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T-56
Engineering Design Specification Report
Design of a Minimally-Invasive
Continuous Glucose Monitor for
Critically Ill Patients
October 6, 2008
Team Members:
Elizabeth Bramblett
([email protected])
Meredith Goolsby
([email protected])
Sonya Parpart
([email protected])
Kimberly Roush
([email protected])
Advisor: Dr. Catherine Preissig
Pediatric Intensive Care Unit
Children’s Healthcare of
Atlanta at Egleston
1405 Clifton Road NE
Atlanta, GA 30322
[email protected]
770-653-6203
Project Description
Description of Design Problem:
For critically ill children, the threat of hyperglycemia is very real. Children with normal
glucose levels when they are healthy can develop hyperglycemia without any warning while they
are in the hospital.1 In fact, based on recent data from Children’s Healthcare of Atlanta (CHOA)
and other studies, 20% of all pediatric intensive care unit (PICU) patients and 85% of all cardiac
pediatric ICU (CICU) patients develop hyperglycemia.2,3,4 The trend seems to be that
hyperglycemia can occur:

once the child has been placed on a ventilator.5

as a result of being placed on continuous renal replacement therapy (CRRT).

once the child requires vasopressors.2,3,4
Though the cause is not entirely understood and is currently of major debate and
study, hyperglycemia is initially a stress response, but persists in some patients.6,7,8 It is likely
due to a combination of insulin resistance, insulin deficiency, interaction of counter-regulatory
hormones, and iatragenic use of pro-hyperglycemic medications used in critically ill patients.6,7,8
As a result, continuous monitoring of these patients is necessary in order to treat the condition as
it arises. Without immediate treatment, the patients risk impaired neurological function,
ketoacidosis, coma, and poor wound healing. It has been shown that control of blood glucose
levels with insulin reduces both morbidity and mortality in ICU patients who are in the ICU for
at least three days.7,8
In the PICU, the standard of care for detecting hyperglycemia is to perform a blood draw
every couple of hours and send this to the lab for processing.6 With multiple lab fees daily, this
process is very expensive and many children must also endure a needle stick for each blood
draw. There is also currently a device in trials, Medtronic’s Guardian, which is placed
subcutaneously and takes readings from the interstitial fluid. However, glucose is better read
from blood as that is how glucose is naturally circulated throughout the body.
Statement of Intended Purpose and Value Proposition:
The intended purpose of our project is the development of a minimally-invasive
continuous glucose monitor for use in critically ill patients in intensive care units. Our product
will read glucose through an IV catheter bathed in blood, which will allow for continuous
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readings after the initial needle stick. In order to reduce the amount of wires, tubes, and sticks a
child and their parents must endure, a minimally-invasive glucose monitor would be ideal. The
probes for this device will be disposable, so after the initial investment into the sensors and
digital readouts, glucose monitoring becomes much less expensive than the current standard of
care. The device is being created specifically for the PICU, with the hopes of monitoring for
hyperglycemia in these patients, but it could also be used in CICUs and adult ICUs. Our device
is superior to blood draws because it requires fewer needle sticks and less trauma to the children
and is also a great reduction in cost. It is better than Medtronic’s Guardian due to its ability to
monitor glucose in blood as opposed to interstitial fluid. Our device, upon successful design,
would most likely become the standard of care for critically ill children and adults due to its ease
of use and minimally-invasive nature.
Market Search:

Total ICUs in US:9 158
o 62 academic PICUs
o 48 CICUs
o 48 adult ICUs

Current Size in US: 79,000 patients per year9
o 1,000 total ICU admissions per year
o 50% of patients admitted meet criteria for glucose monitoring

Underserved: 79,000 patients per year
o All patients are currently monitored hourly
o All patients requiring glucose monitoring are screened
o Trends are not detected since no continuous monitoring system exists

Growth Rate (according to CHOA census for 2000-2007): 1.3% per year

Projected Size
o (Current Size) * (Growth Rate) + (Underserved)
o (79,000) * (0.013) + (79,000) = 80,027 patients

