Timothy K. Williams

Extending the golden hour: Partial resuscitative endovascular balloon occlusion of the aorta in a highly lethal swine liver injury model.

BACKGROUND Combat-injured patients may require rapid and sustained support during transport; however, the prolonged aortic occlusion produced by conventional resuscitative endovascular balloon occlusion of the aorta (REBOA) may lead to substantial morbidity. Partial REBOA (P-REBOA) may permit longer periods of occlusion by allowing some degree of distal perfusion. However, the ability of this procedure to limit exsanguination is unclear. We evaluated the impact of P-REBOA on immediate survival and ongoing hemorrhage in a highly lethal swine liver injury model. METHODS Fifteen Yorkshire-cross swine were anesthetized, instrumented, splenectomized, and subjected to rapid 10% total blood loss followed by 30% liver amputation. Coagulopathy was created through colloid hemodilution. Randomized swine received no intervention (control), P-REBOA, or complete REBOA (C-REBOA). Central mean arterial pressure (cMAP), carotid blood flow, and blood loss were recorded. Balloons remained inflated in the P-REBOA and C-REBOA groups for 90 minutes followed by graded deflation. The study ended at 180 minutes from onset of hemorrhage or death of the animal. Survival analysis was performed, and data were analyzed using repeated-measures analysis of variance with post hoc pairwise comparisons. RESULTS Mean survival times in the control, P-REBOA, and C-REBOA groups were, 25 ± 21, 86 ± 40, and 163 ± 20 minutes, respectively (p < 0.001). Blood loss was greater in the P-REBOA group than the C-REBOA or control groups, but this difference was not significant (4,722 ± 224, 3,834 ± 319, 3,818 ± 37 mL, respectively, p = 0.10). P-REBOA resulted in maintenance of near-baseline carotid blood flow and cMAP, while C-REBOA generated extreme cMAP and prolonged supraphysiologic carotid blood flow. Both experimental groups experienced profound decreases in cMAP following balloon deflation. CONCLUSION In the setting of severe ongoing hemorrhage, P-REBOA increased survival time beyond the golden hour while maintaining cMAP and carotid flow at physiologic levels.

Partial resuscitative balloon occlusion of the aorta (P-REBOA): Clinical technique and rationale

Resuscitative endovascular balloon occlusion of the aorta (REBOA) has continued to evolve as a viable tool of modern trauma resuscitation. Developed from the convergence of trauma and endovascular surgery, REBOA has increasingly been used at select centers as a resuscitative adjunct for trauma patients with life-threatening noncompressible truncal hemorrhage. Even as prospective registry data seek to capture and analyze outcomes of early use of REBOA, ongoing device innovation and technique refinement seek to mitigate potential risks associated with aortic occlusion. It is hypothesized that early use of REBOA preserves cerebral perfusion and coronary filling in the setting of lifethreatening hypotension and hypovolemia secondary to hemorrhage. Laboratory data have demonstrated that the use of REBOA in the setting of hemorrhagic shock results in increased central aortic pressure, carotid flow, and brain oxygenation, and early reports suggest REBOA may improve outcomes in select patient populations. These benefits of REBOAmust be weighed against the consequence of sustained complete aortic occlusion, primarily profound distal ischemia and associated reperfusion

Emerging Endovascular Therapies for Non-Compressible Torso Hemorrhage

ABSTRACT Management of non-compressible torso hemorrhage (NCTH) remains a challenge despite continued advancements in trauma resuscitation. Resuscitative thoracotomy with aortic cross-clamping and recent advances in endovascular aortic occlusion, including resuscitative endovascular occlusion of the aorta, have finite durations of therapy due to the inherent physiologic stressors that accompany complete occlusion. Here, we attempt to illuminate the current state of aortic occlusion for trauma resuscitation including explanation of the deleterious consequences of complete occlusion, potential methods and limitations of existing technology to overcome these consequences, and a description of innovative methods to improve the resuscitation of NCTH. By explaining the complexity and potential deleterious effects of resuscitation augmented with aortic occlusion, our goal is to provide practitioners with a real-world perspective on current endovascular technology and to encourage the continued innovation required to overcome existing obstacles.

