Bovine haemoglobin is more potent than autologous red blood cells in restoring muscular tissue oxygenation after profound isovolaemic haemodilution in dogs

Large Animal Models for Simulating Physiology of Transfusion of Red Cell Concentrates-A Scoping Review of The Literature

Background and Objectives: Transfusion of red cell concentrates is a key component of medical therapy. To investigate the complex transfusion-associated biochemical and physiological processes as well as potential risks for human recipients, animal models are of particular importance. This scoping review summarizes existing large animal transfusion models for their ability to model the physiology associated with the storage of erythrocyte concentrates. Materials and Methods: The electronic databases PubMed, EMBASE, and Web of Science were systematically searched for original studies providing information on the intravenous application of erythrocyte concentrates in porcine, ovine, and canine animal models. Results: A total of 36 studies were included in the analysis. The majority of porcine studies evaluated hemorrhagic shock conditions. Pig models showed high physiological similarities with regard to red cell physiology during early storage. Ovine and canine studies were found to model typical aspects of human red cell storage at 42 days. Only four studies provided data on 24 h in vivo survival of red cells. Conclusions: While ovine and canine models can mimic typical human erythrocyte storage for up to 42 days, porcine models stand out for reliably simulating double-hit pathologies such as hemorrhagic shock. Large animal models remain an important area of translational research since they have an impact on testing new pharmacological or biophysical interventions to attenuate storage-related adverse effects and allow, in a controlled environment, to study background and interventions in dynamic and severe disease conditions.

Ex vivo normothermic preservation of amputated limbs with a hemoglobin-based oxygen carrier perfusate

BACKGROUND

Ex vivo normothermic limb perfusion (EVNLP) preserves amputated limbs under near-physiologic conditions. Perfusates containing red blood cells (RBCs) have shown to improve outcomes during ex vivo normothermic organ perfusion, when compared with acellular perfusates. To avoid limitations associated with the use of blood-based products, we evaluated the feasibility of EVNLP using a polymerized hemoglobin-based oxygen carrier-201 (HBOC-201).

METHODS

Twenty-four porcine forelimbs were procured from Yorkshire pigs. Six forelimbs underwent EVNLP with an HBOC-201-based perfusate, six with an RBC-based perfusate, and 12 served as static cold storage (SCS) controls. Ex vivo normothermic limb perfusion was terminated in the presence of systolic arterial pressure of 115 mm Hg or greater, fullness of compartments, or drop of tissue oxygen saturation by 20%. Limb contractility, weight change, compartment pressure, tissue oxygen saturation, oxygen uptake rates (OURs) were assessed. Perfusate fluid-dynamics, gases, electrolytes, metabolites, methemoglobin, creatine kinase, and myoglobin concentration were measured. Uniformity of skin perfusion was assessed with indocyanine green angiography and infrared thermography.

RESULTS

Warm ischemia time before EVNLP was 35.50 ± 8.62 minutes (HBOC-201), 30.17 ± 8.03 minutes (RBC) and 37.82 ± 10.45 (SCS) (p = 0.09). Ex vivo normothermic limb perfusion duration was 22.5 ± 1.7 hours (HBOC-201) and 28.2 ± 7.3 hours (RBC) (p = 0.04). Vascular flow (325 ± 25 mL·min-1 vs. 444.7 ± 50.6 mL·min-1; p = 0.39), OUR (2.0 ± 1.45 mL O2·min-1·g-1 vs. 1.3 ± 0.92 mL O2·min-1·g-1 of tissue; p = 0.80), lactate (14.66 ± 4.26 mmol·L-1 vs. 13.11 ± 6.68 mmol·L-1; p = 0.32), perfusate pH (7.53 ± 0.25 HBOC-201; 7.50 ± 0.23 RBC; p = 0.82), flexor (28.3 ± 22.0 vs. 27.5 ± 10.6; p = 0.99), and extensor (31.5 ± 22.9 vs. 28.8 ± 14.5; p = 0.82) compartment pressures, and weight changes (23.1 ± 3.0% vs. 13.2 ± 22.7; p = 0.07) were not significantly different between HBOC-201 and RBC groups, respectively. In HBOC-201 perfused limbs, methemoglobin levels increased, reaching 47.8 ± 12.1% at endpoint. Methemoglobin saturation did not affect OUR (ρ = -0.15, r2 = 0.022; p = 0.45). A significantly greater number of necrotic myocytes was found in the SCS group at endpoint (SCS, 127 ± 17 cells; HBOC-201, 72 ± 30 cells; RBC-based, 56 ± 40 cells; vs. p = 0.003).

CONCLUSION

HBOC-201- and RBC-based perfusates similarly support isolated limb physiology, metabolism, and function.

New Applications of HBOC-201: A 25-Year Review of the Literature

If not cured promptly, tissue ischemia and hypoxia can cause serious consequences or even threaten the life of the patient. Hemoglobin-based oxygen carrier-201 (HBOC-201), bovine hemoglobin polymerized by glutaraldehyde and stored in a modified Ringer's lactic acid solution, has been investigated as a blood substitute for clinical use. HBOC-201 was approved in South Africa in 2001 to treat patients with low hemoglobin (Hb) levels when red blood cells (RBCs) are contraindicated, rejected, or unavailable. By promoting oxygen diffusion and convective oxygen delivery, HBOC-201 may act as a direct oxygen donor and increase oxygen transfer between RBCs and between RBCs and tissues. Therefore, HBOC-201 is gradually finding applications in treating various ischemic and hypoxic diseases including traumatic hemorrhagic shock, hemolysis, myocardial infarction, cardiopulmonary bypass, perioperative period, organ transplantation, etc. However, side effects such as vasoconstriction and elevated methemoglobin caused by HBOC-201 are major concerns in clinical applications because Hbs are not encapsulated by cell membranes. This study summarizes preclinical and clinical studies of HBOC-201 applied in various clinical scenarios, outlines the relevant mechanisms, highlights potential side effects and solutions, and discusses the application prospects. Randomized trials with large samples need to be further studied to better validate the efficacy, safety, and tolerability of HBOC-201 to the extent where patient-specific treatment strategies would be developed for various clinical scenarios to improve clinical outcomes.

Colloids Yes or No? - a "Gretchen Question" Answered

Colloid solutions, both natural and synthetic, had been widely accepted as having superior volume expanding effects than crystalloids. Synthetic colloid solutions were previously considered at least as effective as natural colloids, as well as being cheaper and easily available. As a result, synthetic colloids (and HES in particular) were the preferred resuscitation fluid in many countries. In the past decade, several cascading events have called into question their efficacy and revealed their harmful effects. In 2013, the medicines authorities placed substantial restrictions on HES administration in people which has resulted in an overall decrease in their use. Whether natural colloids (such as albumin-containing solutions) should replace synthetic colloids remains inconclusive based on the current evidence. Albumin seems to be safer than synthetic colloids in people, but clear evidence of a positive effect on survival is still lacking. Furthermore, species-specific albumin is not widely available, while xenotransfusions with human serum albumin have known side effects. Veterinary data on the safety and efficacy of synthetic and natural colloids is limited to mostly retrospective evaluations or experimental studies with small numbers of patients (mainly dogs). Large, prospective, randomized, long-term outcome-oriented studies are lacking. This review focuses on advantages and disadvantages of synthetic and natural colloids in veterinary medicine. Adopting human guidelines is weighed against the particularities of our specific patient populations, including the risk-benefit ratio and lack of alternatives available in human medicine.

Relative Efficacies of HBOC-201 and Polyheme to Increase Oxygen Transport Compared to Blood and Crystalloids

BACKGROUND

Because total hemoglobin in circulation ([THb]) is an established predictor of clinical outcomes in anemic individuals, the relative efficacies of resuscitation fluids to increase [THb] can be used to design better hemoglobin-based oxygen carrier (HBOC) clinical trials.

