Anaesthetist's Ventilation

Abstract

An anaesthetist's ventilator includes a cylinder adapted for connection to a respiratory tube connected to an Ayres T-piece and a face mask or endotrachael tube with a gas supply being connected thereto, the cylinder having a vent connecting to atmosphere, a gas flow control valve reciprocable within the cylinder, drive means for reciprocating the valve between end valving positions positionally adjusting the valve in a stepless manner for varying the ratio of the periods of inspiration and expiration with the vent being fully open in one of the end valving positions for the passage of gas from the supply and expired air from the respiratory tube outwardly of the ventilator and with the vent being fully closed in the other of the end valving positions for the passage of gas from the supply to the patient, and adjustment means for adjusting the positioning of the valve.

Description

This invention concerns anaesthetist's ventilators, and has for its object to provide a construction thereof which is particularly, but not exclusively, suitable for use in paediatric anaesthesia in that it passes small tidal volumes, which can be realised in a relatively small and inexpensive form, which is efficient in operation, which can be constructed so as not to require electricity for its operation, and in which provision for varying the ratio of the periods during which inspiration and expiration take place can be made very simply and conveniently.

With this object in view, the present invention provides an anaesthetist's ventilator comprising a cylinder adapted for connection thereto of a respiratory tube connected to an Ayres T-piece which in turn is adapted for connection to a face mask or endotracheal tube and for a gas supply to be connected thereto, said cylinder having one or more vents connecting its interior to atmosphere, a piston being provided within the cylinder, and drive means to reciprocate the piston between end positions in one of which the vent is open to permit gas from the supply and expired air from the respiratory tube to pass out of the ventilator, and in the other of which the vent is closed so that gas from the supply will increase the pressure in the respiratory tube, to pass to the patient.

Preferably the drive means is in the form of a vacuum-powered reciprocating motor.

Advantageously, the drive means is displaceable parallel to the axis of the cylinder to vary the ratio of the periods during which the vent is closed and is open during each reciprocation, thereby to vary the ratio of the periods during which inspiration and expiration will take place in each reciprocation.

In order that the invention may be fully understood, it will be described further, by way of example, with reference to the accompanying drawings, in which:

FIG. 1 is a perspective view, with various of the parts cut away, of a preferred embodiment of the ventilator of the invention;

FIG. 2 is a detached sectional view showing certain of the parts of the ventilator of FIG. 1 and showing, also, diagrammatically, the ventilator connected to a face mask; and

FIG. 3 is a fragmentary perspective view of a part (which has been omitted from FIG. 1) of the top of the ventilator of FIG. 1;

FIG. 4 is a schematic diagram showing how the ventilator of FIGS. 1 to 3 may be modified to provide for suction to be applied to a patient's lungs during expiration; and

FIG. 5 is a view comparable with FIG. 4 but showing the ventilator modified to provide positive end expiratory pressure.

The preferred embodiment of the anaesthetist's ventilator according to the invention and illustrated in the drawings has a casing, indicated generally by the numeral 10, comprising a pair of parallel angle members 12, 14 extending between end plates 16, 18 formed with respective handles 20 and having secured thereto a trough-like bottom part 22 and a complementary top cover 24.

Secured to the end plate 18, by bolts 25, so as to be disposed adjacent to the angle member 12 is a cylinder assembly indicated generally by the reference numeral 26, which is illustrated in cross-section in FIG. 2 of the drawings. This cylinder assembly 26 comprises a tubular cylinder body 28 formed at one end with a taper socket 30 which projects through a respective opening (not visible) in the end plate 18 and serves to receive a spigot 32 provided on one end of a respiratory tube 34 whereby the latter can be connected to the interior 36 of the cylinder body 28. At its other end, the respiratory tube 34 has connected thereto an Ayres T-piece 38 having a gas inlet 40 and connected in turn to a face mask 42.

As can be seen from FIG. 2, the tubular body 28 is located within a housing 44 of the cylinder assembly, being sealed relative to the latter by sealing rings 46.

Close to the socket end of the cylinder body 28 a port 48 is provided through the wall of such body 28. This port 48 registers with a corresponding port 50 through the housing 44 whereby the interior 36 of the cylinder body 28 connects with a space 52 defined by a safety-valve mounting plate 54 sealingly secured to the top of the housing 44. An orifice 56 in the plate 54 is fitted with a safety valve indicated generally by the numeral 58 and comprising a closure member 60 loaded by a spring 64 under a pressure which is manually adjustable by means of a knob 66 which protrudes through a respective opening in the top cover 24 of the casing 10. For normal use such valve 58 will be set to open, so as to connect the space 52 and the interior 36 of the cylinder body 28 with atmosphere, for example at a pressure of about thirty centimetres of water and to close at a substantially lower pressure.

