Blood carbon dioxide levels and adverse outcome in neonatal hypoxic-ischemic encephalopathy

We investigated pCO₂ patterns and the relationship between pCO₂ levels and neurodevelopmental outcome in term infants with hypoxic-ischemic encephalopathy. Blood gases during the first 72 hours of life were collected from 52 infants with hypoxic-ischemic encephalopathy. Moderate hypocapnia (pCO₂ <3.3 kPa), severe hypocapnia (pCO₂ <2.6 kPa), and hypercapnia (pCO₂ >6.6 kPa) were correlated to neurodevelopmental outcome at 24 months. Normocapnia was documented in 416/551 (75.5%) of samples and was present during the entire 72 hours in only 6 out of 52 infants. Mean (standard deviation) pCO₂ values did not differ between infants with normal and abnormal outcomes: 5.43 (2.4) and 5.41 (2.03), respectively. There was no significant association between moderate hypocapnia, severe hypocapnia, or hypercapnia and adverse outcome (odds ratio [OR]=1.84, 95% confidence interval [CI]=0.49 to 6.89; OR=3.16, CI=0.14 to 28.45; and OR=1.07, CI=0.24 to 5.45, respectively). In conclusion, only one in nine newborns had normocapnia throughout the first 72 hours. Severe hypocapnia was rare and occurred only in ventilated babies. Hypercapnia and hypocapnia in infants with hypoxic-ischemic encephalopathy during the first 72 hours of life were not associated with adverse outcome.