Uncontrolled hemorrhage differs from volume- or pressure-matched controlled hemorrhage in swine

Development of a two-hit lethal liver injury model in swine

PURPOSE

Noncompressible truncal hemorrhage remains a leading cause of preventable death in the prehospital setting. Standardized and reproducible large animal models are essential to test new therapeutic strategies. However, existing injury models vary significantly in consistency and clinical accuracy. This study aims to develop a lethal porcine model to test hemostatic agents targeting noncompressible abdominal hemorrhages.

METHODS

We developed a two-hit injury model in Yorkshire swine, consisting of a grade IV liver injury combined with hemodilution. The hemodilution was induced by controlled exsanguination of 30% of the total blood volume and a 3:1 resuscitation with crystalloids. Subsequently, a grade IV liver injury was performed by sharp transection of both median lobes of the liver, resulting in major bleeding and severe hypotension. The abdominal incision was closed within 60 s from the injury. The endpoints included mortality, survival time, serum lab values, and blood loss within the abdomen.

RESULTS

This model was lethal in all animals (5/5), with a mean survival time of 24.4 ± 3.8 min. The standardized liver resection was uniform at 14.4 ± 2.1% of the total liver weight. Following the injury, the MAP dropped by 27 ± 8mmHg within the first 10 min. The use of a mixed injury model (i.e., open injury, closed hemorrhage) was instrumental in creating a standardized injury while allowing for a clinically significant hemorrhage.

CONCLUSION

This novel highly lethal, consistent, and clinically relevant translational model can be used to test and develop life-saving interventions for massive noncompressible abdominal hemorrhage.

Impact of Immunopathy and Coagulopathy on Multi-Organ Failure and Mortality in a Lethal Porcine Model of Controlled and Uncontrolled Hemorrhage

Uncontrolled hemorrhage is a major preventable cause of death in patients with trauma. However, the majority of large animal models of hemorrhage have utilized controlled hemorrhage rather than uncontrolled hemorrhage to investigate the impact of immunopathy and coagulopathy on multi-organ failure (MOF) and mortality. This study evaluates these alterations in a severe porcine controlled and uncontrolled hemorrhagic shock (HS) model. Anesthetized female swine underwent controlled hemorrhage and uncontrolled hemorrhage by partial splenic resection followed with or without lactated Ringer solution (LR) or Voluven® resuscitation. Swine were surveyed 6 h after completion of splenic hemorrhage or until death. Blood chemistry, physiologic variables, systemic and tissue levels of complement proteins and cytokines, coagulation parameters, organ function, and damage were recorded and assessed. HS resulted in systemic and local complement activation, cytokine release, hypocoagulopathy, metabolic acidosis, MOF, and no animal survival. Resuscitation with LR and Voluven® after HS improved hemodynamic parameters (MAP and SI), metabolic acidosis, hyperkalemia, and survival but resulted in increased complement activation and worse coagulopathy. Compared with the LR group, the animals with hemorrhagic shock treated with Voluven® had worse dilutional anemia, coagulopathy, renal and hepatic dysfunction, increased myocardial complement activation and renal damage, and decreased survival rate. Hemorrhagic shock triggers early immunopathy and coagulopathy and appears associated with MOF and death. This study indicates that immunopathy and coagulopathy are therapeutic targets that may be addressed with a high-impact adjunctive treatment to conventional resuscitation.

Dynamic Aortic Pressure Augmentation as a Novel Method of Swine Terminal Blood Extraction

INTRODUCTION

Uncontrolled hemorrhage models require sufficient quantities of donor blood products to support resuscitation. To that end, we describe a novel method of whole blood extraction from donor swine using resuscitative endovascular balloon occlusion of the aorta (REBOA) to support hemodynamics during terminal blood extraction and its impact on the quality of banked blood.

METHODS

Ten adult Yorkshire-cross swine were anesthetized and instrumented with an REBOA catheter, femoral multistage venous cannula, and proximal/distal blood pressure monitoring. Hemodynamics during terminal blood extraction was supported with hand-titrated partial REBOA. Blood samples were taken at set time points for analysis.

RESULTS

The median collected blood volume was 3912 mL, with all animals surviving through the planned blood collection of 60% estimated total blood volume (ETBV). Median lactate and potassium levels remained within normal limits for swine through collection of 40% of the ETBV. Median hemoglobin through collection of 40% ETBV did not significantly change from values measured at the start of hemorrhage.

CONCLUSIONS

This method of whole blood extraction provided sufficient blood volume and blood quality appropriate for transfusion through 40% ETBV, with remaining collected blood likely still acceptable for allogeneic transfusion despite increased lactate levels. This method of whole blood extraction can efficiently provide a large volume of quality blood to support resuscitation for subsequent uncontrolled hemorrhage models.

Early warning: End-tidal carbon dioxide is associated with central venous oxygenation under continuous cardiorespiratory monitoring in a porcine model of hemorrhagic shock and resuscitation

BACKGROUND

End-tidal carbon dioxide (ETCO2) has previously shown promise as a predictor of shock severity and mortality in trauma. ETCO2 monitoring is non-invasive, real-time, and readily available in prehospital settings, but the temporal relationship of ETCO2 to systemic oxygen transport has not been thoroughly investigated in the context of hemorrhagic shock.

METHODS

A validated porcine model of hemorrhagic shock and resuscitation was used in male Yorkshire swine (N ​= ​7). Both ETCO2 and central venous oxygenation (SCVO2) were monitored and recorded continuously in addition to other traditional hemodynamic variables.

RESULTS

Linear regression analysis showed that ETCO2 was associated with ScvO2 both throughout the experiment (β ​= ​1.783, 95% confidence interval (CI) [1.552-2.014], p ​< ​0.001) and during the period of most rapid hemorrhage (β ​= ​4.896, 95% CI [2.416-7.377], p ​< ​0.001) when there was a marked decrease in ETCO2.

CONCLUSIONS

ETCO2 and ScvO2 were closely associated during rapid hemorrhage and continued to be temporally associated throughout shock and resuscitation.

Experimental Models of Traumatic Injuries: Do They Capture the Coagulopathy and Underlying Endotheliopathy Induced by Human Trauma?

Trauma-induced coagulopathy (TIC) is a major cause of morbidity and mortality in patients with traumatic injury. It describes the spectrum of coagulation abnormalities that occur because of the trauma itself and the body's response to the trauma. These coagulation abnormalities range from hypocoagulability and hyperfibrinolysis, resulting in potentially fatal bleeding, in the early stages of trauma to hypercoagulability, leading to widespread clot formation, in the later stages. Pathological changes in the vascular endothelium and its regulation of haemostasis, a phenomenon known as the endotheliopathy of trauma (EoT), are thought to underlie TIC. Our understanding of EoT and its contribution to TIC remains in its infancy largely due to the scarcity of experimental research. This review discusses the mechanisms employed by the vascular endothelium to regulate haemostasis and their dysregulation following traumatic injury before providing an overview of the available experimental in vitro and in vivo models of trauma and their applicability for the study of the EoT and its contribution to TIC.

Effects of hemodilution on coagulation function during prolonged hypotensive resuscitation in a porcine model of severe hemorrhagic shock

Background

Although hemorrhage remains the leading cause of survivable death in casualties, modern conflicts are becoming more austere limiting available resources to include resuscitation products. With limited resources also comes prolonged evacuation time, leaving suboptimal prehospital field care conditions. When blood products are limited or unavailable, crystalloid becomes the resuscitation fluid of choice. However, there is concern of continuous crystalloid infusion during a prolonged period to achieve hemodynamic stability for a patient. This study evaluates the effect of hemodilution from a 6-hour prehospital hypotensive phase on coagulation in a porcine model of severe hemorrhagic shock.

Methods

Adult male swine (n=5/group) were randomized into three experimental groups. Non-shock (NS)/normotensive did not undergo injury and were controls. NS/permissive hypotensive (PH) was bled to the PH target of systolic blood pressure (SBP) 85±5 mm Hg for 6 hours of prolonged field care (PFC) with SBP maintained via crystalloid, then recovered. Experimental group underwent controlled hemorrhage to mean arterial pressure 30 mm Hg until decompensation (Decomp/PH), followed by PH resuscitation with crystalloid for 6 hours. Hemorrhaged animals were then resuscitated with whole blood and recovered. Blood samples were collected at certain time points for analysis of complete blood counts, coagulation function, and inflammation.

Results

Throughout the 6-hour PFC, hematocrit, hemoglobin, and platelets showed significant decreases over time in the Decomp/PH group, indicating hemodilution, compared with the other groups. However, this was corrected with whole blood resuscitation. Despite the appearance of hemodilution, coagulation and perfusion parameters were not severely compromised.

Conclusions

Although significant hemodilution occurred, there was minimal impact on coagulation and endothelial function. This suggests that it is possible to maintain the SBP target to preserve perfusion of vital organs at a hemodilution threshold in resource-constrained environments. Future studies should address therapeutics that can mitigate potential hemodilutional effects such as lack of fibrinogen or platelets.

