WOUND DRESSING CONTAINING A VACUUM PUMP

Abstract

The present invention relates to a wound healing PVA sponge dressing using negative capillary pressure of the dressing material together with auxiliary negative pressure for wound treatment. The PVA sponge dressing is pretreated with gram positive and gram negative biocidal 5 dyes for insertion into or over a wound. A negative pressure pump is mounted to the PVA sponge dressing to produce additional capillary pressure for withdrawing fluid or water vapor from the sponge dressing and a cover is mounted over the sponge material and negative pressure pump forming a unitary sealed package for placement over a wound.

Claims

1. A method for wound treatment comprising: applying negative pressure to a wound using a porous material having a natural capillary pressure; supplementing the negative pressure applied by the porous material using a negative pressure pump connected to the porous material by turning the pump on; turning the pump off; and turning the pump on again.

2. The method of claim 1, wherein supplementing the negative pressure using the pump comprises applying supplemental negative pressure so that a total negative pressure on the wound remains in a therapeutic range.

3. The method of claim 1, wherein: applying negative pressure to the wound using the porous material comprises applying negative pressure that is above a lower therapy threshold; and supplementing the negative pressure using the pump comprises raising a level of pressure on the wound higher in a therapeutic range.

4. The method of claim 1, wherein supplementing the negative pressure using the pump comprises increasing negative pressure applied by the pump.

5. The method of claim 1, further comprising replacing the porous material when the porous material is fully saturated.

6. The method of claim 1, further comprising replacing the porous material when the pump no longer has power sufficient to hold a predetermined level of pressure on the wound.

7. The method of claim 1, comprising varying a ratio of negative pressure contribution from the porous material and pump during the wound treatment.

8. The method of claim 1, further comprising adjusting negative pressure applied by the pump.

9. The method of claim 1, further comprising: detecting when a level of pressure on the wound is outside of a therapeutic range; and turning the pump off when the level of pressure on the wound is above an upper therapy threshold.

10. The method of claim 1, further comprising detecting decay of a level of pressure on the wound.

11. The method of claim 1, further comprising detecting a rate of increase of a level of pressure on the wound.

12. The method of claim 1, wherein the porous material comprises polyvinyl formal, polyvinyl acetal, polyvinyl acetal copolymers of vinyl esters, polyvinyl acetal copolymers of ethylene-containing repeat units, or a combination thereof.

13. The method of claim 1, wherein the porous material comprises polyvinyl formal, polyvinyl acetal.

14. The method of claim 1, further comprising calculating a level of pressure on the wound based on ambient pressure and vacuum in the porous material.

15. The method of claim 14, comprising turning the pump on again if the level of pressure on the wound is at or below a lower predetermined level.

16. The method of claim 15, further comprising turning the pump off again when the level of pressure on the wound subsequently reaches an upper predetermined level.

17. The method of claim 16, further comprising measuring total pressure reduction in a cycle.

18. The method of claim 1, further comprising monitoring battery level, leak detection, microcontroller health, blockage detection, loss of volume capacity, device lifetime, or a combination thereof of a wound negative pressure wound therapy device comprising the porous material and the pump.

19. The method of claim 18, further comprising indicating a warning or shutting down the device when the device is no longer able to maintain pressure above a lower therapy threshold.

20. The method of claim 18, further comprising: tracking elapsed time that the device has provided treatment; and indicating a warning or shutting down the device based on the elapsed time.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The present invention will be described with reference to the appended Figures, in which:

[0027] FIG. 1 is a schematic cross section of the inventive negative pressure wound dressing device;

[0028] FIG. 2 is a schematic cross section of another embodiment of the negative pressure wound dressing device;

[0029] FIG. 3 is a schematic of the negative pressure provided to the wound dressing of FIGS. 1 and 2 using the inventive wound dressing device; and

[0030] FIG. 4 is a schematic of a detailed control circuit of the inventive wound dressing device.

[0031] These and other objects, advantages, and novel features of the present invention will become apparent when considered with the teachings contained in the detailed disclosure along with the accompanying drawings.

