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Objective To evaluate the association between early hypocarbia and 18- to 22-month outcome among neonates with hypoxic-ischemic encephalopathy. Study design Data from the National Institute of Child Health and Human Development Neonatal Research Network randomized, controlled trial of whole-body hypothermia for neonatal hypoxic-ischemic encephalopathy were used for this secondary observational study. Infants (n = 204) had multiple blood gases recorded from birth to 12 hours of study intervention (hypothermia versus intensive care alone). The relationship between hypocarbia and outcome (death/disability at 18 to 22 months) was evaluated by unadjusted and adjusted analyses examining minimum PCO2 and cumulative exposure to PCO2 <35 mm Hg. The relationship between cumulative PCO2 <35 mm Hg (calculated as the difference between 35 mm Hg and the sampled PCO2 multiplied by the duration of time spent <35 mm Hg) and outcome was evaluated by level of exposure (none-high) using a multiple logistic regression analysis with adjustments for pH, level of encephalopathy, treatment group (+/- hypothermia), and time to spontaneous respiration and ventilator days; results were expressed as odds ratios and 95% confidence intervals. Alternative models of CO2 concentration were explored to account for fluctuations in CO2. Results Both minimum PCO2 and cumulative PCO2 <35 mm Hg were associated with poor outcome (P < .05). Moreover, death/disability increased with greater cumulative exposure to PCO2 < 35 mm Hg. Conclusions Hypocarbia is associated with poor outcome after hypoxic-ischemic encephalopathy. (J Pediatr 2011; 158: 752-8)
