Apparatus for infusing medical solutions

An IV infusion method and apparatus includes a plurality of fluid pumps mounted within a portable support housing and coupled to an IV tube. Each separate fluid pump is adapted to deliver fluid at a substantially constant delivery pressure predetermined by the characteristics of the pump. Each fluid pump includes an elastomeric membrane stretched into its region of nonlinear elasticity over a contour surface. Check valves located between the pumps and the IV tube control sequential dispensing of fluids from the pumps. The method and apparatus are especially adapted to a SASH process.

FIELD OF THE INVENTION 
The present invention relates to methods and apparatus for infusing medical 
solutions in a predetermined sequence into patients. The present invention 
is particularly, but not exclusively, useful for infusing medical 
solutions in accordance with a SASH or SAS process automatically and in 
the correct sequence. 
BACKGROUND OF THE INVENTION 
Current intravenous IV site flushing techniques for antibiotics and other 
medicaments use saline and heparin solutions to maintain an IV site. One 
such technique is known in the art as a SASH process. The term SASH refers 
to the sequential infusion of a saline (S) solution for initially flushing 
an IV site, followed by the infusion of a medicant such as an antibiotic 
(A), followed by another saline (S) solution flush, and for those IV sites 
that require it a final infusion of a heparin (H) solution as an 
anti-coagulant. The dosage of the saline and of the heparin is typically 
in the range of 3-5 ml. The dosage of an antibiotic in a diluent may vary 
from about 20-250 ml. 
In the past the SASH process has typically been performed using pre-filled 
medical syringes. This requires separate syringes each having a separate 
needle. Additionally, multiple site access and a sequential site cleaning 
are also required. This relatively complicated procedure is difficult for 
homecare and ambulatory patients to perform. It is critical that the 
procedure be carried out in a proper sequence to insure a non-clogged 
access to the IV site. 
For maximum flexibility in the implementation of an extended and 
comprehensive infusion therapy program there is a recognized need for a 
SASH method and apparatus that can be performed by a greater number of 
untrained personnel such as outpatients. Preferably such a SASH method and 
apparatus could also be set up and operated by an ambulatory patient, with 
little or no additional training from medical personnel. 
One such SASH delivery system that requires additional training is marketed 
by Block Medical, Inc. of Carlsbad, Calif. under the trademark of 
Auto-SASH.TM.. This system includes three separate reservoirs that contain 
two doses of a saline solution and one dose of a heparin solution. Each of 
the reservoirs is coupled to a single IV line and is discharged by a 
manually operated press pump formed integrally with the reservoir. The 
system is designed for treating an IV site while an antibiotic is being 
administered using a separate IV delivery system. Prior to dispensing of 
an antibiotic into the IV site the IV line of the Auto-SASH.TM. is coupled 
to the site. A patient first dispenses a dose of saline solution into the 
site (for flushing the site) by manually pressing the press pump for that 
reservoir. The antibiotic is then dispensed followed by a dose of saline 
from the Auto-SASH.TM.. Finally, a dose of a heparin solution can be 
administered in the same manner. A deficiency of this prior art system is 
that a patient must manually discharge each valve in the proper sequence. 
This requires attentiveness and some training on the part of the patient. 
Additionally, this Auto-SASH.TM. system must be used in combination with a 
separate delivery system, such as a pump or IV pole for the antibiotic. 
The present invention is directed to a portable SASH infusion apparatus 
and method that overcomes these prior art limitations. 
In light of the above it is an object of the present invention to provide a 
method and apparatus to simply and safely infuse medical solutions in the 
proper sequence especially for a mobile or ambulatory patient. Another 
object of the present invention is to provide a method and apparatus for 
infusing medical solutions that can automatically dispense solutions in 
the proper sequence for a SASH process. Still another object of the 
present invention is to provide a portable IV infusion apparatus which 
provides for the complete discharge of separate solutions and for a 
substantially uniform delivery pressure for each separate solution. Yet 
another object of the present invention is to provide a portable IV 
infusion apparatus for multiple solutions which can be reused and 
pre-filled in a ready-to-use configuration for a relatively extended 
period of time while maintaining sterility of the solutions held in the 
apparatus. Another object of the present invention is to provide a 
portable IV infusion apparatus for multiple solutions in the proper 
sequence which is easy to use, relatively simple to manufacture and 
comparatively cost effective. 
