Safety syringe abstract
A safety syringe is disclosed. The safety syringe has a hollow
barrel and a plunger. The plunger enters the barrel from one end
and a retractable needle leaves the barrel from the other end. A
blunt sheath is positioned over the needle. The needle has an exposed
position in which the point of the needle extends beyond the sheath
and a covered position in which the point of the needle is contained
within the sheath. The plunger and the needle are configured to
cause the needle to move from the exposed position to the covered
position upon the depression of the plunger. In operation, the safety
syringe may be filled like a conventional syringe by placing the
needle in a vial of medication and retracting the plunger. Once
the safety syringe is filled, the needle is inserted into the patient.
In one embodiment, the sheath may be inserted into the patient with
the needle. The medication is then injected into the patient by
depressing the plunger. Depressing the plunger will, as stated,
cause the needle to retract into the covered position.
Safety syringe claims
I claim:
1. A safety syringe comprising:
a substantially hollow barrel having a needle end, a plunger end,
and a wall extending between said plunger end and said needle end,
said wall having an interior surface, wherein said needle end, said
plunger end and said interior surface of said wall define a fluid
receiving cavity within said barrel;
a plunger extending from said fluid receiving cavity of said barrel,
said plunger having a thumb end and a washer end, said washer end
configured to create a substantially fluid tight seal between said
washer end and said interior wall of said barrel, whereby operation
of said plunger will vary the volume of said fluid receiving cavity;
a sheath extending from said needle end of said barrel, said sheath
having a tip end, said tip end having an external diameter;
a retractable needle extending from said needle end of said barrel
into said sheath, said needle having a sharp end, a barrel end,
and an external diameter; said needle having an exposed position
wherein said sharp end of said needle extends beyond said tip end
of said sheath, said needle further having a covered position wherein
said sharp end of said needle is contained within said sheath; and
a lever having a control end, a retraction end operatively attached
to said barrel end of said needle, and a fulcrum point between said
control end and said retraction end of said lever, wherein said
control end of said lever is configured to operatively engage said
plunger when said plunger is depressed, whereby said needle may
be transferred from said exposed position to said covered position
by the depression of said plunger.
2. A safety syringe according to claim 1 wherein said washer end
of said plunger is configured to engage said control end of said
lever upon the depression of said plunger whereby said lever can
be pivoted about its fulcrum point to drive said retraction end
of said lever and said needle toward said plunger end of said barrel.
3. A safety syringe according to claim 2 wherein said washer end
contains a recession sized to receive said barrel end of said needle
and said retraction end of lever.
4. A safety syringe according to claim 1 wherein said tip end of
said sheath is sized to be hypodermically insertable with said needle.
5. A safety syringe according to claim 4 wherein said washer end
of said plunger is configured to engage said control end of lever
upon the depression of said plunger whereby said lever can be pivoted
about its fulcrum point to drive said retraction end of said lever
and said needle toward said plunger end of said barrel.
6. A safety syringe according to claim 5 wherein said washer end
contains a recession sized to receive said barrel end of said needle
and said retraction end of lever.
7. A safety syringe according to claim 4 wherein said tip end of
said sheath has an external diameter of not more than about 150%
of said external diameter of said needle.
8. A safety syringe according to claim 4 wherein said tip end of
said sheath has an external diameter of not more than about 133%
of said external diameter of said needle.
9. A safety syringe according to claim 4 wherein said tip end of
said sheath has an external diameter that is between about 118%
and about 125% of said external diameter of said needle.
10. A safety syringe according to claim 4 wherein said tip end
of said sheath has an external diameter of about 110% of said external
diameter of said needle.
11. A safety syringe according to claim 4 wherein said tip end
has a shortest cross-sectional dimension, wherein said needle is
capable of creating a puncture wound having a longest cross-sectional
dimension during hypodermic injection, and wherein the shortest
cross-sectional dimension of said tip end is less than the longest
cross-sectional dimension of a puncture wound createable by said
needle during hypodermic injection.
