Paula F. Moon-Massat

Nitroglycerin attenuates vasoconstriction of HBOC-201 during hemorrhagic shock resuscitation

BACKGROUND Vasoconstriction, an inherent property of Hemoglobin Based Oxygen Carriers (HBOC) potentially due to nitric oxide (NO) scavenging, may increase cardiovascular complications in HBOC resuscitated trauma patients. The purpose of this study was to determine if co-administration of a weak NO donor, intravenous nitroglycerin (NTG), with HBOC-201 during resuscitation from hemorrhagic shock could safely attenuate HBOC-201 vasoconstriction. METHODS AND RESULTS Hemorrhagic shock was induced in 44 swine randomized to receive fluid resuscitation with HBOC, HBOC+NTG10 mcg/kg/min, HBOC+NTG20 mcg/kg/min, HBOC+NTG40 mcg/kg/min, Hetastarch (HES), HES+NTG20 mcg/kg/min, NTG20 mcg/kg/min and Lactated Ringers (LR). HBOC resuscitation from hemorrhagic shock increased mean arterial pressure (MAP=94+/-33 mmHg), mean pulmonary artery pressure (MPAP=29+/-11 mmHg) and systemic vascular resistance (SVR=2684+/-871 dyns/cm(5)) in comparison to HES. Co-administration of NTG during HBOC resuscitation attenuated vasoconstriction with HBOC+40 mcg/kg/min demonstrating the most robust reduction in vasoconstriction (MAP=59+/-23 mmHg, MPAP=18+/-7 mmHg, and SVR=1827+/-511 dyns/cm(5)), although the effects were transient. Co-administration of NTG with HBOC did not alter base deficit, lactate, methemoglobin levels, nor cause profound hypotension during resuscitation. CONCLUSION Nitroglycerin attenuates vasoconstrictive properties of HBOC when co-administered during resuscitation in this swine model of hemorrhagic shock. Translational survival studies are required to determine if this strategy of attenuation of the vasoconstriction of HBOC-201 reduces cardiovascular complications and improves outcome with HBOC fluid resuscitation for hemorrhagic shock.

Regional blood flow after serial normovolemic exchange transfusion with HBOC-201 (Hemopure) in anesthetized swine.

BACKGROUND This study determined individual organ blood flows and global hemodynamic, oxygen delivery and consumption parameters after normovolemic exchange transfusions with the hemoglobin based oxygen carrier (HBOC)-201 in a lightly anesthetized swine model. METHODS The exchange transfusions were performed as a stepped reduction in blood volume to attain volume exchanges of 10%, 30%, and 50% with a 1:1 replacement with HBOC-201 (n = 8) or oncotically matched 5.9% human serum albumin (HSA, n = 8). Four additional animals served as time controls. RESULTS There was no change in the regional blood flows in 8 of 9 organs (brain, heart, kidney, liver, pancreas, gall bladder, small intestines, large intestines, and skeletal muscle) after HBOC-201 compared with controls; only skeletal muscle blood flow decreased. In contrast, with HSA, blood flow increased 150% to 200% of baseline in all organs except muscle where blood flow was unchanged. HBOC-201 effectively restored oxygen delivery after these exchanges. The mean arterial pressure increases in the HBOC-201 group were within 15% to 20% of baseline during the initial 10% exchange and similar to controls during subsequent exchanges. Although peak pulmonary arterial pressure increases in the HBOC-201 group were 10 mm Hg to 15 mm Hg above baseline, cardiac index was unchanged. There were no differences in global oxygen consumption, consistent with unchanged regional blood flow and suggests intact physiologic coupling of oxygen delivery and consumption that was unimpaired by local vasoconstriction. This is in contrast to significant changes of increased cardiac index, decreased arterial pressure, decreased oxygen content, and increased oxygen extraction ratio to maintain normal oxygen consumption in the HSA group. CONCLUSION Although the use of HBOC-201 caused alterations in systemic (minimal) and pulmonary (modest) pressures, these changes had no consequence on regional organ blood flow.

Fluid resuscitation of uncontrolled hemorrhage using a hemoglobin-based oxygen carrier: effect of traumatic brain injury.

