Early Postnatal Hypocapnia and Hypercapnia in Ventilated Preterm Infants: Incidence and Associations with Adverse Outcomes

Background/Objectives: Abnormalities in the partial pressure of carbon dioxide (PCO2) can occur during respiratory support and may contribute to adverse neonatal outcomes. This study aimed to assess the incidence of early hypocapnia and hypercapnia in mechanically ventilated preterm infants and their major associated outcomes. Methods: A single-center retrospective cohort study (2017–2024) was conducted in preterm infants 24 h of invasive ventilation within the first 3 days of life. Perinatal–neonatal data were retrieved from the medical database. Admission blood gas values (arterial and capillary–venous) and the maximum and minimum PCO2 in the first 72 h were evaluated. Normocapnia was defined as PCO2 35–45 mmHg, hypocapnia as 45 mmHg. Primary outcomes were the incidence of PCO2 abnormalities; secondary outcomes included death or severe brain injury (SBI), SBI alone, and bronchopulmonary dysplasia (BPD) among survivors. Logistic regression identified independent predictors of the secondary outcomes. Results: Among the 134 infants evaluated, most experienced both hypercapnia and hypocapnia. Hypercapnia occurred in 81.3% of infants, and hypocapnia in 93.2%. Death or SBI was observed in 51.5%, and SBI alone in 42.5%. Gestational age < 28 weeks, air-leak syndromes, and pulmonary hemorrhage were independent predictors of death or SBI. Among survivors, hypercapnia and gestational age < 28 weeks independently predicted BPD. Infants with adverse outcomes had higher maximum PCO2 values and greater PCO2 variability, although these were not independent predictors of SBI or death. Conclusions: PCO2 instability is highly prevalent in ventilated preterm infants, underscoring the need for individualized ventilation strategies. Extreme prematurity emerged as the primary risk factor for adverse outcomes, while hypercapnia was independently associated with BPD.