Resuscitation of severe chest trauma with four different hemoglobin-based oxygen-carrying solutions

Effect of nitric oxide synthase inhibitors in acute lung injury due to blunt lung trauma in rats

Background

This study aims to investigate the effects of blunt lung trauma performed in experimental rat model on lung tissue and blood as well as proinflammatory cytokines, oxidant-antioxidant enzymes and histopathological parameters after Ngamma-nitro-L-arginine methyl ester and N-iminoethyl-L-ornithine administration.

Methods

The study included 50 adult male Wistar albino rats (weighing 350 to 400 g). Rats were randomly allocated into four groups. Except in the control, moderate-level pulmonary contusion was created in all other groups. Intraperitoneal saline solution was performed in groups 1 and 2, 25 mg.kg-1 Ngamma-nitro-L-arginine methyl ester in group 3, and 20 mg.kg-1 N-iminoethyl-L-ornithine in group 4. Blood and lung tissues were studied biochemically and histopathologically.

Results

Best outcomes were recorded statistically significantly in groups with administration of Ngamma-nitro-L-arginine methyl ester and N-iminoethyl-L-ornithine when malondialdehyde response, mucous and histopathological values were examined. Significant improvement was detected in superoxide dismutase values in the group with administration of competitive nitric oxide synthase inhibitor Ngamma-nitro-L-arginine methyl ester. Nitric oxide values were substantially decreased in N-iminoethyl-L-ornithine group, while no significance was detected.

Conclusion

Free oxygen radicals and lipid peroxidation played a role in pulmonary contusion after blunt lung trauma. According to biochemical and histopathological outcomes, effects of inflammation were decreased and protective effects were formed with administration of both Ngammanitro- L-arginine methyl ester and N-iminoethyl-L-ornithine.

Antioxidant vitamins C, E and coenzyme Q10 vs dexamethasone: comparisons of their effects in pulmonary contusion model

Background

The goal of our study is to evaluate the effects of antioxidant vitamins (vitamin C and E), Coenzyme Q10 (CoQ10) and dexamethasone (Dxm) in experimental rat models with pulmonary contusion (PC).

Methods

Rats were randomly divided into six groups. Except for the control, all subgroups had a moderate pulmonary contusion. Animals in the group I and group II received intraperitoneal saline, group III received 10mg.kg-1 CoQ10 group IV received 100mg.kg-1 vitamin C, group V received 150mg.kg-1 vitamin E, and group VI received 10mg.kg-1 Dxm. Blood gas analysis, serum nitric oxide (NO) and malondialdehyde (MDA) levels as well as superoxide dismutase (SOD) activity assays, bronchoalveolar lavage (BAL) fluid and histopathological examination were performed.

Results

Administration of CoQ10 resulted in a significant increase in PaO2 values compared with the group I (p = 0.004). Levels of plasma MDA in group II were significantly higher than those in the group I (p = 0.01). Early administration of vitamin C, CoQ10, and Dxm significantly decreased the levels of MDA (p = 0.01). Lung contusion due to blunt trauma significantly decreased SOD activities in rat lung tissue compared with group I (p = 0.01). SOD levels were significantly elevated in animals treated with CoQ10, Vitamin E, or Dxm compared with group II (p = 0.01).

Conclusions

In our study, CoQ10, vitamin C, vitamin E and Dxm had a protective effect on the biochemical and histopathological outcome of PC after experimental blunt thorax trauma.

Unusual peroxidase activity of polynitroxylated pegylated hemoglobin: Elimination of H(2)O(2) coupled with intramolecular oxidation of nitroxides

Polynitroxylated hemoglobin (Hb(AcTPO)(12)) has been developed as a hemoglobin-based oxygen carrier. While Hb(AcTPO)(12) has been shown to exert beneficial effects in a number of models of oxidative injury, its peroxidase activity has not been characterized thus far. In the blood stream, Hb(AcTPO)(12) undergoes reduction by ascorbate to its hydroxylamine form Hb(AcTPOH)(12). Here we report that Hb(AcTPOH)(12) exhibits peroxidase activity where H(2)O(2) is utilized for intramolecular oxidation of its TPOH residues to TPO. This represents an unusual redox-catalytic mechanism whereby reduction of H(2)O(2) is achieved at the expense of reducing equivalents of ascorbate converted into those of Hb(AcTPOH)(12), a new propensity that cannot be directly associated with ascorbate.

Control of oxidative reactions of hemoglobin in the design of blood substitutes: role of the ascorbate-glutathione antioxidant system

