Abstract
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 CO2 (ECO2) 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, ECO2 levels were significantly (p<0.0001) related to tidal volumes and CO2 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, ECO2 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. ECO2 levels in preterm infants at birth also correlated with tidal volumes. In each infant, ECO2 levels increased to >10 mmHg 28 (median) (21–36) seconds before the heart rate increased above 100 beats per minute. These data demonstrate that ECO2 levels can indicate the relative degree of lung aeration after birth and can be used to clinically assess ventilation in the immediate newborn period.
Highlights
Infants, premature infants, commonly suffer respiratory failure after birth and require breathing support because their airways are partially liquid-filled [1]
We have demonstrated that expired CO2 (ECO2) levels can provide important information to guide resuscitation immediately after birth when respiratory support fails to improve cardiorespiratory parameters in preterm infants
An increase in ECO2 levels with increasing lung aeration was most closely associated with end-inflation lung volumes, was associated to a lesser degree with VT and was not directly associated with functional residual capacity (FRC)
Summary
Premature infants, commonly suffer respiratory failure after birth and require breathing support because their airways are partially liquid-filled [1]. This restricts the onset of pulmonary gas exchange and delays the cardiovascular changes that underpin the transition to air breathing at birth [1,2,3]. Transcutaneous oxygen saturation (SpO2) and heart rate (HR) are important indicators of adequate ventilation in the delivery room [6,7], which are further improved with respiratory function monitoring to measure gas flows and tidal volumes [8,9] These parameters provide little information on ventilation efficiency and the degree of gas exchange and provide limited feedback to guide clinical care when cardiorespiratory indicators fail to improve
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