Level of evidence

Not applicable-Basic Animal Research.

An Automated Hardware-in-Loop Testbed for Evaluating Hemorrhagic Shock Resuscitation Controllers

Hemorrhage remains a leading cause of death, with early goal-directed fluid resuscitation being a pillar of mortality prevention. While closed-loop resuscitation can potentially benefit this effort, development of these systems is resource-intensive, making it a challenge to compare infusion controllers and respective hardware within a range of physiologically relevant hemorrhage scenarios. Here, we present a hardware-in-loop automated testbed for resuscitation controllers (HATRC) that provides a simple yet robust methodology to evaluate controllers. HATRC is a flow-loop benchtop system comprised of multiple PhysioVessels which mimic pressure-volume responsiveness for different resuscitation infusates. Subject variability and infusate switching were integrated for more complex testing. Further, HATRC can modulate fluidic resistance to mimic arterial resistance changes after vasopressor administration. Finally, all outflow rates are computer-controlled, with rules to dictate hemorrhage, clotting, and urine rates. Using HATRC, we evaluated a decision-table controller at two sampling rates with different hemorrhage scenarios. HATRC allows quantification of twelve performance metrics for each controller configuration and scenario, producing heterogeneous results and highlighting the need for controller evaluation with multiple hemorrhage scenarios. In conclusion, HATRC can be used to evaluate closed-loop controllers through user-defined hemorrhage scenarios while rating their performance. Extensive controller troubleshooting using HATRC can accelerate product development and subsequent translation.

The Story of Blood for Shock Resuscitation: How the Pendulum Swings

Whole blood transfusion (WBT) began in 1667 as a treatment for mental illness, with predictably poor results. Its therapeutic utility and widespread use were initially limited by deficiencies in transfusion science and antisepsis. James Blundell, a British obstetrician, was recognized for the first allotransfusion in 1825. However, WBT did not become safe and therapeutic until the early 20th century, with the advent of reliable equipment, sterilization, and blood typing. The discovery of citrate preservation in World War I allowed a separation of donor from recipient and introduced the practice of blood banking. During World War II, Elliott and Strumia were the first to separate whole blood into blood component therapy (BCT), producing dried plasma as a resuscitative product for "traumatic shock." During the 1970s, infectious disease, blood fractionation, and financial opportunities further drove the change from WBT to BCT, with few supporting data. Following a period of high-volume crystalloid and BCT resuscitation well into the early 2000s, measures to avoid the resulting iatrogenic resuscitation injury were developed under the concept of damage control resuscitation. Modern transfusion strategies for hemorrhagic shock target balanced BCT to reapproximate whole blood. Contemporary research has expanded the role of WBT to therapy for the acute coagulopathy of trauma and the damaged endothelium. Many US trauma centers are now using WBT as a front-line treatment in tandem with BCT for patients suffering hemorrhagic shock. Looking ahead, it is likely that WBT will once again be the resuscitative fluid of choice for patients in hemorrhagic shock.

Evaluation of a novel hydrogel intravascular embolization agent in a swine model of fatal uncontrolled solid organ hemorrhage and coagulopathy

Introduction

Current agents for the intravascular embolization of traumatic hemorrhage are used off-label and have been minimally studied with respect to their performance under differing coagulation conditions. We studied the hemorrhage control efficacy of a novel, liquid, polyethylene glycol-based hydrogel delivered as two liquid precursors that polymerize within the target vessel in a unique animal model of severe solid organ injury with and without dilutional coagulopathy.

Methods

Anesthetized swine (n = 36, 45 ± 3 kg) had laparotomy and splenic externalization. Half underwent 50% isovolemic hemodilution with 6% hetastarch and cooling to 33°C-35°C (coagulopathic group). All animals had controlled 20 mL/kg hemorrhage and endovascular proximal splenic artery access with a 4F catheter via a right femoral sheath. Splenic transection and 5-minute free bleeding were followed by treatment (n = 5/group) with 5 mL of gelfoam slurry, three 6-mm coils, up to 6 mL of hydrogel, or no treatment (n = 3, control). Animals received 15 mL/kg plasma and were monitored for 6 hours with continuous blood loss measurement.

Results

Coagulopathy was successfully established, with coagulopathic animals having greater pretreatment blood loss and earlier mean time to death regardless of the treatment group. All control animals died within 100 minutes. Overall survival without coagulopathy was 5/5 for hydrogel, 4/5 for coil, and 3/5 for gelfoam. With coagulopathy, one hydrogel animal survived to the end of the experiment, with 2/4 hydrogel deaths occurring in the final hour of observation. In noncoagulopathic animals, hydrogel demonstrated improved survival time (P < .01) and post-treatment blood loss (1.46 ± 0.8 mL/kg) over controls (18.8 ± 0.7, P = .001), gelfoam (4.7 ± 1.3, P > .05), and coils (4.6 ± 1.5, P > .05). In coagulopathic animals, hydrogel had improved survival time (P = .003) and decreased blood loss (4.2 ± 0.8 mL/kg) compared with control (20.4 ± 4.2, P = .003).

Conclusions

The hydrogel demonstrated equivalent hemorrhage control performance to standard treatments under noncoagulopathic conditions and improved performance in the face of dilutional coagulopathy. This agent should be explored as a potential preferable treatment for the embolization of traumatic solid organ and other injuries. (JVS–Vascular Science 2021;2:43-51.)

Clinical Relevance

In a translational model of severe solid organ injury hemorrhage with and without coagulopathy, a novel hydrogel transarterial embolization agent demonstrated equivalent hemorrhage control performance to standard agents under noncoagulopathic conditions and improved performance in the face of dilutional coagulopathy. This agent represents a promising future treatment for the embolization of traumatic solid organ and other injuries.

Hemodynamic Parameters in the Assessment of Fluid Status in a Porcine Hemorrhage and Resuscitation Model

BACKGROUND

Measuring fluid status during intraoperative hemorrhage is challenging, but detection and quantification of fluid overload is far more difficult. Using a porcine model of hemorrhage and over-resuscitation, it is hypothesized that centrally obtained hemodynamic parameters will predict volume status more accurately than peripherally obtained vital signs.

METHODS

Eight anesthetized female pigs were hemorrhaged at 30 ml/min to a blood loss of 400 ml. After each 100 ml of hemorrhage, vital signs (heart rate, systolic blood pressure, mean arterial pressure, diastolic blood pressure, pulse pressure, pulse pressure variation) and centrally obtained hemodynamic parameters (mean pulmonary artery pressure, pulmonary capillary wedge pressure, central venous pressure, cardiac output) were obtained. Blood volume was restored, and the pigs were over-resuscitated with 2,500 ml of crystalloid, collecting parameters after each 500-ml bolus. Hemorrhage and resuscitation phases were analyzed separately to determine differences among parameters over the range of volume. Conformity of parameters during hemorrhage or over-resuscitation was assessed.

RESULTS

During the course of hemorrhage, changes from baseline euvolemia were observed in vital signs (systolic blood pressure, diastolic blood pressure, and mean arterial pressure) after 100 ml of blood loss. Central hemodynamic parameters (mean pulmonary artery pressure and pulmonary capillary wedge pressure) were changed after 200 ml of blood loss, and central venous pressure after 300 ml of blood loss. During the course of resuscitative volume overload, changes were observed from baseline euvolemia in mean pulmonary artery pressure and central venous pressure after 500-ml resuscitation, in pulmonary capillary wedge pressure after 1,000-ml resuscitation, and cardiac output after 2,500-ml resuscitation. In contrast to hemorrhage, vital sign parameters did not change during over-resuscitation. The strongest linear correlation was observed with pulmonary capillary wedge pressure in both hemorrhage (r2 = 0.99) and volume overload (r2 = 0.98).

CONCLUSIONS

Pulmonary capillary wedge pressure is the most accurate parameter to track both hemorrhage and over-resuscitation, demonstrating the unmet clinical need for a less invasive pulmonary capillary wedge pressure equivalent.

EDITOR’S PERSPECTIVE

Improved Hemodynamic Recovery and 72-Hour Survival Following Low-Volume Resuscitation with a PEGylated Carboxyhemoglobin in a Rat Model of Severe Hemorrhagic Shock

INTRODUCTION

Hemorrhage is a leading cause of death from potentially survivable civilian and military trauma. As projected conflicts move from settings of tactical and logistical supremacy to hyper-dynamic tactical zones against peer and near-peer adversaries, protracted medical evacuation times are expected. Treatment at the point-of-injury is critical. Although crystalloids like Lactated Ringer's (LR) are ubiquitous, whole blood (WB) is the preferred resuscitation fluid following hemorrhage; however, logistical constraints limit the availability of WB in prehospital settings. Hemoglobin-based oxygen carriers (HBOCs) offer both hemodynamic support and oxygen-carrying capacity while avoiding logistical constraints of WB. We hypothesized that low-volume resuscitation of severe hemorrhagic shock with an HBOC (PEGylated carboxyhemoglobin, [PC]) would improve hemodynamic recovery and 72-hour survival; comparable to WB and superior to LR.

