Haemodynamic changes and skeletal muscle oxygen tension during complete blood exchange with ultrapurified polymerized bovine haemoglobin

Vital organ tissue oxygenation after serial normovolemic exchange transfusion with HBOC-201 in anesthetized swine

This study determined the effects of serial, normovolemic, stepwise exchange transfusions with either 6% human serum albumin (HSA) or the hemoglobin-based oxygen carrier, HBOC-201, on tissue oxygenation of the heart, brain, and kidney in intact anaesthetized pigs. Exchange transfusions to 10%, 30%, and 50% of the pigs' total blood volume were completed at a withdrawal rate of 1.0 mL·kg(-1)·min(-1) followed by an infusion rate of 0.5 mL·kg(-1)·min(-1) of HBOC-201 or iso-oncotically matched 6% HSA. Measurements included invasive systemic hemodynamic (blood pressures, left ventricular end-diastolic pressure), hematolic (hemoglobin, hematocrit, methemoglobin), acid-base (pH, PCO2), and biochemistry (serum lactate) measurements. Brain and kidney tissue oxygenation (tPO2) was determined by electron paramagnetic resonance and heart tPO2 by O2 sensitive fiberoptic probe. The main results demonstrated that tPO2 after HBOC-201 remained stable despite significant decreases in hematocrit and changing hemodynamics. In vivo tPO2 measurements (heart tPO2 average ≥22 mmHg, brain tPO2 average ≥8 mmHg, and kidney tPO2 average ≥10 mmHg) were maintained in all groups at all times. Blood pressures were 20 to 30 mmHg higher after HBOC-201 compared with HSA controls. Heart rate and left ventricular end-diastolic pressure were not different among treatment groups. In conclusion, the administration of HBOC-201 maintained tPO2 in three vital organs after profound hemodilution.

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.

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.

[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.

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.

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.

Confirmation and quantification of hemoglobin-based oxygen carriers in equine and human plasma by hyphenated liquid chromatography tandem mass spectrometry

Oxyglobin (OXY) and Hemopure (HMP) are produced from bovine hemoglobin (Hb) and were developed for the treatment of anemia in animal and human patients, respectively. Hemolink (HML) is a blood substitute of human Hb origin under development. The ability of these agents to carry oxygen in circulating blood and their promise to improve oxygen delivery to tissues supports the potential for their abuse in equine and human athletes. To deter athletes from abuse of these agents, a method has been developed for the detection, confirmation and quantification of OXY, HMP, and HML in equine and human plasma. OXY, HMP, and HML were extracted from equine or human plasma by solid-phase extraction using Bond Elut ENV cartridges and were digested by trypsin at 37 degrees C for 3 h. The tryptic digests were analyzed by LC-MS/MS, and tryptic peptides specific for bovine and human Hbs were targeted. OXY and HMP were detected, quantified, and confirmed using the y14 ion and b8 ion of the tryptic peptide from bovine Hb alpha chain residues 69-90, and HML was quantified using the tryptic peptide from human Hb alpha chain residues 63-91. The limit of detection for OXY in equine plasma and HML in human and equine plasma was 50 and 250 microg/mL for HMP in human and equine plasma. The limit of confirmation was 250 microg/mL for OXY in equine plasma, 500 microg/mL for HML in human and equine plasma, and 1000 microg/mL for HMP in human and equine plasma. The linear range for quantification was 50-5000 microg/mL for OXY in equine plasma and for HML in human and equine plasma, and 250-5000 microg/mL for HMP in human and equine plasma. The intraday and interday CV were less than 17% for quantification of OXY in equine plasma with external calibration. OXY was stable for more than 30 days at -20 and -70 degrees C. OXY was detected and quantified in equine plasma up to 24 h following administration of a very low dose of OXY (32.5 g in 2 x 125 mL per horse), and its presence in equine plasma was confirmed up to 12 h postadministration.

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.

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.

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.

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).

Hydroxyethyl starch (HES) 130/0.4 provides larger and faster increases in tissue oxygen tension in comparison with prehemodilution values than HES 70/0.5 or HES 200/0.5 in volunteers undergoing acute normovolemic hemodilution

