CA2090223A1 - Pressure control device for endotracheal tube cuff - Google Patents

Abstract

A pressure regulating device, to be connected between a patient ventilator and a cuffed endotracheal tube, having a body with an inlet (44) and outlet (46) for the passage of respiratory gases to be sent to the patient, and an additional side outlet (48) to be connected by means of an appropriate tubing to the cuff, in order to adapt the pressure in the cuff to the respiratory pressure.
It consists of a body (42A) containing a spring loaded valve (86), having two oscillating discs (86, 98) moving at the opposite sides of a perforated plate (70) perpendicular to the gas flow.

Description

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 .
--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 ~C) 9~()3~ 0 2 2 3 ,'j`,.'?,.',' 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 ' ' ' ' ~ ~` ~ ' . ' ' ' ~' 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.
,,, 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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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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WV 9~/03176 o,~ , PCr/GB9l/0l450 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 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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Claims (6)

A cuff pressure regulator for connection to an endotracheal cuff, characterised by:
a body (9A, 42A) having an inlet (11, 44) for connection to a supply (10) of respiratory gas; an outlet (14, 46) for connection to breathing apparatus (22) whereby, in use, respiratory gases from the supply (10) flow through the regulator from inlet (11, 44) to outlet (14, 16) and on to a breathing apparatus (30) incorporating the cuff (32); the regulator being subject to pressure variations occurring in the breathing apparatus (30);
2 a spring loaded valve structure (20, 86) within the body (9A, 42A) of the pressure regulator for causing a pressure drop between the inlet (1,44) and the outlet (14, 16), and 3 a port (18, 34) for connection to an endotracheal cuff (32), the port (18, 34) communicating with the interior of the body (9, 42) on the inlet side (11, 44) of the structure so that the port (18, 34) is subjected to the pressure on the inlet side (11, 44) of the structure.

2 A pressure regulator as claimed in Claim 1 characterised in that the structure comprises:

1 a valve seat (17, 70);

2 a valve closure member (20, 86) (which tends to lift from the valve seat (17, 20) when the pressure at the inlet (11, 44 exceeds the pressure at the outlet (14, 86); and 3 a resilient biassing device (28, 92) tending to urge the closure member (20, 86) towards the valve seat (17, 70).

3 A pressure regulator as claimed in Claim 2 characterised in that the valve seat (17, 70) is constituted by a valve plate (16, 70) with at least one aperture (15, 74) and the valve closure member (20, 86), is constituted by a valve closure disc (20, 86) which is resiliently urged against the downstream face of the plate (16, 70) by the resilient biassing device (28, 92) thereby to close-off WO ? PCT/GB91/014500 the aperture (15, 75) in the valve plate (16, 70).

4 A pressure regulator as claimed in Claim 3 characterised in that the valve plate (70) has an inner ring of apertures (74) and an outer circular ring of apertures (76), the valve closure disc (86) serving to close off the apertures of the inner array (74): there being a valve shut-off disc (98) on the opposite side of the valve plate (70) to the closure disc (86), the shut off disc (98) being urged against the upstream face of the plate (70) and closing off the apertures of the outer array (76) whilst the pressure at the inlet (44) exceeds the pressure at the outlet (46).

5 A pressure regulator as claimed in Claim 4 characterised in that the valve plate (70) is fixed in the body (42A) between the inlet (44) and the outlet (46), the closure disc (86) is between the plate (70) and the outlet (46) and the shut off disc (98) is between the inlet (44) and the plate (70), there being a spindle (60) which passes through both discs (86, 98) and the plate (70) and is free to move axially with respect thereto, the spring (92) being between an abutment (90) on the spindle (60) and the shut off disc (98): the spindle (60) having a collar (62) thereon, the closure disc (86) being between the collar (62) and the plate (70) whereby, in the absence of any pressure in the body (42A), the spring (60) presses the shut off disc (98) against the plate (70) and pulls the collar (62) towards the closure disc (86) thus holding the closure disc (86) against the plate (70).

6 A cuffed endotracheal tube system comprising an endotracheal tube with an inflatable cuff encircling the tube characterised by a cuff pressure regulator (9, 42) according to any preceding claim together with a cuff inflation and deflation duct (36) linking the port (18, 34) to the cuff (32) whereby the cuff (32) is subjected to the pressure at the inlet (13, 44) which pressure varies in dependence on the pressure in the breathing apparatus (22).