IE20090238A1 - Humidification in breathing circuits - Google Patents

Abstract

A method for humidifying gas in a ventilator circuit 100, 101, 102, 105, 106 comprises aerosolising a humidifying agent such as water or saline using an aerosol generator 2 and delivering the aerosolised humidifying agent to the inspiration line 101 of the ventilator circuit coupled to the respiratory system of a patient. The aerosol generator 2 comprises a vibratable member 40 having a plurality of apertures extending between a first surface and a second surface. A controller 3 controls the operation of aerosol generator 2, for example in response to the flow of air in the inspiration line 101 as detected by a sensor 11. <Figure 1B>

Description

This invention relates to humidification in breathing circuits for intensive care management of -mechanically ventilated patients.

It) 'λ! During a normal 24 hour period 250-350 ml of water is lost from the respiratory h act.

During normal breathing the upper respiratory tract humidifies and filters the inspired air. This task occurs primarily in the nasopharynx where air is exposed to a large area of highly vascular, moist mucus membrane. On exhalation some ol' the moisture taken to humidify the air during inspiration is recovered but the balance, the 250-350ml, is replaced from systemic reserves over time. However, following intubation of patients on mechanical ventilation these normal upper airway moisture exchanging structures are bypassed and the burden of moistening the gases is passed to the lower respiratory tract, which is not suited to this task A ventilator is used to mechanically move breathable air into and out of patients lungs. For patients who have a long term dependence. on a ventilator an endotracheal tube (ET) is passed directly into the patient's trachea in order tc ensure that air is able to reach the lungs. Tbe ET is connected by tubing to y V shaped junction, known as a wye wnieh is connected to the ventilator.· One limb ofthe wye is active during an inspiration phase during which, air is delivered Into the lungs and the other limb is active during an exhalation phase during which exhaled air is expelled from the lungs.

Heat and moisture exchange (HME) devices are often placed in breathing circuits. They extract heat and moisture from humidified gas exhaled by a patient IE 0 90 2j8 during the exhalation phase and use tlie extracted heat and moisture to humidify the dry inspiration gas from the ventilator. hi passive HME devices exhaled heat and humidity is absorbed and transferred to inhaled gas. Such passi ve heat and moisture exchange systems generally at best only recover 70% of exhaled humidity, creating a humidity deficii. winch can create thick obstructive secretions and inflammatory airway reactions in patients v.nil chronic airways disease. Consequently, passive HME is largely confined to use vv ith patients with relatively healthy lungs.

It is also known to augment passive HME devices with the addition of heat and water to boost inhaled absolute humidity. In one known system there is direct application of water to the HME element, and heat is applied to the HME element. In another known system water is heated and vapour passes through a Goretex membrane between the HME device and the patient airway. in a third known system an active heated humidifier is used in which heat is applied to a body of water, and gas from the ventilator is passed over or through the water as the gas passes along the circuit to the patient, adding water vapour to the gas. Such systems may include heated wires in the inspiratory limp of tire ventilator tubing to add heat, or reduce heat loss of gas in transit to tlie patient.

Some of the problems with known active heated water humidifier systems arc that the heated humidifier is bulky, heavy and must be placed close to the ventilator distal to the patient. In addition, there is a likelihood of rain-out down the ventilator circuit tubing which can block the tubing, saturate the exhalation filter or flood the patient. As heated humidified gas passes through the inspiratory limb of the ventilator circuit., it cools and water condenses in the tubing. 1 his condensate can obstruct the airway, interfere with ventilation and/or increase the growth of pathogens. These problems can be mitigated by heating the condensate with heated wires but such heated wire systems add to cost and complexity. ^ 0 90 2 -3In summary active HME systems add expense with only marginal benefits in humidity. In addition, they add bulk and weight at the airway. t his invention is directed towards providing humidification in breathing circuits which will address al least some of these problems.

Statements of Invention According to the invention there is provided a method for humidify ing gas in a ventilator circuit comprising:aerosolising a humidifying agent using an aerosol generator wherein the aerosol generator comprises a vibratable member having a plurality of apertures extending between a first surface and a second surface thereof: and delivering the aerosolised humidifying agent to a ventilator circuil coupled to the respiratory system of a patient.

In one embodiment the ventilator circuit comprises an endotracheal lube, an inspiration line extending from a ventilator and an exhalation line extending from the ventilator.

The method may comprise the step of controlling the aerosolisation. Accurate control may be achieved via high speed pulsing of the electrical signal to tbe aerosol generator. Accurate changes to the pulse frequency will produce accurate and repeatable changes in aerosol output.

Aerosolisation may be controlled responsive to the flow of ventilation gas in the inspiration line. Greater volumes of gas require proportionally greater fluid flow rate of aerosolised humidifying agent to achieve 100% saturation at a given temperature. The gas flow is measured (via flow or differential pressure sensor) IE 0 9 0 in order to determine and deliver the required volume of humidifying agent io achieve i00% RH. Rapid and accurate measurement of gas flow enables required responsiveness.

The method may comprise controlling the fluid Row rate of the aerosolised humidifying agent.

In one embodiment the method comprises the step of determining the flow rate of ventilation gas in the inspiration line.

In one case the method comprises the step of determining if the humidifying agent is in contact with an aerosol generator. This may involve determining al least one electrical characteristic of the aerosol generator. In one case at ieast electrical characteristics of the aerosol generator over a range of vibration frequencies is determined. he method may comprise s tire step of comparing the at least one electrical characteristic against a pre-defined set of data.

In one ease a humidity meter is included close to the patient to measure the level of humidification of the gas entering the body. In this case a feedback loop to the controller is possible to control output from the nebulizer so as to ensure sufficient humidity is present in the ventilator gas.