SUMMARY OF THE INVENTION 
In accordance with the present invention a portable IV infusion apparatus 
includes a plurality of separate fluid pumps for sequentially dispensing 
medical solutions at different fluid delivery pressures to an IV site. In 
an illustrative embodiment for a SASH process four separate fluid pumps 
are mounted within a transportable support housing and are coupled to a 
single IV tube. The IV tube may include an on-off valve constructed as a 
conventional slide clamp. Each separate fluid pump is adapted to deliver 
solution at a delivery pressure pre-determined by the characteristics of 
the fluid pump. Check valves are located between the separate pumps for 
sequentially dispensing solution from each pump into the IV tube after the 
previous pump is emptied. In use, a patient may use the device by first 
priming the IV line, opening the on-off clamp to occlude the IV line, and 
then hooking the line to a venous access device. The infusion apparatus of 
the invention then automatically delivers the fluid solutions in a proper 
sequence as a result of the pre-determined delivery pressures of the 
infusion apparatus. 
In a broad sense, the portable IV infusion pump may be loaded with the 
operative solutions at a hospital or pharmacy and is then adapted to 
dispense multiple solutions to an IV site by a method that generally 
stated includes the steps of: 
1. connecting a first and a second reservoir to a single IV line; 
2. pressurizing the first reservoir with a first fluid to a pressure of 
P.sub.1 and completely discharging the first reservoir at a substantially 
constant delivery pressure; 
3. pressurizing the second reservoir with a second fluid to a pressure of 
P.sub.2 and completely discharging the second reservoir at a substantially 
constant delivery pressure with P.sub.1 &gt;P.sub.2 ; 
4. controlling fluid flow such that the first reservoir is completely 
discharged of fluid prior to the second reservoir initiating discharge of 
fluid and the second reservoir is then completely discharged of fluid. 
For a SASH process four separate reservoirs are involved, a saline 
containing reservoir at a pressure of P.sub.1, an antibiotic containing 
reservoir at a pressure of P.sub.2, a saline containing reservoir at a 
pressure of P.sub.3, and a heparin containing reservoir at a pressure of 
P.sub.4, with P.sub.1 &gt;P.sub.2 &gt;P.sub.3 &gt;P.sub.4. (For a SAS process three 
separate reservoirs are required.) For sequentially controlling flow from 
the separate reservoirs into the IV tube, check valves may be located 
between the reservoirs and IV line. 
In an illustrative embodiment each separate fluid pump includes a 
pressurized reservoir or fluid chamber formed by an elastomeric membrane 
permanently stretched into a region of nonlinear elasticity. Such a fluid 
pump is disclosed in copending U.S. Patent Application entitled "Portable 
Infusion Pump" and commonly owned by the Assignee of the present 
application. This type of pump is characterized by a substantially 
constant fluid delivery pressure and by a substantially complete discharge 
of fluid from the pumping chamber. For a SASH process four separate pumps 
may be provided to pressurize and deliver fluid at four different 
substantially constant pressures. For a SAS process three pumps are 
required. Alternately, in place of four separate pumps a single pump 
having four separate chambers each pressurized to a different pressure by 
a single elastomer formed with areas of different thicknesses, 
corresponding to the different chambers may be provided. 
The novel features of this invention, as well as the invention itself, both 
as to its structure and its operation, will be best understood from the 
accompanying drawings, taken in conjunction with the accompanying 
description, in which similar reference characters refer to similar parts, 
and in which:

DESCRIPTION OF PREFERRED EMBODIMENTS 
Referring now to FIG. 1, an infusion apparatus for infusing medical 
solutions in accordance with the invention is shown and generally 
designated as 10. As indicated in FIG. 1 the infusion apparatus 10 may be 
worn by a patient 12 during ambulation and can be attached to the patient 
12 by any well known means, such as a belt 14. Further, FIG. 1 shows that 
the infusion apparatus 10 can be connected in fluid communication with the 
patient 12 for the infusion of fluids into the patient 12 through an IV 
line 16. It is also shown that the IV line 16 can include an in-line air 
filter 18 of a type well known in the pertinent art which will prevent the 
infusion of air to the patient 12. Additionally, an on-off valve 20 can be 
operatively associated with the IV line 16 to initiate or terminate the 
flow of fluid from the infusion apparatus 10 through the IV line 16. 
