Q. Is there any information about how much PEEP or CPAP is transmitted to the pleural space?
A. The amount of PEEP transmitted to the pleural space is determined by the compliance of the chest wall and the lung. If lung compliance is low (the lung is stiff), but the chest wall compliance is high, meaning it expands freely, very little PEEP is transmitted to the pleural space, resulting in high transpulmonary pressure (the difference between intrapulmonary pressure and pleural pressure).1 If lung compliance is high and the chest wall compliance is low (chest wall expansion is limited due to external factors, such as obesity or skeletal conditions), much more PEEP is transmitted to the pleural space. In this case, pleural pressure can be significantly higher than atmospheric pressure..1-3
1. Nunn JF: Positive end-expiratory pressure. International Anesthesiology Clinics 1984;22(4):149-164.
2. Mason RJ, Broaddus VC, Martin TR, et al., eds: Murray and Nadel’s textbook of respiratory medicine. 5th ed. Philadelphia: Saunders Elsevier; 2010; No. 1
3. Jardin F, Genevray B, Brun-Ney D, Bourdarias J: Influence of lung and chest wall compliances on transmission of airway pressure to the pleural space in critically ill patients. Chest 1985;88(5):653-658.