Resuscitation from hemorrhagic shock with diaspirin cross-linked hemoglobin, blood, or hetastarch

Polynitroxylated-pegylated hemoglobin attenuates fluid requirements and brain edema in combined traumatic brain injury plus hemorrhagic shock in mice

Polynitroxylated-pegylated hemoglobin (PNPH), a bovine hemoglobin decorated with nitroxide and polyethylene glycol moieties, showed neuroprotection vs. lactated Ringer's (LR) in experimental traumatic brain injury plus hemorrhagic shock (TBI+HS).

HYPOTHESIS

Resuscitation with PNPH will reduce intracranial pressure (ICP) and brain edema and improve cerebral perfusion pressure (CPP) vs. LR in experimental TBI+HS. C57/BL6 mice (n=20) underwent controlled cortical impact followed by severe HS to mean arterial pressure (MAP) of 25 to 27 mm Hg for 35 minutes. Mice (n=10/group) were then resuscitated with a 20 mL/kg bolus of 4% PNPH or LR followed by 10 mL/kg boluses targeting MAP>70 mm Hg for 90 minutes. Shed blood was then reinfused. Intracranial pressure was monitored. Mice were killed and %brain water (%BW) was measured (wet/dry weight). Mice resuscitated with PNPH vs. LR required less fluid (26.0±0.0 vs. 167.0±10.7 mL/kg, P<0.001) and had a higher MAP (79.4±0.40 vs. 59.7±0.83 mm Hg, P<0.001). The PNPH-treated mice required only 20 mL/kg while LR-resuscitated mice required multiple boluses. The PNPH-treated mice had a lower peak ICP (14.5±0.97 vs. 19.7±1.12 mm Hg, P=0.002), higher CPP during resuscitation (69.2±0.46 vs. 45.5±0.68 mm Hg, P<0.001), and lower %BW vs. LR (80.3±0.12 vs. 80.9±0.12%, P=0.003). After TBI+HS, resuscitation with PNPH lowers fluid requirements, improves ICP and CPP, and reduces brain edema vs. LR, supporting its development.

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.

Bench-to-bedside review: oxygen debt and its metabolic correlates as quantifiers of the severity of hemorrhagic and post-traumatic shock

Evidence is increasing that oxygen debt and its metabolic correlates are important quantifiers of the severity of hemorrhagic and post-traumatic shock and and may serve as useful guides in the treatment of these conditions. The aim of this review is to demonstrate the similarity between experimental oxygen debt in animals and human hemorrhage/post-traumatic conditions, and to examine metabolic oxygen debt correlates, namely base deficit and lactate, as indices of shock severity and adequacy of volume resuscitation. Relevant studies in the medical literature were identified using Medline and Cochrane Library searches. Findings in both experimental animals (dog/pig) and humans suggest that oxygen debt or its metabolic correlates may be more useful quantifiers of hemorrhagic shock than estimates of blood loss, volume replacement, blood pressure, or heart rate. This is evidenced by the oxygen debt/probability of death curves for the animals, and by the consistency of lethal dose (LD)_25,50 points for base deficit across all three species. Quantifying human post-traumatic shock based on base deficit and adjusting for Glasgow Coma Scale score, prothrombin time, Injury Severity Score and age is demonstrated to be superior to anatomic injury severity alone or in combination with Trauma and Injury Severity Score. The data examined in this review indicate that estimates of oxygen debt and its metabolic correlates should be included in studies of experimental shock and in the management of patients suffering from hemorrhagic shock.

Hemoglobin-vesicles suspended in recombinant human serum albumin for resuscitation from hemorrhagic shock in anesthetized rats*

OBJECTIVE

Hemoglobin-vesicle (HbV) has been developed to provide oxygen-carrying ability to plasma expanders. Its ability to restore the systemic condition after hemorrhagic shock was evaluated in anesthetized Wistar rats for 6 hrs after resuscitation. The HbV was suspended in 5 g/dL recombinant human serum albumin (HbV/rHSA) at an Hb concentration of 8.6 g/dL.

DESIGN

Prospective, randomized, controlled trial.

SETTING

Department of Surgery, School of Medicine, Keio University.

