Airway pressure release ventilation (APRV)

in PICU: Current evidence

Chor Yek Kee

Sarawak General Hospital

Outline

• Brief introduction of APRV

• History of APRV

• Common confusion in APRV

• Features of APRV and how it works

• Evidences of APRV

• Future of APRV

Natural High Frequency Ventilation

Natural APRV Blowhole of dolphin

Natural APRV

. .. . . . . , . , . ; ‘ . - . . ‘ “ .

. . . . . . . . . . . .

APRV open up lung at FRC Intrinsic lung pathology reduced FRC

Extrinsic compressing factor reduced FRC

Healthy lung at normal FRC

APRV maintained FRC by counter extrinsic pressure

High level CPAP

High level CPAP

Constant Vs Intermitent Recruitment

Open the lung and keep it open

Never let the lung collapse

Lachmann B : Intensive Care Medicine 1992 Joshua Satalin : Ann Transl Med 2016

Mode of ventilation Percentage

APRV 1.6%

Conventional 75.2%

HFPV 16.4%

Non-invasive 8.5%

59 PICU from North America and Europe, Cross sectional study 2007

2013 email survey • 88 respiratory

therapist • 4 countries

• United State • Canada • Saudi Arabia • United Arab

Emirates

History of APRV

APRV is a new way to administer simultaneously a supportive level of CPAP and assist CO2 elimination (1987)

APRV Setting

P High Pressure during CPAP phase

P Low Pressure during release phase

T High Time during CPAP phase

T Low Time during Release Phase

% CPAP Percent CPAP

APRV is a new way to administer simultaneously a supportive level of CPAP and assist CO2 elimination (1987)

• Tremendous variation in setting of APRV

• Impossible to assess efficacy of a single strategy since almost none of the APRV setting were identical

Fixed ( F-APRV)

T High CPAP < 90% of total cycle time.

T Low Fixed T Low , not base on changing of lung mechanic

P Low P low is set > 0 cmH2O

Personalised P-APRV

T High CPAP > 90% of total cycle time

T Low T low is set by the changes in the lung mechanic by analysing the slope of the expiratory flow curve

P Low P low is set at 0 cmH2O

APRV Strategies

APRV BIPAP

Baum M et al : BIPAP- a new form of augmented ventilation. Anaesthetist : 1989

Christine and Down et al. Airway Pressure Release Ventilation. CCM 1987

Superficially similar BUT Fundamentally different

Inspiratory and Expiratory ratio

(I:E ratio)

> 2 : 1 Extreme inversed ratio

1 : 1

BIPAP APRV

FIXED

FUNCTIONAL

APRV is named in various way and can be set in machine with BIPAP mode

1. APRV ( Dragger Evita, Savina and V series, Hamilton G5 )

2. Bi-Vent ( Maquet Servo-I )

3. BiLevel ( Engstrom carestation, Puriton Bennett 840 & 980, Covidien)

4. APRV/BiPhasic ( Viasys Avea )

5. DuoPAP ( Hamilton )

WHY APRV ?

Features of APRV

Elevated CPAP Level

Time Pressure Release

Spontaneous breathing

High Level CPAP in APRV

Open the lung and keep it open

Prolonged CPAP ( P High )--- recruiting the lung

Never let the lung collapse

Minimal release duration ( T Low ) preventing lung collapse

Pressure-volume curve of the lung during inflation and deflation.

Francesca Facchin, and Eddy Fan Respir Care

2015;60:1509-1521

(c) 2012 by Daedalus Enterprises, Inc.

Francesca Facchin, and Eddy Fan Respir Care

2015;60:1509-1521

Pressure-volume curve of the lung

during inflation and deflation.

How does elevated CPAP recruit the lung in

APRV?

Pores of Kohn – Intra Alveolar communication

Fowley and Habashi et al AACN 2001

How does high CPAP level changes lung volume

? Changing in alveolar volume

? changing alveolar numbers

Numbers of alveoli

Size of the alveoli Alveoli wall

length/ microstrain

inflate

Mother and Daughter hypothesis Increasing the numbers of

( less strained) alveoli

Group A -- Sham Group B -- LTV Group C --APRV

Tidal volume 10 ml/Kg PEEP 5 cmH2O Rate 12 bpm FiO2 = 21%

Low tidal volume group Tidal volume 4 to 6 ml/Kg PEEP according to PEEP/FiO2 table

APRV with tidal volume of 10 ml/Kg

Group C Group B

Pressure-volume curve of the lung during inflation and deflation.

