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.

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.

Abdominal aortic and junctional tourniquet versus zone III resuscitative endovascular balloon occlusion of the aorta in a swine junctional hemorrhage model.

BACKGROUND: Junctional hemorrhage is a leading contributor to battlefield mortality. The Abdominal Aortic and Junctional Tourniquet (AAJT) and infrarenal (zone III) resuscitative endovascular balloon occlusion of the aorta (REBOA) are emerging strategies for controlling junctional hemorrhage, with AAJT currently available in select forward deployed settings and increasing interest in applying REBOA in the military prehospital environment. This study compared the hemostatic, hemodynamic, and metabolic effects of these devices used for junctional hemorrhage control. METHODS: Shock was induced in anesthetized, mechanically ventilated swine with a controlled hemorrhage (20 mL/kg) and closed femur fracture followed by uncontrolled hemorrhage from a partial femoral artery transection (40% total hemorrhage volume). Residual femoral hemorrhage was recorded during 60-minute AAJT (n = 10) or zone III REBOA (n = 10) deployment, and the arterial injury was repaired subsequently. Animals were resuscitated with 15 mL/kg autologous whole blood and observed for 6 hours. RESULTS: One animal in each group died during observation. Both devices achieved hemostasis with mean residual femoral blood loss in the AAJT and REBOA groups of 0.38 ± 0.59 mL/kg and 0.10 ± 0.07 mL/kg (p = 0.16), respectively, during the 60-minute intervention. The AAJT and REBOA augmented proximal blood pressure equally with AAJT allowing higher distal pressure than REBOA during intervention (p < 0.01). Following device deflation, AAJT animals had transiently lower mean arterial blood pressure than REBOA pigs (39 ± 6 vs. 54 ± 11 mm Hg p = 0.01). Both interventions resulted in similar degrees of lactic acidemia which resolved during observation. Similar cardiac and renal effects were observed between AAJT and REBOA. CONCLUSION: The AAJT and REBOA produced similar hemostatic, resuscitative, and metabolic effects in this model of severe shock with junctional hemorrhage. Both interventions may have utility in future military medical operations.

Differing Resuscitation With Aortic Occlusion in a Swine Junctional Hemorrhage Polytrauma Model.

BACKGROUND: Resuscitative endovascular balloon occlusion of the aorta (REBOA) and Abdominal Aortic and Junctional Tourniquet (AAJT) have received much attention in recent as methods for temporary control of junctional hemorrhage. Previous studies typically used the animal's shed blood for resuscitation. With current interest in moving REBOA to prehospital environment, this study aimed to evaluate the hemodynamic and metabolic responses to different resuscitation fluids used with these devices. METHODS: In swine (Sus scrofa), shock was induced using a controlled hemorrhage, femur fracture, and uncontrolled hemorrhage from the femoral artery. Infrarenal REBOA or AAJT was deployed for 60 min during which the arterial injury was repaired. Animals were resuscitated with 15 mL/kg of shed whole blood (SWB) or fresh frozen plasma (FFP) or 30 mL/kg of a balanced crystalloid (PlasmaLyte). RESULTS: Animals in the AAJT and REBOA groups did not show any measurable differences in hemodynamics, metabolic responses, or survival with AAJT or REBOA treatment; hence, the data are pooled and analyzed among the three resuscitative fluids. SWB, FFP, and PlasmaLyte groups did not have a difference in survival time or overall survival. The animals in the SWB and FFP groups maintained higher blood pressure after resuscitation, (P < 0.001) and required significantly less norepinephrine to maintain blood pressure than those in the PlasmaLyte group (P < 0.001). The PlasmaLyte resuscitation prolonged prothrombin time and decreased thromboelastography maximum amplitude. CONCLUSIONS: After 60 min, infrarenal REBOA or AAJT aortic occlusion SWB and FFP resuscitation provided better blood pressure support with half of the resuscitative volume of PlasmaLyte. Swine resuscitated with SWB and FFP also had a more favorable coagulation profile. These data suggest that whole blood or component therapy should be used for resuscitation in conjunction with REBOA or AAJT, and administration of these fluids should be considered if prehospital device use is pursued.

Effect of partial and complete aortic balloon occlusion on survival and shock in a swine model of uncontrolled splenic hemorrhage with delayed resuscitation.