Stable hemodynamics and improved rheology are important effects of hemodilution with hydroxyethyl starch (HES) infusions. One clinical indicator of improved rheology is increased tissue oxygen tension (tpO(2)). In this prospective, randomized, double-blinded, crossover study, we examined the effects of acute normovolemic hemodilution with HES 130/0.4 on hemodynamics and skeletal muscle tpO(2) in comparison with conventional HES solutions. Twelve healthy volunteers were randomly enrolled in each group. At an interval of >8 days, volunteers donated 18% of their calculated blood volume within 30 min and randomly received 6% HES 130/0.4, 6% HES 70/0.5, or 6% HES 200/0.5 (crossover design) in a 1:1.2 ratio to their blood loss. Hemodynamic variables, tpO(2) in the quadriceps muscle, hematocrit, plasmatic HES concentrations, plasma viscosity, colloid osmotic pressures, and platelet aggregation were measured until 6 h after the infusion of HES. No differences were found among groups with respect to changes of hemodynamics, hematocrit, or platelet aggregation. With HES 200, colloid osmotic pressures and plasma viscosities were larger than after HES 70 (P < 0.05). HES 130 in comparison with HES 70 and 200 caused the fastest (30 min versus 90 min and 150 min after hemodilution; P < 0.05) and largest increase of tpO(2) in comparison to baseline (+93% versus +33% and 40%; P < 0.05). In healthy volunteers undergoing acute normovolemic hemodilution, the newly designed HES 130/0.4 showed a more pronounced and earlier increase of skeletal muscle tpO(2) in comparison with prehemodilution values than HES 70/0.5 or 200/0.5.

IMPLICATIONS

The effects of three different hydroxyethyl starch (HES) solutions on hemodynamics, rheology, and skeletal muscle tissue tension after acute normovolemic hemodilution were examined in awake volunteers. With HES 130/0.4, increases of tissue oxygen tension in comparison to baseline were larger and more rapid than with HES 70/0.5 or HES 200/0.5.

Rate of NO scavenging alters effects of recombinant hemoglobin solutions on pulmonary vasoreactivity

Many hemoglobin-based oxygen carriers (HBOCs) produce systemic and pulmonary hypertension and may increase microvascular permeability as a consequence of nitric oxide (NO) scavenging. In this study, we examined the effects of two recombinant human hemoglobin solutions, rHb1.1 and rHb2.0 for injection (rHb2.0), with different rates of NO scavenging on vasoconstrictor reactivity and vascular permeability in isolated, saline-perfused rat lungs. We hypothesized that rHb1.1, a first-generation HBOC with an NO scavenging rate similar to that of native human hemoglobin, would exacerbate pulmonary vasoconstriction and permeability and that rHb2.0, a second-generation HBOC with an NO scavenging rate approximately 20- to 30-fold lower than that of rHb1.1, would minimally influence these responses. Consistent with this hypothesis, rHb1.1 enhanced pulmonary vasoconstrictor reactivity to both hypoxia and thromboxane mimetic U-46619 in a dose-dependent fashion. In contrast, rHb2.0 produced little or no change in reactivity to these stimuli. Furthermore, whereas rHb1.1 abrogated pulmonary vasodilation to the NO-donor S-nitroso-N-acetyl-penicillamine (SNAP), dose-dependent responses to SNAP were preserved, albeit attenuated, in lungs treated with rHb2.0. Finally, the capillary filtration coefficient was unaltered by either rHb1.1 or rHb2.0. We conclude that pulmonary hemodynamic responses to rHb2.0 are greatly reduced compared with those observed with rHb1.1, consistent with rHb2.0 having a diminished capacity to scavenge NO. In addition, neither hemoglobin solution measurably altered microvascular permeability in this preparation.

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.

Haemoglobin-based erythrocyte transfusion substitutes

Concerns about the infectious and immunosuppressive risks of allogeneic blood products persist, and the increased disproportion of blood donation and consumption has reinforced the search for alternative erythrocyte transfusion strategies in recent years. With the absence of problems such as nephro-toxicity, increased colloid osmotic pressure and sudden renal clearance, modern haemoglobin based oxygen carriers (HBOC) have shown their effectiveness and tolerability in numerous animal and several clinical studies. HBOC can be infused without prior cross-matching and are now available as stable formulations with long shelf-life. Most clinical studies have been performed with human cross-linked haemoglobin (DCLHb) but all trials were stopped two years ago because of an increased mortality in two clinical trials in patients who received DCLHb after stroke and multiple injury shock. However, experimental trials in animals are in progress with DCLHb and recombinant human haemoglobin. In contrast, Phase III studies with polymerised bovine haemoglobin (HBOC-201) are finished or currently under evaluation showing that infusion of HBOC-201 can avoid or reduce allogeneic blood transfusion needs in specific peri-operative settings. As a consequence, HBOC-2001 was actually approved for treatment of peri-operative anaemia in elective adult surgical patients in South Africa. Other human or bovine haemoglobin solutions are currently being investigated in different clinical studies in cardiac surgery patients, sepsis and tumour patients. More recent investigations have shown that HBOC are not only simple erythrocyte transfusion substitutes but highly effective oxygen donators in terms of tissue oxygenation. HBOC open the door for a new therapeutic strategy: plasmatic oxygen delivery with physiological concentrations of inspired oxygen. In specific situations (e.g., ischaemia or arterial stenosis) HBOC have advantages over red blood cells because they can reach post-stenotic or poorly perfused tissues with the plasma stream, where erythrocytes are not able to pass. In addition to significant plasmatic oxygen transport, HBOC also enhance tissue oxygenation because of the facilitated oxygen release by HBOC and from remaining erythrocytes. Further studies will show, if the outcome of patients with impaired perfusion (e.g., stroke or myocardial infarction) can be improved by prophylactic or therapeutic application of HBOC. Whenever these formulations are globally launched, they will find differential indications as potent oxygen-delivering drugs in addition to the globally recognised goal of red cell substitutes in cases of bleeding.

