Note: Descriptions are shown in the official language in which they were submitted.
` lO9Z467
This invention relates to a flow control device for
example for use in apparatus for the intravenous administration
of liquids.
A known intravenous administration apparatus comprises
a container for the liquid to be administered, a tube connected
to the container, a hollow needle at the end of the tube to be
introduced into the vein of a patient, and a device for con-
trolling the quantity of liquid flowing under gravity out of the
container to the hollow needle, and is known as a gravity-system.
In use the container, such as a bottle or plastic bag, filled
with liquid is connected by means of the flexible tube to the
hollow needle or canula which is in$roduced into the vein.
The container is situated at some height above the
patient. The flow of liquid is adjusted by means of the control
device in the form of an adjustable clamp on the flexible supply
tube which includes a drip chamber to give an indication of the
rate at which liquid~is being administered.
Gravity systems are used for infusion and transfusion.
In the case of infusion, liquids such as glucose and salt-
solutionsj to which medicaments may or may not be added are
administered, whereas transfusion is the administration of blood.
There is no major difference in the administration techniques
and unless otherwise indicated in the following infusion should
be understood to include transfusion.
The duration of uninterrupted administration of in-
fusion liquid can vary from some hours to some days, or even
longer. The quantity of liquid administered per unit of time
is important in particular when some medicaments are added to
the infusion liquid.
In case of the existing gravity systems the quantity
-- 2
~09Z~6'7
of liquid administered per unit of time is not very stable, due
to the principle and the design of these systems. The main
causes of variations occurring in the adjusted flow rate are
changes in:
a) the flow resistance in the tube near the adjusting
clamp and in the hollow needle in the vein,
b) the resistance to outflow near the end of the
needle,
- c) the height of the liquid column in the administra-
tion system,
d) the back pressure of the blood in the vein at the
place of the puncture.
Gravity systems continuously require the attention of
nursing staff for controlling and readjusting the flow rate and
for the timely replacement of the liquid container to prevent
air entering the system when the container becomes empty.
More specifically the causes of the above mentioned
variations in the adjusted flow rate are as follows:
(a) In the gravity system two constrictions are present,
one near the adjusting clamp on the tube and the other in the
hollow needle. A third constriction may be present when-a micro-
filter is included.
The through flow area near the control device is depend-
ent on the adjustment of the device and has a value between O and
about O.l mm . The shape of the flow area in this region of the
flow path is an elongated or circular slot with an average opening
of the order of microns. Infusion liquids may contain very small s~d
components which can cause silting up of the control opening by
which the flo~7 rate decreases. When a filter is used the same
effect can occur with the filter.
-- 3 --
~,.
;~
lO9Z467
A partial clogging of the needle can occur too in
particular if the supply of infusion liquid is too slow or there
is a back-flow of blood.
A second cause can be unintentional readjustment of the
control device. Some systems employ a roll-clamp and other
systems a bending-clamp by which a sharp bend is provided in the
tube. External causes e.g. movement of the patient, or the
visco-elastic properties of the tube material may cause the
opening of the slot to vary.
(b) The hollow needle, which is introduced into the
vein, has a beveled end whereby the outflow opening is elliptical.
The surface of the outflow opening is disposed at a sharp angle
to the wall of the vein. Movement of the patient can cause the
outflow opening to be restricted by the wall of the vein.
(c) The height of the liquid column in the gravity
system affects the flow rate. A change in the height of the
liquid column is caused by the decreasing amount of liquid in the
container and by any change in the posture of the patient. The
height of the liquid column is fixed by the level at which the
? static pressure in the system above the control clamp is equal
to the atmospheric pressure and the rel-ative height of the out-
flow opening of the needle or canula.
The influence of the drop of the liquid level in the
container is a maximum when there is used a plastic bag or a
bottle of the kind to which the air is supplied via an air inlet
hose and which has a rubber cap internally provided with an air
tube which extends to a position above the level of the liquid
in the inverted bottle.
If the interface between the supplied air and the
liquid in the system is situated below the liquid level in the
1092~67
container, the effect of the falling liquid level is smaller
because the pressure above the liquid falls as the level in the
bottle drops.
The maximum pressure variation which can result from a
drop in the liquid level in a bottle or bag of 500 cc contents is
about 15 cm of water, whereas that which can result from a change
in the posture of the patient is about 35 cm of water. Thus the
total possible pressure variation is about 50 cm of water.