BACKGROUND: Resuscitative endovascular balloon occlusion of the aorta (REBOA) is accepted as a resuscitation adjunct and bridge to definitive hemostasis. The ischemic burden of REBOA may be mitigated by a partial REBOA (P-REBOA) strategy permitting longer occlusion times and military use for combat trauma. We evaluated REBOA and P-REBOA in a swine multiple trauma model with uncontrolled solid organ hemorrhage and delayed resuscitation and surgical hemostasis. METHODS: Anesthetized swine (51.9 ± 2.2 kg) had 20 mL/kg hemorrhage and closed femur fracture. Splenic transection was performed and free bleeding permitted for 10 minutes. Controls (n = 5) were hemorrhaged but had no REBOA, REBOA (n = 8) had 60 minutes complete zone 1 occlusion, P-REBOA (n = 8) had 15 minutes complete occlusion and 45 minutes 50% occlusion. Splenectomy was performed and plasma (15 mL/kg) resuscitation initiated 5 minutes prior to deflation. Resuscitation goal was 80 mm Hg systolic with epinephrine as needed. Animals were monitored for 6 hours. RESULTS: An initial study with 120-minute occlusion had universal fatality in three REBOA (upon deflation) and three P-REBOA animals (after 60 minutes inflation). With 60-minute occlusion, mortality was 100%, 62.5%, and 12.5% in the control, REBOA, and P-REBOA groups, respectively (p < 0.05). Survival time was shorter in controls (120 ± 89 minutes) than REBOA and P-REBOA groups (241 ± 139, 336 ± 69 minutes). Complete REBOA hemorrhaged less during inflation (1.1 ± 0.5 mL/kg) than Control (5.6 ± 1.5) and P-REBOA (4.3 ± 1.4), which were similar. Lactate was higher in the REBOA group compared with the P-REBOA group after balloon deflation, remaining elevated. Potassium increased in REBOA after deflation but returned to similar levels as P-REBOA by 120 minutes. CONCLUSION: In a military relevant model of severe uncontrolled solid organ hemorrhage 1-hour P-REBOA improved survival and mitigated hemodynamic and metabolic shock. Two hours of partial aortic occlusion was not survivable using this protocol due to ongoing hemorrhage during inflation. There is potential role for P-REBOA as part of an integrated minimally invasive field-expedient hemorrhage control and resuscitation strategy.

Long-term consequences of abdominal aortic and junctional tourniquet for hemorrhage control.

BACKGROUND: Specialized tourniquets have been deployed to the battlefield for the control of junctional/pelvic hemorrhage despite limited knowledge concerning their safety and duration of use. This study investigated long-term effects of abdominal application of the abdominal aortic and junctional tourniquet (AAJT) in a swine survival model. METHODS: Anesthetized spontaneously air-breathing swine were subjected to bilateral femoral artery injuries and subsequent 40% hemorrhage. Further hemorrhage was controlled by applying the AAJT on the lower abdomen for 0 h (n = 2, controls), 1 h (n = 6), 1.5 h (n = 6), or 2 h (n = 3). Before tourniquet release, arterial injuries were repaired, and mechanical ventilation and rapid crystalloid fluid were provided for at least 5 min. Additional fluid and 500 mL autologous blood were transfused after restoring blood flow. Animals were recovered and their mobility and health monitored up to 2 wk. RESULTS: AAJT application occluded the infrarenal abdominal aorta and stopped bilateral groin hemorrhage with rapid reversal of hemorrhagic shock and improved cranial blood pressure. All animals including controls recovered overnight but regaining hind leg function varied among AAJT-treated groups. In contrast to 1 h AAJT-treated swine that recovered full mobility in 1 wk, 2 h animals developed persistent hind leg paraplegia concurrent with urinary retention and ischemic necrosis of lumber muscles and had to be euthanized 3 d after surgery. Half of the 1.5-h group also had to be euthanized early due to paraplegia, whereas the other half recovered motor function within 2 wk. CONCLUSIONS: The results of this animal study indicated that ischemic reperfusion injuries associated with abdominal application of the AAJT were time-dependent. To avoid permanent injuries, AAJT application on the abdomen to control a groin hemorrhage could not be longer than 1 h. This was consistent with recent instructions for application of this tourniquet on the abdomen in patients.

Damage Control Resuscitation.