ABSTRACT Animal models of combined traumatic brain injury (TBI) and hemorrhagic shock (HS) suggest a benefit of hemoglobin-based oxygen carrier (HBOC)–based resuscitation, but their use remains controversial, and little is known of the specific effects of TBI and high-pressure (large arterial injury) bleeding on resuscitation. We examine the effect of TBI and aortic tear injury on low-volume HBOC resuscitation in a swine polytrauma model and hypothesize that HBOC-based resuscitation will improve survival in the setting of aortic tear regardless of the presence of TBI. Anesthetized swine subjected to HS with aortic tear with or without fluid percussion TBI underwent equivalent limited resuscitation with HBOC, lactated Ringer’s solution, or HBOC + nitroglycerine (vasoattenuated HBOC) and were observed for 6 h. There was no independent effect of TBI on survival time after adjustment for fluid type, and there was no interaction between TBI and resuscitation fluid type. However, total catheter hemorrhage volume required to reach target shock blood pressure was less with TBI (14.0 mL · kg−1 [confidence interval, 12.4–15.6 mL · kg−1]) versus HS only (21.0 mL · kg−1 [confidence interval, 19.5–22.5 mL · kg−1]), with equivalent lactate accumulation. Traumatic brain injury did not affect survival in this polytrauma model, but less hemorrhage was required in the presence of TBI to achieve an equivalent degree of shock suggesting globally impaired cardiovascular response to hemorrhage in the presence of TBI. There was also no benefit of HBOC-based fluid resuscitation over lactated Ringer’s solution, contrary to models using liver injury as the source of hemorrhage, considering wound location is of paramount importance when choosing resuscitation strategy.

Differential Sensitivities of Pulmonary and Coronary Arteries to Hemoglobin-Based Oxygen Carriers and Nitrovasodilators: Study in a Bovine Ex Vivo Model of Vascular Strips

Vasoconstriction is a major adverse effect of first and second generation hemoglobin-based oxygen carriers (HBOCs) that hinders their development as blood substitute. However, intravenous infusion of HBOC-201 (second generation) to patients induces significant pulmonary hypertension without significant coronary vasoconstriction. We compared contractile responses of isolated bovine pulmonary and coronary arterial strips to HBOC-201 and HBOC-205LL.LT.MW600 (third generation), polymerized bovine hemoglobins of different molecular weight, and their attenuation by nitroglycerin, sodium nitroprusside (SNP), and sodium nitrite. Pulmonary arteries developed negligible basal tone, but exhibited HBOC-dependent amplification of phenylephrine-induced contractions. In contrast, coronary arteries developed significant basal tone, and exhibited HBOC-dependent constant force increment to serotonin-induced contractions. Therefore, relative to basal tone, HBOC-induced contractions were greater in pulmonary than coronary arteries. Furthermore, HBOC-205LL.LT.MW600 appeared to be less vasoactive than HBOC-201. Unexpectedly, pulmonary and coronary arteries exhibited differential sensitivities to nitrovasodilators in parallel with their differential sensitivities to HBOC. However, SNP and sodium nitrite induced significant methemoglobin formation from HBOC, whereas nitroglycerin did not. These results suggest that phenotypic differences between pulmonary and coronary vascular smooth muscle cells could explain the differential hypertensive effects of HBOC on pulmonary and coronary circulation in patients. Among the three nitrovasodilators investigated, nitroglycerin appears to be the most promising candidate for attenuating HBOC-induced pulmonary hypertension in older HBOCs.

Effects of a hemoglobin-based oxygen carrier (HBOC-201) and derivatives with altered oxygen affinity and viscosity on systemic and microcirculatory variables in a top-load rat model