12. A safety syringe according to claim 4 wherein said tip end
has a longest cross-sectional dimension, wherein said needle is
capable of creating a puncture wound having a longest cross-sectional
dimension during hypodermic injection, and wherein the longest cross-sectional
dimension of said tip end is less than the longest cross-sectional
dimension of a puncture wound createable by said needle during hypodermic
injection.
13. A safety syringe comprising:
a substantially hollow barrel having a needle end, a plunger end,
and a wall extending between said plunger end and said needle end,
said wall having an interior surface, wherein said needle end, said
plunger end and said interior surface of said wall define a fluid
receiving cavity within said barrel;
a plunger extending from said fluid receiving cavity of said barrel,
said plunger having a thumb end and a washer end, said washer end
configured to create a substantially fluid tight seal between said
washer end and said interior wall of said barrel, whereby operation
of said plunger will vary the volume of said fluid receiving cavity;
a sheath extending from said needle end of said barrel, said sheath
having a tip end, said tip end having an external diameter;
a retractable needle extending from said needle end of said barrel
into said sheath, said needle having a sharp end, a barrel end,
and an external diameter; said needle having an exposed position
wherein said sharp end of said needle extends beyond said tip end
of said sheath, said needle further having a covered position wherein
said sharp end of said needle is contained within said sheath; and
a means for transferring said needle from said exposed position
to said covered position upon the depression of said plunger comprising
a lever having a control end and a retraction end attached to said
barrel end of said needle, said means further comprising a fulcrum
point between said control end and said retraction end.
14. A safety syringe according to claim 13 wherein said washer
end of said plunger is configured to engage said control end of
said lever upon the depression of said plunger whereby said lever
can be pivoted about its fulcrum point to drive said retraction
end of said lever and said needle toward said plunger end of said
barrel.
15. A safety syringe according to claim 14 wherein said washer
end contains a recession sized to receive said barrel end of said
needle and said retraction end of lever.
16. A safety syringe according to claim 13 wherein said tip end
of said sheath is sized to be hypodermically insertable with said
needle.
17. A safety syringe according to claim 16 wherein said washer
end of said plunger is configured to engage said control end of
said lever upon the depression of said plunger whereby said lever
can be pivoted about its fulcrum point to drive said retraction
end of said lever and said needle toward said plunger end of said
barrel.
18. A safety syringe according to claim 17 wherein said washer
end contains a recession sized to receive said barrel end of said
needle and said retraction end of lever.
19. A safety syringe according to claim 16 wherein said tip end
of said sheath has an external diameter of not more than about 150%
of said external diameter of said needle.
20. A safety syringe according to claim 16 wherein said tip end
of said sheath has an external diameter of not more than about 133%
of said external diameter of said needle.
21. A safety syringe according to claim 16 wherein said tip end
of said sheath has an external diameter that is between about 118%
and about 125% of said external diameter of said needle.
22. A safety syringe according to claim 16 wherein said tip end
of said sheath has an external diameter of about 110% of said external
diameter of said needle.
23. A safety syringe according to claim 16 wherein said tip end
has a shortest cross-sectional dimension, wherein said needle is
capable of creating a puncture wound having a longest cross-sectional
dimension during hypodermic injection, and wherein the shortest
cross-sectional dimension of said tip end is less than the longest
cross-sectional dimension of a puncture wound createable by said
needle during hypodermic injection.
24. A safety syringe according to claim 16 wherein said tip end
has a longest cross-sectional dimension, wherein said needle is
capable of creating a puncture wound having a longest cross-sectional
dimension during hypodermic injection, and wherein the longest cross-sectional
dimension of said tip end is less than the longest cross-sectional
dimension of a puncture wound createable by said needle during hypodermic
injection.
Safety syringe description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates generally to hypodermic syringes and particularly
to safety syringes designed to avoid accidental sticks.
