GB2486018A

GB2486018A - Apparatus for monitoring depletion and movement of a medical gas supply

Info

Publication number: GB2486018A
Application number: GB1020415.4A
Authority: GB
Inventors: Steve Tetlow; Jeremy Sizer; Marcus Durand
Original assignee: BEDFORD HOSPITAL NHS TRUST
Current assignee: BEDFORD HOSPITAL NHS TRUST
Priority date: 2010-12-02
Filing date: 2010-12-02
Publication date: 2012-06-06
Anticipated expiration: 2030-12-02
Also published as: GB2486018B; GB201020415D0; WO2012073044A2; WO2012073044A3

Abstract

A medical gas supply depletion monitor is adapted to be coupled to a container of pressurised gas for supply to a human or animal patient. The apparatus monitors the supply of gas in the container and comprises a pressure sensor operable to sense the pressure of a pressurised gas in the container and a controller which is in communication with the pressure sensor. The controller receives a sensed pressure value and a subsequent sensed pressure value and from the two pressure values, which change over time, the controller determines and indicates the remaining duration of the gas supply. Thus, the invention warns in advance of the need to change the gas supple which may be, for example, an oxygen bottle. A further invention is also claimed which relates to a motion sensor which is coupled to a pressurised gas supply. The apparatus may communicate data to a remote station where the movement of the gas supply or the reduction in gas pressure or the remaining time may be monitored.

Description

Measurement and Reporting Apparatus The present invention relates to methods and apparatus for monitoring pressurised gas containers and, more particularly to methods and apparatus for the monitoring of pressurised containers supplying gas to human or animal patients.

In medical applications providing an uninterrupted supply of gases such as oxygen to supplement or replace the air breathed by a patient can be critical for the patient's survival or treatment. Unless supplies are carefully monitored the time taken to replace and refill empty or depleted containers can lead to interruptions in this supply.

US patent 6,326,896 describes a warning device for mounting to a high pressure gas cylinder which operates by monitoring the instantaneous pressure in the cylinder and providing an alarm signal when the measured pressure drops below a threshold level.

Unless specially programmed or adapted for particular types of cylinder such measurements do not provide a reliable indication of the remaining duration of gas supply because they cannot take account of the volume of the cylinder.

In life support systems it can be critical to predict the remaining duration of supply of oxygen to a patient so that replacement oxygen supplies can be obtained before the existing supply becomes depleted. Gas supply containers are produced and distributed in large quantities and regulators and flow control devices are typically fitted to the containers by delivery staff or technicians.

Aspects and examples of the invention are set out in the claims and have the advantage of providing an indication of the remaining duration of gas supply without the need to provide apparatus specially configured for different types of container and/or apparatus that can be programmed with the initial volume of gas in a container.

In an aspect there is provided a medical gas supply depletion monitor, adapted for coupling to a container of pressurised gas for supply to a human or animal patient to monitor the supply of gas in the container, the device comprising: a pressure sensor operable to sense the pressure of a pressurised gas in the container; a controller, in communication with the pressure sensor to receive a sensed pressure value and a subsequent sensed pressure value and configured to determine an indication of the remaining duration of the gas supply based on the sensed pressure values.

In one possibility determining an indication of the remaining duration of the gas supply comprises determining the difference between the sensed pressure value and the subsequent sensed pressure value. In one possibility the indication of the remaining duration of the gas supply is determined based on the sensed pressure value and the difference between the sensed pressure value and the subsequent sensed pressure value. Preferably the remaining duration of the gas supply, tieft, is calculated according to the relationship tieft =tsampie(p'3'p -1), wherein P1 is the sensed pressure value, P2 is the subsequent pressure value, tieft is the remaining duration of the gas supply, and tsample is the time interval between sensing the sensed pressure value and sensing the subsequent sensed pressure value. These and other examples have the advantage that the duration of remaining gas supply can be estimated based on two simple pressure measurements in a computationally efficient manner.

In one possibility the medical gas supply depletion monitor comprised a communication interface coupled to the controller, and wherein the controller is configured to transmit data indicating the remaining duration of the gas supply to a remote device via the communication interface. In one possibility the communication interface comprises a wireless communication interface adapted for wireless radio communication in a frequency band comprising one of: 2.4GHz, 3.7GHz and 5GHz; preferably wherein the wireless communication interface comprises an IEEE 802.11 interface.

