Medical syringe and method for performing an injection

Abstract

A medical injector and method for performing an injection, the medical injector having a forward projecting needle that is selectively retracted after use, and further having a specially configured plunger handle and thumb cap that cooperate to form a recessed pressure application surface (CPAS). The recessed pressure application surface at the rear of the plunger handle enables the medical injector of the present invention to achieve functional advantages, each having an associated therapeutic benefit, that are not achievable when using prior art devices.

Description

Technical Field

[0001] The present invention relates to a medical syringe, and more specifically, to a syringe having a plunger handle including a needle retraction chamber and a recessed pressure application surface that allows the user to inject more easily, comfortably and safely, and to begin retracting the needle into the needle retraction chamber after injection. Background Technology

[0002] Syringes, as previously known, include a syringe barrel, a tubular plunger handle with a flexible seal that slidably engages the inner wall of the syringe barrel, and a forward-extending needle disposed within the front portion of the syringe barrel. In some such syringes, the forward-extending needle and needle retainer are rearwardly biased by a compression spring and restrained by an elastomeric friction ring disposed between the needle retainer and a portion of the inner wall of the syringe barrel, resisting the biasing force. In some such syringes, the needle can be selectively retracted after use into a coaxially aligned needle retraction chamber disposed within the plunger handle. When an injection is administered to a patient by continuously pressing the thumb cap of the plunger handle while maintaining relative pressure on the finger-shaped flange of the syringe barrel, the plunger tip contacts and pushes the friction ring forward away from the head of the needle retainer, while the head of the needle retainer contacts and pushes the plunger rearward within the front opening of the plunger handle. As the friction ring disengages from the needle retainer and the plunger is removed, the rearwardly biased needle and needle retainer are driven rearward into a protected position within the coaxially aligned needle retraction chamber. Ideally, when the compression spring expands after the friction ring releases the needle retainer, the forward-facing needle tip retracts from the patient and enters a protected position within the syringe without the risk of accidental needlestick injury, which could otherwise occur with syringes of different constructions. After needle retraction, the needle tip retracts at least within the front portion of the syringe barrel 12 to prevent accidental needlestick injury, which could otherwise occur with different syringe products. Syringes of this type are disclosed, for example, in U.S. Patents 5,632,733, 5,810,775, 5,997,512, 6,015,438, 6,090,077, 6,572,584, and 7,351,224.

[0003] For prior art medical syringes such as those disclosed in the aforementioned patents, the proximal end of the plunger handle typically includes a flat or protruding "thumb cap" that flares radially outward around a rearward-facing opening in the tubular portion of the handle and has an outer circumference whose outer diameter is designed to abut the proximal end of the syringe barrel sidewall, or to be positioned or "fitted" into an annular recess located in the proximal end of the syringe barrel, to reduce the likelihood that the plunger handle will retract axially from the syringe barrel after needle retraction. The thumb cap portion of the plunger handle typically also includes an inward-facing orifice with a gradually decreasing inner diameter to accommodate an end plug (sometimes colored) inserted into the thumb cap of the plunger handle during syringe assembly to prevent rearward entry into the interior of the needle retraction chamber. The end plug typically engages frictionally with the orifice of the thumb cap and also has a proximal convex surface, such as in U.S. Patent 6,572,584. Figures 1 to 3 As shown. Summary of the Invention

[0004] Unlike syringes disclosed in the prior art, the device disclosed herein is a medical syringe having a forward-extending needle that selectively retracts after use, and a plunger handle with a specially constructed thumbcap and end cap that cooperate to form a recessed pressure application surface (CPAS). The recessed pressure application surface at the rear of the plunger handle enables the medical syringe of the present invention to achieve three functional advantages, each providing a related therapeutic benefit, which are not achievable with prior art devices.

[0005] When using a syringe with a plunger handle having the recessed pressure application surface of the present invention for injection, a first functional advantage is that a larger portion of the forward pressure (thumb force) manually applied by the user's thumb to the thumb cap and end plug of the plunger handle is concentrated and directed inward toward the longitudinal axis of the plunger handle. This improves the utilization of the thumb force applied through the plunger handle, plunger seal, and distally located plunger to propel fluid through the syringe barrel, needle, and into the patient receiving the injection. The associated therapeutic benefits can be particularly noticeable or significant when the user injects relatively large doses of fluids with higher viscosity compared to other injectable fluids or drugs. The provision and use of the proximal recessed pressure application surface formed by the engagement of the plunger handle thumb cap and proximal end plug is also considered to significantly facilitate the smooth and continuous advancement of the plunger handle through the syringe barrel during injection.