Damage control resuscitation (DCR) is a strategy for resuscitating patients from hemorrhagic shock to rapidly restore homeostasis. Efforts are focused on blood product transfusion with whole blood or component therapy closely approximating whole blood, limited use of crystalloid to avoid dilutional coagulopathy, hypotensive resuscitation until bleeding control is achieved, empiric use of tranexamic acid, prevention of acidosis and hypothermia, and rapid definitive surgical control of bleeding. Patients receiving uncrossmatched Type O blood in the emergency department and later receiving cumulative transfusions of 10 or more red blood cell units in the initial 24-hour post-injury (massive transfusion) are widely recognized as being at increased risk of morbidity and mortality due to exsanguination. Ideally, these patients should be rapidly identified, however anticipating transfusion needs is challenging. Useful indicators of massive transfusion reviewed in this guideline include: systolic blood pressure <110 mmHg, heart rate > 105 bpm, hematocrit <32%, pH < 7.25, injury pattern (above-the-knee traumatic amputation especially if pelvic injury is present, multi-amputation, clinically obvious penetrating injury to chest or abdomen), >2 regions positive on Focused Assessment with Sonography for Trauma (FAST) scan, lactate concentration on admission >2.5, admission international normalized ratio ≥1.2-1.4, near infrared spectroscopy-derived StO2 < 75% (in practice, rarely available), BD > 6 meq/L. Unique aspects of out-of-hospital DCR (point of injury, en-route, and remote DCR) and in-hospital (Medical Treatment Facilities: Role 2b/Forward surgical teams - role 3/ combat support hospitals) are reviewed in this guideline, along with pediatric considerations.

Do vented chest seals differ in efficacy? An experimental evaluation using a swine hemopneumothorax model.

OBJECTIVE: Airways compromise was the second leading cause of potentially preventable death among combat casualties. We investigated the ability of five Food and Drug Administration-approved nonocclusive chest seals (CSs) to seal a bleeding chest wound and prevent tension hemopneumothorax (HPTX) in a swine model. METHODS: Following instrumentation, an open chest wound was created in the left thorax of spontaneously air-breathing anesthetized pigs (n = 26; 43 kg). Autologous fresh blood (226 mL) was then infused into the pleural cavity to produce HPTX. The chest wounds were then sealed with CSs. The sealant strength and venting function of CSs were challenged by infusion of 50 mL more blood directly into the chest wound and incremental air injections into the pleural cavity. Tension HPTX was defined as intrapleural (IP) pressure equal to or more than +1 mm Hg and more than 20% deviation in physiologic measurements. RESULTS: An open chest wound with HPTX raised IP pressure (~ -0.7 mm Hg) and caused labored breathing and reductions in PaO2 and SvO2 (p < 0.01). Sealing the wounds with the CSs restored IP pressure, and improved breathing and oxygenation. Subsequent blood infusion into the wound and IP air injections produced CS-dependent responses. Chest seals with one-way valves (Bolin and SAM) did not evacuate the blood efficiently; pooled blood either detached the CSs from skin and leaked out (75%), or clotted and clogged the valve and led to tension HPTX (25%). Conversely, CSs with laminar venting channels allowed escape of blood and air from the pleural cavity and maintained IP pressure and oxygenation near normal levels. Success rates were 100% for Sentinel and Russell (6/6); 67% for HyFin (4/6); 25% for SAM (1/4); and 0% for Bolin (0/4) CSs (p = 0.002). CONCLUSION: The sealant and valve function of vented CS differed widely in the presence of bleeding chest wounds. Medics should be equipped with more effective CSs for treating HPTX in the field.

Does small-volume resuscitation with crystalloids or colloids influence hemostasis and survival of rabbits subjected to lethal uncontrolled hemorrhage?

