Tandem syringe

A syringe for the gravity-feed intravenous administration of drugs and the like comprises three hollow, elongated, cylindrical, outer, middle and inner barrels nested concentrically and tandemly within each other and means for suspending the syringe above a patient. The middle barrel has an open end with a rubber stopper on it slidably and sealingly disposed within the outer barrel to adjustably define a liquid-receiving volume therein. The inner barrel has a hollow interior, an open external end containing a microbial filter through which its interior is vented to ambient pressure, and a closed end having a sharp, hollow needle communicating with the interior and extending outwardly therefrom. Selective advancement of the inner barrel toward the rubber stopper causes the needle to penetrate the stopper and vent the volume to ambient pressure through the interior of the inner barrel and the filter, whereby liquid medication in the volume may gravity-feed through an established primary or secondary I.V. set to the patient.

BACKGROUND 
1. Field of the Invention 
This invention pertains, in general, to medical devices, and in particular, 
to a tandem syringe for the gravity-feed, intravenous administration of 
parenteral liquids, such as medications and the like, and the method of 
its use. 
2. Description of the Related Art 
The intravenous ("I.V.") administration of drugs has increased dramatically 
over the past decade and approximately 40% of all drugs and fluids 
delivered to patients in hospitals today are administered 
intravenously..sup.1 
FNT .sup.1. M. J. Akers, et al., "Intravenous Drug Delivery Primer," American 
Journal of Hospital Pharmacy, Vol. 44, p.2528, et seq., Nov. 1987. 
Over the years, a wide variety of devices and methods have been developed 
to assist the health care practitioner in the I.V. delivery of fluids and 
medicaments. These systems may be broadly catagorized into those which 
accomplish their function immediately or contemporaneously, and those 
which achieve delivery intermittently or continuously over an extended 
period of time. They may be further grouped between those which achieve 
delivery by means of a "push," or positively-applied force acting on the 
fluid, and those which are gravity-feed. 
An example of device which can accomplish I.V. delivery either immediately 
or intermittantly by means of a "push" is the well-known hypodermic 
syringe, which comprises a hollow barrel having a with a needle on it and 
a sliding piston plunger within. Typically, the syringe is used both to 
withdraw the liquid medication from a supply vial and to inject it 
subcutaneously and/or intravenously through the agency of the same needle 
by means of an immediate "push" supplied manually by the health 
practitioner, or intermittently or continuously over a period of time by 
the use of an associated battery- or spring-operated syringe pump. 
Examples of "tandem" syringes having specialized functions, such as the 
push delivery of dual dosages of drugs, may be found in patents to J. L. 
Pizzino (U.S. Pat. No. 4,702,737), S. J. Ashley (U.S. Pat. No. 4,313,440), 
and J. A. Lazarte, et al. (U.S. Pat. No. 2,939,459). E. A. Tischlinger, in 
U.S. Pat. No. 4,059,109, and W. A. Gettig, in U.S. Pat. No. 4,581,016, 
each describe another type of syringe capable of mixing a diluent with a 
dry medication prior to its injection. In U.S. Pat. No. 4,685,910, R. J. 
Schweizer describes a type of syringe capable of delivering secondary 
fluids within a primary I.V. administration set utilizing a peristaltic 
infusion pump. 
An example of apparatus typically utilized for gravity-feed of parenteral 
fluids is found in a patent to R. C. Moore, U.S. Pat. No. 2,866,457. Such 
systems typically comprise a relatively large container, usually a 
flexible plastic bag, of a primary parenteral fluid which is suspended 
above the patient to generate a pressure head greater than the the 
vasopressure of the patient, along with a length of flexible tubing 
terminating in an indwelling venocatheter. Intermediate the container and 
the catheter are typically found a check valve, a flow-control/shutoff 
clamp, and more proximal to the patient, a Y-connector which may be used 
to administer, either by push or gravity-feed, a secondary fluid in the 
"piggyback" fashion described below. 
Gravity-feed I.V. delivery systems almost always are of the catagory which 
operate intermittantly or continuously over a period of time, as opposed 
to immediately. A detailed overview of various types of such intermittent 
I.V. systems, along with their attendent characteristics and problems, is 
provided by R. P. Rapp..sup.2 
FNT .sup.2. R. P. Rapp, "Considering product features and costs in selecting a 
system for intermittent I.V. drug delivery," Am. J. Hosp. Pharm., Vol.44, 
pp.138l-91. 