Market Value
o Estimated cost of device (based on cost analysis below): $1,300
o Value = (Projected Size) * (Cost) = (80,027) * ($1,300) = $104,269,100
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End User and Environment of Use:
Since this device is designed for hospital use, the users of this device would include
critical care nurses and intensivists. This device will be used exclusively in intensive care units
and will not go home with the patients. It is used in conjunction with IV lines for patients who
are severely ill. The hospital environment maintains a high level of sterility, so the sensor and
digital readout should be able to withstand surface sterilization while the probes will be
contained in sterile packaging. Though the patient is being monitored by multiple systems, this
device will not be used in conjunction with any specific system, other than the IV catheter. While
the patients and parents are not direct users of this device, they are affected by it. As a result,
their thoughts and impressions are necessary to consider in the design.
FDA Regulatory Pathways:
The device is best classified as a Class II medical device under LJS: Catheter,
Intravascular, Therapeutic, Long-term greater than 30 days. Our product is substantially
equivalent to existing devices as it has the same intended use and the same technological
characteristics. An example of a device already on the market is the percutaneous, implanted,
long-term intravascular catheter submitted as 510(k) and classified as Class II under LJS (Sec.
880.5970).10 However, our product will have a different implementation; therefore, submission
of a 510(k) is required (see flow chart below). The submission fee for a 510(k) is currently
$3,693.11 The FDA has 90 days to respond once an application is submitted, and the average
time for clearance is roughly 150 days. Once a "clearance and commercialization" letter is
received by the FDA, the continuous blood glucose monitor can proceed to market.12
Flow Chart: Describes the path to market a Continuous Blood Glucose Monitor. A 510(k) will
be submitted to the FDA and must be approved prior to marketing the device.
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Engineering Design Specifications
Customer Requirements:
This continuous blood glucose monitoring device must be able to:

Fit inside a catheter whose minimum size is 1.547 French (24 gauge).

Extend beyond the length of the catheter so that it is continually bathed in circulating
blood.

Remain in the vein for extended periods without causing damage to the vein itself.

Transmit data continuously from the probe through the IV tubing to the sensor.

Communicate wirelessly between the sensor and the digital readout.

