Several types of HFV  HFPPV  HFJV  HFOV

Principles of Oscillation Richard F. Kita BS, RRT, RCP Edited by Paula Lussier, CRT, NPS, RCP, BS

HFOV  Hi-Frequency Oscillatory Ventilation  Small volumes of gas are moved in and out of ETT  Frequency: cycles/min or 3-15 Hz  Vt<Vd  Active Inspiration and Exhalation

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

HFOV Indications  Persistent air leak  PIE

HFOV Indications  Persistent respiratory failure associated with:  RDS  Pneumonia  MAS  Congenital diaphragmatic hernia  Pulmonary hemmorage

HFOV Contraindications  Shock

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.

HFOV - Theory of Operation

 Gas movement occurs by : “shaking gas into and out of the alveoli”  Enhanced molecular movement  Enhanced convection

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

HFOV - Theory of Operation  All pressures are measured at circuit wye.  Distal pressures are lower due to attenuation

Goals of HFOV  Decrease Pulmonary Injury Sequence (PIS)  Oxygenation  Ventilation

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

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

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)

Oxygenation Goals  Optimal Lung Volume strategy:  Start MAP:  Improves Ventilation/Perfusion matching  Dependant on FIO2  Neonatal: 1-2 cwp higher than conventional ventilation  Improves oxygenation

Optimal Lung Volume  For neonates:  Early intervention: MAP cwp  Early lung injury: MAP cwp  Late lung Injury: Map > 18 cwp

Optimal Lung Volume  Determined by CXR  Right diaphragm at ribs of expansion  Intercostal bulging / flattened diaphragms  Once reached, wean FIO2 before MAP

Over Distension  Can cause pCO2 to increase  Compress pulmonary capillary blood vessels  Increase PVR

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

Ventilation  Frequency is measured in Hz  1 Hz = 60 cycles/min  Usual neonatal range: 8-15 Hz  Preterm infant with severe RDS: Hz  Preterm infant with mild RDS or early chronic changes: Hz  Term infant with severe pneumonia or MAS: 8 Hz

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

Ventilation  Amplitude  Neonates:  In general start at same level as PIP on conventional ventilation  Early intervention: Delta P cwp  Lung injury: Delta P > 25 cwp

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

Ventilation  Percent Inspiratory Time is always set to 33%, resulting in an I:E Ratio of 1:2

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 < 1000 grams, flow = 6-8 LPM  Premature infant grams, flow = LPM  Term infant with MAS flow = LPM

Weaning  After reaching Optimal Lung Volume, wean FIO2 < 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