Is permissive hypercapnia helpful or harmful?

Permissive hypercapnia (PHC) is a ventilatory strategy in which high levels of carbon dioxide (CO2) are tolerated as to avoid high tidal volumes, lung over-distention and ventilator induced lung injury. The decrease of mortality and morbidity in asthma, ARDS and neonatal chronic lung disease using lung protective strategies and permissive hypercapnia is described in several studies. In spite of the limitation in knowledge regarding the physiological effects of PHC, there are clinical data demonstrating its benefits in several clinical scenarios. This article describes the physiological effects of PHC, the use of PHC in clinical scenarios and the contra-indications of PHC in neonates and children.