Principles of Oscillation

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Principles of Oscillation

• Richard F. Kita BS, RRT, RCP
• Coordinator
• Department of Respiratory Care
• Loyola University Medical Center

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Several types of HFV

• HFPPV
• HFJV
• HFOV

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HFPPV

• Hi-Frequency Positive Pressure Ventilation
• Conventional Ventilation
• Rates gt/ 120 bpm
• Usually some type of hybrid

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HFJV

• Hi-Frequency Jet Ventilation
• Small volumes of gas are injected at hi-rate,
  through a jet nozzle into ETT
• Frequency 150-600 cycles/min or 2.5 - 11 Hz
• Vt lt Vd
• Passive exhalation

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HFOV

• Hi-Frequency Oscillatory Ventilation
• Small volumes of gas are moved in and out of ETT
• Frequency 180-900 cycles/min or 3-15 Hz
• VtltVd
• Active Inspiration and Exhalation

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HFOV Development

• Improve gas exchange in patients with severe
  respiratory failure
• Decrease ventilator lung injuries
• prevent volutrauma
• decrease exposure to high FIO2
• Reduce lung morbidity
• Allow severe pulmonary airleaks to heal

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HFOV Indications

• Persistent air leak
• Bronchopleural fistula
• PIE

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HFOV Indications

• Persistent respiratory failure associated with
• RDS
• Pneumonia
• ARDS
• MAS
• Lung hypoplasia
• Congenital diaphragmatic hernia
• Hydrops fetalis

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HFOV Contraindications

• Gas trapping / airway obstruction
• Shock

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HFOV - Theory of Operation

• Specifically Sensormedic 3100A
• The driver/oscillator is magnetically driven like
  an audio speaker
• Provides a push/pull of the entire bias gas flow
• Push/pull creates an oscillatory (sinusoidal )
  wave
• E.G. Throwing a stone in a pond.

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HFOV - Theory of Operation
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HFOV - Theory of Operation

• Gas movement occurs by
  shaking gas into and out of the alveoli
• Enhanced molecular movement
• Enhanced convection

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HFOV - Theory of Operation

• Oscillatory Wave is characterized by three
  factors
• Mean Airway Pressure (Paw) - the average
  pressure throughout one cycle
• Amplitude - the size of the pressure wave
• Frequency - the number of cycles per minute
• All controlled by electrical current through the
  electromagnet

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HFOV - Theory of Operation

• All pressures are measured at circuit wye.
• Distal pressures are lower due to attenuation

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Goals of HFOV

• Decrease Pulmonary Injury Sequence (PIS)
• Oxygenation
• Ventilation

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Pulmonary Injury Sequence

• Tidal volume breathing in a surfactant deficient
  lung can lead to injury
• Surfactant replacement can reduce lung injury
• Decreasing tidal volume breathing can reduce lung
  injury
• Optimizing lung volume can reduce lung injury

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Oxygenation Goals

• Maximize gas exchange area
• Oxygenation is related more to alveolar
  recruitment and mean airway pressure
• Minimize pulmonary vascular resistance
• Optimize cardiac/pulmonary blood flow

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Oxygenation Goals

• Directly related to lung inflation
• utilize MAP to create a continuously distending
  lung pressure
• Find the Optimal Lung Volume (maximize gas
  exchange area)
• improve alveolar compliance
• decrease regional over distension
• decrease lung injury / PVR
• Generally increasing MAP
• Recruits alveoli (improved lung volume)

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Oxygenation Goals

• Optimal Lung Volume strategy
• Start MAP
• Improves Ventilation/Perfusion matching
• Dependant on FIO2
• Neonatal 1-2 cwp higher than conventional
  ventilation
• Pediatric 5-8 cwp higher than conventional
  ventilation
• Improves oxygenation

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Optimal Lung Volume

• For neonates
• Early intervention MAP 12-14 cwp
• Early lung injury MAP 15-17 cwp
• Late lung Injury Map gt 18 cwp

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Optimal Lung Volume

• Determined by CXR
• Right diaphragm at 8 - 9 ribs of expansion
• Intercostal bulging / flattened diaphragms
• Radiopacities
• Once reached, wean FIO2 before MAP

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Over Distension

• Can cause pCO2 to increase
• Compress pulmonary capillary blood vessels
• Increase PVR

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Ventilation

• For CV Minute Ventilation Rate x Vt
• For HFOV Minute Ventilation Rate x (Vt)
  squared
• Increase frequency, decrease Vt
• Decrease frequency, increase Vt

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Ventilation

• Frequency is measured in Hz
• 1 Hz 60 cycles/min
• Usual neonatal range 8-15 Hz
• Preterm infant with severe RDS 12-15 Hz
• Preterm infant with mild RDS or early chronic
  changes 10-12 Hz
• Term infant with severe pneumonia or MAS 8 Hz
• General pediatric range 5-10 Hz
• 2-12 Kg. 10 Hz
• 13-30 Kg. 7-8 Hz
• gt30 Kg. 6 Hz

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Ventilation

• Amplitude of the oscillatory wave (delta P) is
  set by adjusting the Power Control
• Increasing Delta P, increases the amplitude of
  the oscillatory wave
• Measured at circuit wye
• Remember, the Delta P is markedly attenuated by
  the time it reaches the alveoli
• Increasing the Delta P, increases chest movement
  and decreases CO2
• Small Delta P changes can result in large CO2
  changes

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Ventilation

• Amplitude
• Neonates
• In general start at same level as PIP on
  conventional ventilation
• Early intervention Delta P 15-25 cwp
• Lung injury Delta P gt 25 cwp
• Pediatrics
• In general start about 5-8 cwp gt than
  conventional ventilation PIP

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Ventilation

• In all patients adjust the Delta P for Chest
  Wiggle
• Chest wiggle is the chest movement observed on
  the patient
• Chest Wiggle Assessment
• 1 to the nipple line
• 2 to the navel
• 3 to or past the groin
• Goal is for chest wiggle to reach the navel

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Ventilation

• Percent Inspiratory Time is always set to 33,
  resulting in an IE Ratio of 12

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Ventilation

• Bias Flow or the continuous flow through the
  circuit is measured in LPM.
• For setup and calibration the flow is adjusted to
  20 LPM
• In general larger patients need more flow
• Premature infant lt 1000 grams, flow 6-8 LPM
• Premature infant 1500-2500 grams, flow 10-12
  LPM
• Term infant with MAS flow 15-20 LPM
• Pediatric patients flow starts at 20 LPM

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Weaning

• After reaching Optimal Lung Volume, wean FIO2 lt
  40 as tolerated
• Wean MAP and Delta P as patient improves
• As compliance increases mean lung volume will
  increase
• MAP goals of 8-12 cwp
• Frequency is usually not changed once initially
  set
• Go slow
• Can be weaned directly from HFOV to extubation,
  or another mode of ventilation