SUBJECTS

Forty male Wistar rats.

INTERVENTIONS

The rats were anesthetized with 1.5% sevoflurane inhalation throughout the experiment. Polyethylene catheters were introduced through the right jugular vein into the right atrium for infusion and into the right common carotid artery for blood withdrawal and mean arterial pressure monitoring.

MEASUREMENTS AND MAIN RESULTS

Shock was induced by 50% blood withdrawal. The rats showed hypotension (mean arterial pressure = 32 +/- 10 mm Hg) and significant metabolic acidosis and hyperventilation. After 15 mins, they received HbV/rHSA, shed autologous blood (SAB), washed homologous red blood cells (wRBC) suspended in rHSA (wRBC/rHSA, [Hb] = 8.6 g/dL), or rHSA alone. The HbV/rHSA group restored mean arterial pressure to 93 +/- 8 mm Hg at 1 hr, similar to the SAB group (92 +/- 9 mm Hg), which was significantly higher compared with the rHSA (74 +/- 9 mm Hg) and wRBC/rHSA (79 +/- 8 mm Hg) groups. There was no remarkable difference in the blood gas variables between the resuscitated groups; however, two of eight rats in the rHSA group died before 6 hrs. After 6 hrs, the rHSA group showed significant ischemic changes in the right cerebral hemisphere relating to the ligation of the right carotid artery followed by cannulation, whereas the HbV/rHSA, SAB, and wRBC/rHSA groups showed less changes.

CONCLUSIONS

HbV suspended in recombinant human serum albumin provides restoration from hemorrhagic shock that is comparable with that using shed autologous blood.

Hemoglobin-based oxygen carrier provides heterogeneous microvascular oxygenation in heart and gut after hemorrhage in pigs

BACKGROUND

In this study, the hypothesis was tested that resuscitation with hemoglobin-based oxygen carriers (HBOCs) affects the oxygenation of the microcirculation differently between and within organs. To this end, we tested the influence of the volume of an HBOC on the microcirculatory oxygenation of the heart and the gut serosa and mucosa in a porcine model of hemorrhage.

METHODS

In anesthetized open-chested pigs (n = 24), a controlled hemorrhage (30 mL/kg over 1 hour) was followed by resuscitation with 10, 20, or 30 mL/kg diaspirin-crosslinked hemoglobin (DCLHb) or isovolemic resuscitation with 30 mL/kg of a 6% hydroxyethyl starch solution (HAES). Measurements included systemic and regional hemodynamic and oxygenation parameters. Microvascular oxygen pressures (microPO2) of the epicardium and the serosa and mucosa of the ileum were measured simultaneously by the palladium-porphyrin phosphorescence technique. Measurements were obtained up to 120 minutes after resuscitation.

RESULTS

After hemorrhage, a low volume of DCLHb restored both cardiac and intestinal microPO2. Resuscitation of gut microPO2 with a low volume of DCLHb was as effective as isovolemic resuscitation with HAES. Higher volumes of DCLHb did not restore cardiac microPO2, as did isovolemic resuscitation with HAES, but increased gut microPO2 to hyperoxic values, dose-dependently. Effects were similar for the serosal and mucosal microPo2. In contrast to a sustained hypertensive effect after resuscitation with DCLHb, effects of DCLHb on regional oxygenation and hemodynamics were transient.

CONCLUSION

This study showed that a low volume of DCLHb was effective in resuscitation of the microcirculatory oxygenation of the heart and gut back to control levels. Increasing the volume of DCLHb did not cause an additional increase in heart microPO2, but caused hyperoxic microvascular values in the gut to be attained. It is concluded that microcirculatory monitoring in this way elucidates the regional behavior of oxygen transport to the tissue by HBOCs, whereas systemic variables were ineffective in describing their response.

DCL-Hb for trauma patients with severe hemorrhagic shock: the European "On-Scene" multicenter study

OBJECTIVE

A major cause of death in patients with severe hemorrhagic shock following trauma is the subsequent occurrence of multiple organ failure due to tissue hypoxia. Early administration of an oxygen carrier may reduce the occurrence of organ failures and improve survival. It may also reduce the need of blood products.

DESIGN AND SETTING

Prospective multicenter study in a university clinic.

