The influence of intratracheal saline upon the dynamic lung-thorax compliance of premature newborn rabbits.

A modern therapy for the respiratory distress syndrome in neonates is the substitution of alveolar surfactant. Supplementary surfactant has to be applied to the lung via an aqueous emulsion. To estimate the effects of fluids instilled into the lungs a total of 144 premature newborn rabbits were used. They were delivered by hysterotomy after 27, 28 or 29 gestational days (term = 31 +/- 1 days; mean +/- SD), anaesthetized (0.5 mg ethylurethane/kg b.w.), paralyzed (1 mg pancuronium bromide/kg b.w.) and ventilated by positive pressure (P = 25 hPa; f = 40/min; I:E = 1:1) with 100% oxygen. By means of body-plethysmography the tidal volume (VT) was recorded before and regularly during 90 min after the application of 0 (controls), 5, 10 or 20 ml saline (0.9% NaCl solution) per kg b.w. intratracheally. Dynamic lung-thorax compliance (Crs) was calculated as VT/P and related to the body weight. The initial Crs values (mean +/- SD) were 0.06 +/- 0.02 (27 days), 0.62 +/- 0.52 (28 days) and 1.08 +/- 0.21 (29 days) ml/hPa/kg, respectively (p less than 0.001). Intratracheal saline application had no detectable effect on Crs in rabbit neonates on day 27 of gestation. On day 28 or 29 of gestation there was a transient (approximately 15 min) Crs reduction, increasing with the volume of applied liquid. At a given saline quantity the severity of Crs reduction depended more on the magnitude of the initial Crs values than on the gestational day.(ABSTRACT TRUNCATED AT 250 WORDS)