Perflubron emulsion improves hepatic microvascular integrity and mitochondrial redox state after hemorrhagic shock

Functional, Metabolic and Morphologic Results of Ex Vivo Donor Lung Perfusion with a Perfluorocarbon-Based Oxygen Carrier Nanoemulsion in a Large Animal Transplantation Model

Background: Ex vivo lung perfusion (EVLP) is a technology that allows the re-evaluation of questionable donor lung before implantation and it has the potential to repair injured donor lungs that are otherwise unsuitable for transplantation. We hypothesized that perfluorocarbon-based oxygen carrier, a novel reconditioning strategy instilled during EVLP would improve graft function. Methods: We utilized perfluorocarbon-based oxygen carrier (PFCOC) during EVLP to recondition and improve lung graft function in a pig model of EVLP and lung transplantation. Lungs were retrieved and stored for 24 h at 4 °C. EVLP was done for 6 h with or without PFCOC. In the transplantation groups, left lung transplantation was done after EVLP with or without PFCOC. Allograft function was assessed by means of pulmonary gas exchange, lung mechanics and vascular pressures, histology and transmission electron microscopy (TEM). Results: In the EVLP only groups, physiological and biochemical markers during the 6-h perfusion period were comparable. However, perfusate lactate potassium levels were lower and ATP levels were higher in the PFCOC group. Radiologic assessment revealed significantly more lung infiltrates in the controls than in the PFCOC group (p = 0.04). In transplantation groups, perfusate glucose consumption was higher in the control group. Lactate levels were significantly lower in the PFCOC group (p = 0.02). Perfusate flavin mononucleotide (FMN) was significantly higher in the controls (p = 0.008). Post-transplant gas exchange was significantly better during the 4-h reperfusion period in the PFCOC group (p = 0.01). Plasma IL-8 and IL-12 levels were significantly lower in the PFCOC group (p = 0.01, p = 0.03, respectively). ATP lung tissue levels at the end of the transplantation were higher and myeloperoxidase (MPO) levels in lung tissue were lower in the PFCOC group compared to the control group. In the PFCOC group, TEM showed better tissue preservation and cellular viability. Conclusion: PFCOC application is safe during EVLP in lungs preserved 24 h at 4 °C. Although this strategy did not significantly affect the EVLP physiology, metabolic markers of the donor quality such as lactate production, glucose consumption, neutrophil infiltration and preservation of mitochondrial function were better in the PFCOC group. Following transplantation, PFCOC resulted in better graft function and TEM showed better tissue preservation, cellular viability and improved gas transport.

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.

Pharmaceutical design and development of perfluorocarbon nanocolloids for oxygen delivery in regenerative medicine

Perfluorocarbons (PFCs) have been investigated as oxygen carriers for several decades in varied biomedical applications. PFCs are chemically and biologically inert, temperature and storage stable, pose low to no infectious risk, can be commercially manufactured, and have well established gas transport properties. In this review, we highlight design and development strategies for their successful application in regenerative medicine, transplantation and organ preservation. Effective tissue preservation strategies are key to improving outcomes of extremity salvage and organ transplantation. Maintaining tissue integrity requires adequate oxygenation to support aerobic metabolism. The use of whole blood for oxygen delivery is fraught with limitations of poor shelf stability, infectious risk, religious exclusions and product shortages. Other agents also face clinical challenges in their implementation. As a solution, we discuss new ways of designing and developing PFC-based artificial oxygen carriers by implementing modern pharmaceutical quality by design and scale up manufacturing methodologies.

Ringer's lactate solution enhances the inflammatory response during fluid resuscitation of experimentally induced haemorrhagic shock in rats

INTRODUCTION

Hemorrhagic shock leads to systemic oxygen deficit (hypoxaemia) that results in systemic inflammatory response syndrome (SIRS), a recognised cause of late mortality in this case. The aim of this study was to analyse the impact of fluid resuscitation, using two Ringer solutions, on the microcirculation changes that take place during experimentally induced haemorrhagic shock.

MATERIAL AND METHODS

A model of the rat cremaster muscle was used to assess microcirculation in vivo. The experimental groups (n = 10 each) included: control (CTRL); shock (HSG); Ringer's acetate (RAG); and Ringer's lactate (RLG). Microhaemodynamic parameters were measured during the experiment.

