Evidence Base for Newer Modes of Mechanical Ventilation

1
Evidence Base for Newer Modes of Mechanical
Ventilation

• Charles B. Spearman, MSEd, RRT, FAARC
• Assistant Professor
• Respiratory Care Programs
• Department of Cardiopulmonary Sciences
• Loma Linda University
• Loma Linda, California

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Evidence Base for Newer Modes of Mechanical
Ventilation Overview

• Background for evidence base levels
• Dual modes of ventilation
• Adaptive Support ventilation (ASV)
• Proportional Assist Ventilation (PAV)
• Airway Pressure Release Ventilation (APRV)

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Evidence Base for Newer Modes of Mechanical
Ventilation Background

• Evidence-based medicinethe integration of
  individual clinical expertise with the best
  available research evidence from systematic
  research and the patients values and
  expectations. D. R. Hess, RC,2004497,
  730-741.

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Evidence Base for Newer Modes of Mechanical
Ventilation Background

• New Horizons Symposium Integrating
  Evidence-based Respiratory Care into
  PracticePublished inRespiratory Care, July
  2004 (497)
• Topics covered
• -What is EBM -EB of New Modes
• -RC Protocols -COPD Manag.
• -Asthma Manag. -ALI/ARDS Manag.
• -NIPPV -Weaning
• Also G. D. Rubenfelds article RCP role in EBM
  use

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Evidence Base for Newer Modes of Mechanical
Ventilation Background

• Other sources for evidence based practice
• Clinical Practice Guidelines
• AARC, ACCP, ATS
• Evidence based guidelines
• Weaning, GOLD, Aerosol Task force, Asthma
  training, etc.

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Evidence Base for Newer Modes of Mechanical
Ventilation Background
From Branson Johanningman, 2004RC,497,
742-760.
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New Modes of Mechanical Ventilation Background

• Introduction of the microprocessor-controlled
  ventilator
• Better control of flow exhalation valves
• Increased monitoring capabilities
• Increased pt-ventilator interaction
• Dual modes of ventilation introduced

From Mosbys R. C. Equip., 6th ed. 1999.
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New Modes of Mechanical Ventilation Examples of
the first dual modes

• Volume Assured Pressure Support (VAPS) Pressure
  Augmentation
• Pressure Regulated Volume Control (PRVC)
  similar modes
• Volume Support Ventilation (VS or VSV) similar
  modes

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Pressure vs. Volume Ventilation(From Branson,
R., Bird product literature)
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Pressure vs. Volume VentilationAdvantages

• Press. Control Press. Support
• Variable flow
• Reduced WOB
• Max Palveolar Max Pairway (or less)
• Palveolar controlled
• Variable I-time pattern (PS)
• Better with leaks

• Volume Control
• Consistent TV
• changing impedance
• Auto-PEEP
• Minimum min. vent. (f x TV) set
• Variety of flow waves

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Pressure vs. Volume VentilationDisadvantages

• Press. Control Press. Support
• Variable tidal volume
• Too large or too small
• No alarm/limit for excessive TV (except some new
  gen. vents)
• Some variablity in max pressures (PC, expir.
  effort)

• Volume Control
• Variable pressures
• airway
• alveolar
• Fixed flow pattern
• Variable effort variable work/breath
• Compressible vol.
• Leaks vol. loss

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Newer Methods of Ventilatory Support dual modes

• 1st generation dual modes VAPS, Press. Aug.,
  PRVC VS
• Allow variable flow delivery and pressure
  targeted ventilation approach
• Attempt to deliver a set tidal volume (TV)
• Allow peak airway pressure to vary breath to
  breath

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VAPS Volume Assured Pressure Support

• Combines volume ventilation pressure support
• (for mech., vol. limited breaths only)
• Uses TV, peak flow, and pressure sup./control
  settings
• Targets PS level with at least set peak flow
  first
• Continues until flow decreases to set peak flow,
  then
• If TV not delivered, peak flow maintained until
  vol. limit
• If TV or more delivered, breath ends

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VAPS Volume Assured Pressure Support

• (From Branson, R., Bird product literature)

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VAPS (and Pressure Augmentation) -
Considerations

• The set TV is the minimum TV the patient will
  receive
• The set pressure support is the minimum the
  patient will receive
• The set peak flow is the minimum the patient will
  receive
• No ventilatory mechanics measured

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Pressure Regulated Volume Control (Servo vents.)

