SCAVENGING SYSTEM

Field of the Invention

The present invention relates to a monitoring apparatus and method for use in a gas scavenging system, and, particularly, but not exclusively, to a monitoring apparatus and method for use in monitoring operation of an air brake for a gas scavenging system.

Background of the Invention

In many facilities there is a requirement for gas scavenging systems to remove waste gases and/or hazardous gases. For example, in anaesthesia, it is necessary to remove anaesthetic gases from anaesthesia delivery systems to reduce or stop leakage into the ambient atmosphere in the surgery. Anaesthetic gases can, of course, be dangerous. There are other circumstances where gases, which may be hazardous or not, need to be removed.

Gas scavenging systems are known, which comprise a number of different types of suction system which are arranged to be connected to equipment containing the gas to be scavenged, in order to remove the gas. Such systems are commonly used in anaesthesia in surgery, veterinary or human, and in other circumstances where anaesthetic is used, such as lab animal processes.

Suction-type scavenging systems apply different levels of suction, depending upon the type of system (and its setting) . As well as being applied to anaesthetic equipment for removing excess anaesthetic gases, these suction scavenging systems are more generally available for removing other gases, e.g. from fume cupboards, ambient air, etc. As anaesthetic delivery is finely regulated (very precise amounts must be delivered to patients, for example), the suction systems are not directly connected to anaesthetic equipment. This could upset the regulation of the delivery of anaesthetic gases to the patient .

Instead, devices are placed between the anaesthetic equipment and the scavenging suction system to eliminate or moderate any effect of the suction system on the anaesthetic delivery to the patient. One such device is an air brake .

Air brakes generally comprise two inlets and an outlet. One inlet is connected to a source of the gas to be scavenged. In the case of anaesthesia, one inlet may be connected to the anaesthetic equipment. The outlet is connected to the scavenging system, generally being a suction source. The other inlet is usually open to the ambient atmosphere. Air is brought in through the other inlet from the ambient atmosphere and is entrained together with the waste gas. Suction applied by the scavenging system, therefore, does not wholly transfer to the source of waste gas (e.g. anaesthetic equipment).

Instead, ambient air will be brought into the air brake. This prevents undue suction being applied to the

anaesthetic equipment so that anaesthesia can be regulated carefully without being affected by the gas scavenging system. The air brake can deal with different rates of delivery of scavenged gas from the anaesthetic equipment, by entraining more or less ambient air. The air brake can also be connected to different types of scavenging systems, which may have different suction rates, and still operate to prevent any affect downstream on the

anaesthetic equipment or other equipment producing gases to be scavenged. The air brake also acts as a reservoir as well as to cope with different delivery amounts over time of the gas to be scavenged. Variable amounts of gas may be produced by anaesthetic circuits, for example, when in operation.

A problem with current air brake arrangements, is that there is no way of knowing whether the gas flow through the air brake is appropriate. For example, there may be circumstances where there is no delivery of scavenged gases or low pressure at that inlet and there is the potential for the direction of flow to reverse or even (of more concern) flow of waste gases out of the ambient atmosphere inlet into the ambient atmosphere . Current air brakes are passive devices which do not provide any indication of their operation. They are also often expected to last a long time, and are often ill maintained and attended, which can lead to malfunction, without any operators knowing that they are malfunctioning.

Summary of Invention

In accordance with a first aspect, the present invention provides a monitoring apparatus for a gas scavenging system, comprising a sensor arranged to detect flow of gas in an air brake for a gas scavenging system, and circuitry arranged to determine whether the gas flow is appropriate and to issue an alarm if the gas flow is not appropriate.

In an embodiment, the circuitry is arranged to determine whether there is any gas flow, and to provide an indication if there is gas flow. In an embodiment, the sensor is arranged to measure gas flow direction in the air brake. The air brake may be attached to a scavenging suction system. If flow

direction is incorrect, it could indicate malfunction.

In an embodiment, the circuitry is also arranged to provide an indicator should gas flow be normal . This may be a visual indicator. The alarm may be a visual and/or audible indicator.

In an embodiment, the indicator is arranged to provide an indication that gas flow is on (suction is on)

In an embodiment, the apparatus comprises a power source. In an embodiment, when the apparatus is not in operation, it is arranged to enter a hibernation mode where the circuitry does not operate, in order to save draining the power source. In an embodiment, the

circuitry is arranged to exit hibernation mode when it detects gas flow. Having a hibernation mode has the advantage that the apparatus can remain dormant for long periods of time without draining power. On detection of gas flow it exits hibernation mode. Advantageously, little maintenance or attention is required, facilitating reliable operation of the device.

