VENTILATOR GRAPHICS

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VENTILATOR GRAPHICS
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Purpose

• Graphics are waveforms that reflect the
  patient-ventilator system and their interaction
• Purpose of monitoring graphics includes
• Monitors the patients disease status (C and Raw)
• Calculates respiratory mechanics
• Assesses patient response to therapy
• Monitors ventilator function
• Allows fine tuning of ventilator to decrease WOB
  and optimize ventilation
• Allows user to interpret, evaluate, and
  troubleshoot ventilator and patients response to
  ventilator

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Types of waveforms

• Scalars plot pressure/volume/flow against
  timetime is the x axis
• Loops plot pressure/volume/flow against each
  otherthere is no time component
• Six basic waveforms
• Rectangular AKA swuare wave
• Descending ramp AKA decelerating ramp
• Ascending ramp AKA accelerating ramp
• Sinusoidal AKA sine wave
• Exponential rising
• Exponential decaying

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Types of waveforms seen

• Pressure waveforms
• Rectangular
• Exponential rise
• Sine
• Volume waveforms
• Ascending ramp
• Sinusoidal
• Flow waveforms
• Rectangular
• Sinusoidal
• Ascending ramp
• Descending ramp
• Exponential decay

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Pressure-Time Scalar

• Machine-triggered breaths have no negative
  deflection at the start
• Patient triggered breaths may have a negative
  deflection at the start if the breath is being
  pressure triggeredthe greater the patient effort
  to trigger the breath, the greater the negative
  deflection seenno deflection see with flow
  triggering
• In volume modes, the shape will be exponential
  rise for mandatory breaths and sinusoidal for
  spontaneous breathsif PS is added to spontaneous
  breaths, then the waveform will be square on the
  spontaneous breaths
• In pressure modes, the shape will be rectangular
  for mandatory breaths and sinusoidal for
  spontaneous breathsif PS added to the
  spontaneous breaths, they will be rectangular
  also
• If PEEP is added, the baseline during expiration
  will be above zero
• The area under the entire curve equals the Paw
  (mean airway pressure)

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Use of Pressure-Time Scalars
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Volume-Time Scalar

• Ascending ramp shape if a square wave flow
  pattern is usedsinusoidal if the sine wave flow
  pattern is usedexponential rise if the
  decelerating flow pattern is used
• Plateaus at the peak of the curve in PC/PS
• If the exhalation side of the curve doesnt
  return to baseline, it could be auto-PEEP or
  there could be a leak (eg-around ETT or through a
  chest tube)

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Use of Volume-Time Scalars
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Flow-Time Scalars

• No evidence supports one flow pattern over
  anotherthe square wave might distribute gas more
  evenly in patients with a unilateral lung
  dxdecelerating ramp may distribute gas more
  evenly because the high burst of flow at the
  beginning would pop alveoli open and allow for
  gas exchange during the entire breath
• If expiratory flow doesnt return to baseline
  before the next breath starts, theres auto-PEEP
  present (air trapping is occurring)
• Volume control on some vents allows you to select
  the flow pattern you want
• All pressure breaths (PC, PS, PRVC, VS) will have
  a decelerating ramp flow pattern
• CPAP has a sinusoidal flow pattern unless PS has
  been added

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Use of Flow-Time Scalars
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Pressure-Volume Loops

• Volume is plotted on the y axis and pressure on
  the x axis (can also be plotted the other way
  around)
• Inspiratory curve is upward and expiratory curve
  is downward
• Spontaneous breaths go clockwise and positive
  pressure breaths go counterclockwise
• The bottom of the loop will be at the set PEEP
  level or be at 0 if theres no PEEP set
• I starts and E ends at the bottom of the loopI
  ends and E starts at the top of the loop
• The loop is almost square in PC/PS because of
  pressure limiting during I