2. Prior Art
The risk of contracting diseases such as HIV or hepatitis from
accidental sticks with dirty needles is a potentially deadly hazard
for medical professionals. Many syringe designs have been created
that attempt to avoid or minimize this risk. Although most designs
provide safety advantages over the conventional syringe, many come
with substantial drawbacks. One of the most serious is the length
of time between the completion of the injection and the covering
of the needle. During this period, a window of opportunity exists
for an accidental stick. Frequently, the minimization of this window
comes at the price of creating a complicated syringe that is operated
quite differently from a conventional syringe. The complicated designs
often result in a syringe that is expensive to manufacture. The
presence of these short comings in the prior art gives rise to the
need for a safety syringe meeting the following objectives.
OBJECTS OF THE INVENTION
It is an object of the invention to provide a safety syringe that
minimizes the window of opportunity for an accidental stick.
It is an object of the invention to provide a safety syringe that
automatically covers the needle upon the administration of the injection.
It is a another object of the invention to provide a safety syringe
that can cover the needle prior to its removal from the patient.
It is another object of the invention to provide a safety syringe
that will cover the needle upon depression of the plunger.
It is another object of the invention to cover the needle by retracting
it within a sheath upon depression of the plunger.
It is another object of the invention to provide a safety syringe
that can be operated with one hand.
It is another object of the invention to provide a safety syringe
that can be used like a conventional syringe.
It is yet another object of the invention to provide a safety syringe
that can be used to draw up medications and to purge air from the
syringe.
It is still another object of the invention to provide a safety
syringe that is relatively easy and inexpensive to manufacture and
that is simple in operation.
These and other objects and advantages of the invention shall become
obvious from the figures and from the following descriptions of
the preferred embodiments of the invention.
SUMMARY OF THE INVENTION
A safety syringe is disclosed. The safety syringe is comprised
of an elongated hollow barrel having a needle end and a plunger
end. (The term "end" is used repeatedly herein. It is
intended to refer to a general region or portion of the object described
rather than the absolute terminus of the object unless otherwise
indicated). A plunger is insertable into the plunger end of the
barrel. The end of the plunger is fitted to the inside of the barrel
so that it creates a fluid tight seal between it and the interior
wall of the barrel. A needle extends from the needle end of the
barrel. The barrel end of the needle is contained within the barrel
while the sharp end is external to the barrel so that the needle
provides fluid passage from the interior of the barrel to its exterior.
Thus, the contents of the syringe may be evacuated through the needle
by depressing the plunger. By inserting the needle into the desired
object and depressing the plunger, the contents of the needle may
be injected into that object.
The needle is slidably disposed within the needle end of the barrel.
The needle has two positions, an extended position and a retracted
position. Initially the needle is positioned. in its extended position
relative to the barrel. The needle is configured to retract relative
to the barrel upon depression of the plunger. Preferably, this is
accomplished by operation of a retraction lever extending from the
barrel end of the needle.
The lever is preferably provided with a fulcrum point such that
motion at one end of the lever will cause motion in the opposite
direction at the opposite end of the lever. On either side of the
fulcrum point are a retraction end and a control end of the lever.
In a preferred embodiment, the retraction end is connected to the
needle at a point spaced at least slightly above the needle end
of the barrel. The fulcrum point is preferably braced against the
needle end of the barrel by a fulcrum while the control end extends
from the fulcrum point to within the barrel. The plunger will encounter
the control end of the lever as the plunger is depressed. Continued
depression of the plunger will depress the control end of the lever.
This will cause the lever to pivot on the fulcrum point which in
turn will elevate the retraction end of the lever and drive the
needle toward the plunger end of the barrel.
A hollow sheath having a tip end and a barrel end extends from
the needle end of the barrel and is disposed over the needle. The
sheath is configured so that the sharp end of the needle extends
from the sheath when the needle is in its exposed position. The
sheath is further configured so that the sharp end of the needle
is contained within the sheath when the needle is in its covered
position. Thus, by depressing the plunger the needle may be retracted
to a position where the needle is covered by the sheath.
