Components of HFOV

Driving system Oscillating pump or diaphragm

Bias flow system Deliver fresh gas

Transmission link

Physiology of HFOV

Sinusoidal wave form High mean airway pressure (Paw) Active expiratory phase Equal positive and negative pressure

generation Symmetric flow pattern Blurs dead space and alveolar ventilation

HFOVGas transport mechanisms

DBF

ASVP

TD

PD

Krishnan JA et al Chest 2000;118:795

ARDSHFOV

ARDSHFOV

“HFOV - Caring for the Baby in Adults” Baby Lung Sitting on

Top of a Consolidated Lung Tidal Volumes of 6-10

ml/kg based on weight Tidal Volumes of 20-

50 ml/kg based on open lung units

Histology is similar to infant lung injury

Proximal and Alveolar Pressures HFOV vs CMV

Gerstmann D.

OxygenationOxygenation

• The Paw is used to inflate the lung and optimize the alveolar surface area for gas exchange.

• Paw = Lung Volume

Open Lung Ventilation: Why?

The most common errors among new users of HFOV

*Inadequate initial lung recruitment Premature reductions in the maintenance

mPaw before recovery of intrinsic alveolar stability

Failure to decrease the mPaw when a marked improvement in oxygenation occurs.

HFOV and open lung concept Disappointing efficacy of HFOV in the past, may due

to did not apply optimum lung volume or open lung strategyBryan AC et al Pediatrics 1991;87:565

Animal studies have clearly shown that recruiting and stabilizing collapsed alveoli are essential in the process of attenuating VILI during HFVMcCulloch PR et al Am Rev Respir Dis 1988;137:1185, Meredith KS et al J Appl Physiol 1989;66:2150

Porcine model demonstrate sustained inflation pressure during HFOV better oxygenation than Conventional mode.Muellenbach RM et al BMC Anes 2006;8:6

Learned that brief, sustained increases in mPaw(RM)with HFOV could produce rapid, large increased in PaO2

HFOV-Open lung concept

“The ability of HFOV to maintain open lung using lower peak airway pressures, smaller tidal volumes than those applied during CV may potentially result in less biotrauma and Ventilator induced lung injuries.” Derdak S et al AJRCCM 2002;166:801

Recent clinical trials demonstrate recruitment maneuver shown to be safe, well tolerated and resulted in rapid and sustained improvement in oxygenation

Ferguson ND et al Crit Care Med 2005;33:479Chan KPW et al Crit Care Med 2005;33:s170Bein T Crit Care Med 2005;33:667Fessler HE et al Crit Care Med 2007;35:1649

HFOV with RMFerguson ND et al CCM;2005:479

25 patients with ARDS Prospective, Multicenter Intervention RM with HFOV

13

Lung Recruitment Maneuver

Perform after initial HFOV transition OR Perform after initial HFOV transition OR for hypoxia prior to increases in for hypoxia prior to increases in mPawmPaw

steps >25 cmH2O, steps >25 cmH2O, OR for de-recruitment [e.g. ↓ SpO2 >5%] from suctioning, bronchoscopy, circuit disconnect,

agitation, re-positioning.

LRM Steps

Raise high mPaw alarm limit to 55cmH2O Remove ETT cuff leak if present. Stop the Piston ( ↓ shear stress form

transmitted ∆P), ↑ mPaw to 40 cmH2O over 10 seconds,

maintain 40 cmH2O X 40 seconds ( max mPaw for LRM is < 45 cmH2O);

LRM steps

Return mPaw to starting level if LRM is done for de-recruitment or next higher level per TABLE 1 if done for hypoxia.

Restore ETT leak if used Restart the piston

Results

Ferguson ND et al Crit Care Med 2005:479

HFOV Algorithm for Oxygenation [Goal: SpO2 90 –94% OR PaO2 60 – 80 mmHg; PaO2 if available

Step 1 2 3 4 5 6 7 8 9FiO2 .4 .4 .5 .5 .5 .5 .6 .6 .7mPaw 22 24 24 26 28 30 30 32 32 __________________________________________________________

______

←if improving oxygentation If worsening oxygenation →Step 10 11 12 13 14 15 16 17 18FiO2 .7 .8 .8 .8 .9 1.0 1.0 1.0 1.0mPaw 34 34 36 38 38 38 40 42* 45*

Fessler HE et al Protocol HFOV Crit Care Med 2007;35:1649

HFOVPV curve

12 infants HFOV (3100A) Dx Pneumonia/MAS BW 1.1-4.2 kg. OI 5.5-19 (mean= 10.1) Step wise MAP

increment to TLC. (*VRIP) Follow with MAP

decrement until CV identified.

Tingay DG et al AJRCCM 2006;173:414-420

*Respiratory inductancePlethysmography (RIP)

HFOVMAP-SaO2

Tingay DG et al AJRCCM 2006;173:414-420

HFOVOpen lung concept

103 preterm infants with RDS (NICU)

HFOV 3100 A OI = 6.8 ± 3.8 (Pre-post) surfactant

treatment, Step wise increasing-decreasing MAP

Able to wean down FiO2 to < 0.25

Jaegere DA et al AJRCCM 2006 ;174:639 Black= CDP, White= FiO2

Pre-surfactant

PEEP:0 5 10 15 20 25

PEEP:0 5 10 15 20 25

30

(cmH2O)

Deflation

Inflation

Electrical Impedance Tomography (EIT)Hahn Physiol Meas 1996, Adler JAP 1997, Kunst Physiol Meas 1998,

Frerichs JAP 2002, Victorino AJRCCM 2004