Bovine hemoglobin increases skeletal muscle oxygenation during 95% artificial arterial stenosis

Red Blood Cell Transfusion

Red blood cell (RBC) transfusions are necessary to increase a patient's oxygen carrying capacity. The optimal transfusion trigger remains elusive, but a restrictive transfusion trigger of 7 g/dL has been shown in studies to reduce RBC transfusions without adversely affecting patient outcomes. Patient blood management programs have been shown effective at reducing RBC transfusions. Hemoglobin-based oxygen carriers and induced pluripotent stem cell derived RBCs are being developed to help mitigate RBC shortages and RBC transfusion limitations. Numerous challenges still exist that need to be overcome before they can have widespread clinical use.

Issues in the development of hemoglobin based oxygen carriers

Hemoglobin based oxygen carriers (HBOCs) have been developed as alternative oxygen transporting formulations for the acute treatment of anemia and ischemia. Efficacy has been demonstrated in a variety of preclinical models and selected human patients; however, a higher overall incidence of mortality and myocardial infarction in those dosed with HBOCs in later stage clinical trials has prevented widespread regulatory approval. Diagnosis of myocardial infarction is confounded by the fact that HBOCs interfere with troponin assays, as well as other clinical chemistry measurements. Analysis of data pertaining to potential toxicity mechanisms suggests that coronary vasoconstriction is an unlikely contributor, but promotion of intravascular thrombosis may occur by several mechanisms. In addition, fluid and anemia management in patients infused with HBOCs has been suboptimal. Elucidation of potential toxicity mechanisms, refinement of use protocols, and definition of improved patient inclusion/exclusion criteria remain active areas of inquiry in understanding the best manner in which to utilize HBOCs.

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.

HBOC-201: the multi-purpose oxygen therapeutic

Clinical and preclinical studies have revealed a diverse array of indications in which the effectiveness of HBOC-201 has been demonstrated or appears likely. Included among these are indications involving cardiac and peripheral ischaemia in which this oxygen therapeutic may prove to be an important tool in the armamentarium of the cardiologist and surgeon. Preclinical studies and clinical trials are under way to further delineate and optimise the role of HBOC-201 as an oxygen therapeutic in cardiovascular medicine.

Modified haemoglobins and perfluorocarbons

After decades of research activities and product improvements in the field of artificial oxygen carriers based on either haemoglobin modifications or perfluorocarbon emulsions, these products have reached a critical stage of their development. Varieties of haemoglobin-based oxygen carriers and perfluorocarbon emulsions are under current clinical investigation. Although the clinical availability of artificial oxygen carriers may result in profound changes of fluid resuscitation from haemorrhage, the transfusion of human blood components as an integral part of medical trauma management will not be replaced. However, a rapid and effective restoration of tissue oxygenation by the use of artificial oxygen carriers in the treatment of severe haemorrhage may bridge time delays until stored and cross-matched human packed red cells are available. Whether artificial oxygen carriers could provide additional clinical benefits by sustaining tissue oxygenation even under conditions of a disturbed macro- or microcirculation is the subject of current investigations. Therefore, the application of safe and effective artificial oxygen carriers would not only be restricted to the treatment of severe haemorrhage, but additional therapeutic indications of artificial oxygen carriers in emergency medicine, trauma anaesthesia and other medical specialities would emerge.

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.

Bovine hemoglobin-based oxygen-carrying solution (HBOC-201) improves flap survival in a rat model of epigastric flap failure

Despite continued improvements in surgical technique and postoperative management of pedicled flaps, partial flap necrosis continues to be a substantial problem. Several researchers sought interventions that would decrease the incidence of this complication. The hypothesis of this study is that a bovine hemoglobin-based, oxygen-carrying solution (HBOC-201) will increase oxygen delivery, thus decreasing the area of necrosis of the marginally perfused portions of a pedicled flap. Eighty male Sprague-Dawley rats were randomly assigned to one of four groups (20 animals in each group): group 1, controls (surgical creation of flap only); group 2, HBOC-201, 2 g i.v., administered preoperatively and on days 3 and 5; group 3, HBOC-201, 4 g i.v., administered preoperatively and on days 3 and 5; and group 4, hemodilution (lactated Ringer's solution) administered preoperatively and on days 3 and 5. A ventral fasciocutaneous flap (5 x 7 cm) was elevated, based on unilateral superficial inferior epigastric vessels, and the flap was replaced and sutured. Animals were examined daily and euthanized on day 7. Prior to euthanasia, digital photographs were taken of each subject, and the images were analyzed for total area of the flap and area of necrosis, using ImagePro software. Using the calculated percentage of necrosis for each animal, a mean value of percent necrosis was obtained for each animal group and used for statistical analysis. Animals in group 2 demonstrated a decreased area of necrosis when compared with the control group (9.14% vs. 22.24%, P = 0.014). In conclusion, the oxygen therapeutic HBOC-201, at a dose of 2 g, administered preoperatively and on days 3 and 5, decreased the area of necrosis in a rat model of epigastric skin-flap failure. Further investigation of this drug and its effects on flap survival is warranted.