Although the particular on-off valve 20 which is shown in the Figures is a 
standard slide clamp, it is to be appreciated that any on-off valve 20 
that is well known in the pertinent art will suffice for purposes of the 
present invention. that is well known in the pertinent art will suffice 
for purposes of the present invention. 
Referring now to FIG. 2 the infusion apparatus 10 is shown. The infusion 
apparatus 10 includes four fluid pumps 22a-d mounted within a single 
carrier housing 24. The infusion apparatus 10 shown is adapted to perform 
a SASH process. Alternatively a lesser or greater number of fluid pumps 
22a-d may be assembled within the carrier housing 24. 
As shown schematically in FIG. 3, the fluid pumps 22a-d are coupled in flow 
communication to the IV line 16. Additionally, each pump 22a-d is coupled 
to a check valve 25a-d. The check valves 25a-b are located between the IV 
line 16 and the fluid pumps 22a-d to regulate a sequence of fluid flow 
from the fluid pumps 22a-d. Each fluid pump 22a-d is adapted to deliver 
fluid at a substantially constant pressure until the pump 22a-d is 
substantially completely discharged. 
Delivery pressure bands, P.sub.1 through P.sub.4, of the pumps 22a-d are 
selected such that P.sub.1 band, corresponding to pump 22a is greater than 
P.sub.2 band corresponding to pump 22b. Likewise P.sub.2 band is greater 
than P.sub.3 band corresponding to pump 22c band and P.sub.3 band is 
greater than P.sub.4 band corresponding to pump 22d. (P.sub.1 band&gt;P.sub.2 
band&gt;P.sub.3 band&gt;P.sub.4 band). 
As used herein the terms P.sub.1, P.sub.2, P.sub.3 and P.sub.4, refer to a 
delivery pressure band. P.sub.1, P.sub.2, P.sub.3 and P.sub.4 are not 
discreet values but bands of pressure which includes the difference in 
start to finish discharge and the manufacturing tolerances of the fluid 
pump 22a-d. 
The check valves 25a-d are each constructed to open at a preselected low 
differential pressure .DELTA.P sensed between the downstream pressure in 
the IV line 16 and an upstream pressure determined by the pump delivery 
pressure of a fluid pump 22a-d. The check valves 25a-d can thus be 
constructed and arranged to allow fluid flow sequentially from pump 22a at 
pressure P.sub.1, pump 22b at Pressure P.sub.2, pump 22c at pressure 
P.sub.3, and pump 22d at pressure P.sub.4. 
The infusion apparatus 10 is thus constructed to operate in a SASH process 
that includes the steps of: 
1. connecting a first reservoir with a dosage of a saline solution, a 
second reservoir with a dosage of an antibiotic solution, a third 
reservoir with a dosage of a saline solution, and a fourth reservoir with 
a dosage of a heparin solution, to an IV line; and 
2. sequentially discharging a dose of saline from the first reservoir at a 
pressure of P.sub.1, a dose of antibiotic from the second reservoir at a 
pressure of P.sub.2, a dose of saline from the third reservoir at a 
pressure of P.sub.3, and a dose of heparin from the fourth reservoir at a 
pressure of P.sub.4 with P.sub.1 &gt;P.sub.2 &gt;P.sub.3 &gt;P.sub.4. 
A suitable fluid pump 22a-d for pumping or discharging fluid solutions at a 
substantially constant pressure is shown in FIGS. 4, 5, 6A and 6B. In 
general each of the fluid pumps 22a-d will be of the same construction but 
the pumps will be sized differently. For example each pump 22a-d may be 
sized to contain a predetermined volume or dosage of solution which may be 
different. As an example the volumetric capacity of a pump 22a-d may be in 
the range of 20-250 ml for an antibiotic and 3-5 ml for saline depending 
on a required dosage. It is anticipated that the pump will be charged with 
a solution at the pharmacy although it is contemplated that a patient may 
charge some solutions. 