In one possibility the controller is configured to transmit the data indicating the remaining duration of the gas supply in the container at controlled time intervals. In one possibility the controller is configured to control the time intervals, for example such that the time interval is held constant. In one possibility the controller is configured to control the time interval in dependence upon the data indicating the remaining duration of the gas supply so that the frequency with which the data is transmitted increases as the remaining duration of the gas supply decreases.

In some possibilities determining an indication of the remaining duration of the gas supply comprises determining the rate of change of the pressure of the pressurised gas supply, for example by fitting a linear data model to the sensed pressure values. The indication of the remaining duration of the gas supply may comprise the estimated time remaining until the pressure in the cylinder reaches a threshold level. Preferably the controller is configured to set the threshold level based on a command received via the communication interface.

In some possibilities a motion sensor and a display are coupled to the controller and the controller is configured to display information in the event that the motion sensor senses that the gas supply depletion monitor is being moved. In some examples the motion sensor comprises at least one of: an accelerometer; a gyroscope, such as an electronic gyroscope; a tilt switch, such as a mercury tilt switch; and a pressure switch arranged to detect lifting of the container. In an example the displayed information comprises the indication of the remaining duration of the gas supply and preferably the displayed information comprises a check list including a plurality of questions and the gas supply depletion monitor comprises a user input means wherein the controller is configured to determine whether user input has been received in response to the questions. The inventors in the present case have appreciated that many problems arise when moving patients (and other gas supply installations) between geographic locations and that these can be mitigated if users are prompted to attend to certain requirements at the time the gas supply is relocated.

Preferably the checklist comprises at least one question relating to matters chosen from the list comprising: whether it is necessary to move the patient using the gas supply; the estimated time of transit for the patient; whether there is a suitable gas supply available at the destination and, if not, whether the remaining gas supply in the container is sufficient to last until a further supply can be obtained; the quantity of gas remaining in the container; whether staff at the destination know that the patient requires a gas supply; whether other emergency equipment is required; the level of expertise needed for the transfer and whether appropriate professionals are available to escort to patient.

In an aspect there is provided a monitoring device adapted for coupling to a pressurised gas supply container and comprising a motion sensor operable to detect movement of the container and display means configured to display information in the event that movement of the device is detected.

In an aspect there is provided a container of gas for supply to a human or animal patient comprising or coupled to a medical gas supply depletion monitor substantially as described herein.

In an other aspect there is provided a method of installing gas supplies in a facility the method comprising: providing a plurality of gas containers in the facility, each gas container containing a pressurised gas supply and being coupled to a monitoring device, said monitoring device arranged to sense a pressure value of the pressurised gas supply and to sense a subsequent pressure value of the pressurised gas supply and to determine data indicating the remaining duration of the gas supply based on the sensed pressure values and being operable to transmit the determined data and a unique identifier of the monitoring device to a remote device; providing, for storage at the remote device, an association between a unique identifier of at least one monitoring device and data indicating the location of the at least one monitoring device; wherein, said remote device comprises receiving means for receiving the determined data to enable gas supplies for the facility to be monitored. Preferably the facility comprises a medical facility such as a hospital building.

In an aspect the remote device comprises data storage means, the method comprising providing, for storage at the remote device, an association between at least one monitoring device of the plurality of monitoring devices and a length of time required to provide a replacement for the gas container to which the monitoring device is coupled.

In some possibilities comparing the determined data indicating the remaining duration of the gas supply with the length of time required to provide a replacement for the gas container to which the monitoring device is coupled and indicating when a gas container should be replaced based upon the comparison. In some possibilities the system comprises a plurality of gas supply depletion monitors as set out in the appended claims or substantially as described herein and a monitoring station operable to receive a message from a gas supply depletion monitor indicating the remaining duration of gas supply in the gas container to which the gas supply depletion monitor is coupled. In one possibility the monitoring station is configured to store an association between at least one gas supply depletion monitor and a length of time required to provide a replacement for the gas container to which the gas supply depletion monitor is coupled.