The effects of a polymerized bovine hemoglobin-based oxygen carrier (HBOC) and two derivatives on arteriolar vasoactivity and tissue oxygen tension were explored by administering HBOC in a dose-response fashion to normovolemic rats. The effect of oxygen affinity (P50) and viscosity was also explored, where the P50 and viscosity of the parent compound (HBOC-201) and its modifications (MP50 and LP50A) were as follows: 40mmHg and 3.0cP (HBOC-20l); 18mmHg and 4.4cP (MP50); and 17mmHg and 12.1cP (LP50A). Anesthetized male Sprague-Dawley rats (N=32) were randomized to receive one of the HBOC solutions, and were administered four infusions that increased in concentration for each dose (2, 22, 230 and 780mg/kg, IV). Data were compared to rats receiving an equivalent volume for each of the four infusions (0.4, 0.4, 3.8, 13.1ml/kg, IV) of iso-oncotic 5.9% human serum albumin (HSA). Increasing doses of either HBOC solutions or HSA were associated with increasing MAP. Doses 3 and 4 of HBOC-201, MP50 and HSA produced significant increases in MAP, whereas similar increases began at a lower dose (Dose 2) with LP50A. There were no significant changes in arteriolar diameters at any dose for any group. Interstitial partial pressure of oxygen (ISF PO2) remained unchanged for HBOC-201, MP50 and HSA, but LP50A caused a significant decrease in ISF PO2 compared to baseline after Doses 3 and 4. In conclusion, there was no evidence that HBOC-201 would perform better with increased oxygen affinity (40 to 18mmHg) or viscosity (3.0 to 4.4cP).

Sodium nitroprusside ameliorates systemic but not pulmonary HBOC-201-induced vasoconstriction: an exploratory study in a swine controlled haemorrhage model.

BACKGROUND Vasoconstriction is a side effect that may prevent the use of haemoglobin based oxygen carrier (HBOC) as blood substitute. Therefore, we tested the hypothesis that the NO donor, sodium nitroprusside (SNP), would mitigate systemic and pulmonary hypertension associated with HBOC-201 in a simple controlled haemorrhage swine model. METHODS After 55% estimated blood volume withdrawal through a venous catheter, invasively anesthetized and instrumented animals were resuscitated with three 10 ml/kg infusions of either HBOC-201 or Hextend (HEX) with or without 0.8 μg/kg/min SNP (infused concomitantly via different lines). Haemodynamics, direct and indirect measures of tissue oxygenation, and coagulation were measured for 2h. RESULTS Haemorrhage caused a state of shock manifested by hypotension and base deficit. HBOC-201 resuscitation resulted in higher systemic (p<0.0001) and pulmonary (p<0.002) blood pressure than with HEX. Elevation of systemic (p<0.0001) but not pulmonary (p>0.05) arterial pressure was attenuated by co-infusion of SNP, without significant group differences in haemodynamics, tissue oxygenation, platelet function, coagulation, methaemoglobin, or survival (p>0.05). CONCLUSION In swine with haemorrhagic shock, co-administration of the NO donor, SNP, effectively and safely reduces HBOC-201-related systemic but not pulmonary vasoactivity. Interestingly, co-administration of the vasodilator SNP with HEX had no deleterious effects in comparison with HEX alone.

Dose Response of Sodium Nitrite on Vasoactivity Associated with HBOC-201 in a Swine Model of Controlled Hemorrhage

Abstract Sodium nitrite (NaNO2) was evaluated in a 55% EBV hemorrhage swine model to mitigate the increased blood pressure due to HBOC-201. Animals were resuscitated by three 10ml/kg infusions of either HBOC-201 or Hextend with and without NaNO2. All vital signs, coagulation and blood chemistry were measured for 2hr. HBOC-201-vasoconstriction was attenuated only after the first 10.8μmol/kg NaNO2 infusion. Complete abolition was obtained with the highest 3 NaNO2 dose, but side effects were observed. There was no reduction in platelet function due to NaNO2. NaNO2 ability to reduce HBOC-201 vasoactivity was transient and 10.8μmol/kg NaNO2 seems an acceptable dose for further investigation.

Perfluorocarbon NVX-108 increased cerebral oxygen tension after traumatic brain injury in rats.

