Note: Descriptions are shown in the official language in which they were submitted.
~ O9S/06506 2 1 6 7 9 3 2 PCT~S94/09118
GAS-SEPARATING FIL~ER
Field Of The Invention
This invention relates generally to filter
S devices and, more particularly, to an intravenous gas-
separating filter device employing a hydrophobic
membrane which is configured for use such that
substantially all gas is separated and vented at the
hydrophobic membrane. This device can include a
hydrophilic membrane for particulate filtering and
redundancy of the gas-separating function.
B~ckqround Of The Invention
When fluids, such as blood, plasma, or other
solutions, are introduced into the body intravenously,
it is important to remove any gas or air suspended in
the fluid and thereby eliminate any risk of an embolism
from gas or air reaching the patient. The removal of
such gas or air from the fluid is typically accomplished
by use of a gas-separating filter.
The typical features of intravenous gas-
separating filters include an inlet chamber and an
outlet chamber separated by a hydrophilic membrane. The
hydrophilic membrane permits the passage of li-quid and
prevents the passage of gas. Thus, liquid passes
through the hydrophilic membrane from the inlet chamber
to the outlet chamber while gas is retained in the inlet
chamber and vented to atmosphere.
In some constructions, a hydrophobic membrane
30 is employed in connection with a vent in the inlet
chamber in order to vent the gas which collects in the
illlet chamber. See for example U.S. Patent Nos.
4,906,260, 4,190,426, and 3,854,907.
It is desirable to configure an intravenous
gas-separating filter device so that it will start up
wog5/~soc PCT~S94/09118
2~67932 ~
(conventionally referred to as "priming") and function
in any orientation relative to the ground. A relatively
low internal volume device having an inlet chamber with
a minimal volume is preferable in order to minimize the
amount of air that must be initially vented from the
inlet chamber. In use, a low internal volume filter can
be quickly primed and initially vented.
In the prior art, gas-separating filter
devices are dependent upon the integrity of the
hydrophilic membrane separating the inlet chamber from
the outlet chamber. A disintegration or absence of the
hydrophilic membrane in prior art filters would cause
them to malfunction. It would be desirable to construct
a filter that would continue to filter air or gas from
the li~uid in the event of disintegration or absence of
the hydrophilic membrane. It would be desirable to
separate gas and air from liquid in the inlet chamber
prior to its p~CcAge through the hydrophilic membrane,
thereby desirably providing a redundant filtering action
for consistent and reliable operation.
SummarY Of The Invention
The gas-separating filter device in accordance
with the present invention is configured for highly
reliable and consistent filtering of gas and air.
Significantly, this is achieved by providing a
hydrophobic membrane in operative association with a
vent opening, with control of liquid flow cooperating
with the venting arrangement to substantially completely
effect filtering and venting of all gas through the vent
opening. While it is presently prefexred that the
present filter also be provided with a hydrophilic
membrane to facilitate particulate filtering, it is
specifically contemplated that gas separation be
~W095/O~C 2 1 6 7 9 3 2 PCT~Ss4/09118
ubstantially completely effected without reliance upon
- the hydrophilic membrane.
The filter device in accor~lA~ce with the
illustrated embodiment of the invention includes a
filter housing having a cover portion and a base portion
in confronting relationship with each other. A
hydrophilic filter membrane is interposed between the
cover and base portions of said housing and thereby
defines an inlet chamber and an outlet chamber. An
inlet port is joined in fluid flow communication with
the inlet chamber. An outlet port is joined in fluid
flow communication with the outlet chamber.
A first vent opening communicates with the
inlet chamber upstream of the hydrophilic filter
membrane for venting gas from liquid passing through the
filter assembly. A hydrophobic filter membrane is
positioned adjacent to said vent opening for preventing
liquid from flowing through the vent opening while
permitting gas flow therethrough so that gas is
separated from liguid flow.
