Pulmonary Vascular Effects of Fat Emulsion Infusion in Unanesthetized Sheep

Abstract

A C T Pulmonary diffusing capacity and arterial blood Po2 decrease in humans when 10% fat emulsion is infused. To study its effects on the pulmonary circulation and lung fluid balance, we infused 0.25 g/kg x h of a 10% fat emulsion (Intralipid, Cutter Laboratories, Inc., Berkeley, Calif.) into an awake sheep lung lymph preparation. The emulsion caused a sustained increase in pulmonary artery pressure to approximately twice base line with little change in left atrial pressure. Pa02 decreased an average 13 torr and lung lymph flow increased two-to threefold. Lymph/ plasma total protein concentration fell as lymph flow increased; the magnitude of the lymph/plasma protein decrease was similar to that reported previously when lung vascular pressures were mechanically elevated. Heparin infusion (loading dose = 4,000 U, mainte- nance dose = 2,000 U/h) cleared the serum of tri- glycerides but did not alter the response to fat emul- sion. Indomethacin infusion (loading dose = 5 mg/kg, maintenance dose = 3 mg/kg x h) blocked the rise in pulmonary artery pressure, the increase in lung lymph flow, and the fall in Pao0. Neither extravascular lung water nor [14C]urea lung vascular permeability sur- face area products were altered by fat emulsion infusion. We conclude that fat emulsion infusion in sheep increases lung microvascular filtration by increasing vascular pressures, but has no effect on vascular permeability. Since the effects are blocked by indo- methacin, they may be prostaglandin mediated.