Spectrum of chronic lung disease in a population of newborns with extremely low gestational age.

AIMS: To determine how the ability to oxygenate the blood develops after birth in infants of extremely low gestational age (ELGANs) and to find risk factors for chronic lung disease. METHOD: A prospective, population-based, cohort study was undertaken in one tertiary-care centre. The alveolar-arterial oxygen pressure difference (AaDO(2)) was monitored. RESULTS: Of 41 survivors, 21 had a period of normal lung function in the first week of life, after which oxygenation deteriorated. Low gestational age and low Apgar score at 5 min were found to be strong and independent predictors of AaDO(2) in the first month of life. Mechanical ventilation did not appear as a risk factor. Lung function at 36 weeks of gestation and duration of oxygen treatment could be better predicted by the severity of lung disease in the first month than by gestational age at birth. CONCLUSIONS: Difficulty in oxygenation was a general observation in ELGANs and not only a particular subset. Gestational age and Apgar score were independent predictors of the degree of difficulty over the first month of life. As oxygenation failure often developed after a few days, the process may be possible to treat or prevent once the pathogenesis is known.

Surfactant replacement therapy improves ventilation inhomogeneity in infants with respiratory distress syndrome.

Surfactant deficiency in newborn infants with hyaline membrane disease (HMD) reduces peripheral airway stability, leading to lung atelectasis, inhomogeneity of distribution of ventilation, ventilation/perfusion mismatch, and hypoxemia. The aim of this study was to evaluate the immediate effect of exogenous surfactant treatment on ventilation inhomogeneity (VIH) in infants with HMD. Homogeneity of ventilation was measured repeatedly in ten infants (median gestational age 30 weeks and birthweight 1.50 kg) after Exosurf, and in six infants (median gestational age 30 weeks and birthweight 1.42 kg) after Survanta treatment. Lung function was measured before and 0.5, 2, and 6 hours after administration of a single dose of surfactant. The multiple breath nitrogen washout method was used to measure the time pattern of nitrogen elimination from the lungs. VIH was evaluated by using both a compartmental lung model and a model-independent moment analysis. The two-compartment lung model was found to dominate before surfactant treatment, while a single-compartment model (implying homogeneous ventilation) fitted the washout data best 6 hours after Exosurf treatment (P < 0.01). The same pattern occurred 2 hours after Survanta administration. Moment analysis confirmed the reduction in VIH by both surfactants. This study supports the hypothesis that the improved oxygenation after surfactant treatment in infants with HMD results from a reduction in VIH and an increase in functional residual capacity (FRC).

Measurement of tidal volume during high frequency ventilation by impedance plethysmography.

Electrical impedance plethysmography was evaluated in lambs as a method of measuring tidal volume (VT). Over tidal volumes ranging from 15 to 414% of estimated dead space, and frequencies of 300 to 1000 breaths/min, correlation between VT measured by the impedance technique and VT measured by whole-body plethysmography was 0.98. Above 600 breaths/min, the correlation between the two methods was 0.94. Independent calibration of the impedance technique using a pneumotachograph at conventional rates of ventilation yielded absolute values of VT which closely corresponded to values obtained with the whole-body plethysmograph (slope = 1.05, intercept = 1.4 ml, r = 0.99). These results support the potential utility of impedance plethysmography in clinical applications of high frequency ventilation.