Hypercapnia and the neonate

‘Permissive hypercapnia’ is a familiar term in neonatal intensive care, given the widespread adoption of low‐tidal‐volume ventilation strategies applied with the goal of decreasing respiratory morbidity. Recent evidence suggesting that hypercapnic acidosis may itself have protective effects on the lung and other organs has led to the coining of a new phrase, ‘therapeutic hypercapnia’, which also encompasses the use of supplemental inspired CO2. Conclusion: Experimental evidence suggests that mild‐moderate hypercapnia can improve tissue oxygenation and perfusion, which may ameliorate injury to the immature lung and brain. However, hypercapnia may also be associated with adverse outcomes, and the range of PaCO2 levels that are both safe and effective for specific subsets of neonates has yet to be determined.