SURFACTANT TREATMENT AT BIRTH REDUCES LUNG VASCULAR INJURY AND EDEMA IN PRETERM LAMBS

To study the effect of surfactant administration on fluid balance in t he premature lung, we measured pulmonary vascular pressures, lung lymp h and pleural liquid flow, and concentrations of protein in lymph, ple ural liquid, and plasma before and after birth in 12 chronically cathe terized preterm lambs (127-128 d gestation) treated with either placeb o or surfactant just before surgical delivery. Eight lambs received in trapulmonary saline (placebo), and four lambs received surfactant; all lambs were mechanically ventilated with O-2 for 8 h after birth. In c ontrol lambs, lung lymph and pleural liquid flow increased from 2.7 +/ - 0.4 mL/h during the 2-4 h before birth to 9.2 +/- 2.1 mL/h by 6-8 h after birth; lymph and pleural space protein drainage increased from 5 8 +/- 7 mg/h during the 2-4 h before birth to 134 +/- 25 mg/h by 6-8 h after birth. In lambs treated with surfactant, there was no significa nt increase in lymph and pleural liquid flow after birth (before birth , 2.3 +/- 0.3 mL/h; 6-8 h after birth, 3.4 +/- 0.9 mL/h); likewise, ly mph and pleural space protein drainage did not change after birth (bef ore birth, 54 +/- 6 mg/h; 6-8 h after birth, 50 +/- 8 mg/h). Postmorte m extravascular lung water was significantly less in lambs treated wit h surfactant compared with control lambs (control, 6.5 +/- 0.3 g/g dry lung; surfactant-treated, 5.0 +/- 0.2 g/g dry lung). Thus, surfactant administration at birth diminishes transvascular movement of fluid ac ross the pulmonary microcirculation, preserves lung vascular protein p ermeability, and reduces pulmonary edema in newborn lambs that are del ivered prematurely.