U.S. patent application number 13/428283 was filed with the patent office on 2012-07-19 for methods and apparatus for buffering anesthetics.
This patent application is currently assigned to Onpharma, Inc.. Invention is credited to Michael I Falkel, Matthew J. Stepovich.
Application Number | 20120180432 13/428283 |
Document ID | / |
Family ID | 41340475 |
Filed Date | 2012-07-19 |
United States Patent
Application |
20120180432 |
Kind Code |
A1 |
Stepovich; Matthew J. ; et
al. |
July 19, 2012 |
METHODS AND APPARATUS FOR BUFFERING ANESTHETICS
Abstract
A device for delivering buffer solution into a buffer cartridge
comprises a needle assembly and a pusher. The septa of a buffer
cartridge and an anesthetic cartridge are advanced onto a transfer
needle, and the pusher advances a plunger into the buffer cartridge
to deliver buffer through the transfer needle into the anesthetic
cartridge. A separate exhaust needle allows excess anesthetic from
the anesthetic cartridge to be exhausted. A compression member is
usually provided to maintain a force against the plunger on the
buffer cartridge to pressurize and stabilize the contents during
sterilization and/or storage.
Inventors: |
Stepovich; Matthew J.;
(Santa Cruz, CA) ; Falkel; Michael I; (Carmel
Highlands, CA) |
Assignee: |
Onpharma, Inc.
Los Gatos
CA
|
Family ID: |
41340475 |
Appl. No.: |
13/428283 |
Filed: |
March 23, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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12406670 |
Mar 18, 2009 |
8162917 |
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13428283 |
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61094669 |
Sep 5, 2008 |
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61054930 |
May 21, 2008 |
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Current U.S.
Class: |
53/428 ;
206/524.1 |
Current CPC
Class: |
A61J 1/201 20150501;
A61J 1/2072 20150501; A61J 1/2013 20150501; A61P 23/00 20180101;
A61J 1/2096 20130101 |
Class at
Publication: |
53/428 ;
206/524.1 |
International
Class: |
B67C 3/22 20060101
B67C003/22; B65D 85/84 20060101 B65D085/84 |
Claims
1. A method for storing a bicarbonate buffer solution, said method
comprising: providing a cartridge having an open interior, a needle
penetrable septum, and a plunger which can be advanced into said
open interior to pressurize contents thereof; filling said
cartridge with a solution of bicarbonate buffer that will evolve
carbon dioxide at room temperature and pressure; and storing the
cartridge while applying a pressure to the solution that is
sufficient to inhibit the evolution of carbon dioxide during
storage.
2. A method as in claim 1, wherein: the buffer comprises sodium
bicarbonate that has a pH in the range from 7.5 to 7.8; and the
applied pressure is above 1.2 atm.
3. A method as in claim 1, wherein the pressure is maintained by
compressing a spring against the plunger
4. A method as in claim 1, wherein the cartridge is placed in a
pressurized vessel that places force against the plunger and
maintains the pressure.
5. A method as in claim 1, wherein the plunger is comprised of a
compressible resilient material, the plunger is compressed against
the solution, and compression is maintained.
6. A method as in claim 1, wherein the pressure is sufficient to
prevent vaporization of volatile species during heat
sterilization.
7. A method as in claim 6, wherein an amount of water is added to
the solution prior to heat sterilization to compensate for water
that escapes past the cartridge plunger during the heat
sterilization process.
8. A bicarbonate buffer storage cartridge assembly, said assembly
comprising: a cartridge having an open interior filled with
bicarbonate buffer solution, a needle penetrable septum, and a
plunger which can be advanced into said open interior to pressurize
the bicarbonate buffer therein; and a compression member which
exerts a force on the plunger which is sufficient to pressurize the
bicarbonate buffer solution at a pressure which inhibits the
evolution of carbon dioxide.
9. A storage cartridge assembly as in claim 8, wherein the open
interior of the cartridge is completely filled with sodium
bicarbonate with substantially no headspace remaining.