DESCRIPTION OF THE INVENTION

[0032] The present invention is a negative pressure wound therapy (NPWT) system where the reduced atmospheric pressure on the wound is achieved by two sources, (1) a porous sponge dressing material and (2) an auxiliary vacuum unit, e.g. a pump. The porous sponge dressing material is a PVA foam which provides a natural capillary pressure of about -20 mmHg to about -72 mmHg on the wound. The auxiliary pump can further reduce the pressure to maintain a therapeutic benefit, e.g. down to about -120 mmHg. The result is a NPWT system that is portable by the user and is significantly smaller than prior art devices and with minimal to no tubing required to connect the dressing to the auxiliary vacuum source.

[0033] As is used herein, reduced or negative pressure levels, such as -X mmHg, represent pressure levels relative to normal ambient atmospheric pressure, which corresponds to 760 mmHg (or 1 atm, 29.93 inHg, 101.325 kPa, 14.696 psi, etc.). Accordingly, a negative pressure value of -X mmHg reflects absolute pressure that is X mmHg below normal ambient atmosphere pressure of 760 mmHg or, in other words, an absolute pressure of (760 mmHg -X mmHg). In addition, negative pressure that is “less” or “smaller” than the X mmHg negative pressure corresponds to pressure that is closer to atmospheric pressure.

[0034] The present invention describes a medical dressing device for the field of wound care of patients and is comprised of a porous sponge dressing material 10, preferably PVA foam sponge material 12, a sealing drape or cover 20, a fluid removal path 30, and a vacuum producing mechanism 40 as seen in FIGS. 2 and 4. The device enables the application of negative pressure to a wound with absorption of fluid to the porous sponge dressing material.

[0035] The porous sponge dressing material of the invention is preferably PVA foam sponge material 12 and acts as a source for negative pressure through its natural capillary action and as a wound exudate collection vehicle. The term PVA foam refers to one or more of the following: Polyvinyl formal, Polyvinyl acetal, PVA copolymers of vinyl esters and PVA copolymers of ethylene-containing repeat units. Copolymers with PVA may be random, block, alternating, periodic or graft. The acetal group may have one or two substituents such as aliphatic or aromatic groups which may be further substituted. Foams may further be comprised of blends of above PVA based polymers with non-PVA polymers. The porous PVA sponge 12 has a surface chemistry and porosity that create capillary flow properties, which in turn provide for a natural capillary pressure leading to exudate being drawn from the wound into the porous material. The reduced pressure created by the capillary action of the porous material enables the auxiliary vacuum unit or vacuum producing mechanism 40 as shown in FIGS. 1 and 2 to do less work, thereby affording smaller and less energy consuming technologies to be employed over current commercial products.

[0036] While the porous sponge dressing material is generally referred to by the numeral 10 and the PVA sponge dressing material is referred to by the numeral 12, these numbers can be interchanged as necessary as both refer to the sponge dressing material.

[0037] The PVA porous dressing material 12 acts as a dressing to the wound surface 14. This material is polymeric in composition where the polymer can be a synthetic substance, a natural substance or combinations thereof. In the preferred embodiment, the polymer is foamed PVA with positive and negative biocidal dyes which impregnate or bind to the sponge receptor sites. The porous PVA sponge dressing material has a morphology characterized by an average pore throat diameter of 10 - 500 pm, a fluid retention of 5.5 - 300 mL fluids/g porous material, a density of 0.05 - 0.15 g polymer/cm3 porous material, and a porosity of 60 - 99.5%. The cell structure is characterized as open / interconnected with through pores that can be evaluated by techniques such as capillary flow porometry and liquid extrusion porosimetry. The natural capillary pressure of the PVA sponge or foam dressing material ranges from about -20 mmHg to about -70 mmHg. This natural capillary pressure ranges and falls within the low to mid-range settings of presently used mechanical vacuum machines.

