Note: Descriptions are shown in the official language in which they were submitted.
WO 92/U3176 PC~I/CB91//11450
~ ~ ~ V 2 2 3
PRESSURE CONTROL DEVICE FOR ENDOTRACHEAL TUBE CUFF
BACKGROUND TO THE INVENTION
This invention relates to pressure control. It is particularly
concerned with the control of pressure within cu~fed endotrache~ tube
systems, and more particularly to a simple apparatus for the
maintenance of a constant pressure difference between the pressure
inside the cuff of an endotracheal tube and the airway pressure, that is
the pressure within the lumen of the endotracheal tube.
To provide for positive pressure ventilation of a patient's lungs while
administering anaesthetic gases or for intensive respirator-y care, a
tube is inserted into the trschea (re~elTed to as an endotracheal
tube). A relatively lsrge volume soft Fing-shaped hollow collapsible
bag Xnown as the "cuff" is attached to the outer surface of the
endotracheal tube at the tracheal end of the tube. In order to prevent
gas escaping past the endotracheal tube, this bag or cuff is inflated
with air so that it forms an air tight seal with the mucosal walls of
the trachea. The inflated cu~f also ser~es to anchor the tracheal tube
within the trachea below the vocal cords.
The cuff needs to be irlflated to a pressure which is greater than air~ay
pressure in order to prevent leakage of gas past the cuff. However the
methods commonly used to achieve this frequently result in much higher
cuff pressures than the peak inflation pressures used for ventilation.
Amongst other reasons for this are: quick and careless irutial o~Ter-
inflation while using a syringe for the purpose; the warming of a g~ven
volume of air injected into the cuff at room temperature up to body
temperature causing the cuff to expand; and the dif~usion into the cuff
of anaesthetic gases such as nitrous oxide.
Excessive cuff pressures may affect per~usion (the blood supply) to the
mucosal lining of the trachea causing damage, and may produce
complicstions which may include for example sloughing of the tracheal
WO 92/03176 c~ PCr/(~;B91/01~150
9~
mucosa, fistula formation, or stenosis. The higher the cuIf pressure
used the poorer the perfusion that results and the greater the Fisk of
causing permanent damage.
- A cuff system should ensure that the lowest cu~f pressures necessary
are used to achieve the desired objective, namely the sealing of the
endotracheal tube. Preferably such as system should automatically hold
the cuff pressure just above airway pressure, that is to say one which
sllows for the variation of airway pressure to be transm~tted to the
cuf f .
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PRIOR ART
A number of designs varying in comple~dty which aim to achieve this
ideal have been described. For instance the most relevant of many
applications include U. S. patent application serial numbers 4 850 349
in the name of Farahsny and 4 825 862 in the name of Sato and others.
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US ~ 850 349 (Farahany) involves a simple device not requiring an
external gas supply to power the deviee, but suffering ~ro-n the
problems related to fixed cuff ~Tolume devices mentioned earlier
induding over-inflation, diffusion of nitrous oxide into the system
and failure to compensate for small leaks. In addition the speci~ic
device will work only with a limited range of cuf~ volumes or sizes.
US 4 825 862 (Sata et al) describes a more elaborate device than
Farahany which does appear to overcome ~everal problems. However it is
more elaborate and more bulky, heavy and expensive. It also requires an
external high pressure gas source to power the device.
SUMMARY OF THE INVENTION
Accord;ng to lhe present in~ention there is provided a pres~ure
regulator powered by the gas supply source to a breathing system for the
maintenance of a constarlt or substantially constant pressure dif~erence
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between the cuff and the lumen in a cuffed elldotracheal tube du:ring
positive pressure ~Tentilation comprising a tubular connecting rneans for
attachment and interposition between thle gas supply machine and the
breathing system and means for connecf.ion to the cuff inflation port oE
an endotracheal tube, the s~id regulator compl~ising a threshold val~e
for the purpose of generating a substantially constant pressure
difference when gases supplying the b~eathing system flow through the
said valve, the pressure differenti~l created by the said threshold
valve being either fixed or adjustable, with upstream connecting means
for attachmeDt to and in open comm rucation with ~e inside of the cuff
of an endotracheal tube for the purpose of transmitting and maintaining
the said upstream pressure to the said cuff ~bove that of the ~ir~ay
pressure by a constant or substantially constant value equall to the
threshold valve ~etting; the regulator beillg provided with a one-way
relief valve allowing gas to flow in the reverse direction, to obviate
any danger associated with faulty connection.