METHODS

Expected efficacies of HBOC-201 (13 g Hb/dL) and packed red blood cells (RBCs) (packed red blood cells [pRBCs], 24 g Hb/dL) to increase [THb] were calculated and interpreted in the context of severe adverse events (SAEs) in the HEM-0115 phase III clinical trial.The PolyHeme phase III clinical trial compared the HBOC, PolyHeme (10 g Hb/dL), with crystalloid control prehospital and packed RBCs in hospital. The comparative abilities of these resuscitation fluids to maintain [THb] were interpreted in the context of mortality.

RESULTS

In HEM-0115, infusion of HBOC-201 increased [THb] by 0.18 ± 0.03 g/dL (N=121) compared with 0.87 ± 0.07 g/dL (n = 115) following one unit of pRBCs. These observed increases in [THb] were similar to expected increases for these fluids. Use of HBOC-201 was associated with 0.34 SAEs per patient compared with 0.25 SAEs per patient in the pRBC arm (P = 0.016).Hemoglobin Deficit was greater in HBOC-201-treated patients than in pRBC controls and emerged as a predictor of SAEs in a logistics model. Randomization to HBOC-201 had no power to predict SAEs.PolyHeme more effectively maintained [THb] than did crystalloid prior to arrival at hospital, associated with initially higher survival in the PolyHeme arm. Thereafter, PolyHeme subjects sustained lower [THb] and higher mortality than controls.

CONCLUSION

Greater anemia in subjects randomized to HBOC-201 was consistent with the relative efficacies of HBOC-201 and pRBCs to increase [THb] and may have contributed to more SAEs in the HBOC arm of HEM-0115 and greater long-term mortality in the PolyHeme trial.

A case study of 10 patients administered HBOC-201 in high doses over a prolonged period: outcomes during severe anemia when transfusion is not an option

BACKGROUND

Hemoglobin-Based Oxygen Carriers (HBOCs) can act as an "oxygen bridge" in acute severe anemia when transfusion is indicated, but not possible. We present data on 10 Expanded Access (EA) patients treated with high cumulative doses of Hemopure (HBOC-201), to assess the ability of HBOC-201 to safely treat life threatening anemia in situations where high volumes of product were administered over an extended period of time.

STUDY DESIGN AND METHODS

Inclusion in this study required that the patient receive at least 10 units of HBOC-201 between 2014 and 2017 under the FDA-sanctioned EA program. Depending on a patient's geographical location, treatment with HBOC-201 was obtained through either a single patient emergency Investigational New Drug (IND) application, or an intermediate size population IND. Of the 41 patients who were treated during this period, 10 patients received 10 or more units of the product. Data were obtained from medical records.

RESULTS

Treatments with HBOC-201 started within 24 hours of signing consent and were administered at an average rate of 1.99 (SD 0.17) units per day over a mean of 8.2 days (SD 2.9), during which patients received on average 16.2 units (SD 5.7 units) of HBOC-201. The median pre-treatment nadir corpuscular hemoglobin (Hb) concentration was 3.3 (SD 0.9) g/dL and post-treatment Hemoglobin was 7.3 (SD 1.7) g/dL. Common side effects included methemoglobinemia, gastrointestinal symptoms, and hypertension. However, no product-related serious adverse events (SAEs) were noted. All patients survived.

CONCLUSIONS

Administration of HBOC-201 over an extended period is a feasible and safe oxygen bridge for severely anemic patients who cannot be transfused with RBC.

Ex-Vivo Normothermic Limb Perfusion With a Hemoglobin-Based Oxygen Carrier Perfusate

INTRODUCTION

Ex-vivo normothermic limb perfusion (EVNLP) has been proven to preserve limb viability better than standard cold storage. Perfusates containing packed red blood cells (pRBC) improve outcomes when compared to acellular perfusates. Limitations of pRBC-based perfusion include limited availability, need for cross match, mechanical hemolysis, and activation of pro-inflammatory proteins. Hemoglobin-based oxygen carrier (HBOC)-201 (Hemopure) is a solution of polymerized bovine hemoglobin, characterized by low immunogenicity, no risk of hemolytic reaction, and enhanced convective and diffusive oxygen delivery. This is a preliminary study on the feasibility of EVNLP using HBOC-201 as an oxygen carrier.

MATERIALS AND METHODS

Three porcine forelimb perfusions were performed using an established EVNLP model and an HBOC-201-based perfusate. The perfusion circuit included a roller pump, oxygenator, heat exchanger, and reservoir. Electrolytes, limb temperature, weight, compartment pressure, nerve conduction, and perfusion indicated by indocyanine green angiography and infra-red thermography were monitored. Histological evaluation was performed with hematoxylin and eosin and electron microscopy.

RESULTS

Three limbs were perfused for 21.3 ± 2.1 hours. Muscle contractility was preserved for 10.6 ± 2.4 hours. Better preservation of the mitochondrial ultrastructure was evident at 12 hours in contrast to crystallization and destruction features in the cold-storage controls.

CONCLUSIONS

An HBOC-201-EVNLP produced outcomes similar to RBC-EVNLP with preservation of muscle contractility and mitochondrial structure.

A safety and efficacy evaluation of hemoglobin-based oxygen carrier HBOC-201 in a randomized, multicenter red blood cell controlled trial in noncardiac surgery patients

BACKGROUND

We present the results of a previously unpublished hemoglobin-based oxygen carrier (HBOC) study conducted in 1998-1999.

METHODS

In a multicenter, randomized, single-blind, comparative study of HBOC-201 versus allogeneic red blood cell (RBC) transfusions, no-cardiac surgery patients received HBOC-201 to a maximum of 7 units (n = 83) or RBCs (n = 77). Patients could be switched to RBCs for safety or any other reason. The efficacy end points were elimination and/or reduction of allogeneic RBC transfusions for 28 days.

RESULTS

The proportion of patients in the HBOC-201 group that avoided RBC transfusion was 0.427 (95% confidence interval, 0.321-0.533). Subjects in the HBOC-201 group received on average 3.2 units of RBCs versus 4.4 units in the control arm (P = 0.004). Seventy-nine (95.2%) subjects in the HBOC-201 group and 72 (93.5%) in the RBC group experienced adverse events (AEs), judged to be associated with study treatment in 59 (71.1%) and 18 (23.4%) subjects, respectively. Thirty-day mortality, 5 (6.0%) vs 4 (5.2%) patients (P = 1.00), incidence of serious AEs, 24 (28.9%) vs 20 (26.0%) (P = 0.73), or time to intensive care unit (log-rank P = 0.15) or hospital discharge (log-rank P = 0.53) were similar for the HBOC-201 and RBC groups, respectively.

CONCLUSIONS

Up to 7 units of HBOC-201 infused over the course of 6 days resulted in RBC transfusion avoidance in 43% of patients. There were no notable differences in mortality and serious AEs incidence. The use of HBOC-201 was associated with a notable excess of nonserious AEs.

Dose-Dependent Hemodynamic, Biochemical, and Tissue Oxygen Effects of OC99 following Severe Oxygen Debt Produced by Hemorrhagic Shock in Dogs

We determined the dose-dependent effects of OC99, a novel, stabilized hemoglobin-based oxygen-carrier, on hemodynamics, systemic and pulmonary artery pressures, surrogates of tissue oxygen debt (arterial lactate 7.2 ± 0.1 mM/L and arterial base excess -17.9 ± 0.5 mM/L), and tissue oxygen tension (tPO2) in a dog model of controlled severe oxygen-debt from hemorrhagic shock. The dose/rate for OC99 was established from a pilot study conducted in six bled dogs. Subsequently twenty-four dogs were randomly assigned to one of four groups (n = 6 per group) and administered: 0.0, 0.065, 0.325, or 0.65 g/kg of OC99 combined with 10 mL/kg lactated Ringers solution administered in conjunction with 20 mL/kg Hextend IV over 60 minutes. The administration of 0.325 g/kg and 0.65 g/kg OC99 produced plasma hemoglobin concentrations of 0.63 ± 0.01 and 1.11 ± 0.02 g/dL, respectively, improved systemic hemodynamics, enhanced tPO2, and restored lactate and base excess values compared to 0.0 and 0.065 g/kg OC99. The administration of 0.65 g/kg OC99 significantly elevated pulmonary artery pressure. Plasma hemoglobin concentrations of OC99 ranging from 0.3 to 1.1 g/dL, in conjunction with colloid based fluid resuscitation, normalized clinical surrogates of tissue oxygen debt, improved tPO2, and avoided clinically relevant increases in pulmonary artery pressure.