MATERIALS AND METHODS

A total of 21 anesthetized male Sprague-Dawley rats underwent severe hemorrhagic shock followed by randomly assigned low-volume resuscitation with LR, WB, or PC, and then recovered from anesthesia for up to 72-hour observation. Mean arterial pressure (MAP) was recorded continuously under anesthesia, and arterial blood gases were measured at baseline (BL), 60 minutes post-hemorrhage (HS1h), and 24 hours post-resuscitation (PR24h). Survival was presented on a Kaplan-Meier plot and significance determined with a log-rank test. Cardiovascular and blood gas data were assessed with one-way analysis of variance and post hoc analysis where appropriate.

RESULTS

All measured cardiovascular and blood chemistry parameters were equivalent between groups at BL and HS1h. BL MAP values were 90 ± 3, 86 ± 1, and 89 ± 2 mmHg for LR, PC, and WB, respectively. Immediately following resuscitation, MAP values were 57 ± 4, 74 ± 5, and 62 ± 3 mmHg, with PC equivalent to WB and higher than LR (P < 0.05). WB and LR were both lower than BL (P < 0.0001), whereas PC was not (P = 0.13). The PC group's survival to 72 hours was 57%, which was not different from WB (43%) and higher than LR (14%; P < 0.05).

CONCLUSIONS

A single bolus infusion of PC produced superior survival and MAP response compared to LR, which is the standard fluid resuscitant carried by combat medics. PC was not different from WB in terms of survival and MAP, which is encouraging because its reduced logistical constraints make it viable for field deployment. These promising findings warrant further development and investigation of PC as a low-volume, early treatment for hemorrhagic shock in scenarios where blood products may not be available.

Resuscitative endovascular balloon occlusion of the aorta in a pediatric swine model: Is 60 minutes too long?

BACKGROUND

Resuscitative endovascular balloon occlusion of the aorta (REBOA) is recommended in adults with a noncompressible torso hemorrhage with occlusion times of less than 60 minutes. The tolerable duration in children is unknown. We used a pediatric swine controlled hemorrhage model to evaluate the physiologic effects of 30 minutes and 60 minutes of REBOA.

METHODS

Pediatric swine weighing 20 kg to 30 kg underwent a splenectomy and a controlled 60% total blood volume hemorrhage over 30 minutes, followed by either zone 1 REBOA for 30 minutes (30R) or 60 minutes (60R). Swine were then resuscitated with shed blood and received critical care for 240 minutes.

RESULTS

During critical care, the 30R group's (n = 3) pH, bicarbonate, base excess, and lactate were no different than baseline, while at the end of critical care, these variables continued to differ from baseline in the 60R group (n = 5) and were worsening (7.4 vs. 7.2, p < 0.001, 30.4 mmol/L vs. 18.4 mmol/L, p < 0.0001, 5.6 mmol/L vs. -8.5 mmol/L, p < 0.0001, 2.4 mmol/L vs. 5.7 mmol/L, p < 0.001, respectively). Compared with baseline, end creatinine and creatinine kinase were elevated in 60R swine (1.0 mg/dL vs. 1.7 mg/dL, p < 0.01 and 335.4 U/L vs. 961.0 U/L, p < 0.001, respectively), but not 30R swine (0.9 mg/dL vs. 1.2 mg/dL, p = 0.06 and 423.7 U/L vs. 769.5 U/L, p = 0.15, respectively). There was no difference in survival time between the 30R and 60R pediatric swine, p = 0.99.

CONCLUSION

The physiologic effects of 30 minutes of zone 1 REBOA in pediatric swine mostly resolved during the subsequent 4 hours of critical care, whereas the effects of 60 minutes of REBOA persisted and worsened after 4 hours of critical care. Sixty minutes of zone 1 REBOA may create an irreversible physiologic insult in a pediatric population.

Does the pediatric hemodynamic cliff exist in response to hemorrhagic shock?

BACKGROUND

The paradigm that children maintain normal blood pressure during hemorrhagic shock until 30%-45% hemorrhage is widely accepted. There are minimal data supporting when decompensation occurs and how a child's vasculature compensates up to that point. We aimed to observe the arterial response to hemorrhage and when mean arterial pressure (MAP) decreased from baseline in pediatric swine.

METHODS

Piglets were hemorrhaged in 20% increments of their total blood volume to 60%. MAP and angiograms of the thoracic aorta (TA) and abdominal arteries were obtained. Percent change in area of the vessels from baseline was calculated.

RESULTS

Piglets (n = 8) had a differential vasoconstriction starting at 20% hemorrhage (celiac artery 36.3% [31.4-44.6] vs TA 16.7% [10.7-19.1] p = 0.0012). At 40% hemorrhage, the differential vasoconstriction favored shunting blood away from the abdominal visceral branches to the TA (celiac artery 54.7% [36.9-60.6] vs TA 29.5% [23.9-36.2] p = 0.0056 superior mesenteric artery 46.7% [43.9-68.6] vs TA 29.5% [23.9-36.2] p = 0.0100). This was exacerbated at 60% hemorrhage. MAP decreased from baseline at 20% hemorrhage (66.4 ± 6.0 mmHg vs 41.4 ± 10.4 mmHg, p < 0.0001), and worsened at 40% and 60% hemorrhage.

CONCLUSION

In piglets, a differential vasocontriction shunting blood proximally occurred in response to hemorrhage. This did not maintain normal MAP at 20%, 40% or 60% hemorrhage.

LEVEL OF EVIDENCE

Level II.

Resuscitative endovascular balloon occlusion of the aorta (REBOA) in a swine model of hemorrhagic shock and blunt thoracic injury

PURPOSE

While resuscitative endovascular balloon occlusion of the aorta (REBOA) is contraindicated in patients with aortic injuries, this technique may benefit poly-trauma patients with less extreme thoracic injuries. The purpose of this study was to characterize the effects of thoracic injury on hemodynamics during REBOA and the changes in pulmonary contusion over time in a swine model.

METHODS

Twelve swine were anesthetized, instrumented, and randomized to receive either a thoracic injury with 5 impacts to the chest or no injury. All animals underwent controlled hemorrhage of 25% blood volume followed by 45 min of Zone 1 REBOA. Animals were then resuscitated with shed blood, observed during a critical care period, and euthanized after 6 h of total experimental time.

RESULTS

There were no differences between the groups at baseline. The only difference after 6 h was a lower hemoglobin in the thoracic trauma group (8.4 ± 0.8 versus 9.4 ± 0.6 g/dL, P = 0.04). The average proximal mean arterial pressures were significantly lower in the thoracic trauma group during aortic occlusion [103 (98-108) versus 117 (115-124) mmHg, P = 0.04]. There were no differences between the pulmonary contusion before REBOA and at the end of the experiment in size (402 ± 263 versus 356 ± 291 mL, P = 0.782) or density (- 406 ± 127 versus - 299 ± 175 HFU, P = 0.256).

CONCLUSIONS

Thoracic trauma blunted the proximal arterial pressure augmentation during REBOA but had minimal impacts on resuscitative outcomes. This initial study indicates that REBOA does not seem to exacerbate pulmonary contusion in swine, but blunt thoracic injuries may attenuate the expected rises in proximal blood pressure during REBOA.

Indices of muscle and liver dysfunction after surviving hemorrhage and prolonged hypotension

BACKGROUND

This study determined the long-term effects of prolonged hypotension (PH) on liver, muscle, and kidney dysfunction. The hypothesis was that longer duration of PH after hemorrhage will result in greater organ dysfunction.

METHODS

Baboons were sedated and hemorrhaged (30% blood volume). Systolic blood pressure greater than 80 mm Hg was maintained for 1 hour (1 hr-PH; n = 5), 2 hours (2 hr-PH; n = 5), or 3 hours (3 hr-PH; n = 5). After PH, hemorrhage volume was replaced. Animals were recovered and monitored for 21 days. Control animals were hemorrhaged and immediately resuscitated (0 hr-PH, n = 3). Data are Mean ± Standard Deviation, and analyzed by 2-way repeated measures ANOVA and Holm-Sidak test.

