A Hyperbaric Warm Perfusion System Preserves Tissue Composites Ex vivo and Delays the Onset of Acute Rejection.

BACKGROUND: Ischemia-reperfusion injury (IRI) precipitates acute rejection of vascularized composite allografts (VCA). Hyperbaric preservation of tissues ex vivo, between harvest and revascularization, may reduce IRI and mitigate acute rejection of VCA. METHODS: A porcine heterotopic musculocutaneous gracilis flap model was used. In phase 1, control autografts (n = 5) were infused with University of Wisconsin Solution (UWS) and stored at 4°C for 3 hours. Intervention autografts (n = 5) were placed in a hyperbaric oxygen organ preservation system for 5 hours and infused with hyperoxygenated UWS at 20°C and 3 atm. Grafts were replanted into the animals' necks. In phase 2, similarly treated control (n = 8) and intervention grafts (n = 8) were allotransplanted into the necks of animals separated by a typed and standardized genetic mismatch. No systemic immunosuppression was given. Systemic markers of IRI, and clinical and histopathological assessments of necrosis and rejection were performed. RESULTS: Autotransplanted tissue composites preserved in the hyperbaric chamber showed histopathological evidence of less muscle necrosis at 3 hours (p = 0.05). Despite a longer period of ischemia, no evidence was found of a difference in systemic markers of IRI following revascularization in these groups. Allotransplanted tissues supported ex vivo within the hyperbaric perfusion device experienced acute rejection significantly later than corresponding controls. CONCLUSION: Hyperbaric warm perfusion preserves musculocutaneous tissue composites ex vivo for longer than standard cold preservation in this model. This translates into a delay in acute rejection of allotransplanted tissue composites.

C1 esterase inhibitor ameliorates ischemia reperfusion injury in a swine musculocutaneous flap model.

PURPOSE: Free tissue transfer is a powerful reconstructive surgical technique. The ischemia reperfusion injury (IRI) at revascularization affects the flap and the patient; reducing this insult could improve outcomes. This study evaluated the effect of C1 esterase inhibitor (C1-inh) on IRI in a porcine musculocutaneous flap model. MATERIALS AND METHODS: A musculocutaneous flap was transferred from the limb to the neck of 12 swine. Flaps underwent a 3-hour ischemic interval prior to revascularization. Intervention group flaps (n = 6) were perfused intra-arterially with 100U C1-inh at the commencement of the ischemic period; controls (n = 6) received heparinized saline solution. Protocol duration was 14 days; markers of reperfusion injury (creatine kinase [CK], aspartate transaminase [AST], tumor necrosis factor-alpha) were evaluated. RESULTS: All flaps from the intervention group were viable at 14 days; five of six control flaps were viable at 14 days (P = 1). Systemic levels of biomarkers of tissue necrosis and inflammation were reduced in the intervention group. On post-operative day one, statistically significant reductions in mean levels of AST and CK were demonstrated (2,293 ± 1 × 103 U/L vs. 1,586 ± 767 U/L [P = 0.04] and 429 × 103 ± 214 × 103 U/L vs. 213 × 103 ± 156 × 103 U/L [P = 0.002], respectively). Flaps of both groups healed in their recipient locations, no adverse reactions were observed. CONCLUSIONS: C1-inh is protective of IRI and may have utility in free tissue transfer, vascularized composite allotransplantation, and spare parts surgery. © 2016 Crown copyright. Microsurgery © 2016 Wiley Periodicals, Inc. Microsurgery 37:142-147, 2017.

A Porcine Orthotopic Forelimb Vascularized Composite Allotransplantation Model: Technical Considerations and Translational Implications.