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.

A novel hemoglobin-based blood substitute protects against myocardial reperfusion injury

HBOC-201 (Biopure; Cambridge, MA) is a glutaraldehyde-polymerized bovine hemoglobin (Hb) solution that is stroma free, has lower viscosity than blood, and promotes O(2) unloading. We investigated the effects of HBOC-201 in a canine model of myocardial ischemia-reperfusion injury. Dogs were anesthetized and subjected to 90 min of regional myocardial ischemia and 270 min of reperfusion. HBOC-201 or 0.9% saline vehicle equivalent to 10% total blood volume was infused 30 min before myocardial ischemia. Hemodynamic data and peripheral blood samples were taken at baseline, 1 h of myocardial ischemia, and 1, 2, and 4 h of reperfusion. At 270 min of reperfusion, the area at risk (AAR) per left ventricle and the area of infarction (Inf) per AAR were determined. The myocardial AARs in the two study groups were similar. In addition, myocardial blood flow (as measured by radioactive microspheres) in the ischemic zone was similar between the vehicle and HBOC-201 groups. HBOC-201-infused dogs demonstrated a significant (P < 0.01) 56% reduction in Inf/AAR. Analysis of blood samples taken at 4 h of reperfusion showed a significant (P < 0.05) reduction in creatine kinase MB isoform for the HBOC-201 group. Histological analysis of the myocardium demonstrated significant (P < 0.01) reductions in neutrophil infiltration in the HBOC-201 group. These data indicate that treatment with HBOC-201 before myocardial ischemia-reperfusion reduces the extent of myocardial inflammation and ischemia-reperfusion injury in the canine myocardium.

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.

Microcirculatory function and tissue damage is improved after therapeutic injection of bovine hemoglobin in severe acute rodent pancreatitis

OBJECTIVES

Stasis of the pancreatic microcirculation initiates and aggravates acute pancreatitis. Bovine hemoglobin has been shown to improve microcirculation in acute pancreatitis if prophylactically infused 15 minutes after initiation of acute pancreatitis. The purpose of this study was to evaluate the therapeutic effectiveness of bovine hemoglobin on pancreatic microcirculation and tissue damage later in the course of experimental acute rodent pancreatitis.

METHODS

In Wistar rats, severe acute pancreatitis was induced by administration of glyco-deoxycholic-acid intraductally and cerulein intravenously. Pancreatic microcirculation was continuously monitored by intravital microscopy. Three hours after the initiation of acute pancreatitis, animals received either 0.8 mL bovine hemoglobin (Oxyglobin), hydroxyethyl starch (HES), or 2.4 mL 0.9% NaCl intravenously at random. After 6 hours, animals were killed, and histopathological damage of the pancreas was assessed using a validated histology score.

RESULTS

Pancreatic microcirculation assessed by leukocyte adherence was significantly improved by the administration of bovine hemoglobin in comparison with normal saline over time (mean difference, 51.6 +/- 9.2; P < 0.001) and HES (mean difference, 24.1 +/- 9.2; P = 0.037). This result was paralleled by decreased tissue damage in the bovine hemoglobin group as opposed to NaCl (6.75 vs. 12; range, 5.25-7.75 vs. 8.25-14; P < 0.001) and HES (6.75 vs. 9; range, 5.25-7.75 vs. 7.5-10.75; P < 0.001).

CONCLUSION

Therapeutic intravenous infusion of bovine hemoglobin improves pancreatic microcirculation and reduces pancreatic tissue damage in severe acute rodent pancreatitis but is not as effective as early (prophylactic) administration.

A Hemoglobin Based Oxygen Carrier, Bovine Polymerized Hemoglobin (HBOC-201) versus Hetastarch (HEX) in an Uncontrolled Liver Injury Hemorrhagic Shock Swine Model with Delayed Evacuation

BACKGROUND

As HBOC-201 improves outcome in animals with hemorrhagic shock (HS), we compared HBOC-201 and HEX (used by U.S. military special operations forces) in a swine model of delayed evacuation and uncontrolled HS.