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BRIEF DESCRIPTION OF THE DRAWINGS
Figure I schematicslly illustrates the relative positions of a system
utilising the present invention showing a cuff pressur~ regulator and
its sttachment to sn anaesthetic machine and bresthing system, and its
connection to the pilot tube of the endotracheal tube cuff.
Figure 2 schematically illustrates a longitudinal section of a
regulator forming a first exemplary emboidiment of the present
invention.
Figure 3A schematically i~lustrates a longitudinal section of a
regulator forming a second exemplary embodiment of the present
invention.
Figure 3B shows an outside view of a part of Figure 3A.
~VO 92/031,6 ~ PCI/GB9l/01450
~ 4
Figures 4 to 8 variously show components generally described in
connection with Figure 3A.
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DETAILED DESCRIPTION OF THE DRAWINGS
Figure 1 shows sn anaesthetic gases su~ply machine 10 to the outlet 16
of which is attached a cuff pressure regulator 18 of the present
invention, which is attached to pilot tube 36 of an endotracheal tube 30
by mesns of a tubular attachment site 19 and by pipe 20 to breathing
system 22. Attached to the breathing system 22 is an endotracheal tube
- 30 near tracheal end 30A of which is attached endotracheal tube cuf~ 32,
which is maintained inflated with gas, i.e. in a pressurised state, via
pilot tube 36. The breathin~ ~ystem 22 may be pressurised
intermittently to achieve positive Pirway pressure ventilaffon by a
ventilating means (in this instsnce a mechanical ventilator 38).
Figure 2 shows a first example of a pres~ure regulator ~or use in
connection with the system generally described in connection with
Figure 1 to which reference shall occasionally be made.
The cuff pressure regulator 9 has a body 9A which is attsched to outlet
16 of anaesthetic gas supply maehine 10 in Figure 1 by means of inlet
channel 13 having a sealing surface ll formillg a gas tight push fit on
to the outlet 18 in accordance with the ISO 221Dm male to female standard
fittings. Anaesthetic supply gases flow through the regulator in the
direction of arrow A. Partition 16 serves to separate upstream channel
13 from the downstream outlet channel 14. At least one channel 15
extends through the partition 1~ whereby anaesthetic gases flow through
the regulator 9. On downstream side of the partition 16 and enclosing
within its periphery any snd all channels 15 there is provided a v~ve
seating edge 17 against which bears a spring loaded val~re seat 20 to
form a gas tight seal at the seating edge 17, when in apposition, uncler
the circumstances of zero or reverse gss flow.
w{~ 92/03176 I'~r/CB91/014SO
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The regulator 9 incorporates a side port 18 providillg for open
commwucaffon with inlet (upstream) cha:nnel 13. The port 18 is
configured on its outer side to provide a tube attachment 19 for
connection to pilot tube 36 in the form of a light non-distensible
tubing This pro~ides for matching of changes in gas pressures between
inlet channel 13 and the inside of the enldotracheal tube cuff 32 (Figure
1) - '
A valve 26, comprising a firm disc shaped seat 21) with centr~l axial
stabilising rod 23 slides freely through a central and axially arranged
channel 35 of an adjusta~le threaded tube 34 held in position by means
of a compression spring 28.