Gastric antisecretory and antiulcer activity of bovine hemoglobin

AIM: To investigate gastric antisecretory and gastroprotective activity of bovine hemoglobin (B-Hb) in rats.

METHODS: Adult Albino-Wistar rats were divided into groups of 6 animals each. B-Hb in doses of 100, 300 and 900 mg/kg body weight was tested for gastric acid secretion and antiulcer activity. Gastric secretions were measured 6 h after pylorus ligation in rats pretreated with B-Hb. The acidity was measured by titrating gastric contents against 0.01 mol/L NaOH to pH 7. Indomethacin ulcers were produced by oral administration of 30 mg/kg bw in the rats pretreated with B-Hb one hour before indomethacin. Six hours after indomethacin stomach removed and ulcer index was recorded. Ethanol ulcer were produced by 1 mL of ethanol in the rats pretreated with B-Hb 30 min before the ethanol. One hour after ethanol stomach were cut open to score ulcers. Histological examination and analysis of gastric wall mucus, non-protein sulfhydryl groups (NP-SH), and myeloperoxidase (MPO) were carried in gastric tissue following ethanol administration.

RESULTS: In control rats pylorus ligation for 6 h resulted in the accumulation of 8.1 ± 0.61 mL of gastric secretion. The treatment of the rats with 100, 300 and 900 mg/kg of B-Hb produced a significant decrease in the volume of gastric secretion 5.6 ± 0.63, 5.5 ± 0.75 and 4.7 ± 0.58 mL respectively as compared to the control group [analysis of variance (ANOVA) F = 4.77, P < 0.05]. The lesion area in the control group was found to be 22.4 ± 3.2 mm² six hours after the administration of indomethacin. Treatment of rats with B-Hb at doses of 100 mg/kg (24.3 ± 3.29 mm²), 300 mg/kg (16.2 ± 1.45 mm²) and 900 mg/kg (12.6 ± 1.85 mm²) produced a dose dependent decreased the lesion scores (ANOVA F = 4.50, P < 0.05). The ulcer index following one hour after 1 mL ethanol was 7.1 ± 0.31. Pretreatment of rats with B-Hb at the doses of 100 mg/kg (2.5 ± 0.42), 300 mg/kg (2.1 ± 0.4) and 900 mg/kg (0.7 ± 0.21) significantly inhibited the formation of gastric lesions (ANOVA F = 63.26, P < 0.0001). Histological examination of gastric mucosa following ethanol showed significant lesions in the form of gastric pits with detachment of the surface epithelium; vacuolation of epithelial cells and elongation of microvessels. The changes were dose-dependently attenuated by B-Hb. The treatment of rats with ethanol significantly decreased the Alcian blue binding capacity of gastric wall mucus (480 ± 25.6 μg Alcian blue/g of tissue) as compared to control rats (667 ± 25.8 μg). Pretreatment of rats with B-Hb at the doses of 100 mg/kg (516 ± 31.6 μg/g), 300 mg/kg (558 ± 28.8 μg/g) and 900 mg/kg (654 ± 33.8 μg/g) significantly attenuated ethanol induced depletion of gastric wall mucus (ANOVA F = 8.05, P < 0.005). A significant and dose dependent increase of gastric mucosal NP-SH (ANOVA F = 19.62, P < 0.001) and decrease in MPO activity (ANOVA F = 3.1, P < 0.05) was observed in B-Hb treated rats.

CONCLUSION: B-Hb possesses significant gastric antisecretory and gastroprotective activity against experimentally induced gastric lesion. The gastroprotective effects of B-Hb are accompanied by inhibition of neutrophils activity, reduction of oxidative stress and maintenance of mucosal integrity.

Comparison of Hb-200 and 6% hetastarch 450/0.7 during initial fluid resuscitation of 20 dogs with gastric dilatation-volvulus

OBJECTIVE

To compare the use of polymerized stroma-free bovine hemoglobin (Hb-200) and 6% hetastarch 450/0.7 (HES 450/0.7) in 0.9% saline during fluid resuscitation of dogs with gastric dilatation-volvulus (GDV).

DESIGN

Prospective, randomized clinical case series.

SETTING

Private specialty and referral clinic.

ANIMALS

Twenty client-owned dogs presenting with GDV.

INTERVENTIONS

Dogs presenting with GDV and abnormal perfusion parameters first received rapid IV infusion of a buffered isotonic replacement crystalloid (15 mL/kg) and IV opioids. Patients were then randomized to receive either Hb-200 (N = 10) or HES 450/0.7 (N = 10). Balanced isotonic replacement crystalloids (10-20 mL/kg IV) were rapidly infused along with either Hb-200 or HES in 5 mL/kg IV aliquots to meet resuscitation end points.

MEASUREMENTS AND MAIN RESULTS

Resuscitation was defined as meeting at least 2 of 3 criteria: (1) capillary refill time 1-2 seconds, pink mucous membrane color, strong femoral pulse quality; (2) heart rate (HR) ≤ 150/min; or (3) indirect arterial systolic blood pressure (SBP) > 90 mm Hg. HR, SBP, packed cell volume, hemoglobin, glucose, venous pH, bicarbonate, base excess, anion gap, and colloid osmotic pressure were compared at hospital entry and within 30 minutes post-resuscitation. Compared to the HES group, the Hb-200 group required significantly less colloid (4.2 versus 18.4 mL/kg) and crystalloid (31.3 versus 48.1 mL/kg) to reach resuscitation end points (P = 0.001). Time to resuscitation was significantly shorter in the Hb-200 group (12.5 versus 52.5 min).

CONCLUSIONS

Dogs with GDV receiving Hb-200 during initial resuscitation required smaller volumes of both crystalloid and colloid fluids and reached resuscitation end points faster than dogs receiving HES 450/0.7 (P = 0.02).

Preoxygenated hemoglobin-based oxygen carrier HBOC-201 annihilates myocardial ischemia during brief coronary artery occlusion in pigs

Because of their ability to perfuse remote regions and deliver oxygen, hemoglobin-based oxygen carriers (HBOCs) may be considered in the treatment of several ischemic conditions such as acute coronary syndromes or high-risk percutaneous intervention. Here we studied the effects of intracoronary infusion of ex vivo preoxygenated HBOC-201 during brief total coronary artery occlusion (CAOs) on myocardial oxygenation and left ventricular (LV) function in a large animal model and investigated the influence of HBOC-201 temperature and infusion rate on these effects. Thirteen open-chest anesthetized swine were instrumented for measurement of global and regional LV function and metabolism. CAOs were induced by inflating an intracoronary balloon catheter; preoxygenated HBOC-201 (12 g/dL) was infused distally through the central lumen of the balloon catheter. Animals underwent consecutive 3-min CAOs interspersed by 30 min of reperfusion, accompanied by different HBOC-201 infusion rates (0, 15, 23, 30, 40, and 50 ml/min) and/or two infusion temperatures (18°C or 37°C) in random order. CAO elicited immediate loss of systolic shortening (SS) in the ischemic region (19 ± 1% at baseline vs. −3 ± 2% at end of CAO), resulting in decreases in maximum rate of rise in LV pressure (15 ± 5%) and stroke volume (12 ± 4%; all P < 0.05). Balloon deflation resulted in marked coronary reactive hyperemia (to 472 ± 74% of baseline), increases in coronary venous concentrations of adenosine + inosine (to 218 ± 26% of baseline; both P < 0.05) and rapid restoration of SS toward baseline. HBOC-201 ameliorated the CAO-induced changes in SS, stroke volume, reactive hyperemia, and coronary venous adenosine + inosine. The effects were temperature and flow dependent with full preservation of SS at 50 ml/min HBOC-201 of 37°C. In conclusion, intracoronary preoxygenated HBOC-201 preserved myocardial oxygenation and LV function in swine during CAO in a dose- and temperature-dependent manner. In our study setting, preoxygenated HBOC-201 can match the oxygen delivery role of endogenous blood in the heart on an almost equivalent-volume basis.

