Spontaneous breathing trial

A spontaneous breathing trial is a test for patients on mechanical ventilation, before they can be extubated and liberated from mechanical ventilation, i.e. return to normal breathing. SBTs are daily tests performed on intubated patients to determine if they meet criteria for extubation.
The SBT involves placing the patient on minimal ventilatory support for a set period, typically 30–120 minutes, and under close monitoring. There are two common methods: In a T-Piece Trial, the ventilator is completely removed, and the patient breathes through a T-piece connected to the endotracheal tube and supplied with humidified oxygen. Because no ventilatory support is provided, this provides a pure test of the patient’s ability to breathe independently, and is more challenging. More commonly, low-level pressure support ventilation can be used, providing some inspiratory pressure with or without Positive End-Expiratory Pressure . Automatic tube compensation or minimal PSV helps patients overcome the added resistance of the endotracheal tube. This method is easier than a T-piece trial and is commonly used in ICU settings. Patients are more likely to be successfully extubated after a PSV trial compared to a T-piece trial.
Spontaneous breathing trials are often combined with spontaneous awakening trials.

Indications for trials of spontaneous breathing

Fraction of inspired oxygen less than 50%
Positive end expiratory pressure less than 8 cm water
"Minimal vent settings"
* e.g., ratio of arterial partial pressure of oxygen to F_IO₂ in the vicinity of 400

Assessment Criteria

A spontaneous breathing trial includes assessment of several criteria, including respiratory parameters, oxygenation, hemodynamics, mental status, and presence of airway/cough reflexes:
Respiratory Parameters

Respiratory Rate : < 35 breaths/min
Tidal Volume : > 5 mL/kg ideal body weight
Rapid Shallow Breathing Index : < 105 breaths/min/L
No excessive accessory muscle use or paradoxical breathing

Oxygenation Criteria

SpO₂: ≥ 90% on FiO₂ ≤ 40-50% and PEEP ≤ 5 cmH₂O
PaO₂/FiO₂ ratio: ≥ 150-200 mmHg

Hemodynamic Stability

Heart Rate : Stable, with no increase >20% from baseline
Blood Pressure : No severe hypotension or hypertension
No new arrhythmias or ECG changes

Neurological and Secretions Criteria

Awake and cooperative
Effective cough and secretion clearance

The SBT is stopped early if the patient shows signs of intolerance, including:

RR > 35 breaths/min for >5 minutes
SpO₂ < 88%
HR > 140 bpm or increase >20% from baseline
SBP >180 or <90 mmHg
Severe diaphoresis, agitation, or anxiety
Use of accessory muscles, paradoxical breathing
Respiratory acidosis

If a patient fails the SBT, they are placed back on ventilatory support, and the cause of failure is assessed. SBTs are typically repeated daily. More performing SBTs more frequently than daily is not associated with increased likelihood of successful extubation.