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Physiologic Basis of Neonatal Ventilation
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  1. Rainbow Babies & Children’s Hospital University Hospitals of Cleveland Physiologic Basis of Neonatal Ventilation Robert L. Chatburn, RRT-NPS, FAARC

  2. Bourns BP200 (neonates) PC-IMV CPAP Bourns LS 104-150 (pediatrics) VC-CMV assist/control VC-IMV CPAP 1979 Ventilator Mode Options

  3. CMV CMV + ASSIST CMV + AUTOFLOW CMV + PRESS LIMIT SIMV SIMV + PRESS SUPPT SIMV + AUTOFLOW SIMV + PRESS SUPPT + AUTOFLOW + ATC PCV PCV + AUTOFLOW MMV MMV + PRESS SUPPT MMV + AUTOFLOW APRV CPAP CPAP + PRESS SUPPT 2005 Ventilator Mode Options (Draeger)

  4. Key Ideas for Understanding Mechanical Ventilation • Mathematical Models • Equation of motion • Time constant • Mean airway pressure • Compliance curves • Control Variables • Pressure, volume, dual • Breath Types/Patterns • Optimum Mode Selection

  5. transairway pressure transrespiratory pressure transthoracic pressure volume elastance = Dpressure /Dvolume Lung Mechanics resistance = Dpressure / Dflow flow

  6. 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 xV+ R xV

  7. Uses for the Equation of Motion • Classify ventilators and modes • ventilator controls only one variable at a time • pressure, volume, or flow • Monitor lung mechanics • resistance & elastance (compliance), time constant • Basis of newest modes • proportional assist • automatic tube compensation • adaptive support

  8. Paw Paw Volume/Flow Control Pressure Control Inspiration Expiration Inspiration Expiration 20 20 Pressure 0 0 2 2 1 0 1 20 20 Volume 0 0 2 2 0 1 0 1 3 3 Flow Time (s) Time (s) 0 0 -3 -3

  9. Dual Control • Use of both pressure and volume signals to control the breath • Example: CMV+AutoFlow Draeger Evita 4 • every breath is mandatory • every breath is pressure limited, time cycled • pressure limit is automatically adjusted to meet set tidal volume target using compliance measurements • Contraindicated if large leaks

  10. Dual Control Advantages • Stable minute ventilation • as with volume control • Better patient synchrony • as with pressure control

  11. 99.8% 100 99.3% 98.2% 95% 86.5% 80 inspiratory volume 63.2% & pressure 60 Percent of Equilibration Value 40 expiratory volume 36.8% & pressure 20 13.5% 5% 1.8% 0.7% 0.2% 0 1 2 3 4 5 6 Time Constants Time Constants (R x C) • the time to reach 63% of equilibrium value • about 5 time constants to passively inhale or exhale completely

  12. Mean Airway Pressure Paw = K(PIP-PEEP)(I / I+E) + PEEP • To Increase Mean Pressure • increase flow • increase PIP • increase I:E • increase PEEP mean pressure

  13. Patient Triggered Inspiration • Proposed advantages • decreased work of breathing • better oxygenation • more consistent tidal volume • better gas exchange • decreased risk of lung damage • decreased risk of IVH • decreased oxygen requirement • decreased duration of ventilation

  14. Effects of Asynchrony IMV SIMV mandatory breaths spontaneous breaths Volume Volume

  15. Static Pressure-Volume Loop Optimum Tidal Volume Range

  16. Dynamic PV Loop (volume control)

  17. Dynamic PV Loop (pressure control)

  18. Problems (leak)

  19. Problems (gas trapping)

  20. Characteristics of a Mode 1. Breathing Pattern • Control variable • Breath sequence 2. Control Type • Setpoint, servo, adaptive, optimal 3. Specific Control Strategy • Phase variables • Operational logic

  21. Breathing Pattern • Control Variable • Pressure • Volume • Dual

  22. Breathing Pattern • Control Variable • Pressure • Volume • Dual • Breath Seqence • Mandatory vs spontaneous

  23. Breath Types • Spontaneous Breath • Patient sets frequency and tidal volume • Both patient triggered and patient cycled • Mandatory Breath • Machine sets frequency and/or tidal volume • Machine triggered and/or machine cycled

  24. Breath Sequences • Continuous Mandatory Ventilation • CMV • all breaths mandatory • Intermittent Mandatory Ventilation • IMV or SIMV • mandatory and spontaneous breaths • Continuous Spontaneous Ventilation • CSV • all breaths spontaneous

  25. Basic Breathing Patterns Control VariableBreathing Sequence Volume Control Continuous Mandatory Ventilation Intermittent Mandatory Ventilation Pressure Control Continuous Mandatory Ventilation Intermittent Mandatory Ventilation Continuous Spontaneous Ventilation Dual Control Continuous Mandatory Ventilation Intermittent Mandatory Ventilation Continuous Spontaneous Ventilation

  26. Potential Confusion • All mandatory breaths are assisted • Spontaneous breaths may be assisted or not

  27. Definition of “Assisted Breath” • Assisted (ventilator does work on patient) • Airway pressure rises above baseline during inspiration (or falls below baseline during expiration). • Un-Assisted • Airway pressure stays constant during inspiration or expiration. • Loaded (patient does work on ventilator) • Airway pressure falls below baseline during inspiration and rises above baseline during expiration.

