EARLY MEASUREMENT OF LUNG-VOLUME - A USEFUL DISCRIMINATOR OF NEONATALRESPIRATORY-FAILURE SEVERITY

Respiratory distress syndrome (RDS) is characterized by lungs having c ollapsed alveoli (atelectasis) which reduces the volume of the gas-con taining spaces of the lung. It seems likely, therefore, that measureme nt of lung volume might discriminate between infants with severe respi ratory failure due to RDS and those with minimal respiratory distress. To test this hypothesis, lung volume was measured at end expiration, that is functional residual capacity (FRC), in 40 infants (median gest ational age 29 weeks, range 24-35) all mechanically ventilated from bi rth. FRC was measured using a helium gas dilution technique at a media n of 3 h of age. The infants were divided into two groups according to their FRC results: group A (n = 29) low FRC (FRC < 24 ml kg(-1)) and group B (n = 11) normal FRC (FRC greater than or equal to 24 ml kg(-1) ). The clinicians were unaware of the FRC results. There was no signif icant difference in the gestational age or birthweight of the two grou ps, but group A were characterized by a significantly greater proporti on requiring surfactant replacement therapy (p < 0.01), a higher maxim um peak inspiratory pressure (p < 0.01) and inspired oxygen requiremen t (p < 0.01). A low FRC had 79% sensitivity and 91% specificity in pre dicting a requirement for surfactant replacement therapy. We conclude that measurement of FRC in the first hours of life does allow discrimi nation of disease severity.