Development of a fluid infusion system was undertaken in response to a need for an intravenous infusion device operable under conditions of zero-g. The initial design approach, pursued in the construction of the first breadboard instrument, was to regulate the pressure of the motive gas to produce a similar regulated pressure in the infusion liquid. This scheme was not workable because of the varying bag contact area, and a major design iteration was made. A floating sensor plate in the center of the bag pressure plate was made to operate a pressure regulator built into the bellows assembly, effectively making liquid pressure the directly controlled variable. Other design changes were made as experience was gained with the breadboard. Extensive performance tests were conducted on both the breadboard and the prototype device; accurately regulated flows from 6 m1/min to 100 m1/min were achieved. All system functions were shown to operate satisfactorily

Hammond, J. C.

English

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N 7 5 - 1 7 0 9 8
F L U I D I N F U S I O N S Y S T E M
B e c k m a n I n s t r u m e n t s , I n c o r p o r a t e d
A n a h e i m , C a l i f o r n i a
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National Technical Information Service
U. S. DEPARTMENT OF COMMERCE
https://ntrs.nasa.gov/search.jsp?R=19750009026 2020-03-22T22:52:48+00:00Z
Beckmarv" INSTRUMENTS. INC.
ADVANCED TECHNOLOGY OPERATIONS
1630 SOUTH STATE COLLEGE
ANAHEIM. CALIFORNIA 92806
TELEPHONE 714/997-0730
Document No. FR-1185-101
Rev Rev Date
NASA CR-
x
TITLE: FINAL REPORT
FLUID INFUSION SYSTEM
• (NASA-CS-141579) FLUID INFUSION S Y S T E M
Final Report (Becicmaa Instruments, Inc.,
Anaheim, Calif.) 14 p HC $3.25 CSCL 06B
N75-17098:
Unclas
G3/54 09612
Prepared by
Approved by
Approved by
Approved by
Manager
<ji j\l( C* \ Z(.-<^—
Contracts (Administration
PREPARED FOR:_ National Aeronautics and Space Administration
Lyndon B. Johpson Space Center
R&T Procurement Branch , ---
Houston, Texas 77058 \
pticES
TECHNICAL
INFORMATION SERVICE
US Department of Commerce
Springfield, VA. 22151
Date
Approved by
Approved by
Approved by
FR-1185-101
FINAL REPORT
FLUID INFUSION SYSTEM
January, 1975
Prepared for:
National Aeronautics and Space .Administration
Lyndon B. Johnson Space Center
R&T Procurement Branch
Houston, Texas 77058
BeckmarV INSTRUMENTS, INC.
ADVANCED TECHNOLOGY OPERATIONS
FUUERTON, CALIFORNIA •
CONTENTS
PARAGRAPH . PAGE
1.0 SUMMARY.
2.0 SYSTEM DESCRIPTION 2
2.1 General 2
2.2 Pneumatic System 5
2.3 Liquid Handling System 6
2.4 Flowmeter 6
3.0 TES-TING.
4.0 PERFORMANCE 8
4.1 Flow Rate 8
4.2 Flow Accuracy 8
4.3 Pneumatic System Performance 9
4.4 Automatic Bag Switching 9
4.5 Bubble Detection 9
4.6 Flowmeter Performance 9
5.0 RECOMMENDATIONS 10
FR-1185-101 -ii-
1.0 SUMMARY
Development of the subject Fluid Infusion System was undertaken by Beckman
ATO in response to a need for an intravenous infusion device operable under
conditions of zero-g. A system offering variable flow rates, as well as a
flowmeter for monitoring flow rate, was required. The ability to infuse
two 500 ml fluid packs in sequence was required, with automatic triggering
from the first to the second bag. An alarm was required to indicate a no-
flow condition or the presence of bubbles in the liquid line. Sterility of
the infused liquid obviously-'was also a requirement.
•
It is necessary to pressurize a fluid to produce flow; so the problem, simply
stated, is to pressurize the fluid using some means other than gravity (static
head). Since the infusion solutions are contained in flexible vinyl bags, a
squeezing action can be used to produce fluid pressure inside the bags, and
this was the approach taken. The infusion solution bags are squeezed between
two rigid flat plates, with regulated pressurized gas used to produce a con-'
trolled force. The resulting liquid flows from the infusion bags are con-
trolled and directed by means of pinch valves; and flow readout is provided
by a clinical flowmeter which is modified and made part of the system.
