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.