Spontaneous Breathing Trial (SBT) Protocol
Definition and Purpose
An SBT is a systematic method of reducing ventilator support to assess a patient's ability to independently maintain gas exchange without excessive respiratory effort, serving as the final objective assessment before extubation. 1, 2
Pre-SBT Screening Criteria
Before initiating an SBT, perform daily protocolized screening to assess eligibility: 3
- Hemodynamic stability (no active myocardial ischemia, no significant vasopressor requirements) 3
- Adequate oxygenation (typically FiO₂ ≤0.4-0.5, PEEP ≤5-8 cm H₂O) 3
- Intact airway reflexes (adequate cough and gag) 3
- Adequate mental status (able to follow commands or appropriate level of consciousness) 3
- Resolution or improvement of the primary cause of respiratory failure 4
SBT Technique: Pressure Support vs T-Piece
The American College of Chest Physicians/American Thoracic Society recommends conducting the initial SBT with inspiratory pressure augmentation of 5-8 cm H₂O rather than T-piece or CPAP alone. 3
Evidence Supporting Pressure Support:
- Higher SBT success rates: 84.6% with pressure support vs 76.7% with T-piece 3
- Higher extubation success rates: 75.4% with pressure support vs 68.9% with T-piece 3, 5
- Trend toward lower ICU mortality: 8.6% with pressure support vs 11.6% with T-piece 3
- A large randomized trial of 1,153 patients demonstrated that 30 minutes of pressure support (8 cm H₂O) resulted in 82.3% successful extubation vs 74.0% with 2-hour T-piece (absolute difference 8.2%, P=0.001) 5
Special Consideration for High-Risk Patients:
For patients at high risk of extubation failure, use CPAP without pressure support augmentation during SBTs for better assessment of extubation readiness. 1 T-piece trials may be more specific (though less sensitive) in identifying patients truly ready for extubation in this population 4
SBT Duration
Conduct SBTs for 30 minutes in standard-risk patients; extend to 60-120 minutes for high-risk patients. 3, 4
- Most SBT failures occur within the first 30 minutes 3, 4
- The 30-minute duration with pressure support is sufficient for most patients and superior to longer, more demanding trials 5
- High-risk patients benefit from longer observation periods to better predict extubation success 3, 4
SBT Failure Criteria (Signs of Poor Tolerance)
Terminate the SBT if any of the following develop: 4
- Respiratory distress: Increased respiratory rate (typically >35 breaths/min), accessory muscle use, paradoxical breathing 4
- Hemodynamic instability: Tachycardia, hypertension, or hypotension 4
- Oxygen desaturation or deterioration in gas exchange 4
- Altered mental status or agitation 4
- Diaphoresis or subjective discomfort 4
Post-SBT Assessment Before Extubation
Passing an SBT does not guarantee successful extubation—the SBT is inadequate as the sole means of detecting patients at risk of extubation failure. 2 Approximately 10% of patients who pass an SBT still fail extubation within 48-72 hours 2, 4
Additional Required Assessments:
- Upper airway patency (perform cuff leak test in high-risk patients) 3, 4
- Bulbar function evaluation (swallowing ability) 4
- Cough effectiveness 2, 4
- Sputum load assessment (excessive secretions) 2, 4
- Absence of respiratory distress during the trial 4
Cuff Leak Testing:
For patients at high risk for post-extubation stridor, perform a cuff leak test before extubation and administer systemic steroids at least 4 hours before extubation if the test fails 3
High-Risk Patient Identification and Management
High-Risk Factors Include: 3, 4
- Prolonged mechanical ventilation (>14 days) 3, 4
- Chronic obstructive pulmonary disease or congestive heart failure 3
- Chronic lung disease 4
- Myocardial dysfunction 4
- Neurologic impairment or neuromuscular disease 4
- Ineffective cough or impaired bulbar function 3
- Previously failed extubation 4
Post-Extubation Strategy for High-Risk Patients:
The American Thoracic Society/American College of Chest Physicians strongly recommends extubation to preventive noninvasive ventilation (NIV) rather than standard oxygen therapy for high-risk patients who pass an SBT. 2, 3
Protocolized Approach
Use a protocolized extubation readiness testing (ERT) bundle that includes the SBT plus additional assessments. 1
Components of ERT Bundle: 1
- Spontaneous breathing trial 1
- Assessment of sedation level 1
- Adequacy of neurologic control of the airway (cough and gag) 1
- Likelihood of postextubation upper airway obstruction 1
- Assessment of respiratory muscle strength 1
- Magnitude of airway secretions 1
- Hemodynamic status 1
- Plan for postextubation respiratory support 1
Implementation of protocolized ERT bundles results in lower extubation failure rates (absolute risk reduction 3.3-11.7%), with sensitivity of 90% and positive predictive value of 94% for extubation success 1
Management After Failed SBT
Do not perform repeat SBTs on the same day after failure. 4 SBT failure indicates the respiratory system cannot yet sustain independent breathing, and forcing a second attempt may lead to respiratory muscle fatigue and worsening respiratory mechanics 4
After Failed SBT: 4
- Document specific reasons for failure 4
- Address reversible causes 4
- Optimize patient condition before next attempt 4
- Consider a different SBT approach for the next day 4
Post-Extubation Monitoring
Close observation for 6-24 hours with continuous pulse oximetry and cardiac monitoring is required. 2
- Consider reintubation before full decompensation if progressive deterioration occurs despite optimized support 2
- Failed extubation (reintubation within 48 hours) is associated with 10-20% higher mortality rates, increased ICU length of stay, and increased risk of ventilator-associated pneumonia 4
Target Extubation Failure Rate
The acceptable extubation failure rate should be 5-10%. 3, 4
- Rates higher than 10% suggest inadequate assessment of readiness 3, 4
- Rates lower than 5% may indicate overly conservative practices delaying liberation 3
Adjunctive Strategies
Implement protocolized sedation minimization for all patients ventilated >24 hours. 3 This approach shows trends toward shorter mechanical ventilation duration, shorter ICU length of stay, and lower short-term mortality 3