Download Volumetric Airflow Gauge - University of Pittsburgh

Volumetric Airflow Gauge
Guy Guimond, UPMC Center for Emergency Medicine
Eric Reiss, Systems Manager, Swanson Institute
Matthew Chakan
Michael Nilo
Justin Kiswardy
April 10, 2007
University of Pittsburgh,
Department of Bioengineering
Background & Significance
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Estimates of over 500k 911 calls daily, 35% involve cardiopulmonary failure1
Most common means of initiating breathing in-field is use of
mechanical ventilator (BVM)
BVM systems used in patient transport w/in hospital or when
true mechanical ventilators not accessible
4
Background & Significance
5
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Most Healthcare Providers trained to “inflate based on
resistance” w/ recommended introduced air @ 400-600ml/cycle
for average adult patient2
As result of HP making on-site estimates, dangerous air flow
rates & pressures administered to patients have been observed
Documented side-effects: lung tissue damage, lung compliance,
gastric distension, regurgitation
Clinical Study showed ~40% patients experienced gastric
distension & 65% morbidity3
Project Objectives


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Design a universal gauge capable of measuring airflow volumes
that is easy to learn, operate, and comprehend for the user
Device must be lightweight, portable, and adaptable to most
standard ventilators/BVM’s (Laerdal, Ambu, First Responder)
Features adaptable for incorporation into a learning environment
(EMT classes)
Design Alternatives
How will the
Disposable
vs. airflow
reusablevolume be measured
pinwheel
using
highly
compliant
metal
•many
electrical
circuit
similar
to mass
flow
device, incorporating
••
BVMmechanism
systems
are
intended
for
one-time
use pin
microcontroller,
thermistors
measure airflow
volume
• no external power
source,to
sterilizable,
inexpensive
(pp. ~$20-50)
manufacturing/
low-level
accuracy,
malfunction
••disposable
systems
come
w/accuracy,
disposable
attachments
high-levelprice-point,
of
reproducible
requires
external power
Decision:
VAG
isdifficult
intended
be
reused
may cost
issues,
rotary
gauge may
bemanufacturing,
fortouser
to
readand higher
source,
computerized
no
autoclave,
(PEEP gauge, pH indicator, etc.)
be sanitized w/ EtOH. Reusable device allows for
• reusable
systems
are able
to be
flashedbroader
via autoclave
higher
production
costs
creating
market.
• market
allows much
higher
costminimizing
(pp. ~$100-400)
Decision:
electrical
circuit
error range &
malfunction issues while maximizing ease of
manufacturing

Basic Component Selection

Air flow sensor requirements:

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
Display requirements:
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

Flow range > 1.6 L/s
Size < 38 in3
Cleanable with medical products (e.g. Isopropanol)
Two decimal place precision → 3-digit
Digit height > ¼”
Microcontroller requirements:


Relatively large RAM and ROM
Enough pins to operate sensors and displays
Component Integration

Electrical needs of basic components were
identified and ordered


9V → 5V → 2.2V
Bridging components were selected
Voltage Regulator (9V → 5V)
 Resistors (5V → 2.2V)


Component compatibility was checked by
verifying complementary electrical
characteristics (AIout < BIin)
Circuit Schematic
Extra Feature Addition

The air volume will change after reaching the patient’s
lungs



The rate of artificial respiration is important


Charles’ Law:
V2 = V1 * (T2/T1)
A thermistor was added to measure ambient temperature
A Flashing LED metronome was added to indicate the rescue
breathing rate
The user needs to know when to replace the batteries

Independent battery sampling and alert systems were added
Completed Circuit
Circuit Operation

A C program was written for the microcontroller to:

Measure:
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
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
Display:
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Instantaneous air flow rate
Ambient temperature
Battery voltages
Cyclic air volume sum
Rescue breathing metronome
Low battery voltages
Hold maximum cyclic air volume sum for easier user reading
Reset air volume sum to zero for next cycle
Product Engineering Objectives

Build a casing that

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Prevents water from contacting the electrical circuit
Diminishes mechanical damage to the circuit
Seals the circuit and all small parts from the airflow path
Houses two 9V batteries
Fits the standard fittings of both the bag and valve attachments
 distal tubing 15mm
 proximal tubing 23mm
Weighs less than 100g without batteries
Is not cost prohibitive
Prototype Development

