Perfluorochemical artificial blood as a volume expander in hypoxemic respiratory failure in dogs

Mini-review: Perfluorocarbons, Oxygen Transport, and Microcirculation in Low Flow States: in Vivo and in Vitro Studies

The in vivo study of microvascular oxygen transport requires accurate and challenging measurements of several mass transfer parameters. Although recommended, blood flow and oxygenation are typically not measured in many studies where treatments for ischemia are tested. Therefore, the aim of this communication is to briefly review cardinal aspects of oxygen transport, and the effects of perfluorocarbon (PFC) treatment on blood flow and oxygenation based mostly on studies performed in our laboratory. As physiologically relevant events in oxygen transport take place at the microvascular level, we implemented the phosphorescence quenching technique coupled with noninvasive intravital videomicroscopy for quantitative evaluation of these events in vivo. Rodent experimental models and various approaches have been used to induce ischemia, including hemorrhage, micro- and macroembolism, and microvessel occlusion. Measurements show decrease in microvascular blood flow as well as intravascular and tissue oxygen partial pressure (PO2) after these procedures. To minimize or reverse the effects of ischemia and hypoxia, artificial oxygen carriers such as different PFCs were tested. Well-defined endpoints such as blood flow and tissue PO2 were measured because they have significant effect on tissue survival and outcome. In several cases, enhancement of flow and oxygenation could be demonstrated. Similar results were found in vitro: PFC emulsion mixed with blood (from healthy donors and sickle cell disease patients) enhanced oxygen transport. In summary, PFCs may provide beneficial effects in these models by mechanisms at the microvascular level including facilitated diffusion and bubble reabsorption leading to improved blood flow and oxygenation.

Effect of supplemental perfluorocarbon administration on hypotensive resuscitation of severe uncontrolled hemorrhage

Recent animal studies of acute hemorrhage in the presence of a vascular injury have demonstrated improved survival and decreased hemorrhage volume with hypotensive resuscitation, but this has occurred at the expense of tissue perfusion. It was hypothesized that addition of an oxygen-carrying perfusate would improve tissue oxygen delivery during hypotensive resuscitation. Hypotensive resuscitation of severe uncontrolled hemorrhage was compared with and without supplementation with Oxygent HT, an emulsion of perflubron (perfluorooctylbromide; PFOB; Alliance Pharmaceutical Corporation, San Diego, CA), an oxygen-carrying perfusate. Fifteen swine (15 to 22 kg) with 4-mm aortic tears were bled to a pulse pressure of 5 mm Hg and then resuscitated (estimated blood loss, 40 to 50 mL/kg). All animals were resuscitated with normal saline (6 mL/kg/min) infused as needed to maintain a mean arterial pressure of 40 mm Hg. One group (PFC) of animals also received an infusion of 6 mL/kg perfluorooctylbromide emulsion. Another group served as controls and received an equal volume of placebo (normal saline). Animals were observed for 120 minutes or until death. Data were compared using repeated measures analysis of variance (ANOVA) the Student's t test, and Fisher's exact. A P value < .05 was considered significant. Two-hour mortality rates were 12.5% and 43% for PFC-treated animals and controls, respectively (P > .05; 95% confidence interval [95% CI] for this difference in mortality is -13% to 74%). Oxygen content and delivery were significantly greater in the treatment group. In conclusion, administration of an oxygen-carrying perfusate significantly improves oxygen delivery in hypotensive crystalloid resuscitation of severe uncontrolled hemorrhage.

Effect of exchange transfusion with a red blood cell substitute on neonatal hemodynamics and organ blood flows

The present study was designed to evaluate the effect of a perfluorocarbon erythrocyte substitute on hemodynamics in the newborn lamb. Isovolumic double volume exchange transfusions were performed with perfluorocarbon emulsion (FC-43) on lambs who were ventilated to maintain normal acid base status. Hematocrit, fluorocrit, viscosity, arterial gas tensions, mean arterial pressure, and heart rate were determined before (control) and after (exchange) exchange transfusion. A radiolabeled microsphere technique was used and cardiac output, organ blood flow, organ vascular resistance, and oxygen delivery were calculated. As the hematocrit and viscosity decreased and the fluorocrit increased, there was a significant increase in PaO2 as well as a significant decrease in A-a gradient and oxygen content. There was no significant change in the acid-base status or the hemodynamic profile (heart rate, stroke volume, cardiac output, and mean arterial pressure). Blood flow to the heart and brain showed a significant increase, whereas flow to the cortex of the kidney showed a significant decrease. There was no significant change in flow to the gastrointestinal tract. Organ vascular resistance in the brain significantly decreased, increased in the kidney, and showed no significant change in the heart and gastrointestinal tract. Oxygen delivery significantly decreased in all organs except the heart. These data suggest that perfluorocarbon emulsions can acutely maintain hemodynamic stability in the newborn lamb and that the intrinsic properties of perfluorocarbons allow for the preservation of adequate oxygenation and acid-base status.

Oxygen delivery from fluorocarbon emulsions--aspects of convective and diffusive transport

Perfluorocarbons (PFCs) deliver oxygen due to their physical characteristics and the convective delivery to tissues; this has been amply demonstrated in numerous animal models and in clinical trials. PFC emulsions have also been used for organ perfusion and augmentation of oxygenation to cell cultures. By reason of their small particle size, PFC emulsions penetrate collateral capillaries of an ischemic microcirculation, both supplying oxygenation and possibly restoring flexibility of acidotically stiffened erythrocytes by reinstituting aerobic metabolism. There is also evidence that PFCs can augment tissue oxygenation by increasing oxygen solubility in the plasma phase of blood; this improves diffusion gradients between plasma and tissues even at relatively low doses of PFC. This hypothesis is supported by the ability of PFCs to increase oxygen tensions in tissues such as blood, brain, liver, kidney, pancreas, skeletal muscle, retina etc. PFCs can also on occasions increase critical oxygen extraction coefficients and should therefore be effective in supporting oxidative metabolism in states of extreme cardio-respiratory insufficiency. This theory represents a new concept in oxygen delivery and may define a new class of therapeutic agents that can improve tissue oxygen supply in various pathological states involving low oxygen delivery and ischemia.

Effects of perfluorochemical hemodilution on coronary blood flow distribution in dogs

To determine the effect of perfluorocarbon (PFC) hemodilution on myocardial vessel capacity to autoregulate, circumflex coronary artery pressure-flow relations were studied in anesthetized dogs under three conditions: maximal vasodilatation before and after PFC; autoregulation before and after PFC with 100% oxygen supplemented with room air ventilation, and autoregulation with PFC hemodilution during either room air or 100% oxygen supplemented with room air ventilation. During coronary vasodilatation, PFC did not modify coronary conductance or zero-flow pressure. During autoregulation after PFC, the lower pressure limit of the autoregulatory pressure-flow relation was shifted leftward. This leftward shift occurred because endocardial blood flow was maintained at a lower coronary perfusion pressure with PFC while epicardial blood flow was unchanged. Endocardial blood flow was also preserved at 50% of control blood flow levels as evidenced by the higher endocardial-epicardial blood flow ratio with PFC. After PFC with 100% oxygen supplemented with room air ventilation, oxygen transport increased significantly when coronary perfusion pressure was below the lower pressure limit; the effect was most prominent in the endocardial tissue layer. Thus, PFC shifts the lower pressure limit to the left because of the increased ability of the endocardial vessel to autoregulate. Consequently, PFC can be considered a useful intervention for improving endocardial oxygen transport at low coronary perfusion pressures.