1. The Evolution of Pediatric Mechanical Ventilators Robert L. Chatburn, RRT, FAARC University Hospitals of Cleveland Case Western Reserve University

2. 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 compensationautomatic tube compensation Double loop “dual” control Ex. between breaths: Siemens 300 and Draeger Babylog Ex. within a breath: Bear 1000 and Bird Adaptive supportAdaptive support (Ex.: Hamilton Galileo) Unanswered Questions

3. 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

4. 1st Generation Improvements Example: Bear Cub Simple analog electronics Pressure controlled IMV mode Advanced alarms control circuit airway pressure (patient related) No monitor

5. 2nd Generation Example: Infant Star Microprocessor electronics Pressure controlled IMV mode Sophisticated alarms/safety features No monitor

6. 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

7. 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

8. 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

9. 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

10. 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

11. Equation of Motion ventilation pressure (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

12. 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

13. 0 1 20 0 01 2 3 -3 0 20 0 2 1 0 01 2 3 -3 0 20 0 2 InspirationExpiration 20 0 0

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

15. 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

16. 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

17. What Does “Control” Mean? 1. Open loop control 2. Closed loop control 3. Double loop “dual” control

18. 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

19. 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

20. 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

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

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

23. Closed Loop Control of Ventilator control circuit controller controlled ? system (patient)

24. 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

25. Advanced Closed Loop Control Proportional Assist Example: Draeger Evita 4 “proportional pressure support” Operator input “volume assist” level (elastance) “flow assist” level (resistance) FiO2PEEP

26. Proportional Assist Advanced single loop pressure control 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)

27. Proportional Assist Phase Variables TriggerpatientLimit resistive pressure (flow assist level) elastic pressure (volume assist level) Cycleflow

28. Proportional Assist Proportional Assist Proportional Pressure Support (Draeger) Muscle Pressure Ventilator Pressure Volume Flow Note: waveforms may be different for each breath

29. 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

30. 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

31. 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

32. 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

33. 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

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

35. Dual Control Between Breaths Dual Control Between Breaths Volume Support (Siemens 300), Volume Guarantee (Draeger Babylog) Muscle Pressure Ventilator Pressure Volume Flow pressure limit increases volume met volume not

36. 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 agitat

37. Dual Control Within Breaths Dual Control Within Breaths Pressure Augment (Bear 1000), VAPS (Bird)

38. 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

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

40. 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

41. Adaptive Support Ventilation Phase Variables Trigger patient or machineLimit inspiratory pressure Cycle time or flow

42. 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

43. Adaptive Support Ventilation

44. 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? Mechanical ventilation is still more art than science

45. 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.