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

Cerebral Vasoactivity and Oxygenation with Oxygen Carrier M101 in Rats

The severity of traumatic brain injury (TBI) may be reduced if oxygen can be rapidly provided to the injured brain. This study evaluated if the oxygen-carrier M101 causes vasoconstricton of pial vasculature in healthy rats (Experiment 1) and if M101 improves brain tissue oxygen (PbtO₂) in rats with controlled cortical impact (CCI)-TBI (Experiment 2). M101 (12.5 mL/kg intravenous [IV] over 2 h) caused a mild (9 mm Hg) increase in the mean arterial blood pressure (MAP) of healthy rats without constriction of cerebral pial arterioles. M101 (12 mL/kg IV over 1 h) caused a modest (27 mm Hg) increase in MAP (peak, 123 ± 5 mm Hg [mean ± standard error of the mean]) of CCI-TBI rats and restored PbtO₂ to near pre-injury levels. In both M101 and untreated control (NON) groups, PbtO₂ was ∼30 ± 2 mm Hg pre-injury and decreased (p ≤ 0.05) to ∼16 ± 2 mm Hg 15 min after CCI. In NON, PbtO₂ remained ∼50% of baseline but M101 administration resulted in a sustained increase in PbtO₂ (peak, 25 ± 5 mm Hg), which was not significantly different from pre-injury until the end of the study, when it decreased again below pre-injury (but was still higher than NON). Histopathology showed no differences between groups. In conclusion, M101 increased systemic blood pressures without concurrent cerebral pial vasoconstriction (in healthy rats) and restored PbtO₂ to 86% of pre-injury for at least 80 min when given soon after CCI-TBI. M101 should be evaluated in a clinically-relevant large animal model for pre-hospital treatment of TBI.

Sanguinate's effect on pial arterioles in healthy rats and cerebral oxygen tension after controlled cortical impact

Sanguinate, a polyethylene glycol-conjugated carboxyhemoglobin, was investigated for cerebral vasoactivity in healthy male Sprague-Dawley rats (Study 1) and for its ability to increase brain tissue oxygen pressure (PbtO2) after controlled cortical impact (CCI) - traumatic brain injury (TBI) (Study 2). In both studies ketamine-acepromazine anesthetized rats were ventilated with 40% O2. In Study 1, a cranial window was used to measure the diameters of medium - (50-100μm) and small-sized (<50μm) pial arterioles before and after four serial infusions of Sanguinate (8mL/kg/h, cumulative 16mL/kg IV), volume-matched Hextend, or normal saline. In Study 2, PbtO2 was measured using a phosphorescence quenching method before TBI, 15min after TBI (T15) and then every 10min thereafter for 155min. At T15, rats received either 8mL/kg IV Sanguinate (40mL/kg/h) or no treatment (saline, 4mL/kg/h). Results showed: 1) in healthy rats, percentage changes in pial arteriole diameter were the same among the groups, 2) in TBI rats, PbtO2 decreased from 36.5±3.9mmHg to 19.8±3.0mmHg at T15 in both groups after TBI and did not recover in either group for the rest of the study, and 3) MAP increased 16±4mmHg and 36±5mmHg after Sanguinate in healthy and TBI rats, respectively, while MAP was unchanged in control groups. In conclusion, Sanguinate did not cause vasoconstriction in the cerebral pial arterioles of healthy rats but it also did not acutely increase PbtO2 when administered after TBI. Sanguinate was associated with an increase in MAP in both studies.

The lack of consistent diaspirin cross-linked hemoglobin infusion blood pressure effects in the US and EU traumatic hemorrhagic shock clinical trials

Hemoglobin solutions have demonstrated a pressor effect that could adversely affect hemorrhagic shock patient resuscitation through accelerated hemorrhage, diminished perfusion, or inadequate resuscitation. Data from two parallel, multicenter traumatic hemorrhagic shock clinical trials in 17 US emergency departments and in 27 EU prehospital systems using diaspirin cross-linked hemoglobin (DCLHb), a hemoglobin-based resuscitation fluid. In the 219 patients, patients were 37 years old, 64% sustained blunt injury, 48% received DCLHb, and 36% expired. Although mean systolic blood pressure (SBP) and diastolic blood pressure values differed at 2 of the 10 measured time points, blood pressure (BP) curve analysis showed no SBP, diastolic blood pressure, or MAP differences based on treatment. Although SBP values 160 and 120 mmHg or greater were 2.2x and 2.6x more frequently noted in survivors, they were not more common with DCLHb use or in DCLHb patients who expired in US study nonsurvivors or in any EU study patients. Systolic blood pressure values 160 and 120 mmHg or greater were 2.8x and 1.3x more frequently noted in DCLHb survivors as compared with normal saline survivors. Only 3% of the BP variation noted could be attributed to DCLHb use, and as expected, injury severity and baseline physiologic status were stronger predictors. In the United States alone, treatment group was not correlated by regression with BP at any time point. Neither mean BP readings nor elevated BP readings were correlated with DCLHb treatment of traumatic hemorrhagic shock patients. As such, no clinically demonstrable DCLHb pressor effect could be directly related to the adverse mortality outcome observed in the US study.