RESULTS

Hemorrhage resulted in mild hypotension. Minimal resuscitation was required during the hypotensive phase, and survival rate was 100%. Significant increases (p < 0.001) in alanine aminotransferase, aspartate aminotransferase, creatine phosphokinase, and lactate dehydrogenase occurred on Day 1 after PH, and were significantly greater (p < 0.001) in the 2 hr- and 3 hr-PH groups than the 0 hr-PH group. Maximum alanine aminotransferase levels (U/L) were 140 ± 56 (0 hr-PH), 170 ± 130 (1 hr-PH), 322 ± 241 (2 hr-PH), and 387 ± 167 (3 hr-PH). Maximum aspartate aminotransferase levels (U/L) were 218 ± 44 (0 hr-PH), 354 ± 219 (1 hr-PH), 515 ± 424 (2 hr-PH), and 711 ± 278 (3 hr-PH). Maximum creatine phosphokinase values (U/L) were 7834 ± 3681 (0 hr-PH), 24336 ± 22268 (1 hr-PH), 50494 ± 67653 (2 hr-PH), and 59857 ± 32408 (3 hr-PH). Maximum lactic acid dehydrogenase values (U/L) were 890 ± 396 (0 hr-PH), 2055 ± 1520 (1 hr-PH), 3992 ± 4895 (2 hr-PH), and 4771 ± 1884 (3 hr-PH). Plasma creatinine and blood urea nitrogen were unaffected by PH (p > 0.10).

CONCLUSION

These results indicate that PH up to 3 hours in duration results in transient liver and muscle dysfunction that was most severe after 2 hr-PH and 3 hr-PH. Prolonged hypotension produced minimal effects on the kidney.

LEVEL OF EVIDENCE

Basic science research, Level of evidence not required for basic science research.

Endovascular Embolization Techniques in a Novel Swine Model of Fatal Uncontrolled Solid Organ Hemorrhage and Coagulopathy

BACKGROUND

Endovascular embolization is increasingly used in treating traumatic hemorrhage and other applications. No endovascular-capable translational large animal models exist and coagulopathy's effect on embolization techniques is unknown. We developed a coagulation-adaptable solid organ hemorrhage model in swine for investigation of embolization techniques.

METHODS

Anesthetized swine (n = 26, 45 ± 3 kg) had laparotomy and splenic externalization. Half underwent 50% isovolemic hemodilution with 6% hetastarch and cooling to 33-35°C (COAG group). All had controlled 20 mL/kg hemorrhage and endovascular access to the proximal splenic artery with a 4F catheter via a right femoral sheath. Splenic transection and 5 min free bleeding were followed by treatment (n = 5/group) with 5 mL gelfoam slurry, three 6-mm coils, or no treatment (n = 3, control). Animals received 15 mL/kg plasma resuscitation and were monitored for 6 hr. Splenic blood loss was continuously measured and angiograms were performed at specified times.

RESULTS

Coagulopathy was successfully established in COAG animals. Pre-treatment blood loss was greater in COAG (11 ± 6 mL/kg) than non-COAG (7 ± 3 mL/kg, P = 0.04) animals. Splenic hemorrhage was universally fatal without treatment. Non-COAG coil survival was 4/5 (326 ± 75 min) and non-COAG Gelfoam 3/5 (311 ± 67 min) versus non-COAG Control 0/3 (82 ± 18 min, P < 0.05 for both). Neither COAG Coil (0/5, 195 ± 117 min) nor COAG Gelfoam (0/5, 125 ± 32 min) treatment improved survival over COAG Control (0/3, 56 ± 19 min). Post-treatment blood loss was 4.6 ± 3.4 mL/kg in non-COAG Coil and 4.6 ± 2.9 mL/kg in non-COAG Gelfoam, both lower than non-COAG Control (18 ± 1.3 mL/kg, P = 0.05). Neither COAG Coil (8.4 ± 5.4 mL/kg) nor COAG Gelfoam (15 ± 11 ml/kg) had significantly less blood loss than COAG Control (20 ± 1.2 mL/kg). Both non-COAG treatment groups had minimal blood loss during observation, while COAG groups had ongoing slow blood loss. In the COAG Gelfoam group, there was an increase in hemorrhage between 30 and 60 min following treatment.

CONCLUSIONS

A swine model of coagulation-adaptable fatal splenic hemorrhage suitable for endovascular treatment was developed. Coagulopathy had profound negative effects on coil and gelfoam efficacy in controlling bleeding, with implications for trauma and elective embolization procedures.

Effects of arterial hemorrhage speed on the blood coagulation/fibrinolysis system and hemodynamics in rats

: The effects of rapid hemorrhage on coagulopathy have been reported. However, the effects of different hemorrhage speeds on the blood coagulation/fibrinolysis system have not been investigated. This study aimed to compare different hemorrhage speeds for clarifying their effects on the coagulation/fibrinolysis system and circulation disorders in rats. Male Sprague-Dawley rats (301-396 g) were randomly assigned to five groups depending on hemorrhage speed and length of procedure: first, rapid (1.4 ml/min, 30-min bleeding); second, rapid-L (1.4 ml/min, 30-min bleeding and observation until 6 h); third, slow (0.1 ml/min, intermittently, 6-h bleeding); fourth, control (30-min observation); and fifth, control-L (6-h observation). Hemorrhage was induced by withdrawing blood until 40% of the estimated blood volume from the femoral artery. We measured vital signs, hematology, general chemistry, blood gas status, coagulation parameters, fibrinolytic markers [tissue-type plasminogen activator and plasminogen activator inhibitor one (PAI-1)], vascular endothelial damage (syndecan-1), and liver PAI-1 mRNA expression. Rapid hemorrhage induced elevation of lactate and syndecan-1 levels and prolonged prothrombin time and activated partial thromboplastin time in the rapid group. In contrast, slow hemorrhage did not induce these changes. Hemorrhage speed had no effect on plasma tissue-type plasminogen activator and hematology. Plasma PAI-1 levels were significantly increased in the rapid-L group, while liver PAI-1 mRNA levels were increased in the slow group. This study shows changes in the circulatory and fibrinolysis systems, depending on the hemorrhage speed. Hemorrhage might promote production of PAI-1, while tissue hypoxia due to rapid hemorrhage might promote release of PAI-1.

Resuscitative endovascular balloon occlusion of the aorta induced myocardial injury is mitigated by endovascular variable aortic control

BACKGROUND

The cardiac effects of resuscitative endovascular balloon occlusion of the aorta (REBOA) are largely unknown. We hypothesized that increased afterload from REBOA would lead to cardiac injury, and that partial flow using endovascular variable aortic control (EVAC) would mitigate this injury.

METHODS

Eighteen anesthetized swine underwent controlled 25% blood volume hemorrhage. Animals were randomized to either Zone 1 REBOA, Zone 1 EVAC, or no intervention (control) for 45 minutes. Animals were then resuscitated with shed blood, observed during critical care, and euthanized after a 6-hour total experimental time. Left ventricular function was measured with a pressure-volume catheter, and blood samples were drawn at routine intervals.

RESULTS

The average cardiac output during the intervention period was higher in the REBOA group (9.3 [8.6-15.4] L/min) compared with the EVAC group (7.2 [5.8-8.0] L/min, p = 0.01) and the control group (6.8 [5.8-7.7] L/min, p < 0.01). At the end of the intervention, the preload recruitable stroke work was significantly higher in both the REBOA and EVAC groups compared with the control group (111.2 [102.5-148.6] and 116.7 [116.6-141.4] vs. 67.1 [62.7-87.9], p = 0.02 and p < 0.01, respectively). The higher preload recruitable stroke work was maintained throughout the experiment in the EVAC group, but not in the REBOA group. Serum troponin concentrations after 6 hours were higher in the REBOA group compared with both the EVAC and control groups (6.26 ± 5.35 ng/mL vs 0.92 ± 0.61 ng/mL and 0.65 ± 0.38 ng/mL, p = 0.05 and p = 0.03, respectively). Cardiac intramural hemorrhage was higher in the REBOA group compared with the control group (1.67 ± 0.46 vs. 0.17 ± 0.18, p = 0.03), but not between the EVAC and control groups.

CONCLUSION

In a swine model of hemorrhagic shock, complete aortic occlusion resulted in cardiac injury, although there was no direct decrease in cardiac function. EVAC mitigated the cardiac injury and improved cardiac performance during resuscitation and critical care.

Evaluation of prolonged 'Permissive Hypotension': results from a 6-hour hemorrhage protocol in swine

Background

Tactical Combat Casualty Care guidelines for hemorrhage recommend resuscitation to systolic blood pressure (SBP) of 85±5 mm Hg during prehospital care. Success depends on transport to definitive care within the ‘golden hour’. As future conflicts may demand longer prehospital/transport times, we sought to determine safety of prolonged permissive hypotension (PH).

Methods

Adult male swine were randomized into three experimental groups. Non-shock (NS)/normotensive underwent anesthesia only. NS/PH was bled to SBP of 85±5 mm Hg for 6 hours of prolonged field care (PFC) with SBP maintained via crystalloid, then recovered. Experimental group underwent controlled hemorrhage to mean arterial pressure 30 mm Hg until decompensation (Decomp/PH), followed by 6 hours of PFC. Hemorrhaged animals were then resuscitated with whole blood and observed for 24 hours. Physiologic variables, blood, tissue samples, and neurologic scores were collected.