BACKGROUND: Prehospital, small-volume resuscitation of combat casualties with a synthetic colloid (6% hydroxyethyl starch [HES] 670/0.75) has been recommended when blood or blood components are unavailable. We studied hemostatic effects of a newer synthetic colloid (6% HES, 130/0.4) compared with either a natural colloid (albumin) or to crystalloids in an uncontrolled hemorrhage model. METHODS: Spontaneously breathing New Zealand white rabbits (3.4 ± 0.1 kg) were anesthetized, instrumented, and subjected to a splenic injury with uncontrolled bleeding. Fifteen minutes after injury, rabbits were in shock (mean arterial pressure [MAP] = 26 ± 1.3 mm Hg, and received colloids (6% HES, 130/0.4 or 5% albumin at 15 mL/kg), or crystalloids (normal saline at 30 mL/kg or 5% hypertonic saline at 7.5 mL/kg) for resuscitation in two intravenous bolus injections (15 minutes apart) to raise their MAP to 65 mm Hg, n = 9/group. Animals were monitored for 2.5 hours or until death, and blood losses were measured. Blood samples were analyzed for arterial blood gas, complete blood count, and coagulation measures. RESULTS: There were no differences among groups in baseline measures and initial hemorrhage volume (11.9 ± 0.6 mL/kg) at 15 minutes postinjury. Twenty minutes after fluid resuscitation (1 hour postinjury), MAP was higher, shock indices were lower, and blood pH was higher in colloids versus. crystalloids groups (p < 0.05). Administration of 6% HES 130/0.4 colloid produced the largest hemodilution (54% decrease in hematocrit, p < 0.05 vs. hypertonic saline). Activated partial thromboplastin time increased approximately 35% above baseline in all groups except in 6% HES 130/0.4 group in which it doubled. Clot strength was reduced (15%) only in the 6% HES 130/0.4 group. 6% HES 130/0.4 resuscitation produced the largest blood loss and 33% survival rate that was not different than the crystalloid groups. Albumin produced the best hemostatic and survival outcomes (78%). CONCLUSION: Small-volume resuscitation with crystalloids appeared inadequate to treat hypovolemic shock and prevent death. 6% HES 130/0.4 was effective hemodynamically but detrimental to hemostasis. Albumin produced the best outcomes consistent with our previous observations. Further studies are needed to prove benefit of albumin solution as a possible resuscitation fluid for treating combat casualties at the point of injury.

Influences of limited resuscitation with plasma or plasma protein solutions on hemostasis and survival of rabbits with noncompressible hemorrhage.

BACKGROUND: Plasma infusion with or without red blood cells is the current military standard of care for prehospital resuscitation of combat casualties. We examined possible advantages of early and limited resuscitation with fresh plasma compared with a single plasma protein or crystalloid solutions in an uncontrolled hemorrhage model in rabbits. METHODS: Anesthetized spontaneously breathing rabbits (3.3 ± 0.1 kg) were instrumented and subjected to a splenic uncontrolled hemorrhage. Rabbits in shock were resuscitated at 15 minutes with Plasma-Lyte (PAL; 30 mL/kg), PAL + fibrinogen (PAL + F; 30 mL + 100 mg/kg), fresh rabbit plasma (15 mL/kg), or 25% albumin (ALB; 5 mL/kg) solution, all given in two bolus intravenous injections (15 minutes apart) to achieve a mean arterial pressure of 65 mm Hg, n = 8 to 9/group. Animals were monitored for 2 hours or until death, and blood loss was measured. Blood samples and tissues were collected and analyzed. RESULTS: There were no differences among groups in baseline measures and their initial bleeding volume at 15 minutes. At 60 minutes after injury, mean arterial pressure was higher with ALB than with crystalloids (PAL or PAL + F), but shock indices were not different despite the large differences in resuscitation volumes. Fibrinogen addition to PAL only increased clot strength. Plasma resuscitation increased survival rate (75%) without significant improvement in coagulation measures. Albumin administration replenished total plasma protein and increased survival rate to 100% (p < .05 vs. crystalloids). No histological adverse events were identified in the vital organs. CONCLUSIONS: Fibrinogen administration added to a compatible crystalloid did not improve hemostatic outcomes. Plasma resuscitation increased survival rate; however, its effects did not differ from those obtained with 25% ALB at one-third of the volume. The ALB advantage was consistent with our previous findings in which 5% ALB was used at a volume equal to plasma. The benefit of plasma for resuscitation may be mostly due to its ALB content rather than its coagulation proteins.

Is limited prehospital resuscitation with plasma more beneficial than using a synthetic colloid? An experimental study in rabbits with parenchymal bleeding.

