FLUID RESTITUTION AND BLOOD-VOLUME REDISTRIBUTION IN ANESTHETIZED RABBITS IN RESPONSE TO VASOACTIVE DRUGS

Background Vasoactive drugs could alter the fluid restitution from the tissue and redistribute blood volume between the macrocirculation and microcirculation. Methods and Results With bolus injections of vasoac tive drugs in anesthetized rabbits, we measured the changes in blood a nd plasma density for the determination of the volume of restitution a nd redistribution. Epinephrine 3.5 mu g/kg caused a fluid loss to the tissue, leading to a transient decrease in total blood volume by 2.30 mL/kg. Because of blood volume redistribution, the peak volume reducti on was accompanied by a volume reduction of 0.81 mL/kg from the macroc irculation and 1.49 mL/kg from the microcirculation. Phenylephrine 70 mu g/kg caused a peak reduction in total blood volume of 1.40 mL/kg (w ith 0.41 mL/kg from macrocirculation and 0.99 mL/kg from microcirculat ion). Nitroprusside 7 mu g/kg increased the blood volume by 1.44 mL/kg (0.83 mL/kg macro and 0.61 mL/kg micro), nitroglycerin 7 mu g/kg by 1 .48 mL/kg (0.97 mL/kg macro and 0.51 mL/kg micro), and isoproterenol 7 mu g/kg by 2.07 mL/kg (0.68 mL/kg macro and 1.39 mL/kg micro). All pl asma (or blood) density changes measured for the five drugs (with epin ephrine, phenylephrine, and nitroprusside done over a wide dosage rang e) correlated linearly with the drug-induced changes in arterial press ures. Conclusions These results indicate that vasoactive drugs alter t otal blood volume and the volume of microcirculation and macrocirculat ion.