PRESSURE CONTROL DEVICE FOR ENDOTRACHEAL TUBE CUFF

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: 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 cuffed endotracheal 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 respiratory care, a tube is inserted into the trachea (referred to as an endotracheal tube) . A relatively large volume soft ring-shaped hollow collapsible bag known 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 cuff also serves to anchor the tracheal tube within the trachea below the vocal cords. The cuff needs to be inflated to a pressure which is greater than airway 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 initial over- inflation while using a syringe for the purpose; the warming of a given volume of air injected into the cuff at room temperature up to body temperature causing the cuff to expand; and the diffusion into the cuff of anaesthetic gases such as nitrous oxide. Excessive cuff pressures may affect perfusion (the blood supply) to the mucosal lining of the trachea causing damage, and may produce complications which may include for example sloughing of the tracheal mucosa, fistula formation, or stenosis. The higher the cuff pressure used the poorer the perfusion that results and the greater the risk of causing permanent damage. A cuff system should ensure that the lowest cuff 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 allows for the variation of airway pressure to be transmitted to the cuff. PRIOR ART A number of designs varying in complexity 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 Farahany and 4 825 862 in the name of Sato and others. US 4 850 349 (Farahany) involves a simple device not requiring an external gas supply to power the device, but suffering from the problems related to fixed cuff volume devices mentioned earlier including over-inflation, diffusion of nitrous oxide into the system and failure to compensate for small leaks. In addition the specific device will work only with a limited range of cuff volumes or sizes . US 4 825 862 (Sata et al) describes a more elaborate device than Farahany which does appear to overcome several 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 According to the present invention there is provided a pressure regulator powered by the gas supply source to a breathing system for the maintenance of a constant or substantially constant pressure difference between the cuff and the lumen in a cuffed endotracheal tube during positive pressure ventilation comprising a tubular connecting means for attachment and interposition between the gas supply machine and the breathing system and means for connection to the cuff inflation port of an endotracheal tube, the said regulator comprising a threshold valve for the purpose of generating a substantially constant pressure difference when gases supplying the breathing system flow through the said valve, the pressure differential created by the said threshold valve being either fixed or adjustable, with upstream connecting means for attachment to and in open communication with the inside of the cuff of an endotracheal tube for the purpose of transmitting and maintaining the said upstream pressure to the said cuff above that of the airway pressure by a constant or substantially constant value equal to the threshold valve setting; the regulator being provided with a one-way relief valve allowing gas to flow in the reverse direction, to obviate any danger associated with faulty connection. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 schematically illustrates the relative positions of a system utilising the present invention showing a cuff pressure regulator and its attachment to an anaesthetic machine and breathing 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 embodiment of the present invention. Figure 3A schematically illustrates 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. Figures 4 to 8 variously show components generally described in connection with Figure 3A. DETAILED DESCRIPTION OF THE DRAWINGS Figure 1 shows an anaesthetic gases supply 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 means 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 cuff 32, which is maintained inflated with gas, i.e. in a pressurised state, via pilot tube 36. The breathing system 22 may be pressurised intermittently to achieve positive airway pressure ventilation by a ventilating means (in this instance a mechanical ventilator 38) . Figure 2 shows a first example of a pressure regulator for 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 attached to outlet 16 of anaesthetic gas supply machine 10 in Figure 1 by means of inlet channel 13 having a sealing surface 11 forming a gas tight push fit on to the outlet 16 in accordance with the ISO 22mm 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 16 whereby anaesthetic gases flow through the regulator 9. On downstream side of the partition 16 and enclosing within its periphery any and all channels 15 there is provided a valve seating edge 17 against which bears a spring loaded valve seat 20 to form a gas tight seal at the seating edge 17, when in apposition, under the circumstances of zero or reverse gas flow. The regulator 9 incorporates a side port 18 providing for open communication with inlet (upstream) channel 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 provides for matching of changes in gas pressures between inlet channel 13 and the inside of the endotracheal tube cuff 32 (Figure 1) . A valve 26, comprising a firm disc shaped seat 20 with central axial stabilising rod 23 slides freely through a central and axially arranged channel 35 of an adjustable threaded tube 34 held in position by means of a compression spring 28. Valve seat 20 contains at least one channel 22 through which gases may flow in the reverse direction to the normal flow of arrow A. This would arise if the apparatus was inadvertently 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 flap 25 has a diameter which exceeds that of the sealing edge 21 but which is less than the diameter of channel 15. The flap 25 is located on the upstream surface of the valve seat 20 so that, should a reverse flow of gas occur, the flexible flap 25 will open in an 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 valve 26 to open against force of a spring 28 to maintain upstream pressure higher than downstream pressure by an amount governed by the spring 28. The flexible elastomeric flap 25 has a central perforation 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 upstream end of the said spindle. Normally the flexible elastomeric 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 orifice 22. The spring 28 is kept under compression by being positioned between the said spindle seat 20 and flange 33 of a central and axially arranged threaded tube 30. The threaded tube 30 comprises a smooth cylindrical portion 34 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 the axial position of threaded tube 30 may be adjusted for the purpose of altering spring force appropriately, 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 alternative 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 enable the spring force to be varied while the regulator is in use. The fixed support structure 40 placed in the downstream channel 14 comprises a central female threaded orifice 42 for the purpose of holding the threaded tube 30 in position and at least one peripherally arranged orifice 41 to allow the free flow of gas in either direction. IN USE (referring 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 inlet of the breathing 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 positive pressure ventilation. 