Permissive hypercapnia and oxygenation impairment in premature ventilated infants.

AIM

In permissive hypercapnia high levels of carbon dioxide (CO) are tolerated in ventilated preterm infants to minimise lung injury, but hypercapnia could directly impair oxygenation. We aimed to quantify the association of elevated CO with oxygenation impairment in preterm infants by measuring the right-to-left shunt and the ventilation/perfusion (V/Q) ratio.

METHODS

Pre-existing datasets from preterm infants during the acute phase of respiratory distress syndrome or with evolving or established bronchopulmonary dysplasia were analysed. Non-invasive paired measurements of the fraction of inspired oxygen (FO) and transcutaneous oxygen saturation (SpO) were used to calculate the degree of right-to-left shunt, right shift of the FO versus SpO curve and the V/Q.

RESULTS

A total of 75 infants (43 male) with a median (IQR) gestational age of 26.4 (24.7-27.7) weeks were studied at 7 (2-31) days. Thirty-six infants (48 %) had an arterial partial pressure of CO (PaCO) above 6 kPa. The PaCO was independently associated with the right shift of the curve [adjusted p < 0.001, unstandardised coefficient; 2.26, 95 % CI: 1.51-2.95] and the right-to-left shunt [adjusted p = 0.016, unstandardised coefficient; 1.86, 95 % CI: 0.36-3.36] after adjusting for confounders. An increase of the PaCO from 5 to 8 kPa, corresponded to a right shift of the curve of 20.2 kPa or a decrease in the V/Q from 0.66 to 0.24.

CONCLUSIONS

Increased carbon dioxide levels were significantly associated with impaired oxygenation in preterm infants with respiratory distress syndrome or bronchopulmonary dysplasia.