BACKGROUND: Reports of survival benefits of early transfusion of plasma with red blood cells (1:1 ratio) in trauma patients suggest that plasma may be a better fluid to replace Hextend for battlefield resuscitation. We studied possible advantages of prehospital resuscitation with plasma compared with Hextend or albumin in a model of uncontrolled hemorrhage. METHODS: Male New Zealand white rabbits (3.3 ± 0.1 kg) were anesthetized, instrumented, and subjected to a splenic injury with uncontrolled bleeding. Ten minutes after injury (mean arterial pressure [MAP] < 40 mm Hg), the rabbits received small and equal volumes (15 mL/kg) of rabbit plasma (n = 10), Hextend (n = 10), or 5% human albumin (n = 9) or no fluid. Fluids were administered in two bolus injections (20 minutes apart) and targeted to a MAP of 65 mm Hg. Animals were monitored for 2.5 hours or until death, and their blood losses were measured. Arterial blood samples were collected at different times and analyzed for ABG, CBC, and coagulation tests. RESULTS: There were no differences in baseline measures among groups. Splenic injury caused similar hemorrhages (9.1 ± 0.4 mL/kg at 10 minutes) and decreased MAP in all subjects. Subsequent resuscitation initiated additional bleeding. At 60 minutes after injury (20 minutes after resuscitation), longer activated partial thromboplastin time and lower fibrinogen concentrations were apparent compared with baseline values with differences among groups. Thrombelastography analysis indicated faster and stronger clot formation with plasma and albumin resuscitation than with Hextend use. Shock indices were increased in all groups, but smaller changes were measured in the albumin group. Total blood loss did not differ among resuscitated rabbits but was higher (p < 0.05) than among nonresuscitated animals. Survival rates were 11% (untreated), 40% (Hextend and plasma), and 89% (albumin, p < 0.05). CONCLUSION: Resuscitation with plasma or albumin better preserved coagulation function than did Hextend. However, despite these improvements, plasma resuscitation did not reduce blood loss or improve survival, while albumin administration seemed beneficial.

Long-term effects of Combat Ready Clamp application to control junctional hemorrhage in swine.

BACKGROUND: Groin application of Combat Ready Clamp (CRoC) in pigs elicits an acute inflammation in underlying ischemic tissues. This study examined functional recovery of pigs' hind leg(s) following 2 hours of CRoC application. METHODS: Left femoral arteries were isolated and injured in anesthetized pigs. Following 25% hemorrhage, CRoC was applied on the inguen for 2 hours (n = 6), and wounds were covered with combat gauze (CG). Bleeding was treated in the control animals (n = 5) with CG only. Next, CRoC and CG were removed, arteries were repaired and reflowed, and animals were recovered. The legs' mobility was scored daily, and their neuromuscular functions were measured on Days 7 and 14. Computed tomographic angiography and blood analysis were performed on Days 0, 2, 7, and 14. Pigs were then euthanized, and tissues were collected for histology. Umbilicus application of CRoC was also tested in four pilot experiments. RESULTS: Inguinal application of CRoC with 524 ± 12 mm Hg pressure occluded iliac arteries and collateral circulation. Following surgical repair, blood flow to the arteries was restored, and five of six CRoC-applied legs recovered full mobility within 9 days. Control-treated legs recovered full function in 3 days (p = 0.001). At 2 weeks, muscle strength of CRoC-applied legs was diminished (p < 0.05 vs. baselines or controls). Injury biomarkers in the CRoC group increased severalfold compared with the controls on Day 2 but returned to baseline afterward. Histologic changes were mostly mild and indicative of ischemia in the CRoC group. Umbilical application of CRoC required higher pressure (625 ± 8 mm Hg) and caused gross ischemic necrosis of lumbar muscles with significant disabilities. CONCLUSION: Two-hour inguinal application of CRoC caused mild and reversible ischemic injuries, which delayed full recovery of the limb function by a few days. In contrast, 2-hour umbilicus application of CRoC resulted in extensive muscle necrosis with functional disabilities. While CRoC seems safe and effective for inguinal application, other tourniquets should be evaluated for treating bilateral junctional bleeding.

Vented versus unvented chest seals for treatment of pneumothorax and prevention of tension pneumothorax in a swine model.