• Combines volume ventilation pressure control
• (for mech., time-cycl. breaths only)
• Set TV is targeted
• Ventilator estimates vol./press. relationship
  each breath
• Ventilator adjusts level of pressure control
  breath by breath

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Pressure Regulated Volume Control (Servo vents,
example)

• First breath 5-10 cm H2O above PEEP
• V/P relationship measured
• Next 3 breaths, pressure increased to 75 needed
  for set TV
• Then up to /- 3 cm H2O changes per breath
• Time ends inspiration

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Pressure Regulated Volume Control (Siemens Servo
300)

• From Siemens prod. literature

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Pressure Regulated Volume Control - Considerations

• Assist-control mode
• Like PC, flow varies automatically to varying
  patient demands
• Constant press. during each breath - variable
  press. from breath to breath
• Time is cycling method delivered TV can vary
  from set

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First dual modes VAPS, Press. Aug. vs. PRVC VS

• VAPS ( Press. Augmentation)
• Use the set TV as a minimum
• Normal cycling occurs at or above the set TV
• Mechanics not measured

• PRVC ( Vol. Support)
• Use the set TV as the target for each breath
• Normal cycling may stop insp. below or above set
  TV
• Pressure used based on mechanics measurements

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First dual modes VAPS, Press. Aug. vs. PRVC VS

• Peak airway pressure can reach high levelsSet
  appropriate high pressure limits
• No settings for maximum tidal volume

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Newer Ventilator Dual Modes

• Adaptive Support Ventilation (ASV) Hamilton
  Galileo

• AutoFlow Drager ventilators Evita 4, Evita 2
  dura

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Newer Ventilator Dual Modes Drager vents
AutoFlow

• First breath uses set TV I-time
• Pplateau measured
• Pplateau then used
• V/P measured each breath
• Press. changed if needed (/- 3)
• Then similar to PRVC

From Drager Mosbys R. C. Equip., 6th ed. 1999.
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Newer Ventilator Dual Modes Drager vents
AutoFlow

• Allows spont. breathing
• expiration and
• inspiration
• Exp. efforts at peak insp. pressure open exh.
  valve Ppeak maintained
• Active exhalation valve is a key feature

From Drager Mosbys R. C. Equip., 6th ed. 1999.
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Newer Ventilator Dual Modes Drager vents
AutoFlow

• Allows spont. breathing
• expiration and
• inspiration

From Drager
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Newer Ventilator Dual Modes Drager vents
AutoFlow - Considerations

• Dual mode similar to PRVC
• Targets vol., applies variable press. based on
  mechanics measurements
• Allows highly variable inspiratory flows
• Time ends mandatory breaths
• Adds ability to freely exhale during mandatory
  inspiration (maintains pressure)
• Adds high TV alarm limit
• Can be used in CMV, SIMV and MMV

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Newer Ventilator Dual Modes Hamilton Galileos
ASV (adapt. sup. vent.)

• Clinician enters pt. data support
• Vent. calculates needed min. vol. best rate/TV
  to produces least work.
• Targeted TVs given as press. control or press.
  support breaths
• Breath is PC if time triggered, PS if pt.
  triggered

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Newer Ventilator Dual Modes Hamilton Galileos
ASV (adapt. sup. vent.)

• Vent. measures analyzes data mechanics each
  breath for
• compliance
• resistance
• inspiratory expiratory time constants
• actual I-time, E-time, total f min. vol.
• pressures
• Press. adjusts in /- 2 cm H2O to achieve TV

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Newer Ventilator Dual Modes Hamilton Galileos
ASV - Considerations

• Mandatory breaths PC, pt. triggered PS
• both at same targeted TV and calculated press.

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ASV Principle mode of ventilation


Flow I Flow E


Pinsp
PEEP
no patient activity machine triggered time
cycled
patient is active patient triggered flow
cycled
From Hamilton Medical
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Newer Ventilator Dual Modes Hamilton Galileos
ASV - Considerations

• Mandatory breaths PC, pt. triggered PS
• both at same targeted TV and calculated press.

• If pt.s f gt set by vent., mode is PS
• If pt.s f lt set by vent., mode is PC-SIMV/PS
• If patient is apneic, all breaths are PC

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Newer Ventilator Dual Modes Hamilton Galileos
ASV Considerations

• Using least work as a criteria
• calculation for needed rate may change,
• therefore calculated TV may change, and
• therefore calculated pressure needed for TV may
  change
• Both max. min. TV limits are used
• As patient improves,support is decreased
• pressure can be reduced to PEEP 5 cm H2O

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Newer Ventilator Dual Modes Summary

• Combined methods of press. volume ventilation
  may replace standard volume ventilation.
• Prudent use of high pressure limits (and volume
  limits if available) and careful monitoring can
  decrease disadvantages of combined modes.

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Newer Ventilator Dual Modes Evidence

• VAPS
• No randomized controlled trials (RCT)
• 2 observational studies, 1 bench study with test
  lung
• Lower level outcomes
• Reduced work
• Evid. levels III, B level V, C

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Newer Ventilator Dual Modes Evidence

• PRVC/VS (also referred to as adaptive PC)
• 2 small randomized controlled trials (RCT)
  post-op pts, no survival benefit, no diff or
  slightly shorter vent time, less interventions
  blood gases
• 3 other randomized cross-over observational
  studies, 5 other cross-over short term obs.
  studies safe, small differences in lower PIP,
  some shorter to extubation
• Lower level outcomes
• Small RCT trials II, grade B evidence
• Small cross-over studies III, grade C

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Newer Ventilator Dual Modes Evidence

