Inactivation of pulmonary surfactant by silicone oil in vitro and in ventilated immature rabbits

Objective: Surface activity of pulmonary surfactant is impaired by exposure to syringes lubricated with silicone oil (SO). These syringes are used daily in clinical practice. Design: In vitro experiments were used for detection of SO, determination of surface activity, and semi quantitative measurement of surfactant protein (SP)-B and -C in SO/surfactant mixtures. Randomized, controlled animal studies were applied for determination of in vivo activity. Setting. University research laboratory. Interventions: Mass spectrometry of SO originating from syringes with and without surfactant was performed. The surface activity of SO plus surfactant phospholipids (PLs) or modified natural surfactant (Curosurf) was measured. SO/Curosurf preparations were further analyzed for changes in the content of SP-B and SP-C using immunoblotting. Neonatal rabbits received mixtures of SO/Curosurf (ratio 0-1.3 mg/mg PL) intratracheally and were then ventilated with a standardized sequence of peak insufflation pressures. Tidal volume curves were recorded, gas volumes of excised lungs were measured, and histologic analysis was performed. Measurements and Main Results., Dissolved SO was found after rinsing syringes with organic solvents or Curosurf. Surface activity of Curosurf was significantly reduced after addition of 0.13-1.3 mg SO/mg PL. Immunoblotting revealed interference of SO with SP-B, but not with SP-C. With increasing SO/Curosurf ratios, patchy alveolar air expansion was observed, lung gas volumes were reduced, and time to inflate the lungs was increased, whereas compliance and tidal volumes remained unimpaired. Conclusions: In vitro SO impairs surface activity of Curosurf and leads to interference with SP-B. SO contamination of exogenous surfactant impairs lung function in animal studies and should be avoided. (Crit Care Med 2009; 37:1750-1756)