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Abnormal PV Loops

• If an imaginary line is drawn down the middle of
  the loop, the area to the right represents
  inspiratory resistance/WOB and the area to the
  left represents expiratory resistance/WOB (just
  the opposite for spont breaths- I is to the left
  and E is to the right)
• The more vertical the loop lays, the lower the
  lung C, the more horizontal it lays, the higher
  the lung C
• The fatter the loop, the higher the airway
  resistanceyou can tell if its I or E resistance
  by looking at whether the right or left side
  bulges out more
• A bird beak at the top of the loop represents
  over-distension
• A pig tail at the bottom indicates patient
  triggeringthe bigger the pig tail, the higher
  the patient WOB to trigger the breath
• The loop wont meet at the bottom with
  airtrapping or leaks

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Use of PV Loops
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Flow-Volume Loops

• Flow is plotted on the y axis and volume on the x
  axis
• Inspiration is above the horizontal line and
  expiration is below (some vents reverse this and
  I is below while E is above)
• The shape of the insp flow curve will match
  whats set on the ventilator
• The shape of the exp flow curve represents
  passive exhalationits long and more drawn out
  in patients with less recoil
• Can be used to determine the PIF, PEF, and Vt
• Looks circular with spontaneous breaths
• Looks squared but set at an angle with PC/PS
  breaths

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Abnormal FV Loops

• The expiratory curve scoops with high
  expiratory resistance
• If the patient is air trapping or has a leak, the
  loop will not meet at the left side where I
  starts/E ends
• If water/secretions are building up in the airway
  or circuit, the loop becomes very jagged

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Use of FV Loops
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Air Trapping (auto-PEEP)

• Causes
• increased exp resistance (either in the airways
  or in the circuit)
• Insufficient expiratory time
• Early collapse of unstable alveoli/airways during
  exhalation
• How to ID it on the graphics
• Pressure time while performing an expiratory
  hold, the waveform rises above baseline
• Flow-time the exp flow doesnt return to
  baseline before the next breath begins
• Volume-time the exp portion doesnt return to
  baseline
• FV Loop the loop doesnt meet at the baseline
• PV Loop the loop doesnt meet at the baseline
• How to Fix
• ID the cause and resolve
• Give a treatment, suction, change the HME,
  decrease It/increase flow, add PEEP

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Airway Resistance Changes

• Causes
• Bronchospasm
• Damp or blocked expiratory valve/filter
• ETT problems (too small, kinked, obstructed,
  patient biting)
• High flow
• Secretion build-up
• Water in the HME

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Airway Resistance Changes

• How to ID
• Pressure-time the PIP increases but the plateau
  stays the same
• Volume-time it takes longer for the exp curve
  to reach the baseline
• Flow-time it takes longer for the exp curve to
  reach baseline and the exp flow rate is reduced
• FV loop decreased exp flow with a scoop in the
  exp curve
• PV loop the loop will be fatterif it bulges to
  the right, its insp resistance and to the left
  its exp
• How to fix
• ID cause and fix it
• Give a tx, sx, drain water, change HME, change
  ETT, add a bite block, decrease PF rate, change
  exp filter

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Compliance Changes

• Decreased compliance
• Causes
• ARDS
• Atelectasis
• Abdominal distension
• CHF
• Consolidation
• Fibrosis
• Hyperinflation
• Pneumothorax
• Pleural effusion
• Just about every pulm dx there is
• How to ID it
• Pressure-time the PIP and plateau both increase
• PV loop lays more horizontal

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Compliance changes

• Increased compliance
• Causes
• emphysema
• Surfactant therapy
• How to ID it
• Pressure-time PIP and plateau both decrease
• PV loop stands more vertical (upright)

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Active Exhalation

• Causes
• Patient is exhaling below FRC due to air trapping
  (vol dumping)
• Pain
• Positional change
• Equipement calibration problem
• How to ID it
• Volume-time exp waveform goes below the
  baseline
• PV loop exp loop goes past the zero point
• FV loop exp part goes past the zero point
• How to fix it
• Reduce air-trapping
• Calibrate equipment
• Relieve pain

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Partial Obstruction

• Causes
• Suction catheter left in ETT
• Tissue flap
• Mucus plug
• Water/secretions in the circuit or airway
• How to ID It
• Flow-volume flow is not steady and constant,
  but varies as the obst moves around
• PV loop jagged instead of smooth
• FV loop jagged with fluctuating flow
• How to fix it
• Pull catheter out of ETT
• Suction
• Drain water
• Change HME
• Move the ETT