METHODS

Twenty-four Yucatan pigs underwent a grade III liver injury and were resuscitated with HBOC-201, HEX, or no fluid (NON). Additional infusions were given for hypotension or tachycardia. After 4 hours, the liver was repaired; IV fluids and blood transfusions were administered. Pigs were monitored for 72 hours.

RESULTS

Survival was 7/8, 1/8, and 1/8 in HBOC-201-, HEX-, and NON-resuscitated pigs, respectively. Compared with HEX, HBOC-201 pigs had higher systemic and pulmonary artery pressures and had comparable cardiac outputs, but were less tachycardic. Transcutaneous tissue oxygenation was restored more rapidly in HBOC-201 pigs, there was a trend to lower lactic acid, and base deficit was less. HBOC-201 pigs had lower fluid requirements, higher urine output, and lower blood loss than HEX pigs.

CONCLUSIONS

Despite evidence of vasoactivity, HBOC-201 more effectively stabilized tissue oxygenation, reversed anaerobic metabolism, decreased bleeding, and increased survival in comparison with HEX. If confirmed in clinical trials, these data suggest that for the resuscitation of combat casualties with delayed evacuation and uncontrolled HS due to solid organ injury, HBOC-201 is a superior low-volume resuscitative fluid.

Increased Cerebral Tissue Oxygen Tension After Extensive Hemodilution with a Hemoglobin-Based Oxygen Carrier

Transfusion of anemic patients with hemoglobin-based oxygen carriers (HBOCs) may improve cerebral oxygen delivery. Conversely, cerebral vasoconstriction, associated with HBOC transfusion, could limit optimal cerebral tissue oxygenation. We hypothesized that hemodilution with a HBOC would maintain cerebral tissue oxygenation, despite the occurrence of cerebral vasoconstriction. Isoflurane-anesthetized rats (100% oxygen) underwent direct measurement of mean arterial blood pressure (MAP), caudate tissue oxygen tension (P(Br)o(2)), and regional cortical cerebral blood flow (rCBF) before and after 50% of the estimated blood volume (30 mL/kg) was exchanged with either an HBOC (hemoglobin raffimer; Hemolink) or pentastarch (n = 6). Hemodilution with hemoglobin raffimer caused a transient increase in P(Br)o(2) from 24.9 +/- 13.3 mm Hg to 32.2 +/- 19.1 mm Hg (P < 0.05), a sustained increase in MAP, and no change in rCBF. Arterial blood oxygen content was maintained despite an increase in methemoglobin and reduced oxygen saturation. Hemodilution with pentastarch caused a transient increase in MAP, no change in P(Br)o(2), and a sustained increase in rCBF (P < 0.05), whereas the hemoglobin concentration and oxygen content were significantly reduced. Hemodilution with hemoglobin raffimer augmented P(Br)o(2) and prevented the increase in rCBF observed after similar hemodilution with pentastarch. These data suggest that transfusion with hemoglobin raffimer may help to maintain cerebral oxygenation during severe anemia.

The use of a hemoglobin-based oxygen-carrying solution (HBOC-201) for extracorporeal membrane oxygenation in a porcine model with acute respiratory distress syndrome

OBJECTIVE

To evaluate whether hemoglobin-based oxygen-carrying solution (HBOC)-201 (Biopure) is an effective alternative to donor blood for extracorporeal membrane oxygenation support in a porcine model of acute respiratory distress syndrome (ARDS).

DESIGN

Randomized animal clinical trial.

SETTING

Animal surgical research laboratory.

SUBJECTS

Immature Yorkshire swine were assigned to one of three groups: 1, noninjured animals, donor porcine blood primed circuit; 2, ARDS-injured, HBOC-201 primed circuit; or 3, ARDS-injured, donor blood primed.

INTERVENTIONS

ARDS injury was induced in groups 2 and 3 with oleic acid infusion before bypass. All animals were placed on full venoarterial extracorporeal membrane oxygenation support for 8 hrs.

MEASUREMENTS AND MAIN RESULTS

Physiologic variables and laboratory samples were measured at baseline and hourly for 8 hrs. Data analysis consisted of repeated-measures analysis of variance with post hoc analysis. We found that 100% of animals survived on extracorporeal membrane oxygenation for the duration of the study period. HBOC-supported animals had comparable oxygen delivery to both donor blood groups. Mean pulmonary artery pressure, heart rate, and lactate concentrations were higher in the injury groups. Blood pressure was mildly increased in HBOC animals (p <.05 vs. control animals). Methemoglobin concentrations in the HBOC group were elevated and increased over time on extracorporeal membrane oxygenation (p <.001).

