HFOV Presented by SAYU ABRAHAM SLE5000 HFOV Presented by SAYU ABRAHAM

High Frequency Ventilation Defined by FDA as a ventilator that delivers more than 150 breaths/min. Delivers a small tidal volume, usually less than or equal to anatomical dead space volume. While HFV’s are frequently described by their delivery method, they are usually classified by their exhalation mechanism (active or passive).

Differences between HFOV and CMV CMV HFOV Rates 0 - 150 180 - 900 Tidal Volume 4 - 20 ml/kg 0.1 - 5 ml/kg Alv Press 0 - > 50 cmH2O 0.1 - 5 cmH2O End Exp Vol Low Normalized

HFV Gas Exchange Henderson first published his findings in 1915, assessing dead space relationship in ventilation. He stated, “there may easily be a gaseous exchange sufficient to support life even when Vt is considerably less than dead space.”

High Frequency Ventilation Types of HFV’s Approved for use in both Neonates and Pediatrics SLE5000 HFOV SensorMedics 3100A HFOV Bird Volumetric Diffusive HFPPV Types of HFV’s Approved for use in Neonates Only Bunnell Life Pulse HFJV Infrasonics Infant Star (discontinued) HFFI

SLE5000 Electrically powered, electronically controlled Conventional and HFOV ventilator Paw of 3 - 35 mbar Delta P from 4 – 180 mbar Frequency of 3 - 20 Hz I:E Ratio 1:1 Active exhalation

“HFOV”: SLE 2000 Insp. Line Resistor (Trigger sensibility) Bias flow 5l/min Peep adjustment Rotating jet Exp. Valve Block

Indications of HFOV Neonatal RDS/HMD Air leak syndromes MAS PPHN CDH

Ventilator Induced Lung Injury Barotrauma Volutrauma Stretch Injury Biochemical Injury

Pulmonary Injury Sequence of the neonatal patient: Absence of Surfactant Atelactasis Tidal Breathing High Distending Pressures Airway Stretch / Distortion Cellular Membrane Disruption Edema / Hyaline Membrane Formation Higher FIO2 , Volumes, Pressures Volutrauma, Barotrauma, Biotrauma PIE, BPD

Pulmonary Injury Sequence If we cannot prevent the injury sequence , then the target goal is to interrupt the sequence of events. High Frequency Oscillation does not reverse injury, but will interrupt the progression of injury.

Ventilator Induced Lung Injury Barotrauma Air leaking into pleural space Air leaking into interstitial space (PIE) Tearing at Bronchio-Alveolar Junction as lung is recruited and allowed to collapse Most occurs in dependent lung zones (transition zone)

Effect of 45 cmH2O PIP Control 5 min 20 min

Ventilator Induced Lung Injury Stretch Injury Alters capillary transmural pressures Changes in transmural pressure causes breaks in capillary endo and epithelium Increases leak of proteinacious material Promotes Atelectasis

Ventilator Induced Lung Injury Volutrauma Caused by cycling of the lung (change in surface area), independent of pressure required Alters Surfactant function Promotes Atelectasis Increases capillary leak of proteinacious material Dreyfuss,D ARRD 1988;137:1159

Ventilator Induced Lung Injury Premature baboon model Coalson J. Univ Texas San Antonio

Ventilator Induced Lung Injury Premature baboon model Coalson J. Univ Texas San Antonio

Pulmonary Injury Sequence There are two injury zones during mechanical ventilation Low Lung Volume Ventilation tears adhesive surfaces High Lung Volume Ventilation over-distends, resulting in “Volutrauma” The difficulty is finding the “Sweet Spot” Froese AB, Crit Care Med 1997; 25:906

Ventilator Induced Lung Injury HFOV with Surfactant as Compared to CMV with Surfactant in the Premature Primate HFOV resulted in Less Radiographic Injury Less Oxygenation Injury Less Alveolar Proteinaceous Debris Jackson C AJRCCM 1994; 150:534

HFOV

Theory of Operation Oxygenation is primarily controlled by the Mean Airway Pressure (Paw) and the FiO2 Ventilation is primarily determined by the stroke volume (Delta-P) and the frequency of the ventilator.

