Indices that predict difficulty weaning


  • Numerous objective indices have been studied to predict failure of ventilator liberation or weaning.
  • None of these indexes alone are sufficiently sensitive and specific to be useful in predicting the success of ventilation discontinuation in an individual patient.
  • Different studies use different cut offs, with different performance characteristics
  • They are not recommended for routine use, the Spontaneous breathing trial (SBT) remains the de facto gold standard test.


  • Respiratory rate <30 breaths per minute
  • Tidal volume >5 ml/kg or >325 mL
  • FVC >15 mL/kg predicts success
  • Minute ventilation <15 L/min
    — Normal 5 – 6 L/min
    — Patient unlikely to wean if > 15 L/min
  • Maximum inspiratory pressure (PImax) < -30 cmH20
    — Measure of respiratory muscle strength
    — Normal -90 to -120 cmH2O
  • Rapid shallow breathing index (RSBI) = f/VT <105 breaths/min/L
    — the ratio of respiratory rate : tidal volume
    — often used in conjunction with SBT to determine if it should continue
    — some evidence that its use in protocols delays ventilator discontinuation
  • P0.1/PImax > 0.3
    — P0.1 is pressure at the airway opening 0.1 s after start of inspiratory flow
    — Correlates with central respiratory drive
  • P0.1 x f/VT <300
  • CROP index (dynamic compliance, respiratory rate, oxygenation, maximum inspiratory pressure index) >13
    — Cdyn x PImax x (PaO2/PAO2)/f
    — >13 good
    — Cdyn = dynamic compliance
  • IWI (integrative weaning index) >25
    — (CRS x SaO2)/(f/VT)
    — CRS = static compliance of the respiratory system
  • CORE index (dynamic compliance, oxygenation, rate, effort) >8
    — Cdyn x (PImax/P0.1) x (PaO2/PAO2)/f


  • the above indices focus on lung function
  • successful ventilar discontinuation and extubation also depends on 2 other domains:
    — general medical condition (e.g. disease resolution, nutrition, anaemia, conditioning, etc)
    — ability to protect airway post-extubation (extubation assessment, separate from weaning assessment)

References and Links


Journal articles

  • El-Khatib MF, Bou-Khalil P. Clinical review: liberation from mechanical ventilation. Crit Care. 2008;12(4):221. PMC2575571.
  • Haas CF, Loik PS. Ventilator discontinuation protocols. Respir Care. 2012 Oct;57(10):1649-62. PMID: 23013902. [Free Fulltext]
  • Macintyre NR. Evidence-based assessments in the ventilator discontinuation process. Respir Care. 2012 Oct;57(10):1611-8. PMID: 23013898. [Free Fulltext]
  • MacIntyre N. Discontinuing mechanical ventilatory support. Chest. 2007 Sep;132(3):1049-56. PMID: 17873200. [Free Fulltext]
  • Yang KL, Tobin MJ. A prospective study of indexes predicting the outcome of trials of weaning from mechanical ventilation. N Engl J Med. 1991 May 23;324(21):1445-50. PMID: 2023603. [Free Fulltext]

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Critical Care


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

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