Which of the following is a typical criterion indicating readiness for a spontaneous breathing trial?

• A. FiO2 ≤ 0.4–0.5 and PEEP ≤ 5–8 cm H2O
• B. FiO2 ≥ 0.8 and PEEP ≥ 12 cm H2O
• C. Absolute hemodynamic instability
• D. High dose vasopressor requirement

Answer: (A)

A typical readiness criterion for a spontaneous breathing trial is adequate oxygenation with minimal ventilator support. This is reflected by a low FiO2 (about 0.4–0.5 or less) and a modest PEEP (roughly 5–8 cm H2O or less). Meeting these thresholds indicates the lungs can exchange gas and stay recruited without relying on high oxygen delivery or heavy positive pressure, making it safer to test breathing without full ventilator support. In contrast, requiring high FiO2 and high PEEP signals ongoing oxygenation risk and substantial support needs, while absolute hemodynamic instability or a high-dose vasopressor requirement suggests the patient may not tolerate the stress of spontaneous breathing.