In a preferred embodiment, the sheath is relatively thin. It should
be thin enough that it may be inserted with the needle into the
patient when an injection is given, in much the same way as a catheter
is inserted. In a preferred embodiment, the sheath should have an
external diameter at the tip end of between about 110% and 150%
of the external diameter of the needle. When this embodiment is
used, the needle can be covered prior to its removal from the patient.
Thus, after the injection, there is never a contaminated sharp needle
exposed, and the possibility for accidental sticks is greatly reduced.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1A is cross sectional view of a preferred embodiment of the
invention just prior to the engagement of the control end of the
lever by the washer end of the plunger.
FIG. 1B is a cross sectional view of a preferred embodiment of
the invention during the movement of the needle from its exposed
position to its covered position.
FIG. 1C is a cross sectional view of a preferred embodiment of
the invention after the plunger has been fully depressed.
FIG. 2A is a cross sectional view of a preferred embodiment of
the invention prior to the administration of an injection to a patient.
FIG. 2B is a cross sectional view of a preferred embodiment of
the invention during the administration of an injection to a patient.
FIG. 2C is a cross sectional view of a preferred embodiment of
the invention at the conclusion of the administration of an injection
to a patient.
FIG. 2D is a cross sectional view of a preferred embodiment of
the invention upon withdrawal of the syringe from a patient after
the administration of an injection.
FIG. 3A is a side view of a preferred embodiment of a lever.
FIG. 3B is a top view of a preferred embodiment of a lever.
FIG. 4A is a perspective view of a conical version of a lever.
FIG. 4B is a perspective view of another conical version of a lever.
FIG. 5 is a bottom view of one preferred embodiment of the invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT OF THE INVENTION
A safety syringe 1 is disclosed. Safety syringe 1 comprises a substantially
hollow barrel 2 having a needle end 3 a plunger end 4 a wall 5
and an interior surface 6 of wall 5. Needle end 3 plunger end 4
and interior surface 6 define a fluid receiving cavity within barrel
2. In a preferred embodiment, calibrated measurement lines are marked
on wall 5. In a preferred embodiment, barrel 2 is made of transparent
or translucent plastic.
A plunger 8 fits within barrel 2. Plunger 8 has a thumb end 9 and
a washer end 10. Washer end 10 is sized to engage interior surface
6 of barrel 2 so that a substantially fluid tight seal is created
between washer end 10 and interior surface 6. In a preferred embodiment,
washer end 10 is made of or covered with rubber while plunger 8
is made of a harder plastic. In another preferred embodiment plunger
8 and washer end 10 are a single composite unit. Upon insertion
of plunger 8 into barrel 2 the volume of the fluid receiving cavity
may be varied by operation of plunger 8.
A hollow needle 11 having a sharp end 12 and a barrel end 13 is
slidably disposed in needle end 3 of barrel 2 through a needle aperture
14. Barrel end 13 of needle 11 is positioned within barrel 2 and
pointed end 12 is positioned external of barrel 2. Thus, needle
11 provides fluid passage into and out of barrel 13.
The connection between needle 11 and needle end 3 of barrel 2 should
satisfy several criteria. First, it should be fluid tight under
normal injection pressures. Second, it should hold needle 11 in
place relative to needle end 3 of barrel 2 while needle 11 is puncturing
skin and tissue during the administration of an injection. Third,
it should allow needle 11 to be retracted upon the application of
force normally associated with the depression of plunger 8 during
the administration of an injection using the mechanical configurations
described more thoroughly below. The satisfaction of these criteria
is a function of the friction coefficient between needle 11 and
the needle aperture 14. Assuming that a conventional needle is used,
the friction coefficient will depend upon the diameter and length
of needle aperture 14 and the material used to make needle end 3
of barrel 2. The inventor contemplates making needle end 3 of barrel
2 out of a rubber or plastic capable of forming the fluid tight
seal with needle 11 required of needle end 3. In one preferred embodiment,
the entire barrel 2 may be made out of the same material as needle
end 3.