The change in the height of the liquid column can amount
to about 50 cm of water. In consequence of this the liquid pres-
sure can decrease 33-50% in case of an original height of 100-
150 cm, resulting in a considerable reduction in the liquid flow
rate.
(d) The venous blood pressure is 0-5 cm water column
(wc). Any variations have minor influence on the liquid flow
rate. ~hen a child is c~ying, however, the peripheral venous
pressure can reach peak values of 100 cm wc. Therefore the
average value of the back pressure can vary strongly. Further-
more, the administration system may become clogged by the back
flow of blood into the gravity system.
The invention aims at providing a device in which the
above mentioned disadvantages are avoided.
In accordance with the invention there is provided a
flow control device for controlling liquid flow rate during an
intravenous administration, comprising a housing defining a
supply chamber having an inlet channel, a filter chamber connected
to the supply chamber by a passage, an outlet chamber connected
to the filter chamber, a first membrane in the supply chamber
arranged to lie under tension covering the passage between the
supply chamber and the filter chamber, the inlet channel opening
-- 5 --
`" 1092~67
into the supply chamber on the same side of the membrane as the
passage, a second membrane in the outlet chamber dividing the
chamber into two separate parts, by-pass channel connecting said
separate parts, control means for adjusting the through flow area
of the by-pass channel, an outlet channel connected to the part
of the outlet chamber downstream of the by-pass channel, the
second membrane being movable towards and away from the outlet
channel to vary the flow area thereof in accordance with the
pressure differential between the two outlet chamber parts.
The flow control device allows adjustment of the liquid
flow rate and automaticaily maintains the adjusted value within
narrow limits. Fur~hermore~ the flow control device operates to
cut off automatically the liquid flow when the pressure of the
liquid in the supply chamber becomes too low, e.g. when a suppiy
container is empty, the pressure on the first membrane being
insufficient to hold it clear of the passage between the supply
chamber and the filter chamber. This is important if the supply
has to be continued and the empty container has to be replaced.
The automatic closing prevents the entry of air into
the system because this remains filled with liquid. The replace-
ment of an empty container can take place some time after liquid
has stopped flowing from the container which simplifies the task
of controlling and replacing liquid containers.
In a preferred embodiment an opening in line with an
outlet end of the inlet channel is provided in a wall of the
supply chamber on the opposite side of the first membrane to the
inlet channel, an element being insertable into the opening to
press the first membrane against and thereby close the outlet end
of the inlet channel.
The element can be a pin or a remote controlled pressure
pin. Further the element can be a pneumatic tube which can be
`` ` ~09Z~67
connected to the opening and by means of which the membrane canbe pressed with pressurized air against the passage between the
supply chamber and the filter chamber.
Preferably the device includes a plurality of supply
channels with separate outlet ends and a corresponding number of
openings in the opposite wall of the supply chamber, elements
being insertable in these openings to open and close selectively
the inlet channels. This allows a corresponding number of liquid
containers to be connected to the flow control device simultane-
ously, and the containers can hold the same liquid, such that aprolonged liquid supply is possible without replacing the con-
tainers, or the containers can hold different liquids for a
mixture of the liquids to be supplied.
In the preferred embodiment a wall of the supply chamber
on the opposite side of the membrane to the passage between the
supply cha~ber and the filter chamber has an opening in line with
the passage and into which an element can be inserted to press
the first membrane into and thereby close the passage.
When the outlet openings of the inlet channels are open
and the passage between the supply chamber and the filter chamber
is closed, the supply channels form a system of communicating
vessels, which can be used for mixing or measuring amounts of
liquids. The element can be operated by hand as well as by a
remote operating system which can be simply fitted. The parti-
cular advantage is that the element does not contact the liquid,
so that no connections have to be disengaged and the sterile
liquid circuit is not penetrated. Said element can be designed
as indicated above. When a pneumatic tube is applied a pulsating
pressure can be exerted on the first membrane, such that the
membrane can work as a pump.
~ .
lO9Z~67
The control means preferably comprises a cylindrical
member rotatable about its axis and having a groove extending
around a part of its circumference, the bottom of said groove
extending along a circular arc which is eccentric with respect
to the axis of the member and the depth of the groove increasing
from O at one end to 0.5 mm at the other end thereof.
This allows a reliable and simply adjustable control of
the flow rate. The groove is preferably V-shaped in cross-section
so that in all positions of the cylindrical member the relation
between the flow area and the outline of this is as favourable as
possible. The optimum shape of the flow area would be a circle,
but an approximation to this is a triangle, preferably with an
angle of 90.
