Once the patient is no longer in shock, has an adequate arterial saturation on a fractional inspired oxygen (FIO2) ≤ 0.5 with a positive end-expiratory pressure (PEEP) ≤ 7.5 cm H2O, and does not have an obviously unsustainable respiratory load (eg, minute ventilation > 20 L / minute), a daily spontaneous breathing trial is done using a T-piece or continuous positive airway pressure (CPAP) of 5 cm H2O.