In an embodiment, the sensor and circuitry are mounted in a housing. The housing is arranged to be connected to the air brake. In one embodiment, the housing forms a cap that fits to one end of an air brake housing .

In accordance with a second aspect, the present invention provides an air brake for a gas scavenging system, the air brake comprising a monitoring apparatus in accordance with the first aspect of the invention. In an embodiment, the air brake comprises a first inlet for receiving waste gas and a first outlet for receiving suction from a gas scavenging system. It also comprises a second inlet for receiving a reservoir fluid flow. The reservoir fluid may be ambient air. In an embodiment, the second inlet is positioned prior to the first inlet and the outlet. In an embodiment, the outlet is positioned between the second inlet and the first inlet. This reduces the likelihood of creating a Venturi effect acting on waste gases from the first inlet.

In accordance with a third aspect, the present invention provides an air brake for gas scavenging system, comprising a first inlet for receiving waste gas, an outlet for receiving suction, and a second inlet for receiving ambient gas, the outlet being positioned between the first inlet and second inlet in relation to the flow of gases when operating. In accordance with a fourth aspect, the present invention provides a method of operating an air brake for a gas scavenging system, the air brake comprising a housing having a first opening, a second opening and a third opening, the method comprising the steps of

operating the air brake so that the first opening is arranged to receive ambient air, the second opening, between the first opening and the third opening, is operated to act as an outlet connected to a source of suction, and the third opening is operated to receive waste gases.

In an embodiment, the apparatus has the advantage that any Venturi effect on the waste gas which may occur because of entrainment in ambient air is reduced or eliminated. Brief description of the Figures

Features and advantages of the present invention will become apparent from the following description of

embodiments thereof, by way of example only, with

reference to the accompanying drawings in which:

Figure 1 is a front view of a monitoring apparatus in accordance with an embodiment of the present invention;

Figure 2 is a view from the top of the apparatus of Figure 1;

Figure 3 is a view from one side of the apparatus of Figure 1;

Figure 4 is a schematic circuit diagram for circuitry of a monitoring apparatus in accordance with an embodiment of the present invention;

Figure 5a is a schematic diagram showing gas flow through an air brake in accordance with an embodiment of the present invention;

Figure 5b is a schematic diagram showing gas flow through an air brake in accordance with an embodiment of the present invention; and

Figure 6 is a front perspective view of an air brake and monitoring apparatus in accordance with an embodiment of the present invention, shown connected in operation.

Detailed Description of embodiments of the invention

Referring to the figures, a monitoring apparatus for a gas scavenging system is generally designated by reference numeral 1. The apparatus is arranged for use with an air brake for a gas scavenging system (reference numeral 2, Figure 5a&b and Figure 6) . The apparatus comprises a sensor (reference numeral 3, Figure 4) which, in this example, is a differential pressure sensor 3. The sensor 3 is arranged to detect flow of gas in the air brake 2. The monitoring apparatus 1 further comprises circuitry (reference numeral 4, Figure 4) which is arranged to determine whether gas flow is appropriate and to issue an alarm if the gas flow is not appropriate.

In this embodiment, an audible alarm 5 and visual alarms 6 are provided.

In this embodiment, a visual indicator 7 is also provided for indicating that the gas flow is appropriate for operation of the air brake.

In more detail, the monitoring apparatus sensor 3 and circuitry 4 are mounted in a housing 10, which is shaped in the form of a lid to the air brake apparatus 2. As can be seen in Figure 6, the monitoring apparatus housing 10 fits over the air brake apparatus 2.

The air brake apparatus 2 is in the form of a cylindrical body having an opening 20 at its top for inlet of ambient air in operation. The housing 10 of the monitoring apparatus 1 is arranged to fit over the top of the air brake 2 body and over the inlet 20 (see Figure 5 and Figure 6) . The housing 10 has a port 11 to allow ambient air into the inlet 20 in operation. The

differential pressure sensor 3 is arranged within the housing to measure the difference in pressure between the atmosphere external to the orifice 11 and pressure internal to the housing, in fluid communication with the air brake inlet 20. Suction created by gas flowing out the Waste Gas OUT port at a greater flow than waste flowing IN from the anaesthetic machine causes air to flow through the orifice in the cap which creates a measureable pressure differential. The pressure differential can be calibrated against flow to enable the pressure signal to be converted to a flow value if required.