RESULTS

A statistically significantly higher level of leukocytes, both those attached to the endothelium and those located in the extravascular space (p < 0.05), was reported in the lactate Ringer (LR) group compared with the AR group. There were significant differences in the activity of A3 arterioles compared with A1 and A2 arterioles. Ringer's lactate solution seemed to the inflammation response during fluid resuscitation from haemorrhagic shock. A3 arterioles are likely to play a role as a pre-capillary sphincter in the skeletal muscle.

CONCLUSIONS

The present study revealed that fluid resuscitation with Ringer's lactate solution exacerbates inflammation in the skeletal muscle. It is worth noting that Ringer's acetate solution reduces local inflammation and could therefore be recommended as the "first line" crystalloid of the fluid resuscitation during haemorrhagic shock.

Hemorrhagic Shock and the Microvasculature

The microvasculature plays a central role in the pathophysiology of hemorrhagic shock and is also involved in arguably all therapeutic attempts to reverse or minimize the adverse consequences of shock. Microvascular studies specific to hemorrhagic shock were reviewed and broadly grouped depending on whether data were obtained on animal or human subjects. Dedicated sections were assigned to microcirculatory changes in specific organs, and major categories of pathophysiological alterations and mechanisms such as oxygen distribution, ischemia, inflammation, glycocalyx changes, vasomotion, endothelial dysfunction, and coagulopathy as well as biomarkers and some therapeutic strategies. Innovative experimental methods were also reviewed for quantitative microcirculatory assessment as it pertains to changes during hemorrhagic shock. The text and figures include representative quantitative microvascular data obtained in various organs and tissues such as skin, muscle, lung, liver, brain, heart, kidney, pancreas, intestines, and mesentery from various species including mice, rats, hamsters, sheep, swine, bats, and humans. Based on reviewed findings, a new integrative conceptual model is presented that includes about 100 systemic and local factors linked to microvessels in hemorrhagic shock. The combination of systemic measures with the understanding of these processes at the microvascular level is fundamental to further develop targeted and personalized interventions that will reduce tissue injury, organ dysfunction, and ultimately mortality due to hemorrhagic shock. Published 2018. Compr Physiol 8:61-101, 2018.

The macrophage stimulating anti-cancer agent, RRx-001, protects against ischemia-reperfusion injury

BACKGROUND

RRx-001, a clinical macrophage-stimulating anti-cancer agent that also produces nitric oxide (NO) was studied in a model of ischemia-reperfusion injury.

METHODS

The production of NO is dependent on the oxygen tension because nitric oxide synthases convert l-arginine to NO and l-citrulline in the presence of O₂. Since the P450 enzymes, which metabolize nitrate esters such as nitroglycerin are dependent on oxygen, the generation of 'exogenous' NO is also sensitive to alterations in tissue PO₂. I/R injury was studied in a hamster chamber window, with compression of the periphery of the window for 1 h to induce ischemia. Animals received RRx-001 (5 mg/kg) 24 h before ischemia and sodium nitrite (10 nmols/kg) was supplemented 10 min after the start of reperfusion. Vessel diameter, blood flow, adherent leukocytes, and functional capillary density were assessed by intravital microscopy at 0.5, 2, and 24 h following the release of the ischemia.

RESULTS

The results demonstrated that, compared to control, RRx-001 preconditioning increased blood flow and functional capillary density, and preserved tissue viability in the absence of side effects over a sustained time period.

CONCLUSION

Thus, RRx-001 may serve as a long-lived protective agent during postsurgical restoration of flow and other ischemia-reperfusion associated conditions, increasing blood flow and functional capillary density as well as preserving tissue viability in the absence of side effects.

Systemic and microcirculatory effects of blood transfusion in experimental hemorrhagic shock

Background

The microvascular reperfusion injury after retransfusion has not been completely characterized. Specifically, the question of heterogeneity among different microvascular beds needs to be addressed. In addition, the identification of anaerobic metabolism is elusive. The venoarterial PCO₂ to arteriovenous oxygen content difference ratio (P_v-aCO₂/C_a-vO₂) might be a surrogate for respiratory quotient, but this has not been validated. Therefore, our goal was to characterize sublingual and intestinal (mucosal and serosal) microvascular injury after blood resuscitation in hemorrhagic shock and its relation with O₂ and CO₂ metabolism.

Methods

Anesthetized and mechanically ventilated sheep were assigned to stepwise bleeding and blood retransfusion (n = 10) and sham (n = 7) groups. We performed analysis of expired gases, arterial and mixed venous blood gases, and intestinal and sublingual videomicroscopy.