BACKGROUND: Unvented chest seals (CSs) are currently recommended for the management of penetrating thoracic injuries in the battlefield. Since no supporting data exist, we compared the efficacy of a preferred unvented with that of a vented CS in a novel swine model of pneumothorax (PTx). METHODS: An open chest wound was created in the left thorax of spontaneously air-breathing anesthetized pigs (n = 8). A CS was applied over the injury, then tension PTx was induced by incremental air injections (0.2 L) into the pleural cavity via a cannula that was also used to measure intrapleural pressure (IP). Both CS were tested on each pig in series. Tidal volume (V(T)), respiratory rate, IP, heart rate, mean arterial pressure, cardiac output, central venous pressure, pulmonary arterial pressure, venous and peripheral oxygen saturations (SvO2, SpO2) were recorded. Tension PTx was defined as a mean IP equal to or greater than +1 mm Hg plus significant (20-30%) deviation in baseline levels of the previously mentioned parameters and confirmed by chest x-ray study. PaO2 and PaCo2 were also measured. RESULTS: PTx produced immediate breathing difficulty and significant rises in IP and pulmonary arterial pressure and falls in V(T), SpO2, and SvO2. Both CSs returned these parameters to near baseline within 5 minutes of application. After vented CS was applied, serial air injections up to 2 L resulted in no significant change in the previously mentioned parameters. After unvented CS application, progressive deterioration of all respiratory parameters and onset of tension PTx were observed in all subjects after approximately 1.4-L air injection. CONCLUSION: Both vented and unvented CSs provided immediate improvements in breathing and blood oxygenation in our model of penetrating thoracic trauma. However, in the presence of ongoing intrapleural air accumulation, the unvented CS led to tension PTx, hypoxemia, and possible respiratory arrest, while the vented CS prevented these outcomes.

In vivo assessment of the Combat Ready Clamp to control junctional hemorrhage in swine.

BACKGROUND: Junctional wounds and associated hemorrhage have become more common and more lethal in the current war. The Combat Ready Clamp (CRoC) has been developed and deployed for treating junctional hemorrhage on the battlefield. This study examined the efficacy of CRoC and its acute effects in an animal model. METHODS: Anesthetized pigs (n = 6) were subjected to laparotomy, splenectomy, and abdominal closure. Next, coagulopathy was induced in animals by hemodilution and hypothermia. The left femoral artery was isolated, punctured (6-mm hole), and allowed to bleed for 15 seconds. The groin wound was packed with gauze, and a CRoC applied and tightened until hemorrhage stopped. It was kept in place for 1 hour (treatment period) and then released for another hour or less (control-period) if animal exsanguinated. Fluid resuscitation was administered, and vascular blood flow was examined by Doppler and CT scans. After death, local tissues were collected for histology. RESULTS: CRoC generated 800 to 900 mm Hg pressure on the wounds, which stopped the hemorrhage and prevented rebleeding during the first hour in all animals. Blood loss was minimal (≤137 mL), and mean arterial pressure remained at or higher than the target level (65 mm Hg) during this period. Removal of the clamp promptly led to rebleeding and exsanguination of five of six pigs during the second hour despite fluid resuscitation. Blood loss, survival, shock indices, and other measures were significantly (p < 0.01) different between the two periods. Doppler tests and CT scans showed no blood flow in the proximal, distal, and collateral arteries of the clamped leg. Minor inflammation was seen on blood vessels (endothelium) and nerves. CONCLUSION: CRoC functioned as an effective hemostatic adjunct for compression and control of groin hemorrhage. Although no acute histological damages were seen in compressed tissues, the short- and long-term effects of CRoC application (e.g., total ischemia) on limb function remain unknown and warrant investigation.

Negative-pressure wound therapy: a hemostatic adjunct for control of coagulopathic hemorrhage in large soft tissue wounds.

BACKGROUND: Negative-pressure wound therapy has been commonly used for treating chronic wounds and recently applied for treatment of traumatic wounds. We investigated the potential hemostatic benefit of negative-pressure wound therapy for control of refractory hemorrhage in a soft tissue wound model in swine. METHODS: Coagulopathy was induced in pigs (n = 38, 36 kg) by hemodilution and hypothermia. Next, a large soft tissue wound (diameter, approximately 20 cm) was created by slicing the gluteus maximus muscle. Free bleeding was allowed for 1 minute, and wounds were then randomly dressed with either laparotomy gauze (G) alone or TraumaPad (TP, a kaolin-coated dressing) alone or in combination with negative pressure (NP, approximately -500 mm Hg). All wounds were sealed with adhesive drapes. Fluid resuscitation was administered and targeted to mean arterial pressure of 60 mm Hg. Pigs were observed for 150 minutes or until death after which tissues were sampled for histologic examination. RESULTS: Induced coagulopathy as measured by increases in prothrombin time (12%) and activated partial thromboplastin time (22%) and decreases in fibrinogen (48%) were similar in all groups. There were no differences in initial bleeding rates (4.5 mL/kg/min). Dressing the wounds with G or TP produced hemostasis only in one pig (1 of 18 pigs). Addition of NP to these dressings secured hemostasis in 70% (G) and 90% (TP) of animals with average hemostasis time of 34 minutes and 25 minutes, respectively. Blood losses and fluid resuscitation requirements were significantly less, and survival times were significantly longer in NP adjunct groups than in the other groups. Survival rates were 80% (G+NP) and 90% (TP+NP) versus 0% (G) and 10% (TP) in the respective groups. Histologic examination showed similar superficial myofibril damages in all groups. CONCLUSION: To our knowledge, the present data provide the first evidence that NP serves as an effective hemostatic adjunct and when combined with standard hemostatic dressing it is able to stop lethal coagulopathic bleeding in large soft tissue wounds.