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Initial prototypes
made of wax
Current SLA
prototype
Finished product
Project Management
Dec.
|
Jan.
|
Feb.
|
Mar.
Project
Introduction
Conceptual
Design
Electrical
Design
Circuit
Program
Mechanical
Design
Casing
Development
V and V
Written
Deliverables
Responsibilites:
Matt Chakan:
Michael Nilo:
Justin Kiswardy:
Circuit Design and Fabrication, Microcontroller C Program
Mechanical Design and Fabrication using SolidWorks
Verification and Validation, Written Deliverables
|
Apr.
Quality Control Considerations
Interpretation


Risk Level
Class
I medical device
Risk Analysis
A
Negligible risk
B
Tolerable risk
• ISO
13485
rule 7.1 &analysis
7.2 “non-invasive devices intended toC act as Undesirable
calibrator,
• Initial
Failure
Modes/Effects
risk
•
hazard
analysis
monitor, or tester while connected to an active type II, III device…..is class
I” Intolerable risk
D
* identified two potentially catastrophic risks: components
of device
• VAG must comply with FDA’s Code of Federal Regulations 21.CFR.868.9
break
andMeans
blocks tubing.
Function orand enter patients airway and device malfunctions
Risk
Failure Mode
Effect on System
Possible Hazards
User Detection of
Applicable Controls
“ventilator
for channeling
gases between
Component tubing is device intended for use as conduitIndex
* risks
minimized
by requiring
that the user isplace
device
the oneventilator and
patient
during ventilation
of patient…device
exempt
fromabove
pre-market
Incomplete circuit,
Design most efficient circuit
User must rely on his/her
Visual inspection; realization of
Electrical circuitry
resistor/thermistor
Display inoperable
B
w/ few parts to minimize pot.
over/under inflation
way valve,
small components
willjudgement
not have direct
access
to inside tubing
notification
procedures”
malfunction
hazard
(casing), ease of incorporation
and
removal from BVM
Loss of power
User doesn’t replace
LED malfunction
Burn out or incomplete
circuit
Reset trigger
B
Realization of loss of power
Suggest time-frame for
battery life & periodic
maintenance
Over/under inflation by
user
C
User awareness of airflow levels
Use microprocessor which
minimizes error in reset
function
Incorrect volume
display to user
Over/under inflation by
user
C
Visual inspection, user awareness of
airflow
Recommend periodic
maintenance
Compromised
airflow to patient
Delayed/failure to
resuscitate patient
D
Visual/ auditory inspection
Set acceptable temp. range
for device use, suggest
periodic maintenance
indicator/training
mechanism
power source/device
doesn’t work properly
Malfunction/no reset
after each cycle
Improper volume
display to user
LCD display
Malfunction/improper
calibration
Tubing
Crack/leak in tubing
due to physical/enviro.
damage
Result: As class I device subject only to general controls. Must register device with
the FDA and comply
with
good
manufacturing techniques providing reasonableStrong-lightweight
assurance
of
Degradation due
to
material,
Exposes
Casing
repetitive use/exposure
Electrical malfunction
B
Visual inspection
recommend disposal after
circuitry/loose parts
safety and effectiveness
to extreme enviro. of product.
6000 cycle use
Verification & Validation
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Optimize power source
• one vs. two 9V batteries: conduct tests to determine difference in battery life
• one 9V=~15 min., two 9V=+2 hrs.
• analyze outcome vs. increased cost/inconvenience to user
Accuracy tests for display
• clinical studies show over-inflation by only 100ml can cause gastric distension
• desired accuracy range +/- 50ml air
• laerdal manikin w/ built in volume gauge
Survey administered to various doctors, nurses, and other Healthcare Providers
involved in the treatment/use with BVM systems.
• Outcome of survey should allow the fine-tuning of the VAG (ie., the
elimination or addition of features) and will be easier to understand specific market
needs
Features & Benefits