10. A storage cartridge assembly as in claim 8, wherein the
compression member comprises a compressible spring which is
maintained in compression and engages the plunger.
11. A storage cartridge assembly as in claim 8, wherein the
compressible spring comprises a coil spring.
12. A storage cartridge as in claim 8, wherein the compression
member is formed as an integral portion of the plunger.
13. A storage cartridge assembly as in claim 8, further comprising
a housing, wherein the cartridge is within the housing and the
compression member is held in compression between the housing and
the solution.
14. A storage cartridge as in claim 8, wherein the solution is held
under sufficient pressure to inhibit vaporization under expected
storage conditions.
15. A storage cartridge as in claim 8, wherein the solution is held
under sufficient pressure to inhibit vaporization under conditions
of heat sterilization.
Description
CROSS-REFERENCES TO RELATED APPLICATIONS
[0001] This application is a divisional of U.S. patent application
Ser. No. 12/406,670 (Attorney Docket No. 36312-705.201), filed Mar.
18, 2009, which claims the benefit of prior provisional application
61/054,930 (Attorney Docket No. 36312-705.101), filed on May 21,
2008, and of provisional application 61/094,669 (Attorney Docket
No. 36312-705.102), filed on Sep. 5, 2008, the full disclosures of
which are incorporated herein by reference in their entirety.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates generally to methods and
apparatus for buffering anesthetics. More particularly, the present
invention relates to methods for preparing and storing sodium
bicarbonate buffering solutions and combining such solutions with
anesthetics stored in small cartridges.
[0004] Aqueous solutions containing bicarbonate ions are used in
various medical applications such as antidotes, dialysates,
artificial cerebrospinal fluid, intraocular irrigating solutions,
cardiac perfusates, cardioplegic solutions, peritoneal irrigating
solutions, and solutions for organ preservation, etc. Of particular
interest to the present application bicarbonates solutions are used
to buffer dental and other anesthetics to control pH. One of the
most commonly used medical bicarbonate solutions consists of sodium
bicarbonate (NaHCO.sub.3) mixed with water (H.sub.2O). In medical
bicarbonate solutions, bicarbonate ions are in equilibrium as
represented by the following expression:
2HCO.sub.3.sup.-.revreaction.CO.sub.2.uparw.+CO.sub.3.sup.2-H.sub.2O
[0005] If the reaction occurs in a closed system, equilibrium is
reached with the amounts of reactants remaining constant. In open
systems, however, the carbon dioxide gas escapes and the reaction
proceeds from the left to the right with bicarbonate (2HCO.sub.3)
evolving into carbon dioxide gas (CO.sub.2), carbonate (CO.sub.3)
and water (H.sub.2O), progressively decreasing the concentration of
bicarbonate ions and increasing the concentration of carbonate
ions. Since carbonate ions are more alkaline than bicarbonate ions,
the pH of the solution will progressively increase.
[0006] Clinical effectiveness of bicarbonate medical solutions
often depends on maintenance of a particular pH range, generally
from 7 to 9. For some applications, maintaining the pH in a more
narrow range is beneficial. To stabilize pH and CO2 content, sodium
bicarbonate solutions are conventionally packed in gas tight
containers that limit leakage of evolved carbon dioxide into the
atmosphere. By limiting the loss of evolved CO2 pH change may be
reduced. As CO2 leaves solution and enters the container's
"headspace" (the gas-filled region above the solution) the partial
pressure of the evolved CO2 will increase and eventually establish
equilibrium between CO2 leaving solution and CO2 returning to
solution.
[0007] The gas tight container most commonly used to store medical
bicarbonate solutions is the glass vial with a pierceable rubber
cap, the cap being referred to as a septum. Such vials allow the
medical practitioner to pierce the septum with a hypodermic needle
and withdraw or "draw up" a desired volume of bicarbonate solution
into a syringe. To facilitate withdrawing the bicarbonate, the
vials typically include a significant headspace that prevents a
vacuum from forming when the practitioner attempts to draw up the
fluid. Once the fluid is drawn up into a syringe, the syringe can
be used to deliver the fluid into a catheter or a blood vessel. Of
particular interest to the present invention, the partially filled
syringe may be used to draw up a second solution, such as a local
anesthetic, from another vial in order to mix the second solution
with the sodium bicarbonate, where the syringe serves as a mixing
and delivery vessel for the resulting pH buffered solution.