Results

In the bleeding group during the last step of hemorrhage, and compared to the sham group, there were decreases in oxygen consumption (3.7 [2.8–4.6] vs. 6.8 [5.8–8.0] mL min⁻¹ kg⁻¹, P < 0.001) and increases in respiratory quotient (0.96 [0.91–1.06] vs. 0.72 [0.69–0.77], P < 0.001). Retransfusion normalized these variables. The P_v-aCO₂/C_a-vO₂ increased in the last step of bleeding (2.4 [2.0–2.8] vs. 1.1 [1.0–1.3], P < 0.001) and remained elevated after retransfusion, compared to the sham group (1.8 [1.5–2.0] vs. 1.1 [0.9–1.3], P < 0.001). P_v-aCO₂/C_a-vO₂ had a weak correlation with respiratory quotient (Spearman R = 0.42, P < 0.001). All the intestinal and sublingual microcirculatory variables were affected during hemorrhage and improved after retransfusion. The recovery was only complete for intestinal red blood cell velocity and sublingual total and perfused vascular densities.

Conclusions

Although there were some minor differences, intestinal and sublingual microcirculation behaved similarly. Therefore, sublingual mucosa might be an adequate window to track intestinal microvascular reperfusion injury. Additionally, P_v-aCO₂/C_a-vO₂ was poorly correlated with respiratory quotient, and its physiologic behavior was different. Thus, it might be a misleading surrogate for anaerobic metabolism.

Electronic supplementary material

The online version of this article (doi:10.1186/s40635-017-0136-3) contains supplementary material, which is available to authorized users.

Perfluorocarbon NVX-108 increased cerebral oxygen tension after traumatic brain injury in rats

BACKGROUND

Hypoxia is a critical secondary injury mechanism in traumatic brain injury (TBI), and early intervention to alleviate post-TBI hypoxia may be beneficial. NVX-108, a dodecafluoropentane perfluorocarbon, was screened for its ability to increase brain tissue oxygen tension (PbtO2) when administered soon after TBI.

METHODS

Ketamine-acepromazine anesthetized rats ventilated with 40% oxygen underwent moderate controlled cortical impact (CCI)-TBI at time 0 (T0). Rats received either no treatment (NON, n=8) or 0.5 ml/kg intravenous (IV) NVX-108 (NVX, n=9) at T15 (15 min after TBI) and T75.

RESULTS

Baseline cortical PbtO2 was 28±3 mm Hg and CCI-TBI resulted in a 46±6% reduction in PbtO2 at T15 (P<0.001). Significant differences in time-group interactions (P=0.013) were found when comparing either absolute or percentage change of PbtO2 to post-injury (mixed-model ANOVA) suggesting that administration of NVX-108 increased PbtO2 above injury levels while it remained depressed in the NON group. Specifically in the NVX group, PbtO2 increased to a peak 143% of T15 (P=0.02) 60 min after completion of NVX-108 injection (T135). Systemic blood pressure was not different between the groups.

CONCLUSION

NVX-108 caused an increase in PbtO2 following CCI-TBI in rats and should be evaluated further as a possible immediate treatment for TBI.

Hextend-perfluorocarbon cocktail inhibits mean arterial pressure response in a rabbit shock model

BACKGROUND

Hextend (HEX) is standard of care resuscitation fluid for combat-related traumatic hemorrhage. Because HEX has limited oxygen-carrying capacity, combination therapy with oxygen therapeutics could improve oxygen delivery after hemodynamic shock. We hypothesized that addition of perfluorocarbon (PFC) to HEX would improve hemodynamics and oxygen delivery marker response in a rabbit model of hemorrhagic shock.

METHODS

Anesthetized New Zealand rabbits (n = 23) were randomly allocated to resuscitation with fresh whole blood (FWB), HEX, or HEX plus PFC (HEX + PFC) after 60 min of hemorrhagic hypotension. Mean arterial pressure (MAP) was sampled every 2-3 min for 120 min postinfusion; MAP profiles were modeled by a one-compartment pharmacokinetic model to determine peak MAP (Pmax), time to peak MAP (tmax), and postinfusion MAP persistence. Arterial blood was sampled every 15 min to examine pH, blood gases PO2 and pCO2, metabolites lactate and glucose, methemoglobin (metHb), and electrolytes.