Alert PICU staff of dangerous blood glucose levels.
Engineering Characteristics:
The digital readout should be approximately 4” x 3” x 1”, keeping in mind that the
smaller the device, the better. The digital LCD screen should be approximately 1.5” x 1”.
Current devices weigh approximately 4 ounces; therefore our device should weigh at most 4
ounces.13 The digital readout should be able to receive information from the sensor from at least
6 feet away. The probe must be able to fit in the smallest catheter, 1.547 French (24 gauge) and
be able to extend past the end of the longest catheter so that it will be fully bathed in circulated
blood. This would require a probe length greater than 1”. The sensor should be approximately 1”
in diameter, but because it is not actually being placed in the body, the dimensions are not
absolutely mandated. A smaller sensor is ideal for mounting on the IV hub.
The probe should be able to sense a wide range of glucose levels. The lowest level it
should sense is 40 mg/dL and the highest level is 500 mg/dL (according to Dr. Preissig in
September 2008). It would be equipped with an alarm to signal personnel in the PICU if the level
dropped below 70 mg/dL or rose above 150 mg/dL. An example of a probe that would sense this
is one that has a drop coating of a ferrycyanide mixture onto the surface of screen-printed carbon
electrodes and then layering on glucose oxidase. This example of a glucose probe takes less than
15 seconds to respond and can sense glucose levels up to 600 mg/dL.14 All IV tubing and
catheters used would be made of polyurethane. The current devices have a digital readout casing
of high impact ABS/polycarbonate composite. Our device should be made of a similar high
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impact plastic that can withstand both standard cleaning and hospital sterilization. Sizes are
similar to those used by the Medtronic Guardian Sensor.13 The sensor itself should also be cased
in a high impact plastic to increase durability.
Manufacturing and Production Methods:
This device may require special manufacturing procedures as the probe requires
manufacturing processes involving nanotechnology. Traditional factories may not be equipped to
deal with these types of manufacturing methods. However, the glucose probe we have found is
already in production at efficient manufacturing plants. This allows cost to be lower and the
probes to be readily accessible. The technology of this device also requires wireless components,
so the manufacturing methods must be equipped to deal with this. Standard IV tubing and
catheters will be used and they require no special manufacturing procedures, only sterilization
prior to use.
Sterilization and Packaging Methods:
Our probe will be sterilized using dry heat before packaging. Since the sensor and the
digital readout will not be used in the body, they only have to be able to withstand sterilization
by 70% ethanol, 10% bleach, or 3% hydrogen peroxide. Standard cleaning would include using
mild detergent, quaternary ammonia, and isopropyl alcohol.13 The probes will be packaged in
sterile wrapping similar to the packaging of needles. It should be stored at room temperature and
has a shelf life of 2 years. No special storage conditions are required, allowing this device to be
kept in the general storage closets of the hospital.
A basic description of the device will be included so that the PICU staff will know the
intended use of the product. The device is designed to fit patients with all size catheters, so a
sizing chart is not necessary. It is understood that the staff already has the knowledge to place an
IV and catheter and this device is designed to fit with these standard products. Since the users are
already technically and medically minded, the instructions can be simple and to the point,
describing assembly and basic use.
Integration with Other Products:
Our device does not directly work with other devices in the ICU. Its sizing must be
compatible with the IV catheter in use, but the device is only communicating with its own digital
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readout. Since our device will be broadcasting a signal from the sensor to the digital readout
wirelessly, we want to ensure that the frequency at which the glucose levels are transmitted does
not interfere with transmissions of any other devices in the PICU.
Costs: (According to the hospital cost given by Dr. Preissig in September 2008)

Current Devices
o Medtronic Guardian

Digital Readout Receiver with Transmitter (Sensor): $1,200

Probe: $35
o Dexcom


All parts: $700
Cost to Hospital
o Average cost for various monitoring systems = ($1,235 + $700)/2 = $967.50

Cost includes about 100 disposable probes and 10 sensors
o Typical hospital discount for buying in bulk: 20%
o Bulk purchase: 10 devices = ($967.50) * (10) * (0.8) = $7,740

Bulk purchase saves $1,935.

All hospitals should buy a maximum of 10 monitors (based on CHOA).
o Expected cost will decrease as existing monitors are currently made by hand.
o These devices are only used for diabetics at home, not in hospitals.
o Since hospitals will have a high demand for this device, an automated
manufacturing process is expected within the next few years for a fraction of the
current cost.

Cost of Blood Work (based on CHOA price - Preissig 2008)
o Patient cost: $63 per blood draw
o Average number of glucose checks: 8 checks per day
o Average ICU stay: 6 days
o Total cost of ICU glucose checks nationwide:

(Current Size) * (Average # of glucose checks) * (Average ICU stay) *
(Patient cost) = (79,000 patients) * (8 checks) * (6 days) * ($63) =
$238,896,000
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
Amount Saved
o One-time cost for hospitals in nation for the first year = (Bulk purchase) * (# of
ICUs) = ($7,740) * (158 ICUs) = $1,222,920
o Nationwide savings for the first year = (Total nationwide cost of blood work) –
(One-time bulk purchase) = ($238,896,000) – ($1,222,920) = $237,673,080
Project Deliverables
Project Planning:
Correspondence with Client:
Our team plans to meet monthly with Dr. Preissig and email updates biweekly. It is our
hope that this will keep her informed and hold us accountable, answering any questions we may
have.
Final Deliverables:
At the end of this semester, we will be delivering a CAD drawing of our device. At this
point, we will also be ordering the parts necessary to construct a functioning prototype of our
glucose monitor. This will allow us to gain IRB approval to test our device in the PICU at
Egleston to gather usability information. We can also gather feedback from the critical care
nurses and the intensivists about our device.
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Signatures
Team Members:
Elizabeth Bramblett: ______________________________________ Date: __________
Meredith Goolsby: _______________________________________ Date: __________
Sonya Parpart: __________________________________________
Date: __________
Kimberly Roush: ________________________________________
Date: __________
Advisor:
Dr. Catherine Preissig: ____________________________________
Page 8 of 10
Date: __________
References
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Surgery Patients: Evidence from the Leuven Randomized Study. Semin Thorac Cardiovasc
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2. Yates AR, Dyke PC, Taeed R, et al. Hyperglycemia is a Marker for Poir Outcome in the
Postoperative Pediatric Cardiac Patient. Pediatr Crit Care Med, 2006;7(4):351-355.
3. Branco R, Garcia R, Piva J, Casartelli C, Seibel V, Tasker R. Glucose level and risk of
mortality in pediatric septic shock. Pediatr Crit Care Med, 2005;6(4): 470-472.
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manage hyperglycemia in a pediatric critical care unit. Pediatr Crit Care Med, 2008 (in
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ICU. N Engl J Med, 2006;354:449-461.
8. Van den Berghe G, Wilmer A, Milants I, et al. Intensive Insulin Therapy in Mixed
Medical/Surgical Intensive Care Units. Diabetes, 2006;55:3151-3159.
9. Frieda Online Database.* AMA Web Site. http://www.ama-assn.org/ama/pub/category/2997.
.html. Updated September 27, 2008. Accessed October 1, 2008.
10. 510(k) Premarket Notification Database. Food and Drug Administration; 2008. 510(k)
number K895712. http://www.accessdata.fda.gov/scripts/cdrh/cfdocs/cfPMN/PMN
SimpleSearch.cfm?db=PMN&id=K895712. Updated December 15, 1989. Accessed
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October 1, 2008.
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8.pdf
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13. Technology and product Specifications. Medtronic Web Site. http://www.medtronic.com/
UK/physicians/guardian_rt_technology.html. Updated September 23, 2008. Accessed
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2006; 304(1):e400-e402.
*Only accessible to ICU staff
The following articles were referenced to formulate ideas:
15. Bland DK, Fankhanel Y, Langford E, et al. Intensive Versus Modified Conventional Control
of Blood Glucose Level in Medical Intensive Case Patients: A Pilot Study. American Journal
of Critical Care, 2005;14(5):370-376.
16. Jeremitsky E, Omert L, Dunham CM, Wilberger J, Rodrigues A.The Impact of
Hyperglycemia on Patients with Sever Brain Injury. J Trauma,2005:58:47-50.
17. Trence DL, Kelly JL, Hirsch IB. The Rationale and Management of Hyperglycemia for InPatients with Cardiovascular Disease: Time for Change. J Clin Endocrinol Meab,
2003:88(6):2430-2437.
18. Klein GW, Hojsak JM, Schmeidler J, Rapaport R. Hyperglycermia and Outcome in the
Pediatric Intensive Care Unit. J Pediatrs, 2008;153:379-384.
19. Branco RG, Tasker RC. Glycemic Level in Mechanically Ventilated Children with
Bronchiolitis. Pediatr Crit Care, 2007;8(6):546-550.
20. Clark L, Preissig C, Rigby MR, Bowyer F. Endocrine Issues in the pediatric Intensive Care
Unit. Pediatr Clin N Am, 2008;55:805-833.
21. Cochran A, Scaife ER, Hansen KW, Downey EC. Hyperglycemia and Outcomes from
pediatric Traumatic Brain Injury. J Trauma, 2003;55:1035-1038.
22. Faustino EV, Apkon M. Persisten Hyperglycemia in Critically Ill Children. J Pediatr,
2005;146:30-34.
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Care in the United States. Pediatrics, 2005;115:e382-e386.
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