[0006] Furthermore, a second functional advantage achieved by using a syringe with a plunger handle having the recessed pressure application surface of the present invention is that, during injection, the majority of the thumb force applied by the user will not be diminished, misdirected, or improperly applied, as would occur if the user's thumb slipped away from or did not fully engage the side of the available surface area, which would happen if the pressure application surface were flat or convex rather than recessed. A related therapeutic benefit is also achieved, as any lateral movement or abrupt change caused by the user's thumb slipping when applying pressure to the proximal end of the plunger handle can cause greater movement of the needle tip within the patient's body, thereby increasing discomfort experienced by the patient during injection.

[0007] A third functional advantage achieved by using a syringe with a plunger handle featuring a recessed pressure application surface is that the CPAS (Constant Pulse Assay) more comfortably adapts to the user's thumb. Conversely, when the user applies opposing resistance to the finger-like flange of the plunger barrel during injection while simultaneously applying thumb force to the convex proximal end of the plunger handle, the user is more likely to experience discomfort due to being "poked" by the proximal end of the plunger handle, and in response to this discomfort, the amount of thumb force applied to the proximal end of the plunger handle can be reduced. This reduction in applied thumb force can prolong injection time and extend the duration of discomfort for both the user and the patient.

[0008] Although the accompanying drawings are not to scale, those skilled in the art will recognize them after reading the references. Figures 3 to 6 As will be understood from the detailed disclosure, the depth of the CPAS measured along the longitudinal axis of the syringe and the diameter of the CPAS measured through the rearwardly extending edge of the thumbcap of the plunger handle can vary depending on the nominal size of the syringe (expressed in volume mL, e.g., 3 mL) and the diameter of the plunger handle. The applicant currently believes that the benefits of the invention are satisfactorily achieved when the ratio of the maximum depth of the recessed portion of the fitted and assembled plunger handle (where the end plug is mounted inside the thumbcap) to the diameter of the inner bore of the thumbcap at the widest portion of the CPAS is in the range of approximately 0.06 to approximately 0.085, with a preferred ratio of approximately 0.078. Attached Figure Description

[0009] The system and method of the present invention are further described and explained with reference to the following figures, wherein:

[0010] Figure 1 This is a rear view illustrating a prior art medical syringe that has some of the same structural elements as the present invention, but has a plunger handle with a conventional thumbscap that does not reflect the structural improvements of the present invention.

[0011] Figure 2 yes Figure 1 Existing technology syringe along Figure 1 The side view of the section cut by line 2-2;

[0012] Figure 3 This is a rear view of a preferred embodiment of the medical syringe of the present invention;

[0013] Figure 4 yes Figure 3 Medical syringe along Figure 3 A longitudinal sectional view taken from line 4-4;

[0014] Figure 5 It is taken from Figure 4 A partially sectional, enlarged, detailed view; and

[0015] Figure 6 It is taken from Figure 5 A magnified detailed view of a partially cut section.

[0016] In the attached diagram Figures 3 to 6 This is an illustration of the structural elements of the present invention, but is not drawn to scale. Detailed Implementation

[0017] Figure 1 and Figure 2 A prior art medical syringe 10 is depicted, which has some of the same elements as the medical syringe 40 of the present invention, as shown below in conjunction with the accompanying drawings. Figures 3 to 6 Further description. Reference Figure 1 , Figure 2 The medical syringe 10 includes a cylindrical syringe 12 having multiple portions of different inner diameters. A needle cap 22 includes a proximal end with a collar portion 23 that frictionally engages an outwardly facing surface portion of the syringe syringe 12. A retractable needle assembly 24 includes a needle retainer 11 and a distally extending needle 20, the assembly being disposed within the front portion of the cylindrical syringe 12. The needle retainer 11 and the needle 20 are rearwardly biased by a coil spring 13, which is held compressed before and during injection by a friction ring 15 or other similar effective retainer disposed between the needle retainer 11 and an inner wall portion of the syringe syringe 12. An elongated tubular plunger handle 14 includes a centrally located needle retraction cavity 18, the handle being inserted into the cylindrical syringe 12 through a rearwardly facing opening located behind radially opposing, radially extending finger-like flanges 26, 28 of the syringe syringe 12.

[0018] The distal portion of the plunger handle 14 also includes an annular elastomeric plunger seal 16 that slidably engages the inner wall of the cylindrical syringe 12 and mates with a plunger plug 25 at the distal end of the plunger handle 18 to define a variable volume fluid chamber 21 between the retractable needle assembly 24 within the syringe 12 and the plunger handle 14.