Toxicity of aluminum silicates used in hemostatic dressings toward human umbilical veins endothelial cells, HeLa cells, and RAW267.4 mouse macrophages.

BACKGROUND: Aluminum silicates have been used to control bleeding after severe traumatic injury. QuikClot (QC) was the first such product, and WoundStat (WS) is the most recent. We recently observed that WS caused vascular thrombosis when applied to stop bleeding. This study investigated the cellular toxicity of WS in different cell types that may be exposed to this mineral and compared the results with other minerals such as bentonite, kaolin, and QuikClot ACS+ (QC+). METHODS: Human umbilical vein endothelial cells (HUVEC), HeLa cells, and RAW267.4 mouse macrophage-like cells (RAW) were incubated directly with different concentrations of each mineral for 24 hours. Cell viability was determined metabolically using the AlamarBlue fluorescent technique. In another experiment, minerals were exposed to HUVEC via Transwell inserts with a polycarbonate filter (0.4-µm pore size) to prevent direct contact between cells and minerals for determining whether direct exposure or leaching compounds from minerals cause cytotoxicity. RESULTS: Incubation of HUVEC and RAW cells with 1 to 100 µg/mL of the minerals for 24 hours resulted in differential toxicities. The cytotoxicity of WS was equal to that of bentonite and higher than kaolin and QC+. Neither cell type survived for 24 hours in the presence of 100 µg/mL WS or bentonite. These minerals, however, had little effect on the viability of HeLa cells. In the second HUVEC experiment, a 10 times higher concentration of these compounds placed in Transwell inserts yielded no decrease in cell viability. This result indicates that leaching toxicants or binding of nutrients by the ion-exchange properties of minerals did not cause the toxicity. CONCLUSIONS: Although aluminum silicates seem relatively innocuous to epithelial cells, all produced some toxicity toward endothelial cells and macrophages. WS and bentonite were significantly more toxic than kaolin and zeolite present in QC+, respectively, at equivalent doses. The cytotoxic effect seemed to be caused by the direct contact of the minerals with the cells present in wounds. These data suggest that the future clearance of mineral-based hemostatic agents should require more extensive cytotoxicity testing than the current Food and Drug Administration requirements.

Assessment of the thrombogenic effect of fibrin sealant dressing in a vascular surgery model in rabbits.

This study's objective was to investigate the potential thrombogenic effects of thrombin-containing fibrin sealant dressings (FSD) in a vascular repair model. Oval-shaped pieces of the rabbit abdominal aorta and vena cava were excised, the injuries were repaired with FSD, and animals were allowed to recover. Thrombus formation was examined by (1) an infusion of indium-labeled platelets into the rabbits following FSD application and estimation of total number of platelets attached to the wounds at 2, 4, and 6 h later (short-term effect, n = 12); and by (2) morphological and histological examinations of the vessels and dressings on days 1, 3, and 7 after repair operation in another group of rabbits (long-term effect, n = 12). Application of FSD sealed the vascular injures and produced immediate hemostasis that was stable up to 1 week. The highest numbers of platelets (both native and labeled) adhered to the arterial and venous repair sites were 6.5 x 106 and 4.4 x 107, respectively, 6 h after operation. The adhered platelets, however, did not form a visible and clinically significant thrombus. In long-term experiments, no evidence of thrombus was found in the lumens of the repaired vessels or on the dressings, and no microthrombi were detected histologically in other tissues at any time point. Although vena caval injuries showed signs of healing at day 7 postoperatively, the aortic wounds expanded progressively (pseudoaneurysm) and were prone to rupture at later times. Thus, direct exposure of FSD does not cause intravascular thrombosis or thrombotic events in rabbits. The dressing appears to be safe and effective for short-term repair of vascular injuries. It may also allow healing of minor venous defects, but cannot replace conventional surgical techniques (suturing) for permanent repair of arterial damages.