The initial design approach, pursued in the construction of the first bread-
board instrument, was simply to regulate the pressure of the motive gas—C02—
and thereby produce a similar regulated pressure in the infusion liquid itself.
; .-' • ' .' :' i . -'
This scheme did not prove workable because of the varying bag contact area, and
a major design iteration was made. A floating sensor plate in the center of the
bag pressure plate was made to operate a pressure regulator built into the
bellows assembly, effectively making liquid pressure the directly controlled
variable. Other design changes were made as experience was gained with the
breadboard.
ORIGINAL PAGE IS
POOR
FR-1185-101 -1-
Extensive testing was performed on both the breadboard and the prototype
device to ensure adequate performance. Accurately regulated flows from 6 ml/
min to 100 ml/min can be achieved, and all system functions operate satisfac-
torily. The system was subjected to acceptance tests before delivery.
The Fluid Infusion System represents a successful development that meets all
program objectives. A design concept has been evolved and consummated in working
hardware. Some areas in which further gains may be made are evident; and other
potentially fruitful avenues may unfold as additional experience with the proto-
type system is gained.
2.0 SYSTEM DESCRIPTION.
2.1 General
• • •
The Fluid Infusion System is a self-contained, portable benchtop unit. Motive
power for expressing infusion solutions from the bags is provided by high-
pressure CO gas cartridges. Control functions are all accomplished mechan-
ically, so that the only electrical power needed by the device is that required
for the electronic flowmeter. The entire system including the electronic flow-
meter is shown in Figure 1.
Two rectangular pockets are provided in the infusion device for receiving the
fluid bags—in the front and in the rear of the unit (see Figure 2). The out-
side faces of the chambers consist of acrylic plastic windows, so that proper
loading of the bags into the chambers may be verified visually. The pneumatic
bellows that provide the bag squeezing force are centrally located, as are the
pushbutton exhaust valves for retracting the pressure plates. One side of the
unit is devoted to the pneumatic system, and the other side houses the liquid
plumbing components. Design of the liquid side is such that a complete tubing
set can be laid into the unit without violating its sterility.
The probe for the Carolina Medical Electronics electromagnetic flowmeter is a
part of the pre-sterilized tubing set. The remainder of the flowmeter is a
FR-1185-101 -2-
VISUAL BUBBLE/NO FLOW ALARM
(AURAL WARNING ALSO PROVIDED)
Figure 1, Fluid Infusion System with Electronic Flowmeter
ORIGINAL PAGE IB
OF POOR
FR-1185-101
-3-
INFUSION BAG
CHAMBERS•
LIQUID SIDE
MANUAL/AUTOMATIC
CONTAINER SELECT
CONTROLSCO CARTRIDGE- I-MODESELECT
SWITCH
LIQUID FLOW CONTROL-
Figure 2. Infusion Unit
FR-1185-101 -4-
separate bench-mounted unit, containing electronics, readout, and the ATO-
designed no-flow/bubble alarm circuit.
2.2 Pneumatic System
The pneumatic system consists of the C0? cartridge, pressure regulator, mode
switch, bellows pressure control valves, bellows, and exhaust valves. The
function of the pneumatic system is to store motive gas, and apply regulated
pressure to the infusion bags under control of the mode switch.
There is no high-pressure plumbing per se, since the CCL bottle is mounted
directly to the high-pressure inlet of the regulator. There is a swivel fitting
for convenience in changing bottles, but no piping or tubing. The maximum
pressure in a fresh CCL bottle is about 1100 psi, and the regulator is rated
for much more. The regulator output pressure is set at 15 psi, which is
sufficiently low that flexible tubing and push-on barbed fittings can be used
on the output side.
The mode switch is a toggle-actuated Clippard miniature three-way valve. It
admits regulated pressure to the bellows pressure control valves in one state
(Pressurize), and dead-ends the regulator output in the other state (Standby).