In one possibility comparing the remaining duration of gas supply with the length of time required to provide a replacement for the gas container and indicating when a gas container should be replaced based upon the comparison.

In an aspect there is provided a gas supply depletion monitor comprising a pressure sensor for sensing the pressure of a pressurised gas supply and a rate determiner coupled to the pressure sensor to determine the rate of change of pressure of the pressurised gas supply.

In an example there is provided a method of adapting an oxygen cylinder comprising assembling a gas supply depletion monitor to the container, wherein the gas supply depletion monitor is substantially as described herein or as set out in the appended claims.

In another example there is provided a gas regulator for coupling to a container of pressurised gas to regulate the pressure of a gas supply provided from the container and comprising a gas supply depletion monitor having the features set out in the appended claims. Examples of the invention include a gas supply depletion monitor substantially as described herein with reference to the accompanying drawings and a gas supply container substantially as described herein with reference to Figure 1.

Embodiments of the invention will now be described in detail, by way of example only, with reference to the accompanying drawings, in which: Figure 1 illustrates a monitoring system including a monitoring device in use with a gas supply container; Figure 2 shows a functional block diagram of a monitoring device; Figure 3 shows a functional block diagram to illustrate functionality of the controller shown in Figure 2; Figure 4 shows a pressure vs. time plot indicating the operation of an embodiment; and Figure 5 shows a facility comprising a plurality of monitoring devices.

Figure 1 shows a pressurised gas container 7 carrying a regulator 5 and a gas supply depletion monitor 9. The regulator comprises an inlet chamber 3 and a biased valve 10 to regulate the flow of gas into an outlet chamber 11. The biasing of the valve 10 is controlled by a user adjustable regulator control 2 and a diaphragm 12 of the outlet chamber 11. The control and diaphragm act together to regulate the pressure in the outlet chamber 11. An outlet pressure monitor 8 measures and displays the regulated outlet pressure of the flow of gas to a patient (not shown). The regulator shown in Figure 1 is merely an example and other types of regulator may be used.

Gas supply depletion monitor 9 comprises a pressure sensor I coupled to measure the flow of gas into the regulator inlet from the gas cylinder 7. In the example of Figure 1, for simplicity a single stage regulator is shown and the sensor is shown measuring pressure in the inlet chamber. However, as will be appreciated the sensor I can be coupled to measure the pressure of the gas in the container by any other appropriate means and where other types of regulator are used the disposition of the pressure sensor I would need to be modified appropriately; the diagram of Figure 1 is merely illustrative.

The pressure sensor I is coupled to a control system 4. Control system 4 is coupled to a communication interface 14 for communicating with a remote monitoring system 15. In the example of Figure 1 the gas container 7 comprises a cylinder of pressurised oxygen suitable for supplying oxygen to a human or animal patient and the pressure sensor I comprises an oxygen safe pressure sensor, having a dynamic range of 0 to 250 bar (0 to 2SOMPa).

In use the pressure sensor I takes measurements of pressure in the container 7 at fixed time intervals and pressure measurement data from the pressure sensor are recorded by control system 4 in a memory register (not shown in Figure 1) to monitor depletion of the gas supply in container 7. The operation of control system 4 is described in greater detail with reference to Figures 2 to 5 below.

Control system 4 may be implemented using software, hardware or firmware and any appropriate combination thereof. For example the control system may comprise a combination of logic gates, an ASIC or a suitably programmed processor or computer.

The remote monitoring system 15 is coupled to a database 108, (described in more detail below with reference to Figure 5) and comprises a communication interface 41 for communication with the gas supply depletion monitor 9 and a user input/output interface 42. In the example of Figure 1 the remote monitoring system 15 is provided by a general purpose computer with a wireless network interface. This enables monitoring of gas containers, such as oxygen cylinders at patient's bedsides, to be performed using a wireless local area network (LAN) so that a monitoring system 15 can monitor a number of devices distributed about a facility, such as a hospital. In the example of Figure 1, the communication interfaces 14, 41 comprise BLEEP (TM) wireless communication interfaces. However any appropriate wireless communication interface may be used, for example a BlueToothTM interface, or a WI-Fl interface such as an IEEE 802.11 a/bIg/n interface or a GSM interface or other radio communications interface. Typically such interfaces (e.g. the IEEE 802.11 interface) operate in a frequency band comprising 2.4 GHz, 3.7GHz or 5GHz. In some possibilities a wired communication interface such as Ethernet, USB or Firewire may be used to communicate between the control system 4 and a remote monitoring system 15.

