Patent ID: 12226611

In the drawings like reference numerals refer to like parts.

DETAILED DESCRIPTION OF SOME EXEMPLIFYING EMBODIMENTS

FIG.1illustrates an arrangement for applying negative pressure wound therapy to a wound site10. A packing material12is placed within a wound cavity, and then a drape14sealed to the surface of the skin around the wound site10forming a fluid tight seal around the perimeter of a wound chamber. A source of negative pressure, such as a pressure control apparatus100is coupled to the wound cavity via a tube16. A fluid collection canister (not shown) may be coupled between the pressure control apparatus100and the wound chamber to collect any wound exudate drawn from the wound site10. The use of the packing material12is optional, and it may be omitted in certain arrangements as appropriate.

Alternatively, a self contained wound dressing may be used in place of the drape, such a wound dressing absorbs wound exudate within the layers of the dressing removing the need for a separate fluid collection canister.

Further details regarding wound dressings that may be used in combination with the embodiments described herein are found in U.S. application Ser. No. 13/092,042, filed Apr. 21, 2011, the entirety of which is hereby incorporated by reference.

It is envisaged that the negative pressure range for the apparatus in certain embodiments of the present invention may be between about −50 mmHg and −200 mmHg (note that these pressures are relative to normal ambient atmospheric pressure thus, −200 mmHg would be about 560 mmHg in practical terms). Aptly, the pressure range may be between about −75 mmHg and −150 mmHg. Alternatively a pressure range of up to −75 mmHg, up to −80 mmHg or over −80 mmHg can be used. Also aptly a pressure range of below −75 mmHg could be used. Alternatively a pressure range of over −100 mmHg could be used or over −150 mmHg.

FIG.2illustrates a schematic representation of a pressure control apparatus100according to embodiments of the invention that can be used to apply negative pressure to a wound site10. The pressure control apparatus includes an inlet102coupled to a pressure sensor116, and also to an inlet of a pump106via a one-way check valve104. The pump is operated by an electric motor108, which draws power from a battery114. A controller112is coupled to the pressure sensor116and provides control signals for controlling the operation of the electric motor108. Indicators110are coupled to the controller112to allow audio and/or visual feedback of status signals to a user. An outlet of the pump106is coupled to an outlet118of the pressure control apparatus. A user can utilise a power button120to initiate or terminate operation.

The pump106shown is a diaphragm pump which may be highly efficient and capable of providing the required negative pressure. It will be appreciated that other types of pump such as peristaltic pumps, or the like can be used. In some arrangements, the one-way check valve104may form part of the pump106, and may not exist as a separate element of the apparatus.

While the apparatus has been described as being battery powered, it will be understood that the apparatus could alternatively draw electrical power from a mains power supply and the battery power cell removed. In some arrangements, the apparatus may be capable of being powered from either a mains power supply or a rechargeable battery that may be recharged from the mains power supply.

In operation, the inlet102is coupled to a wound chamber formed over a wound site10, for example via the length of tube16. The electric motor108drives the pump106under the control of the controller112to provide a negative pressure at the inlet102. The negative pressure can then be communicated to the wound chamber in order to provide a desired negative pressure at the wound site. The check valve104maintains the level of negative pressure at the inlet102when the pump106is not active and helps avoid leaks.

Upon initially connecting the pressure control apparatus100to the wound chamber, the pressure at the wound site will be equal to atmospheric pressure, and an initial pump-down must be performed to establish the desired negative pressure at the wound site. This may require the pump106to be operated for an extended period of time until the desired negative pressure is achieved.

The pressure at the inlet102is indicative of the pressure experienced at the wound site, and this pressure is measured by the pressure sensor116. The controller112receives the pressure value measured at the pressure sensor116, and once the measured pressure reaches the desired negative pressure, the controller deactivates the pump106. The controller112then continues to monitor the pressure at the pressure sensor.

If during the initial pump-down phase, the controller112determines that the desired negative pressure has not been achieved within a certain time (for example 10 minutes or 20 minutes or 30 minutes or 40 minutes or the like), then leaks may be present into the wound chamber, and this condition is signalled via the indicators110to show that the wound chamber has not been correctly sealed, or some other error or fault is present.