In another embodiment the ventilator circuit comprises an inspiration line and an exhalation line which are connected ar a junction, and a patient line extending from the junction for connection to an endotracheal tube, and the method comprises the step of delivering the aerosolised humidifying agent into the patient line between the junction and the endotracheal tube.

In one ease the ventilation circuit comprises a heat and moisture exchange unit in the patient line and the method comprises the step of delivering the aerosolised tt090238 - 5 humidifying agent into tiie patient line between the heat and moisture exchange unit and the endotracheal tube.

Tlie ventilation circuit can comprise a heat and moisture exchange unit in tht pat'enl line and the method comprises delivering the aerosolised - humidifying agent into the heat and moisture exchange unit (HME). in one arrangement a nebuiiser is used to provide humidity at patient side of UME in order to replace humidity tosses to allow patients use the HME for longer periods of time.

.Alternatively a nebuiiser may be integrated with HME (TIME booster prodding humidity to a ventilated patient for longer periods of time possible wi conventional HME.

In one embodiment the inspiratory gas is heaied by providing a healing means such as a heated wire with the nebulizer providing the humidity. In this case a separate HME or hot pot would not be required. in one embodiment the aerosolised humidifying agent is delivered into the heat and moisture exchange unit on the patient side ofthe heat and moisture exchange unit. in one ease the aerosol generator E mounted to the he; I and moisture exchange /5 unit. la one embodiment the aerosol generator is integral with the heat and moisture change unit.

The invention also provides an aerosol introducer for introducing aerosolised humidifying agent into a ventilation circuit comprising an endotracheal tube, an inspiration line extending from a ventilator, and an exhalation line extending IE 0 9 0 2 -6from lhe ventilator, the introducer comprising an aerosol generator and control means tor controlling the operation of the aerosol generator wherein the aerosol generator comprises a vibratable member having a plurality of apertures extending between a first surface and a second surface thereof.

In one· case the ventilator circuit comptises an inspiration line and an exhalation line which are connected at a junction, and a patient line extending from the junction comprising e.g. an endotracheal tube, and the method comprises the step ot' locating the humidifying agent between the junction and the endotracheal tube, or in the inspiratory line prior to the junction.

In one embodiment the controller is configured to control operation ofthe aerosol generator responsive to the flow of gas in the inspiration line. in one case the controller is configured to control the flow rate of the humidifying agent to be aerosolised.

In one embodiment the apparatus comprises a device to determine the fluid flow rate of the gas in the inspiration line. The determining device may comprise a flow rate sensor.

In one embodiment the ventilation circuit comprises a junction for connecting the inspiration line and the exhalation line and a patient line for extending between the junction and the endotracheal tube and wherein the aerosol generator is arranged for delivery of aerosolised humidifying agent into the patient line between the junction and the endotracheal tube. fhe ventilation circuit may comprise a heat and moisture exchange unit lor location in the patient line.

,E 0 90 2s9 -Ί In one arrangement the aerosol generator is arranged for delivery of aerosolised humidifying agent into the patient line between the heat and moisture exchange unit and the endotracheal tube. fhe aerosol generator may be mounted on a connector for connection in the patient line. in one case the aerosol generator is mounted to the heat and moisture exchange unit.

In one embodiment the aerosol generator is integral with the heat and moisture exchange unit.

In one ease the first surface is adapted to receive the humidifying agent to be aerosolised.

The aerosol generator may be configured to generate an aerosol at the second surface. in one case the vibratable member is dome-shaped in geometry. It may also be fat with appropriate stretching. fhe vibratable member may comprise a piezoelectric element.

In one case the apertures in the vibratable member are sized to aerosoiise the humidifying agent by ejecting droplets ofthe water such that the majority of the droplets by mass have a size of less than 5 micrometers.

The apertures in the vibratable member can be sized to aerosoiise the humidifying agent by ejecting droplets of the water such that the majority ofthe droplets by mass have a size of less than 3 micrometers. -8-/£ 0 9 0 2 38 In one case the controller is configured to control the pulse rate at a set frequency of vibration of the vibratable member In one embodiment the controller is impedance matched to the aerosol generator. in another embodiment the apparatus comprises means to determine whether the humidifying agent is in contact with the aerosol generator.

The determining means may be configured to determine at least one electrical 10 characteristic ofthe aerosol generator The determining means can be configured to determine at least one electrical characteristic ofthe aerosol generator over a range of vibration frequencies.

In one case the determining means is configured to compare the at teas! one electrical characteristic against a pre-de lined set of data.

Brief Description ofthe Drawings The invention will be more clearly understood from the following description of some embodiments thereof, given by wav of example only, with reference to the accompanying drawings, in which: 25 fig. IA is a diagram of a delivery system according to the invention; fig. IB is a perspective view ofan apparatus for humidifying gas in a ventilator circuit according to the invention; Fig. 2 is a schematic illustration of a part of an apparatus according to the invention; IE 0 9 0 2 3 θ -9Fig. 3 is a schematic illustration of a part of the apparatus ofi ig. 1; I ig. 4 is an exploded isometric view of an aerosol generator used in the invention; Fig. 5 is a cross-seetionai view of the assembled aerosol generator oi Fig. 4: Fig. 6 is a perspective view of a controller housing used in the apparatus of the invention: Figs. 7(a) and 7(b) arc graphs oi' DC voltage versus time and AC voltage versus time respectively to achieve a 100% aerosol output: logs. 8(a) and 8(b) are graphs of DC voltage versus time and AC voltage versus time respectively to achieve a 50% aerosol output - Fig 8(a) illustrates the waveform output from a microprocessor to a drive circuit and Fig 8(b) illustrates the waveform output from a drive circuit to a nebuliser; Figs. 9(a) and 9(b) are graphs of DC voltage versus time and AC voltage versus time respectively to achieve a 25% aerosol output - Fig 9(a) illustrates the waveform output from a microprocessor to a drive cfrcuit and Fig 9(b) illustrates the waveform output from a drive circuit to a nebuliser; Fig 10 is a graph of z\C voltage versus time; and illustrates an output waveform from a drive circuit to a nebuliser; Fig. il is a graph of frequency versus current for another apparatus according to the invention: IE 0 9 0 2 38 -10 Fig. 12 is a perspective view of another apparatus ofthe invention: and l ig. 13 is a cross sectional view of another apparatus according to the invention.