Pressure sensor I may be provided by a commercially available pressure sensor such as a Parker ASIC PTD (VB25OIAIC2) 2SObar which has an overpressure of 375bar (375Mpa) and a range of 0 to 2SObar (0 to 25 MPa), 1/4in BSP, a DC supply voltage of 9V to 35V, and a signal output range of 0 to 5V. Other examples of pressure sensors may also be used, such as the Honeywell MLO5KPSIPC which has an overpressure of 7SOOpsi (51.7Mpa), a working range of 0 to 5000 psi, (0 to 34.5Mpa), a DC supply voltage of 5V, and a signal output range of 0.5V to 4.5V although any other appropriate pressure sensor or transducer may also be used.

Figure 2 shows an example of the gas supply depletion monitor 9 shown in Figure 1 comprising a pressure sensor I coupled via signal conditioner 32 to an analogue-to-digital converter (ADC) 34 which is coupled to controller 3. A motion sensor 36 is also coupled toADC 34.

In the example of Figure 2 controller 3 is coupled to control an LCD display 30, an audible alarm 28 and a communication interface 14. Control switches 33 are coupled to provide one or more control inputs to controller 3. Controller 3 is also coupled to control the signal conditioner 32.

Electrical power is provided to the monitoring and reporting apparatus 9 by a lithium battery. In the interests of clarity individual power couplings to the various components of the monitoring and reporting apparatus 9 have been omitted from Figure 2 but power management unit 38 is coupled to the battery 39 and to ADC 34 to monitor the remaining battery life.

In operation pressure sensor I is coupled to a gas container 7 (as shown in Figure 1) to measure the gas pressure in the container and to provide an analogue signal, which is dependent upon the measured pressure, to the signal conditioner 32. The signal conditioner 32 receives the analogue signal from the pressure sensor and amplifies and filters the signal to improve measurement accuracy. Some averaging may also be performed either separately or as part of the filtering process. In the example of Figure 2 the signal conditioning unit 32 comprises a band pass filter adapted to reduce DC signal offsets and to reduce high frequency measurement noise.

The ADC 34 converts the analogue signal from the signal conditioner 32 to a digital signal to be provided the controller 3. The controller 3 takes at least two pressure measurements (digital pressure signals provided by the ADC 34) at separate times.

Based on: (1) the time interval between the two pressure measurements, (2) the first of the two pressure measurements and (3) the difference between the two measurements; the controller calculates an estimate of the remaining duration of gas supply, e.g. the time remaining until the pressure of the gas in the container 7 reaches ambient pressure.

In the example of Figure 2 the controller calculates the remaining duration of the gas supply in accordance with equation 1: tieft = tsampie( p -1) (1) where, Pi is the first pressure sample, P2 is the second pressure sample, tieft is the estimated remaining duration of the gas supply, and tsample is the time interval between the first and second pressure samples.

The controller 3 then controls the wireless communication interface 14 to transmit a signal indicating the remaining duration of gas supply to the remote monitoring station 15 (Figure 1). The signal transmitted by the wireless communication interface includes a unique identifier of the gas supply depletion monitor 9. In the example of Figure 1 the remaining duration is reported at intervals which are calculated by the controller 3 based on the estimated remaining duration of the gas supply in the container. Where the remaining duration of the gas supply is short reports are sent more frequently. Where the estimated remaining duration is very long reports can be sent less frequently. This has the benefit of conserving battery power in the gas supply depletion monitor without sacrificing reliability of monitoring. In this example the controller 3 controls the time intervals between sending reports to be linearly dependent upon the remaining duration of the gas supply. Preferably the device provides a user settable minimum reporting frequency. In some examples the minimum reporting frequency is once per hour, once per 40 minutes, once per 15 minutes, once per 5 minutes or once per 2 minutes. In some examples the maximum reporting frequency is once per minute.

In the example of Figure 1 the remaining duration may be displayed on the LCD display to enable the remaining duration of the gas supply to be determined by a visual check.