Uncontrolled oxidative reactions of hemoglobin (Hb) are still the main unresolved problem for Hb-based blood substitute developers. Spontaneous oxidation of acellular ferrous Hb into a nonfunctional ferric Hb generates superoxide anion. Hydrogen peroxide, formed after superoxide anion dismutation, may react with ferrous/ferric Hb to produce toxic ferryl Hb, fluorescent heme degradation products, and/or protein-based free radicals. In the presence of free iron released from heme, superoxide anion and hydrogen peroxide might react via the Haber-Weiss and Fenton reactions to generate the hydroxyl radical. These highly reactive oxygen and heme species may not only be involved in shifting the cellular redox balance to the oxidized state that facilitates signal transduction and pro-inflammatory gene expression, but could also be involved in cellular and organ injury, and generation of vasoactive compounds such as isoprostanes and angiotensins. It is believed that these toxic species may be formed after administration of Hb-based blood substitutes, particularly in ischemic patients with a diminished ability to control oxidative reactions. Although varieties of antioxidant strategies have been suggested, this in vitro study examined the ability of the ascorbate-glutathione antioxidant system in preventing Hb oxidation and formation of its ferryl intermediate. The results suggest that although ascorbate is effective in reducing the formation of ferryl Hb, glutathione protects heme against excessive oxidation. Ascorbate without glutathione failed to protect the red blood cell membranes against Hb/hydrogen peroxide-mediated peroxidation. This study provides evidence that the ascorbate-glutathione antioxidant system is essential in attenuation of the pro-oxidant potential of redox active acellular Hbs, and superior to either ascorbate or glutathione alone.

Effects of early administration of dexamethasone, N-acetylcysteine and aprotinin on inflammatory and oxidant-antioxidant status after lung contusion in rats

INTRODUCTION

This experimental setting was undertaken to elucidate and confirm the role of inflammatory and oxidant-antioxidant mechanisms on blunt injury induced moderate pulmonary contusion (PC). We intended to determine the effects of dexamethasone (DXM), N-acetylcysteine (NAC) and aprotinin (APR) in terms of their ability to diminish the consequences of acute lung injury due to PC.

METHODS

Rats were allocated to five subgroups. Except for the control, all subgroups had a moderate pulmonary contusion. Following 45 min of observation, animals in groups I and II received intraperitoneal saline, group III 10 mg/kg DXM, group IV 500 mg/kg NAC and group V 30,000 kIU/ml APR. After the procedure, 6 h after contusion, blood gas analysis, lung tissue nitric oxide (NO) and malondialdehyde (MDA) levels, superoxide dismutase (SOD) and catalase (CAT) activity, bronchoalveolar lavage (BAL) fluid and histopathological examination were performed.

RESULTS

All PaO(2) values decreased significantly in contused rats as compared with the control group (p<0.05). DXM, NAC and APR resulted in a slight increase in PaO(2) values compared with group II (p<0.05). Lung tissue levels of MDA and NO were higher in the contusion group than in the control (p<0.05). DXM, NAC and APR all decreased the levels of MDA and NO (p<0.05), however the decrease in NO was not found to be significant with APR (p>0.05). SOD and CAT activities increased significantly after contusion compared to control group (p<0.05). There was no significant difference even though SOD levels were elevated in groups III, IV and V compared with contused animals (p>0.05). Neutrophils in BAL fluid significantly increased in contused animals (p<0.05). Only DXM significantly decreased neutrophil population in BAL fluid (p<0.05). Scores for alveolar haemorrhage/oedema were higher in all contusion-performed rats than those in the control (p<0.05). Compared with the other drugs, only APR significantly improved the haemorrhage/oedema scores compared to sham animals (p=0.024).

CONCLUSIONS

Our findings demonstrate that moderate bilateral PC induced by blunt chest trauma leads to an early inflammatory process which is clearly associated with activation of the oxidant-antioxidant cascade. On this basis, early supportive treatment with DXM, NAC and APR may yield favourable results on pulmonary pathophysiological parameters which are adversely affected due to PC.

Animal models for trauma research: what are the options?

Even if trauma patients initially avoid death after trauma (due to massive blood volume loss, primary severe brain injury), they are still at risk for multiple organ failure. Thus, it is crucial to elucidate the underlying pathophysiological mechanisms of trauma/hemorrhagic shock and the immune response involved. As of now, many hemorrhagic shock/trauma studies have used various types of animal models. Despite a large number of results from these efforts, some authors have argued that animal model results are difficult to translate directly into the clinical scenario. This review summarizes the advantages and the disadvantages of using animal models in trauma/hemorrhagic shock studies and discusses the relevance of various animal studies to the clinical scenario.

Hemoglobin-based oxygen carrying compound-201 as salvage therapy for severe neuro- and polytrauma (Injury Severity Score = 27-41)

OBJECTIVE

A prehospital trial in trauma patients has been proposed to evaluate Hemopure (hemoglobin glutamer-250 [bovine], hemoglobin-based oxygen carrying compound [HBOC]-201, Biopure). We tested the hypothesis that HBOC-201 would improve cerebrovascular resuscitation in a unique polytrauma model.

DESIGN

Prospective, randomized, blinded animal study.

SUBJECTS

Thirty-two anesthetized swine (42 +/- 1 kg).

INTERVENTIONS

Blunt trauma to the head, right chest, and bilateral femurs (Injury Severity Score = 27-41) with captive bolt guns was followed by hypoventilation. Resuscitation was divided into phases to simulate conventional treatment in the prehospital, emergency room, and early intensive care unit. For 30-60 mins postinjury, 500 mL of either normal saline (control, n = 14) or HBOC-201 (n = 14) was administered. All received similar care thereafter. For 60-120 mins, normal saline maintained systolic arterial pressure >100 mm Hg and heart rate <100 beats/min plus mannitol (250 mg/kg) for intracranial hypertension. For 120-480 mins, phenylephrine, normal saline, and dextrose were administered to maintain cerebral perfusion pressure >70 mm Hg, filling pressure >12 mm Hg, and plasma glucose >60 mg%, respectively. Two formulations of HBOC-201 (average MW = 250 kDa) were tested: one with <3% 65 kDa tetramers (n = 7) and the other with <0.3% 65 kDa tetramers (n = 7).

