Alternate Modes of Ventilation

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Alternate Modes of Ventilation
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Other Modes

• Airway Pressure Release Ventilation (APRV)
• Closed Loop Ventilation
• PC with volume guarantee
• Eg Autoflow, PRVC, VC
• Volume support
• Proportional assist ventilation (PAV)
• Automatic tube compensation (ATC)

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Airway Pressure Release Ventilation

• APRV

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APRV

• A BiLevel mode of ventilation
• Set 2 CPAP levels (PEEPH and PEEPL) and time for
  each level (TH and TL)
• Ventilation occurs backwards compared to other
  forms of ventilation

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APRV

• TH is set for a longer time than TL
• Volume exchange VT occurs by dropping from PEEPH
  to PEEPL then increasing back up to PEEPH
• TL usually less than 1 second long
• Short enough to not allow complete exhalation
  (intentional auto-PEEP)

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APRV
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Advantages of APRV

• Improves oxygenation
• Recruits alveoli
• Reduces peak pressures

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Disadvantages of APRV

• If there are long time constants (time required
  for lung inflation and deflation), there may not
  be enough time to exhale the tidal volume during
  the short TL
• This may result in inadequate exhaled volumes and
  CO2 removal

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Closed Loop Ventilation
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Closed Loop Ventilation

• Ventilation modes that collect feedback from
  patient ventilation and adjust ventilation to
  meet criteria set by the operator
• Include
• PC with volume guarantee
• Volume support
• Proportional Assist Ventilation (PAV)

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PC with Volume Guarantee

• PRVC, autoflow, VC etc.

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PC with Volume Guarantee

• Different names from different ventilator
  manufacturers
• Autoflow, Drager
• PRVC , Siemens
• VC, Puritan Bennett
• Are all the same mode

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PC with Volume Guarantee

• Operator sets desired VT
• Breath is pressure targeted
• Ventilator normally delivers initial test breath
  either VC volume or PC, then adjusts PC level to
  deliver desired Vt.
• Pressure is then adjusted by max. 3 cmH2O to
  achieve the volume set
• Max. VTI mandatory alarm needs to be set

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PC with Volume Guarantee

• Advantages
• Delivers consistent VT with a PC flow waveform
• Concerns
• If patient wants to increase VT, may increase
  effort to the point where they do all the work of
  breathing

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PC with Volume GuaranteePRVC
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Volume Support (VS)
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Volume Support (VS)

• Delivered during spontaneous ventilation
• Desired Vt is set
• Pressure support level is adjusted to deliver the
  VT set
• Decreasing patient effort would result in
  increased pressure support to keep VT constant

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Volume Support (VS)
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Proportional Assist Ventilation (PAV)

• Proportional Pressure Support (PPS)

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PAV

• Variable pressure support which uses positive
  feedback system for ventilation
• Increases support with increased patient effort
• Operator sets of support based on patient
  compliance and resistance
• 2 settings
• Flow assist
• Volume assist

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PAV

• Ventilator monitors patients inspiratory flow
  and volume inspired
• Inspiratory flow
• As inspiratory flow increases and decreases, PS
  adjusts to reduce WOB due to resistance
• Inspired volume
• As inspiratory volume increases, PS increases to
  reduce WOB due to elastance
• If set too high can cause run away ventilation
• If so, must turn level of volume support down

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PAV Considerations

• Spontaneous mode patient must have adequate drive
  to breathe
• Minimum VE and apnea alarms must be set
• Upper PAW and VT must be set to prevent high
  pressures and volumes
• Must be no leaks in the system eg ETT, BP
  fistula
• Monitor for run away ventilation

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Automatic Tube compensation (ATC)
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ATC

• PS that adjusts the level of support to patients
  inspiratory flow
• Theoretically eliminates the effect of breathing
  through an endotracheal tube (ETT)
• Ventilator monitors inspiratory flow and
  constantly adjusts pressure to compensate for
  resistance of the ETT
• P flow
• R

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ATC

• Some ventilators also provide ATC on exhalation
  by dropping CPAP level to improve exhalation
• Expiratory ATC is can be shut off
• May increase airtrapping in some patients

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ATC

• Advantages
• Provides just enough PS to overcome tube
  resistance
• May be more comfortable for patient than PS
• Disadvantages
• May cause airtrapping in exhalation
• Resistance of ETT may be different than expected
• No studies showing effectiveness yet