[0008] One drawback to using such vial-and-syringe systems for
storing, mixing, and/or delivering bicarbonate solutions is that
drawing up the solution into the syringe reduces pressure over the
bicarbonate solution which allows CO.sub.2 to leave solution and
create CO.sub.2 bubbles in the solution during the transfer. Also,
there can be significant agitation of the solution as the bubbles
enter the syringe, further causing CO.sub.2 to dissolve out of
solution. For these reasons, even if the pH of a sodium bicarbonate
buffering solution in a vial-type storage container were estimated
or ascertained before delivery, drawing up, mixing and/or delivery
of the bicarbonate system may alter the pH of the solution to an
undesirable extent.
[0009] One particular device for combining a buffer solution, such
as sodium bicarbonate, with an anesthetic, such as a dental
anesthetic in a conventional cartridge, is described in U.S. Pat.
No. 5,603,695. The device comprises a buffer cartridge having a
needle which may be penetrated through the septum of the anesthetic
cartridge. The buffer is stored in a cartridge with significant
head space and no provision for maintaining volatile CO.sub.2 in
solution in a bicarbonate anesthetic. Moreover, no provision is
made for displacing anesthetic from the anesthetic cartridge as the
buffer is introduced.
[0010] For these reasons, it would be desirable to provide improved
methods and apparatus for combining buffer solutions with
anesthetics or other medical solutions, particularly where the
buffer solutions are held in conventional glass cartridges. It
would be particularly beneficial if the methods and devices
employed buffer cartridges which maintained the buffer solution,
more particularly sodium bicarbonate solution, in a stable
condition with minimal pH change and carbon dioxide loss prior to
use. It would be still further desirable if the methods and systems
provided for introducing and combining the buffer solutions with
anesthetic solution, where the anesthetic solution is held in
conventional cartridges, without delivering an excess volume of
buffer to the anesthetic cartridge, and relieving or exhausting an
equal volume of anesthetic from the cartridge. At least some of
these objectives will be met by the inventions described
hereinbelow.
[0011] 2. Description of the Background Art
[0012] Glass vials and cartridges for storing medical solutions are
described in U.S. Pat. Nos. 1,757,809; 2,484,657; 4,259,956;
5,062,832; 5,137,528; 5,149,320; 5,226,901; 5,330,426; and
6,022,337. Injection pens which employ drug cartridges are
described in U.S. Pat. No. 5,984,906. A particular disposable drug
cartridge that can find use in the present invention is described
in U.S. Pat. No. 5,603,695. A device for delivering a buffering
agent into an anesthetic cartridge using a transfer needle is
described in U.S. Pat. No. 5,603,695. Devices for maintaining a
dissolved gas in solution in a pouch are described in U.S. Pat.
Nos. 5,690,215; 5,610,170; and 4,513,015, and U.S. Patent Publ. No.
2007/0265593. Other patents and applications of interest include
U.S. Pat. Nos. 2,604,095; 3,993,791; 4,154,820; 4,630,727;
4,654,204; 4,756,838; 4,959,175; 5,296,242; 5,383,324; 5,603,695;
5,609,838; 5,779,357; and U.S. Patent Publ. No. 2004/0175437.
BRIEF SUMMARY OF THE INVENTION
[0013] The present invention provides methods and apparatus for
buffering anesthetics or other medical solutions held in a
conventional cartridge, particularly those having a penetrable
septum and a slidable plunger or plug, such as those generally
described in U.S. Pat. No. 5,603,695 the full disclosure of which
is incorporated herein by reference. Such cartridges are commonly
used in dental practice, particularly for delivering anesthetics to
a patient prior to a procedure. Such cartridges are conventionally
loaded into a syringe or other delivery device, where the syringe
engages the plunger in the cartridge to dispense the anesthetic
through a needle which has penetrated through the septum. To
optimize effectiveness of the anesthetics and to reduce injection
pain, it is desirable to buffer conventional anesthetics, typically
dental anesthetics such as lidocaine, articaine, prilocaine, or
mepivacaine, shortly before use. It is very important, however,
that the buffering solutions themselves have predictable, stable
pHs and chemical compositions in order for the buffered anesthetic
to achieve an optimum effect and minimum injection pain.