MEASUREMENTS AND MAIN RESULTS

Injury severity is reflected by the death of 2 of 32 swine within 30 mins. In survivors (n = 30), systolic arterial pressure was 83 +/- 6 mm Hg, heart rate was 115 +/- 5 beats/min, and lactate was 5.8 +/- 0.4 mM. Intracranial pressure rose from 8 +/- 1 to 18 +/- 1 mm Hg and brain tissue PO2 fell from 17 +/- 1 to 2 +/- 1 mm Hg. Without immediate resuscitation, death occurred within 60 mins (n = 2). With normal saline resuscitation (n = 14), systemic hemodynamics, mixed venous oxygen, renal oxygen, portal oxygen, and muscle oxygen corrected but there were four deaths (two at 45 mins, one at 100 mins, and one at 200 mins). Cerebral perfusion pressure was not restored until mannitol and pressor therapy were initiated at 120 mins. In contrast, with HBOC-201 at 30 mins (n = 14), systolic arterial pressure and cerebral perfusion pressure corrected immediately (both p < 0.05) and there were no deaths (p = 0.0978). After 8 hrs, in both groups, cerebral perfusion pressure, systolic arterial pressure, and heart rate were stable; peripheral oxygen saturations were near normal; lactate was cleared; urine output was adequate. However, with HBOC-201, pressor and fluid requirements were reduced by half, which improved intracranial pressure and brain tissue PO2 (all p < 0.05 vs. control). Reducing tetramer content had no significant effect on the actions of HBOC-201.

CONCLUSIONS

1) A single bolus of HBOC-201 at initial resuscitation rapidly restored cerebral perfusion pressure and stabilized hemodynamics with improved intracranial pressure and brain oxygen for the first 8 hrs; and 2) HBOC-201 could be an effective salvage therapy after severe neurotrauma or as a temporizing measure during prolonged transport of a polytrauma patient.

Lung contusion: pathophysiology and management

Management of severe pulmonary contusion is a challenge for clinicians. The incidence of adult respiratory distress syndrome (5-20%), pneumonia (5-50%), and mortality (5-10%) associated with traumatic lung injury has changed little in the past three decades. Therapeutic options are limited to basic supportive measures such as mechanical ventilation, positive end expiratory pressure, invasive cardiopulmonary monitoring, analgesics and aggressive pulmonary hygiene. Presently, no pharmacological agents can prevent the progressive respiratory embarrassment that is associated with the natural history of the disease, but several drugs have been tested in the laboratory. The purpose of this brief review is to summarize information published since January 2000 related to the clinical management and pathophysiology of lung contusion.

Pulmonary trauma

Pulmonary trauma is common and devastating and is associated with significant morbidity and mortality. The present review highlights recent literature and case reports in this area. Topics of particular significance or interest include mechanisms of injury, potentially fatal intrathoracic vascular injuries, anesthetic management, fluid management (crystalloids as well as hemoglobin-based oxygen-carrying solutions), pain management of severe chest trauma, surgical management, and novel methods of diagnosis.

Vasoactivity of Bovine Polymerized Hemoglobin (HBOC-201) in Swine With Traumatic Hemorrhagic Shock With and Without Brain Injury

BACKGROUND

We previously reported that bovine polymerized hemoglobin (HBOC- 201) improved outcome in swine with hemorrhagic shock (HS) with and without traumatic brain injury (TBI). Herein, we add analyses of blood pressure (BP) responses, associated physiologic data, and HS fluid infusion guidelines.

METHODS

HBOC-201 versus standard fluid resuscitation was compared in four anesthetized invasively monitored swine models: moderate controlled HS, severe controlled HS, severe uncontrolled HS (liver injury), and severe uncontrolled HS/TBI (liver/parietal brain injuries). Pigs received fluid for hypotension and tachycardia, and were followed up to 6 (HS alone) or 72 hours (HS/TBI). The change in mean arterial pressure (DeltaMAP) response severity was stratified and analyzed based on infusion number and HS severity, using Student's t and Fisher's exact tests.

RESULTS

HBOC-201 vasoactivity resulted in higher MAP in all studies. Among HBOC-201 pigs, DeltaMAP responses were significant for the first two infusions and inversely related to HS severity. Among controls, DeltaMAP responses remained significant through the fourth infusion in controlled HS models, and through the first in severe uncontrolled HS/TBI; none were significant in severe uncontrolled HS. DeltaMAP was higher with HBOC-201 through the first infusion in moderate controlled HS, the fifth in severe uncontrolled HS, and the second in severe uncontrolled HS/TBI; there were no group differences in severe controlled HS. No severe MAP responses occurred. Higher DeltaMAP severity did not impact outcome. Hypotension satisfied fluid reinfusion criteria less consistently than tachycardia. Overall, HBOC-201 improved physiologic parameters and survival without causing hypoperfusion; in severe HS, perfusion improved.

