SBIR Phase I – Research Plan

Ashley Danicic, Justin Miller, Joe McFerron

A . Specific Aims

According to the US Census Bureau, the population of aging Americans, 50 years

old and older, represents about 32.3 percent of the total population.1 These Americans

receive more medical procedures than their younger counterparts and therefore are a

target to the health care industry. During a large number of surgeries and other

procedures a pulse lavage is utilized. The use of a heated pulse lavage system decreases

the instance of infection among patients.

Without a heating system, the liquid used to irrigate a wound before and during a

procedure is usually room temperature. The temperature of the body is almost 15 oC

higher at 37 oC. A precarious result of this temperature change is heat loss to the irrigated

tissue. This delays healing and predisposes patients to wound infections. If the solution

was heated prior, the risk of infection would greatly decrease.

The current methods used to warm the solution are costly, variable, or bulky. The

most reliable way to warm the lavage solution is to use a heat exchanger. This device,

although effective, is expensive and cumbersome. Most medical grade heat exchangers

are priced over 1,000 dollars. 2

Another device used in hospitals to warm the IV solution

is a microwave. This method is not recommended because the temperature of the solution

cannot be controlled. Also the IV bag (made of PVC) will deform if heated over 180

degrees Fahrenheit, increasing the risk of fluid leak and bag rupture. 3

After calculating the amount of power needed to operate the heater and

determining the desired warm up temperature, a model of the heated IV bag will be

made. This model, made in CosmosFloWorks, will be used to determine the time it takes

to warm the solution from room temperature to the desired temperature. Once the core

temperature in the modeled IV bag reaches the desired temperature, the simulation will

be stopped and the time recorded. In order to be competitive with heat exchangers the

warm up time should be less than 10 minutes.4

Phase I goals:

1. Design an electric heating system that can provide heated lavage.

2. Don’t alter the basic functionality and simplicity of the existing device.

B. Significance

Pulse lavage is used as an effective and efficient way to irrigate grossly

contaminated and saturated wounds. Pulse lavage was first used in the Vietnam War by

oral surgeons in the U.S. Army. This field experience validated its claims of

advancement and suitability for such uses. Advancement since Vietnam has brought us

to current day modern pulse lavage systems. “These units are ideally suited for military

use as well as clinical use. This is because they allow both first and second-echelon

medical personnel, as well as nurses and physicians to rapidly and effectively

decontaminate wounds with little to no logistic burden.” 5

Pulse lavage also has its place in the fields of orthopedic surgery, particularly total

joint replacements. Pulse lavage allows the surgical site to be aseptically cleansed with

saline to remove blood and fat from either the repairable bone or operable tissue. There is

a major risk involved in total joint replacement that is dealt with in part by pulse lavage

as well. As a result of a total joint replacement, implants attract large amounts of

bacteria. A person’s immune system can have difficulty attacking bacteria that live on

these implants. If infections go untreated or are resilient, the problem can worsen and

develop into a situation that becomes systemic. Saline pulse lavage is used to cleanse

and sterilize the surgical site of such implantations to avoid bacteria from attaching to the

implants and causing infection post operation.

One critical flaw can be seen in a modern pulse lavage system: the dispensed

saline is often at room temperature. Temperature regulation would serve two main

purposes that are not accounted for in modern units. When in a surgical setting, the local

area around a wound drops below body temperature due to both exposure and the use of

room temperature saline via lavage. After surgical procedures, it often takes several

hours for the site to regain physiological temperature. Since most infectious bacteria are

able to grow rapidly and efficiently at temperatures below the average 98.6 degrees F,

this allows a larger block of time in which to grow and spread before the natural

immunity and temperature of the body are restored. It is at this critical time that bacterial

growth is most dangerous to the wound site. 6

A temperature regulator would allow

solution such as saline to irrigate a wound at a temperature at or near that of the rest of

the body. This would greatly decrease the length of time at which the bacteria can

spread, as well as continue to sanitize the area. The temperature settings on the mounted

heating unit would range from approximately room temperature to body temperature. It

will be at the judgment of the user as to what temperature he or she feels is appropriate

for the length and complexity of the procedure. By allowing it to be used at room

temperature, this allows for those who do not wish to use the temperature regulator to

continue using the modified lavage unit just as they had done before. This broadens the

market appeal.

The new temperature controlling system will be distributed for applications for

hospital and clinical use, research and developmental settings, dentistry, as well as

military medical use. Since no other system to date addresses solution temperature, and

the new model also incorporates every aspect of previous models, it should be considered

a superior model for every use.

C. Relevant Experience

Joseph Richard McFerron, Ashley Elizabeth Danicic, and Justin Shields Miller

contributed to this project as co-investigators. Both experimental design and execution

will be carried out by all. The qualifications of the investigators are listed below.