Results

Survival of all groups was 100%. Fluid volumes to maintain targeted SBP in PFC were significantly higher in the hemorrhage group than sham groups. After 24 hours’ recovery, no significant differences were observed in neurologic scores or cerebrospinal fluid markers of brain injury. No significant changes in organ function related to treatment were observed during PFC through recovery, as assessed by serum chemistry and histological analysis.

Conclusions

After 6 hours, a prolonged PH strategy showed no detrimental effect on survival or neurologic outcome despite the increased ischemic burden of hemorrhage. Significant fluid volume was required to maintain SBP—a potential logistic burden for prehospital care. Further work to define maximum allowable time of PH is needed.

Study type

Translational animal model.

Level of evidence

N/A.

Renal effects of three endoaortic occlusion strategies in a swine model of hemorrhagic shock

INTRODUCTION

Trauma patients are predisposed to kidney injury. We hypothesized that in shock, zone 3 REBOA would increase renal blood flow (RBF) compared to control and that a period of zone 3 occlusion following zone 1 occlusion would improve renal function compared to zone 1 occlusion alone.

MATERIALS AND METHODS

Twenty-four anesthetized swine underwent hemorrhagic shock, 45 min of zone 1 REBOA (Z1, supraceliac), zone 3 REBOA (Z3, infrarenal), or no intervention (control) followed by resuscitation with shed blood and 5 h of critical care. In a fourth group (Z1Z3), animals underwent 55 min of zone 3 REBOA following zone 1 occlusion. Physiologic parameters were recorded, blood and urine were collected at specified intervals.

RESULTS

During critical care, there were no differences in RBF between the Z1 and Z3 groups. The average RBF during critical care in Z1Z3 was significantly lower than in Z3 alone (98.2 ± 23.9 and 191.9 ± 23.7 mL/min; p = 0.046) and not different than Z1. There was no difference in urinary neutrophil gelatinase-associated lipocalin-to-urinary creatinine ratio between Z1 and Z1Z3. Animals in the Z1Z3 group had a significant increase in the ratio at the end of the experiment compared to baseline [median (IQR)] [9.2 (8.2-13.2) versus 264.5 (73.6-1174.6)]. Following Z1 balloon deflation, RBF required 45 min to return to baseline.

CONCLUSION

Neither zone 3 REBOA alone nor zone 3 REBOA following zone 1 REBOA improved renal blood flow or function. Following zone 1 occlusion, RBF is restored to baseline levels after approximately 45 min.

A systematic review of large animal models of combined traumatic brain injury and hemorrhagic shock

Traumatic brain injury (TBI) and severe blood loss (SBL) frequently co-occur in human trauma, resulting in high levels of mortality and morbidity. Importantly, each of the individual post-injury cascades is characterized by complex and potentially opposing pathophysiological responses, complicating optimal resuscitation and therapeutic approaches. Large animal models of poly-neurotrauma closely mimic human physiology, but a systematic literature review of published models has been lacking. The current review suggests a relative paucity of large animal poly-neurotrauma studies (N = 52), with meta-statistics revealing trends for animal species (exclusively swine), characteristics (use of single biological sex, use of juveniles) and TBI models. Although most studies have targeted blood loss volumes of 35-45%, the associated mortality rates are much lower relative to Class III/IV human trauma. This discrepancy may result from potentially mitigating experimental factors (e.g., mechanical ventilation prior to or during injury, pausing/resuming blood loss based on physiological parameters, administration of small volume fluid resuscitation) that are rarely associated with human trauma, highlighting the need for additional work in this area.

Location is everything: The hemodynamic effects of REBOA in Zone 1 versus Zone 3 of the aorta

OBJECTIVES

Resuscitative endovascular balloon occlusion of the aorta (REBOA) is an emerging technology to augment proximal blood pressure during the resuscitation of patients with noncompressible torso hemorrhage. Currently, placement choice, supraceliac (Zone 1) versus infrarenal (Zone 3) aorta, depends on injury patterns, but remains a highly debated topic. We sought to compare the proximal hemodynamic support provided by Zone 1 versus Zone 3 REBOA placement and the degree of hemodynamic instability upon reperfusion following intervention.

METHODS

Eighteen anesthetized swine underwent controlled hemorrhage of 25% total blood volume, followed by 45 minutes of Zone 1 REBOA, Zone 3 REBOA, or no intervention (control). They were then resuscitated with shed blood, aortic balloons were deflated, and 5 hours of critical care ensued prior to euthanasia. Physiologic parameters were recorded continuously, and blood was drawn for analysis at specified intervals. Significance was defined as p < 0.05.

RESULTS

There were no significant differences between groups at baseline or during the initial 30 minutes of hemorrhage. During the intervention period, average proximal MAP was significantly greater in Zone 1 animals when compared with Zone 3 animals (127.9 ± 1.3 vs. 53.4 ± 1.1 mm Hg) and greater in Zone 3 animals when compared with control animals (42.9 ± 0.9 mm Hg). Lactate concentrations were significantly higher in Zone 1 animals (9.6 ± 0.4 mmol/L) when compared with Zone 3 animals (5.1 ± 0.3 mmol/L) and control animals (4.2 ± 0.8 mmol/L).

CONCLUSIONS

In our swine model of hemorrhagic shock, Zone 3 REBOA provided minimal proximal hemodynamic support when compared with Zone 1 REBOA, albeit with less ischemic burden and instability upon reperfusion. In cases of impending hemodynamic collapse, Zone 1 REBOA placement may be more efficacious regardless of injury pattern, whereas Zone 3 should be reserved only for relatively stable patients with ongoing distal hemorrhage.

The effect of resuscitative endovascular balloon occlusion of the aorta, partial aortic occlusion and aggressive blood transfusion on traumatic brain injury in a swine multiple injuries model

BACKGROUND

Despite clinical reports of poor outcomes, the degree to which resuscitative endovascular balloon occlusion of the aorta (REBOA) exacerbates traumatic brain injury (TBI) is not known. We hypothesized that combined effects of increased proximal mean arterial pressure (pMAP), carotid blood flow (Qcarotid), and intracranial pressure (ICP) from REBOA would lead to TBI progression compared with partial aortic occlusion (PAO) or no intervention.

METHODS

Twenty-one swine underwent a standardized TBI via computer Controlled cortical impact followed by 25% total blood volume rapid hemorrhage. After 30 minutes of hypotension, animals were randomized to 60 minutes of continued hypotension (Control), REBOA, or PAO. REBOA and PAO animals were then weaned from occlusion. All animals were resuscitated with shed blood via a rapid blood infuser. Physiologic parameters were recorded continuously and brain computed tomography obtained at specified intervals.

RESULTS

There were no differences in baseline physiology or during the initial 30 minutes of hypotension. During the 60-minute intervention period, REBOA resulted in higher maximal pMAP (REBOA, 105.3 ± 8.8; PAO, 92.7 ± 9.2; Control, 48.9 ± 7.7; p = 0.02) and higher Qcarotid (REBOA, 673.1 ± 57.9; PAO, 464.2 ± 53.0; Control, 170.3 ± 29.4; p < 0.01). Increases in ICP were greatest during blood resuscitation, with Control animals demonstrating the largest peak ICP (Control, 12.8 ± 1.2; REBOA, 5.1 ± 0.6; PAO, 9.4 ± 1.1; p < 0.01). There were no differences in the percentage of animals with hemorrhage progression on CT (Control, 14.3%; 95% confidence interval [CI], 3.6-57.9; REBOA, 28.6%; 95% CI, 3.7-71.0; and PAO, 28.6%; 95% CI, 3.7-71.0).

CONCLUSION

In an animal model of TBI and shock, REBOA increased Qcarotid and pMAP, but did not exacerbate TBI progression. PAO resulted in physiology closer to baseline with smaller increases in ICP and pMAP. Rapid blood resuscitation, not REBOA, resulted in the largest increase in ICP after intervention, which occurred in Control animals. Continued studies of the cerebral hemodynamics of aortic occlusion and blood transfusion are required to determine optimal resuscitation strategies for multi-injured patients.

A novel model of highly lethal uncontrolled torso hemorrhage in swine

INTRODUCTION

A reproducible, lethal noncompressible torso hemorrhage model is important to civilian and military trauma research. Current large animal models balancing clinical applicability with standardization and internal validity. As such, large animal models of trauma vary widely in the surgical literature, limiting comparisons. Our aim was to create and validate a porcine model of uncontrolled hemorrhage that maximizes reproducibility and standardization.

METHODS

Seven Yorkshire-cross swine were anesthetized, instrumented, and splenectomized. A simple liver tourniquet was applied before injury to prevent unregulated hemorrhage while creating a traumatic amputation of 30% of the liver. Release of the tourniquet and rapid abdominal closure following injury provided a standardized reference point for the onset and duration of uncontrolled hemorrhage. At the moment of death, the liver tourniquet was quickly reapplied to provide accurate quantification of intra-abdominal blood loss. Weight and volume of the resected and residual liver segments were measured. Hemodynamic parameters were recorded continuously throughout each experiment.