Nearly all known control devices have an elongated or
circular flow control slot. When the flow area is e.g. 0.1 mm2,
the opening of the slot is so small 10.01 mm or less) that solid
particules in the liquid will lead to partial clogging of the
slot and the flow rate is upset.
An advantage of the preferred embodiment of this inven-
tion is that the passage for solid components is at least 10
times larger than in other constructions.
In a transverse plane the groove is semi-circular, the
centre of it being eccentric with respect to the axis of the
cylindrical member. Experimentally it is established that the
flow resistance changes exponentially with the rotation of the
cylindrical member by which a very accurate control at low flow
rates is possible.
Certain regulations require flow control devices to
allow a certain quantity of liquid to flow through per unit of
time (see e.g. British Standard 2463; 1962, paragraph 33). To
-- 8 --
., ~ ,.
~. , -;,
`` lO9Z~67
meet this requirement it is preferred that the cylindrical
member near the end of said groove be provided with a further
groove having a flow area which is at least equal.to that of the
by-pass channel.
A flow control device embodying the invention is des-
cribed in detail below, by way of example, with reference to the
accompanying drawings, in which:
Figure 1 shows a front elevation of the device;
. Figure 2 shows a back elevation of the device with
the filter chamber cover removed and the filter only partially
shown;
Figure 3 is a section taken on the line III-III in
Figure l;
. Figure 4 is a section taken on the line IV-IV in
Figure l;
- Figure 5 is an end view of the flow rate control device.
. The device shown in the drawings consists of two
generally rectangular^parts (with dimensions in the range of
2.5 x 5 cm), namely a casing 1 and a cover plate 2, between which
a rubber film 3 with a thickness of 0.30 mm is disposed. The
casing I and the cover plate 2 are clamped together by means of
screws 4 which pass through openings in the rubber film which
seals between the edges 5 of the casing and the cover and forms
two membranes 6 and 7.
. The casing 1 has three supply channels 8 having outlet
openings 9 connected with a supply chamber 10 and a filter chamber
11. A filter element 12 is installed in the chamber 11 which is
closed by a removable filter cover 13, which allows the filter
element to be readily renewed or replaced.
8etween the supply chamber 10 and the filter chamber 11
_ g _
`` lO~Z467
is a passage 14, with a protruding rim 15 and a passage 16
connects an outlet chamber 17 to the filter chamber 11.
The cover plate 2 is provided with openings 18 lying
opposite the outlet openings 9 of the supply channels 8. In each
of these openings an element such as a pin 19 can be inserted to
close the related outlet opening 9 partially or completely by
pressing the membrane 6 into the outlet opening 9, for example
into the position a in which case the outlet opening 9 is
completely closed. The cover plate 2 also has an opening 20
lying opposite the passage 14 between -the supply chamber 10 and
- the filter chamber 11 and into which an element can be inserted
also to press the membrane 6 into the position a to close
completely the passage 14. In a rest position b the membrane
6 lies against the edge 15 under some tension and when liquid
under pressure (about 10-15 cm water column) is supplied through
a supply channel 8 the membrane 6 is moved into position c.
Liquid can then flow through the passage 14 into the filter
chamber 11 as indicated by arrow 21, along channels formed by
ribs lla through the filter 12 as indicated by arrows 22 into the
grooves formed by ribs 23 on the filter cover 13 and into a
groove 27 into which two passages 16 and 28 open.
The outlet chamber 17 contains the membrane 7 which at
rest lies in the position 25 indicated by a chain dotted line and
which divides the outlet chamber into closed part 17a and a part
17b to which an outlet channel 30 is connected.
As indicated in Figure 4 the groove 27 is connected to
the part 17a of the chamber 17 by the passage 16 and to the part
17b of chamber 17 by the passage 28, an opening 26 in the rubber
film, and a by-pass channel 31a, 31b.
Around the outlet opening 30 a rim 31 is formed. When
-- 10 --
~.~
. .
`` lO9Z467
the pressure of the liquid flowing out of the filter chamber is
higher than the pressure in the outlet channel 30 the membrane
7 moves towards the rim 31 and the membrane 7 closes the channel
30 partially or completely.
