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

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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.

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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)