Note: Descriptions are shown in the official language in which they were submitted.
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Technical Field
This invention relates to the art of elimination of air
or other gasses from physiological f luids.
Background Art
When administering physiological fluids to a patient,
it is desirable to remove excess air or other gasses prior
to introduction of the fluids into the patient.
Devices are known which eliminate gasses from fluids to
be applied to a patient. For example, U.S. Patent 4,190,426
~Ruschke) teaches a gas separating and venting filter
; wherein gas is removed from a fluid by a liguid-wetting
(hydrophilic) membrane which divides the device into inlet
and outlet chambers. The inlet chamber includes a liquid-
repellent (hydrophobic) membrane which passes gas removed by
lS ~ the liquid-wetting filter to the atmosphere~
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U.S. Patents 4,413,990 (Mittleman) and~ 4,571,244
(Knighton) teach devices which also rely upon li~uid-wetting
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filters t~o remove gasses. In the Mittleman devicej a
membrane valve is placed at the bottom of a burette for
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removing gasses. The Knighton apparatus includes a
horizontally disposed cylinder having a liquid-wetting
filter at one end and a liquid-repellent filter at an
opposite end. The fluid to be treated is introduced at a
mid-point of the cylinder.
U.S. Patent 4,572,724 (Rosenberg et al.) teaches a
blood filter for use in a cardiopulmonary by-pass system.
An upper chamber is arranged to receive blood and cause it
to flow in a circular direction whereby air is separated by
the centrifugal forces on the blood. Air bubbles above a
predetermined size which were not removed in the first
chamber are removed by a cylindrical filter made of a
pleated screen.
Summary of the Invention
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15 `~ Air elimination devices which rely upon a hydrophylic
filter for removal of air are generally not useful for
treatment of blood because the filters have pore sizes which
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on a hydrophylic filter, such as the one shown by Rosenberg,
are ~uite complicated and are expensive to manufacture.
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In accordance with the invention, a simple, inexpensive
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phenomena to efficlently eliminate air or other gasses from
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a physiological fluid being administered to a patient. The
device is useful for a wide variety of physiological fluids,
including blood. One preferred use for the air elimination
device of the invention is in series with an apparatus which
heats blood being administered to a patient, the air
elimination device removing gasses which normally accompany
the heating process.
The eliminator of the invention includes a vertically-
oriented column configured to provide a downward flow
velocity for a fluid which is less than the rate at which a
bubble of gas to be removed will rise through the fluid.
The bubbles form and rise through the fluid to the top of a
velocity-reducing plenum, and a liguid-repellent membrane
covers the upper end of the plenum. Air bubbles collect on
the lower surface of the liquid-repellent membrane, and the
air then passes through the membrane into the atmosphere.
In a preferred embodiment, a one-way valve is placed
above the membrane to exhaust gas which has passed through
the membrane to the atmosphere while preventing the flow of
gas in a reverse direction. The one-way valve is a safety
measure and is not reguired if the patient is necessarily
located e-ther above or level with the gas-eliminating
G~.ice.
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Because the elimination device of the invention relies
upon natural forces to remove gas from the fluid, a
liquid-wetting filter as used in the prior art is not
required, and the device may be used with a wide variety of
fluids including blood. If it is desired to ensure that
particulates are removed, a filter screen may be placed in
the flow, but this is not necessary in many instances.
The inlet, outlet, and plenum are configured so that
for a pre-determined pressure difference, the flow rate of
the li~uid in the plenum will be reduced to a rate at which
gas bubbles will form and rise to the top of the plenum
through buoyancy forces.
As will be appreciated from the description below, the
invention is orientation sensitive, and in a preferred
embodiment, the gas-elimination device is in combination
with a support stand which provides a bracket engaging the
air-elimination device in such a manner that it is
necessarily in the proper orientation. The stand may also
. provide supports for the containers of physiological fluids
to produce a desired pressure head.
An object of this invention is to provide a device for
eliminating gas from a fluid, where~y bubbles which are
introduced with the fluid or form naturally in the fluid
rise to th~ top of a plenum.
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Another object of this invention is to provide an
arrangement for eliminating gas from a fluid whereby an air
elimination apparatus is held by a support stand in a
pre-determined orientation.
Brief Description of the Drawings
Figure 1 is a side view of the apparatus of the
invention shown in use with a patient.
Figure 2 is longitudinal cross-section of an
air-elimination device shown in use in Figure 1.
~etailed Description of the Invention
With reference to Figure 1, a preferred embodiment of
the invention is illustrated. An air-elimination device 2
is attached to a support 4 by a bracket 6. As will be
described below, bracket 6 cooperates with the air
eliminator 2 to maintain the air eliminator in a vertical
orlentation. A T-shaped hanger 8 is mounted to support 4 by
a clamp 10. Hanger 8 provides support ~or fluid holding
bags 12 which are in turn connected to air elimination
; device 2 by an lnlet tube 14. The outlet of air elimination
device 2 is connected to a patient 18 by a tube 16.
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Patient 18 is schematically shown resting on a platform
20 which is at a height approximately equal to that of a
normal hospital bed.