Detailed Description She invention provides a method and an apparatus for humidifying gas in a ventilator circuit. In the invention a humidifying agent (sterile water or sterile saline) is aerosolised and then delivered to a ventilator circuit coupled to the respiratory system of a patient.

The humidifying system of the invention is particularly useful in delivering the aerosolised humidifying agent to a patient whose breathing is being assisted by a ventilator 100 as illustrated diagrammaticaUy in Fig. IA. An inhalation or inspiration line 101 extends from the ventilator 100, A return or exhalation line 102 also extends to the ventilator 100 The inspiration and exhalation lines are connected to a junction piece 103. which may be a wye junction. A patient line 105 extends from the wye 103 to an endotracheal tube 106 which extends to the patients lungs. Generally, the various lines 101, 102, 105. 106 are provided by lengths of plastic tubing which are interconnected. The tubing defines lumens for passage of ventilation air, during the inspiration phase, along the inspiration line 101. patient lines 105 and endotracheal tubes 106 into the patients lungs. During the expiration phase exhaled air is delivered along the endotracheal tube 106. patient lines 105 and the expiration iine 102. The wye junction 103 provides a common pathway for inspiration and exhalation between the junction 103 and the patients lungs. The ventilator 100 mechanically assists the flow of oxygenated air to the patient during the inspiration phase and in the exhalation phase a patient exhales, either naturally or by the ventilator applying negative pressure. ΙΕ ΰ SO 2 The apparatus comprises a reset voir 1 for storing sterile water or saline solution, ‘.he aerosol generator 2 for aerosolising the water, and a controller 3 for controlling the operation ofthe aerosol generator 2.

Iti one aspect of the invention, an aerosol generator 2 is used to deliver art aerosolised humidifying agent into the ventilation air during the inspiration phase.

In the arrangement of Fig IB the apparatus also comprises a sensor 11 lor determining flow of air in the inspiration line 10. The sensor 1! ss connected by a control wire 9 to the controller 3, and the aerosol generator 2 is also connected to the controller 3. ihe humidifying agent may be sterile water or sterile saline v/ith a salt concentration in the range from 1 micromolar to 154 millirnoiar Such saline concentrations ean be readily nebulised using the aerosolisation technology used in the invention.

In the invention an aerosol is delivered into the breathing circuit. The distinction between aerosol and vapour is in the size ofthe particles. The majority of aerosol particles that the aerosol generator produces are in the 0.5 to 5.0 micron diameter range. Water vapour on the other hand contains individual water molecules which are approximately 0.00001 microns I.e. 10,000 times smaller than the aerosol 2.5 particles.

In tiie invention medical gases tor those patients on mechanical ventilation ate humidified. The lung is conditioned to receive gas at close to 100% relative humidity (RH) .in the invention when undergoing mechanical ventilation the gas is also at 100% RH when exiting the endotracheal tube. 9 0 2 38 -12The amount of water a gas can hold is directly proportional to the temperature of ihe gas. The table below demonstrates the amount of water that air can hold at various temperatures to give 100% relative humidity Air Temperature °C Amount of HzO required per L to give 100% RH 10 9,4 mg 20 17.4 mg 30 30.5 mg 37 44.1 mg Thus, adding 0.044ml of EEO to IL of dry air at 37°Cwill result in the air having a relative humidity of 100%. making it suitable for patients undergoing mechanical ventilation.

This aerosol generator 2 converts the water into an aerosol of a very definable particle size. The volume mean diameter (vmd) would typically be in the range ot 2 10 microns.

The controller 3 is used to provide electrical power to drive the aerosol generator.

This provides the aerosolising action to convey humidification to the breathing circuit.

Referring to rig. IA and IB. in this ease an aerosol generator is placed between the Wye 103 and the endotracheal tube (ET) 106 to the patient. The aerosol generator is used to generate an aerosol of sterile water or sterile saline to humidity the gas being delivered to the patient. in the arrangement of Fig. IB i00% humidity at the end of the ET tube is achieved by having the nebulizer separate from the HME acting to top-up (boost) the humidity that is lost when using passive humidification via a HME.

IE Ο 9 Ο 2 3 -13ln the ease of an HME booster the aerosol generator 2 is placed between the ET and a HME 120 as illustrated in Eig.l B. for non boosting applications such as active humidification a HME unit is not required and an aerosol generator 2 is placed between the wye junction 103 arid the endotracheal tube 106 as illustrated in Fig. 12. In the arrangement of Fig. 12 100% humidity at the end ofthe ET tube 106 is achieved because all the humiditv for the patient is provided by the nebuliser 2 with no passive humidification.

Aerosol can be delivered continuously, intermittently in short bursts or generated only on inspiration. A flow meter (sensor) 11 may be placed in the inspiratory tubing 101 so that the aerosol output can be adjusted to the inspiratory How. This prov ides feedback to the controller 3 to provide aerosol while the sensor 11 detects flow to the patient which occurs in the inhaled breath. Sterile water or sterile normal saline is used as the humidifying agent and the system is sealed from the atmosphere reducing contamination risk.