[0014] Methods according to the present invention for buffering
such anesthetic cartridges comprise providing a buffer cartridge,
where the buffer cartridge typically also has a septum and plunger
and which may often be similar or identical to the construction of
the anesthetic cartridge. A transfer needle is penetrated through
septums on both the buffer cartridge the anesthetic cartridge to
provide a fluid transfer path therebetween. An exhaust needle is
also penetrated through the septum on the buffer cartridge but not
through the septum on the anesthetic cartridge. By advancing the
plunger on the buffer cartridge, a volume of buffer may be
transferred from the buffer cartridge into the anesthetic cartridge
while an equal volume of anesthetic is expelled from the anesthetic
cartridge through the exhaust needle, usually into a waste
receptacle as described hereinbelow. Simultaneously expelling the
anesthetic allows a predetermined volume of buffer to be introduced
into the anesthetic cartridge without overfilling the anesthetic
cartridge or causing the plunger in the anesthetic cartridge to be
pushed out by the excess volume.
[0015] In a preferred aspect of the present invention, the
stability of the buffer solution may be maintained prior to its use
at or near a specified pH by filling the cartridge with buffering
solution of the desired pH and then applying sufficient pressure to
the buffer solution to inhibit vaporization of a volatile species,
such as vaporization and loss of carbon dioxide from bicarbonate
buffers where the level of pressure depends on the pH as well as
the maximum temperature to be encountered in shipping and storage.
Where, for example, the buffer comprises 8.4% sodium bicarbonate,
the pH is to be maintained at 7.62, and the maximum expected
temperature is 25.degree. C., a force must be applied which is
sufficient to maintain an absolute pressure within the buffer
cartridge at least as high as the equilibrium partial pressure of
carbon dioxide gas in an 8.4% sodium bicarbonate solution at pH
7.62 at a temperature of 25.degree. C. maximum, which according to
the Henderson-Hasselbach equation and Henry's Law, is 1.64
atmospheres. A greater force will usually be applied to create a
margin of safety in case of higher than expected storage or
transport temperatures. Where the cartridge is expected to undergo
heat sterilization, the force applied should be sufficient to
create a pressure of at least 6 atmospheres, typically higher for a
margin of safety.
[0016] In exemplary embodiments, the force is applied by engaging a
spring held under compression against the plunger or by using a
plunger which is formed from a compressible resilient material or
otherwise made compressible so that when compressed a specified
distance by a pusher, the solution in the cartridge will be placed
under a pre-determined amount of pressure. By way of example, if
the target pH is 7.62, the needed pressure is at least 1.64
atmospheres (as described above), and the plunger has an area
exposed to the anesthetic of approximately 37 mm.sup.2, a spring
would need to apply a minimum force against the plunger of 9.4
lbs/in.sup.2. The force will depend both on the spring constant and
the depth of spring compression.
[0017] While the application of a constant positive pressure
against the buffer held in a buffer cartridge would generally be
sufficient to maintain stability, it will be preferred to
completely remove the air and other gases from the buffer cartridge
prior to sealing. By removing all "head space," the volatile
species, such as carbon dioxide in bicarbonate buffers, will be
held in solution by the elevated pressure with little or no loss.
The presence of even a small gas head space will allow the loss of
some carbon dioxide or other volatile species resulting in a small
but measurable change in the pH and composition of the buffer as
the volatile species reaches an equilibrium partial pressure.
Moreover, the lack of a headspace prevents gases in the headspace
from being driven into solution by the positive pressure, which
might alter the chemical properties of the buffer.
