NL2022406B1 - Ventilation Perfusion Protector - Google Patents

Abstract

2017-028 ABSTRACT Ventilation Perfusion Protector Embodiments of the present invention provide an ancillary device for the cardiopulmonary bypass and a ventilator. In particular, invention relates to a device 5 comprising a first sensor, a second sensor and a controller configured to receive signals from said sensors, and an output means producing an alarm when the outputs from the first and the second sensors are less than a threshold value for more than a threshold amount of time. 19

Description

2017-028 Ventilation Perfusion Protector

TECHNICAL FIELD Aspects of the invention relate to medical devices used during open heart surgeries, in particular to an ancillary device for use with a cardiopulmonary bypass machine and a ventilator.

BACKGROUND Cardiopulmonary bypass (CPB) is widely used during open heart surgery. During CPB, the functions of heart and lungs are performed by the CPB machine, thus maintaining oxygen levels in the patient's body. CPB machines are therefore alternatively known as heart-lung machines. Prior to connection of a CPB machine and after disconnection of the CPB machine, a ventilator is used to deliver oxygen and medical gases to the lungs of the patient. A ventilator can be a separate device for ventilation of the lungs of a patient. However, a ventilator is now typically a part of the anaesthesia machine or anaesthesia work station.

The two devices are paramount for supporting vital functions of the patient's body during the surgery, and the correct timing of switching between the two needs to be fully controlled by the team in the operating room. Strict protocols are followed to ensure that either the ventilator or the CPB machine provides a supply of oxygen to the patient’s blood, with gaps in provision being strictly time-limited.

Transition from the ventilator to the CPB machine occurs at the initial stages of the surgery when the patient is anaesthetised and there is a need to open the patient's chest to gain access to the heart and start operating. Once the chest is opened the CPB machine is connected across the heart. At this point oxygenation of the blood is performed by the CPB machine and it temporarily substitutes the functions of the heart and lungs. Once the surgery on the heart is completed, the heart must be re- started, and breathing support needs to be resumed. Finally, the CPB machine is disconnected and the patient's chest is closed.

Unexpected events during surgery can lead to deviation from normal surgical protocols, which can lead to a lapse in provision of oxygenated blood to the patient.

If such a lapse persists for more than about two minutes, then irreversible damage to the patient’s vital organs will begin to occur.

It is an object of embodiments of the invention to at least mitigate one or more of the problems of the prior art.

SUMMARY OF THE INVENTION Aspects and embodiments of the invention provide an ancillary device for a cardiopulmonary bypass and a ventilator as claimed in the appended claims. 1

2017-028 According to an aspect of the invention, there is provided an ancillary device for a cardiopulmonary bypass (CPB) machine and a ventilator, the device comprising: a first sensor configured to produce an output indicative of a blood flow rate output from the CPB machine; a second sensor configured to sense a parameter indicative of whether the ventilator is active or inactive; an output means; and a controller configured to receive signals from the first and second sensors and to control the output means, wherein the controller is configured to: determine whether or not the blood flow rate from the CPB machine is less than a threshold value in dependence on the output from the first sensor; determine whether or the ventilator is active or inactive in dependence on the output from the second sensor; and control the output means to produce an alarm if the output from the first sensor indicates that the blood flow rate output from the CPB machine is less than a threshold value for more than a first threshold amount of time and the output from the second sensor indicates that the ventilator is inactive for more than a second threshold amount of time.

The first threshold amount of time may be equal to the second threshold amount of time.

Advantageously, the device indicates when both the CPB machine and the ventilator are inactive, thereby providing a warning in the event that there is a risk of harm to a patient if the surgeon does not resume additional breathing or cardiopulmonary support.

An additional advantage stems from the fact that the device has its own sensors that are independent of the CPB machine and the ventilator.

This makes the device is compatible with substantially any equipment that may be present in an operating room.

Furthermore, because the sensors directly measure whether or not the CPB machine and the ventilator are active, the output from the ancillary device is not compromised in the event that one of the other machines malfunctions or is switched off at any stage in the procedure.

It will be understood that the parameter indicative of whether the ventilator is active or inactive may be indicative of an output from the ventilator such as the pressure or flow rate at an output of the ventilator.