A second vent opening cor~-lnicates with the
inlet chamber substantially adjacent the hydrophilic
membrane downstream of the first vent opening. A second
hydrophobic filter membrane is adjacent the second vent
opening for permitting flow of gas (but not liquid)
therethrough and thereby initially venting air from the
inlet chamber during initial flow of liquid into the
filter assembly.
The separation of gas from liquid flowing
adjacent the first vent opening is promoted by a
relatively narrow liquid flow region adjacent the first
vent opening. A weir element may optionally be employed
to define the narrow liquid flow region.
In an alternative aspect of the invention, at
least one stand-off projection on the exterior of the
W095~50C 2 1 6 7 9 3 2 PCT~S94losll8 ~
housing is positioned in proximity to the vent openings
to inhibit exterior blockage of the openings.
Preferably, a pair of stand-off projections are
positioned in flanking relationship to the vent
openings.
In a preferred embodiment, the filter assembly
is substantially disc-shaped. Inlet and outlet ports
are diametrically opposed on opposite ends of the
housing. The first and second vent openings are
generally aligned with the inlet and outlet ports. The
stand-off projections are generally aligned with the
inlet and outlet ports in flanking relationship to the
vent op~n;ngs. The hydrophilic filter membrane is D-
shaped.
lS In another aspect of the invention, the filter
assembly has a separation chamber having a vent opening
wherein the back pressure in the filter combined with
the narrow flow region in the separation chamber and a
sufficient residence time within the chamber cause all
gas in the fluid/gas mixture to pass through the vent
opening.
Other features and advantages of the present
invention will become readily apparent from the
following detailed description, the accompanying
drawings, and the appended claims.
Brief DescriPtion Of The Drawing~
FIG. l is a perspective view of a intravenous
gas-separating filter device in ac_ordance with ~he
invention;
FIG. 2 is an exploded perspective view of the
filter device shown in FIG. l;
FIG. 3 is a cross-sectional view taken along
the line 3-3 in FIG. l;
~W095/06S06 2 1 6 7 9 3 2 PCT~S94/09118
FIG. 4 is a cross-sectional view taken along
the line 4-4 in FIG. l;
FIG. 5 is a cross-sectional elevational view
of a model filter device in accordance with the
invention;
FIG. 6 is a cross-sectional view taken along
the line 6-6 in FIG. 5;
FIG 7. is a model filter device as shown in
FIG. 5 wherein a gas film is venting; and
FIG. 8 is a model filter device as shown in
FIG. 5 wherein a gas bubble is venting.
~eta~le~ De~cri~tion Of The Invention
The following is a detailed description of the
invention. The detailed description is not intended to
be an exhaustive description of all embodiments within
the scope of the invention and is not intended to limit
the scope of the claims to the disclosed embodiments.
Other embodiments within the scope of the claims will be
apparent to those skilled in the art.
Referring to FIGS. l and 2, the gas-separating
filter assembly l0 in accordance with the invention
includes a filter housing 12 comprising a cover portion
14 and a base portion 16 which are fitted together in
confronting relationship with èach other. Preferably,
the cover and base portions are constructed from a
rigid, clear plastic material such as an acrylic
polymer. However, any rigid transparent material
suitable for medical use can be used.
A hydrophilic filter membrane 18 is interposed
between the cover 14 and base 16 portions. Preferably,
the hydrophilic filter membrane is a polycell foam
material such as Supor material sold by Gelman Sciences,
Inc. of Ann Arbor, Michigan. However, any hydrophilic
membrane material permitting passage of liquid and
W095~0~50C 2 1 6 7 9 3 2 PCT~S94/o9118 ~
preventing passage of gas suitable for medical use can
be used. In a preferred embodiment, the hydrophilic
filter membrane 18 is generally D-shaped, as shown in
FIG. 2.
Referring to FIG. 3, the hydrophilic filter
membrane 18 is secured to the base portion 16. The
filter membrane 18 may be heat sealed to the base
portion 16 or with an adhesive suitable for medical use.
The hydrophilic filter membrane 18 divides the housing
12 into an inlet chamber 20 and an outlet chamber 22.