CONCLUSIONS

In swine with HS +/- TBI, HBOC-201 had mild to moderate vasoactivity, resulting in significant DeltaMAP responses mainly after initial infusions, no severe/adverse responses, and improved outcome. Our data suggest that use of physiologic parameters (e.g., tachycardia), in addition to hypotension to guide fluid reinfusion during HS resuscitation with HBOC-201, will minimize hypoperfusion risk and maximize potential benefit.

Effect of oxygen affinity and molecular weight of HBOCs on cerebral oxygenation and blood pressure in rats

PURPOSE

This study assessed the effect of oxygen affinity and molecular weight (MW) of o-raffinose cross-linked hemoglobin based oxygen carriers (HBOCs) on cerebral oxygen delivery and mean arterial blood pressure (MAP) following hemorrhage and resuscitation in rats.

METHODS

Isoflurane anesthetized rats (n = 6-7 per group) underwent 30% hemorrhage and resuscitation with an equivalent volume of one of three different HBOCs: 1) High P50 Poly o-raffinose hemoglobin (Poly OR-Hb, P50 = 70 mmHg); 2) High P50 > 128 Poly OR-Hb (MW > 128 kDa, P50 = 70 mmHg) and 3) Low P50 > 128 Poly OR-Hb (MW >128 kDa, P50 = 11 mmHg). Hippocampal cerebral tissue oxygen tension, regional cerebral blood flow (rCBF), MAP, total hemoglobin concentration and arterial blood gases were measured. Data analysis by two-way ANOVA and post hoc Tukey tests determined significance (P < 0.05, mean +/- SD).

RESULTS

Hippocampal tissue oxygen tension increased in all HBOC groups following resuscitation. The rCBF remained unchanged after HBOC resuscitation in all groups. Following resuscitation, the peak MAP was higher in the High P50 Poly OR-Hb group (152 +/- 13 mmHg) when compared to either the Low or High P50 large MW, (> 128 kDa) HBOC group (119 +/- 15 mmHg or 127 +/- 18 respectively, P < 0.05 for both).

CONCLUSIONS

O-raffinose polymerized HBOC, with or without lower MW components, maintained cerebral tissue oxygen delivery following hemorrhage and resuscitation in rats. The higher MW HBOCs showed a decrease in peak MAP, which did not alter oxygen delivery. No significant effect of oxygen affinity on cerebral tissue oxygen tension or blood flow was observed.

Prehospital HBOC-201 after traumatic brain injury and hemorrhagic shock in swine

BACKGROUND

Data are limited on the actions of hemoglobin based oxygen carriers (HBOCs) after traumatic brain injury (TBI). This study evaluates neurotoxicity, vasoactivity, cardiac toxicity, and inflammatory activity of HBOC-201 (Biopure, Cambridge, Mass.) resuscitation in a TBI model.

METHODS

Swine received TBI and hemorrhage. After 30 minutes, resuscitation was initiated with 10 mL/kg normal saline (NS), followed by either HBOC-201 (6 mL/kg, n = 10) or NS control (n = 10). Supplemental NS was administered to both groups to maintain mean arterial pressure (MAP) >60 mm Hg until 60 minutes, and to maintain cerebral perfusion pressure (CPP) >70 mm Hg from 60 to 300 minutes. The control group received mannitol (1 g/kg) and blood (10 mL/kg) at 90 minutes and half (n = 5) received CPP directed phenylephrine (PE) therapy after 120 minutes. Serum cytokines were measured with ELISA and coagulation was evaluated with thromboelastography. Brains were harvested for neuropathology.

RESULTS

With HBOC administration, MAP, CPP, and brain tissue PO2 were restored within 30 minutes and maintained until 300 minutes. Clot strength and fibrin formation were maintained and 9/10 successfully extubated. In contrast, with control, MAP and brain tissue PO2 did not correct until 120 minutes, after mannitol, transfusion and 40% more crystalloid. Furthermore, without PE, CPP did not reach target and 0/5 could be extubated. Lactate, heart rate, cardiac output, mixed venous oxygenation, muscle oxygenation, serum cytokines, and histology did not differ between groups.

CONCLUSIONS

After TBI, a single HBOC-201 bolus with minimal supplements provided rapid resuscitation, while maintaining CPP and improving brain oxygenation, without causing cardiac dysfunction, coagulopathy, cytokine release, or brain structural changes.

Dissociation of local nitric oxide concentration and vasoconstriction in the presence of cell-free hemoglobin oxygen carriers

Cell-free hemoglobin's (CFH) high affinity for nitric oxide (NO) could limit CFH's use as an oxygen-carrying blood replacement fluid because it scavenges NO, causing vasoconstriction and hypertension. However, the extent to which perivascular NO levels change following intravascular administration of hemoglobin (Hb) with different molecular dimensions correlates with vasoconstrictive responses in the microcirculation is unknown. The study objective was to determine vasoconstrictive effects following bolus infusions of (1) alphaalpha cross-linked Hb; (2) polymerized bovine Hb; or (3) polyethylene glycol-decorated Hb (PEG-Hb), by measurements of in vivo microvessel diameter, blood flow, perivascular NO concentration, and systemic hemodynamic parameters. All CFHs caused reductions in perivascular NO levels, not correlated to microvascular responses. PEG-Hb (largest molecular volume) maintained blood flow, while the others caused vasoconstriction and reduced perfusion. All solutions increased mean arterial pressure due to vasoconstriction and blood volume expansion, except for PEG-Hb, which increased blood pressure due to blood volume expansion and maintenance of cardiac output. In conclusion, perivascular NO reduction is similar for all Hb solutions because NO binding affinities are similar; however, effects on vascular resistance are related to the type of molecular modification, molecular volume, and oxygen affinity.