PATIENTS

121 patients with severe hemorrhagic shock.

INTERVENTIONS

Patients were randomly assigned "on-scene" to receive either up to 1000 ml of a 10% diaspirin cross-linked hemoglobin (DCLHb) solution or the study center's standard therapy.

MEASUREMENTS AND RESULTS

Demographic and physiological characteristics of the two treatment groups at baseline were comparable. Organ failures and survival rates until day 5 and day 28 showed no significant differences. The sponsor therefore terminated this trial prematurely after an interim evaluation of the data indicated no evidence of efficacy to offset concerns raised about the safety of DCLHb. Median volumes of cumulative blood products administered on 1 (1595 vs. 3716 ml) and 7 days (3139 vs. 4746 ml) after admission were lower in the DCLHb group.

CONCLUSIONS

The early application of an oxygen carrier (DCLHb) to patients with severe hemorrhagic shock following trauma had no significant effect on the occurrence of organ failure or on 5- and 28-day survival in this abbreviated trial. However, early infusion of up to 1000 ml DCLHb reduces the need for blood products without changing morbidity or survival.

Systemic and microvascular responses to hemorrhagic shock and resuscitation with Hb vesicles

A phospholipid vesicle encapsulating hemoglobin (Hb vesicle, HbV) has been developed to provide O(2)-carrying capacity to plasma expanders. Its ability to restore systemic and microcirculatory conditions after hemorrhagic shock was evaluated in the dorsal skinfold window preparation of conscious hamsters. The HbV was suspended in 8% human serum albumin (HSA) at Hb concentrations of 3.8 g/dl [HbV(3.8)/HSA] and 7.6 g/dl [HbV(7.6)/HSA]. Shock was induced by 50% blood withdrawal, and mean arterial pressure (MAP) at 40 mmHg was maintained for 1 h by the additional blood withdrawal. The hamsters receiving either HbV(3.8)/HSA or HbV(7.6)/HSA suspensions restored MAP to 93 +/- 14 and 93 +/- 10 mmHg, respectively, similar with those receiving the shed blood (98 +/- 13 mmHg), which were significantly higher by comparison with resuscitation with HSA alone (62 +/- 12 mmHg). Only the HSA group tended to maintain hyperventilation and negative base excess after the resuscitation. Subcutaneous microvascular blood flow reduced to approximately 10-20% of baseline during shock, and reinfusion of shed blood restored blood flow to approximately 60-80% of baseline, an effect primarily due to the sustained constriction of small arteries A(0) (diameter 143 +/- 29 microm). The HbV(3.8)/HSA group had significantly better microvascular blood flow recovery and nonsignificantly better tissue oxygenation than of the HSA group. The recovery of base excess and improved tissue oxygenation appears to be primarily due to the increased oxygen-carrying capacity of HbV fluid resuscitation.

Post hoc mortality analysis of the efficacy trial of diaspirin cross-linked hemoglobin in the treatment of severe traumatic hemorrhagic shock

BACKGROUND

The efficacy trial of diaspirin cross-linked hemoglobin (DCLHb) in traumatic hemorrhagic shock demonstrated an unexpected mortality imbalance, prompting a three-step review to better understand the cause of this finding.

METHODS

Patients were enrolled in this DCLHb hemorrhagic shock study using 28-day mortality as the primary endpoint. Mortality data were primarily analyzed using the TRISS method and a nonblinded clinical review, followed by an independent Pennsylvania Trauma Outcome Study (PTOS)-derived probability of survival analyses. Finally, a trauma expert conducted a blinded clinical review of cases incorrectly predicted by these PTOS analyses.

RESULTS

More of the DCLHb patients predicted to survive using TRISS actually died than in the control subgroup (24% vs. 3%, p < 0.002). Nonblinded clinical review noted that 72% of the patients who died had prior traumatic arrest, a presenting Glasgow Coma Scale score of 3, or a base deficit > 15 mEq/L. DCLHb patients predicted to survive using PTOS also more often died than did control patients (30% vs. 8%, p < 0.04). Blinded clinical review determined that 94% of the deaths were clinically justified. Both the TRISS and the PTOS models gave an adjusted mortality relative risk of 2.3, similar to the unadjusted risk data.