For proper operation of the air eliminator 2, the fluid
bags 12 must be higher than a hydro~hobic filter (see Figure
2) located at the upper end of gas eliminator 2. This
provides a fluid pressure head to be exerted on the
hydrophobic filter to cause gas which has separated from the
fluid to pass to the atmosphere. The height at which bags
12 are held by hanger 8 provides a desired pressure head by
the force of gravity alone. If a bag squeezing device of
any type known in the art, for increasing the flow rate of
the fluid, were used, air would pass through the hydrophobic
filter even faster. The height of bracket 6 is such that
the outlet from the gas eliminator is either level with or
below patient 18 whereby no significant negative pressure is
created within the gas eliminator 2, which would cause gas
to flow through the hydrophobic filter from the atmosphere
into the gas eliminator.
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In a preferred embodiment, the gas eliminator outlet is
a maximum of 36 inches above the floor. The hanger 8
supports fluid holding bags 12 at a height normally employed
to provide a flow of fluid through the force of gravity into
patient 18, and this is sufficient to force removed gas
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outwardly through the hydrophobic membrane of the preferred
emb~diment.
With reference to Figure 2, a longitudinal cross
section of the gas eliminator 2 is shown.
A plenum 22 has a fluid inlet 24 and a fluid outlet 26.
In the embodiment shown, plenum 22 comprises a cylndrical
tube 28 closed by end caps 30 and 32 which are cemented to
the tube. These elements may be molded into a single piece
if desired.
As fluid flows through tube 14 into plenum 22, gas
bubbles 34 will form and naturally separate from the fluid.
Generally, the cross-sectional dimensions of plenum 22 are
larger than those of the fluid outlet 26 whereby the
downward vertical velocity of the fluid through plenum 22 is
less than the upward velocity of the air bubbles rising to
the surface. In a preferred embodiment tube 28 has an
inside diameter of from 0.510 to 0.490 in. with 0.500 being
preferred. The diameter of aperture 2~ of inlet 24 and
aperture 27 of outlet 26 is 0.155 in.
The distance between the inlet and outlet is large
enough that bubbles cannot flow directly from the inlet to
the outlet, and is preferably larger than 4 inches. In a
~; preferred embodiment, that dimension is 5 to 5-1/2 inches.
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The top of plenum 22 is eovered by a membrane 36 which
is held in a ring 38. Membrane 36 is preferably made of
expanded polytetrafluoroethylene (PTFE) whlch is
microporous. The pores are preferably from .2 rnicron to 1.2
microns, and the membrane is laminated to a web of
spun-bonded polyester or polypropylene to retain
permeability while providing tensile strength.
The surface area and permeability of the membrane must
be such that sufficient gas will be vented at pressures less
than the pressure required to drive the column of liquid in
plenum 22 downwardly to outlet 26.
In a preferred embodiment, a one-way valve 40 is
secured to the upper end of air eliminator 2. This valve
includes an upper wall 42 with holes 44 therein, for
allowing gas which has passed membrane 36 to escape to the
atmosphere. A flexible umbrella value 46 is attached to
upper wall 42 by a stem 48 and is flexible to allow gas from
the plenum to escape through holes 44 but to ~revent gas
from flowing through holes 44 toward membrane 36.
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One-way valve 40 is a safety measure to prevent gas
from flowing lnto plenum 22 through membrane 36, which would
happen if patient 18 were too low. For example, if patient
18 were below the gas eliminator 2, a negative pressure
: could develop in plenum 22, which would tend to draw gas
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into plenum 22 through membrane 36 in the absence of one-way
valve 40. In those instances where it is assured that the
relative elevations of patient 18 and gas eliminator 2 will
be proper, one-way valve 40 may be eliminated.
A particulate filter 50 may be placed in plenum 22 to
remove particles from the fluid. This filter plays no role
in gas elimination and is preferably made of nylon or
polyester screen.
A cavity 52 at the bottom of air eliminator 2 may be
provided for receiving a projection (not shown~ on bracket
6. Cooperation of bracket 6 and cavity 52 supports the air
eliminator 2 and maintains it in a vertical orientation for
proper operation of the device. Other means for orienting
and supporting gas eliminator 2 will be apparent to those of
skill in the art. For example, a U-shaped bracket may be
used to engage a mid-portion of plenum 22.
In operation, gas eliminator 2 is installed as shown in
Figure 1. As the fluid enters the gas eliminator, it begins
a downward flow with a reduced velocity. The maximum
downward flow rate of the fluid is designed to be less than
the upward velocity of the bubbles so that bubbles rise to
the uppermost part of the plenum. The bubbles 35 accumulate
on the lower surface of membrane ~6, which tends to protect
membrane 36 and prevent it from being clogged with cellular
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materials. The pressure required to vent the air bubbles
through the hydrophobic membrane 36 is less than the
pressure driving the column of fluid downwardly, and gas
passes through the membrane to the atmosphere.
Modifications of the preferred embodiment within the
scope of the following claims will be apparent to those of
skill in the art.
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