Administration of bovine polymerized haemoglobin before and during coronary occlusion reduces infarct size in rabbits

BACKGROUND

Haemoglobin-based oxygen carriers (HBOC) seem to increase the risk of mortality and myocardial infarction in clinical trials. Therefore, we designed this randomized placebo-controlled animal study to evaluate the effects of prophylactic and therapeutic administration of HBOC in a myocardial ischaemia-reperfusion model with respect to infarct size and areas of impaired perfusion (no reflow, NR).

METHODS

Thirty-two anaesthetized, mechanically ventilated rabbits were randomized to one of the four groups. Group G1 received 0.4 g kg(-1) i.v. HBOC-200 25 min before coronary artery occlusion, G2 received the same dose i.v. 10 min after occlusion, and G3 and 4 received i.v. saline. G1, 2, and 3 were subjected to 30 min occlusion of left coronary artery followed by 240 min of reperfusion. G4 was treated without ischaemia-reperfusion. Measurement included assessment of the area at risk and infarct size using triphenyltetrazolium chloride stain and areas of NR using thioflavin stain. Ischaemia-reperfusion was confirmed by microspheres technique.

RESULTS

Infarct size as a percentage of the area at risk was significantly reduced in G1 [25 (sd 13)%, P=0.026] and G2 [22 (20)%, P=0.009] compared with G3 [48 (17)%]. The areas of NR in percentage of the area at risk [G1, 26 (15)%; G2, 34 (22)%; G3, 36 (12)%; G4, 5 (3)%] did not differ between the groups of animals undergoing coronary occlusion and reperfusion.

CONCLUSIONS

Prophylactic and therapeutic administration of HBOC-200 reduces infarct size in myocardial ischaemia and reperfusion in rabbits. This reduction of infarct size is not accompanied by an improvement of areas of NR.

Effects of hemodilution with a hemoglobin-based oxygen carrier (HBOC-201) on ischemia/reperfusion injury in a model of partial warm liver ischemia of the rat

BACKGROUND

Ischemia/reperfusion injury is an unavoidable complication in liver surgery and transplantation. Hemodilution with colloids can reduce postischemic injury but limits oxygen transport. Hemoglobin-based oxygen carriers have been evaluated as blood substitute and provide a plasma-derived oxygen transport. It was the aim of our study to evaluate the combined benefits of hemodilution with a better oxygen supply to reperfused liver tissue by the use of HBOC-201 (Hemopure).

MATERIAL AND METHODS

A model of partial warm liver ischemia in the rat was used. One group served as untreated control, the other groups were hemodiluted either with Ringer's lactate, Dextran-70, HBOC-201 or a mixture of Dextran and HBOC-201. After reperfusion, intravital microscopy studies were done and tissue pO(2) levels and transaminases measured. Statistical analysis was done by one- and two-way ANOVA, followed by pairwise comparison.

RESULTS

Hemodilution with Ringer's lactate did not show any improvement compared to the control group. Dextran and HBOC group were superior to the Ringer and control animals in all parameters studied. Leucocyte adherence in postsinusoidal venules improved from 569.03+/-171.87 and 364.52+/-167.32 in control and Ringer group to 131.68+/-58.34 and 68.44+/-20.31/mm(2) endothelium in Dextran and HBOC group (p<0.001). Concerning tissue pO(2) levels, HBOC (23.4+/-5.0 mmHg) proved to be superior to Dextran (7.9+/-4.4 mmHg; p=0.007).

CONCLUSION

HBOC was equivalent to Dextran in reducing I/R injury in the liver, but improved oxygenation of postreperfusion liver tissue.

Comparison of Hemoglobin-based oxygen carriers to stored human red blood cells

Since the inception of allogeneic blood transfusion, the search for an alternative to the use of stored packed red blood cells has been underway. Over the last 10 years, modified hemoglobin solutions in the form of hemoglobin-based oxygen carriers (HBOCs) have made significant strides toward becoming clinically available and useful. Although HBOCs are not yet ready for regular use in the clinical arena, this may change in the near future as HBOC products continue to improve and as the elucidation of the mechanisms of any adverse effects becomes clearer. In the mean time, we must further the development of alternative strategies for the "hemoglobin bridge" so desperately needed by many critically ill patients.

Influence of the Hemoglobin Solution HBOC-201 on Tissue Oxygenation in the Rat R1H-Tumor

BACKGROUND

HBOC-201 is an ultra purified bovine hemoglobin solution. It has already been used in clinical phase II/III trials for emergency treatments. Animal experiments have shown that HBOC-201 is highly effective in tissue oxygenation. The study was performed in order to assess the potential of low dose HBOC-201 to improve tumor oxygenation.

METHODS

30 rats with a subcutaneously growing rhabdomyosarcoma R1H tumor were randomly assigned either to be ventilated with carbogen (n = 10), or to receive an IV injection of 0.3 g/kg HBOC-201 (n = 10) or a combination of 0.3 g/kg HBOC-201 and carbogen breathing (n = 10). Under general anesthesia the effects of the respective treatment on the tissue oxygen tension (tpO2) of the tumor were determined using a flexible stationary probe at baseline (b) and 15 and 60 min after application of the respective medication.

RESULTS

HBOC-201 alone failed to improve tumor tpO2 (b: 1.3 +/- 1.2mmHg; 15min: 1.4 +/- 1 mmHg; 60min: 1 +/- 1 mmHg). In combination with carbogen the mean tpO2 of the tumor raised in comparison to baseline values (b: 3.1 +/- 4.6 mmHg; mmHg; 15min: 8.5 +/- 11*mmHg; 60min: 4.8 +/- 5mmHg; *p < 0.05 vs. b), but this effect was less pronounced than the increase in tpO2 by carbogen alone (b: 3.4 +/- 3.4mmHg; 15min: 9 +/- 10* mmHg; 60 min: 13 +/- 19* mmHg; *p < 0.05 vs. b).

CONCLUSION

The application of low dose hemoglobin solution HBOC-201 does not result in improvement of tissue oxygenation in the rat rhabdomyosarcoma R1H.

Hemoglobin-Based Oxygen Carrier Does Not Improve Survival of Ischemic Rat Island Groin Flaps

Reducing reperfusion injury to skin flaps is an effective means to improve the survival of the flap. By enhancing oxygen delivery to the microcirculation within the flap, ischemia-reperfusion injury should be decreased, improving the flap's survival. This study evaluated the effects of a hemoglobin-based oxygen carrier (Oxyglobin) on the development of necrosis and survival of ischemic rat island groin flaps. Sprague-Dawley rats were randomly assigned to one of three treatment groups. A groin flap was elevated on each rat and subjected to 9 h of ischemia. Rats in group I were given an intravenous infusion of 0.9% saline prior to elevation of the skin flap. Rats in group II were given an intravenous infusion of Oxyglobin prior to elevation of the skin flap. Rats in group III were given a low-dose intravenous infusion of Oxyglobin following the 9 h of ischemia, just prior to reperfusion. The flaps were monitored for 7 days postoperatively for necrosis. The percentage of flap necrosis was recorded at the end of 7 days. All rats were euthanized at the completion of the study and the flaps were harvested for histopathological analysis. No significant difference was noted in the survival of the flaps or the degree of necrosis in the rats treated with Oxyglobin compared to the control group. Thus, pre-reperfusion treatment with Oxyglobin did not improve the percentage of flap survival, or the degree of severity of necrosis in rat groin flaps subjected to 9 h of ischemia.

