How is optimal PEEP defined?

• A. Maximum inspiratory pressure
• B. Point of maximal alveolar recruitment
• C. Lowest FiO2
• D. Best compliance

Answer: (B)

Optimal PEEP is the level that keeps the lung open by recruiting collapsed alveoli, reaching the point where the greatest number of alveoli are opened and can stay open without causing overdistension. As PEEP rises from very low values, more alveoli recruit, improving gas exchange and apparent compliance. After a certain level, further increases mainly overdistend already open units and can worsen hemodynamics; the recruitment gains plateau. The best PEEP, then, is the PEEP at which alveolar recruitment is maximal. Other choices describe different metrics (inspiratory pressure, FiO2) or use a proxy like overall compliance, but they do not capture the idea of the maximal recruitment point.