Critical Oxygen Delivery Levels during Shock Following Normoxic and Hyperoxic Haemodilution with Fluorocarbons or Dextran

Summary

Fluosol-DA 20% (FDA), an emulsion of fluorocarbons in a glucose electrolyte solution can deliver physiologically significant amounts of oxygen (O₂) to the tissues and improve ischaemic hypoxia. To investigate its effect on critical oxygen delivery level (QO₂c), four groups of six phenobarbitone anaesthetised air-ventilated splenic clamped mongrel dogs were haemodiluted to a haematocrit (Hct) of 25%; two groups with FDA and two with 6% dextran solution. Oxygen consumption (VO₂) was derived from expired gas measurement and analysis, or by using a spirometer and carbon dioxide absorption. Whole body O₂ flux (QO₂) was calculated from mixed venous and arterial O₂ contents and the Fick-derived cardiac output. QO₂ was progressively decreased by haemorrhaging in steps of 1.5–2.5 ml per kg. Hct was kept at 25% using packed cells. VO₂/QO₂ pairs were calculated at each step and QO₂c was determined for each animal by least squares fitting of data with 2 straight lines. Analyses of variance were performed.

QO₂c was significantly less in the FDA and O₂ (F+O) group than either the dextran and O₂ (D+O) or dextran and air (D+A) groups. Analysis of O₂ extraction at QO₂c, which effectively normalized results for differences in resting VO₂, had significantly better extraction in the FDA and air (F+A) than the D+A group. When fluorocarbon- and plasma-dissolved oxygen was subtracted, the O₂ extraction in the F+A group was significantly better than in the D+A and F+O groups. The results imply that normoxic FDA haemodilution in animals respiring air can improve O₂ delivery and that hyperoxia interferes with this process.