[0018] In specific aspects of the method of the present invention,
penetrating the transfer needle may comprise turning a knob which
holds the transfer and exhaust needles to advance the transfer
needle through the buffer cartridge septum. Thus, penetrating the
transfer needle and the exhaust needle through the anesthetic
cartridge septum usually occurs as the anesthetic cartridge is
inserted into a receptacle on the knob. Preferably, the exhaust
needle directs the expelled anesthetic into a reservoir. For
instance in an exemplary embodiment, the expelled anesthetic could
flow into a space in a housing that surrounds the buffer cartridge.
The space may include an absorbent material. Advancing the plunger
on the buffer cartridge usually comprises engaging a pusher against
the plunger and advancing the pusher to cause the plunger to
proceed along the interior of the cartridge, driving the plunger
against the buffer therein, and forcing the buffer into the
transfer needle. Typically, the pusher will be reciprocatably
mounted on the housing in which the buffer cartridge is held.
[0019] In a further specific aspect of the method of the present
invention, the volume of buffer dispensed may be controlled by
advancing the pusher until it engages a first stop, usually on the
housing, which defines a first delivered volume of buffer. Second
and subsequent delivered volumes may be dispensed by advancing the
pusher beyond the first stop until the pusher engages a second stop
to define a second delivered volume, and optionally further stops
to define further delivered volumes. Such multiple delivered
volumes of buffer may be used with a single anesthetic cartridge or
with successive anesthetic cartridges which are connected to the
buffer delivery apparatus sequentially.
[0020] Devices according to the present invention are intended for
transferring a volume of buffer solution from a buffer cartridge
into an anesthetic cartridge. The buffer cartridge typically
comprises a hollow tube sealed on one end and having a slidable
plug on the other with the buffering solution being held in a space
therebetween. The devices also comprise a needle assembly having a
transfer needle and an exhaust needle, where the transfer needle
can be advanced to penetrate the septum on the buffer cartridge.
The needle assembly also detachably receives an anesthetic
cartridge so that the transfer and exhaust needles penetrate a
septum thereon. The devices also comprise a pusher that advances
the plunger on the buffer cartridge to transfer buffer through the
transfer needle into the anesthetic cartridge while excess
anesthetic is exhausted from the anesthetic cartridge as the
anesthetic is displaced by buffer. In alternative embodiments, a
slightly modified buffer cartridge is used. In such embodiments the
cartridge is a hollow tube open on only one end and the slidable
plunger acts as both plunger and septum, meaning that the transfer
needle pierces the plunger itself to create a fluid path for the
buffer solution to flow out of the buffer cartridge and into the
anesthetic cartridge. As the pusher advances the plunger down the
glass tube, the solution is forced out the transfer needle into the
anesthetic cartridge.
[0021] The devices of the present invention will typically further
include a housing having an attachment end, an open end, and an
open interior. The interior of the housing receives the buffer
cartridge with the septum of the buffer cartridge adjacent the
attachment end and the plunger of the buffer cartridge adjacent the
open end. The devices usually further include a knob which
threadably connects to the attachment end of the housing, where the
needle assembly is carried by the knob so that turning the knob
advances the transfer needle into the buffer cartridge. The
transfer and exhaust needles will extend into an anesthetic
cartridge receptacle on the knob so that insertion of the
anesthetic cartridge into the receptacle causes the transfer and
exhaust needles to penetrate through a septum on the anesthetic
cartridge.
[0022] In order to pressurize and stabilize the buffer within the
buffer cartridge, the devices will typically further comprise a
compression member which is disposed between the pusher and the
plunger of the buffer cartridge. The compression member is
compressed or otherwise adapted to apply a predetermined force on
the plunger when the pusher is advanced or positioned at a
predetermined distance relative to the buffer cartridge. Usually,
the compression member will be a coil spring, and the device will
further comprise a lock which holds the pusher at the predetermined
advance distance relative to the buffer cartridge. Advantageously,
once the transfer needle penetrates the septum on the buffer
cartridge, the pressure will be released and the spring or other
compression member will advance and cause a small volume of the
buffer to pass through and prime the transfer needle, removing
residual gases.