RESULTS

This liver injury was rapidly and universally lethal (11.2 ± 4.9 min). The volume of hemorrhage (35.8% ± 6% of total blood volume) and severity of uncontrolled hemorrhage (100% of animals deteriorated to a sustained mean arterial pressure <35 mmHg for 5 min) were consistent across all animals. Use of the tourniquet effectively halted preprocedure and postprocedure blood loss allowing for accurate quantification of amount of hemorrhage over a defined period. In addition, the tourniquet facilitated the creation of a consistent liver resection weight (0.0043 ± 0.0003 liver resection weight: body weight) and as a percentage of total liver resection weight (27% ± 2.2%).

CONCLUSIONS

This novel tourniquet-assisted noncompressible torso hemorrhage model creates a standardized, reproducible, highly lethal, and clinically applicable injury in swine. Use of the tourniquet allowed for consistent liver injury and precise control over hemorrhage. Recorded blood loss was similar across all animals. Improving reproducibility and standardization has the potential to offer improvements in large animal translational models of hemorrhage.

LEVEL OF EVIDENCE

Level I.

Automated variable aortic control versus complete aortic occlusion in a swine model of hemorrhage

BACKGROUND

Future endovascular hemorrhage control devices will require features that mitigate the adverse effects of vessel occlusion. Permissive regional hypoperfusion (PRH) with variable aortic control (VAC) is a novel strategy to minimize hemorrhage and reduce the ischemic burden of complete aortic occlusion (AO). The objective of this study was to compare PRH with VAC to AO in a lethal model of hemorrhage.

METHODS

Twenty-five swine underwent cannulation of the supraceliac aorta, with diversion of aortic flow through an automated extracorporeal circuit. After creation of uncontrolled liver hemorrhage, animals were randomized to 90 minutes of treatment: Control (full, unregulated flow; n = 5), AO (no flow; n = 10), and PRH with VAC (dynamic distal flow initiated after 20 minutes of AO; n = 10). In the PRH group, distal flow rates were regulated between 100 and 300 mL/min based on a desired, preset range of proximal mean arterial pressure (MAP). At 90 minutes, damage control surgery, resuscitation, and restoration of full flow ensued. Critical care continued for 4.5 hours or until death. Hemodynamic parameters and markers of ischemia were recorded.

RESULTS

Study survival was 0%, 50%, and 90% for control, AO, and VAC, respectively (p < 0.01). During intervention, VAC resulted in more physiologic proximal MAP (84 ± 18 mm Hg vs. 105 ± 9 mm Hg, p < 0.01) and higher renal blood flow than AO animals (p = 0.02). During critical care, VAC resulted in higher proximal MAP (73 ± 8 mm Hg vs. 50 ± 6 mm Hg, p < 0.01), carotid and renal blood flow (p < 0.01), lactate clearance (p < 0.01), and urine output (p < 0.01) than AO despite requiring half the volume of crystalloids to maintain proximal MAP ≥50 mm Hg (p < 0.01).

CONCLUSION

Permissive regional hypoperfusion with variable aortic control minimizes the adverse effects of distal ischemia, optimizes proximal pressure to the brain and heart, and prevents exsanguination in this model of lethal hemorrhage. These findings provide foundational knowledge for the continued development of this novel paradigm and inform next-generation endovascular designs.

An Evolving Uncontrolled Hemorrhage Model Using Cynomolgus Macaques

BACKGROUND

Trauma-induced hemorrhagic shock produces hemodynamic changes that often result in a systemic inflammatory response that can lead to multiple organ failure and death. In this prospective study, the pathophysiology of a nonhuman primate uncontrolled hemorrhagic shock model is evaluated with the goal of creating an acute systemic inflammatory syndrome response and a reproducible hemorrhage.

METHODS

Nonhuman primates were divided into 2 groups. A laparoscopic left hepatectomy was performed in groups A and B, 60% and 80%, respectively, resulting in uncontrolled hemorrhage. Resuscitation during the prehospital phase lasted 120 min and included a 0.9% saline bolus at 20 mL/kg. The hospital phase involved active warming, laparotomy, hepatorrhaphy for hemostasis, and transfusion of packed red blood cells (10 mL/kg). The animals were recovered and observed over a 14-day survival period with subsequent necropsy for histopathology.

RESULTS

Baseline demographics and clinical parameters of the two groups were similar. Group A (n = 7) underwent a 57.7% ± 2.4% left hepatectomy with a 33.9% ± 4.0% blood loss and 57% survival. Group B (n = 4) underwent an 80.0% ± 6.0% left hepatectomy with 56.0% ± 3.2% blood loss and 75% survival. Group B had significantly lower hematocrit (P < 0.05) for all postinjury time points. Group A had significantly elevated creatinine on postoperative day 1. Nonsurvivors succumbed to an early death, averaging 36 h from the injury. Histopathologic evaluation of nonsurvivors demonstrated kidney tubular degeneration.

CONCLUSIONS

Nonhuman primates displayed the expected physiologic response to hemorrhagic shock due to liver trauma as well as systemic inflammatory response syndrome with resultant multiple organ dysfunction syndrome and either early death or subsequent recovery. Our next step is to establish a clinically applicable nonhuman primate polytrauma model, which reproduces the prolonged maladaptive immunologic reactivity and end-organ dysfunction consistent with multiple organ failure found in the critically injured patient.

Fibrinogen concentrate administration inhibits endogenous fibrinogen synthesis in pigs after traumatic hemorrhage

BACKGROUND

Fibrinogen plays a central role in coagulation and falls to critical levels early after trauma. Administration of fibrinogen concentrate (FC) to improve hemostasis after severe bleeding seems beneficial, but it is unclear whether its use introduces excessive fibrinogen with a potential risk of thrombosis. This study investigated changes of endogenous fibrinogen metabolism from FC administration following traumatic hemorrhage in pigs.

METHODS

Anesthetized, instrumented pigs were randomized into lactated Ringer's (LR) solution only and LR plus FC groups (n = 7 each). Femur fracture of each pig's left leg was followed by hemorrhage of 60% total blood volume and resuscitation with LR (3× bled volume, LR group) or LR plus FC at 250 mg/kg (LR-FC group). Afterward, a constant infusion of stable isotopes 1-C-phenylalanine (phe, 6 hours) and d5-phe (3 hours) was performed with hourly blood sampling and subsequent gas chromatography-mass spectrometry analysis to quantify fibrinogen synthesis and breakdown rates, respectively. Blood gas and coagulation indices (thromboelastography) were measured on intermittent blood samples, and hemodynamics was continuously monitored. Animals were euthanized after the 6-hour isotope period.

RESULTS

Mean arterial pressure decreased by 50% after hemorrhage but improved after LR resuscitation in both groups. Hemorrhage and LR resuscitation reduced total protein, hematocrit, fibrinogen, and platelets to 50% of baseline values. Moreover, hemorrhage and resuscitation decreased fibrinogen concentration (207 ± 6 vs. 132 ± 7 mg/dL) and clot strength (72 ± 2 vs. 63 ± 2 mm) in both groups (p < 0.05). FC administration restored plasma fibrinogen concentrations and clot strength within 15 minutes, while no changes occurred in the LR group. Fibrinogen synthesis rates in the LR-FC group (1.3 ± 0.2 mg/kg/h) decreased versus the LR group (3.1 ± 0.5; p < 0.05), whereas fibrinogen breakdown rates were similar.

CONCLUSION

Our data suggest an effective feedback mechanism that regulates host fibrinogen availability and thereby suggests that acute thrombosis from FC administration is an unlikely risk.

Fresh frozen plasma: red blood cells (1:2) coagulation effect is equivalent to 1:1 and whole blood

BACKGROUND

Preemptive treatment of trauma-associated coagulopathy involves transfusion of fresh frozen plasma (FFP) at 1:1 ratio with red blood cells (RBCs), but the optimal ratio remains controversial. In combat theaters, fresh whole blood (FWB) is also an option. The objective of this study was to determine the effect of FFP:RBC ratios 1:1, 1:2, 1:3 and FWB on coagulation during resuscitation.

MATERIALS AND METHODS

Thirty-six rats were randomized in the following six groups: Group 1: sham; Group 2: hemorrhage followed by sole lactated Ringer (LR) infusion; Group 3: FFP:RBC (1:1); Group 4: FFP:RBC (1:2); Group 5: FFP:RBC (1:3); Group 6: FWB transfusion. Another 25 animals were used for blood harvesting. Hemorrhage was induced by withdrawing 40% of total blood volume, mean arterial pressure (MAP) decreased to 45% of baseline, and laparotomy. Animals underwent LR infusion followed by blood product transfusion preset for each group. Blood samples were obtained at baseline and in the 105th minute for thromboelastometry and lactate.

RESULTS

Hemorrhage caused a significant decrease in MAP and increase in lactate (P < 0.05). MAP was persistently low in group 2 despite fluid infusion (P < 0.05), but not in the other groups after 20 min of resuscitation. Mean clot formation time, alpha angle, and maximum clot firmness decreased significantly (P < 0.05) in group 2 (LR) and group 5 (1:3) compared with other groups.