Alternatively, the parameter indicative of whether the ventilator is active or inactive may comprise a position or motion of the bellows.

Accordingly, in some embodiments, the second sensor may comprise a pressure sensor, a flow sensor, a motion sensor, a camera, or any other sensor capable of detecting a parameter indicating whether the ventilator is active or 2

2017-028 inactive.

It will be understood that the second sensor is not limited to the specific examples disclosed herein.

In an embodiment, the first sensor is an ultrasonic sensor configured to measure the blood flow rate from an output of the CPB machine.

Optionally, the first sensor is configured to produce an output proportional to the blood flow rate.

Advantageously, this allows constant monitoring the blood flow through the circuit of the CPB machine.

In yet another embodiment, the second sensor comprises a pressure transducer.

Optionally, the second sensor is connected by a luer connector to a sampling port.

Alternatively, the second sensor may be connected to the sampling port by a connection pipe provided with a hose pillar.

Such a pillar may provide a barbed connection onto which a flexible hose may be pushed.

Optionally, the sampling port is a high efficiency particulate air (HEPA) filter.

Optionally, said second sensor is configured to produce an output proportional to a ventilation pressure.

Advantageously, this provides an information about the breathing of the patient by measuring the pressure of gases leaving the ventilator in the direction of patient's airways.

In yet another embodiment, the controller is arranged to determine that the ventilator is inactive if the pressure transducer does not produce a pulsatile output, optionally wherein the output from the pressure transducer is determined to be pulsatile if more than more than a threshold proportion of the measured data points in a given time period fall outside a bandwidth defined as the mean value over the given time period plus or minus a predetermined tolerance value.

Such a controller may be operable to control output means to produce a visual indication that the ventilator is inactive if it is determined that the pressure sensed by the pressure transducer is not pulsatile, and may be configured to output an alarm in the event that the pressure sensed by the pressure transducer is not pulsatile and the flow rate output by the CPB machine is less than a threshold value.

In yet another embodiment, the second sensor comprises a bellows motion sensor comprising: aframe configured to be positioned around a portion of said bellows; a light source located in a first portion of the frame and capable of emitting a light beam towards the bellows; at least one light sensor located a second portion of the frame and configured to detect light reflected off the bellows, whereby the intensity of light detected by the light sensors varies in dependence on a position of the bellows.

Advantageously, such a sensor is compatible with substantially any bellows ventilator.

Furthermore, 3

2017-028 the sensor provides a simple means to directly measure movement of the bellows, which is indicative of whether or not the ventilator is active.

It will be understood that in some embodiments alternative bellows motion sensors could also be employed. For example, the bellows motion sensor may comprise a camera arranged to detect images of the bellows and, the controller may include an image processing module configured to analyse the images to quantify the motion of the bellows.

Optionally, the frame is U-shaped.

Optionally, the light source is a light-emitting diode (LED).

Optionally, the light source is located in a top portion of the frame and the light sensor is located in a side portion of the frame. Advantageously, such a disposition allows the light to be emitted from the light source, reflected from the surface of the bellows during its movement and further detected by the light sensor located in a such a way that the reflected light passes through the second sensor.

In yet another embodiment, the controller is arranged to determine that the ventilator is inactive if the bellows motion sensor does not produce a pulsatile output, optionally wherein the output from the bellows motion sensor is determined to be pulsatile if more than a threshold proportion of the measured data points in a given time period fall outside a bandwidth defined as the mean value over the given time period plus or minus a predetermined tolerance value.

Optionally, the device comprises a plurality of second sensors. Advantageously, this provides a redundant means of controlling breathing support of the patient.

In yet another embodiment, the controller is arranged to determine that the ventilator is inactive if neither of the pressure transducer and the bellows motion sensor produces a pulsatile output. Advantageously, this process ensures that control over the patient's breathing support is maintained continuously and no interruptions of air supply occur.

