Q: The goal of optimum PEEP is to?

A) avoid derecruitment
B) optimize best oxygenation at lowest FiO2
C) best balance between acceptable hypoxemia and permissive hypercapnia
D) minimize Dead space to zero
E) get best compliance  


Answer: A (1)

Optimum PEEP continue to remain a concept of debate among critical care practitioners. To make things complicate optimum PEEP is a not a static component, rather is a constantly changing physiological model depending on the relationship between lung volume, respiratory mechanics, dead space, cardiac output, compliance, shunt and oxygenation. But at the end the primary goal is to avoid de-recruitment. This is a misconception that optimum PEEP is to obtain best oxygenation at lowest FiO2, or playing subjectively with acceptable hypoxemia or permissive hypercapnia. It is impossible to decrease dead space to zero. Arguably, closet choice is the E,  where the best compliance is obtained but compliance can be deceiving depending on number of recruited and decruited alveoli (2) (3).


 References: 

1.  Caironi P, Cressoni M, Chiumello D, Ranieri M, Quintel M, Russo SG, et al. Lung opening and closing during ventilation of acute respiratory distress syndrome. Am J Respir Crit Care Med. 2009;181:578–86.

2. Suter PM, Fairley HB, Isenberg MD. Effect of tidal volume and positive end-expiratory pressure on compliance during mechanical ventilation. Chest. 1978;73:158–62. 

3. Jonson B, Richard JC, Straus C, Mancebo J, Lemaire F, Brochard L. Pressure-volume curves and compliance in acute lung injury: Evidence of recruitment above the lower inflection point. Am J Respir Crit Care Med. 1999;159:1172–8.