Extending resuscitative endovascular balloon occlusion of the aorta: Endovascular variable aortic control in a lethal model of hemorrhagic shock

BACKGROUND The duration of use and efficacy of resuscitative endovascular balloon occlusion of the aorta (REBOA) is limited by distal ischemia. We developed a hybrid endovascular-extracorporeal circuit variable aortic control (VAC) device to extend REBOA duration in a lethal model of hemorrhagic shock to serve as an experimental surrogate to further the development of endovascular VAC (EVAC) technologies. METHODS Nine Yorkshire-cross swine were anesthetized, instrumented, splenectomized, and subjected to 30% liver amputation. Following a short period of uncontrolled hemorrhage, REBOA was instituted for 20 minutes. Automated variable occlusion in response to changes in proximal mean arterial pressure was applied for the remaining 70 minutes of the intervention phase using the automated extracorporeal circuit. Damage-control surgery and whole blood resuscitation then occurred, and the animals were monitored for a total of 6 hours. RESULTS Seven animals survived the initial surgical preparation. After 20 minutes of complete REBOA, regulated flow was initiated through the extracorporeal circuit to simulate VAC and provide perfusion to distal tissue beds during the 90-minute intervention phase. Two animals required circuit occlusion for salvage, while five animals tolerated sustained, escalating restoration of distal blood flow before surgical hemorrhage control. Animals tolerating distal flow had preserved renal function, maintained proximal blood pressure, and rapidly weaned from complete REBOA. CONCLUSION We combined a novel automated, extracorporeal circuit with complete REBOA to achieve EVAC in a swine model of uncontrolled hemorrhage. Our approach regulated proximal aortic pressure, alleviated supranormal values above the balloon, and provided controlled distal aortic perfusion that reduced ischemia without inducing intolerable bleeding. This experimental model serves as a temporary surrogate to guide future EVAC catheter designs that may provide transformational approaches to hemorrhagic shock.

Design of a cost-effective, hemodynamically adjustable model for resuscitative endovascular balloon occlusion of the aorta (REBOA) simulation

ABSTRACT Resuscitative endovascular balloon occlusion of the aorta (REBOA) is an adjunct technique for salvaging patients with noncompressible torso hemorrhage. Current REBOA training paradigms require large animals, virtual reality simulators, or human cadavers for acquisition of skills. These training strategies are expensive and resource intensive, which may prevent widespread dissemination of REBOA. We have developed a low-cost, near-physiologic, pulsatile REBOA simulator by connecting an anatomic vascular circuit constructed out of latex and polyvinyl chloride tubing to a commercially available pump. This pulsatile simulator is capable of generating cardiac outputs ranging from 1.7 to 6.8 L/min with corresponding arterial blood pressures of 54 to 226/14 to 121 mmHg. The simulator accommodates a 12 French introducer sheath and a CODA balloon catheter. Upon balloon inflation, the arterial waveform distal to the occlusion flattens, distal pulsation within the simulator is lost, and systolic blood pressures proximal to the balloon catheter increase by up to 62 mmHg. Further development and validation of this simulator will allow for refinement, reduction, and replacement of large animal models, costly virtual reality simulators, and perfused cadavers for training purposes. This will ultimately facilitate the low-cost, high-fidelity REBOA simulation needed for the widespread dissemination of this life-saving technique.

Small changes, big effects: The hemodynamics of partial and complete aortic occlusion to inform next generation resuscitation techniques and technologies

BACKGROUND The transition from complete aortic occlusion during resuscitative endovascular balloon occlusion of the aorta can be associated with hemodynamic instability. Technique refinements and new technologies have been proposed to minimize this effect. In order to inform new techniques and technology, we examined the relationship between blood pressure and aortic flow during the restoration of systemic circulation following aortic occlusion at progressive levels of hemorrhage. METHODS An automated supraceliac aortic clamp, capable of continuously variable degrees of occlusion, was applied in seven swine. The swine underwent stepwise removal of 40% of their total blood volume in four equal aliquots. After each aliquot, progressive luminal narrowing to the point of complete aortic occlusion was achieved over 5 minutes, sustained for 5 minutes, and then released over 5 minutes. Proximal and distal blood pressure and distal aortic flow were continuously recorded throughout the study. RESULTS Upon release of the clamp, hyperemic aortic flow was observed following 10% and 20% hemorrhage (1,599 ± 785 mL/min, p < 0.01; and 1,070 ± 396 mL/min, p < 0.01, respectively). Proximal blood pressure exhibited a nonlinear relationship to aortic flow during clamp removal; however, distal blood pressure increased linearly with distal flow upon clamp opening across all hemorrhage volumes. CONCLUSIONS Hyperemic blood flow following return of circulation may contribute to cardiovascular collapse. Reintroduction of systemic blood flow after aortic occlusion should be guided by distal blood pressure rather than proximal pressure. Awareness of hemodynamic physiology during aortic occlusion is of paramount importance to the clinical implementation of next-generation resuscitative endovascular balloon occlusion of the aorta techniques and technologies.

