Ventilation

The key advantage of appropriate HFJV is minimised lung trauma through ultra-low tidal volume ventilation at optimal lung volume, minimising also the level of required supplemental oxygen. An additional advantage is that spontaneous breathing is more easily achieved in parallel with HFJV than with HFOV, and may be more comfortable for the infant as end-expiratory pressure is lower than during HFOV. This also potentially allows better lung perfusion than during HFOV due to lower pulmonary vascular resistance.


Advantages of HFJV
The key advantage of appropriate HFJV is minimised lung trauma through ultra-low tidal volume ventilation at optimal lung volume, minimising also the level of required supplemental oxygen. An additional advantage is that spontaneous breathing is more easily achieved in parallel with HFJV than with HFOV, and may be more comfortable for the infant as end-expiratory pressure is lower than during HFOV. This also potentially allows better lung perfusion than during HFOV due to lower pulmonary vascular resistance. During HFJV, the clinician recruits the lung (as required) and identifies an optimal PEEP for alveolar stabilisation. Collapsed lung units are recruited predominantly using PEEP ("ramping" up and down, similar to recruitment with mean airway pressure during HFOV), with the addition of low rate (0-5 breaths/min) background gentle sigh breaths via superimposed conventional ventilation (CV) if required for short intervals. The high velocity low tidal volume jet "pulses" minimise the effective dead space, thereby increasing ventilation efficiency whilst also protecting the alveolar spaces from cyclic volutrauma. Any injured areas of the lungs can rest and heal. In addition, the asymmetric flow profile associated with the rapid inspiration and slow expiration enhances mucociliary clearance. Use of HFJV from birth may limit the severity of lung disease by minimising volutrauma. HFJV may provide benefit in established non-homogeneous lung disease (e.g. pulmonary interstitial emphysema, pneumonia, meconium aspiration syndrome and evolving BPD), by resolution of air trapping and over distension. Additionally, injured areas with highresistance airways are "rested" in inhomogeneous lung disease as the high inspiratory gas flows preferentially ventilate the healthier areas of the lung and bypass the high-resistance airways. PEEP splints the airways open, allowing gas to escape over the longer expiratory phase of each cycle. It is important to remember that whilst HFJV inspiratory pulses occur 4-11 times a second, the tidal volume is delivered in a very short time (ranging from 0.20 to 0.34 s). Hence, the Fresh inspiratory gas is directed down the centre of the airways whilst the slower moving, passively exchanged gas moves outwards along the airway walls. This counter current pattern facilitates airway clearance. Neonatal Guideline inspiratory flows are more similar to the inspiratory flows of very high-frequency HFOV: at an HFJV inspiratory time of 20 ms, the equivalent inspiratory flows in HFOV would be achieved at frequencies of 16.7 Hz (1:2) or 25 Hz (1:1).

Complications associated with HFJV
 ETT Obstruction (same as CV).  Tracheal Injury (same as CV).  Hypercarbia due to inadequate tidal volume consequent to:  inadequate HFJV amplitude,  insufficient inspiratory time,  inadequate HFJV rate.  Hypocarbia resulting from excessive tidal volume consequent to  excessive HFJV amplitude,  excessive inspiratory time,  excessively high HFJV rate. The highest risk of hypocarbia is during initiation of HFJV (due to unrecognised increased efficiency of gas exchange) or during periods of rapid improvement/lung recruitment when delivered tidal volume may increase unless the HFJV pulse amplitude is decreased. Hypocarbia within the first few days of life is associated with the subsequent development of periventricular leukomalacia (PVL) in preterm infants (2) .  Hyperinflation and/or Inadvertent PEEP (air trapping) and potential development of airleak syndrome (pneumothorax, pneumomediastinum, pulmonary interstitial emphysema) consequent to:  Inappropriately high ventilator rate  Excessive PEEP (hyper-inflation without gas trapping)  Atelectasis with risk of hypoventilation and lung injury consequent to:  Inadequate PEEP.

Parent Education
 Explain the purpose and function of the HFJV to the parents, stressing that the neonate will appear to have rapid vibrations of the chest wall, but will also be able to breathe spontaneously.  Promote parental involvement in care as much as possible.  Refer parents to Bunnell Parent Information Page.