[0038] Without wishing to be bound by theory, the porous PVA sponge dressing material has one or more material properties which in combination afford fluid flow through the material to create a natural capillary pressure. Material properties may include the pore properties above, surface chemical structure, surface roughness and the resultant interfacial tensions arising from the porous PVA material surface and the fluid surface in contact with other. Porous PVA materials with natural capillary pressure may be differentiated from porous materials without natural capillary flow by their simplified diffusion coefficient (D) which can be calculated from the general form of the Washbum equation:

[00001]$\text{D=}\frac{{\text{L}}^2}{\text{t}}$

where (L) is the wicking distance of the liquid at time (t).

[0039] In a preferred embodiment the porous PVA sponge dressing material having natural capillary pressure has a simplified diffusion coefficient greater than 0.3 cm.sup.2 1 second; in a more preferred embodiment greater than 0.4 cm.sup.2 / second, and in a most preferred embodiment greater than 0.5 cm.sup.2 / second. As shown in Table 1, dressings used in the field today have little to no natural capillary pressure as measured by their simplified diffusion coefficient whereas the porous PVA foam of the present invention surprisingly has an almost 4-5X ability.

TABLE-US-00001 Negative Pressure Wound Therapy Dressing Negative Diffusion Coefficient (W/s) KCISNAP Dressing 0.00 KCIVAC Whiteman 0.00 Cork Medical NPWT Black Foam 0.00 Cardinal Health NPWT Black Foam 0.00 GelTex NFWI Dressing 0.00 DeRoyal Top Draw Black 0.00 Porous PVA Foam 0.98

[0040] The simplified diffusion coefficient may be determined to suspending a swatch of the dressing (0.5” × 0.25” × 3.0”) in a normal saline solution to allow vertical wicking through the dressing material. Prior to evaluation, all materials are conditioned at ambient temperature for at least 24 hours. The test article is then attached to a suspension fixture and lowered into a test beaker containing saline solution such that one end is slightly submerged in the saline solution. The vertical wicking distance is recorded after 45 seconds. This wicking distance is then corrected to account for the initial height of saline, and the diffusion coefficient is calculated from the corrected wicking distance and wicking time period.

[0041] A biofilm enzymatic solution can also be incorporated into the porous sponge dressing material during the same manufacturing process that binds the antibacterial agents but after addition of the antibacterial agents. During this process, Methylene Blue, Crystal Violet, and biofilm prevention enzyme solution is introduced and allowed to uniformly impregnate or bind to the foam matrix. The product is then dried and processed to final specification and sterilization.

[0042] The porous sponge dressing material may further have agents that bind and/or eliminate toxins from the exudate, e.g. bacteria, mold, spores, endotoxins. The present invention uses foamed polyvinyl alcohol which is treated to open up the binding sites of the foam. The washed foam is soaked with one or more gram positive dyes selected from a group of dyes consisting of Gentian Violet dye, also called Crystal Violet dye, Malachite Green dye, Brilliant Green dye, Quinacrine dye and Acriflavin dye and one or more gram negative dyes selected from a group of dyes consisting of Methylene Blue dye, Dimethyl Methylene Blue dye, New Methylene Blue dye. The preferred dyes used in the invention are Methylene Blue dye and Gentian or Crystal Violet dye are attached to a finite number of the binding sites in the foam. Generally, electronegative (acidic) dyes are more effective on Gram-negative bacteria and electropositive (basic) dyes are more effective on Gram positive bacteria such as Staphyloccus aureus.

[0043] The porous sponge dressing material may be shaped if desired to be conformable to the shape of the wound bed. The porous sponge dressing material may have a surface porosity on the surface distal to the wound that allows for moisture transmission outwards but is impermeable to air (inwards). As a result, the porous sponge dressing material can self-rejuvenate until it is fully loaded with exudate, up to 5x, 10x or even 15x its weight in exudate fluid, at which time the dressing would be replaced.

[0044] This sponge material of the invention may further be combined with clinically safe agents, e.g. saline, hydration fluids, antimicrobial agents, softening agents, stiffening agents, or wetting agents. The agents may be preloaded prior to clinical use or may be loaded by a clinician at the time of clinical use.

