Permissive hypercapnia for neonates given a clean bill of health - almost

Premature, very-low-birth-weight babies have immature lungs and frequently require mechanical ventilation to ensure the gas (O₂, CO₂) exchange necessary for survival. Ventilation sufficiently aggressive to maintain partial pressure of carbon dioxide in blood (pCO₂) within normal limits can cause mechanical damage to the fragile lungs of these babies that may result in chronic lung disease. 

This trauma is minimized by less aggressive ventilation, which inevitably results in raised pCO₂ (hypercapnia). Although the efficacy of this treatment strategy - known as "permissive hypercapnia" - to preserve lung tissue is undisputed, there remains concern that it might increase the risk of intraventricular hemorrhage (IVH), a relatively common complication of extreme prematurity occurring during the first week of life that, if sufficiently severe, causes permanent brain damage and threatens survival.

 To investigate this issue researchers recovered the medical charts of 1162 very premature (<32 weeks gestation) very-low-birth-weight (<1500 g) babies admitted to 16 Wisconsin neonatal intensive care units across the US state of Wisconsin during 2004. 

Using blood gas data, they identified 129 babies who had clearly been assigned to the less aggressive "permissive hypercapnia" treatment strategy and 242 babies who received more aggressive respiratory support and maintained normal pCO₂. 

There was little difference between the two groups in terms of incidence of IVH of any severity (24 % for the permissive hypercapnia group versus 27 % for the normocapnia group) or for severe IVH (11 % versus 10 %). This allowed the researchers to conclude that permissive hypercapnia does not increase the risk of IVH. 

This general conclusion was tempered somewhat by the finding of an unexpected association between 1-minute Apgar score and comparative risk of IVH between the two groups. This analysis suggests that for a small minority of premature low-birth-weight babies with lowest 1-minute Apgar score (<2), permissive hypercapnia might increase the risk of IVH. 

A 2-year follow-up of study survivors revealed no evidence that permissive hypercapnia causes long-term brain damage. Overall, the study provides comforting evidence that permissive hypercapnia is a treatment strategy that does not expose the vast majority of very premature babies to increased risk of IVH and its associated devastating consequences.