CONCLUSIONS

FFP:RBC in a 1:2 ratio optimally harnessed hemostatic resuscitation and prudent use of blood products compared with 1:1 and 1:3 ratios and to FWB transfusion.

Comparison of normal saline, hypertonic saline albumin and terlipressin plus hypertonic saline albumin in an infant animal model of hypovolemic shock

Introduction

In series of cases and animal models suffering hemorrhagic shock, the use of vasopressors has shown potential benefits regarding hemodynamics and tissue perfusion. Terlipressin is an analogue of vasopressin with a longer half-life that can be administered by bolus injection. We have previously observed that hypertonic albumin improves resuscitation following controlled hemorrhage in piglets. The aim of the present study was to analyze whether the treatment with the combination of terlipressin and hypertonic albumin can produce better hemodynamic and tissular perfusion parameters than normal saline or hypertonic albumin alone at early stages of hemorrhagic shock in an infant animal model.

Methods

Experimental, randomized animal study including 39 2-to-3-month-old piglets. Thirty minutes after controlled 30 ml/kg bleed, pigs were randomized to receive either normal saline (NS) 30 ml/kg (n = 13), 5% albumin plus 3% hypertonic saline (AHS) 15 ml/kg (n = 13) or single bolus of terlipressin 15 μg/kg i.v. plus 5% albumin plus 3% hypertonic saline 15 ml/kg (TAHS) (n = 13) over 30 minutes. Global hemodynamic and tissular perfusion parameters were compared.

Results

After controlled bleed a significant decrease of blood pressure, cardiac index, central venous saturation, carotid and peripheral blood flow, brain saturation and an increase of heart rate, gastric PCO₂ and lactate was observed. After treatment no significant differences in most hemodynamic (cardiac index, mean arterial pressure) and perfusion parameters (lactate, gastric PCO₂, brain saturation, cutaneous blood flow) were observed between the three therapeutic groups. AHS and TAHS produced higher increase in stroke volume index and carotid blood flow than NS.

Conclusions

In this pediatric animal model of hypovolemic shock, albumin plus hypertonic saline with or without terlipressin achieved similar hemodynamics and perfusion parameters than twice the volume of NS. Addition of terlipressin did not produce better results than AHS.

A prospective, randomized trial of intravenous hydroxocobalamin versus whole blood transfusion compared to no treatment for Class III hemorrhagic shock resuscitation in a prehospital swine model

OBJECTIVES

The objective was to compare systolic blood pressure (sBP) over time in swine that have had 30% of their blood volume removed (Class III shock) and treated with intravenous (IV) whole blood or IV hydroxocobalamin, compared to nontreated control animals.

METHODS

Thirty swine (45 to 55 kg) were anesthetized, intubated, and instrumented with continuous femoral and pulmonary artery pressure monitoring. Animals were hemorrhaged a total of 20 mL/kg over a 20-minute period. Five minutes after hemorrhage, animals were randomly assigned to receive 150 mg/kg IV hydroxocobalamin solubilized in 180 mL of saline, 500 mL of whole blood, or no treatment. Animals were monitored for 60 minutes thereafter. A sample size of 10 animals per group was determined based on a power of 80% and an alpha of 0.05 to detect an effect size of at least a 0.25 difference (>1 standard deviation) in mean sBP between groups. sBP values were analyzed using repeated-measures analysis of variance (RANOVA). Secondary outcome data were analyzed using repeated-measures multivariate analysis of variance (RMANOVA).

RESULTS

There were no significant differences between hemodynamic parameters of IV hydroxocobalamin versus whole blood versus control group at baseline (MANOVA; Wilks' lambda; p = 0.868) or immediately posthemorrhage (mean sBP = 47 mm Hg vs. 41 mm Hg vs. 37 mm Hg; mean arterial pressure = 39 mm Hg vs. 28 mm Hg vs. 34 mm Hg; mean serum lactate = 1.2 mmol/L vs. 1.4 mmol/L vs. 1.4 mmol/L; MANOVA; Wilks' lambda; p = 0.348). The outcome RANOVA model detected a significant difference by time between groups (p < 0.001). Specifically, 10 minutes after treatment, treated animals showed a significant increase in mean sBP compared to nontreated animals (mean sBP = 76.3 mm Hg vs. 85.7 mm Hg vs. 51.1 mm Hg; p < 0.001). RMANOVA modeling of the secondary data detected a significant difference in mean arterial pressure, heart rate, and serum lactate (p < 0.001). Similar to sBP, 10 minutes after treatment, treated animals showed a significant increase in mean arterial pressure compared to nontreated animals (mean arterial pressure = 67.7 mm Hg vs. 61.4 mm Hg vs. 40.5 mm Hg). By 10 minutes, mean heart rate was significantly slower in treated animals compared to nontreated animals (mean heart rate = 97.3 beats/min vs. 95.2 beats/min vs. 129.5 beats/min; p < 0.05). Serum lactate, an early predictor of shock, continued to rise in the control group, whereas it did not in treated animals. Thirty minutes after treatment, serum lactate values of treated animals were significantly lower compared to nontreated animals (p < 0.05). This trend continued throughout the 60-minute observation period such that 60-minute values for lactate were 1.4 mmol/L versus 1.1 mmol/L versus 3.8 mmol/L. IV hydroxocobalamin produced a statistically significant increase in systemic vascular resistance compared to control, but not whole blood, with a concomitant decrease in cardiac output.

CONCLUSIONS

Intravenous hydroxocobalamin was more effective than no treatment and as effective as whole blood transfusion, in reversing hypotension and inhibiting rises in serum lactate in this prehospital, controlled, Class III swine hemorrhage model.

"Fluidless" resuscitation with permissive hypotension via impedance threshold device therapy compared with normal saline resuscitation in a porcine model of severe hemorrhage

BACKGROUND

One approach to improve outcomes after trauma and hemorrhage is to follow the principles of permissive hypotension by avoiding intravascular overpressure and thereby preventing dislodgement of platelet plugs early in the clotting process. We hypothesized that augmentation of negative intrathoracic pressure (nITP) by treatment with an impedance threshold device would improve hemodynamics without compromising permissive hypotension or causing hemodilution, whereas aggressive fluid resuscitation with normal saline (NS) would result in hemodilution and SBPs that are too high for permissive hypotension and capable of clot dislodgement.

METHODS

Thirty-four spontaneously breathing anesthetized female pigs (30.6 ± 0.5 kg) were subjected to a fixed 55% hemorrhage over 30 minutes; block randomized to nITP, no treatment, or intravenous bolus of 1-L NS; and evaluated over 30 minutes. Results are reported as mean ± SEM.

RESULTS

Average systolic blood pressures (SBPs) (mm Hg) 30 minutes after the study interventions were as follows: nITP, 82.1 ± 2.9; no treatment, 69.4 ± 4.0; NS 89.3 ± 5.2. Maximum SBPs during the initial 15 minutes of treatment were as follows: nITP, 88.0 ± 4.3; no treatment, 70.8 ± 4.3; and NS, 131 ± 7.6. After 30 minutes, mean pulse pressure (mm Hg) was significantly higher in the nITP group (nITP, 32.3 ± 2.2) versus the no-treatment group (21.5 ± 1.5 controls) (p < 0.05), and the mean hematocrit was 25.2 ± 0.8 in the nITP group versus 19 ± 0.6 in the NS group (p < 0.001).

CONCLUSION

In this porcine model of hemorrhagic shock, nITP therapy significantly improved SBP and pulse pressure for 30 minutes without overcompensation compared with controls with no treatment. By contrast, aggressive fluid resuscitation with NS but not nITP resulted in a significant rise in SBP to more than 100 mm Hg within minutes of initiating therapy that could cause a further reduction in hematocrit and clot dislodgment.

The microcirculation: linking trauma and coagulopathy

Survival after severe traumatic shock can be complicated by a number of pathophysiologic processes that ensue after the initial trauma. One of these is trauma-induced coagulopathy (TIC) whose onset may occur before initial fluid resuscitation. The pathogenesis of TIC has not yet been fully elaborated, but evolving evidence appears to link severe tissue hypoxia and damage to the endothelium as key factors, which evolve into measurable structural and biochemical changes of the endothelium resulting in a coagulopathic state. This paper will provide a general review of these linkages and identify knowledge gaps as well as suggest new approaches and areas of investigation, which may both limit the development of TIC as well as produce insights into its pathophysiology. A better understanding of these issues will be necessary in order to advance the practice of remote damage control resuscitation.