Another variant is illustrated in Fig. 13. This shows a combination of an aerosol generator 200 and a HME (Heat and Moisture Exchange) filter 201 that has an inbuilt liquid reservoir 202. This functions as a booster for passive humidification. In the arrangement of Fig 13 100% humidity at the end ofthe ET tube is achieved by providing a top-up (boost) in humidity when using passive humidification via the HME, which is provided by an in-built aerosol generator 200 comprising a vibratable aperture plate which is incorporated into the HME.

The HME unit 201 has a hydrophobic membrane 205 and is provided with a drain 206. The HME unit also has a drain - off port closable by a lid.

The in built liquid reservoir 202 may be replenished as required, so as to ensure an adequate supply of additional humidity t.o the circuit.

Aqueous solution may be stored in the reservoir 1 ofthe nebuliser or the aqueous solution may be delivered to the reservoir 1 ofthe aerosol generator 2 in this case JE 0 9 0 2 3 8 -14irom a supply reservoir 25 along a delivery line 26. The flow of aqueous solution rnay be by gravity and/or may be assisted by an in-line flow controlling device 27 such as a pump and/or a valve which may be positioned in the delivery line 26. Ihe operation of the flow controlling device 27 may be controlled by the controller 3 along a control wire 28 to ensure that the aerosol generator 2 has a supply of aqueous solution during operation and yet does not allow fluid build up which may affect the operation of the aersoliser. The device 27 may be of anv suitable type.

The vibrating mesh aerosol generator can work with many types of micro pumps. blow rates of pumps depend on the application and aerosol output requirements however they are typically in the range of 50 nano litres per minute to 5 millilitres per minute. Such micro pumps can have different means of providing the pumping action and can include membrane pumps, electrohydrodynamic (bill)) pumps, electrokinetic, (bK) pumps, rotary pumps, peristaltic pumps, phase change pumps, and several other types of pumps. Diaphragm pumps that are driven by piezo activation are of particular interest as much of the control circuitry utilised is similar to that used to drive vibrating mesh technology and therefore integration of the circuits is simpler and cheaper to undertake.

The invention allows for the nebulization of liquids with surface tensions lower than water. These solutions are nebulizable but due to the surface tension they leak through the aperture plate when left sitting on it. When dispersed onto the aperture plate in a controlled drop by drop fashion the issue of leakage through the aperture plate wall not occur.

The device also facilitates nebuiisation of solutions that are prone to frothing. The potential to dispense the solution onto the aperture plate in a controlled fashion will prevent the build up of the solution on the aperture plate and the tendency to froth will be eliminated.

IE 0 90 2 3 8 -15The device will reduce unnecessary exposure of solutions that are prone to oxidation or that are light sensitive.

As the pump feed can he located diiectlv behind the aerosol plate It will remove the current restriction of the liquid feed being dependent and will allow the creation of aerosol through 560X1 orientation ofthe device.

Referring to Fig. 14 there is iilustrated another apparatus according to the invention which is similar to that illustrated in rig. IB and like parts are assigned the same reference numerals. In this ease the nebuiiser reservoir 1 has a top opening 400 which is elosabie by removable plug 401. liquid, saline or water for humidifying purposes and/or medicament is delivered into the nebuiiser reservoir through the opening 400. fhe opening 400 is appropriately sized to receive standard nebulas containing liquid to be nebulised. The liquid may be applied by syringe or other suitable deliv ery means. it is also possible to provide the nebuiiser 1 pre-loaded with medicament to avoid the requirement to separately add medicament to the system.

The apparatus of Fig. 14 is operated in a similar way to the modes of operation described with reference to Figs. 2 to 11.

Referring to Fig. 15 there is illustrated another apparatus ofthe invention which is similar to that described above with reference to Fig. 12 and like parts are medicament.

The apparatus comprises a connector 30. in this ease a Ί-piece connector 30 having a ventilation gas conduit inlet 31 and an outlet 32. The connector 30 also assigned the same reference numerals, in this case the nebuiiser reservoir I lias a top opening 4/)0 and a removable pkig/bd 401 as described with reference io Fig. and the apparatus is operated as described above with the liquid being introduced through the opening 400 Again the nebuiiser may be pre-loaded with 'E09J2J, -16eomprises an aerosol supply conduit 34 for delivering the aerosol from the aerosol generator 2 into the gas conduit 105 to entiain the aerosol with the ventilation gas, passing through the gas conduit 105 The entrained aerosoi/ventilation gas mixture passes out ofthe connector 30 through the outlet ’ 32 and is delivered to the endotracheal tube 106.

I ne aerosol supply conduit 34 and the ventilation gas conduit 105 meet at a junction. Referring particularly to Figs. 4 and 5, in the assembled apparatus the aerosol supply conduit ofthe connector 30 may be releasably mounted to a neck 36 of the aerosol generator housing by means of a push-fit arrangement. This enables the connector 30 to be easily dismounted from the aerosol generator housing 36, for example for cleaning. The neck 36 at least partially lines the interior ofthe aerosol supply conduit 34. fhe nebuliser (or aerosol generator) 2. has a vibratable member which is vibrated at ultrasonic frequencies to produce liquid droplets. Some specific, non-limiting examples of technologies for producing fine liquid droplets is by supplying liquid to an aperture plate having a plurality of tapered apertures extending between a first surface and a second surface thereof and vibrating the aperture plate to eject liquid droplets through the apertures. Such technologies are described generally in U.S. Pat. Nos. 5,164,740; 5,938.117; 5,586,550; 5,758,637: 6.014.970. 6,085,740. and IJS2005/021766A, the complete disclosures of which aie incorporated herein by reference. However, it should be appreciated that the present invention is not limited for use only with such devices. iCj ΓΜ Various methods of controlling the operation of such nebulisers or aerosol generators are described in US 6,540.154, US 6,845,770. US 5.938.117 and US 6.546.927. the complete disclosures of which are incorporated herein by reference. in use. the liquid to be aerosolised is received at the first surface, and the aerosol generator 2 generates the aerosolised liquid at the second surface by ejecting IE 0 9 0 2 j8 droplets of the liquid upon vibration of the vibratable member. The apertures in the vibratable member are sized to aerosolise the liquid by ejecting droplets of the liquid such that the majority of the droplets by mass have a size of less than 5 micrometers.