A guage pipe 68 is secured through the plate 54 and this is connected by way of a flexible tube 70 with a three-way cock 72. This cock 72 has an arm 74 connected by way of a flexible tube 76 to a pressure gauge 78 mounted on a plate 80 secured by screws 82 and spacers 84 to the angle members 12, 14, as well as an arm 86 connected to a union, illustrated diagrammatically at 88, which projects through a respective aperture in the end plate 18 and which can be connected, if desired, to a pressure sensing arm (not shown) connecting with the Ayres T-piece 38. The arrangement of the cock 72 is such that in its three positions it provides respectively (i) for the gauge 78 to be connected to the T-piece 38 by way of the union 86, to provide an indication of the pressure in the lungs of a patient to whom the face mask 42 has been applied; (ii) for the gauge 78 to be connected to the interior 36 of the cylinder body 28 to provide an indication of the pressure therein; and (iii) for the gauge 78 to be isolated from the gauge pipe 68 and the latter also to be blanked off from the union 88. A knob 90 of the cock 72, projecting through the top cover 24 of the casing 10 permits manual changing of the setting of the cock 72.

At a position about half way along the cylinder body 28 from the end wherein the socket 30 is provided, a plurality of vent holes 92 are provided through the wall of the cylinder body 28, these holes 92 opening to an external circumferential groove 94 around the body. A vent pipe 96 (see FIG. 1) secured into the housing 44 connects with the groove 94 and enables the latter to be connected, if desired, to an exhauster or like device (not shown) for sucking away unwanted gases.

The cylinder body 28 accommodates a piston 98 which is a close sliding fit therein and which is connected to one end of a piston rod 100 which extends axially out of the cylinder body 28 at its end remote from the socket 30 and is slidingly guided in a bearing block 102 fixed to the underside of a mounting plate 104 which is located by its edges is slotted guideways 106 secured by respective bolts 107 to the respective angle members 12 and 14.

Also mounted on the underside of the mounting plate 104 is a vacuum-powered motor 108. This motor 108 is of the type commonly employed on motor vehicles as a vacuum-operated windscreen wiper motor and comprises a spindle 110 on which is fixed a radial arm 112 which reciprocates with a to-and-fro swinging movement when vacuum is applied to the motor 108. The radial arm 112 projects into a slot 114 in the piston rod 100 and is coupled thereto by means of a pin 116 secured in the rod 100 to extend across the slot 114 and through a slot 118 in the radial arm 112. By this arrangement, swinging movement of the radial arm 112 is translated into reciprocating movement of the piston rod 100 and, of course, of the piston 98 within the cylinder body 28.

The motor 108 is fixed to the mounting plate 104 by bolts 120, and since the mounting plate 104 is located by its edges in the guideways 106 which extend parallel to the axis of the cylinder body 28, the motor 108 can be displaced relative to the casing 10 and relative to the cylinder body 28 in a direction parallel to the axis of the cylinder body 28. This displacement can be effected by means of an adjustment screw 122 carried in brackets 124 mounted on a fixed carrier plate 126 disposed between the mounting plate 104 and the gauge 78, and secured to the angle members 12 and 14 by way of screws 128 and spacers 130. This adjustment screw 122, which is provided with a knurled knob 132 exposed through an opening in the top cover 24 to enable it readily to be rotated manually, extends through a threaded boss 134 fixed to the fixed carrier plate 126.

It will be appreciated that displacement of the mounting plate 104 and with it the motor 108 by means of the screw 122 results in corresponding displacement of the piston rod 100 and of the piston 98. Accordingly, it serves to provide for a single adjustment of the position, during each stroke of the piston 98, at which the vent holes 92 are uncovered or covered. As a consequence, the adjustment varies the relative periods, in each complete reciprocation of the piston 98, during which the vent holes 92 are closed and open. In a typical example, the arrangement will normally be disposed so that the ratio of the closed periods (corresponding to the patient inspiring, as will later be described) to the open periods (corresponding to the patient expiring) can be adjusted between 1:1 and 1:4. This ratio may, for convenience, be regarded as the "inspiration/expiration ratio."