[0045] In another example, the synthetic polymer can be polyvinyl formal. The natural polymer material can be either animal or plant derived, for example, collagen, chitosan, or polyethylene terephthalate.

[0046] The sealing layer, drape or cover 20 acts to form a vacuum seal over the dressing 12 to the wound perimeter. The sealing layer 20 may be polymeric in composition where the polymer can be a synthetic substance, a natural substance or combinations thereof. The sealing layer may also be metallic in composition. The sealing layer may be comprised of multiple polymeric and or metallic layers and may further have adhesives on its surfaces or between layers.

[0047] The vacuum connection assembly 30 acts to apply auxiliary vacuum through the sealing layer 20 to the sponge dressing 12 from the vacuum mechanism 40 via plastic conduits 82 and 80 as seen in FIG. 4, or nipples 42 as seen in FIG. 2, or nipple 30 as seen in FIG. 1. The fluid removal assembly (conduit, T-section, nipples) may be polymeric in composition where the polymer can be a synthetic substance, a natural substance or combinations thereof. The vacuum connection assembly may also be metallic in composition or a combination of polymer and metal. The vacuum connection path may be affixed external to the sealing layer or be imbedded within the sealing layer.

[0048] The vacuum mechanism 40 provides a clinically beneficial negative pressure (up to -120 mm Hg) to the wound site 14 through the porous foam dressing material 10/12. The vacuum mechanism 40 may be affixed external to the sealing layer 20, positioned adjacent the sealing layer or be imbedded within the sealing layer and draws fluid away from the porous foam sponge material through one or more paths. The vacuum or negative pressure is achieved and controlled through many methods known to those skilled in the art. In one embodiment, the vacuum is achieved through an energized device. In another embodiment, the vacuum is achieved through a manual process such as a syringe or squeeze bulb. Preferably, the device is a mechanical pump which is energized or powered by batteries. The vacuum mechanism may allow for filtration of fluid prior to entering the fluid return path. The vacuum mechanism may allow for the addition of clinically safe agents to the fluid prior to entering the fluid return path.

[0049] The medical device described in this invention may be single use and thus disposable or one or more of its components may be reusable. It is envisioned that all components will be disposable and that a whole unit will be disposable as medical waste. The device may be fully assembled when received by the customer or may require assembly at the point of care.

[0050] The NPWT system of the invention may optionally have a sealing layer 20 as shown in FIG. 2 on the porous material surface 10 that allows for vapor or moisture transmission outwards but is impermeable to air (inwards). In other words, the layer 20 is both vapor permeable and an air barrier. As noted above, this would enable the porous sponge material to self-rejuvenate until it is fully loaded with exudate. In one embodiment, the sealing layer covers only the distal facing porous sponge material surface and abuts the auxiliary vacuum unit. In another embodiment, the sealing layer extends over the auxiliary vacuum unit, and the vacuum exhaust passes through the sealing layer. In yet another embodiment, the sealing layer runs under the auxiliary vacuum unit and the vacuum auxiliary units sits above the sealing layer. In a preferred embodiment, the sealing layer is translucent to aid in visualization of the porous sponge material by the clinician or patient.

[0051] As previously noted, the inventive assembly may have a vacuum connection component 30. This component would be located between the auxiliary vacuum unit 40 and the foamed porous material dressing 10/12. In one embodiment of the invention, the vacuum connection component has baffles or channels that aid in equilibrating the vacuum from the auxiliary vacuum unit 40 to the porous material 10/12 or aid in distributing filtered exudate back to the porous material. One or a plurality of fluid removal and/or fluid return chambers may be used where each chamber has one or more of the functions listed above.

[0052] The vacuum connection component may also be provided with a vacuum port/valve. This port/valve component is gas permeable but not liquid permeable and acts to protect the auxiliary vacuum unit from being fouled by exudate. In another embodiment, the assembly may be provided with a check valve to prevent back flow of air into the vacuum connection component and/or the porous sponge material. In yet another embodiment, the vacuum connection component may have a length of tubing to separate the auxiliary vacuum unit from the porous sponge material. One or a plurality of vacuum port/valves may be used where each unit has one or more of the functions listed above.