CONCLUSIONS

HBOC-201 appears to be an effective alternative circuit-priming agent for use during extracorporeal membrane oxygenation. HBOC offers the advantages of rapid availability and diminished donor blood cell exposure. The efficacy of HBOC in longer duration bypass, and its associated methemoglobinemia, need to be further investigated.

Doping with Artificial Oxygen Carriers

There is a long history of science seeking to develop artificial substitutes for body parts damaged by disease or trauma. While defective teeth and limbs are commonly replaced by imitations without major loss of functionality, the development of a substitute for red blood cells has proved elusive. There is a permanent shortage of donor blood in western societies. Nevertheless, despite whole blood transfusions carrying measurable risks due to immunogenicity and the transmission of blood-borne infectious diseases, red blood cells are still relatively inexpensive, well tolerated and widely available. Researchers seeking to develop products that are able to meet and perhaps exceed these criteria have responded to this difficult challenge by adopting many different approaches. Work has focussed on two classes of substances: modified haemoglobin solutions and perfluorocarbon emulsions. Other approaches include the creation of artificial red cells, where haemoglobin and supporting enzyme systems are encapsulated into liposomes. Haemoglobin is ideally suited to oxygen transport when encased by the red cell membrane; however, once removed, it rapidly dissociates into dimers and is cleared by the kidney. Therefore, it must be stabilised before it can be safely re-infused into humans. Modifications concomitantly alter the vascular half-life, oxygen affinity and hypertensive characteristics of raw haemoglobin, which can be sourced from outdated blood stores, genetically-engineered Escherichia coli or even bovine herds. In contrast, perfluorocarbons are entirely synthetic molecules that are capable of dissolving oxygen but biologically inert. Since they dissolve rather than bind oxygen, their capacity to serve as a blood substitute is determined principally by the oxygen pressure gradients in the lung and at the target tissue. Blood substitutes have important potential areas of clinical application including red cell replacement during surgery, emergency resuscitation of traumatic blood loss, oxygen therapeutic applications in radiography (oxygenation of tumour cells is beneficial to the effect of certain chemotherapeutic agents), other medical applications such as organ preservation, and finally to meet the requirements of patients who cannot receive donor blood because of religious beliefs. Given the elite athlete's historical propensity to experiment with novel doping strategies, it is likely that the burgeoning field of artificial oxygen carriers has already attracted their attention. Scientific data concerning the performance benefits associated with blood substitutes are virtually nonexistent; however, international sporting federations have been commendably proactive in adding this category to their banned substance lists. The current situation is vulnerable to exploitation by immoral athletes since there is still no accepted methodology to test for the presence of artificial oxygen carriers.

Systemic intravenous infusion of bovine hemoglobin significantly reduces microcirculatory dysfunction in experimentally induced pancreatitis in the rat

OBJECTIVE

To evaluate the effectiveness of bovine hemoglobin on pancreatic microcirculation and outcome in experimental acute rodent pancreatitis.

SUMMARY BACKGROUND DATA

Stasis of the pancreatic microcirculation initiates and aggravates acute pancreatitis. Hydroxyethyl-starch (HES) has been shown to improve pancreatic microcirculation. Similarly, bovine hemoglobin might improve rheology due to its colloid effect, but additionally supplies oxygen to oxygen depleted pancreatic tissue.

METHODS

In Wistar rats, severe acute pancreatitis was induced by administration of glucodeoxycholic acid i.d. and cerulein i.v. Pancreatic microcirculation was continuously monitored by fluorescence microscopy. Fifteen minutes after the initiation of acute pancreatitis, animals received either 0.8 mL bovine hemoglobin (Oxyglobin), HES, or 2.4 mL 0.9% NaCl i.v. at random. After 6 hours, animals were killed and histopathological damage of the pancreas was assessed using a validated histology score (0-16).

RESULTS

In comparison to controls, pancreatic microcirculation improved significantly in the HBOC group (mean difference of capillary density 31.4%; standard error 5.6%; P < 0.001; 95% confidence interval for difference 17.5-45.3). HES was not as effective as HBOC substitution. The histology score revealed less tissue damage in the HBOC group [6.25 vs. 9.25 (3-8.5 vs. 8-10.75, P < 0.001)] in comparison to controls and also in comparison to the HES group [6.25 vs. 8 (3-8.5 vs. 6.5-10.25, P < 0.006)].

CONCLUSIONS

In severe acute pancreatitis, single i.v. injection of bovine hemoglobin improves pancreatic microcirculation and reduces tissue damage.

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.