BRIEF DESCRIPTION OF THE DRAWINGS Embodiments of the invention will now be described by way of example only, with reference to the accompanying figures, in which: Figure 1 shows a schematic diagram of the use of a prior art CPB machine and anaesthesia machine during an open heart surgery; Figure 2a shows a schematic diagram of an ancillary device in an embodiment of the present invention; Figure 2b shows a schematic diagram of an ancillary device in another embodiment of the present invention; 4

2017-028 Figure 2c shows a display of an output means in an embodiment of the present invention; Figure 3a shows a cross sectional view of a bellows sensor in an embodiment of the present invention Figure 3b shows another view of the bellows sensor shown in figure 3a; Figure 4 shows an exemplary output from a bellows motion sensor and an air pressure sensor during operation of a ventilator; Figure 5 shows discrete points at which a continuously-variable signal can be sampled by an ancillary device in an embodiment of the present invention; and Figure 6 shows a schematic timeline showing control signals in an ancillary device in an embodiment of the present invention at different stages during an open heart surgery procedure.

DETAILED DESCRIPTION Figure 1 is a schematic illustration of a prior art apparatus for use in an operating room during open heart surgery. This apparatus is used to support circulation of oxygenated blood throughout an open heart surgical procedure. In the illustrated embodiment, the apparatus comprises a CPB machine 101 is connected to a patient 102 by means of a plurality of lengths of tubing 104a that are used to mechanically circulate blood while bypassing heart and lungs. The CPB machine 101 normally includes a pump to move the blood to and from the body, and an oxygenator for blood gas control. A pressure sensor (not shown) is used to measure the pressure of a circulated blood outside the body. A bellows-type anaesthesia machine 103 is used during the surgery to support and control the administration of anaesthesia and to support respiration in the anesthetised patient. The anaesthesia machine 103 may incorporate a bellows-type ventilator 105, a suction unit (not shown) and patient monitoring devices (not shown). Ventilator 105 is used to ventilate and to deliver oxygen to the patient 102 when they are anesthetised and unable to breath for themselves. The ventilator 105 is connected to the patient via lengths of tubing 104b. It will be understood that the anaesthesia machine 103 is normally equipped with a variety of safety devices employed to alert the anaesthetist when a failure in the gas supply or changes in airway pressure occur. The sensors and the associated alarm systems of the CPB machine 101 and the anaesthesia machine 103 act independently. During an open heart surgery, the patient 102 is initially anaesthetised and intubated. At this stage, the bellows 105 are used to provide breathing support until the chest is opened to reach the heart and adjoining vascular system. During sawing of the chest, known as median sternotomy, the patient's breathing has to stop. However, the heart 5

2017-028 still carries on functioning.

Because no oxygenation of the blood is provided during median sternotomy, it is essential that this part of the procedure is completed quickly.

Once the median sternotomy is complete, the ventilator 105 may be re-activated to provide oxygenation of the blood while the surgeon prepares to connect the CPB machine 101 across the patient's heart.

The CBP machine needs to be employed for the duration of the surgery to allow the surgeon to operate on the heart as well as to maintain mechanical circulation and oxygenation of blood to maintain perfusion to the other body organs.

At this point the alarm of anaesthesia machine 103 has to be switched off.

At the end of the surgery, the CPB machine 101 is disconnected, the blood flow through the heart is restored and the respiration through the anaesthesia machine 103 is reinitiated, until the anaesthesia wears off and the patient regains the ability to breath for themselves.

The transitions from respiratory support by the anaesthesia machine to cardiovascular support provided by the CPB machine and back may potentially carry high levels of risks associated with the switch between the two kinds of life support.

This is because the transition must be completed within a short period of time (e.g. less than two minutes) to ensure that irreversible damage to the patent's organs due to lack of oxygen does not occur.

Although surgical protocols will usually ensure that this is the case, if an unexpected event occurs it may be necessary for an operating team to depart from the protocol.

Furthermore, during open heart surgery a large number of actions may be performed simultaneously, so the operating team may not be aware of the time taken to perform a transition between the anaesthesia machine and the CPB machine.

The inventors have recognised that there is a need to provide surgeons with a device that would provide a warning when the CPB machine and the ventilator are both inactive, indicating that the patient may suffer harm as a result of a lack of circulating oxygenated blood.

The present invention provides an ancillary device 200 for use with a CPB machine and a ventilator, which, in a first embodiment, is depicted schematically in Fig. 2a.

The ancillary device of the first embodiment comprises a first sensor 202, a second sensor 203a, a controller 201, an output means 204 and a user input means 205. In this embodiment, the first sensor 202 is an ultrasonic flow sensor configured to measure the blood flow rate from an output of the CPB machine.