Early Vasopressin Improves Short-Term Survival after Pulmonary Contusion

Arginine vasopressin (AVP) is a promising treatment for several types of irreversible shock, but its therapeutic potential has not been examined after severe chest trauma. Two series of experiments were performed to fill this gap.

METHODS

Series 1: anesthetized, mechanically-ventilated pigs (n = 20, 29 +/- 1 kg) received a blast to the chest, followed by a "controlled" arterial hemorrhage to a mean arterial pressure (MAP) <30 mm Hg. At 20 minutes, a 10 mL/kg normal saline (NS) bolus was followed by either 0.1 U/kg AVP bolus or NS, in randomized, blinded fashion. From 30-300 minutes, either AVP (0.4 U/kg/hr plus NS) or NS alone was infused as needed to MAP>70 mm Hg. Series 2: Swine (n = 15) received the chest injury followed by partial left hepatectomy to produce "uncontrolled" hemorrhage. Resuscitation was the same as in series 1.

RESULTS

The blast created bilateral parenchymal contusions (R > L), hemo/pneumothorax and progressive cardiopulmonary distress. In Series 1, there were 3/20 deaths before randomization, 0/8 deaths after resuscitation with AVP versus 4/9 deaths with NS (p = 0.029). In surviving animals, with AVP versus NS, fluid requirements and peak airway pressures were lower while P/F was higher (all p < 0.05). In Series 2, with uncontrolled hemorrhage, there were 5/15 deaths before randomization. Upon resuscitation with AVP versus NS, survival time and blood loss were both improved, but the differences did not reach statistical significance.

CONCLUSIONS

After severe chest trauma with controlled hemorrhage, early AVP decreased mortality, reduced fluid requirements and improved pulmonary function. With uncontrolled hemorrhage, early AVP did not increase the risk for bleeding.

MalPEG-hemoglobin (MP4) improves hemodynamics, acid-base status, and survival after uncontrolled hemorrhage in anesthetized swine

OBJECTIVES

MalPEG-hemoglobin, 4 g/dL (MP4), is a hemoglobin-based oxygen carrier with a low hemoglobin concentration, low P50 (oxygen half-saturation pressure of hemoglobin), high colloid osmotic pressure, and high viscosity. This study evaluated resuscitation with MP4 in anesthetized swine hemorrhaged 250 mL by controlled withdrawal, followed by a 5-mm tear in the abdominal aorta.

DESIGN

Randomized, unblinded.

SETTING

Academic animal laboratory.

SUBJECTS

Anesthetized male and female Swedish Landrace pigs.

INTERVENTIONS

Four groups of pigs (n = 7 each) were randomized after hemorrhage by aortic tear to receive 250 mL of MP4, Ringer's acetate, 10% pentastarch, or 4 g/dL of stroma-free hemoglobin, followed by aortic repair and transfusion of 250 mL of autologous blood. End points were 20-hr survival, hemodynamic variables, and acid-base status.

MEASUREMENTS AND MAIN RESULTS

Measurements included continuous aortic, pulmonary arterial, and central venous pressures, cardiac output by thermodilution, arterial and venous blood gases; electrolytes; lactate; base excess; oxygen delivery, consumption, and extraction ratio; hematocrit; hemoglobin; and urine output. Body weight (24-27 kg) and hemorrhage volume (26-33 mL/kg) were similar in the four groups. The nadir of mean arterial pressure (22-28 mm Hg) and the increase in lactic acid (5-8 mEq/L) after hemorrhage were similar in all groups, indicating equivalent shock in the four groups. Survival was greatest in the MP4-treated animals (six of seven) compared with Ringer's acetate (two of seven), 10% pentastarch (one of seven), and stroma-free hemoglobin (two of seven) and was accompanied by an improved recovery of arterial pressure, cardiac output, and lactate. Total hemoglobin concentration was equivalent in all groups. Arterial pressure did not increase above baseline values, and systemic vascular resistance was unchanged following administration of MP4, indicating the lack of peripheral vasoconstriction. Mortality in Ringer's acetate, stroma-free hemoglobin, and 10% pentastarch treated animals was associated with deteriorating acid-base status, low urine output, and hyperkalemia.

CONCLUSION

These data demonstrate that restoration of oxygen delivery with a small volume of MP4 yields significant recovery from hemorrhage without systemic vasoconstriction.

Cerebral Perfusion Pressure Elevation with Oxygen-Carrying Pressor after Traumatic Brain Injury and Hypotension in Swine

BACKGROUND

Previously, we had shown that elevation of cerebral perfusion pressure, using pressors, improved short-term outcomes after traumatic brain injury and hemorrhagic shock in swine. The current study evaluates outcomes after resuscitation with diaspirin cross-linked hemoglobin (DCLHb)--a hemoglobin-based oxygen carrier with pressor activity--in the same swine model of traumatic brain injury and hemorrhagic shock.