Referring to FIG. 4, a plurality of upstAn~ing
ribs 23 extend upwardly from the base portion 16 to
~upport the hydrophilic filter membrane 18. A plurality
of grooves 25 are defined between the ribs 25 to receive
fluid in the outlet chamber 22 and direct it to an
outlet port 26 (FIGS. 2 and 3).
Referring to FIG. 3, an inlet port 24 is
defined on one end of the base portion 16. The inlet
- port 24 is joined in fluid communication with the inlet
chamber 20. An outlet port 26 is defined at the
opposite end of the base portion 16. The outlet port 26
is joined in fluid communication with the grooves 25 of
the outlet chamber 22. Thus, the inlet 24 and outlet 26
ports accommodate the flow of liquid through the filter
assembly 10 from the inlet port 24 to the outlet port
26.
In a current embodiment, the disc-shaped
filter housing is approximately 1-5/16 inches in
diameter and 5/32 inches thick. The inner diameter of
the inlet port is approximately 1/8 inches and the inner
diameter of the outlet port is approximately 3/32
inches. The inlet and outlet ports may be configured to
fit as luer fittings (not illustrated) or tube fittings.
A first vent opening 28 is defined in the
cover portion 14 adjacent the inlet port 24 (FIG. 3).
~WO9S/06S06 2 1 6 7 9 ~ ~ PCT~S94/09118
In a current embodiment, the first vent opening 28 is
provided with a diameter of 0.051 inches, with a 5
degree taper, as shown. The first vent opening 28
communicates with the inlet chamber 20 at a location
that is upstream of the hydrophilic filter membrane 18.
Liquid entering the inlet chamber 20 passes by the first
vent opening 28 before it flows to the hydrophilic
filter membrane 18.
A first hydrophobic filter membrane 30 is
positioned adjacent the first vent opening 28 (FIG. 3).
Preferably, the first hydrophobic membrane 30 is one
manufactured from Teflon~ fibers. However, any
hydrophobic membrane material that permits the passage
of gas and prevents the passage of liquid and is
suitable for medical use can be used. The first
hydrophobic filter membrane 30 is secured to the cover
portion 14 by heat sealing the components or with an
adhesive suitable for medical use.
The first hydrophobic filter membrane 30
permits the passage of gas therethrough out of the inlet
chamber 20 through the first vent opening 28. Thus, gas
is separated from liquid flow at the first vent opening
2~ prior to flow of the liquid to the hydrophilic filter
membrane 18.
In a preferred embodiment, referring to FIG.
3, the inlet chamber 20 defines a relatively narrow
liquid flow region 32 adjacent the first vent opening
28. A narrow liquid flow region causes any gas or air
entrapped in the liquid flow to pass adjacent the first
hydrophobic membrane 30 and through said first vent
opening 28. The depth of the liquid flow region 32 may
be in the range of about 0.015 inches to about 0.060
inches and preferably is about 0.045 inches.
In an alternative embodiment, the narrow
liquid flow region 32 may be defined in part by an
woss/06so6 2 1 6 7 9 3 2 PCT~S94/09118 ~
upst~n~;ng weir 34 element (shown in phantom lines in
FIG. 3).
A second vent opening 3~ is defined in the
cover portion 14 adjacent the hydrophilic filter
membrane 18. Preferably, the vent opening 36 also has a
diameter on the order of 0.05l inçhes~ with a 5 degree
taper. A second hydrophobic filter membrane 38 is
secured, for example heat-sealed, to the cover portion
14 and extends across said second vent opening 36 for
permitting passage of gas and preventing passage of
liquid therethrough.
The second vent opening 36 permits the quick
evacuation of air in the inlet chamber 20 during the
initial introduction of fluid into the filter assembly
lO. Preferably, the second vent opening 36 i5
positioned in the inlet chamber 20 at an end opposite
the location of the first vent opening 28.
