This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Anaesthesia of special situations, Subject name: Anaesthesia
Which of the following is not a role of PEEP 
Select and explain. 
A. Improves oxygenation, B. Decreases cardiac output, C. Decreases atelectasis, D. Decreases the risk of pneumothorax
D: Decreases the risk of pneumothorax
Answer: D: Decreases the risk of pneumothorax 
Explanation: PEEP prevents total collapse of alveoli at end exhalation. The stinting open of the alveoli prior to the next breath helps increase the amount of lung mass paicipating in gas exchange. PEEP decreases V/Q mismatch by decreasing atelectasis and thereby improves both oxygenation and ventilation. PEEP increases intrathoracic pressure, which can be impedance to venous return and cardiac output. PEEP increases, not decreases, the risk of pneumothorax.