BACKGROUND Hypoxia is a critical secondary injury mechanism in traumatic brain injury (TBI), and early intervention to alleviate post-TBI hypoxia may be beneficial. NVX-108, a dodecafluoropentane perfluorocarbon, was screened for its ability to increase brain tissue oxygen tension (PbtO2) when administered soon after TBI. METHODS Ketamine-acepromazine anesthetized rats ventilated with 40% oxygen underwent moderate controlled cortical impact (CCI)-TBI at time 0 (T0). Rats received either no treatment (NON, n=8) or 0.5 ml/kg intravenous (IV) NVX-108 (NVX, n=9) at T15 (15 min after TBI) and T75. RESULTS Baseline cortical PbtO2 was 28±3 mm Hg and CCI-TBI resulted in a 46±6% reduction in PbtO2 at T15 (P<0.001). Significant differences in time-group interactions (P=0.013) were found when comparing either absolute or percentage change of PbtO2 to post-injury (mixed-model ANOVA) suggesting that administration of NVX-108 increased PbtO2 above injury levels while it remained depressed in the NON group. Specifically in the NVX group, PbtO2 increased to a peak 143% of T15 (P=0.02) 60 min after completion of NVX-108 injection (T135). Systemic blood pressure was not different between the groups. CONCLUSION NVX-108 caused an increase in PbtO2 following CCI-TBI in rats and should be evaluated further as a possible immediate treatment for TBI.

Effects of Top-Loading a Zero-Link Bovine Hemoglobin, OxyVita, on Systemic and Microcirculatory Variables

This study was designed to test the effect of top-load infusions of increasing doses of two versions of the novel, high molecular weight hemoglobin-based oxygen carrier, OxyVita and OxyVita C solution ([Hb] = 6 g/dL), on mean arterial pressure (MAP), arteriolar diameter, and tissue oxygenation. Experiments were carried out on 18 anesthetized male Sprague-Dawley rats in which microcirculatory observations were made on the spinotrapezius muscle. Intravenous infusions of four increasing doses of the OxyVita solutions (2, 22, 230, and 780 mg/kg) were made for each group, and a separate group of animals was used for volume control. Tissue oxygenation was measured as interstitial fluid (ISF) PO2 using phosphorescence quenching microscopy. Increasing doses of either OxyVita solution or Lactated Ringers solution (LRS, volume control) were associated with increasing MAP. For LRS infusions, MAP returned to baseline between each incremental dose injected, whereas there was an incomplete return for either of the OxyVita solutions. ISF PO2 for OxyVita was significantly lower than that for either LRS or OxyVita C, whereas ISF PO2 for OxyVita C was never statistically different from LRS. There were no significant changes in arteriolar diameters for LRS and either of the OxyVita solutions.

Effects of N-Acetyl-L-Cysteine and Hyaluronic Acid on HBOC-201- Induced Systemic and Cerebral Vasoconstriction in the Rat

Hemoglobin-based oxygen carrier-201 (HBOC) was developed as a resuscitative fluid but concerns exist over potentially adverse vasoconstriction. This study evaluated whether concurrent IV (intra venous) N-acetyl-L-cysteine (NAC) or hyaluronic acid (HA) would attenuate HBOC-associated vasoconstriction, assessed by systemic blood pressures and cerebral pial microvasculature, when administered to healthy, anesthetized rats. Rats (8-9/group) received a 30 min infusion of 3 ml/kg HBOC, HBOC plus 600 mg/kg NAC (HBOC/NAC), HBOC plus 1.5 mg/kg HA (HBOC/HA) or 3 ml/kg Albumin. Mean (MAP) and systolic (SBP) blood pressures, blood chemistries and cerebral pial vessel diameters were measured at baseline, end of infusion, and intermittently for an additional 90 min. HBOC caused immediate and sustained increases in SBP and MAP (35.3 ± 3.6 and 29.1 ± 2.5 mm Hg peak increases above baseline, respectively; mean ± SEM) and immediate but progressive vasoconstriction (11 µm maximum reduction) in medium-sized (50-100 µm) pial arterioles. When NAC was co-administered, blood pressure changes were attenuated and vessel changes were abolished. Similar trends were noted with co-administration of HA but were not statistically different from HBOC-alone. Small-sized (< 50 µm) pial vessels and blood parameters showed no differences from baseline or among groups. No adverse clinical signs were observed. We demonstrated that it is possible for adjuvant drugs to reduce the vasoconstriction associated with HBOC-201. Coinfusion of the anti-oxidant NAC mitigated HBOC-201-associated increases in blood pressures and vasoconstriction in medium-sized cerebral pial vessels. The drag-reducing polymer HA may be more effective at a higher dose as a similar but non-significant trend was observed.