With reference to FIG. 4 a pump 22a-d is shown. Each pump 22a-d includes a 
housing 27a-d. An elastomeric membrane 26a-d is clamped between rings 
40a-d and 44a-d and is then attached to the housing 27a-d and to a shell 
(not shown), or to the carrier housing 34. FIG. 4 also shows that the 
housing 27a-d is formed with an inlet port 28a-d and an outlet port 30a-d. 
Each outlet port 30a-d of the pumps 22a-d is coupled to an outlet conduit 
31a-d which in turn is coupled to the IV line 16. Each check valve 25a-d 
is located in an outlet conduit 31a-d situated between the outlet port 
30a-d of a pump 22a-d and the IV line 16. The individual components of a 
pump 22a-d, however, are best seen in FIG. 5. 
In FIG. 5 the various components of a pump 22a-d are shown in an exploded 
isometric and are arranged generally in the order in which they are to be 
assembled. Preferably, the housing 27a-d is made of a hard plastic, such 
as polycarbonate, and is of a material which is chemically compatible with 
the fluid to be infused into the user 12. For purposes of the present 
invention, a contour surface 32a-d of housing 27a-d can have any topology 
which will stretch the membrane 26a-d into its nonlinear region of 
elasticity when these components are assembled. Preferably, however, the 
contour surface 32a-d of housing 27a-d will follow and conform to the 
natural topology of the inflated membrane 26a-d as it transitions from 
linear to non-linear. For the case shown in the Figures, contour surface 
32a-d is substantially hemispherical. On the other hand, as shown in the 
Figures, the periphery 34a-d of housing 27a-d is folded outwardly from the 
contour surface 32a-d in order to facilitate the connection of the 
membrane 26a-d onto the housing 27a-d. The housing 27a-d can be 
manufactured using any well known manufacturing procedures, such as 
injection molding. 
A thin wall tube which forms valve sleeve 36a-d, and a valve insert 38a-d 
are shown in FIG. 3 in their positions for insertion into the lumen of 
inlet port 28a-d. When inserted into the lumen of inlet port 28a-d, the 
sleeve 36a-d and valve insert 38a-d establish a one-way valve for the 
housing 27a-d which permits the flow of fluid in only one direction 
through the inlet port 28a-d. Specifically, it is important that each 
fluid pump 22a-d will be filled with fluid through the inlet port 28a-d of 
each chamber but that fluid not be able to leave the fluid pump 22a-d 
through the inlet port 28a-d. A fluid may be loaded into an inlet port 
28a-d under pressure utilizing a medical syringe (not shown). 
Additionally, it is important that during filling of the separate fluid 
pumps the sequence of filling be accomplished from the highest to the 
lowest pressures. 
Each pump 22a-d also includes an upper top ring 40a-d which is engageable 
with a rib 42a-d that is located on the circumference of membrane 26a-d. 
Upper ring 40a-d is also engageable with a lower bottom ring 44a-d to 
effectively grip and hold the rib 42a-d of membrane 26a-d between the 
rings 40a-d and 44a-d. These rings 40a-d and 44a-d can be of any suitable 
rigid material such as polycarbonate which, when the rings 40a-d and 44a-d 
are joined together to support the flexible membrane 26a-d, will provide a 
firm foundation for the membrane 26a-d. 
With specific regard to the membrane 26a-d, it is seen in FIG. 3 that the 
membrane 26a-d is substantially a circular sheet when in its unstretched 
condition. Further, this sheet is formed with a raised rib 42a-d which, as 
mentioned above, can be gripped between the rings 40a-d and 44a-d. 
Although it will be appreciated that most elastomeric materials may be 
suitable for the purposes of the present invention, the membrane 26a-d is 
preferably made of a natural rubber or isoprene having a high elastic 
memory. Regardless of the particular material used for membrane 26a-d, 
however, it is important that the membrane 26a-d be chemically compatible 
with the fluid medicament which is to be infused to the user 12 from each 
pump 22a-d. If there is no compatibility between the membrane 26a-d and 
the fluid medicament a drug barrier needs to be created between the two. 
