Lung lymph response to overinfusion with hydroxyethyl starch in sheep - Comparative studies of high and low molecular weight compounds

Background: Several hydroxyethyl starch (HES) solutions are available clini cally. We performed comparative studies of low and high molecular weight HE S to evaluate the effects on lung lymph flow in sheep, to see the differenc e in the types of HES. Methods: We prepared awake sheep with vascular monitorings and lung lymph f istulas. We measured systemic artery pressure (Psa), pulmonary artery press ure (Ppa), and left atrial pressure (Pla) continuously. Cardiac output (CO) was measured every 30 min. Lung lymph flow (Qlym) was collected every 15 m in. After baseline measurements, two HES solutions were infused over 2 h, r espectively. Experiment 1 (n=6): low molecular weight HES (MW 70 000, subst itution ratio 0.5-0.55), Experiment 2 (n=5): high molecular weight HES (MW 450 000, substitution ratio 0.7). Results: Both low and high molecular HES behaved similarly as a volume expa nder, increasing Psa, CO, Pla and Ppa, and decreasing hematocrit. In additi on, the actual oncotic pressure gradient (plasma - lymph) was widened after the start of either low or high molecular HES, but the value for high mole cular HES was significantly higher than that for low molecular HES. Qlym of low molecular HES rose significantly from the baseline and the percent inc rease in Qlym for low molecular HES was significantly higher than that for high molecular HES. Conclusion: These data suggest that low molecular HES is as useful a plasma substitute as high molecular HES, but may increase lung fluid filtration i n the overinfused state.