Selection Criteria/Indications for Initiating HFJV
HFJV may be started at the discretion of the Consultant, for lung diseases including but not limited to:  Air leak syndrome including PIE or unresolved pneumothorax noted on CXR.  Infants with lung disease who have failed CV and/or HFOV -particularly if they have non-homogeneous lung disease.

Commencing HFJV from Conventional Ventilation (CV)
 Place a transcutaneous CO 2 monitor (TcpCO 2 ) on the infant and continue pulse oximetry monitoring.  Plug the HFJV into the "Uninterrupted Power Supply".  Install circuit into the HFJV (refer to Setting up the HFJV Circuit).  Attach water and place below level of HFJV humidifier. Neonatal Guideline  Attach a clean 2.5, 3.0 or 3.5 mm (as appropriate) HFJV LifePort adaptor to a clean test lung. Attach the pressure monitoring tube to the patient box.  Connect this testing set to the installed circuit.  Turn the ON switch on.  Press SILENCE.  Run the SYSTEM test by pressing the TEST button -the numbers will change in sequence from 0 through to 9.  Press the alarm SILENCE to silence at the end of the test.  Run the FUNCTIONAL test by pressing the ENTER button to start default settings (PIP 20 cmH 2 O, Rate 420 breaths/min, On-Time 0.02 s).  Verify that READY condition can be met (approx. 1½ min.), monitored pressures stable and PEEP is 0.0.  Press STANDBY.  Connect the appropriate sized LifePort adaptor onto the infant's tracheal tube whilst still running conventional ventilation (HFJV remains in STANDBY) remembering to keep pressure port plugged until HFJV circuit is connected.  Connect the circuit to the infant's LifePort adaptor whilst in Standby mode. Connect pressure adjust the SIMV PIP to achieve a tidal volume of ~ 5 mL/kg.  Note baseline monitoring on the HFJV ventilator monitoring display whilst on SIMV (esp, PIP, and mean airway pressure).  Set the HFJV rate (see "Strategies").  Set HFJV PIP (in the 'Controls' section) guided by the average displayed SIMV PIP shown on the conventional ventilator monitoring and monitored on the HFJV (PIP on the HFJV should initially be set at approximately the average PIP used during CV when mandatory (non-triggered) breaths are being delivered).  Check that FiO 2 is the same on both ventilators.  Then in quick succession:  Reduce CV rate to 0-2 breaths/min (see "Strategies").  Turn CV PEEP up by 1-2 cmH 2 O initially.  Press ENTER on the HFJV ventilator.  Increase PEEP to meet the mean airway pressure noted on CV prior to switch to HFJV.  Turn minute volume low alarm down to '0 L/min' then high alarm '> 2 L/min'.  Turn apnoea alarm delay to 'off' on the conventional ventilator.

Adjust HFJV to target desired PaCO 2
 Observe chest movement and increase HFJV PIP as required to achieve appropriate level of chest "wiggle" and appropriate control of PaCO 2 using TcpCO 2 .  Ventilatory adjustments that increase CO 2 removal include:  ↑ HFJV PIP  ↑ HFJV IT  ↑ HFJV Rate (least preferred unless acute RDS in extreme preterm infant)  Initial adjustments to increase CO 2 removal should be made by increasing HFJV PIP  If HFJV PIP increases above 30 cmH 2 O, subsequent HFJV adjustments to achieve adequate ventilation and CO 2 removal should alternate stepwise increases in HFJV PIP with stepwise increases in inspiratory time, up to a maximum inspiratory time of 0.034 s and a maximum HFJV PIP of 40 cmH 2 O.

Inadvertent PEEP
Always monitor HFJV PEEP and CV PEEP . An HFJV PEEP reading which is higher than the CV PEEP is known as "Inadvertent PEEP". Inadvertent PEEP indicates air trapping. Gas trapping occurs when tidal volumes have insufficient time to exit the lungs. Maintain optimal lung volumes as both over-inflation and under-inflation are injurious to the newborn lung. In the case of grossly overexpanded lungs, you will need to deflate considerably before any improvements in oxygenation will result.
 To minimise overexpanded lungs: ↓ CV rate to 0 then ↓ HFJV rate to lengthen exhalation time. HFJV I-time may be increased in compensation to ensure that CO 2 does not increase. Increases in HFJV I-time have minimal impact on the absolute expiratory time, which is a key determinant of the amount of air that can be exhaled during the expiratory phase.  In most cases do not decrease PEEP as hyperinflated lungs are usually a result of air trapping due to airway collapse, not excessive PEEP.