METHODS

Anesthetized and ventilated swine received traumatic brain injury via cortical fluid percussion (6-8 atm) followed by 45% blood volume hemorrhage. One hour later, animals were randomized to either a control group (SAL) resuscitated with normal saline equal to three times shed blood volume or to one of two experimental groups resuscitated with DCLHb. The two experimental groups consisted of a low-dose group, resuscitated with 250 mL of DCLHb (Hb1), and a high-dose group, resuscitated with 500 mL of DCLHb (Hb2). Animals were observed for 210 minutes postresuscitation. Outcomes evaluated were cerebral oxygenation by measuring partial pressure and saturation of oxygen in cerebrovenous blood; cerebral function by evaluating the preservation and magnitude of cerebrovascular carbon dioxide reactivity; and brain structural damage by semiquantitatively assessing beta amyloid precursor protein positive axons.

RESULTS

Postresuscitation, cerebral perfusion pressure was higher in the DCLHb groups (p < 0.05, Hb1 and Hb2 vs. SAL), and intracranial pressure was lower in the Hb2 group (p < 0.05 vs. SAL). Cerebrovenous oxygen level was similar in all groups (p > 0.05). At baseline, 5% carbon dioxide evoked a 16 +/- 1% increase in cerebrovenous oxygen saturation, indicating vasodilatation. At 210 minutes, this response was nearly absent in SAL (4 +/- 4%) (p < 0.05 vs. baseline) and Hb1 (1 +/- 5%), but was partially preserved in Hb2 (9 +/- 5%). There was no intergroup difference in beta amyloid precursor protein positive axons. Five of 20 SAL and 0 of 13 DCLHb animals developed brain death (flat electroencephalogram) (p = 0.05, SAL vs. DCLHb). Postresuscitation, DCLHb animals maintained higher mean pulmonary arterial pressure (28 +/- 1 mm Hg, SAL; 42 +/- 1 mm Hg, Hb1; 45 +/- 1 mm Hg, Hb2) (p < 0.05, Hb1 and Hb2 vs. SAL) and lower cardiac output (3.9 +/- 1.6 L/min, SAL; 2.6 +/- 0.1 L/min, Hb1; 2.7 +/- 0.1 L/min, Hb2) (p < 0.05, Hb1 and Hb2 vs. SAL). Three Hb2 animals died as a result of cardiac failure, and one SAL animal died as a result of irreversible shock.

CONCLUSION

In this swine model of traumatic brain injury and hemorrhagic shock, resuscitation with DCLHb maintained a higher cerebral perfusion pressure. Low-dose DCLHb (minimal increase in oxygen carriage) failed to significantly improve short-term outcome. With high-dose DCLHb (significant improvement in oxygen carriage), intracranial pressure was lower and cerebrovascular carbon dioxide reactivity was partially preserved; however, this was at the cost of poorer cardiac performance secondary to high afterload.

Resuscitation with a novel hemoglobin-based oxygen carrier in a Swine model of uncontrolled perioperative hemorrhage

BACKGROUND

Systemic and pulmonary hypertension, possibly related to nitric oxide scavenging by free hemoglobin (Hb), is often seen during resuscitation with hemoglobin-based oxygen carriers (HBOCs). Recently, a second-generation HBOC, rHb2.0 for Injection (rHb), has been developed using recombinant human Hb that has reduced reactivity with nitric oxide. The current study evaluates the efficacy of this novel compound for resuscitation in a swine model of uncontrolled perioperative hemorrhage.

METHODS

After instrumentation, animals underwent splenectomy and rapid hemorrhage to a systolic blood pressure of 35 mm Hg and isoelectric electroencephalography. 15 minutes of shock was followed by resuscitation over 30 minutes. In phase I, 18 animals were randomized into three resuscitation groups: (1) lactated Ringer's (LR) equal to three times the shed blood, the negative control group; (2) heterologous blood (BL) equal to Hb 2 g/kg, the positive control group; and (3) rHb equal to 2 g/kg, the treatment group. In phase II, six animals underwent the same experiment with a first-generation HBOC, diaspirin cross-linked Hb (DCLHb) equal to 2 g/kg, an additional control group. On day 0 after 2 hours of observation, spontaneously breathing animals were returned to their cages. Surviving animals were redosed on days 1, 2, and 3 (rHb/DCLHb 1 g/kg; LR/BL-LR 500 mL). Survivors were killed on day 5 and organs harvested for histologic examination. Group comparisons were performed using Student's t test, repeated-measures analysis of variance, and chi2 test. Significance was set at 95% confidence intervals.

