Patients can breathe spontaneously through a ventilator circuit; this is sometimes called a T-piece method. The advantage of this approach is that the ventilator can monitor the patient's breathing and activate an alarm if an undesirable circumstance arises. The disadvantage is that some ventilator systems require considerable patient effort to open inspiratory valves to receive gas flow.
A spontaneous breathing trial (SBT) is used to evaluate a patient's readiness to have ventilation discontinued. During the trial, ventilator support is reduced, and the patient is allowed to breathe spontaneously for a brief period (15 to 30 minutes) while the person's vital signs, SpO2, and appearance are monitored. A patient who can tolerate the procedure probably is ready to be weaned from ventilation .
Continuous Positive Airway Pressure: Ventilators can provide CPAP for spontaneously breathing patients. In the acute care setting, CPAP may be helpful for improving oxygenation in patients with refractory hypoxemia and a low FRC, as can occur with acute lung injury (ALI).
As with simple spontaneous breathing, the ventilator can provide a means of monitoring the patient.