The aim of this study was to compare the results of lung function measurements made before and after extubation and ventilator settings recorded immediately prior to extubation with regard to their ability to predict extubation success in mechanically ventilated, prematurely born infants. Immediately after extubation all infants were nursed in an appropriate amount of humidified oxygen bled into a headbox. Functional residual capacity, spontaneous tidal volume and compliance of the respiratory system were measured both within 4 h before and within 24 h after extubation. The peak inspiratory pressure and inspired oxygen concentration immediately prior to extubation were recorded. The results were related to extubation failure: requirement for continuous positive airways pressure or re-ventilation within 48 h of extubation. A total of 30 infants, median gestational age 29 weeks (range 25-33 weeks) were studied at a median postnatal age of 3 days (range 1-6 days). Extubation failed in ten infants, who differed significantly from the rest of the cohort with regard to their post extubation functional residual capacity (FRC) (median 23, range 15.6-28.7 ml/kg versus 28.6, range 18.1-39.2 ml/kg, P<0.01) and their requirement for a higher inspired oxygen concentration post extubation (median 0.30, range 0.21-0.40 versus 0.22, range 0.21-0.36, P<0.05). An FRC of less than 26 ml/kg post extubation had the highest positive predictive value in predicting extubation failure.
Conclusion: A low lung volume performed best in predicting extubation failure when compared to the results of other lung function measurements and commonly used 'clinical' indices, i.e. ventilator settings. A low gestational age, however, was a better predictor of extubation failure than a low lung volume.