CONCLUSION

Mortality analysis in this shock study involved both clinical case reviews and mortality prediction models. Despite the observation that nearly all of the deaths were clinically justified, the TRISS and PTOS models demonstrated excess unpredicted deaths in the DCLHb subgroup. A combined process, using both mortality prediction models and clinical case reviews, is useful in trauma studies that use a mortality endpoint.

Comparison of transfusion with DCLHb or pRBCs for treatment of intraoperative anemia in sheep

Isoflurane-anesthetized sheep were transfused with packed red blood cells (pRBCs) or diaspirin cross-linked hemoglobin (DCLHb) for treatment of intraoperative hemorrhage. A rapid 15-min hemorrhage with lactated Ringer (LR) infusion maintained filling pressure at baseline and reduced blood hemoglobin (Hb) to ~5 g/dl. Sheep received 2 g/kg Hb, DCLHb (n = 6), or pRBCs (n = 7); control group received LR alone (n = 6). After 2 h, anesthesia was discontinued; sheep were monitored in the animal intensive care unit for 48 h. DCLHb expanded blood volume more, but increased total blood Hb less, than pRBCs. Lower Hb and increased methemoglobin resulted in lower arterial oxygen content compared with the pRBCs. DCLHb caused pulmonary hypertension (from 13 to 30 mmHg) and elevated filling pressure (from 6 to 15 mmHg). Cardiac outputs (CO) were similar for all groups during anesthesia; however, during recovery CO increased only in the LR and packed pRBCs groups. DCLHb may limit the reflex ability to increase CO after volume expansion. Hemodynamic effects of DCLHb may be exaggerated when infused after large-volume LR.

Current controversies in shock and resuscitation

Many controversies and uncertainties surround resuscitation of hemorrhagic shock caused by vascular trauma. Whereas the basic pathophysiology is better understood, much remains to be learned about the many immunologic cascades that lead to problems beyond those of initial fluid resuscitation or operative hemostasis. Fluid therapy is on the verge of significant advances with substitute oxygen carriers, yet surgeons are still beset with questions of how much and what type of initial fluid to provide. Finally, the parameters chosen to guide therapy and the methods used to monitor patients present other interesting issues.

Low-volume fluid resuscitation for presumed hemorrhagic shock: helpful or harmful?

For the past 4 decades, the standard approach to the trauma victim who is hypotensive from presumed hemorrhage has been to infuse large volumes of fluids as early and as rapidly as possible. The goals of this treatment strategy are rapid restoration of intravascular volume and vital signs towards normal, and maintenance of vital organ perfusion. The most recent laboratory studies and the only clinical trial evaluating the efficacy of these guidelines however, suggest that in the setting of uncontrolled hemorrhage, today's practice of aggressive fluid resuscitation may be harmful, resulting in increased hemorrhage volume and subsequently greater mortality. This has been demonstrated in animal models representative of penetrating trauma as well as those representative of blunt trauma. The data strongly suggest that limited or hypotensive resuscitation may be preferable for the trauma victim with the potential for ongoing uncontrolled hemorrhage. Limited resuscitation provides a mechanism of avoiding the detrimental effects associated with early aggressive resuscitation, while maintaining a level of tissue perfusion that although decreased from the normal physiologic range is adequate for short periods. Large randomized clinical trials are necessary to confirm this new laboratory data. Future research should focus on developing resuscitation methods that may actually enhance tissue perfusion during limited resuscitation and therefore offset its potential detrimental effects.

Physiological properties of blood substitutes

Blood substitutes (modified hemoglobin solutions, perfluorocarbon emulsions) serve as artificial oxygen carriers and are alternatives to blood transfusions. Hemoglobin solutions mimic the sigmoidal oxygen dissociation curve of natural blood. Perfluorocarbon emulsions exhibit a linear relation between PO2 and dissolved oxygen. The most advanced substances may enter medicine in few years.

Hemoglobin solutions--not just red blood cell substitutes

OBJECTIVE

To review current knowledge about cell-free hemoglobin solutions.