In the event that the controller 3 determines that the remaining duration of gas supply has reached a threshold level an alarm signal is transmitted to the remote monitoring system (15 in Figure 1) via wireless communication interface 14. In addition controller 3 triggers audible alarm 28 to provide an alert. The threshold level may be hard coded into the controller (e.g. it may be stored in a ROM or non-volatile memory) or it may be programmable or settable in response to a command received over the communication interface 14.

Electrical power in the gas supply depletion monitor is controlled by the power management unit 38 which provides power to the system from the lithium ion battery 39 and monitors the remaining charge in the battery 39 and provides an analogue signal to the ADC 34 which is dependent upon the remaining battery charge. In the event that the controller determines that the remaining battery charge has dropped below a threshold battery level it transmits an alarm signal via wireless communication interface 14 to a remote monitoring station (15 in Figure 1) to indicate that the battery needs to be replaced. In one possibility the controller also controls alarm 28 to provide an audible alarm and/or provides an indication that a replacement battery is required on the LCD display. In one possibility the controller may also provide a battery level indication on the LCD screen to enable battery charge level to be monitored during ordinary use. In one possibility, in the event that the battery level drops below a threshold battery charge level the power management unit switches the main system power off to conserve power and controls the display to show a warning message indicating that the container is not being monitored.

The motion detector 36 is configured to detect motion of the device (and/or the container to which it is attached). The controller and motion detector are configured such that, in the event that the motion detector detects motion the controller 3 controls the LCD display 30 to present a checklist of questions to an operator and/or to trigger an alarm signal. The inventors in the present case have appreciated that problems with patient gas supply frequently occur whilst patients are being moved within or between medical facilities and that by ensuring certain basic precautions are taken these problems can be reduced. In a simplified version of the device the motion detector can be provided without the gas supply measurement or communication functions.

An example of the checklist may be set out as follows: Transfer checklist for patients receiving oxygen.

1. Transfers can be risky; is this transfer necessary? 2. How long do you estimate you will be in transit? 3. Is there an oxygen supply at your destination? 4. If not, do you have enough oxygen to last until there is a new supply? 5. How much oxygen is in the container and how long will it last? 6. Do the staff at your destination know that this patient requires oxygen? 7. Do you need other emergency equipment? 8. What level of expertise does the patient need for the transfer, is the escort appropriate? Examples of motion detectors include accelerometers, gyroscopes such as solid state or electronic gyroscopes, tilt switches such as mercury tilt switches, or simple pressure switches arranged under the gas container to indicate when the container is lifted/moved.

Other examples of motion detectors may be used.

The structure and operation of the controller 3 will now be described in greater detail with reference to Figure 3 which shows a functional block diagram of the controller 3 of Figure 2. As shown in Figure 3, controller 3 comprises memory 10 and a data processor 12.

Memory 10 has a data receiver 16 coupled to receive pressure data from the ADO 34 shown in Figure 2. The memory 10 comprises volatile memory operable to store measured pressure data and non-volatile memory to store a unique identifier 35 of the device 9 and/or the controller 3. The memory 10 is operable to store a threshold gas pressure level in one or both of the volatile and non-volatile memory.

Data processor 12 comprises a gradient calculator 18, an extrapolator 20 and a decision module 24. Gradient calculator 18 is coupled to memory 10 and to extrapolator 20.

Extrapolator 20 is coupled between the gradient calculator 18 and the decision module 24. Decision module 24 is connected to memory 10 to retrieve stored data.

In this example data processor 12 and/or memory 10 are coupled to an internal clock signal. The nature of the clock signal is ancillary to the invention and thus, in the interests of clarity, clock signal connections are not shown in the drawings.

In use, the ADO (34 in Figure 2) converts an analogue signal from the pressure sensor into a digital pressure sample. A digital pressure sample output from the ADO is received by the data receiver 16 and written to the memory 10 for storage. At least two pressure measurements Pi and P2 are taken and the estimated remaining duration of gas supply is calculated from these measurements. This can be calculated according to Equation I above (see Figure 4).

