Tapered intravenous cannula

#This invention relates to an improved cannula for communication with the vascular system in order to gain access to a supply of blood for extracorporeal blood processing, for example hemodialysis, hemoperfusion, or any other desired form of extracorporeal blood treatment.

#In the early days of dialysis therapy, extracorporeal blood flows were moderate, at about 200 ml/min. with the result that a dialysis treatment took six hours or more. These treatments, while long, were often uneventful, not least because the extracorporeal pressures were moderate with the low flow rates, typically between −120 mm./Hg (arterial) and +120 mm./Hg (venous). Modern therapy has increased the flow rates to as much as 500 ml./min. or more, with corresponding increases in treatment efficiency. However, the operating pressures have also increased, even to as much as −400 mm./Hg (arterial) and as much +600 mm./Hg (post pump). At these pressures, undesirable events can take place more readily, for example, hemolysis, foaming or clotting of the blood, air emboli, and other alarm conditions, which may be frequent and sometimes severe.

#While the operating pressures could be reduced by increasing the inner diameter of the patient access cannulae, which are typically the narrowest portion of the extracorporeal blood circuit, an increase in the size of the needles, which could significantly reduce pressures, is strongly objected to by the patients. A large needle results in a larger incision. Patients have historically shown reluctance to be penetrated in a fresh site by a needle with a cutting point larger than 15 G (gauge).

#In the drawings, FIG. 1 is an elevational view of a cannula for communication with the vascular system of a patient, the cannula having a proximal end which is connected to a blood flow tube;

#FIG. 1a is an elevational view of a modified cannula that is otherwise similar to FIG. 1;

#FIG. 2 is a substantially sectional view of an implanted artificial port for communication with the vascular system of a patient, shown to be in connection with the cannula of FIG. 1;

#Referring to FIG. 1, a cannula 10 is provided, typically for communication with the vascular system of a patient for high flow hemodialysis, or the like. The cannula 10 comprises a tapered stainless steel tube in this specific embodiment, having a larger proximal end 13 that terminates in a hub 12 and has an inner diameter of 2.85 mm in this specific embodiment. Cannula 10 also has a distal end 14 which has an inner diameter of 1.85 mm, with the bore 16 of cannula 10 tapering in substantially uniform manner along its length from proximal end 12 to distal end 14. However, if desired, a cylindrical segment 18 of the cannula may be provided adjacent to the proximal cannula end 12.

#The outer diameter of cannula 10 at distal end 14 may be about 2.1 mm. The wall thickness of cannula 10 adjacent to distal end 14 and typically along the remainder of the length of the cannula can be about 0.12 mm.

#Distal end 14 carries a bevel 98, or a multi-bevel or compound bevel and ends in a point 99 that is dulled or blunt to provide dilation of a preformed track through the skin.