DATA SOURCES

All studies involving cell-free hemoglobin were retrieved from a computerized MEDLINE search from 1980 to 1998. We also reviewed the reference lists of all available review articles and primary studies to identify references not found in the computerized search.

STUDY SELECTION

Clinical and experimental studies in which cell-free hemoglobin solutions were studied.

DATA EXTRACTION

From the selected studies, information was obtained regarding the experimental model or the study population in which cell-free hemoglobin solutions were investigated, the type of cell-free hemoglobin solution, their deleterious or beneficial effects, and their possible indications.

DATA SYNTHESIS

In many studies, hemoglobin solutions were considered as efficient resuscitative agents and good alternatives to red blood cell transfusion, because of their marked vasopressor effect coupled with their capacity to improve the microcirculation and quickly restore metabolic parameters. Nevertheless, potential problems include an increased susceptibility to infection, immunosuppression, oxidative damage, excessive pulmonary and systemic vasoconstriction, and platelet activation.

CONCLUSIONS

Hemoglobin solutions are more than mere blood substitutes. Promising effects on oxygen transport and the microcirculation need to be confirmed, and the results of continuing research are eagerly awaited.

Diaspirin-crosslinked hemoglobin reduces mortality of severe hemorrhagic shock in pigs with critical coronary stenosis

OBJECTIVE

To evaluate the effects of resuscitation with a 10% diaspirin-crosslinked hemoglobin (DCLHb) solution on global hemodynamic variables, systemic and myocardial oxygen transport and tissue oxygenation, and contractile function of the left ventricle in an experimental model of severe hemorrhagic shock and critical stenosis of the left anterior descending coronary artery (LAD).

DESIGN

Prospective, placebo-controlled, randomized study.

SETTING

Experimental animal laboratory.

SUBJECTS

A total of 20 anesthetized pigs.

INTERVENTIONS

After implementation of a permanent critical LAD stenosis (ie, maintenance of basal blood flow but absence of reactive hyperemia after a 10-sec complete vessel occlusion), hemorrhagic shock (target mean aortic pressure, 45 mm Hg) was induced within 15 mins by programmed withdrawal of blood and maintained for 60 mins. Subsequently, the volume of plasma lost during hemorrhage was replaced by either a balanced electrolyte solution containing 10 g/dL DCLHb (DCLHb group; n = 10) or an 8 g/dL human albumin solution (HSA) oncotically matched to DCLHb (HSA group; n = 10). Data were collected immediately after the infusion of the different solutions and again after 60 mins had elapsed.

MEASUREMENTS AND MAIN RESULTS

Although five of ten HSA-treated animals died of acute left ventricular failure within the first 20 mins after complete fluid resuscitation, all of the DCLHb-treated animals survived the 60-min observation period after resuscitation (p < .05). This significant difference in mortality is explained by higher coronary perfusion pressure in DCLHb-treated animals (75 +/- 17 vs. 27 +/- 17 torr DCLHb vs. HSA group; p < .05) and persistence of subendocardial ischemia and hypoxia (radioactive microspheres method) in HSA-treated animals on resuscitation particularly affecting the LAD-supported myocardium (subendocardial oxygen delivery: 20 +/- 11 vs. 3 +/- 1 mL oxygen x g(-1) x min(-1), DCLHb vs. HSA group; p < .05). Except for enhanced myocardial contractility immediately on infusion of DCLHb (maximal left ventricular pressure increase: 2373 +/- 782 vs. 1730 +/- 543 torr x sec(-1) DCLHb vs. HSA group; p < .05), no differences were detected between groups concerning the variables of systemic oxygen transport, tissue oxygenation, and regional contractile function of the myocardium (determined with microsonometry).

CONCLUSIONS

Fluid resuscitation with 10% DCLHb solution completely reverses hemorrhagic shock-induced subendocardial ischemia and hypoxia in the presence of compromised coronary circulation and thereby prevents early death after resuscitation.

Comparison of various hemoglobin polyoxyethylene conjugate solutions as resuscitative fluids after hemorrhagic shock

BACKGROUND

Previous research suggested that splanchnic hypoperfusion occurs after resuscitation with certain acellular hemoglobin solutions. We examined the influence of maltose content and oxygen affinity on resuscitation with various hemoglobin polyoxyethylene conjugate solutions after hemorrhage.