[0019] During the use of a medical syringe 10 of the prior art, after the needle cap 22 is removed, injectable medication is typically aspirated into a variable-volume fluid chamber 21 located between the retractable needle assembly 24 and the plunger handle 14 within the syringe barrel 12. After the needle 20 is inserted into the patient, injection is performed by advancing the plunger handle 14 within the syringe barrel 12 until the plunger plug 25 contacts the needle holder 11 of the retractable needle assembly 24 and the injection is complete. During injection, the plunger handle 14 typically advances distally within the syringe barrel 12 by applying forward thumb pressure to the protruding end face 32 of the thumb cap 30 of the plunger handle 14, while simultaneously applying relative finger pressure backward to the distally facing surfaces of the opposing, outwardly extending finger flanges 26, 28 of the syringe barrel 12. Upon completion of the injection, continuous thumb pressure applied by the user to the protruding end face 32 of the thumb cap 30 of the plunger handle 14 causes the plunger plug 25 to contact the proximal end of the needle holder 11, thereby disengaging the plunger plug 25 from the distally facing opening of the plunger handle 14. Simultaneously, the distal end of the plunger handle 14 pushes the friction ring 15 forward away from the outer surface of the needle holder 11 into the annular space 17, allowing the compression spring 13 to expand and drive the needle holder 11 and the plunger plug 25 rearward into the needle retraction chamber 18. As the needle holder 11 is driven rearward by the force of the expanding compression spring, the needle 20 is simultaneously retracted from the patient's injection site and carried rearward by the needle holder 11. After needle retraction, the needle tip is retracted at least within the front portion of the syringe 12 to prevent accidental needlestick injuries that could otherwise occur with different syringe products.

[0020] The applicant has now discovered that by modifying the plunger handle, the aforementioned type of medical syringe can be further improved and enhanced to provide the user with greater comfort and control over injection and needle retraction, as well as smoother drug delivery during injection and smoother needle retraction after injection. Medical syringes with the improved plunger handle according to the invention are also particularly effective for using high-viscosity drugs.

[0021] Now for reference Figures 3 to 6 The medical syringe 40 of the present invention includes a syringe barrel 42 having an elongated tubular plunger handle 44 slidably engaged with the inner wall of the syringe barrel 42, an elastomeric plunger seal 46, and a retractable needle assembly 54 disposed within the front portion of the syringe barrel 42. A needle 50 is attached to and extends forward from a needle holder 41 and is covered before use by a removable needle cap 52 having a collar 53 at the proximal end of the needle, which frictionally engages with an outwardly facing wall portion near the front portion of the syringe barrel 42. The needle holder 41 and the needle 50 are rearwardly biased by a coil spring 43, which is held compressed during injection by a friction ring 45 disposed between the inner wall portions of the needle holder 41 and the syringe barrel 42.

[0022] An elongated tubular plunger handle 44 is intended to be inserted into a cylindrical syringe 42 through a rearward-facing opening having an annular recess 88, the inner diameter and depth of which are sufficient to accommodate the outermost portion 86 of the thumbcap 60 in a nested engagement within the recess 88 when the plunger handle 44 is fully advanced into the syringe 42 and the needle 50 is retracted after injection. This nested engagement is intended to prevent possible reuse of the syringe for safety reasons and to prevent the plunger handle 44 from being removed from the syringe 42 after needle retraction, thereby reducing the possibility of accidental needlesticking or accidental pathogen contamination due to contact with blood or other bodily fluids. The distal portion of the plunger handle 44 also includes an annular elastomeric plunger seal 46, which slidably engages the inner wall of the cylindrical syringe 42 and mates with a plunger plug 55 at the distal end of the plunger handle 44 to define a variable-volume fluid chamber 49 between the retractable needle assembly 54 and the plunger handle 44 within the syringe 42. Apart from the elongated tubular plunger handle 44, each of the aforementioned parts of the medical syringe 40 is configured and operated in substantially the same manner as similar parts of the prior art medical syringe 10 described above.

[0023] Now for reference Figures 3 to 6 The portion of the plunger handle 44 shown, located behind the flange members 56, 58 of the syringe 42, is aligned by a combination of a mating thumbcap 60 and a friction-engaged end plug 62, forming a rearward-facing recessed pressure application surface (CPAS) at the rearward-facing end of the plunger handle 44. The syringe 42, plunger handle 44, thumbcap 60, and end plug 62 of the syringe 40 are all preferably made of a moldable thermoplastic material.

[0024] For more specific reference Figure 6 The rearward-facing end face of the end plug 62 is concave, with a center point 70 marking the most forward-extending point of the concave end face, and a circumferentially extending outer edge 72 marking the most rearward-extending portion of the concave end face of the end plug 62. Importantly, the proximal surface of the concave end face of the end plug 62 is adjacent to and fits against the mating curved, inwardly concave surface 76 of the thumbcap 60, which extends rearward from the outer edge 72 of the end plug 62 to the circumferentially extending rear edge 74 of the thumbcap 60. Thus, the mating construction and aligned portion of the end plug 62 and the thumbcap 60 forms a CPAS with a depth “d” representing the longitudinal distance between the lowest point 70 of the end plug 62 and a diameter “OD” equal to the diameter of the circumferentially extending rear edge 74 of the thumbcap 60.