Val~e seat 20 co~tsins at least one ~nnel 22 through which gases may
~: - flow in the reverse directien to the normal flow of arrow A. This would
srise if the apparatus was inadYertently connected in the opposite
direction to the design recommendation. Upstream sealing edge 21 has a
diameter which exceeds the outer border of the more centrally located
channels or perforations 22. Flexible disk shaped ~lap 25 hss a
diameter which exceeds that of the sealillg edge 21 but which is less
than the diameter of channel lS. The flap 25 is locsted on the upstream
surface of the valve seat 20 so that, should a reverse flow of gas
occur, the flexible flap 2S will open in ~n unimpeded manner. With the
proper flow of gas through the regulator in the direction of arrow A the
flap 25 prevents gas from flowing through the seat 20 but will force the
- sralve 26 to open against force of a spFing ~8 to maintain upstream
pressure higher than downstream pressure by an amount governed by the
spring 28.
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The flexible elsstomeric flap 25 has a central per~oration so that the
disc 25 may be held in position by means of a dumbbell shaped portion 24
of the spindle 26. The disc 25 is located at the upstreE~m end of the
said spindle. Normally the flexible elastomelqc disc 25 is maintained : !
in a closed position, closing off the spindle orifice 22. Should gas
flow occur in the opposite direction (under conditions of improper
connection or use) to arrow A gas can freely pass through ori~ice 22.
wo9~ 3176 ,-, 1'Cr/CI~1/01450
The spring 28 is kept under compression by being positioned between the
said spindle seat 20 and flange 33 of a clentral and axially arranged
threaded tube 30.
The threaded tube 30 comprises a smooth cylindrical portion 3~ over
which the spring slides for the purpose of maintaining the spring in a
concentric position with the central channel 35, and a threaded portion
31, screwed into a perforated support structure 40 so that th~ axial
position of threaded tube 30 may be adjusted for the purpose of altering
spring force appropristely, the position of the threaded tube 30 being
adjustable by means of screw driver placed into the slot 32 of the tube
30.
It is envisaged that in an slternative version the regulator can take an
L-shaped form with downstream channel set at an angle to both the
upstream channel and the valve seat so that tube 30 can be extended
through the side of the regulator and equipped with a knob to ensble the
spring force to be varied Yv~3ile the regulator is in use.
The fixed support structure 40 placed in the dowrlstream channel 1~4
comprises a central female threaded orifice 42 for the purpose oE
holding the threaded tube 30 in position and at least one peripherally
arranged orifice ~1 to allow the free floYv of gas in either direction.
IN USE (reEer~ing principally to Figures 1 and 2)
The regulator 9 is connected to the outlet 16 of the anaesthetic gas
supply machine 10 and the regulator 9 is attached to the ir~let of the
breathing system 24, 26 which is in turn attached to sn endotrachesl
tube 30 and with a means for ventilating, such as a mechanical
ventilator 5, for the purpose of achieving positive pressure
~rentilation. The upstream channel 13 of the regulator 9 is also
connected by means of port 18 and tube attachment site 19 to the pilot
tube 3 and so to the inside of the cu~ 2. As 8 consequence when
anaesthetic gas flow9 through the regulator into the anaesthetic
breathing system 22, a constant (OI' substanti~l1y eonstant depending on
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~' 9~/031 lo PCI/~1~91/014;0
~ 2~90223
the characteristics of the spring in use and the flow characteristics
of the regulator) pressure difference is mainta~ned between the
upstream channel 13 and the downstream channel 14 of the regulator. The
higher upstream pressure is maintained and transmitted to the
endotracheal tube cuff 32 with the downstream portion being in direct
communication with the breathing system 22 and therefore the
endotracheal tube 30 or airway pressure.
A rise in airway pressure, when positi~e pressure is generated by the
ventilator during the inspiratory phase of controlled ~Tentilation,
results in an equal rise of pressures within the regulator 9. As the
supp~y gas continues to flow across the regulator ~alve3 the pressure
differential across the regulator rem~uDs unchanged and therefore any
rise in dowIlstream pressure is transmitted to the upstream section
which in turn is transmitted by means of the appropriate flow of gas
from upstream channel 13, side port 181 pilot tube 3 and so into the
endotracheal tube euff 32. The cu~f pressure therefore is continuously
maintained above ~urway pressure by the regulator 10. A faLI in airway
pressure such as occurs during the passive expiratory phase results in
a concomitant fall in pressure in the re~ulator 9 which in turn allows
for gases which accumulated in the cuff dul~ng the inspiratory phase to
flow outwsrds, through pilot tube 3, side port 18 and into upstream
channel 13. That is to say depressurisation of the cuf~ occurs to a
pressure above a~rwsy pressure equ~1 to the opening pressure set across
the valve of the re~ulator 10.