RESULTS

After resuscitation, systemic mean arterial pressure (MAP) (baseline = 107 +/- 15 mm Hg) was 128 +/- 34 and 108 +/- 15 mm Hg in rHb and BL animals, respectively, and remained stable. In LR and DCLHb animals, after normalization, MAP declined to 67 +/- 13 and 84 +/- 34 mm Hg, respectively. The rHb group maintained higher MAP than the LR and BL groups (p < 0.05 vs. both). With resuscitation, mean pulmonary arterial pressure (PAP) (baseline = 25 +/- 5 mm Hg) increased in rHb (40 +/- 4 mm Hg), BL (34 +/- 3 mm Hg), and DCLHb (40 +/- 3 mm Hg) groups, but stayed elevated only in the DCLHb group (36 +/- 3 mm Hg). PAP in the rHb group was similar to the BL group (p > 0.05), and both rHb and BL groups showed a higher PAP than the LR group (p < 0.05 vs. both). PAP was highest in the DCLHb group (p < 0.05 vs. rHb). Cardiac output of rHb and BL groups was similar (p > 0.05) throughout the observation period. Arterial lactate increased to 5.6 +/- 2.5 mmol/L with shock and then normalized to < 2.0 mmol/L in the rHb, BL, and LR groups within 30 minutes of resuscitation. It remained elevated to > 3.5 mmol/L and showed a delayed increase in the DCLHb group (p < 0.05). Causes and number of deaths were as follows: rHb, zero of six; BL-transfusion reaction, one of six; LR-irreversible shock, four of six; and DCLHb-ventricular failure, six of six. There was no significant increase in plasma methemoglobin (rHb) and no difference in liver or cardiac enzymes (rHb vs. BL). No histologic abnormalities were seen in the rHb group except for cytoplasmic vacuolation, a process thought to be related to metabolism of the test article.

CONCLUSION

rHb2.0 for Injection, a second-generation recombinant human HBOC, performs as well as heterologous blood for resuscitation after perioperative blood loss, does not cause sustained pulmonary hypertension, maintains adequate cardiac output and oxygen delivery, and is superior to either LR or DCLHb.

Resuscitation from severe hemorrhagic shock after traumatic brain injury using saline, shed blood, or a blood substitute

The original purpose of this study was to compare initial resuscitation of hemorrhagic hypotension after traumatic brain injury (TBI) with saline and shed blood. Based on those results, the protocol was modified and saline was compared to a blood substitute, diaspirin cross-linked hemoglobin (DCLHb). Two series of experiments were performed in anesthetized and mechanically ventilated (FiO2 = 0.4) pigs (35-45 kg). In Series 1, fluid percussion TBI (6-8 ATM) was followed by a 30% hemorrhage. At 120 min post-TBI, initial resuscitation consisted of either shed blood (n = 7) or a bolus of 3x shed blood volume as saline (n = 13). Saline supplements were then administered to all pigs to maintain a systolic arterial blood pressure (SAP) of >100 mmHg and a heart rate (HR) of <110 beats/min. In Series 2, TBI (4-5 ATM) was followed by a 35% hemorrhage. At 60 min post-TBI, initial resuscitation consisted of either 500 mL of DCLHb (n = 6) or 500 mL of saline (n = 5). This was followed by saline supplements to all pigs to maintain a SAP of >100 mmHg and a HR of <110 beats/min. In Series 1, most systemic markers of resuscitation (e.g., SAP, HR, cardiac output, filling pressures, lactate, etc.) were normalized, but there were 0/7 vs. 5/13 deaths within 5 h (P = 0.058) with blood vs. saline. At constant arterial O2 saturation (SaO2), mixed venous O2 saturation (SvO2), cerebral perfusion pressure (CPP), and cerebral venous O2 saturation (ScvO2) were all higher, intracranial pressure (ICP) was lower, and CO2 reactivity was preserved with blood vs. saline (all P < 0.05). In Series 2, SAP, ICP, CPP, and lactate were higher with DCLHb vs. saline (all P< 0.05). Cardiac output was lower even though filling pressure was markedly elevated with DCLHb vs. saline (both P< 0.05). Neither SvO2 nor cerebrovascular CO2 reactivity were improved, and ScvO2 was lower with DCLHb vs. saline (P < 0.05). All survived at least 72 h with neuropathologic changes that included sub-arachnoid hemorrhage, midline cerebellar necrosis, and diffuse axonal injury. These changes were similar with DCLHb vs. saline. Thus, whole blood was more effective than saline for resuscitation of TBI, whereas DCLHb was no more, and according to many variables, less effective than saline resuscitation. These experimental results are comparable to those in a recent multicenter trial using DCLHb for the treatment of severe traumatic shock. Further investigations in similar experimental models might provide some plausible explanations why DCLHb unexpectedly increased mortality in patients.

Noninvasive cardiac output by partial CO2 rebreathing after severe chest trauma

BACKGROUND

In multiple trauma patients, early continuous cardiac output (CCO) monitoring is frequently desired but is difficult to routinely employ in most emergency departments because it requires invasive procedures. Recently, a noninvasive cardiac output (NICO) technique based on the Fick principle and partial CO2 rebreathing has shown promise under a variety of conditions. Since this method has not been tested after lung damage, we evaluated its utility in a clinically relevant model.

METHODS

Anesthetized, ventilated swine (n = 11, 35-45 kg) received a unilateral blunt trauma via a captive bolt gun followed by a 25% hemorrhage. After 60 min of shock, crystalloid resuscitation was given as needed to maintain heart rate < 100 beats/min and mean arterial pressure > 70 mm Hg. Standard CCO by thermodilution (Baxter Vigilance, Irvine, CA) was compared with NICO (Novametrix Medical Systems Inc., Wallingford, CT) for 8 hr.

