CONSULTANT NEONATOLOGIST

DR ALLAM ABUHAMDA

SLE 5000HFOV

Introduction

• 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)

Introduction

• 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

Indications of HFOVNeonatal

RDS/HMDAir leak syndromesMASPPHNCDH

Ventilator Induced Lung Injury

• Barotrauma• Volutrauma• Stretch Injury• Biochemical Injury

Absence of SurfactantAtelactasisHigh Distending PressuresAirway Stretch / DistortionCellular Membrane DisruptionEdema Higher FIO2 , Volumes, Pressures PIE, BPD

Pulmonary Injury Sequence of the neonatal patient:

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

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

HFOV Principle:Pressure curves CMV / HFOV

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

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

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

“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

CDP=FRC=Oxygenation

HFOV Principle

+ + + + +

- - - - -

AmplitudeDelta P =Tv =Ventilation

I

E

Pressure transmission

Gerstmann D.

Airway Pressure Transmission HFOV :

TransmissionET Tube Trachea Alveolus

CDP / MAP= Lungvolume= Oxygenation

Pressure

AmlitudeDelta P =TV =Ventilation

I

E

+ + +

+ + + + + + +

_ _ _

_ _ __ _ _

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 preparationAvoid leak around the E.T tubeTc PO2,CO2,Pulse oxymeter and invasive

blood pressure monitoringBaseline CXROptimize blood pressure and

perfusion(volume replacement and inotropes)

Muscle relaxant/sedationReusable 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.

Precautions

If chest wiggle diminishes it may be ET tube moved or obstructed.

Chest wiggle on one side indicates patient developed pneumothorax,thus chest wiggle assessment should be performed after repositioning

Precautions

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

Precautions

Evaluation of lung expansion on CXR

Check capillary refill, skin color and temperature

Comparing central and peripheral pulses

Monitoring of ECG TracingFrequent CXR’s blood gases in initial stabilization period

Precautions

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

Precautions

Muscle relaxants are not indicated since spontaneous respiratory effort will be a clinical indicator of adequacy of ventilation

Sedation with opiates is often indicated

THANKS