Inhaled nitric oxide enables artificial blood transfusion without hypertension

BACKGROUND

One of the major obstacles hindering the clinical development of a cell-free, hemoglobin-based oxygen carrier (HBOC) is systemic vasoconstriction.

METHODS AND RESULTS

Experiments were performed in healthy mice and lambs by infusion of either murine tetrameric hemoglobin (0.48 g/kg) or glutaraldehyde-polymerized bovine hemoglobin (HBOC-201, 1.44 g/kg). We observed that intravenous infusion of either murine tetrameric hemoglobin or HBOC-201 induced prolonged systemic vasoconstriction in wild-type mice but not in mice congenitally deficient in endothelial nitric oxide (NO) synthase (NOS3). Treatment of wild-type mice by breathing NO at 80 ppm in air for 15 or 60 minutes or with 200 ppm NO for 7 minutes prevented the systemic hypertension induced by subsequent intravenous administration of murine tetrameric hemoglobin or HBOC-201 and did not result in conversion of plasma hemoglobin to methemoglobin. Intravenous administration of sodium nitrite (48 nmol) 5 minutes before infusion of murine tetrameric hemoglobin also prevented the development of systemic hypertension. In awake lambs, breathing NO at 80 ppm for 1 hour prevented the systemic hypertension caused by subsequent infusion of HBOC-201.

CONCLUSIONS

These findings demonstrate that HBOC can cause systemic vasoconstriction by scavenging NO produced by NOS3. Moreover, in 2 species, inhaled NO administered before the intravenous infusion of HBOC can prevent systemic vasoconstriction without causing methemoglobinemia.

Blood substitutes: hemoglobin-based oxygen carriers

Blood product substitutes, particularly the hemoglobin-based oxygen carriers, represent one of the most exciting fields of research and development in modern medicine. The concept has been several decades in the making, and with products in phase III clinical trials, the use of hemoglobin-based oxygen carriers may be close to reality. The potential applications are limitless with interest from the military and civilian sectors.

Severe hemodilutional anemia increases cerebral tissue injury following acute neurotrauma

Anemia may worsen neurological outcomes following traumatic brain injury (TBI) by undefined mechanisms. We hypothesized that hemodilutional anemia accentuates hypoxic cerebral injury following TBI. Anesthetized rats underwent unilateral TBI or sham injury (n > or = 7). Target hemoglobin concentrations between 50 and 70 g/l were achieved by exchanging 40-50% of the blood volume (1:1) with pentastarch. The effect of TBI, anemia, and TBI-anemia was assessed by measuring brain tissue oxygen tension (Pbr(O(2))), regional cerebral blood flow (rCBF), jugular venous oxygen saturation (Sjv(O(2))), cerebral contusion area, and nuclear staining for programmed cell death. Baseline postinjury Pbr(O(2)) values in the TBI and TBI-anemia groups (9.3 +/- 1.3 and 11.3 +/- 4.1 Torr, respectively) were lower than the uninjured controls (18.2 +/- 5.2 Torr, P < 0.05 for both). Hemodilution caused a further reduction in Pbr(O(2)) in the TBI-anemia group relative to the TBI group without anemia (7.8 +/- 2.7 vs. 14.8 +/- 3.9 Torr, P < 0.05). The rCBF remained stable after TBI and increased comparably after hemodilution in both anemia and TBI-anemia groups. The Sjv(O(2)) was elevated after TBI (87.4 +/- 8.9%, P < 0.05) and increased further following hemodilution (95.0 +/- 1.6%, P < 0.05). Cerebral contusion area and nuclear counts for programmed cell death were increased following TBI-anemia (4.1 +/- 3.0 mm(2) and 686 +/- 192, respectively) relative to TBI alone (1.3 +/- 0.3 mm(2) and 404 +/- 133, respectively, P < 0.05 for both). Hemodilutional anemia reduced cerebral Pbr(O(2)) and oxygen extraction and increased cell death following TBI. These results support our hypothesis that acute anemia accentuated hypoxic cerebral injury after neurotrauma.