It is occasionally desirable to administer a small, secondary dose of 
medication intermittantly or continuously over an interval of time to a 
patient to whom a primary I.V. set is already connected. This is presently 
accomplished by "piggybacking" a "minibag" containing the medication onto 
the primary system and delivering it through the same venipuncture 
utilized by the primary system. 
In such a procedure, the dose is typically withdrawn from the supply vial 
using a conventional disposable hypodermic syringe in the manner described 
above and then injected with that same syringe into a small, sterile, 
plastic "minibag". The dose may be diluted with a larger quantity of the 
primary parenteral fluid or other diluent in the same manner. The minibag 
of solution is then suspended above the container of the primary set and 
connected through a secondary I.V. set to an entry port on the primary 
set's Y-connector. The higher pressure head in the minibag causes a check 
valve in the primary set to close and shut off flow of the primary fluid, 
and secondary infusion is accomplished from the minibag by gravity-feed. 
The minibags used in the above-described procedure are relatively 
expensive, and it would be more cost effective if the same disposable 
syringe which was used to measure and withdraw the medication from the 
supply vial could be used to gravity-feed the medication. A gravity-feed 
syringe system which is said to achieve this end is described by R. P. 
Rapp,.sup.3 and comprises a conventional disposable syringe which is 
suspended by means of plastic bag after it is filled and connected to the 
patient or primary set by means of a secondary set which includes a 
special vented fitting. 
FNT .sup.3. Id., at p. 2535. 
Unfortunately, the special vent fittings used by this system are relatively 
expensive and are occasionally unreliable because they vent the syringe 
through the Luer-lock-type fitting at its bottom, and the medication can 
backflow through the vent by gravity and inadvertently shut off flow 
through the system. 
It is therefore desirable to provide a gravity-feed I.V. delivery system in 
which the same device is capable both of withdrawing and measuring a 
small-to-medium dose of a liquid medication from a conventional supply 
vial, and reliably administering the dose to the patient through a 
conventional primary or secondary I.V. set, and which may be 
cost-effectively disposed of thereafter. These objects and others are 
achieved in the tandem syringe of the present invention. 
SUMMARY OF THE INVENTION 
The syringe of the present invention comprises three hollow, elongated, 
cylindrical barrels, including an outer, a middle and an inner barrel, all 
of which are nested concentrically and tandemly within each other. 
The outer barrel is made of a clear plastic and has measurement markings 
and a tip with a Luer-lock-type fitting on it. 
The middle barrel has an open end with a rubber stopper on it which is 
sealingly slidable within the outer barrel to adjustably define a 
liquid-medication-receiving volume therein. 
The inner barrel has a hollow interior, an open external end which contains 
a microbial filter through which the interior of the barrel is vented to 
ambient pressure, and a closed end slidably received within the middle 
barrel. A sharp, hollow needle communicates with the interior of the inner 
barrel through its closed end and extends outwardly therefrom toward the 
stopper. 
Selective advancement of the inner barrel toward the rubber stopper causes 
the needle to penetrate the stopper and vent the top of the volume to 
ambient pressure through the inner barrel and filter, whereby liquid 
medication in the volume may gravity-feed through an established primary 
or secondary I.V. set to the patient. 
Preferably, a lock in the form of a key and corresponding keyway are 
provided on respective ones of the inner and middle barrels to prevent 
inadvertent advancement of the former into the latter and resultant 
penetration of the stopper. 
Means are provided for suspending the syringe from a pole or stand, and in 
a preferred embodiment, consist of a thumb-loop molded on the external end 
of the inner barrel. 
A better understanding of the syringe of the present invention, its method 
of use, and its many attendent advantages may be had from a consideration 
of the following detailed description of its preferred embodiments and the 
accompanying drawings thereof, a brief description of which now follows.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIG. 1 illustrates a gravity-feed I.V. drug administration system of a type 
with which the tandem syringe of the present invention may be used 
efficaciously. The system illustrated therein comprises a primary delivery 
system 10 and a secondary system 20. 