To establish such a drug barrier, the membrane 26a-d can be appropriately 
coated so that the particular surface of membrane 26a-d which is to be 
placed in contact with the contour surface 32a-d of housing 27a-d will not 
chemically interact with the fluid medicament in the pump 22a-d. 
Alternatively, though not shown in the Figures, a medicament compatible 
membrane can be held with the membrane 26a-d between the rings 40a-d and 
44a-d. With this combination, the medicament compatible membrane is 
positioned between the membrane 26a-d and the contour surface 32a-d of 
housing 27a-d when these components are assembled. For purposes of the 
present invention, the portion of membrane 26a-d which is circumscribed by 
the rib 42a-d is preferably of uniform thickness. It is recognized, 
however, that thickness may be varied across the membrane 26a-d as long as 
the resultant topology creates a nonlinear elastomeric behavior for the 
membrane 26a- d. In addition, the thickness of the membranes 26a-d will in 
part be different for each pump 22a-d for achieving a different operating 
pressure for each pump 22a-d. 
The cooperation of the various structural elements of each pump 22a-d will 
be best appreciated with reference to both FIGS. 6A and 6B. First, in FIG. 
6A it is seen that the upper top ring 40a-d is joined to the lower bottom 
ring 44a-d to grip and hold rib 42a-d of membrane 26a-d therebetween. The 
rings 40a-d and 44a-d can be joined together by any of several means, such 
as ultrasonic welding or solvent bonding. Additionally, as seen in FIG. 
6A, the periphery 34a-d of housing 27a-d is joined to upper top ring 
40a-d. When housing 27a-d is joined to upper top ring 40, the contour 
surface 32a-d of housing 27a-d stretches membrane 26a-d substantially as 
shown. Importantly, the dimensions of both membrane 26a-d and contour 
surface 32a-d are such that this stretching takes the membrane 26a-d into 
its nonlinear region of elasticity. The joining of housing 27a-d to upper 
top ring 40a-d also establishes a potential chamber or reservoir 50a-d 
between the membrane 25a-d and contour surface 32a-d. 
Referring now to both FIGS. 6A and 6B, it can be appreciated that as fluid 
is introduced through the inlet port 28a-d of housing 27a-d and into the 
potential chamber 50a-d under the pressure of a syringe, or some other 
pumping means, any air in the system will first be vented to the outlet 
port 30a-d along the indentation 52a-d which is formed into contour 
surface 32a-d. This, of course, always happens when the air pressure is 
less than the pressure necessary to distend the membrane 26a-d. Then, with 
outlet port 30a-d blocked to prevent the flow of liquid medicament from 
chamber 50a-d, the elastomeric membrane 26a-d will begin to expand as 
additional liquid medicament is introduced into the potential chamber 50. 
It is important to the present invention that in order to create a 
substantially constant fluid pumping pressure in the chamber 50a-d, the 
expansion, and subsequent contraction, of membrane 26a-d be entirely 
accomplished with the exception of the last or lowest pressure fluid pump 
22d while membrane 26a-d is in its nonlinear region of elasticity. As 
previously stated the elastomeric membrane 26a-d is initially stretched 
into its nonlinear region of elasticity during assembly of each pump 
22a-d. It can be appreciated that during subsequent loading of a fluid 
into chamber 50a-d, a pump means such as a medical syringe must overcome 
the force which is exerted by the elastomeric membrane 26a-d. There must 
then be additional non-linear stretching of the membrane 26a-d to form and 
expand the chamber 50a-d as shown in FIG. 6B. 
Viewed from an energy standpoint, a fluid must be introduced under a 
pressure sufficient to overcome the potential energy of the initially 
stretched membrane 26a-d and form the chamber 50 a-d. This total amount of 
energy minus what has been lost through heat loss and elastomeric 
hysteresis is thus available for displacing fluid from the chamber 50a-d 
at a substantially constant delivery pressure. Further, because of the 
initial non-linear stretching of the membrane 26a-d, even after complete 
discharge of a fluid, a residual force is maintained by the membrane 26a-d 
acting upon the contour surface 32a-d. 