Stand-off projections 40 are located on the
exterior of the cover portion 14 in flanking
relationship to the vent openings 28 and 36. The stand-
off projections 40 inhibit exterior blockage of the vent
openings 28 and 36 when the filter assembly lO is placed
adjacent the skin of the patient or another surface
which may potentially cover or block the vent openings
2S 28 and 36.
The construction of the housing 12 and the
outlet port 26, an external or internal restrictor or a
valve can create a back pressure within the filter
assembly lO. Preferably, the back pressure is in the
range of 5-15 psig or, more preferably, lO-ll psig.
Preferably the resulting flow rate is in the range of
O.l cc/hour to 400 cc/hour thus creating sufficient
residence time within the filter assembly lO to
substantially separate all gas from the liquid and pass
the gas through the first vent opening 28. Concomitant
WO9S/06506 2 1 6 7 9 3 2 pcT~s94losllg
.
with the back pressure in the filter, the required vent
pressure in the vent membrane is adjusted to provide
ready venting. This adjustment is made by controlling
the porosity of the vent membrane to contain the fluid
and vent the air by back pressure. In some cases, a
bacteria barrier is also effected. In a preferred
embodiment, the porosity is. 45 microns.
In operation, the filter assembly 10 is
co~ected to an intravenous solution supply at the inlet
port 24. An intravenous catheter device (not
illustrated) is connected to the outlet port 26. Liquid
flows into the inlet port 24 and through the filter
device 10. The filter device 10 is self-priming and
functional in any orientation. When liquid initially
flows into the filter assembly 10, air is purged from
the inlet chamber 20 through the first and second vent
openings 28 and 36. As liquid enters the inlet chamber
20, it passes adjacent the first hydrophobic member 30
adjacent the first vent opening 28. The combination of
a sufficient back pressure, residence time and narrow
fluid flow region 32 adjacent the first vent opening 28
forces all gas or air entrapped in the fluid to pass
through the first hydrophobic member 30 and out of the
first vent opening 28. Thus, the hydrophilic membrane
18 acts as a re~lln~Ant filter means providing a back-up
filtering function within the filter assembly.
The principle of the invention is described
below quantitatively with reference to a model filter as
illustrated in FIG. 5-8.
Referring to FIGS. 5 and 6, the model filter
100 has a separation chamber 103 having rectangular
cross-section of length L, height H and width W. The
fluid retentive membrane at vent 102 permits venting of
gas while retaining fluid at a given back pressure P~.
A fluid/gas mixture flows from right to left through the
woss/o65o6 2 1 6 7 9 3 2 PCT~S94/09118 ~
-- 10 --
separation chamber 103. A gas element 104 is shown
entering the separation chamber 103 at the bottom of the
separation chamber 103.
The following notation for various parameters
is used in the model and indicated in FIGS. 5-8:
Q~ = volumetric flow rate of gas through
the vent 102
V~ = velocity of gas through vent
QF/~ = volumetric flow rate of liquid/gas
mixture through the filter 100
V~ = velocity of gas normal to liquid/gas
flow and toward vent membrane 102
P~ = back pressure
¢m = a constant characterizing the vent
membrane
T1 = time for the gas element 104 to
travel to and through vent member
102
T2 ~ time for the liquid/gas mixture to
travel through the separation
chamber 103
For complete venting of gas from the
separation chamber 103, the time T, for the gas element
104 to travel to and through the vent membrane 102 must
be less than the time T2 for the gas/liguid mixture to
travel through the separation chamber 103. The gas can
vent as a film exten~ing across the height H of the
chamber 103 or as a bubble, as discussed below.
A gas film 106 exte~;ng across the height H
of the chamber 103 is illustrated in FIG. 7. In such
case,V~ = V~.
