the evolution of pediatric mechanical ventilators
TRANSCRIPT
The Evolution of Pediatric Mechanical Ventilators
Robert L. Chatburn, RRT, FAARC
University Hospitals of Cleveland
Case Western Reserve University
Overview Historical Perspective
Key Ideas for Understanding VentilatorsEquation of motionBreath typesBreath patternWhat is a “mode”?”
What does “control” mean? (open, closed)New Modes of Ventilation
Proportional assist Ex.: Draeger Evita 4, also with automatic tube compensation
Double loop “dual” controlEx. between breaths: Siemens 300 and Draeger Babylog
Ex. within a breath: Bear 1000 and BirdAdaptive support (Ex.: Hamilton Galileo) Unanswered Questions
1st Generation
Example: Bourns BP200 Example: Bourns BP200
Simple analog electronics Simple analog electronics Pressure controlled IMV mode Pressure controlled IMV mode
time triggered time triggered
pressure limited pressure limited
time cycled time cycled Simple alarms Simple alarms
control circuit (not related to patient) control circuit (not related to patient)
No monitorNo monitor
1st Generation Improvements
Example: Bear Cub Example: Bear Cub
Simple analog electronics Simple analog electronics
Pressure controlled IMV mode Pressure controlled IMV mode Advanced alarms Advanced alarms
control circuit control circuit
airway pressure (patient related) airway pressure (patient related)
No monitorNo monitor
2nd Generation
Example: Infant Star Example: Infant Star
Microprocessor electronics Microprocessor electronics
Pressure controlled IMV mode Pressure controlled IMV mode
Sophisticated alarms/safety features Sophisticated alarms/safety features
No monitorNo monitor
2nd Generation Improvements
Example: Newport Wave, Infant Star Example: Newport Wave, Infant Star
Microprocessor electronics Microprocessor electronics Advanced modes Advanced modes
pressure triggering (SIMV, CMV) pressure triggering (SIMV, CMV)
high frequency ventilation high frequency ventilation
Sophisticated alarms/safety features Sophisticated alarms/safety features
No monitorNo monitor
3rd Generation
Example: Draeger Babylog Example: Draeger Babylog
Microprocessor electronics Microprocessor electronics Advanced modes Advanced modes
volume triggering (SIMV, CMV) volume triggering (SIMV, CMV)
Sophisticated alarms Sophisticated alarms Sophisticated monitor Sophisticated monitor
pressure, volume, & flow waveforms pressure, volume, & flow waveforms
computer screen user interfacecomputer screen user interface
3rd Generation Improvements
Example: Star Sync, Bird VIP, SAVI Example: Star Sync, Bird VIP, SAVI
Microprocessor electronics Microprocessor electronics Advanced modes Advanced modes
patient triggering patient triggering
pressure, volume, flow pressure, volume, flow
chest movement chest movement
chest impedance chest impedance
Sophisticated alarms Sophisticated alarms Sophisticated monitor add-ons Sophisticated monitor add-ons
pressure, volume, & flow waveformspressure, volume, & flow waveforms
4th Generation
General Purpose Ventilators General Purpose Ventilators Example: Hamilton Galileo, Evita 4 Example: Hamilton Galileo, Evita 4
Microprocessor electronics Microprocessor electronics
Infant, pediatric, & adult application Infant, pediatric, & adult application Advanced modes Advanced modes
dual control & proportional assist dual control & proportional assist
artificial intelligence artificial intelligence Sophisticated user interface Sophisticated user interface
touch screen: virtual instrumenttouch screen: virtual instrument
Three Key Ideas for Understanding Ventilators
1.1.Equation of motion Equation of motion
- ventilator/patient interaction - ventilator/patient interaction
- ventilator control schemes - ventilator control schemes
2. Breath types 2. Breath types
- mandatory vs spontaneous - mandatory vs spontaneous
3. Breath patterns 3. Breath patterns
- general modes- general modes
Equation of Motion ventilationpressure (to deliver tidal volume)=elastic pressure(to inflate lungs and chest wall)+resistive pressure (to make air flow through the airways)
Pmus + Pvent = Pelastic + Presistive
Pmus + Pvent = E x V + R x V
Uses for the Equation of Motion
Classify ventilators and modes Classify ventilators and modes ventilator controls only one thing at a ventilator controls only one thing at a
time time
pressure, volume, or flow pressure, volume, or flow Monitor lung mechanics Monitor lung mechanics
resistance & compliance, time constant resistance & compliance, time constant Basis of newest modes Basis of newest modes proportional Assist proportional Assist automatic tube compensation automatic tube compensation adaptive supportadaptive support
01
20
00 1 2
3
-3
0
20
021
20
00 1 2
3
-3
0
20
02
Inspiration Expiration
20
0
20
0
Breath Types
Mandatory Breath Mandatory Breath Machine triggered or machine cycled Machine triggered or machine cycled
Spontaneous Breath Spontaneous Breath Both patient triggered and patient cycledBoth patient triggered and patient cycled
Breath Patterns
Continuous Mandatory Ventilation Continuous Mandatory Ventilation CMV CMV
all breaths mandatory all breaths mandatory
Intermittent Mandatory Ventilation Intermittent Mandatory Ventilation IMV or SIMV IMV or SIMV
mandatory and spontaneous breaths mandatory and spontaneous breaths
Continuous Spontaneous Ventilation Continuous Spontaneous Ventilation all breaths spontaneousall breaths spontaneous
What is a “Mode”?
