Intravascular mixing and drug distribution: The concurrent disposition of thiopental and indocyanine green

The dispositions of concomitantly administered indocyanine green (ICG) and thiopental were determined in 12 patients undergoing general anesthesia and surgery. These were best characterized by a two-compartment ICG model and a four-compartment thiopental model, chiefly because of data obtained from frequent early arterial blood samples. The models had a common central volume (VI), and the peripheral ICG compartment was the subset of a peripheral thiopental compartment. The two-compartment ICG model described its mixing within the intravascular space. The traditional V_c of three-compartment models of thiopental disposition is described by the present four-compartment model as an initial distribution volume, V_l, codetermined by ICG as central blood volume, and a rapidly equilibrating peripheral volume, V₄. The combined simultaneous ICG-thiopental model more clearly reflects physiology than do the results of earlier curve-fitting techniques and may be useful in studying the pharmacokinetic basis of altered reactivity to thiopental.