The use of haemoglobin glutamer-250 (HBOC-201) as an oxygen bridge in patients with acute anaemia associated with surgical blood loss

For the treatment of substantial blood loss in surgery, allogeneic blood is transfused to maintain stability and organ perfusion and function. Continued concerns about the availability, safety, efficacy and storage-related problems of allogeneic blood products have led to an intense effort to find alternatives that can serve the same physiologic functions. Haemoglobin-based oxygen carriers (HBOCs) are compounds that can match the oxygen-carrying capacity of red blood cells (RBCs), and several HBOCs have reached advanced stages of development and clinical testing. Multi-centre, randomised, Phase III, controlled trials have demonstrated the safety and efficacy of haemoglobin glutamer-250 (bovine) (Hemopure), Biopure Corporation, Cambridge, MA, USA), also known as HBOC-201. HBOC-201 is bovine-derived, modified haemoglobin that has been ultrapurified to remove any plasma proteins, RBC stroma and potential pathogenic material. During the manufacturing process, crosslinking and polymerisation stabilise the haemoglobin molecule, which increases its vascular persistence as well as the efficiency of oxygen transport to tissue. Results from clinical trials indicate that HBOC-201 can be used as an oxygen 'bridge' for patients experiencing anaemia due to surgical blood loss, until their own red blood cells are replenished or have regenerated (haematinic effect). HBOC-201 is generally well-tolerated and is approved for use in South Africa, where it is indicated for use in adult surgical patients who are acutely anaemic, and is used to eliminate, delay or reduce the need for allogeneic RBCs. A Biologics License Application for HBOC-201 is currently under review by the US FDA.

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.

Validation of oxygen saturation measurements in a canine model of hemoglobin-based oxygen carrier infusion

This study was designed to validate oxygen saturation measurements from the NOVA CO-Oximeter (NOVA Biomedical Corporation, Waltham, MA), the i-STAT System (Sensor Devices, Waukesha, WI), and the Corning 170 blood gas analyzer (Bayer Corporation, East Walpole, MA) under conditions similar to the clinical application of a hemoglobin-based oxygen carrier (HBOC, hemoglobin glutamer-200 [bovine]; Oxyglobin, Biopure Corporation, Cambridge, MA). A canine model was used for both in vitro and in vivo experiments. In vivo experiments were conducted in a canine laboratory, and in vitro experiments were conducted in a tonometry laboratory. Study subjects were six mixed-breed dogs, each weighing approximately 30 kg. In the first set of experiments, the target blood po(2) levels were reached by tonometry. In the second set of experiments, quantitative measurements of total oxygen content with the LEXO2CON-K (HOSPEX Fiberoptics, Chestnut Hill, MA) were performed, immediately followed by measurements with the NOVA CO-Oximeter and the i-STAT system. HBOC was added in concentrations of 16.2, 32.5, 65, and 97.5 g/L. To analyze the clinical significance of the differences in the results obtained with the each investigated instrument, blood samples from dogs treated with HBOC after acute hemorrhagic shock were used. Oxygen saturation, oxygen content, and po(2) were measured. There was a strong correlation between the oxygen saturation values measured with the investigated instruments in samples after tonometry and known po(2). The total calculated oxygen content varied by 5% based on results generated by calculations using the investigated instruments. The results did not change with different oxygenation of the sample. The differences among methods were not significant when the HBOC concentration was 16.2 g/L. Higher concentrations of HBOC increased the difference between calculated and measured oxygen content; the i-STAT system demonstrated a greater deviation compared with the results of the other two instruments. Systemic oxygen uptake using the investigated instruments showed a high correlation with values based on LEXO2CON-K measurements (R = 0.97 for CO-Oximeter, R = 0.96 for Corning 170 blood gas analyzer, and R = 0.79 for i-STAT system). Systemic oxygen uptake values based on CO-Oximeter and Corning 170 blood gas analyzer data showed 75% accuracy; i-STAT system accuracy was 63% for control samples and 50% for samples after HBOC infusion.

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.

Use of a hemoglobin-based oxygen-carrying solution in cats: 72 cases (1998-2000)

OBJECTIVE

To determine clinical features and outcome associated with use of a hemoglobin-based oxygen-carrying (HBOC) solution in cats.

DESIGN

Retrospective study.

ANIMALS

72 cats.

PROCEDURE

Medical records of cats that received an HBOC solution were reviewed.

