Expired CO(2) Levels Indicate Degree of Lung Aeration at Birth

As neonatal resuscitation critically depends upon lung aeration at birth, knowledge of the progression of this process is required to guide ongoing care. We investigated whether expired CO(2) (ECO(2)) levels indicate the degree of lung aeration immediately after birth in two animal models and in preterm infants. Lambs were delivered by caesarean section and ventilated from birth. In lambs, ECO(2) levels were significantly (p<0.0001) related to tidal volumes and CO(2) clearance/breath increased exponentially when tidal volumes were greater than 6 mL/kg. Preterm (28 days of gestation; term = 32 days) rabbits were also delivered by caesarean section and lung aeration was measured using phase contrast X-ray imaging. In rabbit kittens, ECO(2) levels were closely related (p<0.001) to lung volumes at end-inflation and were first detected when ∼7% of the distal lung regions were aerated. ECO(2) levels in preterm infants at birth also correlated with tidal volumes. In each infant, ECO(2) levels increased to >10 mmHg 28 (median) (21–36) seconds before the heart rate increased above 100 beats per minute. These data demonstrate that ECO(2) levels can indicate the relative degree of lung aeration after birth and can be used to clinically assess ventilation in the immediate newborn period.