SBT
Formal Definition
Spontaneous breathing trial: a structured assessment of a mechanically ventilated patient's ability to breathe independently by placing them on minimal ventilatory support (pressure support 5–8 cmH2O with PEEP 5, or T-piece) for 30–120 minutes and evaluating for signs of intolerance — the key step before extubation.
How It's Used on the Ward
"SBT passed" or "failed the SBT" — the breathing test that determines whether the tube comes out today.
Example
""SBT criteria met: FiO2 0.35, PEEP 5, sedation off, RASS 0, following commands. Started SBT at 8am: PS 8/PEEP 5. 60 minutes in: RR 16, SpO2 97%, BP stable, patient calm and cooperative. SBT passed — extubation planned, anesthesia notified, family at bedside.""
Clinical Context
SBT failure signs: RR >30–35, SpO2 <90%, HR >120 or >20% change from baseline, BP <90 or >180, agitation, diaphoresis, use of accessory muscles. If the SBT fails, return to full support, determine why (secretions? weakness? pain? cardiac? residual sedation?), and repeat in 24 hours. Passing the SBT predicts successful extubation 70–80% of the time — the remaining failures are from upper airway obstruction, secretion burden, or inability to protect the airway, not respiratory failure.
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