The first sensor 202 is preferably a non-contact flow meter that is preferably clamped onto the outside of the tubing downstream from an output of the CPB machine.

In an another preferred embodiment, said first sensor is selected from, for example, a Doppler flow sensor or an electromagnetic flow sensor.

The flow sensor 202 employs ultrasound to detect 6

2017-028 the flow rate through the tubing, thereby providing an analogue output proportional to the flow rate.

The flow sensor is specifically calibrated for the type of tubing used on the outlet from the CPB machine and using human blood.

Accordingly, the flow rate through the tubing on which the flow sensor 202 is clamped may be inferred from the analogue output provided by the flow sensor 202. In the present embodiment, the flow sensor is obtained from Ultrasonic Flow Management (SONOFLOW CO.55/080). However, it will be understood that various other sensors would also be suitable.

The second sensor 203a is a pressure transducer operable to detect the pressure at an output of the ventilator.

In the present embodiment the pressure transducer is obtained from Epcos TDK (part no.

B58621K1110A54), although it will once again be understood that various other sensors would be suitable.

The pressure transducer can be placed in contact with a flexible diaphragm.

A cavity on the opposite side of the diaphragm to the pressure transducer can then be placed in fluid communication with an output of the bellows via a standard luer connector on an output from a high efficiency particulate air (HEPA) filter.

Accordingly, the pressure transducer 203a is operable to monitor changes in pressure of the gases leaving the HEPA filter, which is in fluid communication with the outlet of the ventilator and the patient's airway.

It will be understood that various other methods of connecting the pressure transducer to an output from the ventilator could be used, for example a hose pillar arranged to connect to a length of flexible tubing.

When the ventilator is in use, the second sensor 203a produces an output proportional to the ventilation pressure in the anaesthesia circuit.

During operation of the ventilator, the second sensor 203a preferably produces a pulsatile output having a pulse frequency equal to the frequency at which the bellows is operated and an amplitude proportional to the pressure differential between the minimum and maximum bellows pressure.

A controller 201 is configured to receive signals from the first and second sensors 202, 203a and to control output means 204 to produce an alarm in dependence on the signals received from the first and the second sensors.

The outputs provided by the control means will be discussed in more detail below.

The user input means 205 may comprise a button.

If the alarm sounds, then a user may press the button to mute the alarm.

With reference to Fig. 2b, a schematic diagram of another embodiment of the present invention is provided.

Ancillary device 200° comprises the same components as ancillary device 200 as shown in figure 2a, and further comprises a complementary second sensor 203b in addition to the pressure transducer 203a described in relation 7

2017-028 to figure 2a.

The complementary second sensor 203b is also connected to the controller 201. The second sensor 203b comprises a light source and a light sensor operable to detect the intensity of light emitted by the light source and reflected off the bellows.

The signal produced by the light sensor therefore varies in dependence on the position of the bellows, such that the controller 201 can determine whether or not the bellows is moving in dependence on the output from the second sensor 203b.

The determination as to whether or not the ventilator is active based on the output from the complimentary second sensor 203b will be described in more detail below.

The controller 201 receives the output from both sensors 203a, 203b responsible for monitoring ventilation, and may output one or more visual or audible alarms in dependence on the received signals.

For example, if the signals indicate that both the ventilator and the CBP machine have been inactive for more than a predetermined amount of time, the controller 201 may also cause the output means to provide an audible alarm via alarm speaker 204a, as shown in figure 2c.

When the CPB machine is operating, the control means 201 may control the output means 204 to provide a visual indication that the bypass flow rate has been determined to be greater than a threshold value on a display 204d, as also shown in figure 2c.

An additional visual indicator 204d may be provided to indicate whether or not the ventilator has been determined to be active.

In some embodiments, the display may give an indication of the instantaneous blood flow rate output by the CPB machine.

Fig. 3 illustrates a front view of the bellows sensor assembly 300, which may be employed as a second sensor 203a or a complimentary second sensor 203b, as shown in figure 2b.

As illustrated, the assembly comprises a U-shaped frame 302 positioned around a portion of the bellows 301. Those skilled in the art will readily appreciate that any other shapes can be used that allow the frame to be positioned around a portion of the bellows.