The bellows pressure control valves are a unique development evolved to over-
come the nonsteady flow characteristics of the original breadboard. The sensed
variable is the actual liquid pressure in the infusion bags, and it is used to
control pressure in the bellows. CO can enter the bellows only as metered
through the bellows pressure control valves. The action of this control system
is to produce a constant pressure in the liquid bags. Movement of the bellows
and pressure plates occurs as necessary when liquid is allowed to flow from the
bags.
The bellows themselves are made from a convoluted tubular reinforced elasto-
meric material. Pressure relief valves are installed in both bellows spaces
to guard against bellows damage in the event of regulator or pressure control
valve failure. The two manual pushbutton exhaust valves allow pressure to*
FR-1185-101 -5-
be bled from the bellows spaces when desired, so that the pressure plates may
be pushed back from the extended position.
2.3 Liquid Handling System
The liquid handling system consists of the bag selector valve, flow control
valve, drug injection port, and flowmeter cell (see Figure 3). Its function
is to select flow from one or the other bag, control that flow, and provide
for injection of drugs and measurement of the flow rate.
The bag selector valve is located at the Y in the tubing set, where it branches
to run to either bag. One or the other tube is pinched shut depending on the
position of the valve handle. The valve may be moved manually to either Bag
No. 1 or Bag No. 2, and is tripped automatically from 1 to 2 by movement of
the No. 1 pressure plate.
The flow control valve is located downstream from the bag selector valve, and
can be used to close off all flow, or to regulate the liquid flow. Like the
bag selector valve, it operates by pinching the vinyl tubing. ~
The flow cell is necessarily a part of the tubing set, since its electrodes/
must be wetted by the fluid. The flow cell must be installed in the tube set
as received from the vendor, and the entire assembly sterilized. The Y-type
drug injection port is standard tubing-set hardware. All these components,
including the flow cell, are mounted by slipping them laterally into clips
or channels in the "liquid side" of the instrument. Thus the sterility of
a pre-stabilized flow cell/tubing set assembly need not be violated at assembly.
2.4 Flowmeter
A flowmeter is needed in the system to allow initial setting of flow rate and
monitoring. Additionally, it was possible to modify the Carolina Medical
Electronics device to give an alarm when flow is interrupted or stopped. The
flow is through the flow cell only, so that the only connections between the
flowmeter electronics chassis and the rest of the system are electrical.
FR-1185-101
FLOWMETER
CELL
ELECTRICAL
LEADS TO
FLOWMETER
BAG
SELECTOR
VALVE
FLOWMETER
ISOLATED
GROUND
LEAD
DRUG INJECTION PORT
FLOW CONTROL VALVE
Figure 3. Detail of Liquid Side of Unit
FR-1185-10-1 -7-
3.0 TESTING
Engineering and Acceptance tests and results are discussed in the test report,
ATP-1185-501.
4.0 PERFORMANCE
Performance characteristics of the prototype Fluid Infusion System are dis-
cussed in Sections 4.1 through 4.6.
4.1 Flow Rate
Usable flow rates are in the range of 6 to 100 ml/minute. The upper limitation
is simply the capacity of the system; i.e., a certain maximum flow is achieved
when the flow control valve is wide open. The lower limit is imposed by the
characteristics of the flexible tubing system. It was observed in testing
that lower flows (less than about 6 ml/minute) would slowly decline—sometimes
by as much as 50% over 500 ml. This was-ascribed to relaxation effects in the
vinyl tubing at the flow control valve. The flow control pinch valve is almost
closed for the lower flows, and any change in geometry of the tubing bore would
have a noticeable effect.
It was possible to establish quite low flows; and the flow decay was pre-
dictable and very gradual so this effect could possibly be tolerated. However,
until the phenomenon is investigated further, it is felt that the lower flow
should simply be stated as the lowest flow offering adequate unattended flow
regulation.
4. 2 Flow Accuracy
Flow regulation accuracy of the system represents a substantial improvement
over current practice (approximately +20% for the decreasing hydrostatic head
method). The flow accuracy achieved with the unit during testing was ±5% at
the higher flow rates (50 and 100 ml/minute), and ±8% at the low flow rate
(5 ml/minute). This advance was made possible by the incorporation of the
bag pressure control valves in the bellows assemblies of the prototype unit.