The decision module 24 compares the estimated time remaining until the gas pressure in the container reaches the threshold pressure level (in this example the threshold level is zero pressure) with a critical time threshold and, in the event that it is determined that the time remaining until the gas pressure in the container drops reaches the threshold pressure level is less than or equal to the critical time threshold, the decision module triggers the controller 3 to transmit an alert signal, for example by triggering an audible and visual alarm and/or causing the wireless communication interface to transmit an alert message to the remote monitoring system 15.

In the event that the decision module 24 determines that the estimated time remaining until the gas pressure in the container reaches the threshold pressure level is greater than the critical time threshold, the decision module passes the estimate of time remaining to the controller which transmits a message to the remote monitoring system over the wireless communication interface 14.

Whether there is an alarm condition or not, the message transmitted via the wireless communication interface 14 comprises a unique identifier (e.g. a MAO address) of the gas supply depletion monitor 9, an indication of the estimated remaining duration of the gas supply in the gas container 7 and an alert identifier.

The memory 10 may comprise a first-in first-out buffer which stores a plurality of pressure samples (e.g. at least two or three) which represent the pressure sampled at equal intervals (e.g. the sample period, which in this example is held constant). The gradient calculator 18 is operable to read the pressure samples from memory 10 and to determine a straight line fit to the samples based on a least squares regression in order to estimate the rate of change of pressure in the container. The calculated estimate of the rate of change of pressure (the pressure gradient) is provided from the gradient calculator to the extrapolator 10. The extrapolator 20 retrieves a threshold pressure from the memory 10 and calculates, based on the pressure samples, the sample period and the estimated gradient, an estimate of the time remaining until the gas pressure in the container reaches the threshold pressure level.

In this example the gradient calculator also calculates an estimate of the error in the straight line fit used to estimate the gradient and passes this to the decision module. The use of least squares has the advantage that an error estimate can be calculated efficiently during the fitting process without adding significant computational burden.

Other algorithms can be used to estimate the gradient such as, for example, a recursive least squares estimator such as a two state Kalman filter or other FIR/IIR signal models and other appropriate algorithms. The estimated time remaining until the gas pressure in the container reaches a threshold pressure level is output from the extrapolator 20 to the decision module 24.

Figure 5 shows a medical facility 100, such as a hospital comprising a plurality of gas containers 102 each coupled to a respective gas supply depletion monitor 104. The gas containers may comprise oxygen cylinders at patient's bedsides. Facility 100 comprises a remote monitoring system 106 in wireless communication with each of the monitoring and reporting devices 104 over a local area network including a wireless LAN. Remote monitoring system 106 comprises a database 108 storing a plurality of associations 121, wherein each association relates a unique identifier 109 of each device of the plurality of devices 104, a container identifier 116 comprising container information relating to the characteristics of the gas supply container being monitored, location information 118 indicating the location in the facility of the device 104, a lead time indicator 112 indicating the time required to replace the container 102 to which that device 104 is attached and a duration indicator 114 indicating the estimated remaining duration of the gas supply in each of the containers 102 as reported by the corresponding gas supply depletion monitor 104. Also linked to each association is a record 119 of the gas supply time durations reported by the monitoring devices. The remote monitoring system may be -14 -provided by a suitably programmed general purpose computer having data storage means and a communication interface.

This database system enables an operator of the facility, such as a hospital, to monitor the gas supply provided to a large number of patients and to collect verifiable and accurate information about each gas supply and the rate at which it is being used.

To install the system described with reference to Figure 5 in a facility a plurality of monitoring devices (e.g. gas supply depletion monitors such as those described above with reference to Figures 1 to 4) are assembled to corresponding ones of a plurality of gas supply containers. Database 108 is then updated, for example by an operator or by a message transmitted from the monitoring device, to store an association between each device 104 and a location 118. Further data is then attached to this association indicating the time it is likely to take to replace the gas container in a given location (lead time 112). This lead time can be based on factors such as the time required for a supplier to arrange delivery and install a replacement gas container.

Subsequently, in use the remaining duration of gas supply in the plurality of containers is reported from the devices 104 to the monitoring system 106 and compared with the corresponding lead time 112. In the event that the remaining duration of gas supply in a container is equal to the lead time a replacement gas container can be obtained by an operator.

Although the supply of oxygen to a human or animal patient has been described above examples of the invention may find application in other circumstances where it is necessary to monitor supplies of pressurised gas.