A control arrangement 29 divides the by-pass channel
into two parts 31a and 31b defined in a casing 32 in which a
cylindrical pin 33 is sealingly located. The pin 33 has a groove
34 which groove extends over a part of the circumference in a
- plane perpendicular to the pin axis, and the bottom of the groove
describes a circular arc with its centre 35 lying eccentric with
respect to the centre 36-of the circular section of the pin 33.
The cross section of the groove is triangular preferably with an
- apex angle of 90. A further groove 37 is provided in the pin
and is connected to the groove 34 at its deeper end.
Liquid flowing out of the filter chamber as indicated
by arrow 24, divides into two portions (arrows 38 and 39). One
portion tarrow 38) flows to the outlet channel 30 (arrows 40) and
the other portion (arrow 39) exerts a pressure on the side of the
membrane 7 remote from the outlet channel 30.
The groove 37 ensures that a certain quantity of liquid
will flow through per unit of time as is required by British
Standards 2463; 1962 paragraph 33. A similar requirement applies
in various other countries also.
The adjustment of the groove 34 with respect to the bv-
pass channel part 31_ is achieved by means of a lever 41 attached
to the pin 33 and rotatable as indicated by the arrow 42. This
adjustment alters the liquid flow rate through the device.
One or more channels 8 are connected to liquid con-
tainers by means of flexible tubes. The outlet channel 30 is
connected to a further flexible tube, the other end-of which is
- -- 11 --
.. ^~ .~
1092~67
provided with a hollow needle or canula which can be introduced
into the vein of a person to which the liquid is to be adminis-
tered. In this further tube a drip chamber is interposed.
The liquid flowing to the supply channel 8 displaces
the membrane 6 from the position b to the position c if the
pressure is sufficient. Then the liquid flows via the passage
14 according to the arrows 21, 22 and 24 to the groove 27 and is
divided there as indicated by the arrows 38 and 39. The liquid
flowing according to the arrow 38 enters the first part 31a of
the by-pass channel 31, the desired through flow quantity being
adjusted by positioning the groove 34 and subsequently flows to
the outlet channel 30 as indicated by the arrows 40. The liquid
diverted according to the arrow 39 exerts a pressure on the
membrane 7 by which the membrane 7 is moved towards the rim 31.
As a result the pressure drop across the partially closed opening
of channel 30 is controlled and the pressure drop across the
control arrangement 29 is kept constant so that the liquid flow
rate remains constant. If before it is used the device is sterile,
during its use those parts through which the liquid flows or is
present remains sterile because the device remains completely
sealed.
It will be clear that the flow control device is
completely automatic. If the liquid pressure in the container
becomes too low, the membrane 6 will engage the edge 15 and the
supply of liquid is interrupted. The liquid flow rate is ad-
justed by the flow control arrangement and is automatically
maintained constant by the membrane 7.
A number of containers containing liquid to be admini-
stered can be connected to the device. When the containers
contain the same liquid administration to the patent can take
- 12 -
`` lO9Z~67
place for a long period without interruption. When the con-
tainers are filled with different liquids to be administered as
a mixture to the patient, it is possible to do this by hand by
adjusting the pins 19 or e.g. by means of a device which operates
according to a fixed system which can be remote controlled. The
latter might be automatically carried out in a simple way
according to a fixed programme.
The described device can be used in other fields
besides administering liquids to patients. Indeed, it could be
used in any application where small quantities of a liquid have
to be dispensed at fixed rates, such as e.g. in chemical processes,
preparing of drinking water, etc.
The described control device can achieve the following
advantages when used in a transfusion or infusion set:-
a) Saving in labour of nursing staff, particularly
since the time between the replacement of the liquid containers
can be 200% that in the case of known devices;
b) Improved safety, due to a better controlled ad-
ministration of medicaments added to the liquid;
c) Augmentation of the technical possibilities in case
of intravenous therapy with retention of the condition that an
administration system can be used which is used only once. The
action of the connection of a remote control system is limited
to putting in pin-shaped elements in the above mentioned openings
in that side of the supply chamber of the flow control device
which is turned away from the filter. The possibility of in-
dependent control of the liquid connections in combination with
a constant liquid flow rate makes it possible to compose in-process
a mixture of a number of liquids or liquid-compositions. This
takes place by controlling each of the connections in cyclic
- 13 -
~ .
~092~67
sequence on different points of time and during short periods.
By this every mixture ratio can be obtained. The mixture ratio
can be constant or variable (by means of a programme). A feed-
back system to the patient is also conceivable - from a technical
point of view.
- 14 -
.~,