BACKGROUND: The restoration of complex tissue deficits with vascularized composite allotransplantation is a paradigm shift in reconstructive surgery. Clinical adoption of vascularized composite allotransplantation is limited by the need for systemic immunosuppression, with associated morbidity and mortality. Small-animal models lack the biological fidelity and preclinical relevance to enable translation of immunologic insights to humans. Large-animal models have been described; however, limitations persist, including the inability of heterotopic models to evaluate functional nerve regeneration, and the sensitivity of primates to toxicity of immunosuppressive drugs. The authors' novel orthotopic porcine limb transplant model has broad applicability and translational relevance to both immunologic and functional outcomes after vascularized composite allotransplantation. METHODS: Recipients underwent amputation at a level corresponding to the mid forearm. Replantation or transplantation of grafts was performed by plate fixation of the radio-ulna, microsurgical repair of brachial artery and median nerve, and extensor and flexor tendon repairs. Viability of replants was monitored clinically and radiologically. Transplants were monitored for clinicopathologic signs of rejection. Animals mobilized freely postoperatively. RESULTS: Replantations remained viable until the endpoint of 14 days. Transplants developed Banff grade 4 acute rejection by postoperative day 7. Doppler sonography and angiography confirmed vascular patency. Serial biopsy specimens of skin and histopathology of replants at endpoint confirmed tissue viability and bone healing. CONCLUSIONS: An orthotopic load-bearing porcine forelimb vascularized composite allotransplantation model was successfully established. Technical, procedural, and logistic considerations were optimized to allow model use for immunologic, bone healing, functional nerve regeneration, and other translational studies.

Wartime vascular injuries in the pediatric population of Iraq and Afghanistan: 2002-2011.

BACKGROUND: Contemporary war-related studies focus primarily on adults with few reporting the injuries sustained in local pediatric populations. The objective of this study is to characterize pediatric vascular trauma at US military hospitals in wartime Iraq and Afghanistan. METHODS: Review of the Department of Defense Trauma Registry (DoDTR) (2002-2011) identified patients (1-17 years old) treated at US military hospitals in Iraq and Afghanistan using ICD-9 and procedure codes for vascular injury. RESULTS: US military hospitals treated 4402 pediatric patients between 2002 and 2011. One hundred fifty-five patients (3.5%) had a vascular injury. Mean age, gender, and injury severity score (ISS) were 11.1 ± 4.1 years, 79% male, and 34 ± 13.5, respectively. Vascular injuries were primarily from penetrating mechanisms (95.6%; 58.0% blast injury) to the extremity (65.9%), torso (25.4%), and neck (8.6%). Injuries were ligated (31%), reconstructed (63%), or observed (2%). Limb salvage rate was 95%. Mortality rate was 9%. CONCLUSIONS: This study is the first to report vascular trauma in a pediatric population at wartime. Vascular injuries involve a high percentage of extremity and torso wounding. Torso vascular injury in children is four times lethal relative to other injury patterns, and therefore should be considered in operational planning both in the military and civilian setting regarding pediatric vascular injuries.

Endovascular Skills for Trauma and Resuscitative Surgery (ESTARS) course: curriculum development, content validation, and program assessment.

BACKGROUND: The management of hemorrhage shock requires support of central aortic pressure including perfusion to the brain and heart as well as measures to control bleeding. Emerging endovascular techniques including resuscitative endovascular balloon occlusion of the aorta serve as potential lifesaving adjuncts in this setting. The Endovascular Skills for Trauma and Resuscitative Surgery (ESTARS) course was developed to provide fundamental endovascular training for trauma surgeons. METHODS: ESTARS 2-day course incorporated pretest/posttest examinations, precourse materials, lectures, endovascular and open vascular instruments, Vascular Intervention System Trainer endovascular simulator, and live animal laboratories for training and testing. Curriculum included endovascular techniques for trauma; review of wires, sheaths, and catheters; as well as regional vascular injury management. Animal laboratories integrated arterial access, angiography, coil embolization, resuscitative endovascular balloon occlusion of the aorta, control of iliac artery injury, and vascular shunt placement. Students completed a knowledge test (precourse/postcourse) and a summative skills assessment. The test measured knowledge and judgment in vascular injury management as defined in the course objectives. Vascular Intervention System Trainer and animal laboratory were used for final examinations. Subjective performance was graded by expert observers using a global assessment scale and performance metrics. RESULTS: Four pilot ESTARS courses were completed, with four participants each. Knowledge and performance significantly improved after ESTARS. Mean test examination scores increased by 77% to 85%, with a mean change of 9 percentage points [paired t (15) = 7.82, p < 0.0001]. The test was unidimensional (Cronbach's α = 0.67). Technical skill significantly improved for both endovascular simulation and live animal laboratory examinations. All participants passed the live animal laboratory practical examination. CONCLUSION: The ESTARS curriculum is effective at teaching a basic set of endovascular skills for resuscitation and hemorrhage control to trauma surgeons. ESTARS was confirmed as a stepwise and hierarchical curriculum demonstrating measurable improvements in performance metrics and should serve as a model for future competency-based structured training in endovascular trauma skills.

