Mechanical Properties of the Lungs of Posttraumatic Rats Are Improved by Including Fat in Total Parenteral Nutrition

Posttraumatic lung failure is often associated with alterations in lung surfactant composition and function. Our previous studies with total parenteral nutrition (TPN) have shown the effect of fat supply on phospholipid composition in pulmonary surfactant. Consequently, we attempted to determine whether fat supply would also improve the functional properties of the lung and surfactant. After polytrauma consisting of laparotomy, hypovolemia, and a single femur fracture, the animals were fed only parenterally for 14 days. Two groups of rats were infused via the jugular vein with isocaloric (260 kcal/kg/day) and isonitrogenous (5.62 gN/kg/day) regimens. The nonprotein calories were given either as glucose alone or 30% of calories as fat. Lung function was assessed by measurement of static lung compliance and total lung capacity. Surfactant isolated from lavage fluid was evaluated by means of a Wilhelmy balance. In agreement with our previous studies, in which we obtained a higher level of saturated lecithin in the fat groups, we found significantly (p < 0.05) increased compliance (2.93 ± 0.54 ml/cm H₂O/kg BW) in the fat group compared to the carbohydrate group (2.02 ± 0.36 ml/cm H ₂O/kg BW). Furthermore, a significantly (p < 0.05) elevated total lung capacity was noted in the fat group (32.60 ± 3.90 us 26.00 ± 1.45 ml/kg BW). The relatively improved surface tension properties as expressed by stability index (S = 0.89 ± 0.24 vs 0.66 ± 0.22) and minimum surface tension (γ min = 18.5 ± 5.01 vs 20.75 ± 2.81) is a characteristic change, and was seen in the fat group. From these data, we conclude that it is possible to influence surfactant composition and to improve lung function properties with a lipid emulsion. Such an emulsion may prove useful in preventing posttraumatic lung complications. (Journal of Parenteral and Enteral Nutrition 11:560-565, 1987)