As shown in Figure 5a and 5b, the air brake 2 housing

21 has an internal wall 22, which 25 for the lesser and potentially variable WAG (waste anaesthetic gas) flow to "accumulate" and mix with the greater room air

"unidirectional by-pass" flow with minimal risk of contamination of the room air (which would require backflow of WAG from its inlet point on the reservoir side of the air brake) . In normal operation room air flows in the inlet 20 and along a pathway indicated by the arrows 40 (Figure 5a) . The housing 21 also has a first port 23 for receiving waste gas and second port 24 for connection to the suction system.

In Figure 6 the first port 23 and second port 24 are shown with connectors 25 and 26 connecting to hoses 27, 28. In the embodiment of Figure 6 the hose 28 is

connected to the outlet of an anaesthetic apparatus, in operation. The hose 27 is connected to suction of a gas scavenging system. This could be a WAG scavenging system, for example, which may be low pressure or high pressure. In the embodiment of Figure 6, a HEPA (high

efficiency particulate arrestance) filter 29 is mounted in the line 28 from the anaesthetic apparatus. This prevents or reduces contamination of the airbrake and suction system downstream of the anaesthetic apparatus (patients that may carry respiratory infections, for example) .

Any brands such as Darvall and company names (AAS Medical and Darvall Vet) used in the drawings are brands only, and the invention is not limited to use of these

The air brake 2 can be operated in two different ways .

Referring to Figure 5a, the first way of operation is to attach apparatus producing the waste gas to the lower port 23 and suction to the upper port 24. When waste gas is being produced and the suction is operating correctly, the gas flow through the air brake 2 is as shown by the broad and narrow solid arrows 40 and 41. Ambient air is brought in via the inlet 20, and entrains the waste gas which comes in via the port 23. The entrained waste gases and ambient air exit via the port 24.

A potential problem with this operation of the air brake 2, is that the flow of ambient air (broad arrows 40) past the port 23 can lead to a Venturi effect causing low pressure on the port 23 and an increasing suction on the anaesthetic apparatus . This may tend to cause undue pressure on the anaesthetic apparatus providing the waste gas resulting in variable anaesthetic depth or death if all gas is "sucked" from the system, then the patients lung. This is disadvantageous. A further disadvantage of operation as shown in figure 5a is the effective reservoir size for WAG to accumulate in is relatively small as the effective area for WAG accumulation is between the WAG inlet port 23 and the port 24 connected to the scavenging system.

An alternative method of operation is shown in Figure 5b with air flow represented by the arrows 42 and 43 (in broken lines) . In this method of operation, the apparatus producing waste gas is connected to the upper port 24 and the suction is connected to lower port 23, similar to the arrangement shown in Figure 6. This arrangement provides a larger effective reservoir (the whole top of the reservoir 25 above the lower port 23) for WAG in case of variable flow from the anaesthetic machine or

alternatively variability in suction flow.

In operation, waste gases 43 are drawn through the port 24 towards the port 23 by suction from the port 23, mixing with the ambient air flow (line 42) . This method of operation reduces the potential for any Venturi effect on the waste gas flow.

Whatever method of operation is applied to the air brake 2, the monitoring apparatus 1 is arranged to determine whether an appropriate gas flow is occurring. As discussed above, different scavenging systems may have different suction pressures. The same scavenging system may have different suction pressures at different times, depending upon the demand occurring. Further, waste gas will not generally be produced at constant flow.

Sometimes there will be a lot of waste gas being produced, such as the end of the expiratory cycle during respiration and sometimes low flow or no flow such as during peak inspiratory flow. The air brake must cope with these variations without malfunctioning. If malfunction does occur, the monitoring apparatus 1 provides an indication. For example, it might provide an indication if no flow is occurring when it should, or if the flow is occurring in the wrong direction (which could indicate waste gases are being expelled into the ambient atmosphere) .

The monitoring apparatus 1 comprises a differential pressure sensor 3 with one side of the transducer located inside the cavity of the WAG airbrake (so isolated from the room air) and the other side vented to the

room/atmosphere plus micro-electronic circuitry 4. See Figure 4. It is arranged to determine whether gas flow is indeed occurring in either direction and in which

direction the gas flow is occurring. As long as gas flow is occurring in the correct direction, as measured by the differential pressure transducer (so pressure within the WAG Airbrake must be less than the room air) , correct operation is indicated by a green LED 7.