Safety syringe 1 is provided with a means for retracting needle
11 upon the depression of plunger 8. This preferably entails at
least one and preferably two or more levers 15. Lever 15 has a control
end 16 and a retraction end 17. Retraction end 17 is attached to
barrel end 13 of needle 11 preferably with an adhesive or other
conventional means. Lever 15 should preferably be attached to needle
11 prior to the insertion of needle 11 into needle end 3 of barrel
2. The connection between retraction end 17 and needle 11 is preferably
hinged or otherwise rendered pivotal. Lever 15 should preferably
be made from plastic.
Between retraction end 17 and control end 16 of lever 15 is a fulcrum
point 18 resting, over a fulcrum 19. Lever 15 should preferably
be initially positioned so that control end 16 is further from needle
end 3 of barrel 2 than retraction end 17 and fulcrum point 18. Lever
15 should also preferably be initially positioned so that retraction
end 17 is positioned closer to needle end 3 of barrel 2 than fulcrum
point 18. Fulcrum 19 should preferably rest against or extend from
needle end 3 of barrel 2. When positioned as described, a downward
force delivered to control end 16 of lever 15 would cause it to
pivot on fulcrum 19 at fulcrum point 18 such that retraction end
17 of lever 15 would be driven rearward. When retraction end 17
of lever 15 is attached to barrel end 13 of needle 11 the rearward
movement of retraction end 17 will cause needle 11 to slide in needle
end 3 of barrel 2 toward plunger end 4 of barrel 2.
Force can be exerted upon control end 16 of lever 15 by washer
end 10 of plunger 8 As plunger 8 is depressed, plunger 8 will engage
control end 16 of lever 15. Continued depression of plunger 8 will
cause control end 16 of lever 15 to move toward needle end 3 of
barrel 2 which in turn will cause lever 15 to pivot on fulcrum 19
at fulcrum point 18. Retraction end 17 of lever 15 will move toward
plunger end 4 of barrel 2 taking needle 11 with it as described
above. Washer end 10 of plunger 8 preferably contains a central
recession to receive barrel end 13 of needle 11 and retraction end
17 of lever 15. In this configuration, the perimeter of washer end
10 can engage control end 16 of lever 15 without washer end 10 impeding
the retraction of needle 11.
Another means for retracting needle 11 upon the depression of plunger
8 comprises a conical version 15A of lever 15. Conical lever 15A
has a control end 16A and a retraction end 17A. In operation, retraction
end 17A will attach to needle 11 at or near needle end 3 of barrel
2. Conical lever 15A should have a fulcrum point 18A located near
retraction end 17A that is preferably braced against needle end
3 of barrel 2 by a fulcrum 19A. Control end 16A of conical lever
15A will extend upward toward plunger 8 so that washer end 10 of
plunger 8 will first encounter control end 16A of conical lever
15A during the depression of plunger. Conical lever 15A should be
made of a flexible resilient material that will deform upon the
application of pressure to control end 16A by plunger 8. Control
end 16A will bend toward needle end 3 of barrel 2 as plunger 8 is
depressed. At some point during the depression of plunger 8 the
deformation of resilient conical lever 15A will cause retraction
end 17A to snap upward to restore the conical shape of conical lever
15A. This motion will. invert the position of conical lever 15A
relative to needle end 3 of barrel 2 such that control end 16A will
be adjacent needle end 3 of barrel 2 while retraction end 17A will
be separated from needle end 3 of barrel 2 by the height of conical
lever 15A. Of course, moving retraction end 3 away from needle end
3 of barrel 2 will also cause needle 11 to move the same distance
in the same direction.