Bone marrow derived mesenchymal stem cells inhibit inflammation and preserve vascular endothelial integrity in the lungs after hemorrhagic shock

Hemorrhagic shock (HS) and trauma is currently the leading cause of death in young adults worldwide. Morbidity and mortality after HS and trauma is often the result of multi-organ failure such as acute lung injury (ALI) and acute respiratory distress syndrome (ARDS), conditions with few therapeutic options. Bone marrow derived mesenchymal stem cells (MSCs) are a multipotent stem cell population that has shown therapeutic promise in numerous pre-clinical and clinical models of disease. In this paper, in vitro studies with pulmonary endothelial cells (PECs) reveal that conditioned media (CM) from MSCs and MSC-PEC co-cultures inhibits PEC permeability by preserving adherens junctions (VE-cadherin and β-catenin). Leukocyte adhesion and adhesion molecule expression (VCAM-1 and ICAM-1) are inhibited in PECs treated with CM from MSC-PEC co-cultures. Further support for the modulatory effects of MSCs on pulmonary endothelial function and inflammation is demonstrated in our in vivo studies on HS in the rat. In a rat “fixed volume” model of mild HS, we show that MSCs administered IV potently inhibit systemic levels of inflammatory cytokines and chemokines in the serum of treated animals. In vivo MSCs also inhibit pulmonary endothelial permeability and lung edema with concurrent preservation of the vascular endothelial barrier proteins: VE-cadherin, Claudin-1, and Occludin-1. Leukocyte infiltrates (CD68 and MPO positive cells) are also decreased in lungs with MSC treatment. Taken together, these data suggest that MSCs, acting directly and through soluble factors, are potent stabilizers of the vascular endothelium and inflammation. These data are the first to demonstrate the therapeutic potential of MSCs in HS and have implications for the potential use of MSCs as a cellular therapy in HS-induced lung injury.

Rabbit model of uncontrolled hemorrhagic shock and hypotensive resuscitation

Clinically relevant animal models capable of simulating traumatic hemorrhagic shock are needed. We developed a hemorrhagic shock model with male New Zealand rabbits (2200-2800 g, 60-70 days old) that simulates the pre-hospital and acute care of a penetrating trauma victim in an urban scenario using current resuscitation strategies. A laparotomy was performed to reproduce tissue trauma and an aortic injury was created using a standardized single puncture to the left side of the infrarenal aorta to induce hemorrhagic shock similar to a penetrating mechanism. A 15-min interval was used to simulate the arrival of pre-hospital care. Fluid resuscitation was then applied using two regimens: normotensive resuscitation to achieve baseline mean arterial blood pressure (MAP, 10 animals) and hypotensive resuscitation at 60% of baseline MAP (10 animals). Another 10 animals were sham operated. The total time of the experiment was 85 min, reproducing scene, transport and emergency room times. Intra-abdominal blood loss was significantly greater in animals that underwent normotensive resuscitation compared to hypotensive resuscitation (17.1 ± 2.0 vs 8.0 ± 1.5 mL/kg). Antithrombin levels decreased significantly in normotensive resuscitated animals compared to baseline (102 ± 2.0 vs 59 ± 4.1%), sham (95 ± 2.8 vs 59 ± 4.1%), and hypotensive resuscitated animals (98 ± 7.8 vs 59 ± 4.1%). Evidence of re-bleeding was also noted in the normotensive resuscitation group. A hypotensive resuscitation regimen resulted in decreased blood loss in a clinically relevant small animal model capable of reproducing hemorrhagic shock caused by a penetrating mechanism.

Initial resuscitation with plasma and other blood components reduced bleeding compared to hetastarch in anesthetized swine with uncontrolled splenic hemorrhage

BACKGROUND

Damage control resuscitation recommends use of more plasma and less crystalloid as initial resuscitation in treating hemorrhage. The purpose of this study was to evaluate resuscitation with either blood components or conventional fluids on coagulation and blood loss.

STUDY DESIGN AND METHODS

Isofluorane-anesthetized, instrumented pigs (eight per group) underwent controlled hemorrhage of 24 mL/kg, 20-minute shock period, splenic injury with 15-minute initial bleeding, and hypotensive fluid resuscitation. Lactated Ringer's (LR) was infused at 45 mL/kg while hetastarch (high-molecular-weight hydroxyethyl starch 6%, Hextend, Hospira, Inc., Lake Forest, IL) and blood component (fresh-frozen plasma [FFP], 1:1 FFP:[red blood cells] RBCs, 1:4 FFP : RBCs, and fresh whole blood [FWB]) were infused at 15 mL/kg. Postresuscitation blood loss (PRBL), hemodynamics, coagulation, hematocrit, and oxygen metabolism were measured postinjury for 5 hours.

RESULTS

Resuscitation with any blood component reduced PRBL of 52% to 70% compared to Hextend, with FFP resulting in the lowest PRBL. PRBL with LR (11.5 ± 3.0 mL/kg) was not significantly different from Hextend (17.9 ± 2.5 mL/kg) or blood components (range, 5.5 ± 1.5 to 8.6 ± 2.6 mL/kg). The volume expansion effect of LR was transient. All fluids produced similar changes in hemodynamics, oxygen delivery, and demand despite the oxygen-carrying capacity of RBC-containing fluids. Compared with other fluids, Hextend produced greater hemodilution and reduced coagulation measures, which could be caused by an indirect dilutional effect or a direct hypocoagulable effect.

CONCLUSIONS

These data suggest that blood products as initial resuscitation fluids reduced PRBL from a noncompressible injury compared to Hextend, preserved coagulation, and provided sustained volume expansion. There were no differences on PRBL among RBCs-to-FFP, FWB, or FFP in this nonmassive transfusion model.

Influence of asymptomatic pneumonia on the response to hemorrhage and resuscitation in swine

INTRODUCTION

Investigation of resuscitation fluids in our swine hemorrhage model revealed moderate to severe chronic pneumonia in five swine at necropsy. Our veterinary staff suggested that we perform a retrospective analysis of prospectively collected data from these animals. We compared the data to that of ten healthy swine to determine the physiologic consequences of the added stress on our hemorrhage/resuscitation model.

METHODS

Anesthetized, immature female swine (40 ± 5 kg) were instrumented for determining arterial and venous pressures, cardiac output and urine production. A controlled hemorrhage of 20 ml/kg over 4 min 40 sec was followed at 30 min by a second hemorrhage of 8 ml/kg and resuscitation with 1.5 ml/kg/min of LR solutions to achieve and maintain systolic blood pressure at 80 ± 5 mmHg for 3.5 hrs. Chemistries and arterial and venous blood gasses were determined from periodic blood samples along with hemodynamic variables.

RESULTS

There were significant decreases in survival, urine output, cardiac output and oxygen delivery at 60 min and O2 consumption at 120 min in the pneumonia group compared to the non-pneumonia group. There were no differences in other metabolic or hemodynamic data between the groups.

CONCLUSION

Although pneumonia had little influence on pulmonary gas exchange, it influenced cardiac output, urine output and survival compared to healthy swine, suggesting a decrease in the physiologic reserve. These data may be relevant to patients with subclinical infection who are stressed by hemorrhage and may explain in part why some similarly injured patients require more resuscitation efforts than others.

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.

Eight hours of hypotensive versus normotensive resuscitation in a porcine model of controlled hemorrhagic shock

OBJECTIVES

The aim of this study was to compare hypotensive and normotensive resuscitation in a porcine model of hemorrhagic shock.

METHODS

This was a prospective, comparative, randomized survival study of controlled hemorrhagic shock using 28 male Yorkshire-Landrace pigs (15 to 25 kg). In 24 splenectomized pigs, the authors induced hemorrhagic shock to a systolic blood pressure (sBP) of 48 to 58 mm Hg (approximately 35% bleed). Pigs were randomized to undergo normotensive resuscitation (sBP of 90 mm Hg, n = 7), mild hypotensive resuscitation (sBP of 80 mm Hg, n = 7), severe hypotensive resuscitation (sBP of 65 mm Hg, n = 6), or no resuscitation (n = 4). The authors also included a sham group of animals that were instrumented and splenectomized, but that did not undergo hemorrhagic shock (n = 4). After the initial 8 hours of randomized pressure-targeted resuscitation, all animals were resuscitated to a sBP of 90 mm Hg for 16 hours.

RESULTS

Animals that underwent severe hypotensive resuscitation were less likely to survive, compared with animals that underwent normotensive resuscitation. Mean arterial pressure (MAP) decreased with hemorrhage and increased appropriately with pressure-targeted resuscitation. Base excess (BE) and tissue oxygen saturation (StO2) decreased in all animals that underwent hemorrhagic shock. This decrease persisted only in animals that were pressure target resuscitated to a sBP of 65 mm Hg.

CONCLUSIONS

In this model of controlled hemorrhagic shock, initial severe hypotensive pressure-targeted resuscitation for 8 hours was associated with an increased mortality rate and led to a persistent base deficit (BD) and to decreased StO2, suggesting persistent metabolic stress and tissue hypoxia. However, mild hypotensive resuscitation did not lead to a persistent BD or to decreased StO2, suggesting less metabolic stress and less tissue hypoxia.