[0023] At least one stop will be provided on the device, typically
on the housing, to control a first advancement stroke of the pusher
to deliver a first predetermined volume of the buffer into the
anesthetic cartridge. Optionally, a second stop may be provided,
again typically on the housing, to control or limit advancement of
the pusher beyond the pusher beyond the first stop to deliver a
second predetermined volume of buffer as the pusher is further
advanced. Additional stops can be incorporated to allow for more
than two predetermined volumes. Other embodiments incorporate
mechanisms that allow the practitioner to adjust the volume to be
delivered.
[0024] In a further aspect of the present invention, a method for
storing the bicarbonate buffer solution comprises providing a
cartridge having an open interior, a needle penetrable septum, and
a plunger which can be advanced into the open interior to
pressurize the contents thereof. The cartridge is filled with a
solution of bicarbonate buffer that will evolve carbon dioxide at
room temperature and pressure. Evolution of the carbon dioxide is
inhibited by storing the cartridge while applying a force to the
plunger, where the force is sufficient to pressurize the
bicarbonate buffer solution at a pressure which inhibits the
evolution of carbon dioxide, thus stabilizing the pH and
composition of the buffer. In exemplary embodiments, the buffer
comprises sodium bicarbonate having a pH in the range from 7.5 to
7.8 and the applied pressure is above 1.2 atmospheres with
preferred pH and pressure ranges set forth above. In further
exemplary embodiments, the force is applied by compressing a spring
or other compression member against the plunger and maintaining the
pressure until the cartridge is used. Preferably, the cartridge is
filled with all gases evacuated (the headspace eliminated) to
further stabilize the pH and carbonate content of the solution.
[0025] In a still further aspect of the present invention, a
bicarbonate buffer storage assembly comprises a buffer cartridge,
as described above, and a mechanism for placing the buffer solution
therein under pressure. In one embodiment, the storage assembly
houses the buffer cartridge and includes a compression member that
exerts a force on the plunger, the force pressurizing the
bicarbonate buffer solution sufficiently to inhibit evolution of
carbon dioxide expected storage temperatures, usually above 1.2
atm. In still other embodiments, the pressure would be sufficient
to inhibit evolution of carbon dioxide at autoclave temperatures,
usually above 5 atm.
[0026] In preferred embodiments, the open interior of the cartridge
is completely filled with sodium bicarbonate with significantly no
head space remaining. The compression member may comprise a
compressible spring which is maintained in compression and engages
the plunger. Usually, the compressible spring is a coil spring, and
the cartridge assembly further comprises a housing where the
cartridge is disposed within the housing and the coil spring is
held in compression between the housing and the plunger.
BRIEF DESCRIPTION OF THE DRAWINGS
[0027] FIG. 1 is a perspective view illustrating the buffer
transfer device of the present invention and a conventional
anesthetic cartridge.
[0028] FIG. 2 is an exploded view of the buffer transfer device
illustrating the knob, housing, buffer cartridge, spring, and
pusher components thereof.
[0029] FIG. 3 is a cross-sectional view of the buffer transfer
device of FIGS. 1 and 2 shown prior to penetrating a transfer
needle through a septum of the buffer cartridge where the spring
remains under compression applying pressure to the buffer within
the buffer cartridge.
[0030] FIG. 3A is a detailed view of a stop member taken along line
3A-3A of FIG. 3.
[0031] FIG. 4 is a cross-sectional view of the buffer transfer
device similar to FIG. 3, except that the transfer needle has been
penetrated through the septum of the buffer cartridge and the
release of pressure has allowed the spring to advance a plunger of
the buffer cartridge to expel a small volume of the buffer and
prime the transfer needle.
[0032] FIG. 5 is an enlarged, detailed cross-sectional view of the
knob and needle components of the buffer transfer device of the
present invention.
[0033] FIG. 5A is a further enlarged, detailed cross-sectional view
illustrating the septum on the buffer cartridge.