FR-1185-101 -8-
These control valves regulate the liquid pressure in the bags directly—a
technique that has proved very desirable since pressure perturbations due to
bag elasticity, wrinkling, and bag contact friction are not, in fact, negligible.
4.3 Pneumatic System Performance
Viability of the CO cartridges as a simple, lightweight, and inexpensive
method of powering the system and making it completely self-contained was
demonstrated. One 25-gram C02 cartridge contains sufficient gas for eight
complete cycles of the unit. If this capacity is not needed, smaller cartridges
are available and are usable in the unit. Leakage from a pierced bottle, with
the mode switch in STANDBY, is virtually nil, with no supply pressure drop
being discernible over a period of many days.
" »•>
4.4 Automatic Bag Switching
Flow is automatically switched from Bag No. 1 to Bag No. 2 at a preset point.
This is accomplished entirely mechanically, without the need for solenoids or
other active components. The trip point is wrench-adjustable; manual selection
can be performed at any time. This feature has consistently performed well.
4.5 Bubble Detection
The Carolina Medical Electronics blood flowmeter is modified to give a visual
and aural alarm when liquid flow ceases or is interrupted by bubbles. This
feature of the device works consistently, with some variability at the threshold
of bubble detection. Its performance is presented in quantitative terms in the
aforementioned test report.
4.6 Flowmeter Performance
Flow indication accuracy of the Carolina Medical Electronics flowmeter is well
within the manufacturer's stated tolerance; i.e., ±5% of full scale. The type
of flow cell furnished as part of the system is their most accurate type, and
the manufacturer stated verbally that ±1% of full scale accuracy may be expected
of it (full scale is 1999 ml/minute). During all testing to date, the device
has, in fact, indicated flow to an accuracy of better than ±1% full scale. In
ORIGINAL
Ni» POOR
FR-1185-101 -9-
some cases erratic indications were noted, but this was invariably an indi-
cation that the manufacturer's probe cleaning routine needed to be done. A
device for accomplishing this, and instructions, are included with the flowmeter,
5.0 RECOMMENDATIONS
The Prototype Fluid Infusion System developed under this contract meets all
established performance goals, and has proven easy and convenient to use.
Examination and use of the completed, prototype system reveal several areas
where further effort should be considered. This is not surprising, of course,
as this is one of the primary reasons for constructing a prototype.
Examination of the complete-system on the bench immediately reveals that a
disproportionately large share of the total volume, weight, and cost is taken
•
up by the flowmeter. Its technique is also inherently invasive when used on
plastic tubing, and thus it complicates sterilization procedures. Replacement
of the electromagnetic unit with a cheaper, simpler, inherently noninvasive
device is highly desirable, and should be pursued. An ultrasonic device
similar to flowmeters currently under development at Beckman ATO would meet
these criteria, and additionally would not depend on ionic conductivity in
the solution for its operation.
Accuracy of flow regulation is good over the flow range of the device, 6 to
100 ml/minute. Below the range, an unexpected phenomenon was encountered—
the flow would very slowly decrease even though the bag liquid pressure control
valve was holding constant pressure in the bag. This effect is thought to be
caused by relaxation effects in the plastic tubing where it is most highly
stressed; i.e., the flow control valve. That it is due to the flexible tubing
and not the valve itself is suggested by the fact that substitution of a com-
mercial pinch valve has no effect.
The phenomenon only appears at these very low flow rates; however, if fine
regulation is desired at extremely low flows for metering medications, etc.,
the problem is probably amenable to solution. A different technique for
ORIGINAL PAGE IS
FR-1185-101 -10- °F POOB
restricting the plastic tubing to produce lower stresses and/or a different
stress distribution in the plastic material may provide a solution. This
would require redesign of the flow control valve, and regardless of other
changes, more sensitivity would certainly be built into the device. The present
knob is somewhat "touchy" at the low end of the flow range. Incorporation of a
differential screw thread, in the device would yield any desired degree of sensi-
tivity, and could be easily implemented. There is also the possibility that a
suitably designed flow control valve, with much greater sensitivity and
detenting or indicating capabilities, could be used to set the flow rate in
an open loop manner. A simple calibration to match its indication to the
characteristics of the particular plastic tubing in use would probably
be necessary.
FR-1185-101 -11-


Fluid infusion system

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