What Does It Mean If a Patient Passes an SBT?
A patient who passes a spontaneous breathing trial has demonstrated the ability to breathe without significant ventilator support for a defined period (typically 30 minutes to 2 hours) without signs of respiratory distress, indicating they are likely ready for extubation—though passing an SBT does not guarantee successful extubation, as approximately 10% of patients who pass will still fail extubation within 48-72 hours. 1, 2
Definition of a Successful SBT
A successful SBT means the patient completed the trial period without exhibiting signs of poor tolerance, including: 1, 2
- No respiratory distress (increased respiratory rate, accessory muscle use, paradoxical breathing)
- Hemodynamic stability (absence of significant tachycardia, hypertension, or hypotension)
- Adequate oxygenation (no oxygen desaturation)
- Maintained mental status (no agitation or altered consciousness)
- Absence of diaphoresis or subjective discomfort
Clinical Implications of Passing an SBT
Immediate Next Steps
Passing an SBT indicates weaning readiness, but additional assessments are required before extubation: 2, 3
- Upper airway patency evaluation - assess for stridor risk
- Bulbar function assessment - evaluate swallowing ability
- Cough effectiveness - weak cough (grade 0-2) increases extubation failure risk 4-fold 3
- Secretion burden - moderate-to-abundant secretions increase failure risk 8.7-fold 3
- Combined assessment - weak cough plus excessive secretions increases failure risk 31.9-fold 3
Expected Outcomes After Passing SBT
When patients pass an SBT and are extubated, expected success rates vary by trial method: 1, 4
- With pressure support (5-8 cm H₂O): 75.4% extubation success, 84.6% SBT completion rate
- With T-piece (no support): 68.9% extubation success, 76.7% SBT completion rate
- 30-minute pressure support trial: 82.3% successful extubation 4
- 2-hour T-piece trial: 74.0% successful extubation 4
Critical Distinction: SBT Success vs. Extubation Success
Extubation success is defined as not requiring reintubation or noninvasive ventilation within 48 hours (some studies use 72 hours). 1, 2
Why Some Patients Fail Despite Passing SBT
The 10% failure rate after successful SBT occurs because: 2, 3
- Upper airway obstruction develops post-extubation (not assessed during SBT)
- Inadequate airway protection from poor cough or bulbar dysfunction
- Excessive secretions that cannot be cleared effectively
- Post-extubation work of breathing exceeds what was demonstrated during pressure-supported trials
Risk Stratification After Passing SBT
High-Risk Patients Requiring Enhanced Monitoring
Even after passing an SBT, certain patients warrant preventive noninvasive ventilation: 1, 2
- Prolonged mechanical ventilation (>14 days)
- Chronic lung disease (especially COPD with hypercapnia)
- Myocardial dysfunction
- Neurologic impairment or neuromuscular disease
- Previously failed extubation
- Borderline SBT passage (marginal parameters)
- Ineffective cough or impaired bulbar function
For these high-risk patients who pass an SBT, the American Thoracic Society/American College of Chest Physicians strongly recommends extubation to preventive noninvasive ventilation rather than standard oxygen therapy. 1
Common Clinical Pitfalls
Overreliance on SBT Alone
The SBT is inadequate as the sole means of detecting patients at risk of extubation failure. 2 Clinicians must also screen for:
- Ineffective cough strength (use white card test or graded assessment) 3
- Excessive secretions requiring frequent suctioning 3
- Swallowing disorders or aspiration risk 2
- Altered consciousness affecting airway protection 2
Underestimating Post-Extubation Work
Pressure-supported SBTs may underestimate the actual post-extubation work of breathing, potentially leading to premature extubation. 2 This is particularly relevant when using 5-8 cm H₂O pressure support, as this reduces inspiratory effort compared to breathing through an endotracheal tube without support.
Timing Considerations
Most SBT failures occur within the first 30 minutes of the trial. 2 However, for high-risk patients, a longer trial of 60-120 minutes provides better prediction of extubation success. 2
Post-Extubation Monitoring
After extubating a patient who passed an SBT: 2, 5
- Monitor closely for 6-24 hours depending on initial respiratory failure severity
- Continuous pulse oximetry and cardiac monitoring
- Watch for signs of respiratory distress requiring escalation of support
- Reintubate before full decompensation if progressive deterioration occurs despite optimized support
Failed extubation requiring reintubation is associated with 10-20% higher mortality compared to successful extubation, increased ICU length of stay, and increased risk of ventilator-associated pneumonia. 2