Fo~ any filter member characterized by a
constant ¢~, the following holds true:
~ogs~ oc 2 1 6 7 9 3 2 PCT/USg4/09118
-- 11 --
Q~ - ¢, (Area) (Pressure Differential)
- or
Q~ = ¢~ WL P~
vTherefore,
V~ = Q~ = ~ P~
WL
and the time Tl for the gas element 104 of the film 106
in FIG. 7 to travel across the separation chamber 103
and through the vent 102 is as follows:
T1 = H = H = H
VG~ VGV ¢m P~
The time T2 for the liguid/gas mixture to
travel through the separation chamber 103 is a function
of Vr~G and L. Therefore,
T2 = L = L = LHW
Vr/G QF/C QF/G
HW
Since Tl must be less than T2, then
H < LHW or 1 ~ _LW
¢~ PB QF/G ¢In PB QF/G
This is the relationship between parameters for film
venting of a filter device in accordance with the
invention.
Referring to FIG. 8 for the case of bubble
venting, V~ depends upon where the bubble 108 is
located. When it is against the vent 102, V~ = Vw as
in the case of film venting discussed above.
When the bubble 108 is in the fluid and spaced
from the vent 102, it has a V~ denoted V~. V~ is
determined by turbulence, fluid deflection, natural
migration of gas toward the vent, and orientation with
respect to gravity. The bubble 108 must travel a
distance H-D at a velocity Vp in order to reach the vent
- 102 and then travel through the vent 102 a distance D in
order to pass from the separation chamber 103 through
the vent 102. Therefore, the time Tl for the bubble to
travel to and through the vent member 102 is as follows:
WOsS/o6so6 2 1 6 7 9 3 2 PCT~S94/09118 ~
- 12 -
Tl = H-D + D = H-D + D
V~3 VGV VB ¢~, PB
Tl must be less than T2 as discussed above.
T2 = LHW . Since Tl < T2, then
QF/G
H--D + D < HW
V8 ¢~ P~ QF/G
This is the relationship between parameters for bubble
venting of a filter device in accordance with the
invention.
Note that when H = D , then film venting
occurs and the above relationship between parameters for
bubble venting reduces to the relationship between
parameters for film venting, i.e. 1 < LW .
¢m PB QF/G
The velocity VB f the bubble can be increased
by directing flow of fluid/gas mixture against the vent
102 with ramps, weirs, etc. VB can be optimized
empirically.
Better venting can be achieved by increasing
T2 relative to Tl. This can be achieved by reducing H
or QF/G~ and/or increasing V~, ¢m~ P~ L or W.
Film venting is not sensitive to orientation
relative to gravity and is easier to control than bubble
venting.
In an anticipated embodiment of a filter in
accordance with the invention, a saline solution is the
anticipated fluid in a filter having the following
parameters:
H = .031 inches
¢~ = .55 Free L
min-cm2-Psi = lg.6 x 103 CC at 10 Psi
Hr-cm2
P~ = lO Psig
Q~/G = 500 cc/hr
L = .2 inches = .508 cm
W = .1 inches = .254 cm
~W095t06S06 ~l 6 ~ 9 ~ ~ PCT~S94/09118
Thus, for film venting,
T~ 5.1 x 10-6 Hr
C:~ PB
and
T2 = LW 2 2.6 x 10-~ Hr
Q./c
T, is less than T2, which should vent, and has been
tested to do 80.
For bubble venting, controlling the parameters
to fall within the ranges shown below is the anticipated
construction for filters for medical use and should
provide complete venting:
H: .010-0.50 inches
W: 0.20-l.00 inches
L: 0.1-6.00 ;nches
Pn: 2-20 Psig
¢m 1-52 Free liters
min-cm2 -10 Psi
D: .001-.050 inches
QF/G . 1 1000 cc/hr
VH: 0-4 . 4 X 105 cm/min
The filter of the present invention can be
used in a variety of medical applications where fluids
are a~ini~tered, as for example, in the intravenous
A~;n;~tration of blood, plasma, drugs or saline.
From the foregoing, it will be observed that
numerous modifications and variations can be effected
without departing from the true spirit and scope of the
n~vel concept of the present invention. It is to be
understood that no limitation with respect to the
specific embodiment is intended or should be inferred.
The disclosure is inten~e~ to cover by the appended
claims all such modifications as fall within the scope
o the claims.
