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Pressure Ulcers: E-VAC- Two therapies in one
University of Illinois at Chicago
Bioengineering Department
Bioengineering 250
Facilitator: Dr. Andreas Linninger
Team 6- Mark Connolly, Diego Sanchez, Marzia Yasmin, Enas EL-Khatib
22 March 2013
E-VAC 2
E-VAC Combining Electrical Stimulation and Vacuum-Assisted Closure Therapy
Mark Connolly, Enas EL-Khatib, Diego Sanchez, Marzia Yasmin
University of Illinois at Chicago, Chicago Illinois
Abstract:
Two common treatments of pressure ulcers are electrical stimulation and vacuum-assisted
closure therapies. Combining the two into one device and treatment may improve the healing of
these wounds. A look into the various physiological effects of the two treatments reveals a
possible protocooperation. The negative pressure applied in a vacuum-assisted closure
removes exudate, increases blood flow and creates a moist wound bed. It is of note that
electrical stimulation across moist wounds further promotes the current of injury as optimal
bioelectric charge is maintained due to the stimulation of the electrolytic concentration of wound
fluid. This interaction along with the other studied benefits of the two treatment options may
necessitate the design of one device that applies two treatments. A possible design for this
device is proposed and analyzed on considerations of the physiological characteristics of
pressure ulcers, electrical stimulation and vacuum-assisted closure therapies.
Problem Statement
Individuals with limited or no mobility, such as paraplegics and quadriplegics, are prone
to pressure ulcers, also known as pressure/bed sores. Pressure ulcers are localized wounds of the
skin and the underlying tissue, but usually over a bony region such as the heel or the sacrum
[1,12]. Please refer to Table 1: Illustration of the five stages of pressure ulcers, located in the
Appendix. Successful care can provide a patient with a pain free environment, better quality of
life, reduced number of hospitalizations, and overall, decrease infection. Combining vacuum
assisted closure therapy and electrical stimulation methods may create an effective and efficient
smart bandage. Applying electrical stimulation across the wound along with negative pressure
directly to the wound (later referred to as E-VAC) may introduce an optimal amount of strain to
induce an improved healing of pressure ulcers via protocooperation between the two treatments.
Constraints and Design Criteria
Constraints
Provide treatment for Stage 3 and 4 pressure ulcers
E-VAC 3
Please refer to Table 1: Illustration of the five stages of Pressure Ulcers for more
information on Stages 3 and 4.
In a less severe situation, wound dressing and ointment may be able to heal stages 1 and 2
pressure ulcers, however are not capable in healing stages 3 and 4 due to the seriousness of the
pressure ulcers [2]. Therefore, the proposed model, E-VAC method, is used to help heal the more
serious stages of wound depth. One of the components of the E-VAC method is called the
polyurethane foam which lies in the wound bed. The foam can be altered to fit these various
dimensions for the depth of the wound.
Infection Control
A device must address the risk of infection. Preventing and caring for infection is
significant to wound care. A wound can become severely infected, which will slow down the
healing process [3]. Vacuum-assisted closure therapy has been shown to limit the risk of
infection due to creating a closed wound [4]. Using hydrogel before applying our smart bandage
is designed to hold moisture in the surface of the wound and also providing the ideal
environment for both cleaning the wound, and assisting the body to rid itself of necrotic tissue. In
addition, the moisture in the wound is essential in pain management. Furthermore, the hydrogel
is very soothing and cooling. Therefore, with high moisture content, hydrogel helps to prevent
bacteria and oxygen from reaching the wound, providing a barrier for infections. [5,15]. Another
component of the device is the seal, which is created by the foam and transparent film. It reduces
the risk of external contamination. Lastly, using electrical simulation and negative pressure
therapy together may improve blood perfusion, lower the risk of colonization, and stimulate the
formation of granulation tissue, which might increase resistance to infection. [4].
Maintain Negative Pressure and Electrical Stimulation Simultaneously
Vacuum therapy utilizes negative pressure to remove fluid from open wounds through a
sealed dressing and tubing, which is connected to a collection container. It increases wound
blood flow, speeds the formation of granulation tissue, and decreases accumulation of fluid,
bacteria, and accelerates healing. Therefore, it leads to quicker closure for pressure sores and
significantly increases skin graft success rate when used as a bolster over the freshly skin grafted
E-VAC 4
wound [6]. The partial vacuum created by negative pressure therapy causes the entire foam to
shrink and this draws the wound margins to the centre, thereby facilitating wound closure [4].
