Hypodermic needle guard

An apparatus for preventing injury from a used hypodermic needle. Prior to withdrawal from below the skin, a spring-loaded mechanism is deployed which advances a protective sheath towards the tip of the hypodermic needle. As the needle is withdrawn the protective sheath advances beyond the tip of the needle where a positive locking mechanism positively and irreversibly encapsulates the tip of the needle.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
Hypodermic needles are commonly used to both inject substances into and 
extract substances out of human and animal bodies. Such hypodermic needles 
are typically disposable and are discarded after one use. The problem 
presented by the disposal of a hypodermic needle, and indeed, any handling 
of the hypodermic needle after its use, is the potential for being injured 
by the sharp end of the needle. This is particularly dangerous because 
following the perforation of a patient's skin, the needle may be 
contaminated and therefore capable of spreading diseases, such as 
hepatitis and AIDS. 
2. Description of Related Art 
A number of devices have been described that provide for some form of 
protective shield about the tip of a hypodermic needle, see, for example, 
the following: 
Bastien, U.S. Pat. No. 2,571,653 
Adams, U.S. Pat. No. 2,847,995 
Armao, U.S. Pat. No. 3,134,380 
Bloch, U.S. Pat. No. 3,354,881 
Alvarez, U.S. Pat. No. 4,139,009 
Wickham, U.S. Pat. No. 4,237,882 
Kling, U.S. Pat. No. 4,373,526 and 
Larson, U.S. Pat. No. 4,639,249 
The disadvantage inherent in the above devices is that none provide 
positive protection. In each case, a used hypodermic needle could 
conceivably still perforate a subsequent handler's skin. While the devices 
described by McFarlane in U.S. Pat. No. 4,500,312 and 4,573,981 do provide 
positive protection once in place, considerable risk of perforation is 
presented in replacing the sheath. The devices described by Leeson et al., 
U.S. Pat. No. 3,890,971; Sampson, U.S. Pat. No. 4,573,976 and Mitchell, 
U.S. Pat. No. 4,631,057, are affixed to a syringe and, subsequent to an 
injection, can be extended beyond the exposed needle and locked into 
position. The disadvantage inherent in these designs is that a 
non-automatic deliberate movement is required to slide the guard in place. 
This leaves the needle tip exposed for a period of time. Furthermore, the 
needle tip is merely retracted and not actually encapsulated, and finally, 
these devices envelope the entire syringe and are therefore of 
considerable size and cost. Such a configuration precludes such a design's 
use in conjunction with a multi-draw blood drawing device. Recently ICU 
Medical, Inc. introduced a product called "High Risk Needle," which has a 
similar disadvantage in that a deliberate movement is required after its 
use leaving the needle tip exposed for a period of time. 
SUMMARY OF THE INVENTION 
It is an object of this invention to provide a hypodermic needle guard 
which is automatically deployed to shield the tip of the hypodermic needle 
at the time of withdrawal from below the skin so that the needle tip is 
not exposed subsequent to use. It is also an object of the present 
invention that the needle guard provide positive protection by providing 
an impenetrable encapsulation of the needle tip. It is a further object of 
the present invention to make this device as small and unobtrusive as 
possible. 
In the preferred embodiment of the present invention, a protective sheath 
is slidably affixed about the hypodermic needle. A spring, once released 
via a trigger mechanism, causes the forward most portion of the protective 
sheath to advance to just beyond the tip of the needle. This position 
allows a ball to be forced into the path of the needle thereby preventing 
its re-emergence from within the protective sheath. The protective sheath 
can be deployed by release of the spring while the needle tip is still 
under a patient's skin. As the needle is withdrawn, the spring pushes the 
sheath to just beyond the tip of the needle where it is inextricably and 
impenetrably encapsulated. As the entire device attaches about the 
hypodermic needle only and does not encompass the syringe portion, it is 
very small in size and bulk.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The following description is provided to enable any person skilled in the 
field of medical devices to make and use the present invention and sets 
forth the best modes contemplated by the inventor of carrying out his 
invention. Various modifications, however, will remain readily apparent to 
those skilled in the art, since generic principles of the present 
invention have been defined herein specifically to provide an improved 
hypodermic needle guard. 
The device of the present invention is adaptable for combination with the 
hypodermic needle itself and can therefore be used in conjunction with any 
number of injection or extraction apparatuses. 
FIG. 1 shows the device attached to the hypodermic needle in its retracted 
position prior to an extraction of blood. At this point, the needle is 
used exactly as any unguarded needle would be used. FIG. 2 shows the 
device in its extended position prior to withdrawal of the needle from the 
arm. After a blood sample is extracted but prior to withdrawal of the 
needle from the arm, the ampule 11 is forced to the bottom of the ampule 
holder 13 which causes extension of the release collar 17 as shown. This 
in turn allows disengagement of the hook 29 and the spring 27 forces the 
protective sheath 25 towards the skin. As the needle 19 is withdrawn from 
under the skin, the protective sheath simultaneously slides towards and 
just beyond the tip, at which point the ball 37 is forced into the chamber 
41 effectively and irreversibly encapsulating the needle tip. The used 
hypodermic needle may now be handled without danger of accidental injury. 
