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

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 PaCO2 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 PaCO2, fluctuation of PaCO2, maximal and minimal PaCO2, 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 (PaCO2 <30 mm Hg), 47% were normocapnic (PaCO2 35–45 mm Hg), 26.5% had mild hypercapnia (PaCO2 45–55 mm Hg), 13% had moderate hypercapnia (PaCO2 55–65 mm Hg), and 6.5% had severe hypercapnia (PaCO2 ≥ 65 mm Hg). There were no adverse events associated with hypocapnia. Subjects with death/severe intraventricular hemorrhage had a higher mean PaCO2 of 52.3 versus 44.7 (odds ratio [OR] 1.16, 95% CI 1.04–1.29, P = .006), higher variability of PaCO2 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 PaCO2 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.