Once the desired negative pressure has been established, the controller112monitors the pressure at the inlet of the pressure control apparatus. From time to time, leaks of fluid may occur into the wound chamber, reducing the level of negative pressure experienced at the wound site, or in other words increasing the absolute pressure at the wound site. The pressure value measured at the pressure sensor116and provided to the controller112will therefore increase as fluid leaks into the wound chamber. When the measured negative pressure value drops below a certain defined pressure level, the controller112will reactivate the pump106in order to re-establish the desired negative pressure at the wound site. The desired negative pressure and the defined pressure level at which the controller reactivates the pump provide hysteresis limits between which the pressure should be maintained to apply topical negative pressure to the wound site.

However, if a leak forms that allows fluid, for example air, to leak into the wound chamber with a flow rate greater than the maximum pump capacity106, it will not be possible for the pressure control apparatus100to maintain the desired negative pressure at the wound site. If the pressure control apparatus100continued to attempt to re-establish the desired negative pressure in the presence of such a leak, the battery power cell114would become depleted. Furthermore, continued operation of the pump in the presence of a large leak can draw contaminants into the wound site, and lead to excessive drying of the wound site which is undesirable. Therefore, the controller112is configured to deactivate the pump106if the desired negative pressure is not re-established after operation of the pump106for a predetermined period of time. For example sometime between around 30 minutes and 4 hours.

The formation of leaks into the wound chamber may occur due to a range of factors. One common cause of such leaks is movement of a patient being treated with the pressure control apparatus100. For example, a leak may form when a patient moves from a lying to a sitting position, or during the normal range of movement when walking. Such leaks may be transient, and have been found to regularly reseal as the patient continues to move or returns to their previous position. Thus, there is a risk that the pump106may be deactivated due to the detection of a leak that subsequently reseals. However, once the leak reseals, operation of the pressure control apparatus would be able to re-establish the desired negative pressure within the wound chamber.

According to embodiments of the invention, the controller112is configured to deactivate the pump106after the pump has operated for a certain period of time without the desired level of negative pressure being reached in the wound chamber. That is a timeout event occurs. The controller then waits for a further period of time before a retry attempt is made to re-establish the desired negative pressure at the wound site using the pump106. If the leak has resealed while the pump has been temporarily deactivated, the retry attempt to re-establish the desired negative pressure will be successful, and operation of the pressure control apparatus100can continue as normal. However, if the leak is still present a further timeout event will occur and the pump will be deactivated for the further period of time.

This cycle of deactivating the pump106and then attempting to re-establish the desired negative pressure may be repeated a number of times in order to provide an opportunity for any leaks to reseal. However, once a timeout event occurs the negative pressure at the wound site will start to degrade, and therefore there will be a break in the negative pressure wound therapy applied to the wound site. While a short break in therapy may not be a concern, an extended period in which the negative pressure is not applied should preferably be avoided. Furthermore, if a leak path into the wound chamber exists for an extended period of time, the potential for contaminants reaching the wound site increases. Thus, if a number, N, of unsuccessful attempts are made to re-establish the desired negative pressure it can be assumed that the leak is permanent, and not transient, and the controller112disables operation of the pressure control apparatus100and provides a signal via an audio and/or visual cue to a user that attention is required. This allows a patient or caregiver to arrange for any dressings or drapes to be changed to thereby reform the wound chamber and allow the negative pressure wound therapy to be continued. Aptly N is an integer between 1 and 5 inclusive.

Alternatively, the pump106and motor108may be omitted, and the negative pressure may be provided via an external source of negative pressure, such as by connection to a vacuum line or vacuum reservoir.FIG.3provides a schematic representation of a further pressure control apparatus200for use with an external source of negative pressure, and which can be used to provide negative pressure to a wound site10. Pressure control apparatus200includes a controllable valve202coupled between an inlet102and an outlet118. The outlet118is coupled to the external source of negative pressure. Controller212provides control signals to the valve202to control the coupling of the external source of negative pressure to the inlet102, and thereby to the wound chamber. The pressure at the inlet102is monitored by a pressure sensor116, coupled to the inlet, and this monitored pressure is supplied to the controller212.

The operation of the pressure control apparatus200ofFIG.3is similar to that of the pressure control apparatus100, except that pressure is controlled by operating the valve202to couple the wound chamber to the external source of negative pressure. Controller112is able to control the level of negative pressure at the inlet102by controlling the valve202. By monitoring the pressure at the inlet via the pressure sensor116, the controller212can control the valve to provide the desired negative pressure at the wound site.