Referring particularly to Figs 4 and 5. in one ease tbe aerosol generator 2 comprises a vibratable member 40. a piezoelectric element 41 and a washer 42. which are sealed within a silicone overmould 43 and secured iri place within the housing 36 using a retaining ring 44. The vibratable member 40 has a plurality of tapered apertures extending between a first surface and a second surface thereof. The first surface of the vibratable member 40, which in use faces upwardly, receives the liquid from the reservoir 1 and the aerosolised liquid, is generated at the second surface of the vibratable member 40 by ejecting droplets of liquid upon v ibration of the member 40. In use the second surface faces downwardly. In one case, the apertures in the vibratable member 40 may be sized to produce an aerosol in which the majority of the droplets by weight have a size of less than 5 micrometers.

The vibratable member 40 could be non-planar, and may be dome-shaped in geometry. l he complete nebuliser may be supplied in sterile form, which is a significant advantage for use in breathing circuits.

Referring particularly to Fig 3. the controller 5 controls operation of and provides a power supply to the aerosol generator 2. The aerosol generator has a housing whieh defines the reservoir 1. The 'rousing has a signal interface port 38 fixed to the lower portion of the reservoir 1 to receive a control signal from the controller 3. The controller 3 may be connected to the signal interface port 38 by means of a control lead 39 which has a docking member 50 for mating with the port 38. A control signal and power may be passed from the controller 3 through the lead 39 ,Ε Ο 9 0 2 3818~ and the port 38 to the aerosol generator 2 to control the operation of the aerosol generator 2 and to supply power to the aerosol generator 2 respectively.

Ihe power source for the controller 3 may be an on-board power source, such as .? a rechargeable battery, or a remote power source, such as a mains power source, or an insufflator power source. When ’he remote power source is an .AC mains power source, an AC-DC converter may be connected between the AC now or source and the controller 3. Λ power connection lead may be provided to connect a power socket of the controller 3 with the remote power source.

Referring particularly to Fig. 6 the controller 3 has a housing and a user interface to selectively control operation of the aerosol generator 2. Preferably the user interface is provided on the housing which, in use, is located remote from the aerosol generator housing. The user interface may be in the form of, for example, an on-off button. In one embodiment a button can be used to select pre-set values for simplicity of use. In another embodiment a dial mechanism can be used to select from a range of values irom 0-100%.

Status indication means are also provided on the housing to indicate the operational state of the aerosol generator 2. For example, the status indication means may be in the form of two, visible LED's, with one LED being used to indicate power and the other LED being used to indicate aerosol delivery. Alternatively one LED may be used to indicate an operational state of tire aerosei generator 2. anu the other LED may be used to indicate a rest state of the aerosol generator. 2.

A fault indicator may also be provided in the form of an LED on the housing. A battery charge indicator in fhe form of an LED may be provided al tbe side of the housing.

Referring particularly to Figs IA and IB. the liquid in the reservoir 1 flows by gravitational action towards the aerosol generator 2 at the lower medicament ΙΕ°9023β -19outlet. The controller 3 may then be activated to supply power and a control signal to the aerosol generator 2. which causes the piezoelectric element 41 to vibrate the non-planar member 40. This vibration ofthe non-planar member 40. causes the aqueous solution at the top surface of the member 40 to pass through the apertures to the lower surface where the aqueous solution is aerosolised by the ejection of small droplets of solution.

Referring particularly to Figs 4 and 5. the aerosol passes from the aerosol generator 2 into the neek 36 ofthe aerosol generator housing, which is mounted within the aerosol supply conduit ofthe connector 30 and into the gas conduit of the connector 30 (flow A). The aerosol is entrained in the ventilation gas conduit witli gas, which passes into the gas conduit through the inlet 31 (flow B). The entrained mixture of the aerosol and the ventilation gas then passes out ofthe gas conduit through the outlet 32 (flow C) and on to the endotrachael tube 106.

The How rate sensor/meter 11 determines the flow rate of the ventilation gas. In response to the fluid flow rate ofthe ventilation gas. the controller 3 commences operation of the aerosol generator 2 to aerosolise the aqueous solution. The aerosolised aqueous solution is entrained with the ventilation gas, and delivered to the patient. in the event of alteration of the fluid flow rate of the ventilation gas, the flow rate sensor/meter 11 determines the alteration, and the controller 3 alters the pulse rate of the vibratable member of the nebuiiser accordingly.

The controller 3 is in communication with the flow rate sensor/meter 11. The controller 3 is configured to control operation of the aerosol generator 2. responsive to the fluid flow rate of the ventilation gas and also independent ofthe fluid flow rate of the ventilation gas as required.

In one case, the controller 3 is configured to control operation of the aerosol generator 2 by controlling the pulse rate at a set frequency of vibration of the -20ΙΕ 0 90 2 38 vihratable member, and thus controlling the fluid flow rate of the aqueous solutions.

