Notes

Outline

The Evolution of Pediatric Mechanical Ventilators

Overview Historical Perspective Key Ideas for Understanding Ventilators Equation of motion Breath types Breath pattern What 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” control Ex. between breaths: Siemens 300 and Draeger Babylog Ex. within a breath: Bear 1000 and Bird Adaptive support (Ex.: Hamilton Galileo) Unanswered Questions

1st Generation Example: Bourns BP200 Simple analog electronics Pressure controlled IMV mode time triggered pressure limited time cycled Simple alarms control circuit (not related to patient) No monitor

1st Generation Improvements Example: Bear Cub Simple analog electronics Pressure controlled IMV mode Advanced alarms control circuit airway pressure (patient related) No monitor

2nd Generation Example: Infant Star Microprocessor electronics Pressure controlled IMV mode Sophisticated alarms/safety features No monitor

2nd Generation Improvements Example: Newport Wave, Infant Star Microprocessor electronics Advanced modes pressure triggering (SIMV, CMV) high frequency ventilation Sophisticated alarms/safety features No monitor

3rd Generation Example: Draeger Babylog Microprocessor electronics Advanced modes volume  triggering (SIMV, CMV) Sophisticated alarms Sophisticated monitor pressure, volume, & flow waveforms computer screen user interface

3rd Generation Improvements Example: Star Sync, Bird VIP, SAVI Microprocessor electronics Advanced modes patient  triggering pressure, volume, flow chest movement chest impedance Sophisticated alarms Sophisticated monitor add-ons pressure, volume, & flow waveforms

4th Generation General Purpose Ventilators Example: Hamilton Galileo, Evita 4 Microprocessor electronics Infant, pediatric, & adult application Advanced modes dual control & proportional assist artificial intelligence Sophisticated user interface touch screen: virtual instrument

Three Key Ideas for Understanding Ventilators 1. Equation of motion - ventilator/patient interaction - ventilator control schemes 2. Breath types - mandatory vs spontaneous 3. Breath patterns - general modes

Equation of Motion

Uses for the Equation of Motion Classify ventilators and modes ventilator controls only one thing at a time pressure, volume, or flow Monitor lung mechanics resistance & compliance, time constant Basis of newest modes proportional Assist automatic tube compensation adaptive support

Pressure and Volume/Flow Control Waveforms

Breath Types Mandatory Breath Machine triggered or machine cycled Spontaneous Breath Both patient triggered and patient cycled

Breath Patterns Continuous Mandatory Ventilation CMV all breaths mandatory Intermittent Mandatory Ventilation IMV or SIMV mandatory and spontaneous breaths Continuous Spontaneous Ventilation all breaths spontaneous

What is a “Mode”? Particular control variable pressure, volume, or flow Particular pattern of breaths CMV, IMV, CSV Particular set of phase variables trigger, limit, cycle Particular control logic for changing phase 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 periods Imagine a furnace and on/off timer Furnace turns on for an arbitrary 5 minutes/hour

Open Loop Control Mechanism Advantages simple, inexpensive Disadvantages room temperature not well controlled because outside air temperature (ie, weather) changes 5 minutes may be too long or too short

Open Loop Control of Ventilator Example Mechanical pressure release on older infant ventilators and some transport ventilators Advantage Easy to understand and use Disadvantage Leaks in system cause pressure to be less than desired

Closed Loop Control Mechanism (feedback/servo) 1. Preset control circuit to desired output 2. Measure actual output 3. Change controller to get desired output if target not met Imagine a thermostat and furnace Furnace turns off when room temperature preset value

Closed Loop Control Mechanism Advantages Maintains constant room temperature regardless of outside air temperature changes Disadvantages More complex and expensive

Closed Loop Control of Ventilator

Closed Loop Control of Ventilator Example Pressure controlled ventilation with sensors and microprocessor Advantage Maintains inspiratory pressure even with leaks Disadvantage Delivered volume changes with changes in lung mechanics: unstable blood gases

Advanced Closed Loop Control Proportional Assist Example: Draeger Evita 4 “proportional pressure support” Operator input “volume assist” level (elastance) “flow assist” level (resistance) FiO2 PEEP

Proportional Assist Advanced single loop pressure control Ventilator automatically adjusts pressure

Proportional Assist Phase Variables Trigger patient Limit resistive pressure (flow assist level) elastic pressure (volume assist level) Cycle flow

Proportional Assist

Proportional Assist Potential Advantages support matched to need only abnormal load is supported better machine-patient synchrony theoretically the best mode Potential Disadvantages leaks defeat ventilator algorithm no ventilation if patient stops breathing

Automatic Tube Compensation Example: Draeger Evita 4 Operator input endotracheal tube size % compensation Ventilator automatically sets flow assist level pressure control for resistive pressure eliminates resistive WOB

Automatic Tube Compensation Potential Advantages simulates breathing without tube decreases patient work of breathing Potential Disadvantages actual tube resistance may change secretions, kinking may not simulate actual extubation conditions of upper airway swelling may increase WOB

Double Loop (Dual) Control Mechanism 1. Preset control circuit to desired output 2. Measure actual output 3. Change controller to desired output 4. Automatically change desired output as overall conditions change Imagine timer changing thermostat setting for day versus night room temperatures Furnace automatically turns off at one temperature during day, another at night

Dual Control of Ventilator Dual Control Between Breaths All breaths pressure controlled to preset pressure limit Automatic change in pressure limit to maintain target tidal volume Dual Control Within Breaths Switch from pressure control to volume control within breath to maintain target tidal volume

Dual Control of Ventilator Advantage Stabilizes delivered volume and blood gase values Improves synchrony Disadvantage Automatic changes may be inappropriate

Dual Control Between Breaths

Dual Control Between Breaths Potential Advantages better synchrony like PCV stable tidal volume like VCV automatic weaning as patient improves Potential Disadvantages may result in autoPEEP may inappropriately decrease support patient increases drive due to agitation

Dual Control Within Breaths

Dual Control Within Breaths Potential Advantages better matching of flow to patient need like PVC stable tidal volume like VCV Potential Disadvantages difficult to understand and set properly may be uncomfortable for patient to switch between pressure and volume control

Advanced Dual Control Adaptive Support Ventilation Example: Hamilton Galileo Operator input ideal body weight FiO2 % of minute ventilation to support PEEP

Adaptive Support Ventilation Advanced dual control (between breaths) Ventilator monitors minute ventilation lung mechanics (expiratory time constant) automatically adjusts minute ventilation rate pressure limit inspiratory time minimizes work of breathing

Adaptive Support Ventilation Phase Variables Trigger patient or machine Limit inspiratory pressure Cycle time or flow

Adaptive Support Ventilation Potential Advantages matches ventilation to lung condition quicker, automatic weaning decreased risk of lung damage Potential Disadvantages leaks may defeat algorithm operator must select appropriate % of minute ventilation to support deadspace may cause problems

Adaptive Support Ventilation

Unanswered Questions How do newer modes affect outcome? Which patients - which modes Incidence of adverse effects Duration of ventilation Length of hospital stay Cost per episode of care How to train users?

Final Thought