Ventilators

Indications:

• Need for independent oxygenation and ventilation

• Difficulty oxygenating well despite high pressure settings

Unique Features:

• Exhalation on HFOV is active.

How to Initiate:

• Can set 5 settings:

  • MAP

    • For neonates, initial MAP should be 2-4 cm above the MAP on CMV

    • For infants, initial MAP should be 4-6 cm above the MAP on CMV

    • Increase by 1-2 cm usually until achieving goal SpO2, but can increase as high as 2-4 cm if on high FiO2 (close to 100%) (max MAP ~40 cm)

    • Goal expansion on CXR ~T7-9

      • Overdistension can impede venous return to the heart (small appearing heart on CXR and hypotension)

  • Amplitude

    • Start with an amplitude of ~(MAP x 2), then assess chest wiggle and adjust from there in increments of 2

    • Change amplitude/delta P by 2-3 cm H2O to change CO2 ± 2-4 mm Hg  

    • Change amplitude/delta P by 4-7 cm H2O to change CO2 ± 5-9 mm Hg

    • Change amplitude/delta P by 8-10 cm H2O to change CO2 ± 10-15 mm Hg

  • Hz (cycles per second; rate of 360 breaths per minute = 6 breaths / second = 6 Hz)

    •  Initial settings:

      • 8 Hz (480 BPM) for children between 6-10 kg

      • 10 Hz (600 BPM) for term infants ( > 2.5 kg)

      • 12 Hz (720 BPM) for premature infants (1.5 -  ≤ 2.5 kg)

      • 14 Hz (840 BPM) for preterm infants ( 1.0 - < 1.5 kg)

      • 15 Hz (900 BPM) for preterm infants < 1.0 kg

    • Lower frequency leads to longer iT, increasing your tidal volumes (thus, improving ventilation)

    • If not ventilating at the initial starting frequency on a Power/Amplitude/Delta P that clearly results in good chest wall vibrations then decrease the frequency by 2 Hz, at a time, to significantly increase the delivered TV.  

      • Remember during HFOV, alveolar ventilation (Ve) ≈ (TV)2F as compared to conventional ventilation where Ve ≈ TV(R).

  • iTime

    • Standard I:E ratio of 1:2 (fixed ratio; so, 33% of time spent in inspiration)

      • Usually standard and set by RT; diverging from this increases risk of breath stacking and subsequent pneumothorax

    • I.T. can be decreased to 30% to heal airleaks by lengthening the I:E ratio (30%:70%).

    • For premature infants < 1000 grams, can consider setting I.T. initially at 30% to minimize air trapping by also using a longer initial I:E ratio (30%:70% or 1:2.3).

  • Bias flow (LPM)

    • The bigger the infant, the higher the flow

    • Usually set by RT

Complications:

• • Hyperinflation, hypocarbia, hypotension, air leaks, secretions

Indications: Failure of the conventional mechanical ventilator (CMV) for PPHN, meconium aspiration, pneumonia, or pulmonary hemorrhage

How to Use:

• Alveolar Ventilation (Ve) on a HFJV is different from conventional ventilator (RR X Vt):

  • Ve = (Vt)2 x freq 

  • Notice tidal volume plays a much bigger role than the rate in high frequency ventilation

• Initial Jet Rate for First Intention Use:  

  • < 24 weeks GA or < 600g:           300 BPM (I:E of 1:9)  

  • 24-26 weeks GA or 600-1000g:  360 BPM (I:E of 1:7)  

  • ≥ 27 weeks GA or ≥ 1000g:         420 BPM (I:E of 1:6) 

  • Frequency changes to be made in increments of 60 BPM (1 Hz)

    • Can adjust by 20 BPM when in 240-300 range

    • Decrease frequency (so, less time spent in inhalation = decrease I:E ratio) to reduce risk of PTX and PIE or reduce hypocarbia when delta P is minimal (5-6 cm)

    • Increase frequency to increase ventilation when facing severe hypercarbia despite high delta P

  • Delta P = PIP - PEEP = Tidal volume

    • iT determines tidal volume as well (maximally reached at iT of 0.034)

    • Increased delta P (usually by increasing PIP and/or decreasing PEEP) leads to increased minute ventilation

  • PIP: can start with 22-24 cm H2O or enough PIP to generate adequate chest wiggle or 2 cm less than the PIP on conventional/HFOV

    • To change PaCO2 ± 2 - 4 mm Hg adjust PIP by 1-2 cm H2O 

    • To change PaCO2 ± 5 - 9 mm Hg adjust PIP by 3-4 cm H2O 

    • To change PaCO2 ± 10 - 14 mm Hg adjust PIP by 5-6 cm H2O 

    • Check a blood gas 15-20 minutes after any significant change in PIP. 

  • PEEP: can start with 5 cm H2O, then obtain CXR and adjust from there (rib expansion to T9) as well as based on oxygenation

    •  When converting to JET, aim for 2 cm MAP on conventional/HFOV

    • Set on the conventional ventilator running in line with the JET - set whatever pressure necessary to generate your desired PEEP on the JET (so, might need PEEP 7 on the conventional for the JET to read a PEEP of 5)

    • Setting a PEEP too high may lead to barotrauma, PIE, decreased preload (thus reduced cardiac output and cerebral blood flow)

Complications:

• Atelectasis – increase the PEEP, or increase the PIP, and/or the sigh breath rate, PIP, and IT.

• Hypotension - decrease PEEP and PIP to decrease MAP and/or decrease the JET rate to minimize air trapping.

• Overinflation - decrease PEEP and PIP and/or decrease JET rate.

• Apnea - Increase delta P (Jet PIP if PCO2 not < 50), increase sighs from 4 to 6-12 BPM, increase sigh PIP to ensure adequate chest wall excursion or consider converting to conventional ventilation. HFJV is not optimal mode for the management of apnea.

• Hypercapnea - because of the unique nature of gas flow within the large airways, proper endotracheal tube position is critical. Optimal ventilation is achieved when the jet stream travels down the center of the airway unimpeded. This occurs when the head is in midline and slightly extended, with the endotracheal tube at least 1 cm above the carina. If the tube is too close to the carina, the jet stream either hits the carina and partially disperses or preferentially travels down one or the other mainstem bronchus, leading to uneven ventilation. Turning of the head sharply to one side results in the endotracheal tube entering the trachea at an angle, causing the jet stream to hit the wall of the trachea and disperse, causing deterioration of clinical status and possibly also contributing to mucosal injury. An acute change in PaCO 2 is almost always related to endotracheal tube malposition or secretions in the airway and must be promptly recognized and corrected. 

Oxygenation index (OI) is routinely used as an indicator of severity of hypoxemic respiratory failure (HRF) in neonates: 

• Mild HRF: 15 or less 

• Moderate HRF: 16-25

• Severe HRF: 26 - 40 

• Very severe HRF: more than 40 

Should consider requesting ECMO consult once OI > 30.