Furosemide reduces lung fluid filtration in lambs with lung microvascular injury from air emboli

To study the effects of furosemide on the neonatal pulmonary circulation in the presence of lung injury, we measured pulmonary arterial and left atrial pressures, cardiac output, lung lymph flow, and concentrations of protein in lymph and plasma of nine lambs that received furosemide, 2 mg/kg iv, during a continuous 8-h intravenous infusion of air. Air embolism increased pulmonary vascular resistance by 71% and nearly tripled steady-state lung lymph flow, with no change in lymph-to-plasma protein ratio. These findings reflect an increase in lung vascular protein permeability. During sustained lung endothelial injury, diuresis from furosemide led to a rapid reduction in cardiac output (average 29%) and a 2-Torr decrease in left atrial pressure. Diuresis also led to hemoconcentration, with a 15% increase in both plasma and lymph protein concentrations. These changes were associated with a 27% reduction in lung lymph flow. In a second set of studies, we prevented the reduction in left atrial pressure after furosemide by inflating a balloon catheter in the left atrium. Nevertheless, lymph flow decreased by 25%, commensurate with the reduction in cardiac output that occurred after furosemide. In a third series of experiments, we minimized the furosemide-related decrease in cardiac output by opening an external fistula between the carotid artery and jugular vein immediately after injection of furosemide. In these studies, the reduction in lung lymph flow (average 17%) paralleled the smaller (17%) decrease in cardiac output. These results suggest that changes in lung vascular filtration pressure probably do not account for the reduction in lung lymph flow after furosemide in the presence of lung vascular injury.(ABSTRACT TRUNCATED AT 250 WORDS)