Redesign of ECMO Circuit Pressure Alarm System

Desiree Bonadonna

Apryle Craig

Laura Gilmour

University of PittsburghSenior Design - BioE1161

Summary

• Market review

• Problems

• Regulations

• Solutions

• Implementing the design

• Testing

• Future work

Need for Pressure Monitor Redesign

• >120 Neonatal/Pediatric ECMO Centers in United States, increasing at a rate of ~2-5/year

• Growing number of private perfusion groups

• Sold through distributors and consultants

• Clots in the circuit are the most common mechanical complication (19%)

• Expenditure may be between $80,000 and $100,000 per life saved

• Insurance reimbursement rate 60-70%

Expense Breakdown Cost/day Cost/patient

ECMO $112  

Disposables - $4,000

PICU bed $3,400  

Physician $520  

Respiratory +  

Blood Bank +  

Need for Pressure Monitor Redesign

• Current system with roller pump is analog• Current system with centrifugal is digital

Redesign of the ECMO pressure system includes:• Digital system for roller pump• Additional pressure monitor • Audible and visual alarm

Users: Healthcare Workers•Perfusionists•ECMO Technicians•Nurses•Physicians

User Requirements

• Accurate to within +/- 15mmHg

• Refresh rate should not exceed 15 seconds

• Cost effective

• Safe and reliable

• Meets medical device regulations

Imprecise/inaccurate readings

• Convert to digital display

Unknown post-heat exchanger pressure• Add a third pressure gauge

Requires constant monitoring

• Add audible and visual alarms

Cluttered

• Design the device to hang on an IV pole

Current ECMO Circuit Pressure Problems and Proposed Solutions:

Regulations

Classification: • Class II, CFR 870.2100

• Cardiovascular blood flowmeter

Predicate device:• Digibio Digital Blood Pressure Monitor

Electronic Regulations:• IEC 61000-4-2

• IEC 60601-1-2

Goal #6: Improve the effectiveness of clinical alarm systems.a)    Implement regular preventive

maintenance and testing of alarm systems.

b)    Assure that alarms are activated with appropriate settings and are sufficiently audible with respect to distances and competing noise within the unit.

JCAHO 2004 National Patient Safety Goals

Project Objectives and Features: Programmable Alarm Range

“Assure that alarms are activated with appropriate settings…”

Adjustable range for anthropometric differences and

varying pathologies

Project Objectives and Features: Audible Alarm

“…are sufficiently audible with respect to distances and competing noise

within the unit.”

• Immediate notification of deviation

• Alarm=120dB• Mean unit noise level = 80-89dB

• Startle response occurs at 30dB > mean noise

• Max Impulses = 1016-P/10 = 8,913

Project Objectives and Features:Visual Alarm

Indicates which pressure is deviant from set range

Project Objectives and Features: Digital Display

Human FactorsDecrease Human Error

Ease of Use

Project Objectives and Features: Additional Pressure Indicator

Pressure drop across heat exchanger can be determined and differentiated

from patient

Design Alternatives

Based on human factors

Design Alternatives

Engineering Technologies/Methodologies

Technologies

• SolidWorks

• PSpice

• Rapid Prototyping

• Excel

Methodologies

• Circuitry analysis

• Digital logic

Schematic of One Display Unit

ADC & Display

Visual Alarm

Audible Alarm

Op-Amp

2 Stages of A/D Converter Choice:•1st type produced larger error and required more circuitry•2nd type (ICL7107) included built-in display driver

3 Stages of Op-Amp Design:•Scaled down 0-10V to 0-.2V and included another inverting op-amp•Scaled down 0-1V to 0-.2V •Eliminated 2nd inverting op-amp since input was determined to be negative

Visual Alarm Highlights:•Programmable range•Comparators for high and low•Switches to view range while adjusting it•LED lights when out of range

Audible Alarm Highlights:•Inverters needed between comparator and OR-gate •OR-gate will be 6:1 in final design

Experimental DesignA/DTP-001

• Tests linearity of input voltage to output reading

PCTP-001• Tests deviation of first-generation prototype

from known pressure

VACTP-001• Tests accuracy and independence of visual

alarms

AACTP-001• Tests accuracy and independence of audible

alarm

Display vs. Voltage Input

y = 4712.9x - 21.333

R2 = 0.9982

y = 4707.9x - 20.935

R2 = 0.9982

y = 4711.9x - 20.195

R2 = 0.9983

-200

0

200

400

600

800

1000

0.00 0.05 0.10 0.15 0.20 0.25

Voltage Input (V)

Dis

play

Trial 1

Trial 2

Trial 3

Linear (Trial 3)

Linear (Trial 2)

Linear (Trial 1)

A/DTP-001 Results

PCTP-001 Results

PCTP-001 Results Trial 1

40

60

80

100

120

140

160

180

1 6 11

Sample

Pre

ssu

re (

mm

Hg

)

Manometer

Existing

Proposed

PCTP-001 Results

PCTP-001 Results Trial 2

0

50

100

150

200

250

300

0 5 10 15

Sample

Pre

ssu

re (

mm

Hg

)

Manometer

Existing

Proposed

Statistical Analysis

% error vs. known pressure

0.00

2.00

4.00

6.00

8.00

10.00

12.00

0 50 100 150 200 250 300

Pressure (mmHg)

% e

rror

Existing 1

Proposed 1

Existing 2

Proposed 2

Within the physiological range, the percent error of our device is lower than that of the currently used technology at CHP.

Statistical Analysis

Statistical Analysis of Deviation from Manometer

0

2

4

6

8

10

12

Mean Maximum

Pre

ssu

re (

mm

Hg

)

Exisitng 1

Proposed 1

Existing 2

Proposed 2

Competitive Analysis

• Analog Pressure Gauges

• Custom Made Digital Monitors

• COBE Cardiovascular

• SIII Pump Modules

• Console mounted control unit

• Strengths• Smaller• Not part of a kit• Less expensive• Hangs on IV pole

• Weaknesses• Does not monitor all circuit information such as temperature, etc.

Team Roles

Project ManagementBioE 1160 Goals BioE 1161 Accomplishments

Model circuitry in PSpice X

Build working circuit X

Test A/D Converter X

Test First Generation Prototype X

Add Visual Alarm X

Test Addition of Visual Alarm X

Implement Results of Testing

Add Audible Alarm X

Test Addition of Audible Alarm

Implement Results of Testing

Design Casing X

Future Work

• Further Testing

• Visual Alarm VACTP-001

• Audible Alarm AACTP-001

• Electrical Prototyping

• Second Generation Prototype

Acknowledgements

University of Pittsburgh

Department of Bioengineering

Department of Electrical Engineering

Michael Shaver, CCP

Steven Jacobs, PhD

Vikram Sundararaman

Questions?