[0034] FIG. 6 is a cross-sectional view of a buffer transfer device
similar to that shown in FIGS. 3 and 4 except that an anesthetic
cartridge has been inserted into a receptacle formed in the knob to
cause the transfer needle and an exhaust needle to penetrate a
septum of the anesthetic cartridge.
[0035] FIG. 7 is a cross-sectional view similar to those of FIGS.
3, 4, and 6, except that the pusher has been advanced through a
first length of travel in order to deliver a first volume of buffer
from the buffer cartridge into the attached anesthetic
cartridge.
[0036] FIGS. 8A-8D are schematic illustrations of stop members on
the housing which limit and control travel of the pusher to allow
first and second sequential volume deliveries from the buffer
transfer device.
DETAILED DESCRIPTION OF THE INVENTION
[0037] Referring to FIGS. 1 and 2, a buffer transfer device 10
comprises a knob 12, and housing 14, a buffer cartridge 16, a
spring 18 or other compression member, and a pusher 20. The knob 12
is rotatably mounted on threads 22 at the distal end of the housing
14 and the buffer cartridge 16 may be inserted into an open
proximal end 24 of the housing. The pusher 20 is introduced through
the open end 24 and compresses the spring 18 engaged against a
proximal end 26 of the buffer cartridge 16, as will be described in
greater detail below. The buffer transfer device 10 detachably
receives a conventional anesthetic cartridge 28 within a receptacle
44 (best seen in FIG. 5) at the distal end 30 of the knob 12, which
also will be described in greater detail below.
[0038] Typically, buffer transfer device 10 will be fully assembled
at a central, sterile location and distributed for use. While the
temperature and other conditions of distribution can be somewhat
controlled, it will be appreciated that a variety of temperatures
and other potentially destabilizing conditions might be encountered
during distribution and storage prior to use of the device for
buffering the anesthetic cartridge. A mechanism for maintaining
pressure on the buffer solution within the buffer cartridge 16 will
be provided in order to limit the loss of carbon dioxide or other
volatile components from bicarbonate or other buffering solutions.
The details of the pressurization mechanism are described
below.
[0039] Referring now to FIG. 3, the buffer transfer device 10 in
its pre-use or storage configuration is illustrated. The knob 12
includes a transfer needle 36 and an exhaust needle 38, both of
which can be more clearly seen in the detailed view of FIG. 5. The
transfer and exhaust needles 36 and 38 are illustrated as separate
hypotubes or other tubular structures. It will be appreciated,
however, they could also be formed as a single, bi-lumen structure,
although in all cases, a distal tip 40 of the transfer needle
should extend distally beyond a distal tip 42 of the exhaust needle
38. The distal portions of both needles 36 and 38 extend into a
receptacle region 44 which receives the septum end 32 of the
anesthetic cartridge 28, as will be described in more detail below
with respect to FIGS. 5 and 6. By axially spacing apart the distal
tips 40 an 42 of the transfer and exhaust needles 36 and 38, mixing
between the buffer which is being introduced through the transfer
needle and the anesthetic which is being expelled through the
exhaust needle will be minimized.
[0040] The transfer needle 36 has a proximal end 50 which extends
into a threaded region 13 of the knob 12, as best seen in FIG. 5.
Proximal end 50 extends sufficiently far so that it will penetrate
a septum 15 (best seen in FIG. 5A) formed over the neck 17 of the
buffer cartridge 16 when the knob 12 is fully tightened on the
threads 17 of the housing 14, as shown in FIG. 4. In contrast,
proximal end 52 of the exhaust needle 38 terminates distally of the
septum 15 even when the knob is fully tightened.
[0041] The knob 12 will be tightened over the housing 14 before the
anesthetic cartridge 28 is introduced to the receptacle 44. Prior
to tightening the knob, the septum 15 remains intact and pressure
of buffer within the interior 54 of the cartridge 16 remains above
atmospheric as provided by the pressure of spring 18. Spring 18, in
turn, remains compressed between extension member 56 of the pusher
20 and a plunger 58 which is slidably received within the open
proximal end of the buffer cartridge 16. As soon as the proximal
end 50 of transfer needle 36 penetrates the septum 15, as shown in
FIG. 4, the pressure on the buffer in interior 54 is released,
causing a small flow of buffer through the transfer needle and out
through the distal tip 40 in order to prime the transfer needle.
