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

LITFL

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


CCC 700 6

Critical Care

Compendium

Chris is an Intensivist and ECMO specialist at the Alfred ICU in Melbourne. He is also the Innovation Lead for the Australian Centre for Health Innovation at Alfred Health and 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 two amazing children.

On Twitter, he is @precordialthump.

| INTENSIVE | RAGE | Resuscitology | SMACC

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