A light source 304 is located in a top portion of the frame 302 at a position such that the light emitted from the light source is directed towards the top of the bellows 301. The directed light 305 is then reflected 306 from the surface of the bellows 301 towards a light sensor unit 307, which comprises a plurality of light sensors.

In the illustrated embodiment the sensor unit 307 comprises two light sensors, although it will be understood that in alternative embodiments more sensors may be provided, or a single sensor operable to detect light falling on a relatively large area may be used.

Sensor unit 307 is located in a side portion of the frame 302. In another preferred embodiment, said light source is located at the side portion of the frame 302 and said sensor unit 307 is located in a top portion of the frame 302. 8

2017-028 As the bellows 301 move upwards and downwards when providing respiratory assistance, the intensity of the light reflected from the surface of the bellows 301 and detected by the light sensor unit 307varies.

The intensity of light detected by the light sensor unit 307is dependent on the position of the bellows 301. In the illustrated embodiment, the light source 304 is a light-emitting diode, however other light sources may be provided in alternative embodiments.

The light sensor unit 307a produce an output depending on the intensity of the detected light, which output is received by the controller 201. Accordingly, the controller 201 is operable to determine whether or not the bellows 301 is moving, and therefore whether or not the ventilator is active, based on the output from the light sensor 307 unit.

The determination as to whether or not the ventilator is active based on the output from sensors 307 will be described in more detail below. it will be understood that the controller 201 instructs the output means 204 to produce an audible alarm only if the outputs from the connected sensors indicate that the ventilator and the CPB machine have been inactive for more than a pre- determined amount of time.

The alarm can be muted by pressing bution 204e on the display of the ancillary device, as shown in figure 2c.

It is straightforward to determine whether or not the CPB machine is active based on the signal from the flow sensor 202; the blood flow rate output by the CPB machine and detected by the flow sensor may simply be compared with a threshold value, and the CPB machine may be considered active if the threshold value is exceeded, and inactive if not.

The threshold value will vary with the size of the patient, but may be between 0.5 L/min and 2,5 L/min.

Preferably, the threshold value will be around 2.0 L/min.

However, determination based on a simple threshold value is not feasible for the second sensors 203a, b, which determine whether or not the ventilator is active.

This is because both types of second sensor are expected to detect pulsatile signals when the ventilator is active.

Fig. 4 shows a graph 400 showing the of the amplitude of pulsatile signal from the pressure sensor 402 and the pulsatile signal from the bellows sensor 401 against time during the respiratory cycle.

Lines 401 and 402 show the pulsatile waveforms indicative of a process of supported respiratory motion, with the difference between the highest (crest) and the lowest (trough) points of the waveform being proportional to the tidal volume during assisted air inhalation and exhalation.

A method for detecting whether or not the ventilator is active based on the reading from the pressure sensor 203a and/or the bellows sensor 203b is described below.

Fig. 5 shows a continuous signal 500 which is representative of the analogue signal output by either the pressure sensor 203a or the bellows sensor 203b.

It will be 9

2017-028 understood that it is necessary for the controller 201 to digitise the signal, so the analogue signal is sampled at a number of discrete sample points 501, 502, 503, 504, 505. To determine whether or not the signal 500 indicates that the ventilator is active, the controller 201 is configured to calculate a mean value of the signal over a predetermined time period.

The mean value in figure 5 is illustrated by the horizontal line A.

In the present embodiment, the predetermined time period is six seconds, although it will be appreciated that other time periods, for example between one second and fifteen seconds, may also be suitable.

What is important is that the time period is long enough that pulsations at normal breathing frequencies can be observed within the time period, so that it can be reliably determined whether or not a signal is pulsatile.

However, it is also important to ensure that the time period is not so long that it causes an unacceptable delay in the detection of a dangerous condition.

Accordingly, six seconds is preferred, as this is long enough to observe an entire pulsation, even at a very low breathing frequency of 10 breaths/min.

Once the mean value has been calculated, it is determined whether or not each of the recorded data points falls within bandwidth 506, which is defined as the mean value plus or minus a predetermined tolerance value.

For the pressure transducer, the tolerance values may be indicative of a pressure change of plus or minus 10% from the maximum value, which may be approximately 0,1 bar.