RESULTS

The most common clinical signs and physical examination findings prior to infusion of the HBOC solution were associated with anemia; vomiting, neurologic signs, and respiratory abnormalities were also detected. The HBOC solution was given as a supportive measure in treatment of anemia in 70 cats, most often because compatible blood was not readily available. There were 80 separate HBOC solution infusion events (mean dose, 14.6 ml/kg [6.6 mg/lb]; mean rate of infusion, 4.8 ml/kg [2.2 ml/lb] per hour). Improvements in 37 of 43 of the more closely monitored cats included increased rectal temperature, blood hemoglobin concentration, blood pressure, appetite, and activity. Adverse events in 44 cats included pulmonary edema (n = 8), pleural effusion (21), mucous membrane discoloration (21), pigmenturia (11), vomiting (4), and neurologic abnormalities (4). Twenty-three cats were discharged from the hospital, and 49 cats died or were euthanatized. Necropsy examination of 23 cats did not reveal evidence of renal or hepatic toxicosis associated with HBOC administration.

CONCLUSIONS AND CLINICAL RELEVANCE

Although administration of an HBOC solution may provide temporary support to anemic cats, the development of pulmonary edema or pleural effusion potentially associated with rapid infusion rate and large volume of infusion of the HBOC solution should be investigated further before use of the solution can be recommended in cats.

Influence of cell-free Hb on local tissue perfusion and oxygenation in acute anemia after isovolemic hemodilution

BACKGROUND

Oxygen-carrying solutions are intended to eliminate the blood transfusion trigger. Their ability to maintain microvascular perfusion and to deliver oxygen to tissue when they replace the RBCs as oxygen carriers has not been directly measured.

STUDY DESIGN AND METHODS

Microvascular response to exchange transfusion with a polymerized bovine cell-free Hb (PBH) solution after acute isovolemic hemodilution with a plasma expander was investigated by using the hamster window model. In vivo functional capillary density (FCD), blood flow, and high-resolution oxygen distribution in microvascular networks were measured by noninvasive methods.

RESULTS

Exchange transfusion of PBH solution after a 60-percent isovolemic hemodilution with dextran 70 (MW, 70 kDa) resulted in a Hct of 11 percent and a Hb content of 6.7 g per dL. FCD was 0.37 of baseline. Interstitial pO2 was reduced from 21.0 mm Hg to 0.3 mmHg. Arteriolar and venular blood flows were ratios of 0.75 and 0.76 relative to baseline. In a previous study, tissue pO2 after hemodilution to 5.6 g of Hb per dL with dextran 70 was 23.0 mmHg. Hypervolemic injection of PBH solution increased blood pressure and caused vasoconstriction.

CONCLUSION

Using PBH solution to replace RBC oxygen-carrying capacity during low Hb content conditions (<50%) causes abnormally low tissue oxygenation and FCD, while the same level of hemodilution with dextran maintains normal microvascular conditions.

Hypotensive resuscitation using a polymerized bovine hemoglobin-based oxygen-carrying solution (HBOC-201) leads to reversal of anaerobic metabolism

BACKGROUND

Traditional resuscitation regimens have been recently challenged. This study evaluates hypotensive resuscitation with a hemoglobin-based oxygen-carrying (HBOC) solution after severe hemorrhage in a porcine model. We hypothesized that HBOC-201 restores tissue perfusion at a lower mean arterial pressure than standard resuscitation fluids.

METHODS

Yorkshire swine (55-65 kg, n = 30), were rapidly hemorrhaged to a mean arterial pressure (MAP) of 30 mm Hg, maintained hypotensive for 45 minutes, and randomized into groups. Group I was resuscitated with an HBOC solution to a MAP of 60 mm Hg. Groups II and III were resuscitated to a MAP of 80 mm Hg with lactated Ringer's solution (LR) alone or LR (40 mL/kg) followed by shed blood, respectively. Group IV was resuscitated with shed blood alone to a MAP of 60 mm Hg. Group V received an HBOC solution to a MAP of 50 mm Hg. Hemodynamic variables, Swan-Ganz parameters, blood gas samples, and lactate levels were followed for 5 hours. Data were analyzed by analysis of variance/Duncan multiple range test.

RESULTS

There were no significant differences in mortality between any groups. Groups I, IV, and V had lower (p < 0.05) cardiac output, pulmonary artery wedge pressure, and MAP than either group II or group III. Svo2 was significantly lower in the HBOC groups. There were no significant differences in arterial pH or lactate between groups I, III, and IV. Lactate levels, base excess, and arterial pH were significantly worse in the LR-alone and HBOC-50 groups.

CONCLUSION

Hypotensive resuscitation with HBOC-201 at a MAP of 60 mm Hg after a controlled hemorrhage in swine provides sufficient tissue perfusion and oxygen delivery to reverse anaerobic metabolism on the basis of global physiologic markers despite continued hypotension, hypovolemia, and low cardiac output.