The primary system 10 comprises a large container 11 of primary liquid 
parenteral I.V. infusion material. The container may be in the form of an 
unvented flexible plastic bag with an outlet 12 and an optional injection 
port 13 of penetrable rubber through which drugs or other materials may be 
injected directly into the primary I.V. fluid. 
The primary system 10 also includes a primary I.V. tubing set, which 
typically comprises a length of flexible tubing 14 connected at its distal 
end to the container 11 by means of a drip chamber 15 attached to the 
container's outlet 12, and at its proximal end to the patient through a 
venous catheter (not illustrated). 
Intermediate of the two ends of the tubing 14 are a Y-connector 16 proximal 
to the patient and a check valve 18 distal thereof. The check valve 18 
prevents flow therethrough when the pressure of the fluid below it exceeds 
the pressure of that above it. The Y-connector includes an entry port 19 
for the introduction of the secondary delivery system 20. A flow control 
device in the form of a roller clamp (not illustrated) is usually included 
in the primary set to control the rate of fluid flow to the patient. 
The secondary system 20 illustrated comprises a secondary tubing set, which 
includes a second length of tubing 22 which is connected at its proximal 
end to the entry port 19 of the Y-connector 16 by means of a male fitting 
24 or a hypodermic needle 25. At its distal end, the secondary set is 
connected to the container from which it is desired to infuse a secondary 
drug or liquid, and in the prior art, this container typically comprises a 
minibag (not illustrated) of the type described hereinabove. The secondary 
set may also include a shutoff or roller clamp 26 for flow control. 
Both the primary system 10 and the secondary system 20 are suspended above 
the patient by means of the arms 27 of an I.V. pole or stand 28, and 
suspension may involve the use of a hangar 29 to achieve the height 
difference between the primary and secondary containers necessary to shut 
the check valve 18 and initiate secondary flow. 
In the system illustrated in FIG. 1, the container for the secondary fluid 
comprises the tandem syringe 30 of the present invention. A better 
understanding of this syringe and its operation may be had from a 
consideration of the more detailed views therof provided in FIGS. 2-7. 
Referring in particular to FIG. 2, a preferred embodiment of the syringe 30 
of the present invention illustrated therein comprises three hollow, 
elongated, cylindrical barrels, including an outer barrel 32, a middle 
barrel 34, and an inner barrel 36. The barrels are nested concentrically 
and tandemly within one another to define a pair of tandem syringes in 
which the middle barrel 34 comprises the plunger of one syringe and the 
inner barrel 36 comprises the plunger of a second. 
The outer barrel 32 includes a tip 38 through which an opening 40 extends 
outwardly from the interior of the barrel. The tip 38 is configured 
externally to conform to a male Luer-lock-type fitting to facilitate its 
connection to a hypodermic needle or female adapter 42 of that type. In 
the preferred embodiment illustrated, the outer barrel is molded from a 
clear or translucent plastic for visibility, and includes volumetric 
graduations or markings 44 to facilitate the measurement of the volume of 
liquid medication to be administered. The outer barrel also preferably 
includes a pair of finger flanges 46 for manual gripping, as do the other 
barrels 34 and 36. 
The middle barrel 34 has an open end 48 with a penetrable rubber diaphragm, 
or stopper, 50 fitted on it which is sized to be sealingly slidable in the 
distal direction within the outer barrel and to define an adjustable, 
liquid-medication-receiving volume or chamber 52 therein and, with the aid 
of the vacuum created thereby, draw that volume of medication into the 
chamber through a hypodermic needle fitted on the tip 38 from a supply 
vial, in the same manner as a conventional hypodermic syringe is loaded. 
The stopper 50 may be molded to include a ramped needle guide 54 or, as 
illustrated in an alternative embodiment of the middle barrel 34a 
illustrated in FIG. 7, this feature may be molded into the open end of the 
barrel itself. 
The inner barrel 36 has a hollow interior 56, an open external end 58, and 
a closed internal end 60. Sealingly fitted into the open end of the inner 
barrel is a cap or plug 62 which contains a microbial air filter 64 
capable of filtering out particulate matter as small as from about 0.22 to 
about 0.45 microns in size, and through which the interior of the barrel 
is always vented to ambient pressure. 