Particular control variableParticular control variablepressure, volume, or flow pressure, volume, or flow
Particular pattern of breaths Particular pattern of breaths CMV, IMV, CSV CMV, IMV, CSV
Particular set of phase variables Particular set of phase variables trigger, limit, cycletrigger, limit, cycle
Particular control logic for changing Particular control logic for changing phase variables automaticallyphase variables automatically
What Does “Control” Mean?
1. Open loop control
2. Closed loop control
3. Double loop “dual” control
Open Loop Control Mechanism
1. Preset control circuit to desired on/off 1. Preset control circuit to desired on/off periods periods Imagine a furnace and on/off timer Imagine a furnace and on/off timer
Furnace turns on for an arbitrary 5 Furnace turns on for an arbitrary 5 minutes/hourminutes/hour
Open Loop Control Mechanism
Advantages Advantages simple, inexpensive simple, inexpensive
Disadvantages Disadvantages room temperature not well controlled room temperature not well controlled
because outside air temperature (ie, because outside air temperature (ie, weather) changes weather) changes
5 minutes may be too long or too short5 minutes may be too long or too short
Open Loop Control of Ventilator
Example Example Mechanical pressure release on older infant Mechanical pressure release on older infant
ventilators and some transport ventilators ventilators and some transport ventilators
Advantage Advantage Easy to understand and use Easy to understand and use
Disadvantage Disadvantage Leaks in system cause pressure to be less Leaks in system cause pressure to be less
than desiredthan desired
Closed Loop Control Mechanism (feedback/servo)
Preset control circuit to desired output Preset control circuit to desired output
Measure actual output Measure actual output
Change controller to get desired output if Change controller to get desired output if target not met target not met
Imagine a thermostat and furnace Imagine a thermostat and furnace
Furnace turns off when room temperature Furnace turns off when room temperature preset valuepreset value
Closed Loop Control Mechanism
Advantages Advantages Maintains constant room temperature Maintains constant room temperature
regardless of outside air temperature regardless of outside air temperature changes changes
Disadvantages Disadvantages More complex and expensiveMore complex and expensive
Closed Loop Control of Ventilator
control
circuit
controller
controlled ?
system
(patient)
Closed Loop Control of Ventilator
Example Example Pressure controlled ventilation with sensors Pressure controlled ventilation with sensors
and microprocessor and microprocessor
Advantage Advantage Maintains inspiratory pressure even with Maintains inspiratory pressure even with
leaks leaks
Disadvantage Disadvantage Delivered volume changes with changes in Delivered volume changes with changes in
lung mechanics: unstable blood gaseslung mechanics: unstable blood gases
Advanced Closed Loop ControlProportional Assist
Example: Draeger Evita 4 Example: Draeger Evita 4 ““proportional pressure support” proportional pressure support”
Operator input Operator input ““volume assist” level (elastance) volume assist” level (elastance)
““flow assist” level (resistance) flow assist” level (resistance)
FiO2 FiO2
PEEPPEEP
Proportional Assist
Advanced single loop pressure control Advanced single loop pressure control Ventilator automatically adjusts pressure Ventilator automatically adjusts pressure
flow assist level = flow x pathologic resistance
= resistive pressure (or load)
volume assist = volume x pathologic elastance
= elastic pressure (or load)
pressure = (flow x resistance) + (volume x elastance)
Proportional AssistPhase Variables
Trigger Trigger patient patient
LimitLimitresistive pressure (flow assist level) resistive pressure (flow assist level)
elastic pressure (volume assist level) elastic pressure (volume assist level)
Cycle Cycle flowflow
Proportional AssistProportional AssistProportional Pressure Support (Draeger)
• Muscle • Pressure• Ventilator • Pressure• Volume• Flow• Note: waveforms may be different for
each breath
Proportional Assist
Potential Advantages Potential Advantages support matched to need support matched to need
only abnormal load is supported only abnormal load is supported better machine-patient synchrony better machine-patient synchrony
theoretically the best mode theoretically the best mode
Potential Disadvantages Potential Disadvantages leaks defeat ventilator algorithm leaks defeat ventilator algorithm
no ventilation if patient stops breathingno ventilation if patient stops breathing
Automatic Tube Compensation
Example: Draeger Evita 4 Example: Draeger Evita 4
Operator input Operator input endotracheal tube size endotracheal tube size
% compensation % compensation
Ventilator automatically sets flow assist Ventilator automatically sets flow assist level level pressure control for resistive pressure pressure control for resistive pressure
eliminates resistive WOBeliminates resistive WOB
Automatic Tube Compensation
Potential Advantages Potential Advantages simulates breathing without tube simulates breathing without tube
decreases patient work of breathing decreases patient work of breathing