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Overdistension

• Causes
• Vt set too high (vol vent)
• Pressure set too high (press vent)
• Could occur in pressure vent with C or Raw
  changes
• How to ID it
• PV loop bird beak at the top of the loop
• How to fix it
• Reduce Vt (vol vent)
• Reduce pressure (P vent)

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Leaks

• Causes
• Expiratory leak air leak through a chest tube,
  BP fistula, ETT cuff leak, NG tube in trachea
• Inspiratory leak loose connections, ventilator
  malfunction, faulty flow sensor
• How to ID it
• Pressure-time decreased PIP
• Volume-time decreased Vtexp leaks keep exp Vt
  from returning to baseline
• Flow-time PEF decreases
• PV loop exp side doesnt return to the baseline
• FV loop exp part doesnt return to baseline
• How to fix it
• ID source of leak and fix it
• Do a leak test and make sure all connections are
  tight

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Rate Asynchrony

• Causes
• Neurological injury/swelling
• Air hunger
• How to ID it
• Pressure-time patient tries to inhale/exhale in
  the middle of the waveform, causing a dip in the
  pressure
• Flow-time patient tries to inhale/exhale in the
  middle of the waveform, causing erratic
  flows/dips in the waveform
• PV loop dips in the loop during either I or E,
  showing patient efforts to breathe
• FL loop dips in the loop during either I or E,
  showing patient efforts to breathe
• How to fix it if neurological, may need
  paralytic or sedative to reduce respiratory
  driveif air hunger, adjust settings (try
  increasing the flow rate/decreasing the It or
  increasing the set rate to capture the patient)
  or changing the mode - sometimes changing from
  partial to full support will solve the problem

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Flow Asynchrony

• Causesflow rate set incorrectly for the patient
  demands (volume vent onlyin pressure ventilation
  the flow is a function of the pressure setting
  and the patients lung characteristics you
  dont set it or have any control over it)
• How to ID It
• Pressure-time curve patient pulls off the
  pressure curve and it becomes concave
• Pressure-volume loop the inspiratory side will
  scoop inward with a decrease in pressure
• How to fix it increase the peak flow setting

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Trigger Asynchrony

• Causes sensitivity not set correctlypatient
  has to do excessive work to trigger a breath,
  autoPEEP
• How to identify it
• Pressure-time curve there will be a huge
  negative deflection before each pressure curve
  and/or negative pressure deflections that dont
  result in a breath delivery
• Flow-time curve there will be a blip where the
  patient attempts to trigger
• Pressure-volume loop there will be a large pig
  tail on the loop
• How to fix it set sensitivity so that minimal
  effort is required to trigger the ventilator,
  eliminate the autoPEEP

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Setting the Rise Time

• The faster the flow valve opens, the faster the
  set pressure is reached in pressure modes
• If the valve opens so fast that the flow is
  instantaneously delivered to the airway, you can
  get an overshoot in the pressure curve with
  ringing (Bart Simpson hair)you need to increase
  the rise time if this occurs this makes the
  flow valve open a bit more slowly
• If the valve opens too slow, the pressure curve
  becomes rounded when it should be square in a
  pressure modethis will decrease Vt deliveryyou
  need to decrease the rise time if this occurs

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Volume-Targeted Ventilation
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Suggested Websites

• www.adhb.govt.nz/newborn/TeachingResources/Ventila
  tion/RespiratoryFunctionMonitoringandGraphics.htm
• www.rtmagazine.com/issues/articles/2002-02_04.asp
• www.rcsw.org/Download/2006_RCSW_conf/Presentation
  20200620RCSW20Waveforms_in_ARDS20Dean20H.pdf
• www.aarc.org/education/webcast/archives/waveforms/
  03.01.05/ppt256,1,Using the Ventilator To Probe
  Physiology Monitoring Graphics and Lung
  Mechanics During Mechanical Ventilation
• www.brighamandwomens.org/respiratorytherapy/advmec
  ven2.ppt