For the bellows sensor the tolerance values may be indicative of a movement of the bellows equal to approximately 30% of the maximum stroke length of the bellows.

In both cases, the tolerance values will typically be empirically determined.

The patient is assumed to be ventilated if a more than a predetermined proportion of the data points lie outside the bandwidth 506. Otherwise, the signal is considered to be indicative of the ventilator being inactive.

The predetermined proportion may be approximately between 30 and 50%, typically around 40%. If the signal indicates that the ventilator is active, no alarm is activated.

When the ventilation is interrupted, the signal received from the second sensor 203a, 203b is no longer pulsatile, so the time points 501 to 505 will fall within the bandwidth 5086. If a less than the predetermined proportion of the data points fall outside the bandwidth 506, the signal is considered to be inactive.

If the controller determines that the ventilator is inactive but the signal from the first sensor indicates that the CPB machine is active, then no audible alarm is sounded, as the patient is provided with oxygenated blood by the CPB machine.

However, if the signals received by the controller from the first and second sensors indicate that both the CPB machine and the ventilator are inactive, then a countdown is started.

The countdown may last 10

2017-028 approximately 12 seconds (i.e. two of the six-second time periods defined above) after the inactivity is first detected at the end of a time period. It will be understood that if an inactive condition begins part way through a time period then it is possible that detection of the inactive condition may not occur until the end of the next time period.

If the signals do not change to indicate that at least one of the CPB machine and the ventilator has become active when the countdown ends, then the audible alarm is triggered via speaker 204a or visual alarm 210, warning the surgical team that the CPB machine and the ventilator have been inactive for more than the predetermined amount of time, and that action is needed to provide the patient with oxygenated blood.

In the embodiment described above, the countdown is the same irrespective of which of the machines was last determined to be active. However, in other embodiments the length of the countdown may be different depending on which of the machines was last detected to be active.

As shown in figure 2c, the display 204 of the ancillary device provides respective visual indications as to whether or not pulsatile pressure is detected in the ventilation tube, whether or not the blood flow through the CPB machine exceeds the threshold value, and whether or not the bellows sensor detects movement of the bellows, via labelled light bulbs 204d. These visual indications may reassure the surgical team that the correct one of the CPB machine and the ventilator is active, and that the ancillary device is monitoring the CPB machine and the ventilator correctly. In the event that the alarm sounds, the surgical team may mute it by pressing the reset button 204e.

The process of a typical procedure and the control signals produced and received by the controller 201 at different times during the procedure will now be described with reference to figure 6. Figure 6 illustrates the signal 604 received by the controller 201 from the first sensor 202. Figure 6 also illustrates first and second binary control signals 602, 603, which indicate whether or not the ventilator has been determined to be active in dependence on the signals received from the second sensors 203a and the complimentary second sensor 203b, respectively. The amplitude of the received signals on the vertical axis and the time on the horizontal axis are both shown in arbitrary units.

In the illustrated embodiment, five major phases can be defined. The first phase 601 is the process of anaesthetising the patient, wherein he/she is connected to the anaesthesia machine to substitute natural breathing, and ventilatory support is provided by means of supplying a mixture of medical gases into the lungs of the 11

2017-028 patient to anesthetise the patient. During this stage the signals from the second sensors 203a, 203b is constantly indicative of the ventilator being active, indicative of the respiration under the control of the anaesthesia machine. The signal 604 generated by the CPB machine 101 is inactive as no blood flow is yet detected by the ultrasonic sensor, however no audible alarm is triggered because the ventilator is active. A visual indication showing no flow is shown on display 204d. The second phase 605 shows the signals during the sternotomy process, where the respiration is set to hold to allow the chest plate to be cut and the CPB machine 101 is yet not in use. During this phase, no active signal is produced by both the first 202 and the second sensors 203a, 203b. When the deactivation of the ventilator is detected on the basis of the signals from the second sensor 203a and the complementary second sensor 203b, a timer is started by the controller 201. If the median sternotomy is not completed and the ventilator re-activated before the timer exceeds the predetermined time period, the controller 201 is configured to cause an alarm to be produced by speaker 204a. It is important to have an alarm indicative of air/blood circulation at this stage, as the alarm reminds the team that the patient is without vital supplies, and that ventilation or CPB must be initiated soon to avoid irreversible harm to the patient. This alarm can be manually deactivated by pressing button 210. The alarm will also cease to sound if the signals from the first and second sensors indicates that the ventilator has been re-activated or flow through the CPB machine exceeds the threshold value. After the median sternotomy is completed, the procedure moves on to the third stage