RESULTS

Compared with FWB and HEX, HEX + PFC administration resulted in delayed peak MAP and less persistent (P < 0.0001) MAP elevation; metHb was significantly elevated (P < 0.0001) compared with FWB and HEX. There were no significant differences in PO2, pCO2, or pH. Glucose, hematocrit, and hemoglobin of both HEX and HEX + PFC were significantly lower relative to FWB. Lactate clearance was modest and transient for all treatments; base deficit was significantly more negative for HEX + PFC.

CONCLUSIONS

Addition of PFC to HEX did not improve hemodynamics or acidosis. Further dose- and volume-range studies are required to test efficacy of PFC in combination with HEX for hemorrhagic shock.

Safety of poly (ethylene glycol)-coated perfluorodecalin-filled poly (lactide-co-glycolide) microcapsules following intravenous administration of high amounts in rats

The host response against foreign materials designates the biocompatibility of intravenously administered microcapsules and thus, widely affects their potential for subsequent clinical use as artificial oxygen/drug carriers. Therefore, body distribution and systemic parameters, as well as markers of inflammation and indicators of organ damage were carefully evaluated after administration of short-chained poly (vinyl alcohol, (PVA)) solution or poly (ethylene glycol (PEG))-shielded perfluorodecalin-filled poly (d,l-lactide-co-glycolide, PFD-filled PLGA) microcapsules into Wistar rats. Whereas PVA infusion was well tolerated, all animals survived the selected dose of 1247 mg microcapsules/kg body weight but showed marked toxicity (increased enzyme activities, rising pro-inflammatory cytokines and complement factors) and developed a mild metabolic acidosis. The observed hypotension emerging immediately after start of capsule infusion was transient and mean arterial blood pressure restored to baseline within 70 min. Microcapsules accumulated in spleen and liver (but not in other organs) and partly occluded hepatic microcirculation reducing sinusoidal perfusion rate by about 20%.

Intravenous infusion of high amounts of PFD-filled PLGA microcapsules was tolerated temporarily but associated with severe side effects such as hypotension and organ damage. Short-chained PVA displays excellent biocompatibility and thus, can be utilized as emulsifier for the preparation of drug carriers designed for intravenous use.

Transport of nitric oxide by perfluorocarbon emulsion

Perfluorocarbon (PFC) emulsions can transport and release various gases based on concentration gradients. The objective of this study was to determine the possibility of carrying and delivering exogenous nitric oxide (NO) into the circulation by simply loading PFC emulsion with NO prior infusion. PFC was equilibrated with room air (PFC) or 300 ppm NO (PFC-NO) at atmospheric pressure. Isotonic saline solution was used as a volume control (Saline). PFC and PFC-NO were infused at a dose of 3.5 mL/kg in the hamster window chamber model. Blood chemistry, and systemic and microvascular hemodynamic response were measured. Infusion of PFC preloaded with NO reduced blood pressure, induced microvascular vasodilation and increased capillary perfusion; although these changes lasted less than 30 min post infusion. On the other hand, infusion of PFC (without NO) produced vasoconstriction; however, the vasoconstriction was followed by vasodilatation at 30 min post infusion. Plasma nitrite and nitrate increased 15 min after infusion of NO preloaded PFC compared with PFC, 60 min after infusion nitrite and nitrate were not different, and 90 min after infusion plasma S-nitrosothiols increased in both groups. Infusion of NO preloaded PFC resulted in acute vascular relaxation, where as infusion of PFC (without NO) produced vasoconstriction, potentially due to NO sequestration by the PFC micelles. The late effects of PFC infusion are due to NO redistribution and plasma S-nitrosothiols. Gas solubility in PFC can provide a tool to modulate plasma vasoactive NO forms availability and improve microcirculatory function and promote increased blood flow.

Perfluorocarbon-based oxygen carriers: review of products and trials

A viable blood substitute is still of great necessity throughout the world. Perfluorocarbon-based oxygen carriers (PFCOCs) are emulsions that take advantage of the high solubility of respiratory gases in perfluorocarbons (PFCs). Despite attractive characteristics, no PFCOC is currently approved for clinical uses. Some PFCOCs have failed due to secondary effects of the surfactants employed, like Fluosol DA, whereas others to adverse cerebrovascular effects on cardiopulmonary bypass, such as Oxygent. Further in-depth, rigorous work is needed to overcome the annotated failures and to obtain a safe PFCOC approved for human use. The aim of this study is to review in detail the most-used PFCOCs, their formulation, and preclinical and clinical trials, and to reflect upon causes of failure and strategies to overcome such failures.