The controller 3 may comprise a microprocessor 4, a boost circuit 5, and a drive circuit 6. Fig. 2 illustrates the microprocessor 4, the boost circuit 5. the drive ei’euit 6 comprising impedance matching components (inductor), the nebuliser 2. and the aerosol. The inductor impedance is matched to the impedance of the piezoelectric element of the aerosol generator 2. The microprocessor 4 generates a square waveform of 128KHz which is sent to the drive circuit 6. The boost circuit 5 generates a 12V DC voltage required by the drive circuit 6 from an input of either a 4.5V battery or a 9V AC/DC adapter. The circuit is matched to the impedance of the piezo ceramic element to ensure enhanced energy transfer. A drive frequency of 128 KHz is generated to drive the nebuliser at close to its resonant frequency so that enough amplitude is generated to break off droplets and produce the aerosol. If this frequency is chopped at a lower frequency such that aerosol is generated for a short time and then stopped for a short time this gives good control ofthe nebuliser's flow rate. This lower frequency is called the pulse rate.

Tne drive frequency may be started and stopped as required using the microprocessor 4. T his allows for control of flow rate by driving the nebuliser 2 for any required pulse rate. The microprocessor 4 may control the on and off times to an accuracy of milliseconds.

The nebuliser 2 may be calibrated at a certain pulse rate by measuring how long it lakes to deliver a know quantity of solution. There is a linear relationship between the pulse rate and the nebuliser flow rate. This may allow for accurate control over the delivery rate of the aqueous solution.

The nebuliser drive circuit consists of the electronic components designed to generate output sine waveform of approximately 100V AC which is fed to nebuliser 2 causing aerosol to be generated. The nebuliser drive circuit 6 uses ,Εθ 90 238 -21inpuls from microprocessor 4 and boost circuit 5 io achieve its output. The cireuit is matched to the impedance of the piezo ceramic element to ensure good energytransfer.

The aerosol generator 2 may be configured to operate in a variety ei' different modes, such as continuous, and/or phasic, and/or optimised. for example, referring to fig 7(a) illustrates a 5V DC square waveform output from the microprocessor 4 to the drive circuit 6. Fig 7(b) shows a low power. -400V AC sine waveform output from drive circuit 6 to nebuliser 2. Doth waveforms have a period p of 7.8qS giving them a frequency of 1/7.8qs which is approximately l28KHz. Both waveforms are continuous without, any pulsing. Tiie aerosol generator may be operated in this mode to achieve 100% aerosol output.

Referring lo bigs 8(a) in another example, there is illustrated a 5V DC square waveform output from the microprocessor 4 to ihe drive circuit 6. Fig 8(b) shows a tow power, 100V AC sine waveform output from the drive circuit 6 to the nebuliser 2. Both waveforms have a period p of 7.8pS giving them a frequency of l/7.8qs which is approximately 128KHz. In both cases the vvavefoms are chopped (stopped/OFF) for a period of time x. In this case the off time x is equal to the on time x. The aerosol generator may be operated in this mode to aehicve 50% aerosol output.

In another ease, referring to Figs 9(a) there is illustrated a 5V DC square waveform output from microprocessor 4 lo drive circuit b. Fig 9(b) shows a tow 2. Both waveforms have a period p of 7,8pS giving them a frequency of 1 /7Aus whieh is approximately 128KHz. In both cases the wavefoms are chopped (stopped/OFF) for a period of time x. In this case the off time is 3x while the on time is x. The aerosol generator may be operated in this mode to achieve 25% aerosol output. power. 100V AC sine waveform output from the drive circuit 6 to the nebuliser ,£ 0 9 Ο 2 38 -22Referring to Fig 10. in one application pulsing is achieved by specifying an ontime and off-time for the vibration of the aperture plate. If the· on-time is set to 200 vibrations and off-time is set to 200 vibrations, the pulse rate is 50% (½ on '/2 off). This means that the flow rate is half of that of a fully driven aperture plate. Any number of vibrations can be specified but to achieve a linear relationship between flow rate and pulse rate a minimum number of on-time vibrations is specified since it takes a Unite amount of time for the aperture plate to reach its maximum amplitude of vibrations.

The drive frequency can be started and stopped as required by the microprocessor; this allows control of flow rate by driving the nebuliser for any required pulse rate. The microprocessor can control the on and off times with an accuracy of microseconds.

A nebuliser can be calibrated at a certain pulse rate by measuring how long it takes to deliver a known quantity of solution. There is a linear relationship between the pulse rate and that nebuliser's flow rate. This allows accurate control of the rate of delivery of the aerosolised aqueous solution. l he pulse rate may be lowered so that the velocity of the emerging aerosol is much reduced so that impaction rain-out is reduced.

Detection of when the aperture plate is dry can be achieved by using the fact that a dry apertuie plate has a well defined resonant frequency, if the drive frequency is swept from 1 20kHz to 145kHz and the current is measured then if a minimum current is detected less than a set value, the apeiture plate must have gone dry, A wet aperture plate has no resonant frequency. The apparatus ofthe invention may be configured to determine whether there is any of the first fluid in contact with the aerosol generator 2. By determining an electrical characteristic of the aerosol generator 2, for example the current flowing through the aerosol generator 2, over a range of vibration frequencies, and comparing this electrical characteristic -23,Ε 0 90 238 against a pre-defined set of data, it is possible to determine whether tiie aerosol generator 2 has any solution in contact with the aerosol generator 2. Fig. 11 illustrates a curve 80 of frequency versus current when there is some of the solution in contact with the aerosol generator 2, and illustrates a curve 90 of frequency versus current when there is none of the solution in contact w ith the aerosol generator 2. Fig. 11 illustrates Ihe wet aperture plate curve 80 and the dry aperture plate curve 90.

II an application requires a constant feed from a drip bag then a pump can be 10 added in line to give fine control of the liquid delivery rate which can be nebulised drip by drip. The rate would be set so that liquid would not build up in the nebuliser. This system is particularly suitable for constant low dose delivery’.

