Indices that predict difficulty weaning

OVERVIEW

  • 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.

INDICES THAT PREDICT SUCCESSFUL VENTILATOR DISCONTINUATION

  • 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

OTHER CONSIDERATIONS

  • 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

LITFL

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]

CCC 700 6

Critical Care

Compendium

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