METHODS

Fifteen swine underwent hemorrhage and equal volume resuscitation with pyridoxalated hemoglobin polyoxyethylene conjugate containing 0% or 8% maltose, or low P50 conjugate, which also contained 8% maltose. Five control animals were monitored but not bled. Regional blood flow was determined by using radioactive microspheres, gastric mucosal perfusion was estimated with tonometry, and gut histopathology was evaluated.

RESULTS

All hemoglobin solutions produced vasoconstriction, manifested by elevated mean systemic and pulmonary artery pressures without a significant decrease in cardiac index compared with the sham group. Resuscitation with maltose-containing solutions elevated arterial and regional PCO2 and depressed arterial pH and gastric pHi (p < 0.05 for all). Splanchnic and renal blood flows were reduced in the low P50 + 8% maltose group (p < 0.05 vs. sham and baseline for renal blood flow), possibly indicating greater regional vasoconstriction in this group. Ileal mucosal damage was more severe in the maltose-containing groups and correlated with decreased pHi.

CONCLUSION

Vasoconstriction occurred in all groups but was more severe in the low P50 + 8% maltose group. Maltose-containing solutions caused respiratory acidosis, decreased pHi, and histologic evidence of mucosal injury. Pyridoxalated hemoglobin polyoxyethylene conjugate without maltose was a superior resuscitation solution in this swine model.

[Vascular loading in the first 24 hours following severe head injuries]

The main goal at the acute phase of head injury is to prevent a decrease in blood pressure, which promotes cerebral ischemia. Volume loading is therefore frequently indicated. A normal or increased plasma osmolarity should be maintained. Thus hypotonic fluids should be avoided. Hyperglycaemia is also a risk factor for brain injury and glucose use has to be restricted in the first hours after trauma. Isotonic saline 0.9% is the first solution to be infused. Lactated Ringer solutions are mildly hypotonic as approximately 114 mL of free water is contained in each litre of the solution. Isotonic colloids are indicated to replace blood losses, but have no advantage over cristalloids, concerning the development of cerebral oedema. Fluid restriction minimally affects cerebral edema. Because of the severe consequences of hypovolaemia and hypotension, fluids should not be restricted until haemodynamic stability is achieved. Hypertonic fluids rapidly restore intravascular volume and decrease intracranial pressure. Although they probably have a place in prehospital intensive therapy, the demonstration of their benefit is still lacking. Monitoring of intravascular volume is essential. Continuous arterial pressure and central venous pressure monitoring are mandatory. New monitoring techniques as the measurement of systolic pressure variations or transoesophageal Doppler echocardiography will probably find a place in the management of trauma patients in the near future.

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.

Pharmacodynamic characterization of hemoglobin-induced vasoactivity in isolated rat thoracic aorta

The origin and mechanism of vasocontraction observed after vascular exposure to acellular Hbs remain controversial. To help resolve the underlying mechanism, we characterized Hb-induced vasoactivities in terms of Hb purity, heme iron oxidation state, and ligand and pharmacodynamic properties. Isolated rat thoracic aortic rings with intact endothelium were suspended in oxygenated Krebs buffer, and isometric tension responses to various test Hb preparations were measured. In norepinephrine tone-enhanced aortic rings, both crude and purified Hbs exhibited similar dose-response characteristics; stroma-free Hb and HbA0, two Hb preparations with disparate purity, were equally potent in inducing vessel ring contraction. Purified Hb preparations significantly attenuated vasodilatory potency of both acetylcholine, an endothelium-dependent NO generator, and glyceryl trinitrate, an endothelium-independent NO generator. With the exception of nitrosylated Hb, ferrous Hbs, oxy Hb, and carbon monoxy Hb elicited contraction, whereas ferric derivatives, met Hb, and cyanomet Hb did not. In addition, NEM-Hb, an Hb with blocked cysteine residues, did not notably attenuate Hb vasoactivity. These results indicate that Hb itself is directly responsible for inducing contraction in the rat thoracic aortic rings. A primary mechanism for the Hb-induced vasoactivity appears to be heme iron inactivation of endothelium-derived NO. Nonheme interaction with endothelial NO does not appear to play a prominent role in this vascular model. In conclusion, Hb elicits dose-dependent contraction in isolated rat thoracic aorta with intact endothelium. Vasoactivity of Hbs, however, could greatly vary with heme iron oxidation state, nature of heme ligand, and model vessels used in the evaluation.