Isovolemic exchange transfusion with increasing concentrations of low oxygen affinity hemoglobin solution limits oxygen delivery due to vasoconstriction

O2-carrying fluids based on hemoglobin (Hb) are in various stages of clinical trials to determine their suitability as O2-carrying plasma expanders. Polymerized Hb solutions are characterized by their vasoactivity, low O2 affinity, oncotic effect, prolonged shelf life, and stability. Physiological responses to facilitated O2 transport after exchange transfusion with polymerized bovine Hb (PBH) were studied in the hamster window chamber model during acute moderate anemia to determine how PBH affects microvascular perfusion and tissue oxygenation. The anemic state [29% hematocrit (Hct)] was induced by hemodilution with a plasma expander (70 kDa dextran). After hemodilution, animals were randomly assigned to different exchange transfusion groups. Study groups were based on the concentration of PBH used, namely: PBH at 13 g Hb/dl [PBH13], PBH diluted to 8 (PBH8) or 4 (PBH4) g Hb/dl in albumin solution at matching colloidal osmotic pressure (COP), and no PBH (only albumin solution) at matching COP (PBH0). Measurement of systemic parameters, microvascular hemodynamics, capillary perfusion, and intravascular and tissue O2 levels was performed at 18% Hct. Restitution of O2-carrying capacity with PBH13 increased arterial pressure and triggered vasoconstriction, low perfusion, and high peripheral resistance. PBH4 and PBH0 exhibited lower arterial pressures compared with PBH13. Exchange transfused animals with PBH8 and PBH4 better maintained perfusion and functional capillary density than PBH13. Blood gas parameters and acid-base balance were recovered proportional to microvascular perfusion. Arterial O2 tensions were improved with PBH4 and PBH8 by preventing O2 precapillary release and increasing O2 reserve. Further studies to establish PBH optimal dosage, efficacy, safety, and its effect on outcome are indicated before Hb-based O2-carrying blood substitutes are implemented in routine practice.

Clinical use of a haemoglobin-based oxygen carrying solution (Oxyglobin) in 48 cats (2002-2006)

The objective of this retrospective study was the evaluation of the administration of a haemoglobin (Hb)-based oxygen carrying solution (Oxyglobin) to cats over a time period of 4 years. Indication, infusion volume/24h, number of Oxyglobin infusions/cat, Hb concentration pre- and post-infusion, adverse events, and patient outcome were evaluated. Forty-eight anaemic cats received 65 Oxyglobin infusions. Prior to administration of Oxyglobin, Hb concentration ranged from 2 to 7.8 g/dl (median 4.9 g/dl), the volume of Oxyglobin administered was 4.4-25 ml/kg/24h (median 9.8 ml/kg/24h). An increase of Hb was noted after 41 of 49 infusion events. Severe side effects were noted in seven cats with cardiac disease, which developed pulmonary oedema (five), pleural effusion (three), and respiratory distress (one). They received 6.7-19.8 ml/kg/24h (median 12.3 ml/kg/24h) of Oxyglobin. Four of these seven cats received whole blood transfusions on the same day; five cats died and one was euthanased. Overall 24-h survival rate was 77%. Administration of Oxyglobin efficiently increased the Hb concentration. However, in cats suffering from cardiac disease, there is a high risk of life-threatening circulatory overload at the doses used in this study.

Oxygen carriers and cancer chemo- and radiotherapy sensitization: bench to bedside and back

After over a century of preclinical and clinical development, a number of artificial oxygen carriers based either on perfluorochemicals or hemoglobins are currently in advanced clinical trials for their ability to replace red blood cells and to ensure adequate tissue oxygenation in case of acute anemia or infarction. On the other hand, intravenous administration of perflourocarbone emulsions or hemoglobin solutions were effective in increasing the oxygenation throughout experimental tumors, and fueled by exciting new developments in the field, some products are experimentally and clinically investigated as cancer chemo- and radiosensitizing agents. This review is to provide a first overview of the current status of artificial oxygen carriers as a oxygen therapeutics in cancer chemo- and radiotherapy sensitization.

Expectations and implications of blood sparing with hemoglobin based oxygen carriers

To gain insight into the degree to which hemoglobin based oxygen carriers may replace the need for transfusion in surgical patients experiencing blood loss, a simple mathematical model was developed. This model predicts the amount of blood sparing resulting from a bolus infusion of different doses of hemoglobin solution as a function of circulating hemoglobin half-life and degree of erythropoesis enhancement subsequent to treatment. The results of this analysis are consistent with published clinical data and imply that blood sparing increases with increasing oxygen carrier dose and half-life, as well as increasing levels of erythropoesis enhancement. The analysis also predicts that the total circulating hemoglobin content in patients infused with HBOC solutions may reach a minimum value up to ten days after treatment.

Deferoxamine lowers tissue damage after 80% exchange transfusion with polymerized hemoglobin

Hemoglobin (Hb) solutions have been proposed as potential substitutes for erythrocytes to maintain oxygen-carrying capacity in situations in which blood is not available. This study investigated systemic and microvascular hemodynamics as well as tissue oxygenation and viability after an 80% exchange transfusion with an oxygen-carrying blood substitute based on polymerized bovine hemoglobin (PBH). Studies were carried in unanesthetized hamsters prepared with a window-chamber model for microcirculation evaluation. Heme iron-mediated injury to the tissue was analyzed by using deferoxamine (an iron chelator), which reduces free iron toxicity. Exchange transfusion led to a significant decrease in hematocrit (Hct) and an increase in plasma Hb, in addition to a significant decrease of arteriolar and venular diameters, flow velocity, and, therefore, microvascular blood flow. Capillary perfusion was severely compromised after exchange, but tissue pO2 increased above baseline, and oxygen extraction was reduced. Apoptotic and necrotic cells increased significantly after the exchange; however, this effect was only partially due to the toxicity of free iron. Iron therapy decreased the microvascular and oxygenation changes but did not fully reverse the adverse effects. Assessment of tissue viability after exchange suggests that chelation treatment in cases of large exchange transfusions with acellular Hb could be potentially beneficial.

MICROVASCULAR PERSPECTIVE OF OXYGEN-CARRYING AND -NONCARRYING BLOOD SUBSTITUTES

The development of an alternative to natural blood has evolved from the initial goal of replicating blood properties to the current objective of formulating a fluid that can be used to replace blood while preserving microvascular function and delivering oxygen. The properties of this fluid are counterintuitive and different from blood because it has high viscosity, oxygen affinity, and a low oxygen carrier concentration when compared with blood. The optimal oxygen carrier devised presently is poly-ethylene-conjugated human hemoglobin, a material demonstrated to be vasoinactive and void of the toxicities present in previous hemoglobin formulations. A feature of this material is that it is effective in small quantities, and therefore amplifies the equivalent supply of blood derived from blood donations.

Bovine polymerized hemoglobin (hemoglobin-based oxygen carrier-201) resuscitation in three swine models of hemorrhagic shock with militarily relevant delayed evacuation--effects on histopathology and organ function

OBJECTIVE

To test our hypothesis that hemoglobin-based oxygen carrier (HBOC)-201 resuscitation in hemorrhagic shock (HS) will not lead to increased organ injury and dysfunction.

DESIGN

Three swine HS models simulating military-relevant delayed evacuation: a) moderate controlled HS, b) severe controlled HS, and c) severe uncontrolled HS.

SETTING

Military research laboratory.

SUBJECTS

Swine.

INTERVENTIONS

Swine were anesthetized/intubated and instrumented. To induce HS, in two controlled hemorrhage experiments, 40% (moderate controlled HS) or 55% (severe controlled HS) of blood volume was withdrawn; in an uncontrolled HS experiment, the liver was crushed/lacerated. During a 4-hr "prehospital phase," pigs were resuscitated with HBOC-201 (HBOC) or Hextend (HEX) or were nonresuscitated (NON). Upon "hospital arrival," liver injury was repaired (severe uncontrolled HS), blood or saline was infused, hemodynamics were monitored, and blood was collected. Upon animal death and/or 72 hrs, necropsy was followed by histopathologic evaluation of organ injury (hematoxylin and eosin, electron microscopy) and immunohistochemistry of oxidative potential (3-nitrotyrosine). Significance (p < .05) was assessed by Kruskal-Wallis, analysis of variance/Bonferroni, and mixed procedure tests.