Co-Investigator 1

Joe McFerron is a fourth year undergraduate student at the University of

Pittsburgh. His undergraduate major is bioengineering with a biomechanics

concentration. His interests include human body performance as well as full body

biomechanics. He has limited laboratory experience in controlled laboratory settings as a

result of his curriculum at the university. He plans to graduate from the university in

April of 2005.

Co-Investigator 2

Ashley Danicic is a fourth year undergraduate student at the University of

Pittsburgh. Her undergraduate major is bioengineering with a concentration in

biotechnology and artificial organs. Her primary interest involves research and

development in the field of tissue engineering. She has limited laboratory experience in

controlled laboratory settings as a result of her curriculum at the university. However in

addition she currently is interning in the Cellomics laboratory and McGowan Institute. In

particular she remains focused on stem cell research, artificial organs and prosthetics.

She plans to graduate from the university in December of 2005.

Co-Investigator 3

Justin Miller is a fourth year undergraduate student at the University of

Pittsburgh. His undergraduate major is bioengineering with a biotechnology and artificial

organs concentration. His interests include natural and synthetic tissue engineering, with

emphasis on stem cell research and development. He has limited laboratory experience

in controlled laboratory settings as a result of his curriculum at the university. However

in addition he currently has an internship working in the Rangos Research Center where

he researches bone and muscle derived stem cell cultures. He plans to graduate from the

university in December of 2005.

D. Experimental Design and Methods

This project aimed to modify a functional pulse lavage system into one that

administers a heated saline solution at a controlled temperature. The first step taken was

procurement and investigation of popular lavage models currently available. One

similarity between all models quickly became apparent: the devices all connected directly

to a saline bag and utilized only a small device for the pulsing mechanism (AC/DC pump,

O2 connection). That is, no external reservoir or complex hardware existed. Since it was

imperative not impinge upon the simplicity of an existing device, the following final

design was proposed.

The only aspect of the lavage system that needs to be affected is the saline bag

itself. Therefore, we only concerned ourselves with the heating of the IV bag and no

direct portion of the lavage. It can be seen that our device is ‘universal’ as it can be used

to heat any IV bag.

After deciding to concentrate on bringing a normal 1-liter intravenous saline bag

to temperatures up to 36°C, the search a proper method of heat transfer began.

Conduction was concluded to be the simplest and most effective means of heat transfer.

This requires the source of heat to be in direct contact with the surface of the bag. The

fact that the shape of the bag is already irregular and that its shape changes as the lavage

drains fluid from it constrained the options for a heat source. The solution decided upon

resulted from noticing how pipes are often kept warm. Flexible heaters are used since

they can be wrapped around a surface and provide more than an adequate amount of heat.

They are made from various materials that allow for many different applications.

Research was conducted into an appropriate heater for the project. The first

aspect considered was power. Eq. 1 was used to get a general estimate for the amount of

heat required, where ‘P’ is power, ‘m’ is mass of the substance to be heated (1 kg), ‘Cp’ is

the specific heat of the substance to be heated (4.184 J g-1

K-1

), ‘Tf’ and ‘Ti’ are the final

and initial temperatures (36°C and 20°C), and ‘t’ is the total time for heating (5 min).

t

TTCmP

ifp

upwarm

)(_

−⋅

= (1)

This provided a thermal envelope of approximately 230 W. More advanced modeling

and validation was done with Solidworks and Cosmosworks (SolidWorks Corporation,

Concord, MA). A cylinder the size of a 1-L IV bag was modeled in Solidworks. The

outer 1 mm was given the properties of PVC and the entirety of the inside was modeled

as water. The entire outer surface had a uniform heat source totaling 230 W placed on it

with Cosmosworks. The results after 9 minutes are shown in Figure 1. This was the first

time point to have a temperature of 36°C at a radius of zero. This model validates that

our initial estimation of power was generally correct.

Figure 1, Cross-section view of modeled, heated saline bag after 9 minutes

120 VAC was chosen to be the electricity source since it is widely available in a

clinical setting. Other aspects of heater specification include size, which was decided to

be approximately 6”x10”. This allows for the majority of the surface of a full IV bag to

be contacted and for contact to remain as the solution is drained during use, given proper

mounting. Electrocution was a small concern since no moisture is present under normal

operation, but it was still considered. Any heater used should therefore be water

resistant.

Minco (Minneapolis, MN) supplies many different types and sizes of flexible

heaters and accessories. To build the initial prototype, Minco part #HR5528R44.1L12B

was used (Figure 2). It is a 6.9” x 9.0” flexible heater made from Kapton, a water

resistant material. When fed 120 VAC, it provides 326 watts of total power.

