Syringe assembly

#The present invention relates to pumping devices, and more particularly to syringes.

#Syringes are in common use today by physicians, nurses, and other hospital personnel for a variety of purposes. Frequently, syringes have been utilized to pump fluid into a body cavity of a patient or a cavity in a therapeutic device under circumstances where the pressure attained in the cavity should be limited to a predetermined value. For example, during a spinal anesthesia procedure an anesthetic solution is pumped from a syringe through a needle into the sub dural space which is essentially an inelastic pouch, and thus only a specified maximum amount of the solution should be pumped into the space as determined by the pressure in the space. Similarly, various types of cardiovascular catheters are often threaded into blood vessels, after which a balloon adjacent the distal end of the catheter is inflated through use of a syringe. If the balloon is overinflated, particularly when the catheter is placed in a smaller vessel, the vessel may be ruptured. Numerous other catheters, such as endotracheal tubes and Foley catheters, are frequently provided with retention balloons which should not be overinflated, particularly when the balloon is obstructed by a body passage.

#Few of the hospital personnel realize the considerable pressures which can be generated by a hand-operated syringe. For example, a 10 c.c. syringe may readily generate pressures in the range of 50-60 lbs./sq. in., the smaller syringes being capable of developing greater pressures for the same amount of force applied to the syringe plunger. It is thus apparent that considerable care must be exercised by the user when a syringe is utilized to pump fluid into a cavity space where only a limited amount of pressure is desired. In the past, tactile sense has been used when forcing the plunger into the syringe to determine when the maximum pressure has been attained by resistance to plunger movement. Such a procedure produces speculative results, at best, in preventing harm to the patient, particularly since the syringe may readily generate relatively high pressures.

#FIG. 1 is a sectional view of one embodiment of the syringe assembly of the present invention as attached to a hollow needle;

#FIG. 2 is a fragmentary sectional view of pressure limiting means in the syringe assembly of FIG. 1 as actuated above a predetermined pressure;

#FIG. 3 is a fragmentary elevational view of the syringe assembly of FIG. 1;

#Referring now to FIGS. 1-3, there is shown a syringe assembly or syringe means generally designated 20 comprising a syringe 22. The syringe 22 has a hollow barrel 24 having a chamber 26 for retaining fluid. The syringe also has a plunger 28 having a flexible plug 30 adjacent one end 32 of the plunger received in one end of the chamber 26. The plug 30 sealingly engages against the inner surface 33 of the syringe barrel 24, with the plunger being pushed into the chamber 26 to pump fluid out of the chamber.

#The syringe 22 has an extension or extension means 34 projecting from an end of the barrel 24 remote the plunger 28, with the extension 34 having a tip 36 receivable in the hub H of a hollow needle N. Of course, the tip 36 of the syringe extension 34 may be connected to any other suitable device, such as a catheter, as described below. The extension 34 has a passageway 38 which communicates with the syringe chamber 26 and the hollow needle N, when attached, and has a flexible balloon 40 which communicates with the passageway 38 through an opening 42 in the wall of the extension 34. The balloon 40 comprises a flexible sleeve which surrounds the extension 34, and has a pair of edges 44a and 44b secured to the outer surface of the extension 34 by suitable means 46a and 46b, such as adhesive. Thus, the balloon or sleeve 40 has its edges 44a and b sealed peripherally around the extension 34, such that it defines a cavity 48 intermediate the sleeve and the outer surface of the extension 34 which communicates through the opening 42 with the passageway 38.

#The balloon 40 is constructed to inflate when a predetermined pressure has been reached in the passageway or chamber of the syringe, the particular pressure at which the balloon inflates being selected for the particular use contemplated for the syringe assembly. The pressure at which the balloon inflates may be controlled by a number of factors including the particular material used for the balloon, such as latex, and the thickness, durometer, and elasticity of the balloon, as well as the transverse and longitudinal radii of the balloon, according to the law of Laplace which holds that the pressure required to inflate a balloon is directionally proportional to its tangential tension and inversely proportional to its transverse and longitudinal radii.