PotentialPotential Disadvantages Disadvantages actual tube resistance may change actual tube resistance may change
secretions, kinking secretions, kinking
may not simulate actual extubation may not simulate actual extubation conditions of upper airway conditions of upper airway
swelling may increase WOBswelling may increase WOB
Double Loop (Dual) Control Mechanism
1.1. Preset control circuit to desired output Preset control circuit to desired output
2.2. Measure actual output Measure actual output
3.3. Change controller to desired output Change controller to desired output
4.4. Automatically change desired output as Automatically change desired output as overall conditions change overall conditions change Imagine timer changing thermostat setting for Imagine timer changing thermostat setting for
day versus night room temperatures day versus night room temperatures
Furnace automatically turns off at one Furnace automatically turns off at one temperature during day, another at nighttemperature during day, another at night
Dual Control of Ventilator
Dual Control Between Breaths Dual Control Between Breaths All breaths pressure controlled to preset All breaths pressure controlled to preset
pressure limit pressure limit
Automatic change in pressure limit to Automatic change in pressure limit to maintain target tidal volume maintain target tidal volume
Dual Control Within Breaths Dual Control Within Breaths Switch from pressure control to volume Switch from pressure control to volume
control within breath to maintain target control within breath to maintain target tidal volumetidal volume
Dual Control of Ventilator
Advantage Advantage Stabilizes delivered volume and blood gase Stabilizes delivered volume and blood gase
values values
Improves synchrony Improves synchrony
Disadvantage Disadvantage Automatic changes may be inappropriateAutomatic changes may be inappropriate
Dual Control Between BreathsDual Control Between BreathsVolume Support (Siemens 300), Volume Guarantee
(Draeger Babylog)
Muscle PressureVentilator PressureVolumeFlowpressure limit increasesvolume metvolume not
Dual Control Between Breaths
Potential Advantages Potential Advantages better synchrony like PCV better synchrony like PCV
stable tidal volume like VCV stable tidal volume like VCV
automatic weaning as patient improves automatic weaning as patient improves
Potential Disadvantages Potential Disadvantages may result in autoPEEP may result in autoPEEP
may inappropriately decrease support may inappropriately decrease support
patient increases drive due to agitatpatient increases drive due to agitat
Dual Control Within BreathsDual Control Within BreathsPressure Augment (Bear 1000), VAPS (Bird)
Dual Control Within Breaths
Potential Advantages Potential Advantages better matching of flow to patient need like better matching of flow to patient need like
PVC PVC
stable tidal volume like VCV stable tidal volume like VCV
Potential Disadvantages Potential Disadvantages difficult to understand and set properly difficult to understand and set properly
may be uncomfortable for patient to switch may be uncomfortable for patient to switch between pressure and volume controlbetween pressure and volume control
Advanced Dual ControlAdaptive Support Ventilation
Example: Hamilton Galileo Example: Hamilton Galileo
Operator input Operator input ideal body weight ideal body weight
FiO2 FiO2
% of minute ventilation to support% of minute ventilation to support
PEEPPEEP
Adaptive Support Ventilation
Advanced dual control (between breaths) Advanced dual control (between breaths)
Ventilator monitors Ventilator monitors minute ventilation minute ventilation
lung mechanics (expiratory time constant) lung mechanics (expiratory time constant) automatically adjusts minute ventilation automatically adjusts minute ventilation
rate rate
pressure limit pressure limit
inspiratory time inspiratory time
minimizes work of breathingminimizes work of breathing
Adaptive Support VentilationPhase Variables
Trigger Trigger patient or patient or
machine machine
LimitLimitinspiratory pressure inspiratory pressure
Cycle Cycle time or time or
flowflow
Adaptive Support Ventilation
Potential Advantages Potential Advantages matches ventilation to lung condition matches ventilation to lung condition quicker, automatic weaning quicker, automatic weaning decreased risk of lung damage decreased risk of lung damage
Potential Disadvantages Potential Disadvantages leaks may defeat algorithm leaks may defeat algorithm operator must select appropriate % of operator must select appropriate % of
minute ventilation to support minute ventilation to support deadspace may cause problemsdeadspace may cause problems
Adaptive Support Ventilation
Unanswered Questions
How do newer modes affect outcome? How do newer modes affect outcome? Which patients - which modes Which patients - which modes Incidence of adverse effects Incidence of adverse effects Duration of ventilation Duration of ventilation Length of hospital stay Length of hospital stay Cost per episode of care Cost per episode of care
How to train users?How to train users?Mechanical ventilation is still more art
than science
Final Thought
"A computer lets you make more mistakes faster than any invention in human history - with the possible exceptions of handguns and tequila." Mitch Rathliffe.