Pulmonary Gas Trapping in Premature Infants

Abstract

Extract: Measurements of thoracic gas volume and functional residual capacity were performed serially from birth on 26 premature infants to determine the presence and time course of gas trapping. Nitrogen washouts were carried out on 16 of these infants and urinary-alveolar nitrogen gradients (uADN2) were measured in 7. The infants were divided into two groups, those above and those below 1750 g birth weight. Trapped gas was documented in both groups, but in the smaller infants the condition persisted for a longer time. The mean thoracic gas volume (TGV) in infants over 1750 g birth weight was 2.0 ± 0.7 ml/cm at birth, with a mean functional residual capacity (FRC) of 1.3 ± 0.4 ml/cm; by day 9, the TGV and FRC were 1.5 ± 0.3 and 1.2 ± 0.2 ml/cm, respectively. Infants under 1750 g birth weight had a mean TGV of 1.7 ± 0.2 ml/cm at birth with an FRC of 0.9 ± 0.2 ml/cm; by week 2 of life, mean TGV and FRC were 0.9 ± 0.2 and 0.8 ± 0.2 ml/cm, respectively. When gas trapping was present, nitrogen washouts and uADN2 indicated that the lung was a single well ventilated space with no evidence of an abnormal distribution of ventilation. This indicated that ventilation of the trapped areas was so small that it could not be measured. The possibility that gas trapping is related to the presence of lung fluid and very compliant airways is considered. Speculation: Low birth weight infants have been shown to have high airway resistance, compliant airways, and low lung volume. This combination of findings has been associated with airway closure in adults. The possibility arises that a volume of gas is “trapped” with each expiration until airways are sufficiently stiff and remain patent with every breath.