The plunger 58 advances under the force of spring 18, and the
buffer transfer device 10 is in the condition illustrated in FIG.
4. Note that the proximal movement of the pusher 20 is prevented by
a stop member 62 fixed in a wall of the housing 14, as illustrated
in FIG. 3A. Stop member 62 engages an edge of window 64 formed in
the wall of the pusher 20, as will be described in greater detail
below in connection with FIGS. 8A-8D. Preventing the pusher 20 from
moving proximally is necessary to maintain the pressure applied by
spring 18 on the anesthetic within the interior 54 of the
anesthetic cartridge 16.
[0042] Referring now to FIG. 6, after the knob 12 has been
tightened and the proximal tip 50 of transfer needle 36 has
penetrated the septum 15 of buffer cartridge 16, the neck 32 of
anesthetic cartridge 28 may be inserted into the receptacle 44 of
knob 12, as illustrated in FIG. 6. A first volume of the buffer may
then be advanced from the interior 54 of buffer cartridge 16
through transfer needle 36 by distally advancing the pusher 20, as
shown in FIG. 7. The length of travel of pusher 20, and thus volume
of buffer delivered into the anesthetic cartridge 28, is controlled
by travel of the stop member 62 in the window 64. Prior to
transferring any buffer, the stop member 62 is positioned at a left
hand edge of the window 64, as seen in FIG. 6. The pusher 20 may
then be advanced until the stop member 62 engages a right hand edge
of the window 64, as shown in FIG. 7.
[0043] As the plunger is advanced, transferring buffer through
transfer 36 into the anesthetic cartridge 28, an equal volume of
anesthetic will flow through the distal end 42 of the exhaust
needle 38 and out the proximal end 52 thereof into the neck region
17 of the housing 14. While the exhausted anesthetic is wasted, it
is desirable that it be contained within the buffer transfer device
to avoid spilling and contamination. To that end, an exhaust
passage 70 (FIG. 5) may be formed in the neck 17 to allow the
excess anesthetic to flow into a waste receptacle 72 which is
formed in the interior of the housing 14 surrounding the exterior
of the buffer cartridge 16.
[0044] Referring now to FIGS. 8A-8D, advancement of the pusher 20
relative to the housing 14 as controlled by the stop members 62
will be described in more detail. In FIG. 8A, the pusher is shown
in the configuration of FIGS. 3, 4, and 6 before the plunger has
been advanced or otherwise moved. The stop members 62 (only one of
which is visible in FIGS. 3, 4, and 6) are engaged against the left
hand wall (as shown in FIGS. 8A-8D) of window 64. When the pusher
20 is advanced to transfer buffer into the anesthetic cartridge, as
shown in FIG. 8B, the stop members 62 translate to engage the right
hand edge of window 64, stopping advancement of the pusher. If only
a single delivery is required, no further structure or
manipulations would be needed. However, by providing a second
window 82 and the ability to rotate the pusher 20 about its axis, a
second delivery volume may be provided. A passage 80 is provided
between windows 64 and 62 to allow rotation of the pusher 20 so
that the stop members 62 move from window 64 into the second window
82. As the second window 82 is offset to the right relative to the
first window 64, further leftward travel out of the pusher is now
allowed, until the stop members 62 engage the right hand edge of
window 82, as shown in FIG. 8B. A second measured volume of the
buffer may be delivered. It will be appreciated that still further
window mechanisms could be provided for allowing third, fourth, and
perhaps even more volumes of buffer to be delivered from a single
buffer transfer device.
[0045] While the above is a complete description of the preferred
embodiments of the invention, various alternatives, modifications,
additions, and substitutions are possible without departing from
the scope thereof, which is defined by the claims.
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