The febrile reaction to PFC based blood substitutes was purported (Donat R Spahn, Blood substitutes Artificial oxygen carriers: perfluorocarbon emulsions. Crit Care. 1999; 3(5): R93–R97) to be related to particle size of the emulsified infusion fluid. Lower particle size was stated to reduce the uptake by the reticuloendothelial system, which increased tolerability, as that stimulation of phagocytosis, and what must be (unmentioned) feedback loops, was deemed responsible for fever and flu like symptoms in patients receiving the blood substitues.

Spahn quotes statistics for IV administration of Oxygent “Intravascular half life is dose-dependent, and for Oxygent was found to be 9.4 ± 2.2 h for a dose of 1.8 g/kg [4]. After the initial uptake of the perfluorocarbon emulsion into the RES the droplets are slowly broken down, and the perfluorocarbon molecules are taken up in the blood again (bound to blood lipids) and transported to the lungs, where the unaltered perfluorocarbon molecules are finally excreted via exhalation. At present no metabolism of fluorocarbon molecules is known in humans.”

I didn’t see any micrographs which gave clue as to “break-down” of droplets, so this is confusing.  I have seen completely solid “footprints” of fluorocarbons, round and with lysosomal enzymes, sometimes a lot, surrounding or off to one side of a droplet, I have also seen the frothy huge lysosomal inclusions which do not have the orderly rounded appearance.