Attenuation of the effects of rat hemorrhagic shock with a reperfusion injury-inhibiting agent specific to mice

Death after hemorrhagic shock (HS) may be caused by a generalized reperfusion injury, particularly noticeable in the gut. A period of tissue ischemia followed by reinstitution of perfusion produces severe inflammation that can be blocked in mice by preventing the binding of a pathogenic natural immunoglobulin M (IgM) of defined specificity to antigens in reperfused tissue by using a soluble peptide analogue of the IgM tissue target. We hypothesize that this agent can improve end points of rat HS: death, intestinal injury, and lung injury. Male Sprague-Dawley rats were anesthetized; 50% of calculated blood volume was removed for 120 min, shed blood, then returned; and animals were sacrificed at 72 h. One group of rats received i.v. analogue ([N2] 300 microg) with the return of shed blood. Small intestine and lung were evaluated by histological examination and immunohistochemistry. Lung edema was assessed by Evans blue extravasation and histological examination. I.v. N2 decreased experimental mortality from 62% to 12% (P < 0.05). Associated with this was diminution of gut injury score from 57.8% +/- 5.5% to 19.5% +/- 2.5% (P < 0.05), lung injury from 21.4 +/- 1.5 to 14.8 +/- 1.3 polymorphonuclear leucocytes per high-power field x400 (P < 0.05), and Evans blue extravasation index from 0.61 +/- 0.14 to 0.18 +/- 0.06 (P < 0.05). As well, the deposition of IgM and C3 that is seen in intestinal villi from HS was not present in N2-treated rats. The N2 peptide agent that blocks reperfusion injury in mice prevents death from rat HS, as well as attenuates gut reperfusion injury and its remote target injuries. These data suggest that death from HS is caused by reperfusion injury, and that an agent derived from mice is effective in rats when given in real therapeutic time.

Perfluorocarbon in microcirculation during ischemia reperfusion

BACKGROUND

The effects of perfluorocarbon (PFC) emulsions administered at a nonhemodiluting dose were studied in the hamster window chamber model to determine the difference in ischemia-reperfusion injury associated with PFC delivery before and after an ischemic episode.

STUDY DESIGN

Ischemia was induced by compressing the periphery of the window chamber for 1 hour. Vessel diameter, red blood cell velocity, rolling and adherent leukocytes, and functional capillary density (FCD) were assessed by intravital microscopy. The animals received an infusion (10% blood volume) of PFC emulsion or equivalent volumes of saline, before or after ischemia. Two groups were studied in each experimental protocol: A, infusion after ischemia; and B, infusion before ischemia, where a fraction of the infused material stagnated in the ischemic zone during the occlusion time. Measurements were made before induced ischemia and at 0.5, 2, and 24 hours of reperfusion.

RESULTS

Animals treated with PFC after ischemia had substantially decreased leukocytes rolling and sticking in postcapillary venules and recovered functional capillary density and blood flow when compared with saline-treated controls. Conversely, administration of PFC before ischemia considerably reduced functional capillary density and increased leukocyte activation after reperfusion.

CONCLUSIONS

Results indicate that PFC without stagnation within an ischemic zone attenuates postischemic reperfusion injury of striated skin muscle, presumably through the reduction of leukocyte-endothelial cell interactions. Accordingly, PFC effects on ischemia-reperfusion injury are determined mainly by the time of administration relative to the ischemic episodes.

Shock and hemorrhage: an overview of animal models

Shock resulting from life-threatening blood loss (hemorrhage) remains a common complication of traumatic injury. Intensive experimental efforts are needed if we are to understand the pathological effect(s) of hemorrhagic shock, alone or in association with traumatic tissue injury, and to reverse this deleterious process in trauma patients. Here, we overview selected studies that are representative of the different hemorrhagic shock models, considering their advantages and disadvantages from a scientific and clinical perspective. Fixed-pressure versus fixed-volume versus uncontrolled hemorrhage models, with or without tissue injury, will be discussed, as well as small versus large animal models. Most of these models are nonlethal in nature, and allow the researcher to understand the changes that contribute to increased susceptibility to subsequent infection or the development of multiple organ failure. We also consider some of the confounders in these models, including anesthesia, the nature of resuscitation, and the use of anticoagulants. The selection of model must take into consideration not only the need for experimental control but must also adequately reflect the clinical pathobiology of shock if we are to develop better pharmacological interventions.