607. During the third stage the ventilator is re-activated whilst the surgeon connects the CPB machine across the patient's heart. The respiration support via the ventilator is switched on again in order to resume oxygenation of the blood while priming of the CPB machine and building up occurs. This temporary switch is needed as connecting a CPB machine to the vascular system of the patient and filling it with patient’s blood can be time consuming, and the oxygen supply to the tissues and organs has to be constantly maintained. The intensity of the signal 604 from the blood flow sensor 202 briefly increases while the pump of the CPB machine is being primed, as illustrated by the small peak 610. The flow is then reduced to zero whilst the surgeon connects the tubing of the CPB machine to the appropriate veins and arteries to allow the CPB machine to bypass the heart. Once the CPB machine is connected, ramping up of the flow through the CPB machine occurs, as illustrated by increasing signal 610, until the maximum flow rate is attained. Soon after the maximum flow rate through the CPB machine is attained, the ventilator is switched 12

2017-028 off, so that the CPB machine alone is responsible for providing oxygenated blood to the patient.

The fourth phase 611 occurs once the switch between the anaesthesia machine and a CPB has occurred, and the patient is fully dependent on the CPB machine 101, therefore the anaesthesia machine 103 is no longer in use.

The signal from the first sensor is indicative of the blood flow from the CPB machine being above the predetermined threshold value, so no audible alarm is triggered.

In the event of malfunctioning of the CPB machine 613 the blood flow may be interrupted, as shown during time period 614. This would mean that the patient is left without any extracorporeal support for a period of time, which, if not resumed, may lead to irreversible harm during the surgery.

If malfunction of the CPB machine persists for longer than the predetermined period of time, then an alarm will be triggered by the controller 201. At the end of the intervention, in the fifth phase 615, normal breathing and heart functions have to be restored, and the CPB machine action needs to be discontinued.

Blood circulation through the CPB machine is gradually reduced and the ventilator of the anaesthesia machine is switched on again in order to restore breathing support.

During the transition from the CPB to the native circulation the signal from the second sensors 616, 617 indicative of artificial respiratory support is active until the patient is reperfused, and the signal from the first sensor 618 indicative of the blood flow within the CPB machine is diminished.

It is essential to ensure that the ventilator is switched back on before or very soon after the flow through the CPB machine is reduced.

Advantageously, the ancillary device of the present invention will provide a warning in the event that the surgical team forget to switch the ventilator on in time after the CPB machine has been deactivated.

A particular advantage of the ancillary device of the present invention is that it is provided with its own sensors to determine whether or not the CPB machine and the ventilator are providing the required support to the patient.

This ensures that the device is compatible with the CPB and anaesthesia machines of a variety of manufacturers, and does not interfere with the software or hardware of those devices.

Furthermore, because the ancillary device is independent of the ventilator and the CPB machine, in the event that the control systems of one of those machines malfunctions, the ancillary device of the present invention will still monitor the actual outputs from the CPB machine and the ventilator, so that an alarm will sound if the actual output from the CPB machine and ventilator indicate a dangerous condition, even if the control signals produced by the CPB machine and ventilator would indicate that a dangerous condition does not exist. 13

2017-028 A device according to an embodiment of the present invention has been installed in an operating room, and has been used in 120 open heart surgery procedures.

During this time, an alarm indicating that the CPB machine and the ventilator had been switched off for more than the predetermined amount of time was triggered on four occasions.

No false alarms were triggered.

These data indicate that embodiments of the present invention may improve patient safety during open heart surgery.

It will be appreciated that embodiments of the present invention can be realised in the form of hardware, software or a combination of hardware and software.

Any such software may be stored in the form of volatile or non-volatile storage such as, for example, a storage device like a ROM, whether erasable or rewritable or not, or in the form of memory such as, for example, RAM, memory chips, device or integrated circuits or on an optically or magnetically readable medium such as, for example, a CD, DVD, magnetic disk or magnetic tape.