MEASUREMENTS AND MAIN RESULTS

Survival was significantly higher with HBOC than HEX only with severe uncontrolled HS (p = .002). Myocardial necrosis/fibroplasia, fluid requirements, cardiac output, and cardiac enzymes were generally similar or lower in HBOC than HEX pigs, but creatine kinase-MB (but not creatine kinase-MB/creatine kinase ratio) was higher with HBOC in moderate controlled HS. Alveolar/interstitial pulmonary edema was similar with HBOC and HEX, but Po2 was higher with HBOC in severe uncontrolled HS. Jejunal villar epithelial and hepatocellular necrosis were similarly minimal to moderate in all groups. Minimal biliary changes occurred exclusively with HBOC. Aspartate aminotransferase, lactate dehydrogenase, and alkaline phosphatase were generally higher with HBOC than HEX. Mild renal papillary injury occurred more frequently with HBOC, but consistent patterns for urine output, blood urea nitrogen, and creatinine, were not seen. The 3-nitrotyrosine staining intensity was not different.

CONCLUSIONS

In comparison with hetastarch, HBOC-201 resuscitation of swine with HS increased survival (with severe HS), did not increase evidence of oxidative potential, and had histopathologic and/or functional effects on organs that were clinically equivocal (myocardium, lungs, hepatic parenchyma, jejunum, and renal cortex/medulla) and potentially adverse (hepatobiliary and renal papilla). The effects of HBOC-201-resuscitation in HS should be corroborated in controlled clinical trials.

Oxygen radical formation does not have an impact in the treatment of severe acute experimental pancreatitis using free cellular hemoglobin

AIM: Microcirculatory dysfunction and free oxygen radicals are important factors in the pathogenesis of severe acute pancreatitis. Additional oxygen delivery might enhance lipid peroxidation but may also improve pancreatic microcirculation. This study assesses the effect of free cellular bovine hemoglobin on the formation of oxygen radicals and microcirculation in a rodent model of severe acute pancreatitis.

METHODS: Fifteen minutes after induction of acute pancreatitis Wistar rats received either 0.8 mL bovine hemoglobin (HBOC-200), hydroxyethyl starch (HES) or 2.4 mL of normal saline to ensure normovolemic substitution. After 6 h of examination the pancreas was excised and rapidly processed for indirect measurement of lipid peroxidation products malondialdehyde (MDA) and reduced glutathione (GSH) in pancreatic tissue.

RESULTS: The single application of HBOC-200 improved pancreatic microcirculation and reduced histopathological tissue damage significantly. Tissue concentration of MDA did not differ between the groups. Also no differences in GSH levels were detected.

CONCLUSION: Though the single application of HBOC-200 and HES improve pancreatic microcirculation, no differences in lipid peroxidation products were detected. The beneficial effect of additional oxygen supply (HBOC-200) does not lead to enhanced lipid peroxidation.

Improvement of impaired microcirculation and tissue oxygenation by hemodilution with hydroxyethyl starch plus cell-free hemoglobin in acute porcine pancreatitis

AIMS

To avoid the progression from mild edematous acute pancreatitis (AP) to the severe necrotizing form, one therapeutic option is to improve pancreatic microcirculation and tissue oxygenation. The aim of the study was to evaluate the influence of improved rheology (isovolemic hemodilution) plus enhanced oxygen supply (bovine hemoglobin HBOC-301) on pancreatic microcirculation, tissue oxygenation and survival in severe acute experimental pancreatitis.

METHODS

Severe AP was induced in 39 pigs (25-30 kg BW) by stimulation with intravenous administration of cerulein plus a pressure- and volume-controlled 10-min intraductal infusion of glycodeoxycholic acid. Seventy-five minutes after induction of AP, animals were randomized and hemodiluted isovolemically (PAOP constant) with either 10% hydroxyethyl starch (HES) 200,000/0.5 plus HBOC-301 (+0.6 g/dl plasmatic hemoglobin; Oxyglobin, Biopure, Cambridge, Mass., USA), or 10% HES 200,000/0.5, or Ringer's solution to a hematocrit of 15%. Hemodynamics, oxygen transport parameters, pancreatic microcirculation and tissue oxygen tension were evaluated over 6 h. Then the abdomen was closed, animals were extubated and observed for 6 days. After that, the surviving animals were sacrificed and specimens were taken from the pancreas. The histopathologic findings were scored by two blinded pathologists who quantified acinar necrosis, fat necrosis, inflammation and edema.

RESULTS

Isovolemic hemodilution with HES plus HBOC-301 reduced mortality and preserved pancreatic microcirculation compared with Ringer's solution, but was not significantly different from hemodilution with HES alone. Only treatment with HES plus HBOC-301 normalized pancreatic tissue oxygen tension compared with IHD with HES or Ringer's solution alone.

CONCLUSIONS

IHD with HES plus HBOC-301 as a combination of rheologic and O(2)-delivering therapy may represent a novel therapeutic option for treatment of AP.

[Artificial oxygen carriers as an alternative to red blood cell transfusion]

The expected cost-explosion in transfusion medicine (increasing imbalance between donors and recipients, treatment of transfusion-associated complications) increases the socio-economic significance of the development of safe and effective synthetic oxygen carriers as an alternative to the transfusion of allogeneic red blood cells. Currently two types of artificial oxygen carriers have been tested for safety and efficacy in cases of severe anemia otherwise requiring transfusion. Solutions based on human or bovine hemoglobin (HBOC) possess vasoconstrictor properties in addition to their oxygen transport capacity. The impact of vasoconstriction on tissue perfusion and organ function is however not yet fully understood. Nevertheless, in 2001 the bovine HBOC Hemopure was approved in South Africa for treatment of acutely anemic surgical patients. The purely synthetic perfluorocarbon (PFC) emulsions increase the physically dissolved portion of arterial oxygen content. Due to their particulate nature (emulsion droplets) PFCs may only be infused in low doses to avoid overload and malfunction of phagocytic cells of the reticulo-endothelial system. As part of a multimodal blood conservation program (including normovolemic hemodilution and hyperoxia) the low-dose administration of Oxygent effectively increases intraoperative anemia tolerance. Although reduction of perioperative allogeneic blood transfusion has already been demonstrated for HBOC and PFC, the global clinical establishment of artificial oxygen carriers is not to be expected in the near future.

Enhanced central organ oxygenation after application of bovine cell-free hemoglobin HBOC-201

PURPOSE

While the effects of dilutional anemia or isovolemic hemodilution (IHD) on the oxygen extraction and tissue oxygenation in peripheral organs after application of hemoglobin-based oxygen carriers like HBOC-201 have been studied intensively, little is known about tissue oxygenation properties of hemoglobin solutions in central organs like the liver.

METHODS

Twelve Foxhounds were anesthetized and then randomized to either a control group without hemodilution (Group 1) or underwent first step isovolemic hemodilution (pulmonary artery occlusion pressure constant) with Ringer's solution (Group 2) to a hematocrit of 25% with second step infusion of HBOC-201 until a hemoglobin concentration of +0.6 g.dL(-1) was reached. Tissue oxygen tensions (tpO2) were measured in the gastrocnemius muscle using a polarographic needle probe, and in the liver using a flexible polarographic electrode.

RESULTS

While arterial oxygen content and oxygen delivery decreased with hemodilution in Group 2, global liver and muscle oxygen extraction ratio increased after hemodilution and additional application of HBOC-201. Hemodilution and application of HBOC-201 provided augmentation of the mean liver tpO2 (baseline: 48 +/- 9, 20 min: 53 +/- 10, 60 min: 67 +/- 11*, 100 min: 68 +/- 7*; *P < 0.05 vs baseline and Group 1), while oxygen tensions in Group 1 remained unchanged. Oxygen tension in the skeletal muscle increased after hemodilution and additionally after application of HBOC-201 in comparison to baseline and to the control group (P < 0.05).