Use of perftoran emulsion to decrease allogeneic blood transfusion in cardiac surgery: clinical trial

Perflurocarbon emulsions (PFC) have the capacity of transporting oxygen through the bloodstream and may be safe and effective alternatives to allogeneic blood transfusions during surgical procedures. Perftoran was the PFC used in a randomized clinical trial conducted at Hospital de Especialidades Centro Medico La Raza, Mexico City. The clinical trial took a sample group, n = 30, of patients that were scheduled for elective cardiac valvuloplasty surgery in combination with preoperative acute normovolemic hemodilution and an inspiratory oxygen fraction (FI02) of 1.0. The participants were randomly divided into a Control group (n = 15) and a Perftoran (PFC) group (n = 15). The PFC group had significantly higher intraoperative PaO2 levels and needed less allogeneic red blood cell packs than the Control group. There were no complications or deaths in either group. These results suggest that Perftoran is safe, efficacious, and reduces the need for allogeneic blood and blood derivatives in patients undergoing cardiac surgery.

Resuscitation of severe but brief haemorrhagic shock with PFC in rabbits restores skeletal muscle oxygen delivery and does not alter skeletal muscle metabolism

Studies have demonstrated that perfluorocarbon (PFC) emulsions associated with hyperoxia improved whole body oxygen delivery during resuscitation of acute haemorrhagic shock (HS). Nevertheless the microcirculatory effects of PFC and the potential deleterious effects of hyperoxic reperfusion are still of concern. We investigated (i) the ability of a newly formulated, small sized and highly stable PFC emulsion to increase skeletal muscle oxygen delivery and (ii) the effect of hyperoxic reperfusion on skeletal muscle metabolism after a brief period of ischaemia using an original, microdialysis-based method that allowed simultaneous measurement tissue oxygen pressure (PtiO2) and interstitial lactate and pyruvate. These measurements were carried out in anaesthetised and ventilated (FiO2 = 1) rabbits subjected to acute HS (50% of blood volume withdrawal) and either resuscitated with a PFC emulsion diluted with a 5% albumin solution (16.2 g PFC per kg body weight) (n = 10) or with a modified fluid gelatin solution (Gelofusine) (n = 10). We found no difference between the two groups for the haemodynamic and haematological variables (except for the venous oxygen partial pressure). However, a significant difference was observed in the slope of the regression linear relationship exhibited between the mean arterial pressure (MAP) and the PtiO2, PFC group showing a much steeper slope than Gelofusine group. In addition, PtiO2 values increased linearly with decreasing haematocrit (Hct) values in PFC-resuscitated animals and decreased linearly with decreasing Hct values in Gelofusine-resuscitated animals. There were no differences between the two groups concerning the blood and interstitial lactate/pyruvate ratios suggesting no deleterious effect of hyperoxic resuscitation in skeletal muscle. In conclusion these results suggest that resuscitation of severe, but brief, HS with PFC increased skeletal muscle oxygen delivery without measurable deleterious effects.

Oxygent as a top load to colloid and hyperoxia is more effective in resuscitation from hemorrhagic shock than colloid and hyperoxia alone

Perfluorocarbon (PFC) emulsions are intravascular oxygen therapeutics that temporarily enhance tissue oxygenation in dilutional anemia. However, PFC emulsions are not resuscitation fluids because PFCs only work optimally in the presence of high O2 partial pressure (hyperoxia); moreover, because they have no oncotic potential, dosing limitations prevent their use to permanently replace large hemorrhage volumes. Our objective was to clarify whether in the presence of hyperoxia a conventional colloid therapy supplemented by PFC is more efficacious than colloid alone. To answer this question, 22 anesthetized, ventilated dogs were hemorrhaged to a mean arterial pressure of 45 mmHg and were kept at this level until a metabolic O2 debt of 120 mL kg(-1) body weight had evolved. Hyperoxia was established and dogs were randomly allocated to receive colloid (6% HES, Hydroxy Ethyl Starch shed blood volume) or colloid together with Oxygent (perflubron emulsion, 60%, w/v; Alliance Pharmaceutical Corp., San Diego, CA; single dose, 4.5 mL kg(-1); i.e., 2.7 g PFC kg body weight) in a blinded fashion. Hemodynamic and O2 transport parameters, intestinal mucosal blood flow (microspheres), and O2 partial pressure (MDO-Electrode; Eschweiler, Kiel, Germany) were measured at baseline, in shock, and during 3 h post-therapy. In the presence of hyperoxia, Oxygent improved the amount of physically dissolved O2 in plasma and increased the contribution of physically dissolved O2 to global O2 delivery (P < 0.05) and thus whole body O2 consumption when compared with colloid alone (P < 0.05). As a result, Oxygent reduced intestinal mucosal hypoxia and global O2 debt within the first hour post-therapy (P < 0.05). We conclude that under hyperoxic conditions, fluid resuscitation supplemented by Oxygent was more efficacious than colloid and hyperoxia alone. PFC temporarily enhanced intestinal mucosal tissue oxygenation during resuscitation.

