Airway Pressure Release Ventilation (APRV)
OVERVIEW
- Airway pressure release ventilation (APRV) is inverse ratio, pressure controlled, intermittent mandatory ventilation with unrestricted spontaneous breathing
- based on the Open Lung Approach To Ventilation first described by Stock et al 1987
USE
- rescue therapy for severe ARDS
DESCRIPTION
- Two levels of PEEP: high (P-high) and low (P-low)
- patient breaths spontaneously during P-high and P-low
- time in P-high (T-high) is longer than P-low (T-low) to maintain recruitment (85-95%)
- results in a degree of autoPEEP due to the short release time (T-low)
METHOD OF USE
Initial settings
- P-high= Pplateau up to a maximum of 30 cmH20
- P-low = 0 cmH20
- T-high = 4.5-6.0 seconds
- T-low = 0.5 – 0.8 s
- automated tube compensation is set on to allow spontaneous breathing
Adjust oxygenation
- FiO2
- Mean airway pressure (dependent primarily on P-high and T-high)
Adjust ventilation
- pressure gradient (P-high minus P-low)
- airway pressure release time (T-low)
— in practice this is set at about 1 time constant such that so that the pressure release ends when expiratory flow reaches approximately 40% of the peak expiratory flow (look at the flow time curve) - airway pressure release frequency
- spontaneous breathing (titrate sedation to allow this to account for about 10-30% of minute ventilation)
Weaning
- lower P-high by 2 to 3 cm H2O at a time and lengthen T-high by increments of 0.5 to 2.0 seconds
- once P-high is ~16 cmH2O and T-high is at 12-15 s, can change to CPAP
PROS AND CONS
Advantages
- alveolar recruitment and improved oxygenation
- preservation of spontaneous breathing
- reduction of left ventricular transmural pressure and therefore reduction of left ventricular afterload
- potential lung-protective effect
- better ventilation of dependent areas
- lower sedation requirements to allow spontaneous breathing
Disadvantages
- risks of volutrauma from increased transpulmonary pressure
- increased work of breathing due to spontaneous breathing
- increased energy expenditure due to spontaneous breathing
- worsening of air leaks (bronchopleural fistula)
- Increased right ventricular afterload, worsening of pulmonary hypertension
- Reduction of right ventricular venous return: may worsen intracranial hypertension, may worsen cardiac output in hypovolemia
- Risk of dynamic hyperinflation
EVIDENCE
- no evidence that APRV improves clinically significant outcomes such as mortality
- improvement of physiological variables in animals and humans
OTHER INFORMATION
Time constant
- time constant (t) is the time it takes to empty 63% of the lung volume; t = C x R (compliance x resistance)
- a rule of thumb is that complete emptying requires 4 x time constant (this is not achieved in APRV, hence autoPEEP results)
References and Links
CCC Ventilation Series
Modes: Adaptive Support Ventilation (ASV), Airway Pressure Release Ventilation (APRV), High Frequency Oscillation Ventilation (HFOV), High Frequency Ventilation (HFV), Modes of ventilation, Non-Invasive Ventilation (NIV), Spontaneous breathing and mechanical ventilation
Conditions: Acute Respiratory Distress Syndrome (ARDS), ARDS Definitions, ARDS Literature Summaries, Asthma, Bronchopleural Fistula, Burns, Oxygenation and Ventilation, COPD, Haemoptysis, Improving Oxygenation in ARDS, NIV and Asthma, NIV and the Critically Ill, Ventilator Induced Lung Injury (VILI), Volutrauma
Strategies: ARDSnet Ventilation, Open lung approach, Oxygen Saturation Targets, Protective Lung Ventilation, Recruitment manoeuvres in ARDS, Sedation pauses, Selective Lung Ventilation
Adjuncts: Adjunctive Respiratory Therapies, ECMO Overview, Heliox, Neuromuscular blockade in ARDS, Prone positioning and Mechanical Ventilation
Situations: Cuff leak, Difficulty weaning, High Airway Pressures, Post-Intubation Care, Post-intubation hypoxia