Francesca Facchin, and Eddy Fan Respir Care

2015;60:1509-1521

(c) 2012 by Daedalus Enterprises, Inc.

Francesca Facchin, and Eddy Fan Respir Care

2015;60:1509-1521

APRV and Pulmonary vascular resistance

PVR and Safe Zone Correlation

Toronto Sick Kid ( 2007 to 2009) • Prospective crossover cohort

study • Recruited 20 patients : 9 TOF

and 11 cavo-pulmonary shunt • Measure lung perfusion and

cardiac output

Elevated CPAP Level

• Gradually recruit lung to achieve FRC via collateral respiration

• Reduction of micro-strain to the alveoli that prevent ventilator induced lung injury

• At FRC, improve pulmonary perfusion and oxygen delivery

Features of APRV

Elevated CPAP Level

Time Pressure Release

Spontaneous breathing

Intermitent release ( T low )

•Setting T PEFR ( EEFR/PEFR ) 50 to 75% with P Low of 0 cmH20 •Determine the amount of end expiratory lung volume ( EELV) that is retained.

•Maintained alveolar stability

Expiratory flow pattern of different

pathology with PEEP of 0 cmH2O

a - normal lung b - restrictive c - obstructive

PEFR = Peak expiratory flow rate

EELV = End expiratory lung volume

Lung will collapse if expiratory time is too short in restrictive lung e.g. ARDS

More restrictive lung shorter T Low

Despite P low is 0 cm H2O Actual tracheal pressure never reach 0 cmH2O (Green line)

AutoPEEP which maintain alveolar stability

APRV ventilation at T-PEFR 75% There is only 10% of variation of alveolar volume between end inspiration and

release phase at injured animal lung model

Normal alveoli

No stain Alveoli duct and alveoli sac

Alveolus

Injured rat model

Time Pressure Release

• Titration based on lung mechanic that maintained stability of lung

• At T-PEFR of 75%, there is significant reduce in conducting airway microstrain

Features of APRV

Elevated CPAP Level

Time Pressure Release

Spontaneous breathing

Spontaneous breathing at APRV

• Spontaneous breathing enhance cardiopulmonary and organ perfusion benefit.

• Spontaneous breathing without pressure support favor gas distribution to dependent area

APRV

60

PubMed Search 1987 to 2015 Excluding NIV, review, editorials and case studies

(52 articles)

32 animal studies

28 human studies

Wide variety of APRV setting have all been used in literature making comparison between studies difficult

Study designs are mainly • Cossover • Randomized prospective • Retrospective case control • Retrospective review

1. None of the studies reviewed showed a worse outcome using APRV as compared with CPPV

2. Many studies showing significant benefits in cardiopulmonary variables

3. P-APRV personalized, adaptive mechanical breath may prove more efficacious at treating and preventing ARDS than the current standard of care

4. More studies are needed using consistent and well-defined settings to identify the optimal APRV breath necessary to maximize lung protection

Let’s see

APRV in Neonate

APRV in Premature Piglet

APRV in Paediatric

Halt the progression of ARDS using APRV?

Systemic review • 16 articles • 66,199 patients

What is actually happening out there?

Respiratory Care June 2017

15 questions survey regarding clinical management strategies with APRV • Started January 4 , 2016 • Total 60 respondent from 60

different hospital. • 74% of these hospital use APRV

as initial rescue strategy for patient failing conventional ventilator .

Respiratory Care June 2017, respcare.05494

Respiratory Care June 2017, respcare.05494

Respiratory Care June 2017, respcare.05494

Amato et NEJM 2015

Amato et NEJM 2015

Conclusion from current evidence

1. Tremendous variation in setting of APRV, most of the study regarding the setting were physiology concept, animal data and small clinical trial

2. Impossible to assess efficacy of a single strategy since almost none of the APRV setting were identical.

3. Studies compare between APRV and CPPV did not show worse outcome but showing significant benefit in cardiopulmonary variables.

4. Personalized APRV (P-APRV) may prove more efficacious at treating and preventing ARDS.

5. APRV reduces sedation and neuromuscular blocker requirements

Thank you