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Chapter 42 Mechanical Ventilators

Chapter 42 Mechanical Ventilators. Learning Objectives. Discuss the basic design features of ventilators. Classify ventilators and describe how they work. Define what constitutes a mode of ventilation. Classify and discuss modes of ventilation. Learning Objectives (cont.).

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Chapter 42 Mechanical Ventilators

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  1. Chapter 42Mechanical Ventilators

  2. Learning Objectives • Discuss the basic design features of ventilators. • Classify ventilators and describe how they work. • Define what constitutes a mode of ventilation. • Classify and discuss modes of ventilation.

  3. Learning Objectives (cont.) • Explain the indications for the basic modes of ventilatory support. • Describe the application of selected modes of ventilatory support.

  4. Mechanical Ventilator (MV) • 4 basic functions • Input power • Electrical, pneumatic, manual • Power transmission & conversion • Control system • Output

  5. Control System

  6. All of the following are functions of mechanical ventilation, except: • Turbo power • Input power • Power transmission and conversion • Control system

  7. Power Transmission & Conversion • Drive mechanism • Generates force needed to deliver gas to patient under pressure • Mechanisms can either be • Gas from pressure-reducing valve • Driven by electric motor or compressor • Output control valve • Regulates flow of gas to patient • Can be just on/off valve or one that modifies output waveform

  8. Volume & Pressure Ventilation:Characteristic Waveforms

  9. Control Circuit • System that allows ventilator to manipulate pressure, volume, & flow • May be composed of mechanical, pneumatic, electric, electronic, or fluidic components • Most modern vents combine two or more • May be advantages to components used • MRI: Fluidic controls have no metal & are immune to failure due to electromagnetic interference

  10. Control Circuits may be composed of all of the following components, except: • Mechanical • Pressure • Electric • Pneumatic

  11. Control Variables • Primary variable ventilator controls to cause inspiration • 3 possible explicit variables • Pressure controlled • Volume controlled • Flow controlled • Only one can be controlled; other two become dependent variables

  12. All of the following are possible explicit variables except: • Pressure controlled • Volume controlled • Flow controlled • Loop controlled

  13. Control Variables (cont.)

  14. Control Variables (cont)

  15. Pressure Controller • Ventilator controls pressure (P), but volume & flow vary with changes in compliance (C) & resistance (Raw) • Pressure waveform will be square (constant) during inspiration • Positive or negative pressure controlled • i.e., iron lung controls with negative P

  16. Volume & Flow Controllers • Volume controller • Ventilator controls volume so will be constant • Flow is volume/time, so flow is also constant • Pressure will vary with changes in C & Raw • Flow controller • As above, flow & thus volume constant • Pressure varies with changes in C and Raw • Old neonatal ventilators used flow interruption to deliver volume during inspiration

  17. Phase Variables • Ventilator uses variables to initiate or limit each phase of ventilation • Initiation of inspiration (E to I) • Inspiration • End of inspiration (I to E) • Expiration

  18. Phase Variables

  19. All of the following are variables that initiate or limit each phase of ventilation, except: • Initiation of inspiration (E to I) • Inspiration • End of inspiration (I to E) • End of expiration

  20. Initiation of Inspiration • Trigger variable • Machine triggered • Time: determined by rate control • Patient triggered • Pressure • Flow (least work for patient to trigger) • Volume (rare) • Most ventilators provide a manual breath button that operator activates

  21. Inspiration: Target Variable • Limits inspiration but does not terminate the phase • Pressure limited • Limits peak inspiratory pressure (PIP) during inspiration • Volume limited • Limits amount of tidal volume (VT) delivered during inspiration to set amount • Flow limited • Limits the amount of flow during inspiration

  22. Target Variable

  23. End of Inspiration • Cycle variables terminate inspiratory phase • Pressure cycled • Inspiration terminates as preset pressure reached (hit alarm level) • Volume cycled • Inspiration terminates at preset VT • Flow cycled • Inspiration terminates when flow drops to preset value (PSV) • Time cycled • Inspiration terminates when set inspiratory time is reached • Includes any inspiratory holds

  24. Expiration: Baseline Variable • Defined by how baseline or end expiratory pressure (EEP) relates to atmospheric pressure • PEEP Positive or supra- atmospheric EEP • NEEP Negative or sub-atmospheric EEP • ZEEP Zero EEP equals sub-atmospheric pressure

  25. All of the following are all baseline variables, except: • ZEEP • MEEP • PEEP • NEEP

  26. Primary Breath Control Variable • Volume control: VT/flow set, while P depends on those settings & pulmonary mechanics • Pressure control: P set, VT /flow depend on P setting & pulmonary mechanics • Dual control: Mixture of volume & pressure • Either starts breath in volume control & ends with pressure control or the reverse

  27. Two Breath Types • Spontaneous • Patient triggers & cycles the breath • Patient effort may be supported by manual or mechanical ventilator • Mandatory • Ventilator initiates and/or cycles breath • See Box 42-2.

  28. Modes of Ventilation • 3 possible sequences of breaths • CMV: all breaths mandatory, “full support” • Patient & machine-initiated breaths are same • CSV: all breaths spontaneous • Patient triggers & cycles all breaths • IMV: Breaths can be mandatory or spontaneous • When tied to control variable, nine possible combinations

  29. Breath Sequence

  30. Breath Sequence

  31. Modes of Ventilation (cont.)

  32. Control Type • Open loop control: Most basic early ventilators were flow, volume, or pressure, are determined by pulmonary mechanics & ventilator system • Closed loop control: Flow/volume or pressure are set & measured, with feedback to drive mechanism altering output to maintain desired (set) levels

  33. Importance of Defining Modes • Modern ventilators, modes may look similar on graphics but must be set up differently • Clear understanding & definition of each mode will avoid potentially dangerous patientventilator mismanagement

  34. Ventilator Waveforms • Ventilator graphics are to ventilator management , what ECGs are to managing the heart, or pressure waveforms from a PA catheter are to hemodynamic management • Graphics provide wealth of information at a glance

  35. Ventilator Waveforms (cont.)

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