- Chris Nickson
OVERVIEW
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
PREDICTORS OF FAILURE TO WEAN
See Indices that predict difficulty weaning
IDENTIFICATION OF PATIENTS SUITABLE FOR SBT
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.
METHOD
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
CRITERIA TO STOP SBT
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
REASONS FOR REINTUBATION FOLLOWING SUCCESSFUL SBT
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
MINIMAL VENTILATOR SETTINGS
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
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
LITFL
- CCC — Weaning from mechanical ventilation (Hot Case)
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
Critical Care
Compendium
more CCC…
Chris Nickson
Chris is an Intensivist and ECMO specialist at theAlfred ICU in Melbourne. He is also a Clinical Adjunct Associate Professor at Monash University.He is a co-founder of theAustralia and New Zealand Clinician Educator Network(ANZCEN) and is the Lead for theANZCEN Clinician Educator Incubatorprogramme. He is on the Board of Directors for theIntensive Care Foundationand is a First Part Examiner for theCollege 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 educationwebsite,INTENSIVE. He created the ‘Critically Ill Airway’ course and teaches on numerous courses around the world. He is one of the founders of theFOAMmovement (Free Open-Access Medical education) and is co-creator oflitfl.com,theRAGE podcast, theResuscitologycourse, and theSMACCconference.
His one great achievement is being the father of three amazing children.
OnTwitter, he is@precordialthump.
| INTENSIVE | RAGE | Resuscitology | SMACC
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