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The quantity of gas in the endotracheal tube cuff 2 is continuously
changing to allow for the equalisation of pressures within the system
apart from the specific pressure difference set across the regulator 9.
A particular benefit arises from the simp~icity of being powered by
anaesthetic gases supplying the breathing systern. It overcomes the ~-
problems of constant volume ~ devices. It also serYes to o~ercome a
potential hazsrd of any device powered by an external high pressure gas
source where a high pressure gas souree may by some means communicate
WO 92/03176 5~ , ` PCr/CE~i91/01450
with the cuff so that a safety blow off pressure release Yalve IDay
therefore be necessary. In this case no such safety relesse ~alve is
required in this invention.
Should the said regulator device 9 be connected to the outlet instead of
the inlet of an anaesthetic breathing system, the potential danger of a
unidirectional flow device is removed by the facility of permitting
re~erse flow through the spindle valve seat 20 via ~rifice æ2 and past
the said flap 25. The device is the~eby made much safer for use in the
clinical setting and so fulfilling the objective of its design.
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FIGURES 3 TO 8
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These sihow an alternative version of a regulP~tor for use in a similar
way to that described in connection with Figure 2 and can indeed ~e
substituted for regulator 9.
:. Figures 3A and 3B variously show regulator 42 with a body 42A of ~.
cylindrical form incorporating a stepped bore B which is largest at
inlet end I with inlet channel 4~ to outlet end O with outlet channel
~6. Gas flow through the regulator 42 is normally in the direction of. arrow A.
On step 54 of the bore B there is seated a rigid support disc 66 shown in
Figure 5. The support disc 66 contains a central bore 64 and a large
number of bores, typically~ bore 68.
v
On step 56 of the bore B there is seated a 2igid mounting disc 70 shown
in Figure 6. The mounting disc 70 contains an outer ring of apertures
76 and an inner r;ng 74. Both rings of apertures are separated by
radial aRms, typically arm 80 extending from a central mounting support
ring 78 pierced by bore 72.
On its downstream side mounting disc 70 h~s mounted a flexible disc 86
shown in Figure 7. The disc 86 is mounted on spindle 60 by way of a
central aperture 88.
WO 92/03176 ,~ PCI~ I/01450
. 9
The mounting disc 70 has mounted on its upstream side a flexible disc 98
shown in Figure ~. Disc 9~ is pierced by apertures 74.1 corresponding
in shape and axi~ 1ocstion to the inner ~ing of apertures 74 on disc
70. Radi~ arms 80.1 ~kewnse correspondls to arm B0 on mounting disc
70. Central annulus 78.1 aligns with support ring 78 OI disc 70. The
annulus 78 has bore 96 by means o~ which spindle 60 extends through disc
9~ .
Spindle 60 (Figure 4) is supported at the axial centre of bore B by way
of central bores 64, 72 in, respectively, support disc 66 and mounting
disc 70. The spindle 60 has an integral boss 62. The boss 62 serves as
sn end ~top for :Elexible disc 86. A spring washer 90 is locked OII to the
right hand end of the spindle to serve as an end stop for the left hand
end of spnng 92 whose right hand end presses against disc 98 by way of
a plastic collar 9~. The support disc ~0 and the flexible disc 98 are
mounted so that the arrays of apertures 7~ and arms 80 of disc 70 are
aligned with apertures 74.1 snd arms 80.1 of disc 98 to provide ~or the
least restriction to flow of gases through the apertures 74, 74.1 when ~ !
open .