  28. Assisted Spontaneous Breaths • Pressure Support • patient triggered, pressure limited, flow cycled • patient controls timing and size of breath • Automatic Tube Compensation • patient triggered, pressure proportional to flow2, flow cycled • active on inspiration and expiration • patient controls timing and size of breath

  29. Characteristics of a Mode 1. Breathing Pattern • Control variable • Breath sequence 2. Control Type • Setpoint, auto-setpoint, servo, adaptive, optimal 3. Specific Control Strategy • Phase variables • Operational logic

  30. Control Types • Setpoint • user sets pressure, volume, flow, limit • Auto-Setpoint • ventilator chooses limit variable (pressure vs flow) • Servo • ventilator delivers pressure in proportion to patient’s inspiratory flow • Adaptive • ventilator chooses pressure setpoint to achieve operator selected volume setpoint • Optimal • ventilator chooses both volume and pressure setpoints

  31. Evolution of Ventilator Control Types Tactical Control (within-breaths) • setpoint (PC-IMV) • auto-setpoint (Pmax) • servo (Automatic Tube Compensation) operator-selected, static setpoints Strategic Control (between breaths) • adaptive (CMV+AutoFlow) • optimal (ASV) ventilator-selected, dynamic setpoints static model Intelligent Control (between patients) • knowledge based • artificial neural network ventilator-selected, dynamic setpoints dynamic model ability to learn from experience

  32. CMV CMV + ASSIST CMV + AUTOFLOW CMV + PRESS LIMIT SIMV SIMV + PRESS SUPPT SIMV + AUTOFLOW SIMV + PRESS SUPPT + AUTOFLOW + ATC PCV PCV + AUTOFLOW MMV MMV + PRESS SUPPT MMV + AUTOFLOW APRV CPAP CPAP + PRESS SUPPT Ventilator Mode Options (Draeger)

  33. VOLUME CONTROL VC-CMV VC-IMV Ventilator Mode Options (Draeger) PRESSURE CONTROL • PC-CMV • PC-IMV • PC-CSV DUAL CONTROL • DC-CMV • DC-IMV

  34. Selecting the Best Mode (benefit/cost) • Benefits • Clinical • maintenance of stable gas exchange • reduced work of breathing • optimum patient-machine synchrony • Technical • learnability (easy to understand) • efficiency (minimum setup and maintenance) • low error rate (inappropriate settings)

  35. Selecting the Best Mode (benefit/cost) • Costs • Clinical • adverse reactions (lung stretch damage) • associated complications (blood loss) • Technical • cost to patient (length of stay) • cost to hospital (clinician interventions)

  36. VOLUME CONTROL VC-CMV VC-IMV Ventilator Mode Options (Draeger) PRESSURE CONTROL • PC-CMV • PC-IMV • PC-CSV DUAL CONTROL • DC-CMV • DC-IMV

  37. DC-CMV DC-IMV DC-IMV + PRESS SUPPT DC-IMV + ATC (automatic tube compensation) DC-IMV + MMV (mandatory minute ventilation) DC-IMV + PRESS SUPPT + ATC DC-IMV + PRESS SUPPT + MMV DC-IMV + MMV + ATC Dual Control Options (Draeger)

  38. Benefit Cost Mode Clinical Technical Clinical Technical DC-CMV -Stable tidal volume with each breath -Least work of breathing because all breaths are equally supported -Nearly optimum synchrony -Easy to understand and monitor -Fewest breath parameters to adjust during weaning or increasing support -More stable intracranial pressure -Requires fewer adjustments and perhaps fewer blood gases -Fewer adjustments may lead to lower LOS and less operator time at bedside

  39. Benefit Cost Mode Clinical Technical Clinical Technical DC-IMV -Stable volume for mandatory breaths only -Increased WOB for spontaneous breaths -Easy to understand and monitor -Necessary to select correct frequency -Less stable intracranial pressure -Less stable minute ventilation -May require more ABGs more blood loss -Weaning means “dumbing down” the ventilator -More adjustments may lead to longer LOS and operator time

  40. Benefit Cost Mode Clinical Technical Clinical Technical DC-IMV + anything pressure support ATC -Stable mandatory breaths only -Variable WOB for spontaneos breaths depending on options and settings -Difficult to understand and monitor -Necessary to correctly balance many settings -Decreased operator efficiency -Less stable intracranial pressure -Less stable minute ventilation -May require more ABGs more blood loss -Weaning means “dumbing down” the ventilator -More adjustments may lead to longer LOS and operator time

  41. VOLUME CONTROL VC-CMV VC-IMV Ventilator Mode Options (Draeger) PRESSURE CONTROL • PC-CMV • PC-IMV • PC-CSV DUAL CONTROL • DC-CMV • DC-IMV

  42. DC-CMV Tidal volume infrequent PEEP FiO2 Weaning automatic Ventilator Management Requirements PC-IMV + Press Support • Peak inspiratory pressure • frequent • PEEP • Frequency • Pressure support level (?) • FiO2 • Weaning • manual • may be ineffective with PS

  43. DC-CMV Tidal volume infrequent PEEP FiO2 Weaning automatic Ventilator Management DC-IMV + Press Support • Tidal volume • infrequent • PEEP • Frequency • Pressure support level (?) • FiO2 • Weaning • mandatory breaths automatic • spontaneous breaths manual • more manual as rate decreases

  44. Thought For The Day “In some ways we are as confused as ever, but we believe we are confused on a higher level and about more important things.” A.R. Feinstein, MD

  45. WWW.AARC.ORG e-learning system at the AARC store