Mechanisms and efficacy of fluorochemical oxygen transport and delivery

Fluorochemicals for medical use are metabolically inert liquids with a high solubility for gases, and can dissolve 50 percent or more of their own volume of oxygen (O2) at ambient pressures. The solubility is directly proportional to the oxygen tension (PO2) and transport is thus not saturable, unlike the O2 saturation of hemoglobin (Hb) which follows the well known "S" shaped relationship with PO2. Intravenously-injected emulsions of fluorocarbons transport only about one seventh as much O2 as Hb on a gram for gram basis, even when high concentrations of O2 are respired. However, because of the high O2 extraction from fluorocarbons in these circumstances, their contribution to O2 consumption is more than 65% of that of Hb. O2 delivery to the tissues depends on the product of the cardiac output and the arterial oxygen content. When red cells are transfused, blood viscosity increases and cardiac output decreases. This lessens the efficacy of blood in comparison to that of fluorocarbons, and increases the relative transport of O2 in the metabolically readily-accessible plasma compartment. This provides an interesting application for low dose fluorocarbons during surgery in combination with autologous blood use. The efficacy of fluorocarbons in this setting can be predicted by computer modelling.