Direct cerebral oxygenation monitoring--a systematic review of recent publications

This review has been compiled to assess publications related to the clinical application of direct cerebral tissue oxygenation (PtiO2) monitoring published in international, peer-reviewed scientific journals. Its goal was to extract relevant, i.e. positive and negative information on indications, clinical application, safety issues and impact on clinical situations as well as treatment strategies in neurosurgery, neurosurgical anaesthesiology, neurosurgical intensive care, neurology and related specialties. For completeness' sake it also presents some related basic science research. PtiO2 monitoring technology is a safe and valuable cerebral monitoring device in neurocritical care. Although a randomized outcome study is not available its clinical utility has repeatedly been clearly confirmed because it adds a monitoring parameter, independent from established cerebral monitoring devices. It offers new insights into cerebral physiology and pathophysiology. Pathologic values have been established in peer-reviewed research, which are not only relevant to outcome but are treatable. The benefits clearly outweigh the risks, which remains unchallenged in all publications retrieved. It is particularly attractive because it offers continuous, real-time data and is available at the bedside.

Electrophoretic, size-exclusion high-performance liquid chromatography and liquid chromatography-electrospray ionization ion trap mass spectrometric detection of hemoglobin-based oxygen carriers

Hemoglobin-based oxygen carriers (HBOCs) are blood substitutes based on hemoglobin of either bovine or human origin and they can potentially be misused in elite sports to improve endurance performance. Recently, three methods have been proposed in doping control analysis to allow HBOCs screening and identification by application of electrophoresis, size-exclusion chromatography coupled with HPLC and LC coupled with tandem mass spectrometry (LC/MSMS). In view of the Athens 2004 Olympic Games, modifications were introduced in order to increase the specificity of these methods. The sample preparation protocols of the electrophoretic and SEC-HPLC methods were modified with the introduction of sequential ultra filtration steps to remove all heme containing material below 100 kDa, thus leaving only HBOCs material for analysis. Furthermore, a modification of the LC/MSMS methodology was introduced to allow full scan MS-MS spectra of peptide segments arising from the tryptic digestion of bovine HBOCs. These relatively simple methodological modifications have major impact, as far as time and cost effectiveness is concerned in doping control procedures, because they provide a useful tool in order to identify which suspect samples from the initial visual screening are due to hemolysis and exclude them from further analysis.

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.

A hemoglobin-based oxygen carrier, bovine polymerized hemoglobin (HBOC-201) versus hetastarch (HEX) in a moderate severity hemorrhagic shock swine model with delayed evacuation

OBJECTIVE

To evaluate the efficacy of HBOC-201 for resuscitation of hemorrhagic shock in a swine model incorporating soft tissue injury and delayed evacuation.

METHODS

A muscle crush injury and 40% estimated blood volume controlled hemorrhage was completed in 24 Yucatan mini-pigs. Pigs were untreated or resuscitated with HBOC-201 or 6% hetastarch (HEX) at 20 min. Invasive hemodynamics and clinical variables were monitored for 4 h (pre-hospital phase) and subsequent fluid infusions were administered for severe hypotension or tachycardia. Animals were recovered from anesthesia and monitored non-invasively to 72 h (hospital phase).

RESULTS

100% (8/8) of HBOC-201-, 88% (7/8) of HEX-, and 63% (5/8) of non-resuscitated pigs, survived to 72 h (p=0.27). Mean arterial pressure, mean pulmonary arterial pressure and systemic vascular resistance index were higher in HBOC-201 pigs. By 90 min, cardiac index was restored to baseline in the HBOC-201 group and was 1.4-fold greater than baseline in the HEX group. HBOC-201 pigs had lower fluid requirements than HEX pigs (18.8+/-1.8 and 29.9+/-1.1 ml/kg, p<0.001) in the pre-hospital phase and required fewer blood transfusions (1.3+/-1.3 and 9.4+/-0.6 ml/kg, respectively, p<0.001) in the hospital phase. Urine output and blood creatinine were comparable in HBOC-201 and HEX pigs. Tissue oxygenation levels were highest in the HBOC-201 group.

CONCLUSIONS

As HBOC-201 restored hemodynamics and tissue oxygenation and decreased fluid requirements, in comparison with HEX, HBOC-201 was at least as efficacious and possibly a superior resuscitative fluid in a military-relevant delayed evacuation hemorrhagic shock swine model.