Effects of haemoglobin-based oxygen carrier hemoglobin glutamer-200 (bovine) on intestinal perfusion and oxygenation in a canine hypovolaemia model

The objective of this investigation was to study the effects of the first marketed haemoglobin-based oxygen carrier, Hemoglobin glutamer-200 (bovine) (Hb-200) (Oxyglobin) on splanchnic perfusion and oxygenation in a canine model of acute hypovolaemia. Twelve anaesthetized dogs [mean weight 30.8 (S.D. 1.4) kg] were instrumented for recordings of heart rate (HR), mean arterial pressure (MAP), central venous pressure (CVP), cardiac output and cranial mesenteric arterial (CMA) and venous blood flows (CMV). Total and plasma haemoglobin (Hb), oxygen content and saturation, lactate concentration, pH and blood gases were analysed in arterial, mixed venous and mesenteric venous blood samples. Measurements were made before (baseline) and after 1 h of haemorrhage, after which animals were resuscitated with either shed blood (controls) or Hb-200 until HR, MAP and CVP returned to prehaemorrhage levels. Recordings were repeated immediately and 3 h after termination of fluid resuscitation, after which organ specimens were obtained for microscopic examination. Haemorrhage (average 32 ml kg(-1)) reduced MAP to 50 mm Hg, increased HR and systemic vascular resistance (SVR), and was accompanied in both the systemic and the splanchnic circulation by significant decreases in blood flow, Hb content and oxygen delivery (DO2), and lactic acidosis. In controls, all variables recovered to baseline after isovolaemic resuscitation with shed blood. In dogs resuscitated with a small volume of Hb-200 (10 ml kg(-1)), HR, MAP, CVP and CMA and CMV blood flows returned to baseline. However, cardiac output, total Hb, oxygen content and systemic and mesenteric DO2 remained depressed while SVR increased further. Mesenteric and systemic acid-base status recovered in both groups, and there was no difference in microscopic tissue damage between groups. Thus, Hb-200 reconstituted splanchnic perfusion and oxidative metabolism in spite of pronounced systemic vasoconstriction and insufficient restoration of CO and DO2; it may improve diffusive oxygen transport in the microvasculature by virtue of haemodilution and its high efficiency in the uptake and release of oxygen.

Inadequacy of low-volume resuscitation with hemoglobin-based oxygen carrier hemoglobin glutamer-200 (bovine) in canine hypovolemia

Stroma-free hemoglobin-based oxygen carriers (HBOC) have been developed to overcome problems associated with transfusion of allogeneic blood. We have studied the efficacy of the first licensed veterinary blood substitute, hemoglobin glutamer-200 bovine (Oxyglobin; Biopure, Cambridge, MA, USA, Hb-200), in a canine model of acute hypovolemia and examined whether clinically commonly used criteria are adequate to guide fluid resuscitation with this product. Twelve anesthetized dogs were instrumented for measurements of physiological variables including hemodynamic, oxygenation, and blood gas and acid-base parameters. Dogs were bled to a mean arterial pressure (MAP) of 50 mmHg for 1 h followed by resuscitation with either shed blood (controls) or Hb-200 until heart rate (HR), MAP and central venous pressure (CVP) returned to baseline. Recordings were repeated immediately and 3 h after termination of fluid resuscitation. Hemorrhage (average 32 mL/kg) caused significant decreases in total hemoglobin (Hb), mean pulmonary arterial pressure (PAP), cardiac output (CO) and oxygen delivery (DO2I), increases in HR and systemic vascular resistance (SVRI), and lactic acidosis. In controls, only re-transfusion of all shed blood returned HR, MAP and CVP to prehemorrhage values, whereas in other dogs this endpoint was reached with infusion of 10 mL/kg Hb-200. Unlike blood transfusion, Hb-200 infusion failed to return CI and DO2I to baseline and to increase arterial oxygen content (CaO2) and total Hb; SVRI further increased. Thus, commonly used criteria (HR, MAP, CVP) to guide transfusion therapy in patients posthemorrhage prove insufficient when HBOCs with pronounced vasoconstrictive action are used and lead to inadequate volume repletion.

