This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Respiratory system, Subject name: Medicine
Theoretical "Optimal PEEP" in ARDS is 
Select and explain. 
A. 0 - 5 mm Hg, B. 5 - 12 mm Hg, C. 12 - 15 mm Hg, D. 15 - 18 mm Hg
C: 12 - 15 mm Hg
Answer: C: 12 - 15 mm Hg 
Explanation: In most clinical settings, positive end-expiratory pressure (PEEP) is empirically set to minimize Fio2 (inspired O2 percentage) and maximize Pao2 (aerial paial pressure of O2). On most modern mechanical ventilators, it is possible to construct a static pressure-volume curve for the respiratory system. The lower inflection point on the curve represents alveolar opening (or "recruitment"). The pressure at this point, usually 12-15 mmHg in ARDS, is a theoretical "optimal PEEP" for alveolar recruitment.Ref: Harrison 19e pg: 1738