Reporting from monitoring devices installed on gas containers has been described with reference to wireless communication and particular reference has been made to a wireless LAN. However other wireless communication methods such as GSM, GPRS or Bluetooth may also be used also wired communication such as Ethernet connections may be used where appropriate. Reporting may also be performed over a mixed network involving, for example a wireless LAN and a wired network and/or the internet. The memory has been described as storing a unique identifier of the device and/or the controller. In some examples a unique identifier, such as a MAC or IP address, may be associated with the communication interface and therefore a separate unique identifier need not be stored separately in memory in the controller.

The gas supply depletion monitors may be configured to communicate with the remote monitoring station using wireless communication as described above with reference to Figures 1 and 5. In some examples communication may include communication over a wireless LAN and communication over another network such as the internet or other IP based network. In these examples devices in different locations (for example in a number of hospitals) can be monitored at one location.

Claims

CLAIMS: 1. A medical gas supply depletion monitor, adapted for coupling to a container of pressurised gas for supply to a human or animal patient to monitor the supply of gas in the container, the device comprising: a pressure sensor operable to sense the pressure of a pressurised gas in the container; a controller, in communication with the pressure sensor to receive a sensed pressure value and a subsequent sensed pressure value and configured to determine an indication of the remaining duration of the gas supply based on the sensed pressure values.
2. The medical gas supply depletion monitor of claim I wherein determining an indication of the remaining duration of the gas supply comprises determining the difference between the sensed pressure value and the subsequent sensed pressure value.
3. The medical gas supply depletion monitor of claim 2 wherein the indication of the remaining duration of the gas supply is determined based on the sensed pressure value and the difference between the sensed pressure value and the subsequent sensed pressure value.
4. The medical gas supply depletion monitor of any preceding claim in which the remaining duration of the gas supply, t/eft, is calculated according to the relationship cft =tsampie(p'p -1), wherein Pi is the sensed pressure value, P2 is the subsequent pressure value, tiefi is the remaining duration of the gas supply, and tsample is the time interval between sensing the sensed pressure value and sensing the subsequent sensed pressure value.
5. The medical gas supply depletion monitor of any preceding claim comprising a communication interface coupled to the controller, and wherein the controller is configured to transmit data indicating the remaining duration of the gas supply to a remote device via the communication interface.
6. The medical gas supply depletion monitor of claim 5 in which the communication interface comprises a wireless communication interface adapted for wireless radio communication in a frequency band comprising one of: 2.4GHz, 3.7GHz and 5GHz; preferably wherein the wireless communication interface comprises an IEEE 802.11 interface.
7. The medical gas supply depletion monitor of claim 5 or 6 in which the controller is configured to transmit the data indicating the remaining duration of the gas supply in the container at controlled time intervals.
8. The medical gas supply depletion monitor of claim 7 in which the controller is configured to control the time intervals.
9. The medical gas supply monitor of claim 8 in which the controller is configured such that the time interval is held constant.
10. The medical gas supply depletion monitor of claim 8 in which the controller is configured to control the time interval in dependence upon the data indicating the remaining duration of the gas supply so that the frequency with which the data is transmitted increases as the remaining duration of the gas supply decreases.
11. The medical gas supply depletion monitor of any preceding claim in which determining an indication of the remaining duration of the gas supply comprises determining the rate of change of the pressure of the pressurised gas supply.
12. The medical gas supply depletion monitor of claim 11 in which determining the rate of change of the pressure comprises fitting a linear data model to the sensed pressure values.
13. The medical gas supply depletion monitor of any preceding claim in which the indication of the remaining duration of the gas supply comprises the estimated time remaining until the pressure in the cylinder reaches a threshold level.
14. The medical gas supply depletion monitor of claim 13 in which the controller is configured to set the threshold level based on a command received via the communication interface.
15. The medical gas supply depletion monitor of any preceding claim wherein a motion sensor and a display are coupled to the controller and the controller is configured to display information in the event that the motion sensor senses that the gas supply depletion monitor is being moved.
16. The medical gas supply depletion monitor of claim 15 in which the motion sensor comprises at least one of: an accelerometer; a gyroscope, such as an electronic gyroscope; a tilt switch, such as a mercury tilt switch; and a pressure switch arranged to detect lifting of the container.