Insights from studies of blood substitutes in trauma

Most authorities believe that the greatest need for blood substitutes is in patients with unanticipated acute blood loss, and trauma is the most likely scenario. The blood substitutes reaching advanced clinical trials today are red blood cell (RBC) substitutes, derived from hemoglobin. The hemoglobin-based oxygen carriers (HBOCs) tested currently in FDA Phase III clinical trials are polymerized hemoglobin solutions. The standard approach to restoring oxygen delivery in hemorrhagic shock has been crystalloid administration to expand intravascular volume, followed by stored RBCs for critical anemia. However, allogenic RBCs may have adverse immunoinflammatory effects that increase the risk of postinjury multiple organ failure (MOF). Phase II clinical trials, as well as in vitro and in vivo work, suggest that resuscitation with a HBOC--in lieu of stored RBCs--attenuates the systemic inflammatory response invoked in the pathogenesis of MOF. Specifically, an HBOC has been shown to obviate stored RBC provoked neutrophil priming, endothelial activation, and systemic release of interleukins 6, 8, and 10. Based on this background and work by others, we have initiated a multicenter prehospital trial in which severely injured patients with major blood loss (systemic blood pressure <90 mmHg) are randomized to initial field resuscitation with crystalloid versus HBOC. During the hospital phase, the control group is further resuscitated with stored RBCs, whereas the study group receives HBOC (up to 6 units) in the first 12 h. The primary study endpoint is 30-day mortality, and secondary endpoints include reduction in allogenic RBCs, hemoglobin levels <5 g/dL, uncrossmatched RBCs, and MOF. The potential efficacy of HBOCs extends beyond the temporary replacement for stored RBCs. Hemoglobin solutions might ultimately prove superior in delivering oxygen to ischemic or injured tissue. The current generation of HBOCs can be lifesaving for acute blood loss today, but the next generation might be biochemically tailored for specific clinical indications.

Current Status of Artificial o2 Carriers

This article describes currently evaluated artificial O2 carriers, summarizes their efficacy, and discusses their side effects, based on and restricted to published data. For compounds in phase III testing, approximately 500 to 1000 patients have been dosed, and similar numbers of control patients have been investigated. For compounds in phase I or II testing, the number of patients dosed is significantly less. Unfortunately, there is a significant amount of nonpublished data, which renders the overall assessment difficult, and the direct comparison among different types of artificial O2 carriers is significantly limited by the virtual nonexistence of studies that directly compare different products.

EFFECTS OF COLLOID RESUSCITATION ON PERIPHERAL MICROCIRCULATION, HEMODYNAMICS, AND COLLOIDAL OSMOTIC PRESSURE DURING ACUTE SEVERE HEMORRHAGE IN RABBITS

We examined the effects of hydroxyethyl starch (HES) on the microcirculation, hemodynamics, and colloidal osmotic pressure in a rabbit model of hemorrhagic shock. A total of 40 rabbits was anesthetized with pentobarbital and isoflurane, and they were mechanically ventilated. An ear chamber was prepared to examine blood vessels by intravital microscopy. Shock was induced by removing nearly half of the circulating blood volume. Twenty rabbits received 20 mL of HES by intravenous infusion immediately after blood letting. Additional HES was then administered intravenously to a total volume of 100 mL. The other 20 rabbits (control) were intravenously given 40 mL of lactated Ringer's solution (LR), followed by additional LR to a total volume of 200 mL, administered under the same conditions as HES. After blood letting, arteriolar diameter decreased similarly in the the HES and LR groups (HES, 40.5% +/- 14.8% of the baseline value versus LR, 43.3% +/- 13.1%). After the completion of infusion, arteriolar diameter significantly recovered to 90.8% +/- 10.2% of the baseline value in the HES group as compared with only 62.6% +/- 10.7% in the LR group (P < 0.005). Recovery of arterial blood flow velocity and blood flow rate was also significantly better in the HES group than in the LR group (P < 0.005). Mean arteriolar pressure, central venous pressure, and plasma colloid osmotic pressure after the completion of infusion were significantly greater in the HES group than in the LR group (P < 0.005). We conclude that intravenous infusion of HES effectively maintains the microcirculation, hemodynamics, and colloidal osmotic pressure in a rabbit model of acute severe hemorrhage.