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 cuff 2. As a consequence when anaesthetic gas flows through the regulator into the anaesthetic breathing system 22, a constant (or substantially constant depending on the characteristics of the spring in use and the flow characteristics of the regulator) pressure difference is maintained 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 positive pressure is generated by the ventilator during the inspiratory phase of controlled ventilation, results in an equal rise of pressures within the regulator 9. As the supply gas continues to flow across the regulator valve, the pressure differential across the regulator remains unchanged and therefore any rise in downstream 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 18, pilot tube 3 and so into the endotracheal tube cuff 32. The cuff pressure therefore is continuously maintained above airway pressure by the regulator 10. A fall in airway pressure such as occurs during the passive expiratory phase results in a concomitant fall in pressure in the regulator 9 which in turn allows for gases which accumulated in the cuff during the inspiratory phase to flow outwards, through pilot tube 3, side port 18 and into upstream channel 13. That is to say depressurisation of the cuff occurs to a pressure above airway pressure equal to the opening pressure set across the valve of the regulator 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 simplicity of being powered by anaesthetic gases supplying the breathing system. It overcomes the problems of constant volume cuff devices . It also serves to overcome a potential hazard of any device powered by an external high pressure gas source where a high pressure gas source may by some means communicate with the cuff so that a safety blow off pressure release valve may therefore be necessary. In this case no such safety release valve 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 reverse flow through the spindle valve seat 20 via orifice 22 and past the said flap 25. The device is thereby made much safer for use in the clinical setting and so fulfilling the objective of its design. FIGURES 3 TO 8 These show an alternative version of a regulator for use in a similar way to that described in connection with Figure 2 and can indeed be 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 44 to outlet end O with outlet channel 46. 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. On step 56 of the bore B there is seated a rigid mounting disc 70 shown in Figure 6. The mounting disc 70 contains an outer ring of apertures 76 and an inner ring 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 has mounted a flexible disc 86 shown in Figure 7. The disc 86 is mounted on spindle 60 by way of a central aperture 88. The mounting disc 70 has mounted on its upstream side a flexible disc 98 shown in Figure 8. Disc 98 is pierced by apertures 74.1 corresponding in shape and axial location to the inner ring of apertures 74 on disc 70. Radial arms 80.1 likewise corresponds to arm 80 on mounting disc 70. Central annulus 78.1 aligns with support ring 78 of disc 70. The annulus 78 has bore 96 by means of which spindle 60 extends through disc 98. 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 an end stop for flexible disc 86. A spring washer 90 is locked on to the right hand end of the spindle to serve as an end stop for the left hand end of spring 92 whose right hand end presses against disc 98 by way of a plastic collar 94. The support disc 70 and the flexible disc 98 are mounted so that the arrays of apertures 74 and arms 80 of disc 70 are aligned with apertures 74.1 and arms 80.1 of disc 98 to provide for the least restriction to flow of gases through the apertures 74, 74.1 when open. Spring 92 serves to drive spindle 60 to the left causing disc 86 to seat on the downstream side of support disc 70 unless lifted therefrom by gas flow through apertures 74.1 in disc 100 and corresponding apertures 74 in support disc 70. In this event disc 86 is driven off the support disc 70 to allow the passage of gas through to the outlet passage 46 and onto the endotracheal tube 30. Inlet channel 44 has an outlet tapping formed by side port 34 opening into outlet tube 48 by means of which the regulator 42 is coupled to a pilot tube corresponding to pilot tube 36 of Figure 1. The regulator operates in general terms in a similar way to the regulator 9 described in connection with Figure 2. Regulator 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 and 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 positive 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 and 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 constant depending on the characteristics of the spring in use and the flow characteristics of the regulator) pressure difference is maintained between the upstream channel 44 and the downstream channel 46 of the regulator 42. 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 positive pressure is generated by the ventilator during the inspiratory phase of controlled ventilation, results in an corresponding rise of pressure within 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 against 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 46 which in turn is transmitted by means of the appropriate flow of gas from upstream channel 44, side port 34, pilot tube 3 and so into the endotracheal tube cuff 32. The cuff pressure therefore is continuously maintained above airway pressure by the regulator 42. A fall in airway pressure such as occurs during the passive expiratory phase results in a concomitant fall in pressure in the regulator 42 which in turn allows for gases which accumulated in the cuff during the inspiratory phase to 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 airway pressure equal to the opening pressure set across the valve disc 70 of the regulator 42. 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. Should the regulator device 42 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 reverse flow through the spindle valve seat 70 via outer ring of apertures 74 and past the flap 98 whose outer periphery is displaced axially. Under normal flow conditions the flexible disc 98 is pressed into contact with disc 70 allowing gas flow only through the inner ring of apertures 74.1 and 74. The device is thereby made much safer for use in the clinical setting and so fulfilling the objective of its design.

Claims: CLAIMS 1 A cuff pressure regulator for connection to an endotracheal cuff, characterised by: 1 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 the aperture (15, 75) in the valve plate (16, 70) . 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) . A pressure regulator as claimed in Claim 4 characterised in that the valve plate (70) is fixed in the body (42 A) 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) . 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) .

Inventors: MILLER DONALD MUNRO, MILLER, DONALD, MUNRO
Applicants: MILLER DENT LTD, MILLER DENT LIMITED
Application year: 1991
Main classification: A61M16
IPC codes: A61M16