Based on the input from the pressure sensor 3 the microprocessor can determine the direction of gas flow within the air brake and determine correct operation or fault conditions. For example, in an embodiment

embodiment "normal" suction operation flows are defined as 30 to 80 litres per minute. Other embodiments may operate in a range of 10 to 40 litres per minute or 50 to 100 litres per minute. The microprocessor can be configured to determine whether the level of output from the

differential pressure sensor is indicative of a flow rate within this target range, for example, based on boundary criteria. In an embodiment the microprocessor is

programmed with at least a low pressure threshold value, indicative of the differential pressure sensor output for a pressure differential required to achieve the minimum air flow rate through the air brake. The determination of operation within target range may be based directly on the pressure sensor output, with target range or threshold values stored in the microprocessor memory being for the pressure sensor output being indicative of the target flow rate range . It should be appreciated that in some embodiments the microprocessor may be programmed to calculate the actual flow rate based on the measured differential pressure (calibrated against flow and the data stored as a "look-up table) and compare this with a target flow rate range to determine whether or not the air brake is operating within the normal range .

Faulty/abnormal operation of the air brake can include:

Fault conditions where there is no air flow so no delivery of scavenged gasses or suction flow to the scavenging unit; (this will also occur when the air brake is not in use and the monitor is in "sleep mode")

Low pressure fault conditions where there is low pressure at the inlet so Waste Gas may not be removed at the rate it is delivered;

Extreme low flow or fluctuating flow conditions where there is potential for the direction of flow to reverse resulting in flow of Waste Gas into the room air - occupational safety hazard; and

Flow reversal conditions where the flow of waste gasses is out into the atmosphere.

The microprocessor can be programmed to determine the various faulty operating conditions based on the actual pressure levels and relative relationship of the ambient vs intra-device sides of the transducer (i.e. positive or negative direction of pressure = flow) . A characteristic measured by the pressure sensor. For example, if the pressure sensor indicates a lower pressure in the external atmosphere, outside the inlet 11, then this is indicative that the suction is not adequate or is in the wrong direction (which could result in waste gases flowing into the ambient atmosphere) or the Waste Gas flow has

increased relative to suction flow, and an alarm is provided. This is provided by visual indication (red LED 6) and audible alarm 5 (a beeper) . A software alarm 8 can also be provided connected to other monitoring apparatus, for example.

Where there is no pressure differential this may indicate the scavenging device is off (and the air brake not in use) wherein the monitor may enter a "sleep mode", or that very low pressure or fluctuating pressure

conditions are occurring. In such circumstances the microprocessor may on an intermittent but timed basis do a pressure check and if there is "active" differential pressure "switch on" or in cases where it is "already in operation" and conditions have changed, generate an immediate warning and continue to monitor conditions. For example, the scavenging system may have been not turned on or just switched off, a typical response to an alarm by an operator in such circumstances may be to also turn off the monitor device (if this is an option) or mute the alarm, the device can then determine if the pressure differential stays at zero - then the scavenging system is likely turned off and the device may enter a hibernation state (or "sleep mode") to conserve power and periodically "wake" to check that there is no pressure differential. However, if the pressure differential does not remain at zero this can be indicative of the air brake supposed to be in operation with the scavenging system but a failure occurring somewhere within the air brake or scavenging system. An alarm can be generated in response to

determining operation is outside normal operating

parameters .

An operative can therefore easily determine whethe: correct gas flow is occurring, Any incorrect operation will lead to an alarm.

The microprocessor can be programmed to compare pressure sensor outputs with criteria for one or more fault conditions to determine whether or not to output an alarm. For example, if the differential pressure sensor indicates positive and negative pressure fluctuations between successive measurement periods this may indicate loss of suction or reduced suction from the scavenging interface while an anaesthetic breathing apparatus is connected to the air brake - the pressure fluctuations being indicative of air flow from the anaesthetic waste gasses (i.e. on exhalation) exceeding the suction rate from the scavenging device. A pressure differential of higher pressure within the device to the external atmosphere indicated flow reversal, triggering an immediate warning. Flow reversal can result in waste gases being ejected into the external atmosphere - a clear fault condition.

The microprocessor may be programmed with fault condition detection criteria for a plurality of fault scenarios . The microprocessor may be programmed to follow a decision tree for fault analysis, where the output of one assessment determination is used to indicate the next assessment step, until a fault condition or normal operating condition is determined. In an embodiment the microprocessor may also be configured to operate as a state machine.

It should be appreciated that the microprocessor may be programmed in a variety of ways to achieve the outcome of comparing differential pressure sensor outputs (for one or more readings of the pressure differential) with defined criteria for fault conditions to enable automatic detection and alerting of fault conditions in the air brake and/or scavenging system.