RESUSCITATION FROM HEMORRHAGIC SHOCK WITH MalPEG-ALBUMIN: COMPARISON WITH MalPEG-HEMOGLOBIN

Our aim was to determine the efficacy of polyethylene glycol-conjugated human albumin (MalPEG-Alb) in restoring circulatory volume after 1 h of hemorrhagic shock. Experiments were performed in the awake condition in the hamster skin fold preparation. Microhemodynamic parameters and tissue Po2 were assessed with intravital microscopy and the use of the phosphorescence quenching technique. One hour after shock induction by withdrawal of 50% of the blood volume, animals were resuscitated with MalPEG-Alb (n = 6). Systemic and microhemodynamic parameters following resuscitation were identical to those obtained with the same protocol using MalPEG-Hb (1). However, parameters related to microvascular oxygen distribution were significantly lower in the MalPEG-Alb group compared with the previous data from the MalPEG-Hb group in that tissue oxygen partial pressure was 5 +/- 2 mmHg (vs. 8 +/- 3 mmHg, P < 0.05), oxygen delivery was reduced to 60 +/- 27% (P < 0.05), and oxygen consumption was reduced to 69 +/- 28% (P < 0.05). Both molecules were matched in composition (4.2 g/dL) and surface chemistry. MalPEG-Alb colloid osmotic pressure was 37 mmHg (vs. 49 mmHg for MalPEG-Hb), and viscosity was 2.7 cP (vs. 2.5 cP for MalPEG-Hb). The present results show that both solutions are efficacious plasma expanders and that the hemoglobin-based solution provides improved oxygen distribution and tissue Po2 in the hamster chamber model.

Improving Microcirculation is More Effective Than Substitution of Red Blood Cells to Correct Metabolic Disorder in Experimental Hemorrhagic Shock

Microcirculatory perfusion deficits and impaired tissue oxygenation in nonvital organs frequently occur after hemorrhage and they contribute to potentially lethal complications. The aim of this study was to test the influence of colloid osmotic pressure, viscosity, and red blood cell (RBC) content of the resuscitative fluid on metabolic disorder, perfusion, and oxygenation in peripheral tissues. Awake hamsters were subjected to hemorrhage of 50% and were resuscitated with 25% of blood volume with solutions containing 6% pegylated bovine albumin only (PEG-BSA 0) and 6% PEG-BSA mixed with autologous RBCs to reach 4 g/dL (PEG-BSA 4) and 8 g/dL (PEG-BSA 8) of hemoglobin. PEG-BSA had a viscosity of 4.2 cP and a COP of 116 mmHg. Microhemodynamics and tissue pO2 were assessed in the hamster chamber window preparation with intravital microscopy. Arterial base excess tended to be lower than baseline for PEG-BSA 0 and PEG-BSA 4 (ns), whereas base deficit remained significantly decreased for PEG-BSA 8 (P<0.05 vs. baseline). Oxygen extraction was 91% +/- 2% of the oxygen delivery for PEG-BSA 0 compared with 85% +/- 2% for PEG-BSA 8 (P<0.05). Functional capillary density was 61%, 47%, and 45% for PEG-BSA 0 (P<0.05 vs. other groups), PEG-BSA 4 and PEG-BSA 8, respectively. We conclude that arterial base excess and oxygen extraction ratio in the tissue was better restored if a higher fraction of PEG-BSA and less RBCs were infused. This was attributed to a more homogeneous distribution of oxygen, as reflected by functional capillary density. Our results suggest that the transfusion trigger in hemorrhagic shock may be shifted toward lower hemoglobin concentrations if highly viscous and oncotic solutions are used.