[0053] The auxiliary vacuum unit 40 of the invention (see vacuum motor 78 in FIG. 4) supplements the negative pressure provided by the foam porous dressing material 12 so that the total negative pressure on the wound remains in a clinically beneficial range. In one example (FIG. 3), the porous material 12 alone provides negative pressure that is above the clinically beneficial threshold, and the auxiliary unit supplements that pressure by raising the pressure higher in the therapeutic range. As exudate is drawn into the foam porous dressing material 12, air or moisture exhaust from the system and/or leaks occur in the system, the pump can apply vacuum to maintain the therapeutic range. As the porous material gets filled, its contribution to maintenance of the therapeutically beneficial negative pressure decreases and the auxiliary vacuum unit’s contribution increases. When the porous material is fully saturated, and/or the auxiliary vacuum no longer has power sufficient to hold a therapeutic negative pressure, the NPWT system can be replaced with a new device. It should be recognized that the system’s design allows for different ratios of negative pressure contribution from the porous material and auxiliary vacuum unit, and that the ratio may vary over the course of the treatment period.

[0054] As previously noted, the auxiliary vacuum unit can be powered by a mechanical action, e.g. a syringe force. The auxiliary vacuum unit (pump) is preferably powered with an electrical supply, most preferably a battery. Examples of battery powered pumps that could be used in the auxiliary vacuum unit include Models Compact/OEM and KPV-14A available from Cole Parmer, Model NMP 03 KP DC-S available from KNF Neuberger, Inc. and Model SX-1 from Binaca Products.

[0055] While the auxiliary vacuum unit 40 can sit on the distal (outward) facing surface of the porous material 10/12, the auxiliary vacuum unit 40 can be embedded or encased in the porous material 10/12 to provide a low-profile system.

[0056] The auxiliary vacuum unit 40 may have addition features including: [0057] Pressure feedback loop enabling constant pressure adjustment [0058] Pressure feedback loop enabling intermittent pressure adjustment (cycling) [0059] Pressure cut off detection when pressure is beyond therapeutic level [0060] Leak detection when pressure decay is too rapid [0061] Pressure ramp up detection when rate (mm Hg/sec) of pressure increase is too steep, indicating the porous material or fluid removal/fluid return chamber is saturated or exhausted [0062] Total pressure reduction in a cycle, which when above a threshold, indicates the porous material or fluid removal/fluid return chamber is saturated or exhausted

[0063] The auxiliary vacuum unit 40 is provided with an integral motor 78 and can also be provided with a vacuum exhaust component that allows escape of air and moisture vapor that has traveled through the auxiliary vacuum unit. The vacuum exhaust component may sit on the surface of the auxiliary vacuum unit or be attached to the auxiliary vacuum unit through a length of tubing. One or a plurality of vacuum exhausts may be used. The auxiliary vacuum unit may also serve as a check valve to prevent back flow of air into the auxiliary vacuum unit.

[0064] The NPWT system may further have a sealing drape layer 20. The sealing drape layer 20 acts to seal the wound bed in an airtight manner. It can also act as the moisture vapor transmission layer described above. In this case, the sealing layer may cover the auxiliary vacuum unit, porous material and other components of the device. In another modification, the sealing drape layer is non-permeable. In this case it would run from the healthy skin to the moisture vapor transmission layer, or it would still cover the entire NPWT system where moisture transmission would be through the auxiliary vacuum unit or vacuum exhaust component.

[0065] The overall system is a single use, disposable product. The system is supplied sterile and have a useful lifetime of approximately 1 day, more preferably 2-3 days, and most preferably up to 7 days depending upon the type and severity of the wound.