FIG. 4 shows the device of the present invention affixed to a hypodermic 
needle used to draw blood. The hypodermic needle 19, attached to a 
threaded base 21 has been screwed into an ampule holder 13 via the 
receiving threads 23. An evacuated ampule 11 capped by a penetrable rubber 
septum 15, has been partially inserted into the ampule holder 13. The 
protective sheath 25 is shown in its retracted position. A coil spring 27 
biases the sheath towards the tip of the needle but is restrained from 
actually extending towards the needle tip by the hook 29 engaged over 
catch 31. The position of the release collar 17 prevents the hook from 
lifting and disengaging the catch. Prior to threading the needle base 21 
onto the ampule holder 13 and hence prior to positioning the hook 29 under 
the release collar 17 to prevent its disengagement, the hook is held in 
place by the outer cap 32. This outer cap 32 insures that the needle 
remains sterile until its use and also prevents accidental injury. Once 
the needle base 21 is screwed into the ampule holder 13 and just prior to 
use, the outer cap 32 is pulled off. At this point, the hypodermic needle 
can be used in the normal manner. When the needle tip has penetrated a 
vein, the ampule 11 is forced further into the ampule holder 13 so that 
the needle pierces the rubber septum 15 and the rubber septum just engages 
the release collar 17. The vacuum within the ampule draws the blood sample 
up into the ampule. The device in its retracted position is so small and 
unobtrusive that it does not interfere in use of the needle. 
Due to its central anchor point 33, the single spring 27 is simultaneously 
able to bias the protective sheath towards the needle tip and the slider 
member 35 towards the end of the protective sheath. Alternatively, the 
anchoring can be achieved by a slight crimp in the protective sheath 25 at 
this same location. The angled configuration of the interior of the 
protective sheath adjacent to the chamber of reduced diameter insures that 
the ball, under compression of the spring, is constantly being urged 
towards the center axis of the sheath regardless of the positioning or 
orientation of the hypodermic needle. Whether upside down or right side 
up, the ball is being pressed towards the center of the chamber. Only the 
presence of the needle 19 prevents the ball 37 from entering the smaller 
chamber 41, the diameter of which is approximately equal to but larger 
than the diameter of the ball. 
FIG. 5 shows the device in its extended position wherein a positive locked 
protection is offered from the sharp end of the needle. When the blood 
drawing operation is completed, the ampule 11 is forced the remaining 
distance to the extreme end of the ampule holder 15. This in turn pushes 
the release collar 17 to a position which allows disengagement of the hook 
29 from the catch 31 via movement through the recessed portion 43 of the 
release collar 17. FIG. 8 illustrates the movement of the hook 29 as the 
release collar 17 is pushed further and further outward. The hook 29 has a 
degree of flexibility or displaceability that allows it to contort out and 
around the catch 31. The spring 27 forces the protective sheath 25 to a 
position at which the tip of the hypodermic needle 19 no longer intrudes 
into the chamber 41. This allows the outer portion of the spring 27 to 
push the ball 37 via the slider 35 into the chamber 41 effectively 
blocking a re-extension of the hypodermic needle 19 through the orifice 
39. FIG. 9 shows a transient position of the ball 37 as it proceeds into 
the chamber 41 when the protective sheath 25 is extended out beyond the 
needle tip. The chamber is dimensional such that the needle cannot be 
forced in between the ball 37 and the walls of the chamber. A 3/64" 
diameter ball, for example, calls for a cylindrical chamber 0.050" in 
diameter and 0.050" deep. As the depth of the chamber is comparable to the 
diameter of the ball, the possibility of the ball being forced out of the 
chamber by any downward force of the needle is precluded. While the ball 
prevents the sheath from moving back down towards the base of the needle, 
the spring retains the protective sheath and prevents its extension 
completely beyond the needle tip. 
FIG. 7 shows an alternative to the hook and catch depicted in FIGS. 4 and 
5. The receiving slot is raised above the needle base 21 as opposed to the 
recessed design depicted in FIGS. 4 and 5. Prior to engagement of the 
hypodermic needle 19 with the ampule holder 13, the hook 29a is held in 
place by the outer cap in contact with the angled portion 30 of the hook. 
Once engaged with the ampule holder 13, the release collar contacts the 
outer most portion of the hook at 29a. 
FIG. 3 shows an exploded view of the parts shown in cross-section in FIG. 4 
and FIG. 5, while FIG. 6 shows the parts assembled in the retracted 
position. It is clearly visible how the ball 37 is denied access to the 
chamber of reduced diameter 41 due to the presence of the needle 19. Not 
shown is how the outer sheath 32 would prevent the hook 29 from 
disengaging slot 31 and forcing the protective sheath 25 to the tip of the 
needle and beyond. 
Obviously many modifications and variations of the present invention are 
possible in light of the above teachings. It is therefore to be understood 
that within the scope of the appended claims the invention may be 
practiced otherwise than as specifically described.