A protective sheath 20 extends from needle end 3 of barrel 2. Needle
11 is disposed within sheath 20. Sheath 20 has a tip end 21 opposite
barrel 2. Prior to the retraction of needle 11 at least a portion
of sharp end 12 of needle 11 extends from tip end 21. This is the
exposed position 22 of needle 11. Upon retraction of needle 11
sharp end 12 of needle 11 will be withdrawn into sheath 20. This
is the covered position 23 of needle 11. Thus, needle 11 can be
moved from exposed position 22 to covered position 23 simply by
depressing plunger 8 as would ordinarily be done during the administration
of an injection.
Needle 11 may be locked in covered position 23 by providing a detent
arm 26 between plunger 8 and barrel 2 so that plunger 8 will be
locked into place when it has been fully depressed. Alternatively
or additionally, a detent mechanism might be positioned between
needle 11 and needle end 3 of barrel 2 so that needle 11 might not
re-extend into exposed position 22 after it has been retracted.
Another means for preventing needle 11 from re-entering exposed
position 22 would include making thumb end 9 of plunger 8 substantially
headless or otherwise sizing thumb end 9 to allow plunger 8 to be
inserted into the fluid receiving cavity inside barrel 2. This will
help prevent the accidental retraction of plunger 8. All of the
aforementioned means may help prevent accidental or intentional
reuse of safety syringe 1.
In a preferred embodiment, sheath 20 is sized to be hypodermically
insertable with needle 11. Needle 11 will have an external diameter
24. Likewise, sheath 20 will have an external diameter 25. While
preferred embodiments of both needle 11 and sheath 20 are generally
cylindrical, it is recognized that both may have other shapes such
that their cross section is not a circle. When needle 11 and sheath
21 are not circular, needle 11 will have a shortest cross-sectional
dimension 201 and a longest cross sectional dimension 203. Similarly,
sheath 21 will have a shortest cross-sectional dimension 202 and
a longest cross-sectional dimension 204. In such cases, diameter
is intended herein to refer to the longest cross sectional dimension
of the respective article unless otherwise indicated. External diameter
25 of sheath 20 at tip end 21 should be close enough to external
diameter 24 of needle 11 to allow tip end 21 of sheath 20 to be
inserted with needle 11 when safety syringe 1 is used to administer
an injection. As needle 11 is inserted into tissue, it will create
a puncture wound or tear in that tissue that is somewhat larger
in diameter than external diameter 24 of needle 11. Sheath 20 and
particularly tip end 21 should be sized to permit at least tip end
21 of sheath 20 to be inserted simultaneously with needle 11 into
the puncture wound created by needle 11 during hypodermic injection.
In designing sheath 20 there are two competing goals, strength
or puncture resistance and patient comfort. The thinner sheath 20
is, the more comfortable it will be for the patient when sheath
20 is inserted with needle 11 during injection, assuming the hypodermically
insertable version of sheath 20 is in use. However, as sheath 20
is made thinner, it becomes less resistant to punctures and thus
less able to perform its task of preventing accidental sticks. Therefore,
a balance must be struck between these two competing goals when
sheath 20 is designed. Of course, where this balance will fall will
depend upon the characteristics of the materials used to make sheath
20. Currently, the inventors contemplate using plastic, Teflon.RTM.,
or a metal such as braided stainless steel. However, other acceptable
rigid or semi-rigid substances may be available now or developed
in the future which may affect the thickness of sheath 20. Furthermore,
it is anticipated that a non-rigid substance such as soft rubber
which relies on needle 11 for its rigidity during insertion would
perform adequately as a substance from which sheath 20 might be
constructed. Sheath 20 may also be made from the same material as
barrel 2 such that sheath 20 and barrel 2 could be constructed in
a single composite piece.
When sheath 20 is to be hypodermically insertable, the thickness
of sheath 20 will also vary with the size of needle 11. Needles
come in twenty five standard gauges, where gauge is a measure of
external diameter 24. Standard needles range from 30 gauge which
has an external diameter of 12/1000 of an inch to 6 gauge which
has an external diameter of 200/1000 of an inch. The incremental
change in diameter between gauges is not uniform. For example, 29
gauge has a diameter of 13/1000 of an inch, only 1/1000 more than
30 gauge. At the other end of the spectrum, 7 gauge has an outer
diameter of 180/1000 of an inch, 20/1000 less than 6 gauge.