Muscle and nerve conductivity and intercellular communication are enabled by
bioelectric processes. An electric current necessary for a live cell to function flows because of
the gradient of ion concentration in the cells and their different electric potentials [8]. Therefore,
the influence of electric current by electrical simulation through electrodes, to the healthier skin
which is close to the wound, are significantly larger reductions in wound surface area and
volume than ulcers treated with standard care only. The electric simulation works as the surface
of healthy human skin has a slightly negative electric potential (compared with the deeper layers
of tissue), while wounds are a positive electric potential. Therefore, the difference in potentials
generates an electric current that stimulates wound healing [8]. Voltage induced by ES amplifies
the current usually present in wounds. Electrically stimulating the wound surface has been shown
to attract neutrocytes, leukocytes, macrophages, and fibroblasts [8]. In vivo studies have shown
that the application of electric current significantly increases synthesis of adenosine triphosphate
and proteins. Moreover, the flow of an electric current has been observed to increase adenosine
triphosphate synthesis in human wounds and to accelerate the incorporation of amino acids into
cell protein [8,17].
Introducing the combination of electrical stimulation and negative pressure into one
device should create a protocooperative relationship. The two techniques should not interfere
with each other or even worse cause harm to the wound and patient.
Design Criteria
Improved healing time
Without care, pressure ulcers continue to grow in diameter and depth and are
exceptionally difficult to heal [9,13]. For faster healing of pressure ulcers, a device combining
techniques of negative pressure and electrical stimulation is designed. Negative pressure is
described as a pressure that is below normal atmospheric pressure. At room temperature and at
sea level a defined volume of air contains molecules moving in random directions. These moving
molecules exert a force that is equal to the normal atmospheric pressure of 760mmHg. Negative
pressure can be achieved by transferring gas molecules away from the area of pressure ulcer
E-VAC 5
wound with a suction pump or fan. This technique is a non-invasive, mechanical wound care
treatment that supports and encourages the wound healing process. The negative pressure is
applied in continuous or intermittent cycles via an evacuation tube connected to a computerized
and programmable pump, with equal distribution to every surface of the wound ensured by an
open-cell polyurethane foam dressing. This process: increases local blood flow, reduces edema,
stimulates formation of granulation tissue and cell proliferation, removes soluble healing
inhibitors from the wound, reduces bacterial load, and draws the wound edges closer together
[9].
Pressure ulcers may be healed faster not only by reducing external pressure, but also by
increasing the patient's resistance to pressure by directly influencing tissue oxygenation. The
electrical stimulation therapy provide high-voltage pulsed galvanic stimulation (75 V, 10 Hz)
applied to the back at spinal level T6 in spinal cord- injured persons lying supine raises sacral
transcutaneous oxygen tension levels to the normal ranges. [9,13]. This process improves local
blood flow and oxygen delivery, has antibacterial effects, helps with debridement and
thrombolysis, decreases pain and is associated with greater relative reduction in area of pressure.
One device
The model is designed as one device with two techniques: Negative Pressure/Vacuum-
assisted closure and electrical stimulation. The center of the bandage is the hydrophilic
polyurethane foam with the same size of wound. A plastic, hollow and flexible tube is attached
into the foam and the entire wound is airtight sealed with transparent film. The tube connects to a
container and is put under negative pressure via fan connected to the container. A transparent
film which is made of polyurethane or synthetic polymer sheets is used to cover the foam to
create closed vacuum environment on wound. This film is also attached with two electrodes in
pre-cut areas. These electrodes must be on skin that is not affected and also attached with the
voltage sources for electrical stimulation.
No more complicated than application of original therapies
The design will be able to be used by those already trained with vacuum-assisted closure
or electrical stimulation therapies. Before applying this smart bandage, the use of hydrogels will
prevent granulation tissue from growing into the foam and also moisturizes the wound.
E-VAC 6
Model and Design
For the model portion, please refer to the Appendix for figures 1-5. For the materials being used
in the model design, please refer to the Appendix for Tables 2 and 3.
Figure 6 - Circuit Model;
Nodes A and B represent Electrodes; Voltage is supplied from a voltage source; R has a resistance
determined by the Wound and Foam
Description
The circuit model represents the basic circuit the electrical stimulation will create. The
impedance from the wound and foam of the bandage will have to be considered while applying
the current. First the polyurethane foam will be cut to the dimensions of the wound and placed
with the use of hydrogels to prevent granulation tissue from growing into the foam. Then the
film will be placed along with a plastic tube connecting to the foam. This will create a closed
wound environment from a previously opened environment. Two electrodes will then be placed
in pre-cut areas on the film. Note that the electrodes must be on skin that is not wounded. The
tube and wires connect to a source device. Negative pressure is applied through a fan that pumps
air out of the machine. This draws exudate from the wound into a 300 mL container. A filter
must be placed before the fan to ensure that only clean air leaves the machine. The battery also
supplies electrical stimulation and is all part of the same device. Both the electric stimulation and
negative pressure will be controlled via a computer interface that will rely on sensors placed in
the device.