In the invention the aerosol generator is placed at the patient's endotracheal tube 15 so there is little to no rain - out in the tubing.

The device is very light and unlike the full heated wire system and very silent unlike the jet nebulizer. Non - heated single patient use ventilator tubing can be used, These bring considerable benefits: reduced cost of maintenance (care giver time) reduced heat/power cost (in excess of 10 fold) reduced cost of capital equipment and circuits reduced background noise 1 he supply io the aerosol generator is sealed from the atmosphere as it is in a closed circuit and so minimises infection risk even though tlie aerosol particle size is large enough to carry bacteria.

Intermittent short bursts of aerosol can be programmed to optimize water and heat replenishment of the HME, without requiring more complex aerosol generation patterns. -24IE Ο 9 0 2 3 8 Λ drip feed line fed into a small volume reservoir allows the nebuliser to work in almost any orientation, reducing work and risk for the care giver. This aiso can provide a very low weight, low proIIle device.

A ith the aerosol used to augment the WME. another nebulizer for medication deliver. can be placed between the TIME and the patient ET, as described for example in IJS2OO5/O139211 A. the entire contents of which are incorporated herein bv reference. 'ihc invention can be applied to systems used to ventilate all patients requiring mechanical ventilation or having bypassed upper airways requiring supplemental humidification.

AS! patients on mechanical ventilation require humidification either with a heated wire humidifier or a heal moisture exchanger. This system can be configured to add supplemental humidity to a 11ME (heat moisture exchange) only system thereby increasing the capacity ofthe system to adequately humidify patients for longer periods of time than is possible with current embodiments. The system can also be configured to fully replace the humidification element of a heated 2G wire humidifier system by adding sufficient amounts of aerosol to the inspired air.

A major problem with the use of nebulizers in the past was contamination ofthe patient, This has generally been ascribed to the fact that the aerosol particles are of sufficient size to carry bacteria whereas vapour particles are riot, the fact that the Aerogen nebulizers can be sterilized and aiso have the capacity to have a continuous feed of sterile liquid wit! overcome this reported disadvantage. '1 he key advantageous features ofthe invention are: 3(1 * small/compact * quiet fed from a sterile sealed system IE 0 9 0 2 3 8 -25* no large power supply lower cost ’ position independent operation Ute invention is not limited to the embodiments hereinbefore described, which may be varied in construction and detail.

Claims (2)

1. CI aims 1. A method for humidifying gas in a ventilator circuit eomprising;5 aerosolising a humidifying agent using an aerosol generator wherein the aerosol generator comprises a vibratable member having a plurality of apertures extending between a first surface and a second surface thereof; and 10 delivering the aerosolised humidifying agent to a ventilator circuit coupled to the respiratory system of a patient. 2. A method as claimed in claim 1 wherein the ventilator circuit comprises an endotracheal tube, an inspiration line extending from a ventilator and 15 an exhalation line extending from the ventilator. 3. A method as claimed in claim 2 comprising the step of controlling the aerosolisation. 20 4. A method as claimed in claim 3 comprising controlling the pulse rate at a set frequency of vibration ofthe vibratable member. 5. A method as claimed in claim 3 or 4 comprising controlling aerosolisation responsive to the flow of ventilation gas in the inspiration line. 6. A method as claimed in any of claims 3 to 5 comprising controlling the fluid flow rate ofthe aerosolised humidifying agent. 7. A method as claimed in claim 5 or 6 wherein the method comprises the step of determining the flow rate of ventilation gas in the inspiration line. IE Ο 9 Ο 2 3 θ -27A method as claimed in claim 7 comprising determining the Bow rate of ventilation gas using a flow sensor. 9. in A. method as claimed in claim 7 comprising determining the ilov. rale of ventilation gas using a chile rent iai pressure sensor. method as claimed in any of claims i to 9 comprising measuring the level of humidification in tlie ventilator circuit, downstream of the delivery or aerosolised humidifying agent. A method as claimed in claim 10 comprising controlling the output of the nebuliser responsive to the level of humidification in the ventilation circuit. 15 12. A method as claimed in any of claims 1 to 1! wherein the method comprises the step of determining if the humidifying agent is in contact with an aerosol generator 13 A method as claimed in claim 12 comprising determining at least one 20 electrical characteristic of the aerosol generator. 14. A method as claimed in claim 13 comprising determining at least electrical characteristics of the aerosol generator over a range of vibration frequencies. 15. Λ method as claimed in claim 12. or 13 wherein the method comprises the step of comparing the at least one electrical characteristic against a predefined set of data. 16. A method as claimed in any of claims 1 to 15 wherein the ventilator circuit comprises an inspiration line and an exhalation line which are connected at a junction, and a patient line extending from the junction lor IE 0 9o 2 -28conneetion to an endotracheal tube, and the method comprises the step of delivering the aerosolised humidifying agent into the patient line between the junction and the endotracheal tube. 17. A method as claimed in claim 16 wherein the ventilation circuit comprises a heat and moisture exchange unit in the patient line and the method comprises the step of delivering the aerosolised humidifying agent into the patient line between the heat and moisture exchange unit and the endotracheal tube. 18. A method as claimed in claim 16 wherein the ventilation circuit comprises a heat and moisture exchange unit in the patient line and the method comprises delivering the aerosolised humidifying agent into the heat and moisture exchange unit. 19. Λ method as claimed in claim 18 wherein the aerosolised humidifying agent is delivered into rhe heat and moisture exchange unit on the patient side ofthe heat and moisture exchange unit. 20. A method as claimed in claim 18 or 19 wherein the aerosol generator is mounted to the heat and moisture exchange unit. 21. Λ method as claimed in any of claims 18 to 20 wherein the aerosol generator is integral with the heat and moisture exchange unit. 2.

