Consensus (Crit Care Med 2007;35:1649)
Oscillate Trial No Benefit, potential harm (10.1056/NEJMoa1215554)
Oscar Trial No mortality benefit (10.1056/NEJMoa1215716)
Review article international journal of emergency and intensive care medicine
- Smaller Vt
- Keeps alveoli open at a constant pressure
- Enhanced gas mixing
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
Frequency, measured in hertz
? of necrotizing tracheobronchitis if gas not humidified
Look for bilateral chest wiggle as breath sounds can not be assessed
Avoid disconnecting for any reason.
Ventilators in Shock States
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.pptand: 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.
Another review from chest (2007;131:1907)
Using APRV vent for HFOV
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
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