Spring 92 serves to dlive spindle 60 to the left causing disc 86 to seat
on the downstream side of support disc 70 Imless lifted therefrom by gas
flow through apertures 7~,1 in disc 100 and correspondiIlg apertures 74
in support disc 70. In this event disc 86 is dIiven o:ff the support
disc ~0 to allow the passage of gas through to the outlet passage 46 and
onto the endotracheal tube 30.
Inlet channel 44 hss an outlet tapping ~rmed by si~e port 34 opening
into outlet tube 48 by rneans of which the regulator ~2 is coupled to a
pilot tube corresponding to pilot tube 36 of Figure 1.
The regulator operstes in general terms in a similar way ': the
regulator 9 described in connection with Figure 2. RegL. ~ or 42 is
connected (Figure 1) to the outlet 16 of the anaesthetic gas supply ::
machine 10 and the regulator 9 is attached to the inlet of the breathing
system 24, 26 which is in turn attached to an endotracheal tube 30 snd
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system 24, 26 which is in turn attached to an endotracheal tube 30 and
with a means for ventilating, such as a mechanical ventilator 5, for the
purpose of achieving pos;tive pressure ventilation. The upstream
channel 44 of the regulator 42 is also connected by means of port 34 and
tube 48 to the pilot tube 3 anll so to the inside of the cuff 2. As a
consequence when anaesthetic gas flows through the regulator 42 into
the anaesthetic breathing system 22, a constant ~or substantially
constsnt depending on the characteri~tics of the sprirlg in use and the
flow characteristics of the regulator) pressure difference is
maintained between the upstream channel 44 ~nd the downstream channel
46 of the regulator 42. The higher upstream pressure is maintauled and
transmitted to the endotracheal tube cuff 32 with the downstream
portion being in direct communication with the breathing system 22 and
therefore the endotracheal tube 30 or airway preEsure.
A rise in airway pressure, when posiffve pressure is generated by the
ventilator during the inspiratory phase of controlled ventilation,
results in an corresponding rise of pressure w~thin the regulator 42.
The supply gas flows across the regulator valve 70 in the direction of
arrow A by way of apertures 74.1 in disc 98 and apertures 74 in disc 70
and displaces the disc 86 ag~unst the action of spring 92 resulting in
the spindle 60 being drawn to the right allowing the passage of gas
through the disc system from inlet channel 44 to outlet channel 46. In
this normal flow condition the pressure differential across the
regulator 42 remains unchanged and therefore any rise in downstream
pressure is transmitted to the upstream section ~6 which ~n turn is
transmitted by means of the appropriate flow of gas from upstrealD
channel ~4, side port 34, pilot tube 3 and 80 into the endotracheal tube
cuff 32. The cuf~ pressure therefore is continuously maintained above
airway pressure by the regulator 42. A fall in airway pressur~ such as
occurs during the p~ssive expiratory phase results in a concomitant
fall in pressure in the regulator 42 which in tu~ allows for gases
which accumulated in the cuff during the inspiratoF~ phase ts~ flow
outwards, through pilot tube 3, side port 34 and into upstream channel
44. That is to say depressurisation of the cuff occurs to a pressure
above aiF~ay pressure eQual to the opening pressllre set across the
~ ~ , .. . .. . . . .
WO 9'/03i,6 PCr/CB91/01450
2~ nO223
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vslve disc 70 of the regulstor 42.
The quantity of gas in the endotracheal tube cuf~ 2 is continuously
changing to allow for the equalisation oi. pres~ures Yithin the system
apart from the specific pressure ~ifference set across the regulator 9.
Should the regulator device 42 be connected to the outlet inste~d of the
inlet of an a~iaesthetic bresthing system the potential danger of
unidirectional flow device is removed by the facility of permitting
reverse flow through the spindle v~lve seat 70 ~ria outer ring ~
apertures 74 and past the flap 98 r~hose outer peFiphery is displaced
axially. Under normal flow condiffons the fle~ible disc 98 is pressed
into contact with dLisc 70 allowing gas flow only through the inner ~qng
of apertures 74.1 and 74. The device is thereby made much safer for use
in the cbnto~l ~etting and so Vul~illing the ob3ecbve of its design.
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