2. A method as claimed in any of claims 1 to 16 comprising heating inspiration gas and delivering Ihe aerosolised humidifying agent into the heated inspiration gas. 23. An aerosol introducer apparatus for introducing aerosolised humidifying agent into a ventilation circuit comprising an endotracheal tube, an inspiration line extending from a ventilator, and an exhalation line extending from the ventilator, the introducer comprising an aerosol generator and control means for controlling the operation of the aerosol generator wherein the aerosol generator comprises a vibralable member having a plurality of apertures extending between a first surface and a 5 second surface thereof. 24. An apparatus as claimed in claim 23 wherein the controller is configured to control operation ofthe aerosol generator responsive to the (low of gas in the inspiration line. 25. An apparatus as claimed in claim 23 or 24 wherein the controller is configured to control the flow rate of the humidifying agent to be aerosolised. 15 26. An apparatus as claimed in any of claims 23 to 25 wherein the apparatus comprises a device to determine the fluid flow' rate of the gas in the inspiration line. 27. An apparatus as claimed in claim 26 wherein the determining device 20 comprises a flow rate sensor. 28. An apparatus as claimed in claim 27 wherein the determining device comprises a differential pressure sensor. 25 29. An apparatus as claimed in any of claims 23 to 27 wherein the ventilation circuit comprises a junction for connecting the inspiration line and the exhalation line and a patient line for extending between the junction and the endotracheal tube and wherein the aerosol generator is arranged for delivery of aerosolised humidifying agent into the patient line betw een the 30 junction and the endotracheal tube, 30. An apparatus as claimed in claim 29 wherein the ventilation circuit comprises a heat and moisture exchange unit for location in the patient line. 5 31. An apparatus as claimed iu claim 30 wherein the aerosol generator is arranged for delivery of aerosolised humidifying agent into the patient line between the heat and moisture exchange unit and the endotracheal tube, 8. 10 32. An apparatus as claimed in claim 31 wherein the aeioso! generator is mounted on a connector for connection in the patient line. 33. An apparatus as claimed in claim 31 wherein the aerosol generator is mounted to the heat and moisture exchange unit, 34. An apparatus as claimed in claim 33 wherein the aerosol generator is integral with the heat and moisture exchange unit. 35. An apparatus as claimed in claim 33 or 34 wherein the heat and moisture 20 exchange unit has a drain-off port. 36. An apparatus as claimed in any of claims 23 to 29 comprising heating means for heating inspiration gas. 37. An apparatus as claimed in claim 36 wherein the heating means comprises a heated wire extending along at least a portion ofthe inspiration line. 38. An apparatus as claimed in any of claims 23 to 37 wherein the first surface is adapted to receive the humidifying agent to be aerosolised. 39. An apparatus as claimed in any of claim 23 to 38 wherein the aerosol generator is configured to generate an aerosol at the second surface. -31 40. 41. y\n apparatus as claimed in any of claims 23 to 39 wherein the vibraiable member is dome-shaped in geometry. An apparatus as claimed in any of claims 23 to 39 wherein the vibratable member is of stretched flat shape. member comprises a piezoelectric element. 43. An apparatus as claimed in any of claims 23 to 42 wherein the apertures in the vibratable member are sized to aerosolise the humidifying agent by ejecting droplets of the water such that the majority of the droplets by mass have a size of less than 5 micrometers. 44. An apparatus as claimed in any of claims 23 to 42 wherein the apertures in the vibraiable member are sized to aerosolise the humidifying agent by ejecting droplets of the water such that the majority of the droplets by mass have a size of less than 3 micrometers. 45. An apparatus as claimed in any of claims 23 to 42 wherein the apertures in the vibratable member are sized to aerosolise the first fluid by ejecting droplets of the first fluid such that the majority of the droplets by mass have a size range of less than 10 micrometers. 46. An apparatus as claimed in claim 45 wherein a range band is from 1 to 3 micrometers. 47. An apparatus as claimed in claim 45 or 46 wherein a range band is from 7 to 9 micrometers. IE Ο 90 2 48. An apparatus as claimed in any of claims 23 to 47 wherein the controller is configured to control the pulse rate at a set frequency of vibration ofthe vibratable member. 49. An apparatus as claimed in am of claims 23 to 48 wherein the controller is impedance matched to the aerosol generator. 50. An apparatus as claimed in any of claims 23 to 49 wherein the apparatus comprises means to determine whether the humidifying agent is in contact with the aerosol generator. 52. An apparatus as claimed in claim 50 wherein the determining means is configured to determine at least one electrical characteristic ofthe aerosol generator. An apparatus as claimed in claim 51 w'herein the determining means is configured to determine at least one electrical characteristic of the aerosol generator over a range of vibration frequencies. 20 53. An apparatus as claimed in claim 51 or 52 wherein the determining means is configured to compare the at least one electrical characteristic against a pre-defined set of data. 54. An apparatus as claimed in any of claims 23 to 53 comprising a flow 25 controlling device for delivery of fluid to be aerosolised to the aerosol generator. 55. An apparatus as claimed in claim 54 wherein the flow controlling device comprises a micropump. 56. An apparatus as claimed in claim 55 wherein the micropump comprises a diaphragm pump. /£ 0 90 2 Jg 57. An apparatus as claimed in claim 56 wherein the diaphragm pump is driven by piezo activation. 58. An apparatus as claimed in any of claims 54 to 57 wherein the flow controlling device comprises a microvalve. 59. An apparatus as claimed in claim 53 wherein the valve is a solenoid valve. 60. An apparatus as claimed in any of claims 54 to 59 wherein the controller controls the operation ofthe How controlling device.