New hemoglobin substitutes

Blood transfusion is an essential and ubiquitous component of medical therapy. Despite careful screening and processing, allogeneic blood still carries a small but definable risk of the transmission of severe viral disease and the induction of immunological reactions. The logistics of its storage and transport continue to present a challenge, and its dependence on human donors will always keep it a scarce resource. It is not surprising that in the latter half of the 20th century efforts to develop blood substitutes have gained increasing momentum.

Plasma volume expansion with solutions of hemoglobin, albumin, and Ringer lactate in sheep

We have measured plasma volume expansion (Evans blue and hematocrit changes) and hemodynamic responses in conscious hemorrhaged and normovolemic splenectomized sheep after a 30-min infusion of either 20 ml/kg of diaspirin cross-linked hemoglobin (DCLHb), 20 ml/kg of human albumin (Alb), or 60 ml/kg of a solution of Ringer lactate (RL). All regimens expanded blood volume and increased blood pressure and cardiac output after hemorrhage. However, only 15 +/- 3% of the infused volume of RL was evident as intravascular expansion 10-min postinfusion, compared with 67 +/- 16% and 139 +/- 139% for Alb and DCLHb, respectively. DCLHb infusions were associated with higher blood pressures and lower cardiac outputs compared with RL and Alb infusions, but the increased oxygen content of blood with DCLHb resulted in systemic delivery of oxygen similar to that of the other infusions. These differences in hemodynamics and vascular volume continued for 6 h, and at 24 h vascular volume and all hemodynamics were similar in all three groups. The better volume expansion with DCLHb may be due to greater mobilization of endogenous interstitial protein or reduced transcapillary loss as total intravascular endogenous plasma protein increased after infusion of DCLHb, whereas there was an apparent loss of endogenous intravascular protein after infusions of Alb and RL. Vasoconstriction by DCLHb is one mechanism that could lower blood-to-tissue transport of fluid and protein. In addition to its oxygen-carrying capacity and vasoactivity, DCLHb is associated with volume expansion properties out of proportion to its colloid osmotic pressure.

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.

Filtration of diaspirin crosslinked hemoglobin into lung and soft tissue lymph

Diaspirin crosslinked hemoglobin (DCHb) is a new blood substitute manufactured from human blood. To evaluate its microvascular filtration properties, we infused DCLHb into unanesthetized sheep (10%, 20 ml/kg) and measured the flow and composition of lung and soft tissue lymph. For comparison, we also infused human serum albumin (HSA; 10%, 20 ml/kg). DCLHb raised systemic and pulmonary arterial pressures from baseline values of 83 +/- 7 and 13 +/- 2 mm Hg, respectively, to peak values of 113 +/- 9 and 26 +/- 3 mm Hg (p < 0.05 versus baseline). These increases were significantly greater than those associated with HSA, which raised systemic and pulmonary arterial pressures from baseline values of 86 +/- 4 and 13 +/- 2 mm Hg, respectively, to peak values of 97 +/- 3 and 21 +/- 7 mm Hg (p <= 0.05 versus baseline and versus DCLHb). These differences reflect the known pressor properties of DCLHb. Accordingly, DCLHb raised lung and soft tissue lymph flows to peak values of 12.2 +/- 3.8 and 1.6 +/- 0.7 ml/30 min, respectively, while HSA raised lung and soft tissue lymph flows to peak values of 7.5 +/- 4.8 and 4.6 +/- 1.9 ml/30 min, respectively (p <= 0.05 versus DCLHb). The half-times of DCLHb equilibration from plasma into lung and soft tissue lymph of 1. 0 +/- 0.3 and 2.1 +/- 1.1 h, respectively, were significantly faster than HSA equilibration half-times of 3.1 +/- 0.2 and 3.8 +/- 0.9 h. Filtration differences between DCLHb and HSA appear to be due to the pressor properties DCLHb.