As previously stated each pump 22a-d must be sized to deliver a 
predetermined volume of fluid solution over a substantially constant 
predetermined delivery pressure. A size of the pump 22a-d may thus be 
adjusted to achieve a predetermined volume. For achieving a predetermined 
delivery pressure a thickness of the elastomeric membrane 26a-d as well as 
the material may be selected as required. 
In general, the delivery pressure of a pump 22a-d will vary with the 
thickness of the elastomeric membrane 26a-d. Likewise the delivery 
pressure will vary with the modulus of elasticity of the material selected 
for the elastomeric membrane 26a-d. 
FIGS. 7A and 7B illustrate representative volume versus pressure 
characteristics of the four fluid pumps 22a-d. Curves C.sub.a-d of FIG. 7A 
illustrate the volume versus pressure characteristics of pumps 22a-d 
respectively. In general each pump 22a-d is constructed to deliver fluid 
over a relatively constant pressure band. As is apparent pump 22a operates 
at the highest pressure band followed by pump 22b, 22c and 22d 
respectively. These operating pressures correspond to the operating 
pressures or pressure bands P.sub.1 &gt;P.sub.2 &gt;P.sub.3 &gt;P.sub.4 shown in 
FIG. 3. An illustrative range of pressures may be in the range of 1-20 
psig. FIG. 7B illustrates a volume delivered by the separate chambers over 
a time sequence. 
The check valves 25a-d for each pump 22a-d must be configured to crack with 
a relatively small pressure differential .DELTA.P between the respective 
operating pressures P.sub.1 -P.sub.4 for the pumps 22a-d. Such check 
valves 25a-d are commercially available and in general function as shown 
in the schematic illustration of FIG. 8. Additionally, the check valve 25a 
downstream of pump 22a may be eliminated if desired. 
In addition the configuration noted in FIG. 2 with four separate fluid 
pumps 22a-d may also be varied, as long as four separate reservoirs or 
chambers each at a different pressure are provided. As an example, a 
single pump having a single elastomeric membrane that covers a plurality 
of juxtaposed chambers may be provided. The thickness of the elastomeric 
membrane may be varied to provide a pressure differential between the 
separate chambers. 
FIG. 9 illustrates such an alternative embodiment infusion apparatus. 
Alternate embodiment infusion apparatus 51 includes a housing 53 having a 
plurality of contour surfaces 54a-d formed thereon. A single concentric 
elastomeric membrane 56 is mounted in operative alignment with the contour 
surfaces 54a-d substantially as described for elastomeric membrane 26a-d. 
Concentric elastomeric membrane 56 is formed however, with a varying 
thickness for providing chambers corresponding to contour surfaces 54a-d. 
The pumping or delivery pressure from each chamber can thus be varied as 
required. 
As shown in plan view in FIG. 10 a single infusion apparatus 60 for a SASH 
process may include four separate chambers S,A,S,H, concentrically 
arranged and divided. FIG. 10A illustrates a single infusion apparatus 62 
having three separate and concentrically arranged chambers (S,A,S). In 
either case the largest chamber (A) is in the center. 
FIG. 11 illustrates yet another infusion apparatus 64 formed with a shell 
68 and separate chambers formed by a single elastomeric membrane 66. The 
shell 66 may be sized to contain a fixed volume for each separate chamber. 
Thus the invention provides a method and apparatus for infusing a plurality 
of medical solutions in a controlled sequence. The apparatus of the 
invention is simple in construction and may operate automatically in a 
SASH process. Moreover the method and apparatus of the invention is 
suitable for use by a mobile or ambulatory patient. 
While the particular portable IV infusion apparatus as herein shown and 
disclosed in detail is fully capable of obtaining the objects and 
providing the advantages herein before stated, it is to be understood that 
it is merely illustrative of the presently preferred embodiments of the 
invention and that no limitations are intended to the details of the 
construction or design herein shown other than as defined in the appended 
claims.