An alternative embodiment of the plug 62a is illustrated in the enlarged 
isometric view of FIG. 6, in which a penetrable rubber needle port 66a is 
disposed adjacent to the filter 64a to permit, for example, a second 
tandem syringe to be piggybacked onto the one illustrated. 
In the embodiment illustrated in the figures, means for suspending the 
syringe from the arm 27 of an I.V. pole are provided in the form of an 
enlarged thumb-loop 68, which is molded onto the external end of the inner 
barrel. Alternatively, these means can take the form of a simple plastic 
strap having an aperture in either end, one of which is slipped around the 
outer barrel and the other of which is slipped over the arm of the stand. 
The closed end 60 of the inner barrel 36 is slidably received within the 
middle barrel 34, and a hollow needle 70, which has a sharp end 72 on it, 
communicates with the interior 56 of the inner barrel through the closed 
end and extends proximally outward therefrom and toward the stopper 50. 
In the preferred embodiment illustrated in FIG. 5, the needle 70 is a 
vented, bayonet-type needle, so-called because it includes a closed, 
slicing type of sharp end 72 and is vented through a lateral aperture 74 
through the sidewall of the needle adjacent to the end. This form of 
needle prevents the possibility of "coring" of the rubber stopper, 
especially by a larger size of needle. The sharp end of the needle may, to 
the same effect, be conical in shape, like a football inflation needle, 
provided it is sharp and closed. In a preferred embodiment in which the 
needle is steel, the needle is molded into the end of the plastic inner 
barrel, and more preferably, is molded of plastic along with the inner 
barrel as a single piece. 
To prevent inadvertent penetration of the stopper by the needle, the inner 
barrel is provided with a key 76 which is sized to prevent proximal 
movement of the barrel within the middle barrel so long as the key is 
misaligned with a corresponding keyway 78 formed in the middle barrel, 
which is the configuration of the syringe illustrated in FIG. 2. When 
penetration and venting are desired, the inner barrel is rotated within 
the middle barrel until the key is aligned with the keyway and the inner 
barrel is slid proximally as far as it will go, causing the tip of the 
needle to penetrate the stopper and vent the contents of the medication 
chamber 52 to atmospheric pressure, whereby the medication may flow by 
gravity out the tip of the syringe and in the direction of the arrow 
illustrated in FIG. 3. 
The method of use of the syringe of the present invention is fairly 
straightforward. In one such method, the syringe is provided sterile and 
empty in a sterilized tearaway bag. A conventional hypodermic needle is 
fitted to its tip and used to draw the desired volumetric dose of 
medication into the chamber, as described above. The needle is then 
removed and the tip of the syringe is connected to the input fitting of 
either a conventional primary or secondary I.V. tubing set, depending on 
whether the fluid is to be administered as a primary fluid or as a 
secondary fluid piggybacked onto an established primary set. 
The syringe is then suspended above the patient and, if used as a secondary 
system, at a position higher than the primary fluid container. The 
proximal end of the set is connected to the patient or an input port on 
the primary system's Y-connector. 
When it is desired to commence flow of the system, the key is aligned with 
the keyway and the inner barrel advanced proximally until the needle 
penetrates the stopper and vents the chamber, at which point flow 
commences, as described above. 
By now, skilled practitioners will recognize that other modifications may 
be made in the materials, construction, and method of use of the tandem 
syringe disclosed herein. For example, it is feasible to provide 
respective ones of the outer and inner surfaces of the inner and middle 
barrels with mating screw threads such that, with rotation of the inner 
barrel within the outer, the inner barrel is caused to advance proximally 
therein, and is prevented thereby from doing so otherwise. 
Likewise, the syringe may be provided preloaded and capped for refrigerated 
or frozen storage for extended periods before I.V. delivery to the 
patient. Alternatively, the the syringe can be supplied preloaded with a 
dry medication in solute form and stored for long periods, then used both 
to mix the medication with a liquid solvent and then administer it to a 
patient. 
Other variations and modifications will suggest themselves, depending upon 
the particular application at hand. Accordingly, the scope of the present 
invention should be limited only be the claims appended hereafter.