Unlike the pressure control apparatus ofFIG.2, an extended attempt to provide the desired negative pressure in the presence of a leak will not lead to depletion of a battery power cell. However, longterm it is still undesirable to continue to apply a negative pressure in the presence of a leak due to the possibility of drawing contaminants into the wound chamber, and of drying out the wound site due to the flow of air through the chamber. Thus, the controller212ofFIG.3implements the same control flow as described above with respect to the pressure control apparatus100. That is, controller212is configured to de-couple the inlet102from the external source of negative pressure by closing the valve if the desired negative pressure is not established at the wound site within a predetermined period of time. A number of attempts may then be made to re-establish the desired negative pressure in order to provide the opportunity for transient leaks into the wound chamber to reseal.

Thus, the pressure control apparatus ofFIGS.2and3are able to control the application of negative pressure to a wound site, and advantageously reduce the number of alarms due to transient leaks of fluid into the wound chamber. When a leak forms that allows air into the wound chamber at a flow rate above a certain level, the pressure control apparatus is configured to disable the provision of negative pressure to the wound chamber for a predetermined period of time, providing an opportunity for the leak to reseal. Then, if the leak is transient and reseals, the desired negative pressure may then be re-established at a subsequent attempt. This avoids the need to indicate an alarm condition for transient leaks, and also avoids the problem of drawing contaminants and excessive amounts of air into the wound chamber. This also avoids a pump motor being repeatedly energised and de-energised which avoids concerning noise level changes and helps improve pump motor longevity.

Controller112,212may be implemented as a microcontroller, or an application specific integrated circuit, or the like, and may execute instructions to provide the above described control functions. For example, a suitable microcontroller would be one from the STM8L MCU family from ST Microelectronics, for example ST Microelectronics STM8L151G4U6, or one from the MC9S08QE4/8 series from Freescale, such as the Freescale MC9S08QE4CWJ.

The operation of the controller112may be described as a finite state machine. The operation of the controller is described below with reference toFIG.4which shows a state diagram300describing the operation of the controller112for the pressure control apparatus shown inFIG.1.

FIG.5illustrates one embodiment of controller112. The controller comprises a memory502, which may hold program code for implementing the control functions. The memory is coupled to a microcontroller504able to execute the instructions. The microcontroller is coupled to inputs506and outputs508through which the microcontroller is able to monitor the operation of the system and provide control signals to other parts of the pressure control apparatus.

Referring again toFIG.4upon activation310of the pressure control apparatus100which may occur when an activation strip is pulled for the first time or a user button is pressed or the like, the controller112performs a power-on self test (POST)302to ensure that the pressure control apparatus is operating correctly. If the power-on self test is failed the pressure control apparatus should not be used. Therefore, after a failed POST, the controller transitions to a non-recoverable error state304and the error is signalled to the user via indicators110. If the POST is passed, the controller112transitions to an operational state308via a standby state, and performs an initial pump down312when a user indicates via a button, in which the pump106is operated until a desired negative pressure is established in the wound chamber. Alternatively, the controller may wait on a user input before performing the initial pump-down in state312.

Once the desired negative pressure has been successfully established, the controller transitions to the monitor pressure state316. However, if after a predetermined period of time the desired pressure has not been established and the initial pump down state312is unable to establish the desired negative pressure (indicative of a leak), a timeout occurs. On the first timeout, the controller will transition to a wait state314, in which the controller waits for a period of time before transitioning back to the initial pump down state312. Further timeouts may occur from the initial pump-down state312, and the controller maintains a count of the number of retry attempts made. Once the desired negative pressure has been established, the number of retry attempts may be reset.

If a timeout occurs and the number of retry cycles is greater than a predefined maximum number of retry attempts allowed, the controller transitions to a paused state306. While in the paused state306the controller will transition from the paused state306to the initial pump down state312in response to a user input, or after a maximum pause time.

In the monitor pressure state316, the controller monitors the pressure measured at the pressure sensor116and, if the pressure drops out of the desired pressure range, the controller transitions to a maintenance pump-down state318. In the maintenance pump-down state318, the suction pump is activated either for a predetermined period of time, for example between around 10 and 60 seconds, or until the desired negative pressure is re-established in the wound chamber, whichever occurs sooner.