It will be appreciated that the storage devices and storage media are embodiments of machine-readable storage that are suitable for storing a program or programs that, when executed, implement embodiments of the present invention.

Accordingly, embodiments provide a program comprising code for implementing a system or method as claimed in any preceding claim and a machine readable storage storing such a program.

Still further, embodiments of the present invention may be conveyed electronically via any medium such as a communication signal carried over a wired or wireless connection and embodiments suitably encompass the same.

All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive.

Each feature disclosed in this specification (including any accompanying claims, abstract and drawings), may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise.

Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.

The invention is not restricted to the details of any foregoing embodiments.

The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.

The claims should not be construed to cover merely the 14

2017-028 foregoing embodiments, but also any embodiments which fall within the scope of the claims.

Claims (16)

2017-028 CONCLUSIONS An auxiliary device for a cardiopulmonary bypass (CPB) machine and a ventilator, the auxiliary device comprising: - a first sensor configured to produce an output indicative of a blood flow rate output from the CPB machine; - a second sensor configured to sense a parameter indicating whether the ventilator is active or inactive; - an export means; and - a controller configured to receive signals from the first and second sensors and to control the output means, the controller configured to: determine whether or not the blood flow rate of the CPB machine is less than a threshold value depending on the output of the first sensor; determining whether the ventilator is active or inactive depending on the output of the second sensor; and controlling the output means to produce an alarm if the output from the first sensor indicates that the blood flow rate output from the CPB machine is less than the threshold for longer than a first threshold amount of time and the output from the second sensor indicates that the ventilator has been inactive for more than a second threshold amount of time. The device of claim 1 wherein the first sensor is an ultrasonic sensor configured to measure the blood flow rate of an output from the CPB machine. The device of claim 1 or 2, wherein said first sensor is configured to produce an output proportional to the blood flow rate. The apparatus of claim 1 wherein the second sensor comprises a pressure transducer. The device of claim 4, wherein said second sensor is connected to a Luer terminal on a sampling port. The device of claim 5 wherein the sampling port is a high efficiency particulate air (HEPA) filter. 16 2017-028 The device of claim 4 or 5, wherein said second sensor is configured to produce an output proportional to the ventilation pressure. The device of any of claims 4-7 wherein the controller is arranged to determine that the ventilator is inactive when the pressure transducer is not producing a pulsed output, optionally wherein the output of the pressure transducer is determined to be pulsed if more then a threshold proportion of the measured data points in a given time period fall outside a defined bandwidth defined as the average value over a given time period plus or minus a predetermined tolerance value. The apparatus of any preceding claim, wherein the second sensor comprises a bellows motion sensor, comprising: a frame configured to be positioned around a portion of said bellows; a light source located on a first part of the frame and capable of emitting a light beam, said beam reflected from the bellows housing; at least one light sensor located on a second part of the frame and configured to have light reflected from the bellows, the intensity of light detected by the light sensors varying depending on a position of the bellows. The device of claim 9 wherein the frame is U-shaped. The device of claim 9 or 10, wherein the light source is a light-emitting diode (LED). The device of any of claims 9-11, wherein the light source is located in an upper portion of the frame and the light sensor is located in a side portion of the frame. The device of claim 9 wherein the controller is arranged to determine that the ventilator is inactive if the bellows motion sensor is not producing a pulsating output, optionally wherein the output of the bellows motion sensor is determined to be pulsating if more than a threshold proportion of the measured data points in a given time period falls outside a bandwidth defined as the average value over a given time period plus or minus a predetermined tolerance value. 17 2017-028 The device of any of the preceding claims, comprising a plurality of second sensors. The device of claim 14 where dependent on claims 4 and 9, wherein the controller is arranged to determine that the ventilator is inactive when the pressure transducer and the bellows motion sensor produce a pulsating output, optionally wherein the output of each of the pressure transducer and bellows motion sensor is determined to be pulsating if more than a threshold portion of the measured data points in a given time period falls outside a bandwidth defined as the average value over a given time period plus or minus a predetermined tolerance value. The device of any preceding claim, wherein the first threshold amount of time is equal to the second threshold amount of time. 18