Colloids versus crystalloids and tissue oxygen tension in patients undergoing major abdominal surgery

The effects of intravascular volume replacement regimens on tissue oxygen tension (ptiO(2)) are not definitely known. Forty-two consecutive patients scheduled for elective major abdominal surgery were prospectively randomized to receive either 6% hydroxyethyl starch (HES) (mean molecular weight 130 kd, degree of substitution 0.4, n = 21) or lactated Ringer's solution (RL, n = 21) for intravascular volume replacement. Fluids were administered perioperatively and continued for 24 h on the intensive care unit to keep central venous pressure between 8 and 12 mm Hg. The ptiO(2) was measured continuously in the left deltoid muscle by using microsensoric implantable partial pressure of oxygen catheters after the induction of anesthesia (baseline, T0), 60 min (T1) and 120 min thereafter (T2), at the end of surgery (T3), and on the morning of the first postoperative day on the intensive care unit (T4). HES 130/0.4 2920 +/- 360 mL and 11,740 +/- 2,630 mL of RL were given to the patients within the study period. Systemic hemodynamics and oxygenation (PaO(2), PaCO(2)) did not differ significantly between the two volume groups throughout the study. From similar baseline values, ptiO(2) increased significantly in the HES-treated patients (a maximum of 59% at T4), whereas it decreased in the RL group (a maximum of -23% at T4, P < 0.05). The largest differences of ptiO(2) were measured on the morning of the first postoperative day. We conclude that intravascular volume replacement with 6% HES 130/0.4 improved tissue oxygenation during and after major surgical procedures compared with a crystalloid-based volume replacement strategy. Improved microperfusion and less endothelial swelling may be responsible for the increase in ptiO(2) in the HES 130/0.4-treated patients.

IMPLICATIONS

In patients undergoing major abdominal surgery, a colloid-based (with hydroxyethyl starch [HES] 130/0.4) and a crystalloid-based (with lactated Ringer's solution [RL]) volume replacement regimen was compared regarding tissue oxygen tension (ptiO(2)) measured continuously by microsensoric implantable catheters. The ptiO(2) increased in the HES-treated (+59%) but decreased in the RL-treated (-23%) patients. Improved microcirculation may be the mechanism for the better ptiO(2) in the HES group.

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.

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.

The effects of increased doses of bovine hemoglobin on hemodynamics and oxygen transport in patients undergoing preoperative hemodilution for elective abdominal aortic surgery

In two consecutive studies (Study A and Study B), we evaluated the effects of increasing doses of HBOC-201, a bovine hemoglobin-based oxygen carrier, on hemodynamics and oxygen transport in patients undergoing preoperative hemodilution for elective abdominal aortic surgery. After the induction of anesthesia and the exchange of 1 L of blood for 1 L of lactated Ringer's solution, 24 patients (12 in each study) were randomly assigned to receive, within 30 min, a predetermined volume of either HBOC-201 or 6% hydroxyethyl starch (Study A 6.9 mL/kg; Study B 9.2 mL/kg). Monitored variables included systemic and pulmonary arterial pressures, arterial and mixed venous blood gases, and calculations of cardiac index (CI), systemic (SVRI) and pulmonary (PVRI) vascular resistance indices, oxygen delivery index (DO2I), oxygen consumption index (VO2I), and oxygen extraction ratio (O2ER). In both studies, the infusion of HBOC-201 was associated with increases in SVRI (Study A 121%; Study B 71%) and PVRI (Study A 70%; Study B 53%) and with a decrease in CI (29% both studies). Hemodilution with HBOC-201 maintained the arterial oxygen content at levels higher than hemodilution with hydroxyethyl starch, but the advantage of a greater oxygen-carrying capacity was offset by the increase in SVRI, with a resulting net decrease in both CI and DO2I (Study A 30%; Study B 28%); VO2I was maintained by increased O2ER. In terms of hemodynamics and oxygen transport, hemodilution with bovine hemoglobin in these doses provided no apparent benefit over hemodilution with hydroxyethyl starch.

IMPLICATIONS

Bovine hemoglobin in doses ranging between 55 and 97 g of hemoglobin increased vascular resistance and decreased cardiac output in anesthetized surgical patients. In terms of hemodynamics and oxygen transport, hemodilution with bovine hemoglobin in these doses provided no apparent benefit over hemodilution with hydroxyethyl starch.