Hydrogen sulfide mitigates reperfusion injury in a porcine model of vascularized composite autotransplantation.

BACKGROUND: Devastating extremity injuries are prevalent but often survivable on the modern battlefield. These complex injuries require advanced methods of reconstruction, involving prolonged ischemic periods and reperfusion injury. Using our group's validated porcine model of gracilis myocutaneous flap transplantation, this study demonstrates that an interim perfusion of hydrogen sulfide (H2S) mitigates the effects of reperfusion injury in the setting of delayed restoration of blood flow. METHODS: A gracilis myocutaneous flap (200-400 g; surface area, 250 cm²) was procured from the hind limb of a Yorkshire swine (70-90 kg, n=16). The right external carotid artery and the internal jugular vein are the recipient axis. Group 1 (control, n = 6) underwent delayed anastomosis with a 3-hour ischemic period. Group 2 (n=10) underwent a similar delayed anastomosis with an interim perfusion of H2S during the ischemic period. The animals survived for 14 days. Systemic biomarker assays for skeletal muscle tissue injury (creatine kinase, lactate dehydrogenase, and aspartate transaminase) and proinflammatory markers (tumor necrosis factor α and interleukin 6) provide assessment of reperfusion injury at the cellular level. RESULTS: The control animals (3 hours of ischemia with an interim perfusion of heparinized saline) demonstrated increased levels of injury biomarkers and proinflammatory cytokines compared with the animals receiving H2S infusion and identical ischemic interval. The control flaps had a mean creatine kinase level of 280³×10 U/L (±80×10³), compared with the H2S group, which had a mean of 99×10³ U/L (±14×10³; P=0.0007 at postoperative day 2). lactate dehydrogenase levels (mean) were 26×10³ U/L (±8×10³) versus 9×10³ U/L (±3×10³; P=0.0004) and aspartate transaminase levels (mean) were 1651 U/L (±324) versus (873 U/L [±279]; P=0.0013) for the control and treatment groups, respectively. Similarly, an intergroup difference in IL-6 was found, although not statistically significant. Tumor necrosis factor α levels (mean) were 93 pg/mL (±14) versus 39 pg/mL (±4; P=0.0013) for the control and treatment groups, respectively. CONCLUSIONS: This study demonstrated the mitigating properties of H2S on reperfusion injury. Interim perfusion with H2S resulted in diminution of ischemia-dependent biomarkers after 3 hours of ischemia. Follow-up studies will translate these findings as an evolving method for reconstructing previously unreconstructable injuries.

A novel fluoroscopy-free, resuscitative endovascular aortic balloon occlusion system in a model of hemorrhagic shock.

BACKGROUND: Resuscitative endovascular balloon occlusion of the aorta (REBOA) is a potentially lifesaving maneuver in the setting of hemorrhagic shock. However, emergent use of REBOA is limited by existing technology, which requires large sheath arterial access and fluoroscopy-guided balloon positioning. The objectives of this study were to describe a new, fluoroscopy-free REBOA system and to compare its efficacy to existing technology. An additional objective was to characterize the survivability of 60 minutes of REBOA using these systems in a model of hemorrhagic shock. METHODS: Swine (70-88 kg) in shock underwent 60 minutes of REBOA using either a self-centering, one component prototype balloon system (PBS, n = 8) inserted (8 Fr) and inflated without fluoroscopy or a two-component, commercially available balloon system (CBS, n = 8) inserted (14 Fr) with fluoroscopic guidance. Following REBOA, resuscitation occurred for 48 hours with blood, crystalloid, and vasopressors. End points included accurate balloon positioning, hemodynamics, markers of ischemia, resuscitation requirements, and mortality. RESULTS: Posthemorrhage mean arterial pressure (mm Hg) was similar in the CBS and PBS groups (35 [8] vs. 34 [5]; p = 0.89). Accurate balloon positioning and inflation occurred in 100% of the CBS and 88% of the PBS group. Following REBOA, mean arterial pressure increased comparably in the CBS and PBS groups (81 [20] vs. 89 [16]; p = 0.21). Lactate peaked in the CBS and PBS groups (10.8 [1.4] mmol/L vs. 13.2 [2.1] mmol/L; p = 0.01) 45 minutes following balloon deflation but returned to baseline by 24 hours. Mortality was similar between the CBS and PBS groups (12% vs. 25%, p = 0.50). CONCLUSION: This study reports the feasibility and efficacy of a novel, fluoroscopy-free REBOA system in a model of shock. Despite a significant physiologic insult, 60 minutes of REBOA is tolerated and recoverable. Development of lower profile, fluoroscopy-free endovascular balloon occlusion catheters may allow proactive aortic control in patients at risk for hemorrhagic shock and cardiovascular collapse.

