Early ventilatory management and lung function in the immature newly born. Experimental studies in lambs

Abstract: Using an animal model, the thesis explores how the initial ventilation of the lungs, and surfactant therapy, should best be managed after premature birth. Material and measurements: The studies were made in newborn lambs delivered by cesarean section. Spread of exogenous surfactant was analysed by mixing it with technetium-labelled macroaggregated human serum albumin and imaging the radioactivity with a gamma camera. The effect of surfactant supplementation and different ventilation strategies was analysed with static pressure volume (PV) curves of the respiratory system and by histologic assessment. Main findings: Intratracheally instilled surfactant spread quickly and reached its final place within one minute. If instilled before the first breath, the intrapulmonary distribution of surfactant was uniform. In contrast, giving five large breaths (20 mL/kg) before surfactant resulted in a very uneven distribution, mainly to dependent lung parts. Immature lambs treated in this way also had poorer lung function. However, hyperinflation of the lungs was not always harmful. Notable lung function derangement occurred only if the large breaths were given immediately after birth. Preceding surfactant instillation did not completely protect against the adverse effect of such very early hyperinflations, but already at 10 minutes of age the large breaths were no longer harmful. Also, giving large breaths at 30 min after birth in order to recruit lung volume before delayed surfactant treatment had no positive or negative effect. In lambs given surfactant at birth and not subjected to large breaths, the shape of the P-V curve was investigated. The expiratory, but not the inspiratory, part of the curve was found to be useful for determining optimal positive end-expiratory pressure during mechanical ventilation. Possible clinical implications: In immature newborns, the way ventilation is initiated immediately after birth may determine both the response to surfactant and subsequent lung morbidity.