It is noted that some hysteresis is built into the desired pressure range, such that the pressure value, a minimum desired negative pressure, that triggers a transition from the monitor pressure state316to the maintenance pump-down state318is lower than the desired negative pressure established in the wound chamber by operation of the pump during the maintenance pump-down state318. For example, taking the operating pressure ranges discussed above, the desired negative pressure may be −150 mmHg and the minimum desired negative pressure may be −75 mmHg. Alternatively, the controller may act to maintain the pressure within a certain percentage range of the desired negative pressure, for example a 5% hysteresis may be used.

If the desired negative pressure is reached before the suction pump has been operating for the predetermined period of time, the controller transitions back to the monitor pressure state316.

However, if the pump operates for the predetermined period of time without the desired negative pressure being re-established in the wound chamber, normally due to a leak into the wound chamber, the pressure control apparatus will signal the presence of a leak. If the pressure is within the hysteresis limits, i.e. between the minimum desired negative pressure and the desired negative pressure, this signifies the presence of a high leak, having a flow rate similar to the capacity of the pump. In this situation, the pump continues to operate until the desired negative pressure is re-established, or until the pressure at the wound site is no longer held within the hysteresis limits.

If in the presence of a large leak, the desired negative pressure is restored before a maximum maintenance time is reached, the controller will transition back to the monitor pressure state316, but will signal the presence of a leak. However, if the suction pump is operated for more than the maximum maintenance time to restore the desired negative pressure, the controller will transition to the paused state306, while signalling the presence of a leak.

If during the maintenance pump-down state318, the pressure in the wound chamber is not maintained within the hysteresis limits, a catastrophic leak has occurred, and the controller transitions to the wait state314.

In some embodiments, if after a predetermined period of time, the desired pressure has not been established and the maintenance pump down state318is unable to establish the desired negative pressure before the maximum maintenance time is reached, a timeout occurs. On the first timeout, the controller will transition to the wait state314, in which the controller waits for a period of time before transitioning back to the initial pump down state312. Further timeouts may occur from the maintenance pump-down state318, and the controller maintains a count of the number of retry attempts made. Once the desired negative pressure has been established in the maintenance pump down state318, the number of retry attempts may be reset. If a timeout occurs and the number of retry attempts is greater than a predefined maximum number of retry attempts allowed, the controller transitions to the paused state306, as described above.

Thus, if the leak is such that it is over a prescribed limit and the pump duty cycle (DC) as defined, in some embodiments, as pump on time divided by pump off time is over a predetermined limit then the pump shall continue to operate within the hysteresis limits for a particular time duration. For example, around 30 minutes as shown inFIG.4. Thus, in the monitor pressure loop if the duty cycle is less than a predetermined limit then all is okay. If the duty cycle is greater than a particular limit but less than a time out time the pump continues to run for up to 30 minutes. If DC is greater than time out then a paused state306is entered.

At any time while in the operational state308, the controller may be placed in the pause state306in response to a user input. Once the battery voltage reaches a low voltage cut off level or the lifetime of the pressure control apparatus has been reached, the controller de-activates the pressure control apparatus and an End of Life state is reached.

The controller212described with respect of the pressure control apparatus200ofFIG.3operates in a similar manner as described above except that the initial pump-down and maintenance pump-down states are replaced with valve activation states in which the inlet102is coupled to the external source of negative pressure connected to the outlet118via controllable valve element202.

Alternatively, the POST state302may be omitted.

The pressure control apparatus may be configured to be re-useable and be provided with a switch to allow the apparatus to be turned on and off as required. Such a re-usable apparatus may include rechargeable power cells, and may provide a low power indication in order to allow the power cells to be replaced/recharged.

In a disposable single use pressure control apparatus, activation may be provided by pulling an activation strip and it may not be possible to deactivate the apparatus once activated until the apparatus is to be discarded.

Throughout the description and claims of this specification, the words “comprise” and “contain” and variations of the words, for example “comprising” and “comprises”, means “including but not limited to”, and is not intended to (and does not) exclude other moieties, additives, components, integers or steps.

Throughout the description and claims of this specification, the singular encompasses the plural unless the context otherwise requires. In particular, where the indefinite article is used, the specification is to be understood as contemplating plurality as well as singularity, unless the context requires otherwise.

Features, integers, characteristics, compounds, chemical moieties or groups described in conjunction with a particular aspect, embodiment or example of the invention are to be understood to be applicable to any other aspect, embodiment or example described herein unless incompatible therewith.