Microvascular porcine model for the optimization of vascularized composite tissue transplantation.

BACKGROUND: Devastating extremity injuries are prevalent but most often survivable on the modern battlefield. The complexity of these injuries requires advanced methods of reconstruction. This study is designed to validate the feasibility of gracilis myocutaneous flap transplantation via microvascular free tissue transfer in a porcine model. This model will facilitate study of autotransplant physiology as well as vascularized composite allotransplantation as an evolving method for reconstructing previously nonreconstructable injuries. MATERIAL AND METHODS: A donor gracilis myocutaneous flap is procured from Yorkshire swine. The right external carotid artery and internal jugular vein are prepared as the recipient axis for microvascular anastomoses. Group 1 undergoes immediate microvascular anastomosis with resultant 1-h ischemic period. Group 2 undergoes delayed anastomosis with 3-h ischemic period. Markers of ischemia-reperfusion injury are evaluated after anastomosis and on postoperative days 1, 2, 7, and 14. RESULTS: A novel porcine model for microvascular composite tissue transplantation is demonstrated. Ischemia period-dependent elevations in circulating biomarkers (lactate dehydrogenase [LDH], creatine kinase [CK], and aspartate transaminase [AST]) demonstrate the effects of prolonged ischemia. Both groups showed marked LDH elevation without significant statistical intergroup difference (P=0.250). The difference in CK and AST levels at 24h showed strong significance (P<0.0001). CONCLUSIONS: A novel method of vascularized gracilis myocutaneous flap transplantation was validated in the Yorkshire swine. Assays for skeletal muscle tissue injury (LDH, CK, and AST) showed ischemia period-dependent response providing assessment of ischemia-reperfusion injury at the cellular level. Subsequent studies will evaluate agents that mitigate ischemia-reperfusion injury and transition these findings to potentiate vascularized composite allotransplantation.

Aortic balloon occlusion is effective in controlling pelvic hemorrhage.

BACKGROUND: The objective of this study was to evaluate the efficacy of resuscitative endovascular aortic balloon occlusion (REBOA) of the distal aorta in a porcine model of pelvic hemorrhage. METHODS: Swine were entered into three phases of study: injury (iliac artery), hemorrhage (45 s), and intervention (180 min). Three groups were studied: no intervention (NI, n = 7), a kaolin-impregnated gauze (Combat Gauze) (CG, n = 7), or REBOA (n = 7). The protocol was repeated with a dilutional coagulopathy (CG-C, n = 7, and REBOA-C, n = 7). Measures of physiology, rates of hemorrhage, and mortality were recorded. RESULTS: Rate of hemorrhage was greatest in the NI group, followed by the REBOA and CG groups (822 ± 415 mL/min versus 11 ± 13 and 0.2 ± 0.4 mL/min respectively; P < 0.001). MAP following intervention (at 15 min) was the same in the CG and REBOA groups and higher than in the NI group (70 ± 4 and 70 ± 11 mm Hg versus 5 ± 13 mm Hg respectively; P < 0.001). There was 100% mortality in the NI group, with no deaths in the CG or REBOA group. In the setting of coagulopathy, the rate of bleeding was higher in the CG-C versus the REBOA-C group (229 ± 295 mL/min versus 20 ± 7 mL/min, P = 0.085). MAP following intervention (15 min) was higher in the REBOA-C than the CG-C group (71 ± 12 mm Hg versus 28 ± 31 mm Hg; P = 0.005). There were 5 deaths (71.4%) in the CG-C group, but none in the REBOA-C group (P = 0.010). CONCLUSION: Balloon occlusion of the aorta is an effective method to control pelvic arterial hemorrhage. This technique should be further developed as an adjunct to manage noncompressible pelvic hemorrhage.