What are the recommended vent settings for a Spontaneous Breathing Trial (SBT)?

Recommended Ventilator Settings for Spontaneous Breathing Trials (SBT)

For patients requiring mechanical ventilation for more than 24 hours, SBTs should be conducted with inspiratory pressure augmentation (5-8 cmH2O) rather than without pressure support (T-piece or CPAP alone). 1

Patient Selection for SBT

Before initiating an SBT, ensure the patient meets these readiness criteria:

• FiO₂ < 0.50
• PEEP ≤ 5-8 cmH2O
• Intact airway reflexes
• Hemodynamic stability
• Adequate mental status 1

Optimal SBT Settings

Primary Recommendation

• Pressure Support: 5-8 cmH2O 1, 2
• PEEP: 5 cmH2O 1, 2
• Duration: 30-120 minutes 2

Evidence Supporting Pressure Support

Pressure-augmented SBTs demonstrate clear advantages over non-augmented trials:

• Higher SBT success rates (84.6% vs 76.7%) 1
• Higher extubation success rates (75.4% vs 68.9%) 1
• Trend toward lower ICU mortality (8.6% vs 11.6%) 1

A 2020 study of high-risk patients showed that PSV-based SBTs resulted in:

• Higher successful extubation rates at 72 hours (67% vs 56%) compared to T-piece trials 3
• Higher initial extubation rates (77% vs 63%) without increased reintubation risk 3

SBT Protocol Implementation

1. Initial Assessment: Confirm patient meets all readiness criteria

2. SBT Setup:

   • Set pressure support at 5-8 cmH2O
   • Set PEEP at 5 cmH2O
   • Set FiO₂ to maintain SpO₂ ≥ 88-90%

3. Monitoring During SBT: Watch for signs of poor tolerance:

   • Respiratory rate > 35 breaths/min or increase by > 50%
   • SpO₂ < 90%
   • Heart rate > 140 beats/min or increase by > 20%
   • Systolic BP > 180 mmHg or < 90 mmHg
   • Agitation, diaphoresis, or anxiety

4. Decision Point:

   • If signs of poor tolerance develop: Resume previous ventilator settings
   • If patient tolerates the full trial: Proceed to extubation

Special Considerations

Alternative Approaches

For patients who fail an initial pressure-supported SBT:

• Consider extending the trial with the same settings
• For difficult-to-wean patients, a recent 2024 study found no advantage to using combined PS (7 cmH2O) with PEEP (5 cmH2O) over standard T-piece trials 4

Risk Factors for SBT Failure

Be cautious with patients showing these risk factors for failing a 120-minute SBT despite passing at 30 minutes 5:

• Chronic cardiopulmonary disease
• Multiple previous SBT attempts
• Advanced age
• Elevated PaCO₂

Common Pitfalls to Avoid

1. Premature Termination: Don't terminate SBT too early based on minor changes in vital signs
2. Inadequate Duration: SBTs should last 30-120 minutes; shorter trials may miss delayed deterioration 2
3. Overlooking Readiness: Daily assessment for SBT readiness is crucial to avoid unnecessary prolongation of mechanical ventilation 1
4. Unrecognized Auto-PEEP: Especially in COPD patients, which may cause increased work of breathing during SBT
5. Ignoring Post-Extubation Support: Consider prophylactic NIV immediately after extubation for high-risk patients 2

The evidence strongly supports using pressure-augmented SBTs as they increase success rates and improve outcomes compared to non-augmented trials. This approach balances the need to adequately test a patient's ability to breathe independently while not imposing excessive work of breathing.