HFOV effectively decouples: Oxygenation & Ventilation

HFOV Principle: Pressure curves CMV / HFOV Injury Injury

Principles of the SLE5000 HFOV “Super-CPAP” system to maintain lung volume

Optimized Lung Volume Strategy: Increase Lung Volume above critical opening pressure to the Optimum and keep it there in Inspiration and Expiration. Benefits: - homogenous gas distribution - reduced regional atelectasis - maximized gas exchange area and pulmonary blood flow - better matching of ventilation/perfusion - reduction of intrapulmonary shunting - reduced Oxygen exposure

Optimized Lung Volume Strategy: Decrease Tidal Volumes to less or equal to dead space and increase frequency. Benefits: - enhanced gas exchange due to combined gas transport mechanisms - no excessive volume swings - reduced regional over-inflation and stretching - reduced Volutrauma

Oxygenation The Paw is used to inflate the lung and optimize the alveolar surface area for gas exchange. Paw = Lung Volume

Paw = CDP CDP = Lung Volume CT 2 CT 1 CT 3 Continuous Distending Pressure

“Open up the lung up and keep it open!” Burkhard Lachmann, 1992

Primary control of CO2 is by the stroke volume produced by the Delta P Setting.

Regulation of stroke volume The stroke volume will increase if The amplitude increases (higher delta P) Stroke volume

Secondary control of PaCO2 is the stroke volume produced by the set Frequency.

Regulation of stroke volume The stroke volume will increase if The amplitude increases (higher delta P) The frequency decreases (longer cycle time) Stroke volume

HFOV Principle: I + + + + + Amplitude Delta P = Tv = Ventilation CDP=FRC= Oxygenation E - - - - - HFOV = CPAP with a wiggle !

Pressure transmission Gerstmann D.

Airway Pressure Transmission HFOV : Amlitude Delta P = TV = Ventilation I E + _ CDP / MAP = Lungvolume = Oxygenation ET Tube Trachea Alveolus Transmission

HFOV Mechanisms of Gas Transport

Mechanisms of HFOV Gas Exchange There are six mechanisms of gas exchange during HFOV Convective Ventilation Asymmetrical Velocity Profiles Taylor Dispersion Pendeluft Molecular Diffusion Cardiogenic Mixing

Practical preparation Avoid leak around the E.T tube Tc PO2,CO2,Pulse oxymeter and invasive blood pressure monitoring Baseline CXR Optimize blood pressure and perfusion(volume replacement and inotropes) Muscle relaxant/sedation Reusable low compliance circuits must be used

NURSING CARE Perform through suction before connecting to the oscillator. Assess patient upon commencement of HFOV.Monitor vital signs, chest wiggle must be evaluated upon initiation and followed closely thereafter. If chest wiggle diminishes it may be ETtube moved or obstructed. Chest wiggle on one side indicates patient developed pneumothorax,thus chest wiggle assessment should be performed after repositioning. Auscultation the chest by putting in standby mode. A closed suction should be used. It is not necessary to disconnect the patient to suction as this will potentially derecruit lung volumes. The point at which the ET tube is cut and secured at lips should be initially noted this measurement is reference.

Continued……… Evaluation of lung expansion on CXR Check capillary refill, skin color and temperature Comparing central and peripheral pulses Monitoring of ECG Tracing Frequent CXR’s blood gases in initial stabilization period Optimal lung volume for oxygenation is 8-9 rib inflation Blood pressure and perfusion should be optimized prior to HFOV,any volume replacement should be completed and inotropes commenced if necessary

Continued……… Muscle relaxants are not indicated since spontaneous respiratory effort will be a clinical indicator of adequacy of ventilation Sedation with opiates is often indicated THANKYOU