 Potential
Summarydisadvantages
of features
•
cost-effective
volumetric
airflow gauge that(increases
can be incorporated
• aperiodic
battery
replacement/testing
into any standard
systemof user)
maintenance
tasksBVM
required
• provides numeric display of air volume introduced to patient during
• non-sterilizable
(limit market size)
in-field/hospital
rescue
•
does not
account
air escaping
face/mask seal
• provides
high
level of for
accuracy
(w/in +/-50ml)
• may be disinfected for repetitive use
• eliminates comorbidity associated w/ over/under inflation (gastric
distension, lung damage, regurgitation), reduces hospital stay/costs
• built in LED metronome may be used for training purposes/user
awareness
6
Market Potential
& pricing
Market
Currentsize
competition
2005 sales: transport
Zoll med.ventilators:
~$248 mil.,manually
Ambu ~$116
••mechanical
set the desired
(respiratory
flow rate, care)
pulsatile flow based on PIP and PEEP, bulky (20-40
lbs.), expensive
• more than
(>$1500)
$1.3 billion spent (US) on ventilators, oxygen
therapy•systems,
andmonitors:
airway management
deviceslightweight,
in 2004
hand-held
battery operated,
complicated
• reusable
setup,
PEEP
expensive
valves(+$400)
$100-200, disposable pH indicators
$50-100
• Future competition?
• r&d geared towards design of eff.
volume gauge
8
9 7
10
Moving Forward
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Finish testing and validation
• make necessary adjustments according to results of
survey
• testing through UPMC Center for Emergency Medicine
Design packaging and instruction/troubleshooting manual
Submit SBIR phase I proposal
Acknowledgements
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Mr. Guy Guimond & UPMC Center for Emergency Medicine
Dr. Hal Wrigley and Dr. Linda Baker for providing funding
Department of Bioengineering, University of Pittsburgh
Thank You
Department of Bioengineering
University of Pittsburgh
Flow Rate vs. Voltage Ratio
1.8
Q = 1024.41819(Vo/Vi)5 - 1221.16987(Vo/Vi)4 + 577.76204(Vo/Vi)3 - 128.05109(Vo/Vi)2 + 14.86963(Vo/Vi) - 0.67579
R2 = 0.99993
1.6
Flow Rate (SLPS)
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0
0.00
0.05
0.10
0.15
0.20
0.25
0.30
Voltage Ratio (Vout / Vin)
0.35
0.40
0.45
0.50
Printed Circuit Board Design
Overview
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Incorporation of volumetric airflow gauge into a standard
mechanical ventilator/bag-valve-mask system (BVM)
Intended to provide user w/ volume of air introduced to patient
with each squeeze of the bag
Intended users include: EMT specialists, trained nursing staff,
doctors and other healthcare providers
Citations
Citations
1.
Davidoff F, DeAngelis CD, Drazen JM, Hoey J, Hojgaard L, Horton R (2006). Emergency Cardiac Care. Prehospital Emergency
Care; Vol. 10; 36-48.
2.
Kuhns R., Davis J. (2004). A work measurement evaluation of emergency medical services. IIE Annual Conference and
Exhibition 2004; 3431-3467.
3.
American Heart Association (2005). AHA guidelines for CPR and ECC. Vol. 112; Issue 4; 14-20; 126-131.
4.
Von Goedecke A, Wagner-Berger H, Stadlbauer K, Krismer A, Jakubasko C, Bratschke C, Wnzel V, Keller C. (2004). Effects of
decreasing peak flow rate on stomach inflation during bag-valve-mask ventilation. Resuscitation; 63: 131–136.
5.
6.
International Liaison Committee on Resuscitation. 2005 International Consensus on Cardiopulmonary Resuscitation and
Emergency Cardiovascular Care Science With Treatment Recommendations. Circulation. 2005; 112: III-1–III-136.
Nolan J. (2001). Prehospital and resuscitative airway care: should the gold standard be reassessed? Current Opinion in Critical
Care; 7: 413–421.
7.
Wenzel V, Keller C, Ahamed H, Volker D, Lindner K, Brimacombe J (1999). Effects on smaller tidal Volumes during basic
life support ventilation in patients with respiratory arrest: good ventilation, less risk? Resuscitation; 43: 25–29.
8.
Sheperd C.,(2006). Reflection on a patient's airway management during a ward-based resuscitation. Nursing in Critical
Care; Vol. 11, 217-2 23
Life Medical Supplier, www.lifemedical.com
Miraclemed, www.miraclemed.com, Seattle, WA.
9.
10.