Although safety syringe 1 may be used with any size needle 11
needles in the middle of the standard needle range--24 to 18 gauge--are
expected to be used most often. A 24 gauge needle has an external
diameter of 22/1000 while 18 gauge is 50/1000. When needle 11 falls
into this middle range, it is anticipated that sheath 20 or at
least tip end 21 should have an external diameter 25 of not more
than about 150% of external diameter 24 of needle 11. In this size
range, it is anticipated that the external diameter 25 of sheath
20 or at least tip end 21 should preferably be between about 118%
and about 125% of external diameter 24 of needle 11. With larger
needles 11 such as 6 or 7 gauge, it is expected that sheath 20
or tip end 21 should have an external diameter 25 of not more than
about 133% and preferably about 110% of external diameter 24 of
needle 11. It should be appreciated that the construction and composition
of sheath 20 may allow it to be made thinner than the ranges given
above in furtherance of the goal of patient comfort. Similarly,
different construction and composition may force sheath 20 to be
thicker in order to satisfy the goal of puncture resistance. Additional
information regarding the construction of sheath 20 may be found
in U.S. Pat. No. 5460611 PCT Application US95/11426 and allowed
U.S. patent applications Ser. No. 08/727756 now U.S. Pat. No.
5720727 and Ser. No. 08/746580 now U.S. Pat. No. 5846228
all of which are hereby incorporated by reference in their entirety
to the extent they are not contrary to the teachings herein.
In operation, safety syringe 1 will either come prefilled or it
will come empty. A cap may be provided to protect sharp end 12 while
needle 11 is in exposed position 22 prior to usage. The cap may
also be used to help prevent leakage when prefilled versions of
safety syringe 1 are used. If safety syringe 1 is empty, it will
be filled in the same manner as a normal syringe, that is by inserting
needle 11 into a vial of liquid medication and then withdrawing
plunger 8 until the requisite amount of liquid is obtained. Once
safety syringe 1 is full, any air trapped in the syringe should
be expelled. This is done by pointing needle 11 up and depressing
plunger 8 until a small amount of liquid is expelled from needle
11. At this point, safety syringe 1 is ready to be used.
The person administering the injection will sterilize the skin
in the region that is to receive the injection. Needle 11 will then
be inserted into the muscle or other tissue. Preferably, needle
11 will be inserted far enough so that tip end 21 of sheath 20 is
also inserted into the tissue when the hypodermically insertable
version of sheath 20 is used. To avoid unnecessarily deep injections,
the distance between exposed position 22 and covered position 23
should be minimized although it should be noted that when a deep
injection is needed, it may be desirable to configure sheath 20
so that substantially more than tip end 21 is insertable with needle
11. In a preferred embodiment, this distance between exposed position
22 and covered position 23 is about 1/8 of an inch. Once needle
11 is injected to the desired depth, plunger 8 will be depressed
until washer end 10 engages control end 16 of lever 15. Continuing
to depress plunger 8 will cause lever 15 to pivot on fulcrum 19
pushing retraction end 17 away from needle end 3 of barrel 2. Retraction
end 17 will pull needle 11 in the same direction, thereby causing
needle 11 to move from exposed position 22 to covered position 23.
If the hypodermically insertable version of sheath 20 is used, needle
11 may be moved into covered position 23 prior to its removal from
the patient. Additionally, if a detent mechanism, or other means
for preventing needle 11 from re-entering exposed position 22 is
used, needle 11 may be locked into place prior to its withdrawal
from the patient.
It is anticipated that these and other uses and embodiments will
be apparent to those skilled in the art in view of the foregoing
description and drawings and are intended to be covered by the scope
of the following claims. |