Tissue perfusion and oxygenation with blood substitutes

As an alternative to transfusion of red blood cells, intravenously (iv) administered artificial oxygen (O(2)) carriers are intended to increase the reduced O(2) carrying capacity of blood in the case of acute severe anemia, i.e. hemorrhagic shock or extreme normovolemic hemodilution (ANH). Actually, two groups of artificial O(2) carriers are investigated: ultrapurified, stroma-free hemoglobin solutions (SFH) of human or bovine origin and synthetically produced perfluorocarbons (PFC). SFH may be administered in large amounts and are suitable for 1:1 replacement of blood losses in case of hemorrhage as well as for isovolemic exchange of blood during ANH. In both situations SFH solutions effectively restore (hemorrhagic shock) and maintain (extreme ANH) tissue oxygenation despite extremely low hematocrit values. The vasopressor property of the isolated Hb molecule leads to a species-dependent (rodent>pig>human) increase in systemic and pulmonary vascular resistance, but leaves overall distribution of cardiac output uninfluenced. Due to the particulate nature of PFC emulsions, iv administration has to be restricted to small doses (3-4.5 ml/kg body weight for the actually investigated 60% w/v perflubron emulsion) in order to avoid overload of the reticuloendothelial system. Thus PFC emulsions are unsuitable for isovolemic blood replacement in hemorrhagic shock or ANH. Low-dose iv PFC administration in already hemodiluted subjects, however, creates an additional margin of safety to guarantee adequate tissue oxygenation which allows for further, extreme ANH, without risking tissue hypoxia.

Current status of artificial oxygen carriers

Artificial oxygen carriers may be grouped into modified hemoglobin solutions and fluorocarbon emulsions. In animal experiments, both have been shown to be efficacious in improving tissue oxygenation and as substitutes for blood transfusions. Advantages and disadvantages are being discussed in this article as well as the latest steps in the clinical development.

Effects of primary resuscitation from shock on distribution of myocardial blood flow

Hemorrhagic shock alters heterogeneity of regional myocardial perfusion (RMP) in the presence of critical coronary stenosis in pigs. Conventional resuscitation has failed to reverse these effects. We hypothesized that improvement of the resuscitation regime would lead to restoration of RMP heterogeneity. Diaspirin-cross-linked hemoglobin (10 g/dl; DCLHb) and human serum albumin (8.0 g/dl; HSA) were used. After baseline, a branch of the left coronary artery was stenosed; thereafter, hemorrhagic shock was induced. Resuscitation was performed with either DCLHb or HSA. At baseline, the fractcal dimension (D) of subendocardial myocardium was 1.31 +/- 0.083 (HSA) and 1.35 +/- 0.106 (DCLHb) (mean +/- SD). Coronary stenosis increased subendocardial D slightly but consistently only in the DCLHb group (1.39 +/- 0.104; P < 0.05). Shock reduced subendocardial D: 1.21 +/- 0.093 (HSA; P = 0.10), 1.25 +/- 0.092 (DCLHb; P < 0.05). Administration of DCLHb increased subendocardial D in 7 of 10 animals (1.31 +/- 0.097; P = 0.066). HSA was ineffective in this respect. DCLHb infusion restored arterial pressure and increased cardiac index (CI) to 80% of baseline values. Administration of HSA left animals hypotensive (69 mmHg) and increased CI to 122% of the average baseline value. Shock-induced disturbances of the distribution of RMP were improved by administration of DCLHb but not by HSA.

Blood substitutes. Haemoglobin therapeutics in clinical practice

Early approaches to the development of oxygen carriers involved the use of stroma-free hemoglobin solutions. These solutions did not require blood typing or crossmatching and could be stored for long periods. In addition, a variety of methods have been developed in chemically modifying and stabilizing the hemoglobin molecule. Several hemoglobin therapeutics are now in clinical trials as temporary alternatives to blood or as therapeutic agents for ischemia. The various hemoglobin products under development are derived from three principal sources: human, bovine and genetically engineered hemoglobin. Diaspirin cross-linked hemoglobin (DCLHb), administered at doses ranging from approximately 20-1000 ml, has been investigated in a number of clinical trials in patients undergoing orthopedic, abdominal aortic repair, major abdominal surgery, cardiac surgery and in critically ill patients with septic shock. In several studies, DCLHb was effective in avoiding the transfusion. However, Baxter Healthcare Corporation (Chicago, Illinois, USA) stopped the development of DCLHb after two unsuccessful trials in trauma patients. Bovine polymerized hemoglobin has also been extensively studied. Several phase II and phase III trials have been performed with this product in hemorrhagic surgery, cardiac surgery and vascular surgery, but data have not yet been published. Hemoglobin therapeutics could provide an important new option as an alternative to blood transfusion. Furthermore, they may be able to provide an immediate on-site replacement for traumatic blood loss, prevent global ischemia and organ failure, treat focal ischemia, and provide effective hemodynamic support for septic shock-induced hypotension.