Some embodiments of the system directly utilise the pressure differential measurement output for assessment operating conditions. Utilising the pressure sensor output directly, rather than calculating flow rate may enable more efficient processing to determine whether or not the ait brake is operating normally or exhibiting fault conditions . In particular for battery powered operation (or even solar powered embodiments) efficient processing through minimising calculations and

instructions being executed by the microprocessor will reduce the power consumption of the microprocessor and extend battery life. When the device is not being operated, i.e. when there is no flow for a set time, it will go into a

"hibernation" or sleep mode. This saves power. As air brakes tend to sit in labs and surgeries and not be regularly serviced, the sleep mode ensures that minimal or no power is utilised when the device is not being used. At predetermined intervals the device circuitry 4 checks whether there is any gas flow. If it does detect gas flow it will switch on and start monitoring. The monitoring apparatus is therefore always available to work, even if it is being forgotten about.

The circuitry 4 comprises a micro-controller 100 which is programmed to implement a state machine. The states are detailed in table 1 below.

The circuitry, as well as a programmed microprocessor 100, incorporates a pressure comparator 101 to determine required pressure. It also comprises a power supply in the form of a battery 102. A DC jack supply connector 103 may also be provided. A low battery comparator 104 is provided to detect if the power supply goes low, in which case a warning will be issued (see Table 1) . This may be omitted for mains powered embodiments.

As the monitoring apparatus is arranged to hibernate when it is not in use, it preserves power. In this embodiment, the microprocessor and transducer may be low power circuitry.

In other embodiments, solar power may be provided charge a rechargeable battery, so that battery life is maintained. Other long life power sources may be

utilized .

The mute button 105 is arranged to mute the alarm for a set time and then unmute automatically. It also has the other functions listed in Table 1. In order to preserve power the visual and audible alarms are arranged to use minimal power (e.g. by pulsing) .

In this embodiment "normal" suction operation flows are defined as 30 to 80 litres per minute. The apparatus is not limited to this range. Other ranges of pressure may define normal suction, depending on application. Table 1

In the above embodiment, a differential pressure sensor is used to determine flow. Pressure sensors have an advantage of being able to provide pressure measurement data indicative of a wide range of flow rates, thereby enabling a single differential pressure sensor to be used across the full operating range of the scavenging system. Further pressure sensors do not require regular

maintenance, thus enabling a low maintenance (battery change only) or maintenance free operation of the

monitoring apparatus . Other sensors could be used to determine flow. For example, embodiments may also (or alternatively) utilise flow meters, however, such devices may require several flow meters to cover an equivalent operating range to pressure sensor embodiments . Further flow meters require regular maintenance to ensure correct operation .

In the above embodiment a microprocessor is used to implement a state machine to control the monitoring apparatus . The invention is not limited to this. Other embodiments could use bespoke circuitry or any other kind of arrangement to monitor the sensor and determine appropriate flow states .

In the above embodiment, a monitoring apparatus is mounted in a housing forming a cap to an air brake. The invention is not limited to this. An advantage of this embodiment is the monitoring apparatus may be configured to fit existing air brakes. In other embodiments, the monitoring apparatus may be integral with an air brake, for example, or may be mounted elsewhere on an air brake

In the above embodiment, the monitoring apparatus is used to monitor waste gas removal from an anaesthetic system. The invention is not limited to this. The monitoring apparatus may be used with air brakes for monitoring scavenging of any gas from any system.

In the above embodiment, the air brake has an inlet for dragging in ambient air to mix with the waste gases . The invention is not limited to this . Any other type of gas could be used as the "ambient" gas. For example, a source of nitrogen could be provided.

Please note that any dimensions included in the drawings are example dimensions only, and the apparatus is not limited to the dimensions . Other embodiments may have other dimensions. It will be appreciated by persons skilled in the art that numerous variations and/or modifications may be made to the invention as shown in the specific embodiments without departing from the spirit or scope of the

invention as broadly described. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive.

It is to be understood that, if any prior art publication is referred to herein, such reference does not constitute an admission that the publication forms a part of the common general knowledge in the art, in Australia or any other country.

In the claims which follow and in the preceding description of the invention, except where the context requires otherwise due to express language or necessary implication, the word "comprise" or variations such as "comprises" or "comprising" is used in an inclusive sense, i.e. to specify the presence of the stated features but not to preclude the presence or addition of further features in various embodiments of the invention.