Group B Streptococcal) and Pulmonary Haemorrhage:
 Choose an initial CV Rate of 0-5 breaths/min depending on the severity of the disease process and the degree of under inflation. Maintain alveolar inflation using a PEEP of 6-12 cmH 2 O depending on the severity of the disease. HFJV PIP is started at ≈ CV PIP (see above).  For patients with a very poor compliance, it may take a higher background CV PIP level to recruit atelectatic alveoli (e.g. 26-34 cmH 2 O), but once recruited, optimal PEEP can be used to prevent loss of lung recruitment. The CV PIP and CV Rate can then be weaned appropriately. As compliance improves, FiO 2 should be decreased before weaning PEEP. CV PIP and CV rate should be kept as low as possible. Clinically, improved compliance can be recognised by an increase in Servo Pressure (refer to Understanding Servo Pressure).

Air leak:
 Choose an initial CV Rate of 0 breaths/min (i.e. CPAP mode), or up to 2 breaths/min if coexistent atelectasis is a concern and there is no gross airleak (no pneumothorax).  Maintain alveolar inflation using a PEEP of 6-8 cmH 2 O depending upon the severity of the disease.  Start HFJV PIP below the CV PIP and increase HFJV PIP as required to achieve slight wiggle. This strategy is appropriate for most infants with PIE or pneumothorax.  Preference increase in HFJV I-time rather than increase in HFJV rate to improve CO 2 removal once adequate chest wiggle is achieved.
Non-Homogeneous Lung Disease e.g. Meconium Aspiration Syndrome and focal Pneumonia:  Use lower HFJV rate (240-360 breaths/min) to avoid gas trapping.  Use higher PEEP (8-12 cmH 2 O) to splint airways and allow meconium/secretions to evacuate in the swirling HFJV expiratory flow.

Cleaning and Storage
When High Frequency Jet Ventilation (HFJV) has been ceased, leave the Jet Ventilator by the bedside until completely satisfied the infant will not require the ventilator. A satisfactory blood gas sample, good TcpCO 2 readings and oxygen saturations will confirm the decision to cease HFJV.
 The HFJV with its accompanying conventional ventilator can now be cleaned and set up ready for use.  HFJV circuit -The whole patient circuit is disposable including the humidifier cartridge and green oxygen tubing. The Jet adaptor is also disposable.  Non-disposable parts -Wipe over the patient whisper box, HFJV, Conventional Ventilator and its humidifier together with temperature probe and adaptor with hospital grade disinfectant.  Set up as per Setting up HFJV Circuit procedure.  Always check the conventional ventilator settings and function prior to moving for storage. Neonatal Guideline

Setting-Up the HFJV Circuit
 Open new circuit which comes as one complete piece with all connections secured.  Open humidifier door to slide cartridge in and lock.  Firmly attach the green tubing to "Gas Out" on the front left of the ventilator.  Attach the thin clear purge tubing to "Purge" on the front right of the ventilator and to the Whisper Jet Patient Box (patient box) on the ventilator side.  Place a red IV cap on the end of the circuit (water pump tube) and then attach the Pinch tubing to the other side of the red cap to keep the circuit clean.  Place the circuit into a plastic drawstring bag for protection until used. Note: Leave the jet set up at this point when placing the jet into storage. The pinch tube will become damaged if stored loaded into the pinch valve. It is important to only proceed with the next steps just prior to the HFJV being used.
 Open water pump and insert the clear water inlet tube from the bottom right of the humidifier cartridge. Mind fingers when snapping the pump door closed.  Press the "push to load" button on the top of the patient box and gently stretch the pinch tube into the pinch valve under the plexiglass cover on the patient box.  Connect the water inlet tube to the short giving set and connect the water transfer tubing to the 1 L water for irrigation bag and unclamp the transfer tubing. (Keep bag below ventilator to avoid gravity filling the humidifier cartridge).