[0025] As described above, those skilled in the art, with reference to the accompanying drawings, Figures 3 to 6Upon reading this disclosure, it will be understood that the depth of the CPAS measured along the longitudinal axis of the syringe 40 and the OD of the CPAS measured across the circumferentially extending rear edge 74 of the thumb cap 60 can vary depending on the nominal size of the syringe (expressed in mL volume, e.g., 3 mL) and the diameter of the plunger handle. The applicant currently believes that the benefits of the invention are satisfactorily achieved when the ratio of the maximum depth “d” of the recessed portion of the fitted and assembled plunger handle 44 (where the end plug 62 is mounted inside the thumb cap 60) to the diameter “OD” of the inner bore of the thumb cap at the widest portion of the CPAS is in the range of approximately 0.06 to approximately 0.085, with a preferred ratio of approximately 0.078. This dimensional ratio is believed to provide a recessed pressure application surface that will satisfactorily and comfortably concentrate the thumb force applied by the user onto the rear of the plunger handle 44 during injection, without the obvious risk of lateral sliding of the thumb on the thumb cap 60 or discomfort to the user or patient, which might otherwise occur. Furthermore, using a syringe 40 with a recessed pressure application surface (CPAS) formed by a mating and aligned thumb cap 60 and end plug 62 will facilitate the injection of highly viscous drugs or other fluids while reducing discomfort to the user and patient.

[0026] The end plug 62 also desirably includes an inwardly tapering, forward-extending skirt 65 that inserts into at least a portion of the stepped inner wall defining the tubular orifice of the plunger handle 44, and is sized to frictionally engage with this portion. Outwardly projecting annular protrusions 78, 82 on the outer side of the skirt 65 of the end plug 62 loosely engage aligned recesses 80, 84 to allow air to escape from the tubular orifice surrounding the end plug 62 during needle retraction after injection. (See again) Figures 3 to 6 Channels 64 and 66 are provided in the thumb cap 60 of the syringe 40 to engage with aligned recesses 80 and 84, thereby facilitating this venting even when thumb pressure is still applied to the CPAS of the plunger handle 44.

[0027] After reading this disclosure in relation to the accompanying drawings, other modifications and alterations to the apparatus disclosed herein will be apparent to those skilled in the art, and it is intended that the scope of the invention disclosed herein be limited only by the broadest interpretation of the appended claims to which the inventors are legally entitled.

Claims

1. A medical syringe, comprising: Syringe; a rearwardly biased, selectively retractable needle assembly coupled to the syringe and including a forward-extending needle; The syringe includes a plunger that slidably engages the inner cylindrical wall of the syringe and includes a plunger handle, a thumbscap, and an end plug, wherein the thumbscap and the end plug cooperate to form a rearwardly recessed pressure application surface to which a user applies a forward-pointing thumb force, and wherein the end plug includes one or more outwardly extending annular protrusions that loosely engage one or more mating recesses on the inner wall of the thumbscap to allow air to escape from the interior of the syringe around the end plug when the plunger handle is fully advanced into the syringe and the needle assembly is retracted into the syringe.

2. The medical syringe according to claim 1, wherein, The end plug has a recessed proximal surface that is adjacent to and aligned with the inwardly curved, concave surface of the thumbcap.

3. The medical syringe according to claim 2, wherein, The matingly curved, inwardly facing concave surface of the thumbcap extends rearward from the outer edge of the end plug to the circumferentially extending rear edge of the thumbcap.

4. The medical syringe according to claim 1, wherein, The pressure-applying surface of the recess is coaxially aligned with the plunger handle and has a depth-to-diameter ratio in the range of 0.06 to 0.

085.

5. The medical syringe according to claim 4, wherein, The depth-to-diameter ratio is 0.

078.

6. The medical syringe according to claim 1, wherein, The plunger handle and the thumb cap are integrally molded from thermoplastic resin.

7. The medical syringe according to claim 1, wherein, The end plug is molded from thermoplastic resin and frictionally engages with the rearward-facing opening in the thumb cap.

8. The medical syringe according to claim 1, wherein, As the plunger handle advances fully into the syringe and the needle assembly retracts into the syringe, the plunger handle vents to release pressurized air between the thumb cap and the end cap.

9. The medical syringe according to claim 1, wherein, When the plunger handle is fully advanced into the syringe, the thumb cap can be nested within the rearward-facing opening of the syringe.

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