[0066] The control system 70 as schematically shown in FIG. 4 comprises a low power microcontroller 71, a three LED indicators 72, one or more push button switches 74, ambient 76a and vacuum 76b pressure sensors, a vacuum motor 78, motor power control 79, one or more batteries 77 and a tactile feedback device 72a. The vacuum pressure sensor has a “T” attachment 82 connecting it to the plastic conduit 80 (for vacuum connection component 30) which connects the vacuum motor to the wound dressing 10 placed on the patient wound 14. The ambient pressure sensor 76a is open to the atmosphere. The microcontroller implements the logic described herein with the C source code language compiled and downloaded for execution to the microcontroller.

[0067] The clinically therapeutic negative pressure range for the device is about -60 mmHg to about -120 mmHg which is shown in FIG. 3 by the letter R. A normal working cycle is shown in FIG. 3. The ramp up is shown by the letter A and the decay is shown by the letter D. However, it is preferred that the negative pressure should fall within about -80 mmHg to about -100 mmHg and most preferably about -85 mmHg to about -95 mmHg.

[0068] The negative pressure cut-off value for the device is about -120 mmHg. Beyond this value, the patient experiences discomfort.

[0069] The push button and three LED’s provide the device user interface. When the push button is first pushed, the device starts up, performs an initial operational check and indicates it is ready for operation by illuminating a green LED. The second time the push button is pushed, the device initiates treatment and starts monitoring operational status. Good status is indicated by an illuminated green light. Warning status is indicated by an illuminated yellow light and a unique tactile feedback pattern. Error status is indicated by an illuminated red light and a different unique tactile feedback pattern.

[0070] Having separate ambient and vacuum absolute pressure sensors have advantages over a single differential sensor common the state of the art. Differential pressure sensors require that the path to the ambient pressure be physically adjacent to the path to the vacuum pressure. Separate sensors allow the paths to be physically separated. Differential pressure sensors are bulky and difficult to mount, whereas absolute pressure sensors are small with a wide variety at mounting options. The ambient pressure sensor provides barometric pressure, which can provide an input to the volume calculations to determine the operational status.

[0071] At the onset of treatment with the dressing properly secured with no leaks, the device undergoes initial start-up. The vacuum motor 78 will turn on and remain running until it reaches the upper therapy threshold, at which point the vacuum motor is turned off and the pressure control will start.

[0072] Pressure control consists of reading the ambient and vacuum pressure sensors periodically. Each time a sensor is read, the vacuum level is calculated as the difference between the ambient and vacuum pressure sensors. If the vacuum is at or below the lower therapy threshold, the vacuum motor is turned on. When the vacuum subsequently reaches the upper therapy threshold, the vacuum motor is turned off.

[0073] Research has shown that a variable vacuum level may provide more effective therapy than a constant vacuum level. During the course of therapy, the microcontroller may optionally change the upper and lower threshold values in a redetermined pattern over the course of several minutes to improve the therapy effectiveness. In another embodiment, the pressure is held constant.

[0074] Operational status monitoring will run continuously once the NPWT device is started with the first push of the button. The status monitoring will include battery level, leak detection, microcontroller health, blockage detection, loss of volume capacity and device lifetime. The battery level will be monitored using both coulomb counting methods, and voltage level measurements. A warning level and error level will be established for battery monitoring based on battery characteristics. Leak rate will be calculated by summing the time of the ramp up (A in FIG. 3) over a known time combined with the vacuum pump characteristics. The warning level will be established based on a projection of the loss of 20% of the lifetime of the device. The error level will be the point where the device is no longer able to maintain the pressure above the lower therapy threshold or the projected lifetime of the device due to the leak is less than 12 hours. The microcontroller health will be monitored by a hardware watchdog, which will turn off the device if the microcontroller does not run the pressure control logic at the selected periodic rate. The microprocessor will track the elapsed time that the NPWT has provided therapy. When the elapsed time is within 12 hours of a predetermined lifetime, the device will shut down the therapy, and turn off all the indicator LED’s.

[0075] The principles, preferred embodiments and modes of operation of the present invention have been described in the foregoing specification. However, the invention should not be construed as limited to the particular embodiments which have been described above. Instead, the embodiments described here should be regarded as illustrative rather than restrictive. Variations and changes may be made by others without departing from the scope of the present invention as defined by the following claims: