HIGH FREQUENCY OSCILLATORY VENTILATION(HFOV) in NEONATES

HFOV is a type of non-conventional mechanical ventilation. HFOV uses constant Distending pressure (MAP) with pressure variations oscillating around the MAP at very high rates (up to 900 cycles/ min)

 ie., instead of delivering a set number of breaths at a certain pressure or volume, HFOV provides volumes equal to or less than the anatomical dead space using respiratory rates with a range of 3 to 10 Hertz (Hz)

 In conventional ventilation, large pressure change (ie., the difference between PEEP and PIP) creates physiological Tidal volume, and gas exchange is dependent on bulk convection ( expires gas exchange for inspired gas )

The lungs are partially inflated to maximize surface area for gas exchange, and the fast breaths allow for a large volume of gas exchange to occur. 

HFOV- an alternate mechanism for gas exchange such as

Molecular diffusion,

Taylor dispersion,

Turbulence

Asymmetric velocity profiles

Pendelluft

Cardiogenic mixing & Collateral ventilation

Conventional ventilation causes VILI ( Ventilator Induced Lung Injury) and CLD ( Chronic Lung Disease) which may be reduced in HFOV

HFOV with increased airway pressure impaired cardiac output and may cause hypotension. hence, the neonate may need inotropic and volume expansion therapy.

HFOV is only a rescue therapy. Can be used in

• Failure of conventional ventilation in term neonates

PPHN (Persistent pulmonary hypertension of neonates )

MAS( Meconium Aspiration Sydrome)

• Air leak syndromes

Pneumothorax

Pulmonary interstitial emphysema (PIE)

• In preterm (failure of conventional ventilation)

Severe RDS (Respiratory distress Syndrome); may increase the risk of IVH

PIE

Pulmonary Hypoplasia

Or to reduce barotrauma when conventional ventilator settings are high.

 

TERMINOLOGY TO REMEMBER FOR HFOV

• Frequency – rate –Hz (1 Hz= 60 breaths or cycle) = ie., when 10 Hz is set; 600 cycle/minis delivered
• MAP –PEEP/Mean Airway Pressure
• Amplitude- Delta P or Power variation around the MAP
• Oxygenation – Depends on the MAP &FiO2 where MAP= CPAP/PEEP
• Ventilation – is different from oxygenation and also from conventional ventilation. CO2 dependent on amplitude and frequency

INITIAL SETTINGS

Optimal lung volume strategy – aims to maximize recruitment if alveoli

Set MAP 2-3 CmH20 above the MAP on conventional ventilation around 1-2 Cm H2o until oxygenation improves

Set frequency up to 10 Hz

Amplitude on adequate chest wall vibration

RECRUITMENT MANOEVERE’S

Low volume strategy – aim to minimize lung trauma

MAKING ADJUSTMENT

Oxygenation 

Poor – Increase FIO2

           Increase MAP (1-2 CmH2O)

Over – Decrease FIO2

           Decrease MAP (1-2 Cm H20)

Ventilation

Under ventilation – increase the amplitude

                            Decrease frequency (1-2 Hz) if amplitude maximal

 Over ventilation – decrease the amplitude

                            Increase frequency (1-2 Hz) if amplitude minimal

CHEST RADIOGRAPH

Initial CXR – baseline lung volume

Follow up 4-6 hrs – assess the expansion

CXR – if acute change in patient condition

WEANING

Decrease FiO2 to < 40% before weaning MAP

Decrease MAP when CXR – evidence of over expansion

Decrease MAP to 1-2 Cm H20 increments to 8-10 Cm H2O

In air leak syndrome (low lung volume strategy) – reducing MAP takes priority over weaning the FiO2

Weaning the amplitude 2-4 CmH2O

Do not wean the frequency

Discontinue weaning; when MAP 8-10 CmH2O and Amplitude 20-25

In a stable infant; if oxygenation in ABG is good then change to conventional / CPAP to minimal to extubate

SUCTIONING

Indicated only when chest wiggle (diminished chest movement )

Elevated PCO2 / decreased PaO2 suggest ETT obstruction or any visible/ audible secretion.

Avoid in the first 24 hours, unless clinically indicated

Inline suctioning must be used.

An important consideration to swift from conventional to non-conventional

Oxygenation index (OI)

OI> 10 –HFOV

OI>15 – iNO

OI>25 - ECMO.

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