17. The medical gas supply depletion monitor of claim 16 in which the displayed information comprises the indication of the remaining duration of the gas supply
18. The medical gas supply depletion monitor of any of claims 15 to 17 in which the displayed information comprises a check list including a plurality of questions and the gas supply depletion monitor comprises a user input means wherein the controller is configured to determine whether user input has been received in response to the questions.
19. The medical gas supply depletion monitor of claim 18 in which the checklist comprises at least one question relating to matters chosen from the list comprising: whether it is necessary to move the patient using the gas supply; the estimated time of transit for the patient; whether there is a suitable gas supply available at the destination and, if not, whether the remaining gas supply in the container is sufficient to last until a further supply can be obtained; the quantity of gas remaining in the container; whether staff at the destination know that the patient requires a gas supply; whether other emergency equipment is required; the level of expertise needed for the transfer and whether appropriate professionals are available to escort to patient.
20. A monitoring device adapted for coupling to a pressurised gas supply container and comprising a motion sensor operable to detect movement of the container and display means configured to display information in the event that movement of the device is detected.
21. The monitoring device of claim 20 having the features of any of claims 4 to 19.
22. A container of gas for supply to a human or animal patient comprising or coupled to a medical gas supply depletion monitor according to any of claims I to 19 or a monitoring device according to claim 20 or 21.
23. A method of installing gas supplies in a facility the method comprising: providing a plurality of gas containers in the facility, each gas container containing a pressurised gas supply and being coupled to a monitoring device, said monitoring device arranged to sense a pressure value of the pressurised gas supply and to sense a subsequent pressure value of the pressurised gas supply and to determine data indicating the remaining duration of the gas supply based on the sensed pressure values and being operable to transmit the determined data and a unique identifier of the monitoring device to a remote device; providing, for storage at the remote device, an association between a unique identifier of at least one monitoring device and data indicating the location of the at least one monitoring device; wherein, said remote device comprises receiving means for receiving the determined data to enable gas supplies for the facility to be monitored.
24. The method of claim 23 in which the remote device comprises data storage means, the method comprising providing, for storage at the remote device, an association between at least one monitoring device of the plurality of monitoring devices and a length of time required to provide a replacement for the gas container to which the monitoring device is coupled.-20 -
25. The method of claim 24 in which providing, for storage at the remote device, an association between at least one monitoring device of the plurality of monitoring devices and a length of time required to provide a replacement for the gas container to which the monitoring device is coupled comprises transmitting a message comprising data indicating the association from the at least one monitoring device to the remote device, for example wherein the message is transmitted over a wireless communication interface.
26. The method of claim 24 or 25 further comprising comparing the determined data indicating the remaining duration of the gas supply with the length of time required to provide a replacement for the gas container to which the monitoring device is coupled and indicating when a gas container should be replaced based upon the comparison.
27. A monitoring system for monitoring containers of pressurised gas, the system comprising a plurality of gas supply depletion monitors according to any of claims I to 19 or 21 and a monitoring station operable to receive a message from a gas supply depletion monitor indicating the remaining duration of gas supply in the gas container to which the gas supply depletion monitor is coupled.
28. A monitoring system according to claim 27 in which the monitoring station is configured to store an association between at least one gas supply depletion monitor and a length of time required to provide a replacement for the gas container to which the gas supply depletion monitor is coupled.
29. The method of claim 28 further comprising comparing the remaining duration of gas supply with the length of time required to provide a replacement for the gas container and indicating when a gas container should be replaced based upon the comparison.
30. A gas supply depletion monitor comprising a pressure sensor for sensing the pressure of a pressurised gas supply and a rate determiner coupled to the pressure sensor to determine the rate of change of pressure of the pressurised gas supply.
31. A method of adapting a gas supply container comprising assembling to the -21 -container a gas supply depletion monitor according to any of claims I to 19.
32. A gas regulator for coupling to a container of pressurised gas to regulate the pressure of a gas supply provided from the container and comprising a gas supply depletion monitor having the features of any of claims I to 19.
33. A gas supply depletion monitor substantially as described herein with reference to the accompanying drawings.
34. A gas supply container substantially as described herein with reference to Figure 1.