Figure 2, Photo of flexible heater

The other aspect of this device is the control. The temperature of the saline

solution needs to be monitored and the heater needs to be controlled based upon this

temperature. To provide simple and reliable feedback control, Minco part # CT16A2010

was used (Figure 3). It monitors any type of thermocouple/thermal ribbon and closes or

opens a switch depending on the feedback temperature. It allows for straightforward

operation. It also provides adjustable hysteresis control. That is, the point at which it

switches on and off is not the same. It switches on at a lower temperature than it

switches off as to reduce rapid switching.

Figure 3, Technical drawing of temperature controller

The final major component to be decided upon was the temperature sensing

device. The project required an element that was:

1. Small enough to allow for an IV-port insertion.

2. Water-proof, since it would be in direct contact with saline

3. Be able to be sterilized, since saline make contact with the body

Minco again provided this element, part # S665PDY40B (Figure 4). It is a thermal

ribbon with a platinum sensing element encased in a polyimide film with elastomer cover

coat. It makes accurate temperature readings with a fast response time, is small enough

for port insertion, is water-proof and the elastomer can be sterilized.

Figure 4, Photo (left) and technical drawing (right) of thermal ribbon

The general outline of the control mechanism is presented in Figure 5. The

temperature controller is constantly making readings of and displaying the IV

temperature via the thermal ribbon. If the temperature is below the hysterisis-

compensated set-point temperature (variable from 1 to 25 °C below desired temperature),

the SSR (relay) output is switched on. If the temperature is above the set-point, the

output is switched off. The SSR output is fed 9V via battery which subsequently drives

an additional 120 VAC relay when switched on. This second relay switches electricity

on and off to the heater.

Figure 5, Schematic of control

The controller was mounted in a bud box along with a master switch, battery,

relay, and plugs for outlet power, thermocouple input, and heater output (Figure 6).

Temperature Controller

Heating Element

120 VAC

Temperature Sensor

IV Bag

Relay

9 V

1

2

3

4

5

6

1—Display

2—Controls

3—Main Switch

4—Thermal Ribbon Input

5—Heater Output

6—Main Power Input

Figure 6, Photos of front (left) and rear (right) of controlling box

Verification testing consisted of a setup resembling a clinical setting. The heater

was securely attached. The method of attachment for this prototype was simple plastic

clips, which provided steady, firm contact between the heater and the surface of the bag.

The thermal ribbon was fed from through the top of the IV bag via small hole, with the

sensing element remaining 1cm above the bottom edge of the bag. The ambient

temperature was 20 °C. The device was set for a desired temperature of 36 deg C.

Figure 7 displays the results of this test. The temperature of the bag rises in nearly a

linear manner to 36 °C in 7 minutes at which time the heater is turned off. The high

specific heat of water allows for the saline to retain its temperature for a relatively long

amount of time. It wasn’t until t=24.5 minutes until the temperature dropped below 35

°C at which point the heater turned back on. The results of this test show that the device

is in fact a viable solution to heat an IV bag to and remain at a controlled temperature.

This test yielded a few concerns though. Although the outside of the heater is

insulated, its temperature became quite hot, exceeding 50°C at some points. Even brief

contact could cause burns to the user. This needs to be addressed; the best solution

would likely be additional insulation. Also, the placement of the thermal ribbon is very

important. The difference in temperature between the center of the bag and the outer

edge of the bag was up to 5°C and the difference between the bottom and top was up to

9°C. Therefore, a better attachment system and detailed instructions to caregivers need to

be considered. The proper thermal ribbon attachment mechanism is believed to be via IV

port and attached to a rigid rod that would guarantee correct placement.

Time vs. Temperature, Heating from 21 °C

20

22

24

26

28

30

32

34

36

38

0 100 200 300 400 500 600

Time (sec)

Tem

pera

ture

(°C

)

Figure 7

Other useful improvements include a well though-out method of attaching the

heater to the bag. The current solution of plastic ties is marginal at best, as draining the

bag lowers the tension of attachment and reduces the surface area of heater contact.

Some sort of elastic tie would allow for good heater-bag contact throughout the use of a

bag. A customized controller circuit would also provide for reduced weight and size of

the overall device as the current controller possess many features that are not utilized.

Works Cited 1. http://www.census.gov/

2.http://sales.varian.com/webapp/commerce/command/CategoryDisplay?cgmenbr=

1&cgrfnbr=2&cgname=Heat%20Exchangers

3. http://plc.cwru.edu/tutorial/enhanced/files/polymers/therm/therm.htm

4. http://www.surgicaloncology.com/psmmeth.htm

5. www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&

db=PubMed&list_uids=9866365&dopt=Abstract

6. http://www.disknet.com/indiana_biolab/b062.htm