CONCLUSION

In the present animal model, IHD with Ringer's solution and additional application of HBOC-201 increased oxygen extraction and tpO(2) in the liver and skeletal muscle, in parallel and in comparison with baseline values and a control group.

Cardioprotection before revascularization in ischemic myocardial injury and the potential role of hemoglobin-based oxygen carriers

Despite the availability of interventional catheterization for patients with acute coronary syndromes, there is an unavoidable delay until the occluded coronary artery(s) can be revascularized, during which time persistent ischemia may lead to irreversible myocardial damage despite subsequently high patency rates. Accordingly, there has been an intense effort to develop early interventions that will preserve the viability of ischemic myocardium before revascularization. A number of novel strategies have been studied, including hemoglobin-based oxygen carriers. These compounds transport oxygen in the plasma to help maintain more normal oxygen delivery to the myocardium supplied by a thrombosed vessel, and they also release oxygen to tissue more efficiently than intraerythrocytic hemoglobin.

Hemoglobin substitutes

Orthopaedic patients frequently require blood transfusions to treat peri-operative anemia. Research in the area of hemoglobin substitutes has been of great interest since it holds the promise of reducing the reliance on allogeneic blood transfusions. The three categories of hemoglobin substitutes are (1) cell-free, extracellular hemoglobin preparations made from human or bovine hemoglobin (hemoglobin-based oxygen carriers or HBOCs); (2) fluorine-substituted linear or cyclic carbon chains with a high oxygen-carrying capacity (perfluorocarbons); and (3) liposome-encapsulated hemoglobin. Of the three, HBOCs have been the most extensively studied and tested in preclinical and clinical trials that have shown success in diminishing the number of blood transfusions as well as an overall favorable side-effect profile. This has been demonstrated in vascular, cardiothoracic, and orthopaedic patients. HBOC-201, which is a preparation of cell-free bovine hemoglobin, has been approved for clinical use in South Africa. These products may well become an important tool for physicians treating peri-operative anemia in orthopaedic patients.

Increased tissue PO2 and decreased O2 delivery and consumption after 80% exchange transfusion with polymerized hemoglobin

The O2-carrying blood substitute based on polymerized bovine hemoglobin (PBH) was used to determine efficacy in maintaining tissue Po2 after an 80% isovolemic blood exchange leading to a hematocrit of 19% [5.4 g Hb/dl from red blood cells (RBCs) and 6.3 g Hb/dl from PBH]. Effects were studied in terms of O2 delivery, O2 extraction, and tissue Po2 at the microcirculatory level at 1, 12, and 24 h after exchange transfusion in awake hamsters prepared with a window chamber model. At 1 h after exchange, arteriolar and venular diameters were decreased compared with baseline. Arteriolar diameter did not fully recover at 12 h after exchange, but venular diameter returned to normal. At 24 h after exchange, arteriolar and venular diameters were not different from baseline. Combining diameter and flow velocity data allowed us to calculate arteriolar and venular flows. At 1 h after exchange, arteriolar and venular flow was reduced compared with baseline. Arteriolar flow was lower at 12 h after exchange and recovered after 24 h. The number of capillaries with RBC passage [functional capillary density (FCD)] at 1 h after exchange with PBH was significantly lower than baseline. FCD remained decreased at 12 h; at 24 h after exchange transfusion, FCD was fully recovered. Tissue Po2 was maximal at 1 h after exchange and decreased progressively at 12 and 24 h after exchange. O2 release to the tissue was minimal at 1 h and increased at 12 and 24 h after exchange. These results suggest the impairment of tissue O2 metabolism after introduction of PBH into the circulation, which is mitigated as PBH concentration declines.

Hemolysis and Heinz body formation associated with ingestion of red maple leaves in two alpacas

Two adult female alpacas were evaluated for acute onset of weakness, pale mucous membranes, and signs of depression of unknown etiology. Both alpacas had intravascular hemolysis, anemia, and Heinz body formation and had been fed wilted red maple leaves. Clinical signs developed several days after ingestion of the leaves. No other toxin exposure was reported, and no parasites were detected. Dietary copper and nitrate-nitrite concentrations were evaluated and determined to be within reference limits. Both alpacas continued to become profoundly anemic with continued hemolysis. This necessitated blood transfusion as a life-saving intervention; however, prior to whole blood being available, transfusion with bovine hemoglobin glutamer was necessary. Both alpacas recovered without complications.

Low-Volume Resuscitation with a Polymerized Bovine Hemoglobin-Based Oxygen-Carrying Solution (HBOC-201) Provides Adequate Tissue Oxygenation for Survival in a Porcine Model of Controlled Hemorrhage

BACKGROUND

We have shown in a previous work that HBOC-201 is able to reverse anaerobic metabolism at low volumes in a porcine model of controlled hemorrhage. On the basis of these results, we hypothesize that low-volume resuscitation with HBOC-201 in a porcine model of controlled hemorrhage provides adequate tissue oxygenation to limit end-organ damage and allow for survival of the animal.

METHODS

Twenty-four Yorkshire swine (55-65 kg) were rapidly hemorrhaged to a mean arterial pressure (MAP) of 30 mm Hg, maintained hypotensive for 45 minutes, and then divided into four groups. The first group, Shed Blood (BL), was resuscitated with shed blood to baseline MAP. A second group, Shed Blood (60), underwent resuscitation for four hours at an MAP of 60 mm Hg with shed blood. The third group, LR + Blood, was resuscitated with lactated Ringer's (maximum, 40 mL/kg) followed by shed blood to baseline MAP. The final group, HBOC (60), underwent resuscitation for 4 hours at an MAP of 60 mm Hg with HBOC-201. Hemodynamic variables, urine output, blood gas analyses, lactate levels, and jejunal oximetry were followed throughout the experiment. Animals were allowed to survive and underwent necropsy on postinjury day 3. Histologic comparisons were made. Data were analyzed using analysis of variance/Duncan's multiple range test.

RESULTS

All animals survived the hemorrhage/resuscitation. One animal in the LR + Blood group died on postinjury day 1. Heart rate, MAP, and arterial pH were similar between groups. Cardiac output was significantly lower throughout resuscitation in the HBOC (60) group. Jejunal oximetry was similar throughout the experiment in all groups, revealing a decline in Po2 during hemorrhage and return to baseline or near baseline during resuscitation. There was no evidence of renal dysfunction. Histologically, one animal in the LR + Blood group and four of six animals in the HBOC (60) group demonstrated mild hepatocellular damage. All other tissues examined were found to have no significant abnormalities. Elevations in serum aspartate aminotransferase levels were noted when comparing the HBOC (60) group to the Shed Blood (BL) and Shed Blood (60) groups on day 2. Significant decreases in hemoglobin levels were noted in the HBOC (60) group compared with all other groups beginning on day 2.

CONCLUSION

Low-volume resuscitation with HBOC-201 provides adequate tissue oxygenation for survival in a porcine model of controlled hemorrhagic shock with no long-term organ dysfunction identified. Although some animals did show mild hepatocellular damage with elevations of aspartate aminotransferase at day 2, these findings did not appear to have clinical relevance, and the enzyme elevations were trending toward normal by the third postoperative day. Decreases in hemoglobin levels at the later time points were expected, given the half-life of the product.

Clinical application of a hemoglobin-based oxygen-carrying solution

Oxyglobin, a hemoglobin-based oxygen-carrying fluid, is indicated in the treatment of anemia in dogs and may be life saving if compatible red blood cells are not available for transfusion. The colloidal properties of Oxyglobin allow for expansion of the circulatory volume, which may be helpful in patients with hypovolemia, especially hemorrhagic shock. Oxyglobin's colloidal properties can also lead to circulatory overload, with development of pulmonary edema and pleural effusion, however, necessitating careful monitoring of the rate of administration and of the respiratory rate and effort of the patient. Measurement of total or plasma hemoglobin concentration can be used as an aid in monitoring patients receiving Oxyglobin.