Validation
E-VAC 7
The following concepts have to be validated through the design of the E-VAC device: (1)
the voltage and current across the electrodes, (2) the negative pressure applied by the fan with
different dimensions of polyurethane foam, (3) decreased prevalance of infection and bacteria.
Confirming the E-VAC device addresses these considerations and meets the design criteria and
goals is critical before clinical use.
Testing the Negative Pressure Applied With Different Dimensions of Polyurethane Foam
Stage 3 and 4 pressure ulcers vary in dimension [1]. The polyurethane foam must be cut
and shaped to fit the dimension of a given pressure ulcer, thus allowing a closed environment
and negative pressure to be applied. The E-VAC device must maintain a constant negative
pressure of 125 mm Hg in accordance to standard treatment conditions used for vacuum assisted
closure therapy [10]. This negative pressure should not vary based on the dimension of the foam.
This allows for the full effect of the negative pressure therapy to influence the healing process of
the wound. The removal of exudate, necrotic tissue and increased blood flow may be maintained.
The Voltage and Current Across the Electrodes
A voltage of 80-200 V and a pulsed charge of 10-15µC must be found across the
electrodes. These values are in accordance of standard application of electrical stimulation
therapy [11,14]. The use of electrical stimulation impacts the impedance of necrotic skin, mimics
the current of injury, stimulates the wound healing process (particularly the inflammation phase)
and promotes blood flow and oxygenation. It is noted that moist wounds further promote the
current of injury as optimal bioelectric charge is maintained due to the stimulation of the
electrolytic concentration of wound fluid [11]. A moist wound environment is created through
the use of the VAC therapy, however it should be considered that foam may increase the
impedance the voltage between the electrodes may encounter. A larger voltage may be required
to offset the resistance of the polyurethane foam.
Decreased prevalence of Infection and Bacteria
As stated in the goals and constraints area, there is a direct relationship between ulcer
stage and threat of infection and bacteria formation. With a controlled environment, bacteria
formation and infection on the ulcer cite can be controlled and localized. At these ulcer stages,
E-VAC 8
there will be a copious amount of wound exudate. This is a natural response to inflammation or
infection. However, exudate must be managed to demonstrate and initiate proper wound healing.
This results in a cleaner ulcer site with less dead tissue prone to infection and an environment
that is promoting successful regeneration.
Works Cited
[1] "Pressure Ulcer Assessment and Treatment." NursingCEU.com, a Division of Wild Iris
Medical Education, Inc. N.p., n.d. Web. 18 Mar. 2013.
<http://www.nursingceu.com/courses/343/index_nceu.html>.
[2] Niezgoda, Jeffrey A., and Susan Mendez-Eastman. "The Effective Management of Pressure
Ulcers." ADVANCES IN SKIN & WOUND CARE. N.p., Jan.-Feb. 2006. Web. 18 Mar. 2013.
<http://www.nursingcenter.com/lnc/journalarticle?Article_ID=636557>.
[3]K. Bumpus and M.A. Maier, “The ABC’s of Wound Care, “ Peripheral Vascular Disease,
New York, 2013.
[4] Calne, Suzie. "Topical Negative Pressure in Wound Management." European Wound
Management Association (EWMA). MEDICAL EDUCATION PARTNERSHIP LTD, 2007.
Web. 18 Mar. 2013.
E-VAC 9
<http://ewma.org/fileadmin/user_upload/EWMA/pdf/Position_Documents/2007/EWMA_Eng_0
7_final.pdf>.
[5] "Hydrogel Dressings in Wound Care." Hydrogel Dressings Wound Dressing. N.p., n.d. Web.
18 Mar. 2013. <http://skin-wound-care.medical-supplies-equipment-company.com/hydrogel-
dressings-641.htm>.
[6] "Wound Bed Preparation for Pressure Ulcers." Wound Bed Preparation for Pressure Ulcers.
N.p., n.d. Web. 18 Mar. 2013.
<http://www.worldwidewounds.com/2005/july/Romanelli/Wound-Bed-Preparation-Pressure-
Ulcer.html>.
[7] Kuffler, Damien P. "Techniques for Wound Healing with a Focus on Pressure Ulcers
Elimination." The Open Circulation and Vascular Journal (2010): 72-84. Institute of
Neurobiology, University of Puerto Rico, 201 Blvd. Del Valle, San Juan, PR 00901, USA. Web.
18 Mar. 2013. <http://www.benthamscience.com/open/tocvj/articles/V003/72TOCVJ.pdf>.
[8] Franek, Andrzej, Roman Kostur, and Edward Blaszczak. "Using High-Voltage Electrical
Stimulation in the Treatment of Recalcitrant Pressure Ulcers: Results of a Randomized,
Controlled Clinical Study." E-STIM USED TO TREAT PRESSURE ULCERS. OSTOMY
WOUND MANAGEMENT®, Mar. 2012. Web. 18 Mar. 2013. <http://www.o-
wm.com/files/owm/pdfs/OWM_March2012_Polak.pdf>.
