Incidence of Hypocapnia, Hypercapnia, and Acidosis and the Associated Risk of Adverse Events in Preterm Neonates

Abstract

Background: Permissive hypercapnia is a lung-protection strategy. We sought to review our current clinical practice for the range of permissive hypercapnia and identify the relationship between P_aCO2 and pH and adverse outcomes.

Methods: A secondary analysis of a delayed cord-clamping clinical trial was performed on all arterial blood gas tests in the first 72 h in infants < 32 weeks gestational age. All arterial blood gas values were categorized into a clinical range to determine the percent likelihood of occurring in the total sample. The univariate and multivariate relationships of severe adverse events and the time-weighted P_aCO2 , fluctuation of P_aCO2 , maximal and minimal P_aCO2 , base excess, and pH were assessed.

Results: 147 infants with birthweight of 1,206 ± 395 g and gestational age of 28 ± 2 weeks were included. Of the 1,316 total samples, < 2% had hypocapnia (P_aCO2 <30 mm Hg), 47% were normocapnic (P_aCO2 35-45 mm Hg), 26.5% had mild hypercapnia (P_aCO2 45-55 mm Hg), 13% had moderate hypercapnia (P_aCO2 55-65 mm Hg), and 6.5% had severe hypercapnia (P_aCO2 ≥ 65 mm Hg). There were no adverse events associated with hypocapnia. Subjects with death/severe intraventricular hemorrhage had a higher mean P_aCO2 of 52.3 versus 44.7 (odds ratio [OR] 1.16, 95% CI 1.04-1.29, P = .006), higher variability of P_aCO2 with a standard deviation of 12.6 versus 7.8 (OR 1.15, 95% CI 1.03-1.27, P = .01), and a lower minimum pH of 7.03 versus 7.23 (OR 0, 95% CI 0-0.06, P = .003). There was no significant difference in any variables in subjects who developed other adverse events.

Conclusion: The routine targeting of higher than normal P_aCO2 goals may lead to a low incidence of hypocapnia and associated adverse events. Hypercapnia is common, and moderate hypercapnia may increase the risk of neurologic injury and provide little pulmonary benefit.

Keywords: blood gas analysis; bronchopulmonary dysplasia; carbon dioxide; hypercapnia; hypocapnia; intraventricular hemorrhage; mortality; premature; ventilator-induced lung injury; very low birthweight infant.