What are the criteria and procedure for a spontaneous breathing trial (SBT) in a stable adult patient with a history of respiratory failure who has been mechanically ventilated for an extended period?

Spontaneous Breathing Trial: Criteria and Procedure

Primary SBT Technique Recommendation

For adult patients mechanically ventilated for more than 24 hours, conduct the initial spontaneous breathing trial with inspiratory pressure augmentation of 5-8 cm H₂O rather than T-piece or CPAP alone. 1, 2

This recommendation is based on moderate-quality evidence showing that pressure-augmented SBTs achieve:

• Higher SBT success rates (84.6% vs 76.7% for T-piece) 2
• Higher extubation success rates (75.4% vs 68.9% for T-piece) 2
• Trend toward lower ICU mortality (8.6% vs 11.6% for T-piece) 2

A 2019 randomized trial of 1,153 patients demonstrated that 30 minutes of pressure support ventilation (8 cm H₂O) resulted in 82.3% successful extubation compared to 74.0% with 2-hour T-piece trials, with significantly lower hospital mortality (10.4% vs 14.9%, P=0.02). 3

Pre-SBT Screening Criteria

Before initiating an SBT, perform daily screening to verify the patient meets ALL of the following criteria:

• Intact airway reflexes (adequate cough and gag) 2
• Hemodynamic stability (no vasopressor requirement or minimal/stable doses) 2
• Adequate mental status (able to follow commands or appropriate arousal level) 2
• Resolution or improvement of the underlying cause of respiratory failure 4
• Adequate oxygenation (typically FiO₂ ≤0.4-0.5, PEEP ≤5-8 cm H₂O) 4

SBT Duration Protocol

Standard-risk patients: Conduct SBT for 30 minutes 2, 3

High-risk patients: Extend SBT duration to 60-120 minutes 2

The rationale is that most SBT failures occur within the first 30 minutes, but longer trials provide additional safety margin for patients at elevated risk of extubation failure. 2 The 2019 JAMA trial definitively showed that 30-minute pressure support trials were superior to 2-hour T-piece trials for standard patients. 3

SBT Failure Criteria

Immediately terminate the SBT and resume mechanical ventilation if any of the following occur:

• Respiratory rate >35 breaths/minute for >5 minutes
• Oxygen saturation <90%
• Heart rate >140 beats/minute or sustained increase >20%
• Systolic blood pressure >180 mmHg or <90 mmHg
• Increased anxiety or diaphoresis
• Signs of increased work of breathing (accessory muscle use, paradoxical breathing)

5, 4

Post-SBT Management for High-Risk Patients

For patients at high risk of extubation failure who successfully pass an SBT, extubate directly to preventive noninvasive ventilation (NIV). 1, 2

This is a strong recommendation with moderate-quality evidence showing superior outcomes for extubation success, ICU length of stay, and both short- and long-term mortality. 1

High-Risk Factors Include:

• COPD or congestive heart failure 1, 2
• Prolonged mechanical ventilation (>14 days) 2
• Hypercapnia during the SBT 1
• Older age with multiple comorbidities 1
• Ineffective cough or impaired bulbar function 2

Cuff Leak Test Protocol

For patients at high risk for post-extubation stridor, perform a cuff leak test before extubation. 1, 2

If the cuff leak test fails but the patient is otherwise ready for extubation, administer systemic steroids at least 4 hours before extubation; a repeated cuff leak test is not required. 1, 2

Adjunctive Strategies to Optimize Liberation

Implement protocolized sedation minimization for all patients ventilated >24 hours, as this shows trends toward shorter mechanical ventilation duration, shorter ICU stays, and lower short-term mortality. 1, 2

Use ventilator liberation protocols to standardize the weaning process and ensure consistent daily screening. 1, 2 A landmark 1996 trial demonstrated that daily screening followed by SBTs reduced median ventilation duration from 6 days to 4.5 days (P=0.003) and complications from 41% to 20% (P=0.001). 4

Target Extubation Failure Rate

Aim for an extubation failure rate of 5-10%. 2

• Rates >10% suggest inadequate assessment of readiness for extubation 2
• Rates <5% may indicate overly conservative practices that unnecessarily prolong mechanical ventilation 2

Common Pitfalls to Avoid

Do not use T-piece or CPAP alone for the initial SBT in patients ventilated >24 hours, as this results in significantly higher SBT failure rates (22% vs 14% with pressure support, P=0.03) without improving patient selection. 5

Do not delay extubation in high-risk patients who pass an SBT without planning for preventive NIV, as this strong recommendation is supported by evidence of mortality benefit. 1

Do not perform excessively long SBTs (>2 hours) in standard-risk patients, as the 2019 JAMA trial showed 30-minute pressure support trials were superior to 2-hour T-piece trials. 3