Spontaneous Breathing Trial


Spontaneous breathing trials (SBT) are used to identify patients who are likely to fail liberation from mechanical ventilation

  • SBT is “the defacto litmus test for determining readiness to breathe without a ventilator”
  • Ideally, during an SBT we want to observe the patient under conditions of respiratory load that would simulate those following extubation


See Indices that predict difficulty weaning


Patients that pass the following daily ‘wean screen’ should undergo SBT:

  • lung disease is stable/ resolving
  • low FiO2 (< 0.5) and PEEP (< 5-8cmH2O) requirement
  • haemodynamic stability (little to low inopressors)
  • able to initiate spontaneous breaths (good neuromuscular function)

This indicates patients suitable for a spontaneous breathing trial, those who pass also to be assessed for extubation.


SBT involves the following steps:

  • It be conducted while the patient is still connected to the ventilator circuit, or the patient can be removed from the circuit to an independent source of oxygen (T-piece)
  • When using the ventilator a PS of 5 – 7 cmH2O and 1-5 cmH20 PEEP (so called ‘minimal ventilator settings’) will overcome increased work of breathing through the circuit (i.e. ETT)
  • If still on the ventilator the patient should have ‘minimal ventilator settings”
  • Initial trial should last 30 – 120 minutes
  • If it is not clear that the patient has passed at 120 minutes the SBT should be considered a failure
  • In general, the shorter the intubation time the shorter the SBT required

80% of patients who tolerate this time can be permanently removed from the ventilator


No single parameter should be used to judge SBT success or failure, but a combination of the following are often used:

  • Respiratory rate RR >38 bpm for 5 minutes or <6bpm
  • SpO2 < 92%
  • Tidal volume (TV) < 325 mL
  • Heart rate: HR > 140 OR 25% above baseline OR HR<60
  • Blood pressure: SBP 40 mm Hg above baseline
  • Worsening agitation, anxiety or discomfort despite reassurance
  • Rapid shallow breathing index (RSBI) = RR/ TV
    • Most consistent and powerful predictor
    • RSBI > 105 min/L predicted failure well, but if used rigidly may slow the weaning process


A successful SBT does not guarantee that the patient will avoid reintubation:

  • Upper airway resistance (supraglottic edema)
  • poor cough and excessive secretions
  • poor airway reflexes leading to aspiration
  • Respiratory weakness masked by pressure support
  • Increased cardiac load induced by removal of CPAP
  • Onset of new pathology


The concept of ‘minimal ventilator settings’ is controversial:

  • Martin Tobin has argued that adding either 5 cm H2O as “physiologic” PEEP or pressure support of 7 cm H2O to overcome the resistance in an endotracheal tube (or both, as is usually done) may actually reduce the “spontaneously” breathing patient’s workload by >40%
  • It has been shown experimentally that the work of breathing through an endotracheal tube, compared to the work of breathing following extubation, is almost identical due to upper airway edema resulting from an ETT being in place for several days
  • Tobin argues for wider use of true T-piece spontaneous breathing trials, especially in those at high risk of failed extubation and when the consequences of failed extubation may be catastrophic
  • An alternative is to have the ventilator set on “flow-by,” with pressure support and PEEP set at zero
  • There is no strong evidence in favour of any of these approaches

References and Links


Journal articles and textbooks

  • Esteban A, Frutos F, Tobin MJ, Alía I, Solsona JF, Valverdú I, Fernández R, de la Cal MA, Benito S, Tomás R, et al. A comparison of four methods of weaning patients from mechanical ventilation. Spanish Lung Failure Collaborative Group. N Engl J Med. 1995 Feb 9;332(6):345-50. PubMed PMID: 7823995. [Free Fulltext]
  • Macintyre NR. Evidence-based assessments in the ventilator discontinuation process. Respir Care. 2012 Oct;57(10):1611-8. Review. PubMed PMID: 23013898. [Free Fulltext]
  • Sassoon CS, Light RW, Lodia R, Sieck GC, Mahutte CK. Pressure-time product during continuous positive airway pressure, pressure support ventilation, and T-piece during weaning from mechanical ventilation. Am Rev Respir Dis. 1991 Mar;143(3):469-75. PubMed PMID: 2001053.
  • Tobin MJ. Extubation and the myth of “minimal ventilator settings”. Am J Respir Crit Care Med. 2012 Feb 15;185(4):349-50. doi: 10.1164/rccm.201201-0050ED. PubMed PMID: 22336673. [Reply to Letters to the Editor]

Social media and web resources

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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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