Short-term effects of surfactant therapy on lung function and intrapulmonary pressure in prematures < 1500 g

Objectives. To evaluate the changes in respiratory mechanics of VLBW after application of exogenous surfactant and to study the conditions for the dev elopment of an inadvertent PEEP. Patients and Methods. Respiratory mechanics were assessed in 9 ventilated V LBW with RDS (gestational age 27 +/- 2 weeks, birth weight 945 +/- 174 g) u sing a computer-controlled interrupter technique before and 10, 20,30,60 mi n and 3,6,12,24 h after application of 100 mg/kg Survanta (R). Results. After application of surfactant compliance decreased within 30 min , returned to the initial value and increased significantly after 24 h. The expiratory time constant also increased after 12 to 24 h. At this time 2 p atients showed an inadvertent PEEP (> 1,0 cm H2O). These patients had respi rator settings with an expiratory time <4 time constants. Conclusions. We speculate that exogenous surfactant initially leads to over distension of ventilated alveoli and later to ventilation of formerly atele ctatic parts of the lung thus explaining the observed changes in lung funct ion. Insufficient adjustment of expiratory time to expiratory time constant may cause an inadvertent PEEP.