RESULTS

The severity of the injury is reflected by seven deaths (average survival time = 4.25 hr). Trauma increased dead space ventilation (19%), airway resistance (30%), and lactate (3.2 mmol/L), and decreased dynamic compliance (48%) and Pao2/Fio2 (54%). In these extreme conditions, the time course and magnitude of change of CCO and NICO were superimposed. Bland-Altman analysis reveal a bias and precision of 0.01 +/- 0.69 liters/min. The linear relationship between individual CCO and NICO values was significant (p < 0.0001) and was described by the equation NICO = (0.74 +/- 0.1)CCO + (0.65 +/- 0.16 liters/min) but the correlation coefficient (r2 = 0.541) was relatively low. The cause for the low correlation could not be attributed to increased pulmonary shunt, venous desaturation, anemia, hypercapnia, increased dead space ventilation, or hyperlactacidemia.

CONCLUSION

NICO correlated with thermodilution CCO, but underestimated this standard by 26% in extreme laboratory conditions of trauma-induced cardiopulmonary dysfunction; 95% of the NICO values fall within 1.38 liters/min of CCO; and with further improvements, NICO may be useful in multiple trauma patients requiring emergency intubation during initial assessment and workup.

Haemodynamic and volumetric monitoring during haemorrhagic shock in swine

Various studies have been performed concerning haemodynamics in the shock state. The aim of this study was to examine if a haemodynamic approach based on volumetric indices can offer a new method of evaluation. Volumetric measurements of ventricular filling and cardiac function were compared with classical haemodynamic variables during induced haemorrhagic shock in swine. Twelve hybrid swine were anaesthetized and underwent arteriectomy to induce haemorrhagic shock. Blood was collected in ACD treated bags and reinfused via the same vein after a shock period of 90 min. Haemodynamic and volume measurements were evaluated. Seven swine survived to complete the protocol and reached the final experimental time (90 min after reinfusion), while the remaining five died 1 h after reinfusion. Concerning the haemodynamics, afterload changes characterized the haemorrhagic shock period, while blood volume distribution dictated ventricular filling and ventricular kinetics during the post-reinfusion period. Systemic vascular resistance was different in the two groups. This study suggests that blood volumetric evaluations can offer better comparative data than pulmonary catheterisation for a precise assessment of cardiac output. Preload values have turned out to be of greater relevance than traditional pressure variables.

Macrophage cyclooxygenase expression, immunosuppression, and cardiopulmonary dysfunction after blunt chest trauma

BACKGROUND

Two series of experiments were performed in swine who received severe blunt chest trauma. The goals were to determine the time course of constitutive and inducible cyclooxygenase (COX) isozyme expression in pulmonary macrophages (Mphis), and to determine whether COX expression and cardiopulmonary dysfunction were altered when neutrophils (PMNs) were pharmacologically depleted with cyclophosphamide (CYC).

METHODS

In series 1 (n = 17), anesthetized, mechanically ventilated swine were subjected to right chest trauma via captive bolt gun, hemorrhage, and a 60-minute shock period. In series 2 (n = 41), CYC (50 mg/kg intravenously) was administered 4 days before trauma, and the shock period was shortened to 30 minutes. In both series, hemodynamic support and supplemental oxygen were provided for an additional 60 to 90 minutes after shock. Mphis were isolated from serial bilateral bronchoalveolar lavages (BALs) and COX protein expression was measured with Western blots.

RESULTS

In series 1, death occurred in 11 of 17. In survivors, Mphi COX-1 peaked at > 100 times baseline in both right BAL and left BAL by 60 minutes (before resuscitation). Changes in Mphi COX-2 were minimal. In series 2, before trauma, CYC (n = 16) reduced circulating and BAL PMNs by > 90% relative to control (n = 25, both p < 0.05) with no complicating side effects. After trauma, death occurred in 11 of 25 controls versus 9 of 16 with CYC. In survivors, PaO2/FIO2 was < 250 and PaCO2 was 25% higher on constant minute ventilation, indicating mismatched ventilation/perfusion; both changes were reduced with CYC (p < 0.05). In controls, bilateral histologic damage included edema, alveolar hemorrhage, and interstitial infiltrates. These changes were reduced by one third with CYC (p = 0.08). Trauma-induced changes in BAL protein, BAL elastase, or Mphi COX expression were not lessened by CYC.

CONCLUSION

After unilateral chest trauma, Mphi COX-1, not COX-2, is induced bilaterally and before fluid resuscitation; CYC prevented PMN infiltration and attenuated structural and functional changes after resuscitation, which suggests that PMNs have a role in the pathogenic mechanism of secondary lung injury; Mphi COX expression and other injury markers were not altered by CYC; and since Mphis continued to express proinflammatory COX protein even after pretreatment with a powerful nonspecific immunosuppressant, and since there is residual alveolar capillary damage even in the absence of PMNs, it is logical to conclude that no single cell type or mediator is a practical therapeutic target and that novel resuscitation strategies must address multiple elements in the inflammatory cascade.