EMCrit.org | Emergency Critical Care - High Frequency Ventilation

Does not really use Vt but change in pressure amplitude ~150 cc @ 5 breaths per second.

Adjust Paw, mean airway pressure, increasing this increases oxygenation without changing card output

In an animal model, normal or higher RRs were associated with impaired hemodynamics. Low RR (6-8 bpm) attenuated this effect while maintaining good oxygenation and ventilation (J Trauma 2003;54:1048-1057)

Crit Care Med 25(6) 1997

Need to be paralyzed or deeply sedated
Initial Settings
fiO2 1.0
frewuency 5 Hz
Insp time 33%, may increase to 50% if trouble oxygenating
bias flow 30 L/min
mPaw 5 cmH20 above mean pressure on conventional ventilator
Power to acheive Delta P: PaCO2 60 use 60, 60-70 use 75, >70 use 90
or enough to achieve wiggle to mid thighs or 20+PaCO2

Wean FiO2 then Paw

Three types of High frequency ventilation
HFJV jet
HFPV percussive
conventional ventilator with percussor above ET tube which allows dual mode of gas exchange. Cuff is partially deflated. Mobilizes secretions just like HFOV
and HFOV oscillatory

1 HZ=60 breaths per minute
4-6 Hz is the normal range in adults, 10 to 15 in children

Bias flow-continuous flow rate of humidiifed oxygen through circuit

Paw
Driving Pressure (Delta P)
I-time
Oscillatory Frequency
FiO2

Reduce Paw only if chest xray shows diaphragm at level of 8th or 9th ribs

High delta p is equivalent to greater tidal volumes
initally set it to achieve wiggle down to the groin

I time is eventually set at 33% to allow 1:2 I:E

Increase freqeuncy when CO2 is low and decrease when it is high. Adjusted only when changing delta P has failed

Consider HFOV when mPaw is >24 on conventional ventilatory strategies and fio2>60%
generally will have already failed high peep strategies

prior to intiating hfove, patient must be well suctioned with a patent airway as the fewer disconnects for suctioning after intiation the better. Generally inline suction is not used with HFOV because the bend in the circuit and additional deadspace reduces the efficacy of the technique

consider performing bronch prior to intiating HFOV to check the tube for biofilm and/or clots

may have hypotension transiently after intiation of HFOV
Some clinicians will start on a higher Paw (40 cmH20) as an alveolar recruiting technique

sometimes it may take hours to see the improvement in oxygenation as alveoli are slowly recruited.

It may be necessary to increase the bias flow in order to get Paw in patients with large airleaks or bronchopleural fistulas

Ventilation
Decrease the freqency and increase the delta p ino order to blow off CO2
do the opposite if CO2 is low

If necessary, you can disconnect the aptient from the HFOV vent and vigorously ventilate with a PEEP valve equipped BVM.

Deliberatey induced cuff leak may actually benefit ventialtion
Acts like tracheal insufflation of gas, washes out dead space allowing gradient
Withdraw air from the cuff sufficent to lower Paw by 5 cmH2o then readjust the Paw to its previous value

Positioning
if possible, put head of the bed at 30

Complications
Hypotension
Relative hypovolemia may be present even at seemingly high CVP/PAWP. If the PAWP goes up by 5 with no change, add pressors

Pneumothorax
you cna not hear breath sounds while the patient is on HFOV
Loss of chest wiggle unilaterally si probably one of the best indicationsHFOV actually provides good support for patients with pneumothorax

Weaning
Reduce fio2 to 40% as first maneuver.
then little by little, reduce the Paw
Once at 20-24 mPaw, a trial of conventional ventilation can be attempted.
Wean to PCV mode

"High-Frequency Ventilation Basics and Practical Application" (from Drager

Medical):

http://www.draeger.com/MT/internet/pdf/CareAreas/PerinatalCare/pc_baby8000_vent_en.pdf

Viasys (Sensormedics)

http://www.viasyshealthcare.com/prod_serv/prodref.aspx?config=ps_prodref

HFV History :

http://www.viasyshealthcare.com/powerpoint/DOCUMENTS/SMC/HFV_History.ppt

Gas transport:

http://www.viasyshealthcare.com/powerpoint/DOCUMENTS/SMC/Gas_Transport.ppt

and:

1. Pillow JJ. High-frequency oscillatory ventilation: mechanisms of gas

exchange and lung mechanics. Crit Care Med 2005;33(3 Suppl):S135-41.

2. Pillow JJ, Wilkinson MH, Neil HL, Ramsden CA. In vitro performance

characteristics of high-frequency oscillatory ventilators. Am J Respir Crit

Care Med 2001;164(6):1019-24.

3. Van de Kieft M, Dorsey D, Morison D, Bravo L, Venticinque S, Derdak S.

High-frequency oscillatory ventilation: lessons learned from mechanical test

lung models. Crit Care Med 2005;33(3 Suppl):S142-7.

4. Hatcher D, Watanabe H, Ashbury T, Vincent S, Fisher J, Froese A.

Mechanical performance of clinically available, neonatal, high-frequency,

oscillatory-type ventilators. Crit Care Med 1998;26(6):1081-8.

RR 60
Ti 0.6 seconds
Te 0.4 seconds
Pressure High 40-50 (adjust per MAP goal, watch for BP drop on initiation---if such occurs reduce and/or add preload if such a “gauntlet” does the trick)
Rise Time 100%
Pressure Low 0

High Frequency Oscillatory Ventilation (HFOV)