Development of a large animal model of lethal polytrauma and intra-abdominal sepsis with bacteremia

A combat casualty relevant dismounted complex blast injury model in swine

BACKGROUND

Improvised explosive devices have resulted in a unique polytrauma injury pattern termed dismounted complex blast injury (DCBI), which is frequent in the modern military theater. Dismounted complex blast injury is characterized by extremity amputations, junctional vascular injury, and blast traumatic brain injury (bTBI). We developed a combat casualty relevant DCBI swine model, which combines hemorrhagic shock (HS) and tissue injury (TI) with a bTBI, to study interventions in this unique and devastating military injury pattern.

METHODS

A 50-kg male Yorkshire swine were randomized to the DCBI or SHAM group (instrumentation only). Those in the DCBI group were subjected to HS, TI, and bTBI. The blast injury was applied using a 55-psi shock tube wave. Tissue injury was created with bilateral open femur fractures. Hemorrhagic shock was induced by bleeding from femoral arteries to target pressure. A resuscitation protocol modified from the Tactical Combat Casualty Care guidelines simulated battlefield resuscitation for 240 minutes.

RESULTS

Eight swine underwent the DCBI model and five were allocated to the SHAM group. In the DCBI model the mean base excess achieved at the end of the HS shock was -8.57 ± 5.13 mmol·L -1 . A significant coagulopathy was detected in the DCBI model as measured by prothrombin time (15.8 seconds DCBI vs. 12.86 seconds SHAM; p = 0.02) and thromboelastography maximum amplitude (68.5 mm DCBI vs. 78.3 mm in SHAM; p = 0.0003). For the DCBI models, intracranial pressure (ICP) increased by a mean of 13 mm Hg, reaching a final ICP of 24 ± 7.7 mm Hg.

CONCLUSION

We created a reproducible large animal model to study the combined effects of severe HS, TI, and bTBI on coagulation and ICP in the setting of DCBI, with significant translational applications for the care of military warfighters. Within the 4-hour observational period, the swine developed a consistent coagulopathy with a concurrent brain injury evidenced by increasing ICP.

Defining Endotheliopathy in Murine Polytrauma Models

INTRODUCTION

"Endotheliopathy of trauma" is recognized as endothelial dysfunction following traumatic injury leading to poor patient outcomes. Acute post-traumatic disruptions in endothelial cell function have been associated with profound physiologic, hemodynamic, and coagulation derangements. The goal of this study was to define the generation and extent of endotheliopathy in murine polytrauma models by evaluating the post-traumatic release of serum biomarkers of ongoing cellular injury.

METHODS

Mice were randomized to undergo moderately severe concussive TBI by weight drop, 60-min hemorrhagic shock to MAP 25 mmHg with subsequent resuscitation with Lactated Ringer's, submandibular bleed (SMB), and/or midline laparotomy with rectus muscle crush. Mice were sacrificed at 1, 4, or 24 h for serum biomarker evaluation.

RESULTS

Serum biomarkers revealed differential timing of elevation and injury-dependent release.At 24 h, soluble thrombomodulin was significantly elevated in combined TBI + shock + lap crush compared to untouched, and shock alone. Syndecan-1 levels were significantly elevated after shock 1 to 24 h compared to untouched cohorts with a significant elevation in TBI + shock + lap crush 24 h after injury compared to shock alone. UCHL-1 was significantly elevated in shock mice at 1 to 24 h post-injury compared to untouched mice. UCHL-1 was also significantly elevated in the TBI + shock cohort 24 h after injury compared to shock alone. Hyaluronic acid release at 4 h was significantly elevated in shock alone compared to the untouched cohort with further elevations in TBI + shock + lap crush and TBI + shock compared to shock alone at 24 h. Hyaluronic acid was also increased in lap crush and laparotomy only cohort compared to untouched mice 24 h after injury.

CONCLUSIONS

A murine model of polytrauma including TBI, hemorrhagic shock, and laparotomy abdominal crush is a reliable method for evaluation of endotheliopathy secondary to trauma as indicated by differential changes in serum biomarkers.