- Stable ventilatory and hemodynamic status defined by positive end- expiratory pressure ≤ 8 cm H2O, inspiratory oxygen fraction ≤ 40%, ratio of arterial oxygen partial pressure to fractional inspired oxygen ≥ 150, respiratory rate ≤ 35 breaths per minute, heart rate ≤ 130 beats per minute and systolic blood pressure between 90 and 160 mmHg.