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.

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.OBJECTIVES Despite clinical reports of poor outcomes, the degree to which 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 to partial aortic occlusion (PAO) or no intervention. METHODS 21 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%CI 3.6-57.9; REBOA 28.6%, 95%CI 3.7-71.0; and PAO 28.6%, 95%CI 3.7-71.0). CONCLUSIONS In an animal model of TBI and shock, REBOA increased carotid flow 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. LEVEL OF EVIDENCE Level IV.

Technical and Early Outcomes Using Ultrasound-Guided Reentry for Chronic Total Occlusions

BACKGROUND Subintimal angioplasty is a common treatment for chronic total occlusions (CTOs) in the iliac and infrainguinal arteries. Although technical success has been described using intravascular ultrasound-guided reentry devices (IVUS-RED), outcomes are still not well defined. This report describes the technical aspects and longitudinal follow-up after intravascular ultrasound-guided reentry of iliac and infrainguinal CTOs. METHODS A retrospective review was performed of 20 patients with lower extremity CTO treated with IVUS-RED from 2011 to 2013. A matched cohort of patients who underwent lower extremity interventions without the use of IVUS-RED was also identified. Procedural success, patency estimates, ankle-brachial indices (ABIs), complications, and limb salvage were analyzed. RESULTS Twenty patients (mean age, 69 ± 13 years), including 11 men and 9 women, underwent attempted IVUS-RED-guided recanalization. Median follow-up was 4.3 months (range, 0.4-24). Eleven patients presented with critical limb ischemia (CLI), and 9 presented with claudication. Technical success was achieved in 18 (90%) patients. Ten common iliac arteries, 3 external iliac arteries, and 5 superficial femoral arteries (SFA) were treated. No intraoperative complications resulted from device use. After procedure, ABIs significantly increased (0.5-0.9; P < 0.01) in the 13 patients with follow-up. Primary patency for the entire cohort was 62% at 12 months. No patient treated for claudication required reintervention, whereas 3 (27%) of those treated for CLI required repeat interventions. During follow-up, 2 patients died unrelated to the procedure, 1 patient required an amputation, and 1 patient eventually required open revascularization. When the IVUS-RED group was compared with a cohort matched on Trans-Atlantic Inter-Society Consensus and age, no difference was found in runoff scores and patency between the 2 groups during follow-up (P > 0.05). CONCLUSIONS Recanalization of CTO using IVUS-RED is safe and effective. Use of IVUS-RED does not adversely impact outcomes in conjunction with other endovascular techniques. Early follow-up demonstrates acceptable patency, especially in patients with claudication, and freedom from reintervention.

Direct site endovascular repair (DSER): A novel approach to vascular trauma.

ABSTRACT Peripheral vascular injuries carry significant risk for permanent functional impairment, limb loss, and death. Definitive correction of these injuries requires significant operative time and has traditionally been resource and skill set intensive. In the initial surgical treatment of the physiologically depleted trauma patient, faster techniques may prove more appropriate. Damage control techniques, including vascular shunting, rapidly restore distal flow but require additional vascular intervention and risk shunt thrombosis with prolonged use. To address these challenges, we present a technique, using an off-the-shelf endovascular device, for treatment of peripheral arterial injuries. Direct-site endovascular repair (DSER) is an open vascular surgical reconstruction technique using conventional endovascular stent grafts to create a “sutureless” anastomosis. We believe this technique to be a valuable adjunct to current repair options. The values of this technique are that it is (1) rapid, (2) of low technical complexity, (3) requires very little equipment, and (4) may offer extended durability in damage control scenarios. We describe three patients where this technique was used. In the first case, the technique was used to provide a temporary arterial shunt in a patient with a local infection and arterial disruption. In the second case, DSER was used for definitive repair of an injured artery after penetrating trauma. The third case involves DSER for definitive of both an artery and vein after penetrating trauma.