Polarographic Cerebral Oxygen Availability, Fluorocarbon Blood Levels and Efficacy of Oxygen Transport by Emulsions

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Abstract
In order to relate blood perfluorocarbon (PFC) level to brain tissue oxygen availability (a02) and respiratory oxygen (F102), twelve conscious rabbits with chronically implanted platinum cathodes were infused with six types of emulsions in 14 infusions and their response to oxygen and carbogen breathing recorded. Blood was removed for sampling and to avoid a volume overload. Blood lactate was measured as an indicator of adequacy of perfusion. Glucose, osmotic pressure, packed cell volume, PFC by combustion and volatilization were also measured in blood samples. Methyl prednisolone was administered to 5 rabbits. Blood PFC levels measured by the commonly used centrifugation method (Fluorocrit) were subject to considerable variation, depending mainly upon centrifugation time. Fluorocrit values after Oxypherol infusion decreased from an average of 43% for 5 minutes to 15% for 30 minutes centrifugation. Fluorocrit tended to slightly increase with time of centrifugation when phospholipid was used as the emulsifier, early in PFC infusion and on the next day. Blood fluorocarbon was always lower, about half that of 30 minutes of centrifugation, when determined by combustion or by volatilization, than by centrifugation. The increase in brain a O# response to oxygen and carbogen was observed at a lower PFC blood level than expected and in some animals appeared in either the right or left hemisphere, but not in both, suggesting that oxygen transport, at least near the electrode, was by other than oxygen solubility in blood PFC. Blood lactate proved to be an excellent monitor of whole body perfusion. Animals with a blood lactate above 5mM/L at 1 hour post infusion died the following day. The fluorocrit after 5, 10, 20, and 30 minutes of centrifugation, which we have named the “fluoro-gram,” can have a sharp downward, a slight upward curve, or stay level, depending upon the type of emulsifier, the amount of PFC circulating and the time it has circulated. The fluorocarbon-induced increases in aO2 persist through the third day. This enhanced cerebrocortical aO2 current can be very roughly calculated as: aO2 current equals the air aO2 current plus (the 30 minute fluorocrit times K) where K. for oxygen is 0.05 and for carbogen is 0.07. Some enhancement of the aO2 current in oxygen lingers to the fifth day after the blood PFC level is vanishingly small. Methyl prednisolone has a transient effect in suppressing the PFC enhanced oxygen and carbogen a02 responses and no effect on the Oxypherol fluorogram. The striking increase in brain oxygen availability after fluorocarbon emulsion administration may have clinical application in the treatment of stroke (1), myocardial infarction (2), and cancer (3,4,5).