Troubleshooting: Autotriggering of the ventilator, High airway and alveolar pressures / pressure alarm, Ventilator Dyssynchrony
Investigation / Indices: A-a gradient, Capnography and waveforms, Electrical Impedance Tomography, Indices that predict difficult weaning, PaO2/FiO2 Ratio (PF), Transpulmonary pressure (TPP)
Extubation: Cuff Leak Test, Extubation Assessment in ED, Extubation Assessment in ICU, NIV for weaning, Post-Extubation Stridor, Spontaneous breathing trial, Unplanned extubation, Weaning from mechanical ventilation
Core Knowledge: Basics of Mechanical Ventilation, Driving Pressure, Dynamic pressure-volume loops, flow versus time graph, flow volume loops, Indications and complications, Intrinsic PEEP (autoPEEP), Oxygen Haemoglobin Dissociation Curve, Positive End Expiratory Pressure (PEEP), Pulmonary Mechanics, Pressure Vs Time Graph, Pressure vs Volume Loop, Setting up a ventilator, Ventilator waveform analysis, Volume vs time graph
Equipment: Capnography and CO2 Detector, Heat and Moisture Exchanger (HME), Ideal helicopter ventilator, Wet Circuit
MISC: Sedation in ICU, Ventilation literature summaries
Journal articles
- Modrykamien A, Chatburn RL, Ashton RW. Airway pressure release ventilation: an alternative mode of mechanical ventilation in acute respiratory distress syndrome. Cleve Clin J Med. 2011 Feb;78(2):101-10. doi: 10.3949/ccjm.78a.10032. Review. Erratum in: Cleve Clin J Med. 2011 Apr;78(4):240. PMID: 21285342.
- Myers TR, MacIntyre NR. Respiratory controversies in the critical care setting. Does airway pressure release ventilation offer important new advantages in mechanical ventilator support? Respir Care. 2007 Apr;52(4):452-8; discussion 458-60. PMID: 17417979. [Free Full Text]
- Putensen C, Wrigge H. Clinical review: biphasic positive airway pressure and airway pressure release ventilation. Crit Care. 2004 Dec;8(6):492-7. PMC1065046.
FOAM and web resources
- DerangedPhysiology.com — APRV: Airway Pressure Release Ventilation
- Maryland CCP — Nader Habashi: Airway Pressure Release Ventilation (APRV) – A mechanistic and physiologic view (2014)
- Resus Review — APRV (2013)
Critical Care
Compendium
Chris is an Intensivist and ECMO specialist at the Alfred ICU in Melbourne. He is also a Clinical Adjunct Associate Professor at Monash University. He is a co-founder of the Australia and New Zealand Clinician Educator Network (ANZCEN) and is the Lead for the ANZCEN Clinician Educator Incubator programme. He is on the Board of Directors for the Intensive Care Foundation and is a First Part Examiner for the College of Intensive Care Medicine. He is an internationally recognised Clinician Educator with a passion for helping clinicians learn and for improving the clinical performance of individuals and collectives.
After finishing his medical degree at the University of Auckland, he continued post-graduate training in New Zealand as well as Australia’s Northern Territory, Perth and Melbourne. He has completed fellowship training in both intensive care medicine and emergency medicine, as well as post-graduate training in biochemistry, clinical toxicology, clinical epidemiology, and health professional education.
He is actively involved in in using translational simulation to improve patient care and the design of processes and systems at Alfred Health. He coordinates the Alfred ICU’s education and simulation programmes and runs the unit’s education website, INTENSIVE. He created the ‘Critically Ill Airway’ course and teaches on numerous courses around the world. He is one of the founders of the FOAM movement (Free Open-Access Medical education) and is co-creator of litfl.com, the RAGE podcast, the Resuscitology course, and the SMACC conference.
His one great achievement is being the father of three amazing children.
On Twitter, he is @precordialthump.
| INTENSIVE | RAGE | Resuscitology | SMACC