The Effect of the Bovine Hemoglobin Oxygen Therapeutic HBOC-201 on Human Neutrophil Activation In Vitro

BACKGROUND

We previously demonstrated that HBOC-201 is an efficient resuscitation fluid. However, little is known about its immunomodulatory effects. The goal of this study was to investigate human neutrophil activation after exposure to HBOC-201 and other low-volume resuscitation fluids.

METHODS

Whole blood from 10 healthy volunteers was serially diluted with HBOC-201, 7.5% hypertonic saline (HTS), 7.5% hypertonic saline-6% dextran 70 (HSD), Hextend, or PentaLyte. After an incubation period, samples were analyzed for oxidative burst and CD11b expression using flow cytometry.

RESULTS

Increases in both CD11b and oxidative burst activity were noted in samples diluted with HBOC-201, Hextend, PentaLyte, and lactated Ringer's solution. Samples maximally diluted with HBOC-201 demonstrated increased CD11b expression when compared with lactated Ringer's solution and Hextend (196.11% vs. 22.68% and 33.97%; p = 0.018 and p = 0.033).

CONCLUSION

Although differences were noted only at the highest dilutions, further studies investigating the effects of HBOC-201 are warranted.

Arterial oxygenation and oxygen delivery after hemoglobin-based oxygen carrier infusion in canine hypovolemic shock: a dose-response study

OBJECTIVE

To compare effects of 6% hetastarch (Hextend) and hemoglobin-based oxygen carrier hemoglobin glutamer-200 (Hb-200) (bovine; Oxyglobin) on hemodynamics, arterial oxygen content, and systemic oxygen delivery in a canine hemorrhagic shock model.

DESIGN

Randomized laboratory investigation.

SETTING

University surgical research facility.

SUBJECTS

Twenty-four anesthetized healthy, adult, mongrel dogs (28 +/- 1 kg; 7 female, 17 male).

INTERVENTIONS

Dogs were instrumented for determinations of heart rate, arterial, central venous, pulmonary arterial, and pulmonary arterial occlusion pressures, and cardiac index. Total solids, colloid oncotic pressure, arterial oxygen content, Hb, lactate, pH, and blood gases were analyzed in blood samples. Recordings were made before, after 1 hr of hemorrhagic shock, and immediately and 3 hrs after infusion of either 30 mL/kg hetastarch (group 1), 10 mL/kg Hb-200 + 20 mL/kg hetastarch (group 2), 20 mL/kg Hb-200 + 10 mL/kg hetastarch (group 3), or 30 mL/kg Hb-200 (group 4).

MEASUREMENTS AND MAIN RESULTS

Hemorrhage (35 +/- 1 mL/kg) reduced mean arterial pressure to 50 mm Hg and caused significant decreases in total Hb, mean pulmonary arterial pressure, cardiac index and systemic oxygen delivery, increases in heart rate and systemic vascular resistance, and lactic acidosis. In group 1, hetastarch infusion was accompanied by increases of pulmonary arterial pressure, cardiac index, and blood oxygen extraction above baseline, and decreases of systemic vascular resistance, total Hb, total solids, arterial oxygen content, and systemic oxygen delivery below baseline (p <.05). Other data returned to baseline. In groups 2 to 4, hemodynamic functions (except pulmonary arterial pressure) recovered, yet neither total Hb (i.e., plasma and red blood cell Hb) nor arterial oxygen content increased despite increases in plasma Hb of 2 to 5 g/dL and proportionate increases in total solids. Systemic oxygen delivery improved dose-dependently with Hb-200 but did not return to baseline (p <.05), reaching values comparable to hetastarch group only at 30 mL/kg Hb-200. In all groups, oxygen extraction remained above baseline. Metabolic acidosis and lactatemia resolved significantly faster in groups 2 to 4, and colloid oncotic pressure after resuscitation was greater in groups 2 to 4 than in controls (p <.05).

CONCLUSIONS

In hemorrhagic shock, Hb-200 infusion may not improve oxygen delivery more than hetastarch, likely due to hemodilution caused by its high colloid oncotic pressure, but may facilitate diffusive oxygen transport to tissues.

Hemoglobin-based oxygen carrier HBOC-201 provides higher and faster increase in oxygen tension in skeletal muscle of anemic dogs than do stored red blood cells

BACKGROUND

Increasing need for and potential shortage of blood products have intensified the search for alternative oxygen carriers. A solution to this problem could be use of the bovine hemoglobin-based oxygen carrier HBOC-201. While hemodynamic reactions to cell-free hemoglobin have been studied, little knowledge exists about tissue oxygenation properties of hemoglobin solutions, especially in comparison with red blood cells (RBCs).

STUDY DESIGN AND METHODS

Tissue oxygenation in skeletal muscle of 12 anesthetized dogs was examined after decrease of hemoglobin concentrations by means of hemodilution to hematocrit 10% and subsequent transfusion with either HBOC-201 or autologous banked RBCs. In addition to hemodynamic parameters, blood gas concentrations and oxygen content in arterial and muscular venous blood, tissue oxygen tension (tPO(2)) were measured in the gastrocnemius muscle with a polarographic needle probe.

RESULTS

Hemodilution increased muscular blood flow and oxygen extraction and decreased tPO(2). Transfusion decreased muscular oxygen extraction in the RBC group but not in the HBOC-201 group (P <.01). The 10th percentile of tPO(2) increased by 400% after the first dose of HBOC-201 (P <.001 vs posthemodilution) but only by 33% after equivalent RBC transfusion (P <.01 vs HBOC-201). Increases in the 50th (120%, P <.05) and 90th (31%) percentiles and all percentiles of tPO(2) after the second and third HBOC-201 dose were less pronounced but higher than in the RBC group.

CONCLUSION

Compared with RBC transfusion, infusion of low doses of HBOC-201 maintain enhanced oxygen extraction after extended hemodilution and provide faster and higher increase in muscular tissue PO(2).

Hemoglobin solutions and tissue oxygenation

Oxygen (O2) delivery to tissues plays an important role in determining microcirulatory autoregulatory responses. The balance between O2 delivery by whole blood and tissue O2 consumption likely has evolved based on regulatory processes designed to accommodate the encapsulation of hemoglobin (Hb) within red blood cells (RBCs). The hemodynamic, rheologic, and physical properties of blood, or an alternate O2-carrying solution, can have important consequences for O2 delivery to tissue. The development of acellular hemoglobin-based oxygen carriers (HBOC) requires reassessment of the O2 loading and unloading charactistics of Hb. the effects of altering the rheologic properties of blood, and the impact of these changes on microcirculatory autoregulation and tissue oxygenation. A variety of experimental and clinical studies have demonstrated beneficial effects of HBOCs. However, mechanisms responsible for HBOC-facilitated, O2-dependent autoregulatory changes in the microcirculation have not been completely elucidated.

The Pharmacology of Tissue Oxygenation by Biopure’s Hemoglobin-Based Oxygen Carrier, Hemopure® (HBOC-201)

Biopure's hemoglobin-based oxygen carrier, HBOC-201 (Hemopure), enhances oxygen transport by promoting both the convective and diffusive components of transport in the microcirculation. Convective transport is modified by HBOC-201 in three ways; (i) volume expansion promotes organ and tissue perfusion, (ii) the low viscosity of HBOC-201 improves flow to tissues, and (iii) oxygen delivery by HBOC Hb in the plasma is relatively insensitive to mechanisms regulating RBC distribution in the microcirculation. Diffusive oxygen transport is increased by the higher P50 compared with native RBC Hb which increases the off-loading of oxygen to tissues. Oxygen transport is also increased by reducing the diffusional barrier to oxygen transport associated with the plasma, in which oxygen is sparingly soluble. Biopure's HBOC solutions have been shown in vitro and in vivo to take up and off-load oxygen more efficiently than RBC Hb, and when added to blood can increase the efficiency of RBC oxygen transport.