[9] C. Sussman and B. Bates-Jensen, ”Pressure Ulcers: Pathophysiology, Detection, and
Prevention” in Wound Care A Collaborative Practice Manual for Health Professionals, 4th ed.,
Baltimore, Maryland: Lippincott Williams and Wilkins, 2012.
[10] C. Sussman and B. Bates-Jensen, “Management of the Wound Environment with Negative
Pressure Wound Therapy” in Wound Care A Collaborative Practice Manual for Health
Professionals, 4th ed., Baltimore, Maryland: Lippincott Williams and Wilkins, 2012.
[11] C. Sussman and B. Bates-Jensen, “Electrical Stimulation for Wound Healing” in Wound
Care A Collaborative Practice Manual for Health Professionals, 4th ed., Baltimore, Maryland:
Lippincott Williams and Wilkins, 2012.
E-VAC 10
[12] M. Benbow, “Classification and treatment of different wound types: chronic wounds” in
Evidence-Based Wound Management, Philadelphia: Whurr Publishers, 2005.
[13] M. Benbow, “Documenting wound care” in Evidence-Based Wound Management,
Philadelphia: Whurr Publishers, 2005.
[14] M. Benbow, “Modern wound management technologies” in Evidence-Based Wound
Management, Philadelphia: Whurr Publishers, 2005.
[15] C. Sussman and B. Bates-Jensen, “Tools to Measure Wound Healing” in Wound Care A
Collaborative Practice Manual for Health Professionals, 4th ed., Baltimore, Maryland: Lippincott
Williams and Wilkins, 2012.
[16] D.R. Thomas, “Prevention and treatment of Pressure Ulcers: What works? What doesn’t?”
Cleveland Clinic Journal of Medicine, vol. 68, no. 8, Aug. 2001.
[17]S. Guo and L.A. DiPietro, “Factors Affecting Wound Healing,” Critical Reviews in Oral
Biology and Medicine, Chicago, 2010.
Appendix
Stages Description Illustration
I Pink color, hot or cold to the
touch, sensitive to the touch
II Open pink wound bed. It may
either be intact or an open
blister.
E-VAC 11
III Full exposed tissue, but no
bone, muscle, and tissue is
exposed.
IV Full exposed tissue with
either the bone, tendon or
muscle showing. All can be
shown individually or at once.
V Everything has been exposed.
This stage is untreatable and
unmanageable. Necrotic
Tissue. Slough has formed.
NA
Table 1: Illustrations of the five stages of the Pressure Ulcers
Material Dimensions Quantity Function
Self-Adhesive Electrodes;
Carbon-Impregnated
1cm x 2cm x 5 mm 2 Multiple use, apply
current across wound
Wires; covered with
rubber
Diameter: .5 cm
Length: 5 feet (longer or
shorter depending on
dimensions of hospital
room)
2 Carry charge from
positive and negative
terminals of battery for
electrical stimulation
Adhesive Film 4 cm x 6 cm x 5 mm 1 Creates closed vacuum
environment on wound
Polyurethane Foam Variable depending on
wound size
1 Cut to dimensions of
wound that contribute to
closed vacuum
environment
Hollow Flexible Plastic
Tube
Diameter: 1 cm
1 Removal of exudate
E-VAC 12
Length: 5 feet (longer or
shorter depending on
dimensions of hospital
room)
Table 2 - Material Description for Bandage
Material Dimensions Quantity Function
Battery Source Container 2 in x 2 in x 2 in 1 Holds battery source and
prevents short circuiting
Battery Source 1.5 in x 1.5 in x 1.5 in 1 Application of Electrical
Stimulation
Computer Interface 2 in x 2 in x 2 in 1 Allows a user to regulate
the amount of electrical
stimulation and pressure,
also should alert if closed
environment is broken
Filter Diameter: 2 in
Width: 2 cm
1 Prevent liquid and solid
particles to leave the
container
Plastic Container Volume: 300 mL and 75
mL
2 Collection of exudate;
should be removable to
clean and dispose of
waste
Metal Container Volume: 100 mL 1 Contains fan
Fan Diameter: 2 in 1 Creates a negative
pressure environment
Table 3 - Material Description for Negative Pressure and Electrical Stimulation Sources
E-VAC 13
Figure 1 - Negative Pressure and Electrical Stimulation Source/Container
Figure 2 - Negative Pressure Source; Fan Diameter and Volume
E-VAC 14
Figure 3 - Bandage Apparatus (Foam dimensions vary based on wound)