As has been shown in FIGS. 1 and 3, a rack 136 is provided on the top surface of the mounting plate 104, and this rack 136 is engaged by a toothed wheel 138 provided on a spindle 140 journalled in the top cover 24, the wheel 138 being below the cover 24. Secured to the spindle 140 above the cover 24 is a pointer 142 which co-operates with a scale 144 marked on a transparent window member 146 secured to the top cover 24 so as to overlie and protect the point 142. The scale 144 is calibrated to indicate inspiration/expiration ratios, e.g., in the range 1:1 to 1:4 as above explained, so that the pointer 142 gives an immediate reading of the particular ratio at which the ventilator is set, according to the position of the mounting plate 104 as adjusted by the screw 122. From FIG. 3 it will be appreciated that when the mounting plate 104, motor 108 and piston 98 are displaced in a direction towards the pressure gauge 78 the toothed wheel is rotated to swing the pointer 142 across the scale 144, in an anti-clockwise direction as viewed in the figure, and that return movement will then swing the pointer 142 back in the clockwise direction.

A vacuum tube 148 from the vacuum-powered motor 108 connects, by way for a coupling block 150 and a flexible tube 152, with a vacuum-control valve 154 which, in turn, is connected to a vacuum tube 156 provided with a nozzle 158 projecting through a respective opening in the end plate 18 so as to be accessible for connection to a vacuum service line (not shown).

In operation of the ventilator, the face mask 42 is applied over the patient's face (not shown) so that the interior of the respiratory tube 34 is coupled to the patient's respiratory system. This is illustrated diagrammatically in FIG. 2 wherein the patient's lungs have been represented at 160. As an alternative to the mask 42, the Ayres T-piece 38 may be connected to an endotracheal tube (not shown) by which the apparatus is connected to the patient.

Compressed gas is supplied to the T-piece 38 by way of the gas inlet 40 and the gauge 78 is used to measure the pressure developed in the patient's lungs 160. Vacuum is applied to the motor 108 by way of the vacuum tube 148 to cause reciprocating swinging movement of the radial arm 112, the frequency of reciprocation being adjusted, of course, by adjusting the vacuum control valve 154. With available vacuum up to 300 mm. of mercury, a range of frequency from 0 to about 80 reciprocations per minute will generally be available using a commercially-available windscreen-wiper motor as the motor 108.

When the radial arm 112 displaces the piston 98 inwards of the cylinder body 28, before the piston 98 reaches the end of its stroke it closes the vent holes 92. As a result, the incoming compressed gas supplied through the gas inlet 40 to the T-piece 38 is applied to the patient's lungs 160 in an inspiration phase of each cycle of operation of the ventilator, to cause inflation of the lungs 160. In the return stroke of the piston 98 in the opposite direction, the piston 98 clears the vent holes 92, thereby opening the ports 48 and 50 and the gauge pipe 68, and the patient's lungs 160, to the vent pipe 96. Accordingly the pressure in the cylinder's interior 36 drops, the compressed gas supplied to the T-piece 38 can escape through the vent type 92 to the vent pipe 96 and air is expired from the patient's lungs in an expiratory phase of each cycle of operation of the ventilator.

As has already been mentioned, the inspiration/expiration ratio can be adjusted by displacement of the motor 108 and piston rod 100 by means of the screw 122. This ratio being known, and the compressed gas flow to the T-piece 38 by way of the gas inlet 40 also being known (e.g., from a rotameter, not shown, connected to the inlet 40 at an appropriate location) the volume of fresh gas supplied to the patient per unit of time can readily be calculated. Thus, for example, with a fresh gas flow of 6 litres per minute and an inspiration/expiration ratio of 1:2, the patient receives 2 litres per minute of fresh gas, since the inspiration phase of each cycle occupies one third of each cycle. If the tidal volume (i.e., the volume of fresh gas passing to the patient during each cycle of the ventilator) is required to be known, it is only necessary to ascertain the frequency of reciprocation of the radial arm 112 and piston 98 (e.g., by counting the number of cycles occurring per unit of time) and divide the gas volume passing to the patient by this frequency.

The ventilator of the invention can be employed, if desired, where negative phase ventilation and positive end expiratory pressure ventilation are required to be performed, and FIGS. 4 and 5 of the drawings, respectively illustrate, diagrammatically how this may be achieved.

Referring to FIG. 4, use is made, in conjunction with the Ayres T-piece 38, of a Venturi, indicated at 200. A gas supply tube 202 is connected firstly to the inlet 40 of the T-piece 38 by way of a stop valve 204 and secondly to a jet 206 of the Venturi 200. With the stop valve 204 open, this arrangement operates substantially in the same way as the embodiment above described with reference to FIGS. 1 to 3. When the valve 204 is closed, however, the flow of gas from the jet 206 through the Venturi 200 during the expiratory phase of each cycle (i.e., when the vent holes 92 are open) is such as to induce a reduced or negative pressure in the patient's lungs 160, so that negative phase ventilation is achieved. In this figure, the Ayres T-piece 38 is shown as having a pressure sensing arm 208, this arm being adapted to be connected to the union 88 of the ventilator.

In FIG. 5, substantially the same components are employed, but in this case use is made of a Venturi 210 whose jet 212, instead of being directed towards the cylinder assembly 26 in the system, is directed towards the patient. This has the effect of assuring that positive end expiratory pressure is achieved in the expiratory phase of each cycle of operation of the ventilator.

Naturally, the invention is not confined to the precise details of the foregoing examples which, as already mentioned, are only diagrammatically illustrated in the drawings. It will be understood that the ventilator can be constructed as a unit within a casing 10 of relatively small dimensions, with the gauge, valves, cock and other components mounted so as to be readily accessible and the scale 144 readily visible. Further, the unit can, if desired, incorporate appropriate connections and shut-off valves to enable it to be set up for use either as illustrated in FIGS. 1 to 3 or in FIGS. 4 and 5, it being understood that in the latter case the Venturi 200 or 210 will be provided as a plugin accessory which can be incorporated or not as required.

Claims

I claim:

1. An anaesthetist's ventilator comprising: a face mask for application to a patient,

a T-piece connected to the face mask,

a gas supply means connected to the T-piece for continuous gas supply to the face mask,

a cylinder,

means connecting the cylinder to the T-piece for the continuous supply of gas to the cylinder,

vent means in the cylinder,

a piston alternatingly reciprocable in the cylinder between a position of closing off the vent means for the preclusion of gas escape therethrough and a position of opening the vent means for the allowance of gas escape and a consequent drop in the pressure of the gas supply to the face mask, and means for reciprocating the piston.

2. An anaesthetist's ventilator comprising:

a face mask for application to a patient,

a T-piece connected to the face mask,

a gas supply means connected to the T-piece for continuous gas supply to the face mask.

a cylinder,

means connecting the cylinder to the T-piece for the continuous supply of gas to the cylinder,

vent means in the cylinder,

a piston reciprocable in the cylinder between a position of closing off the vent means for the preclusion of gas escape therethrough and a position of opening the vent means for the allowance of gas escape and a consequent drop in the pressure of the gas supply to the face mask,

means for reciprocating the piston, and adjustment means for permitting variation of the ratio of the periods during which the vent means is open and closed in each reciprocation of the piston.

3. An anaesthetist's ventilator comprising:

a cylinder connected to a respiratory tube connected to a T-piece adapted for connection to a face mask or endotracheal tube, a gas supply connected to the T-piece,

a vent in the cylinder connecting the cylinder to atmosphere, a piston reciprocable within the cylinder,

drive means for alternatingly reciprocating the piston between opposite end positions in one of which the vent is open to permit gas from the gas supply and expired air from the respiratory tube to pass out of the ventilator and in the other of which the vent is closed so that gas from the gas supply will increase the pressure in the respiratory tube to pass to the patient, adjustment means for permitting a variation of the ratio of the periods during which the vent is closed and opened during each reciprocation of the piston and during which inspiration and expiration ensues,

a base,

guideways attached to the base, a mounting plate slidably engaged in the guideways,

the drive means being mounted on the mounting plate and being displaceable parallel to the cylinder axis, said cylinder attached to the base,

the adjustment means serving to adjust the position of the mounting plate with respect to the guideways and thereby to adjust the end positions of the piston and the opening and closing of the vent.

4. The anaesthetist's ventilator claimed in claim 3 and further including a visual indication means for delineating the setting of the ventilator as determined by the position of the mounting plate.

5. The anaesthetist's ventilator claimed in claim 4 with the indication means including a pointer on a spindle carrying a toothed wheel for engaging a toothed rack on the mounting plate.