds to Figure 3, but shows the invent¬ ion; Figure 9 basically corresponds to Figure 4, but shows the advantage achieved by the invention; Figure 10 and Figure 11 show a preferred embodiment of the invention (compare with Figure 7); Figure 12 shows the preferred embodiment and corresponds to Figure 9; Figure 13 shows the preferred embodiment and corresponds to Figure 6; As mentioned above all cannulae on the market at present are of the kind as shown in Figure 1, designed as shown in Figure 2 with the edge of the point being provided in the part of the cannula wall that is intended to lie in contact with the skin. hen used. This is diagrammatically shown in Figure 2, and the accidents that may occur when the cannula is used are illustrated in Figures 3 - 6. In Figure 3 cannula 1 with point area 2 and the associated plastic tube 7 is positioned to penetrate the skin 8 and vene 9 by also piercing one vene wall 9b. Figure 4 shows what may happen if the cannula is inserted too steeply or forcefully. The opposite vene wall 9c is puctured, which will cause a hazard of blood oozing out of the vene with a consequent haematoma. The patient, thus, must be pierced once more. In use, blood and medicament may then ooze out of opening 9c, so that there is also an accummulation of liquid outside the vene with further hazard of injuries to tissue and necrosis, see Figure 5. Figure 6 shows a situation which may occur due to the fact that the point of the cannula is moved inside the cannula tube, the latter may be punctured at 7a. As mentioned above, it is an object of the invention to remedy the shortcomings of known technology, and according to the general design of the invention this is achieved by placing the cutting edge 3 of the cannula point 2 along th portion of the cannula wall which is intended to face awa from the skin in use. Generally, the cutting edge is achieved by simple angula cutting of the cannula, however it is possible both o conventional cannulae and on cannulae according to th invention to sharpen the cutting cannula edge, as indicate in Figure 2, so as to provide a regular point 4 in stead o the present oval arch. The cannula according to the inventinn is illustrated i Figures 8 and 9 with Figure 8 corresponding to Figure 3 immediately before the skin is punctured. In Figure 9 the situation shown is immediately after cannula 1 with plastic tube 7 has penetrated the skin 8 and one vene wall 9a. It will appear that by placing the cutting edge according to the invention a more flat "underside" of the point area 2 is achieved, which will substantially reduce the hazard of puncturing the other vene wall 9b, as shown in Figure 4. The embodiment shown in Figures 7 - 9 represents an essential improvement as compared to known technology, as illustrated in Figures 3 - 6. There is, however, a certain though strongly reduced hazard of unintentional penetration of a vene wall upon insertion of the cannula, also in connection with the object of the present invention. This is shown directly in Figure 4, but even after successful insertion a puncture may occur on the side where the point of the cannula is placed. The preferred embodiment of the invention, as mentioned above, should solve this problem too, and this is the case with the embodiment generally shown in Figure 10. It is achieved by reshaping the point area 2 to move the cutting edge 3 of the cannula from the outer diameter to the inner diameter or light opening, indicated by numeral 6 in Figures 7 and 10. By moving the cutting edge 3 the hazard of unintentionally puncturing the vene wall is substantially reduced, as there is provided a further surface 11 as will appear, e.g. from Figure 12. Said surface may slide against the vene wall preventing the point from getting caught in the vene wall and unintentionally puncturing the wall. According to the invention as disclosed above a cannula is achieved in a simple and inexpensive manner, and safety in operation and use is enhanced without sacrificing the safety of known cannulae and, additionally, without causing essentially increased costs. The invention, thus, represents an essential improvement as regards operation and use of cannulae in connection with puncturing and cannulation of veneε.

Claims: AMENDED CLAIMS [received by the International Bureau on 6 February 1992 (06.02.92); original claim 1 replaced by amended claim 1 (1 page)] Cannula (1) with a bevelled point (2) which forms a cuttin edge (3), c h a r a c t e r i z e d i n that the cuttin edge (3) of the point (2) extends along the portion of th light opening (6) of the canula (1) which, before th penetration of the skin (8), is furthest away from the ski

Inventors: HEIMREID BENT, HEIMREID, BENT
Applicants: HEIMREID BENT, PREISS OTTO T, HEIMREID, BENT, PREISS, OTTO, T.
Application year: 1991
Main classification: A61M5
IPC codes: A61B17, A61M5, A61M25