• ASV
• 2 small randomized controlled trials (RCT) no
  survival benefit, sub-group (10 infants) shorter
  vent time, less BPD adult study showed only less
  PIP in PRVC
• 3 other cross-over observational studies, lower
  PIP, (better gas exchange in animal study only)
• Lower level outcomes
• Small RCT trials II, grade B evidence
• Small cross-over studies III for humans, V for
  animal study, all grade C

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Lung protective strategies influence on
ventilators modes

• Lung protective strategies may include
• Control of peak alveolar press. (e.g. lt 30
  H2O)or low TV (e.g. 6 ml/kg IBW)
• PEEP above lower inflection point
• Peak pressure below upper inflection point
• of static compliance curve

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Lung protective strategies influence on
ventilators modes

• Lung protective strategies influence on
  ventilators modes

From PB product lit.
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New Modes of Mechanical Ventilation Bi-level
ventilation methods

• Ventilation methods that allow spontaneous
  breathing at two airway pressures
• BiPAP (Drager E-4 E-2 dura)
• BiLevel (NPB 840)
• APRV (NPB 840, Drager E-4 E-2 dura)
• Pressure targeted strategy spont. Breathing
• can fit lung protective criteria

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BiLevel Ventilation NPB 840

• Uses two levels of pressure for two time periods
• Mandatory breaths at the higher pressure are
  time cycled
• Spontaneous breaths can be pressure supported

From PB product lit.
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BiLevel Ventilation NPB 840

• Uses 2 pressure levels for 2 time periods
• PEEPlow PEEPhigh, Thigh and Tlow
• Patient triggering cycling can change phases

From PB product lit.
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BiLevel Ventilation NPB 840

• Pressure support may be applied at both pressures
  during a spont. breath
• If PS is set higher than PEEPH, the PS pressure
  is applied to a spontaneous effort at upper
  pressure

From PB product lit.
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BiLevel Ventilation NPB 840

• If PS is set lower than PEEPH, PS is applied to
  patient efforts at the lower pressure, PEEPL

From PB product lit.
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APRV (Drager ventilators)

• Airway Pressure Release Ventilation
• Like BiPAP/BiLevel but time at the lower pressure
  (release time) is usually short, 1-1.5 seconds
• Spontaneous breathing still allowed throughout
  low high pressures

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APRV (Drager ventilators)

• Airway Pressure Release Ventilation

From Mosbys R. C. Equip. 6th ed. 1999.
46
Newer Methods of Ventilatory Support
Proportional Assist Ventilation

• PAV - currently on PB 840 in US
  prototype/research ventilators, Drager Evita 4
  Respironics BiPAP Vision
• Allows free flow based on patient effort
• Targets portion of patients work during
  spontaneous breaths
• Automatically adjusts flow, volume and pressure
  needed each breath

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Methods of Ventilatory Support PAV continued

• Vol. assist reduces work of elastance
• Flow assist reduces work of resistance's
• Pressure adjusts during each breath to control
  work level
• Increased patient effort causes increased applied
  pressure (and flow volume)

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Methods of Ventilatory Support PAV continued

• From Younes, M Ch.15, in Tobin, MJ Prin.
  Pract. Of Mech. Vent. 1994 McGaw-Hill, Inc.

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Methods of Ventilatory Support PAV continued

• Other controls useful for PAV
• High pressure limit
• High volume limit
• Back-up ventilation mode
• Typical alarms etc.

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Methods of Ventilatory Support PAV continued

• Proportional Pressure Support (PPS), Drager Evita
  4 ventilators PAV mode
• Has high press. and high tidal volume limits
• Has apnea ventilation back-up
• set f and TV
• or for peds, set f and inspiratory pressure
• Maximum I-time 4 seconds (1.5 for peds.)

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Methods of Ventilatory Support PAV -
Considerations

• Consistent level of support per breath
• Patient controls breathing pattern
• Patient triggered mode
• (Unless back-up mode present)
• Reduced support with Auto-PEEP
• Cannot compensate for leaks (prototypes)

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Methods of Ventilatory Support PAV -Evidence

• Huge number of studies since 1992.
• BUT, almost no large RCTs. Most were small, short
  term observational comparing PAV to pressure
  support.
• Largest trial in NIPPV for ARF showed no
  difference for intubation, stay, mortality.
  Better comfort for PAV
• Most all other trials rated level III, grades or
  C.

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New Modes of Mechanical Ventilation Other neat
stuff
54
New Modes of Mechanical Ventilation Other neat
stuff

• Patient Simulation Venturi ventilator
• Exhalation assist Venturi ventilator
• reduce expiratory work
• Auto mode switching more support to less and
  less to more (without alarms)
• Servo 300s Auto Mode
• VC or PRVC ? VS or PC ? PS
• Galileos ASV PC ? PS

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New Modes of Mechanical Ventilation Other neat
stuff

• Automatic tube compensation Drager Evita 4

From Drager prod. lit.
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New Modes of Mechanical Ventilation Summary

• Older modes ventilators
• passive, operator-dependant tools
• New modes on new generation ventilators
• adaptively interactive
• goal oriented
• patient centered
• Adapted from John J. Marini, MD AARC congress,
  11/98