Porcine Model of Ruptured Abdominal Aortic Aneurysm Repair

Novel Experimental Technique to Create Size-Controlled Retroperitoneal Bleeding in the Infrarenal Aorta of Anesthetized Pigs

OBJECTIVE

Rupture of abdominal aortic aneurysm (rAAA) with a contained retroperitoneal hematoma is potentially fatal. Physiological studies are difficult to perform in patients suffering from life-threatening conditions such as rAAA. A translational model of the condition is therefore needed. The aim was to develop and validate an endovascular animal model for retroperitoneal bleeding of the abdominal aorta with contained hematoma.

METHODS

In anesthetized pigs, a puncture hole was made in the posterolateral portion of the infrarenal aorta by an Outback re-entry catheter device. The hole was gradually enlarged using angioplasty balloons to a specific diameter of either 4 mm (n = 6), 6 mm (n = 7), or 8 mm (n = 6). Onset of bleeding was verified by angiography and macroscopically examined on completion of the experiments. Survival up to 180 min was the primary outcome. Hemodynamic and metabolic markers in arterial blood were secondary outcomes.

RESULTS

Aortic injury with a contained retroperitoneal hematoma was achieved in all animals. Survival rate at 180 min after onset of bleeding was higher in the 4 mm group compared to the 6 mm (P = 0.021) and 8 mm groups (P = 0.002), but not when comparing the 6 mm and 8 mm groups. Systemic hypotension, arterial acidosis, and lactatemia were provoked in the 6 mm and 8 mm groups but not in the 4 mm group.

CONCLUSIONS

A porcine model for a controlled contained left posterolateral retroperitoneal bleeding was created using endovascular methods and validated. This model makes it possible to study the pathophysiology of a retroperitoneal hematoma.

Acute aortic wall injury caused by aortic cross-clamping: morphological and biomechanical study of the aorta in a swine model of three aortic surgery approaches

Background

Aortic cross-clamping and balloon occlusion of the aorta could lead to damage to the aorta wall.

Objective

The aim of this study was to investigate changes to the aorta wall related to the method used to interrupt flow (clamping or balloon) in the different techniques available for aortic surgery.

Methods

Experiments were performed on 40 female pigs, weighing 25-30kg, which were randomly allocated to 4 study groups: S (n=10), no intervention (sham group); C (n=10), midline transperitoneal laparotomy for infrarenal abdominal aortic access with 60 min of cross-clamping; L (n=10), laparoscopic infrarenal abdominal aortic surgery with 60 min of cross-clamping; EV (n=10), remote proximal aortic control with transfemoral arterial insertion of aortic occlusion balloon catheter, inflated to provide continued aortic occlusion for 60min. After euthanasia, the aortas were removed and cross-sectioned to obtain histological specimens for light microscopic and morphometric analyses. The remaining longitudinal segments were stretched to rupture and mechanical parameters were determined.

Results

We observed a reduction in the yield point of the abdominal aorta, decrease in stiffness and in failure load in the aortic cross-clamping groups (C and L) compared with the EV group.

Conclusions

Aortic cross-clamping during open or laparoscopic surgery can affect the mechanical properties of the aorta leading to decrease in resistance of the aorta wall, without structural changes in aorta wall histology.

REBOA for the IVC? Resuscitative balloon occlusion of the inferior vena cava (REBOVC) to abate massive hemorrhage in retrohepatic vena cava injuries

BACKGROUND

The use of resuscitative endovascular balloon occlusion as a maneuver for occlusion of the aorta is well described. This technique has life-saving potential in other cases of traumatic hemorrhage. Retrohepatic inferior vena cava (IVC) injuries have a high rate of mortality, in part, due to the difficulty in achieving total vascular isolation. The purpose of this study was to investigate the ability of resuscitative balloon occlusion of the IVC to control suprahepatic IVC hemorrhage in a swine model of trauma.

METHODS

Thirteen swine were randomly assigned to control (seven animals) versus intervention (six animals). In both groups, an injury was created to the IVC. Hepatic inflow control was obtained via clamping of the hepatoduodenal ligament and infrahepatic IVC. In the intervention group, suprahepatic IVC control was obtained via a resuscitative balloon occlusion of the IVC placed through the femoral vein. In the control group, no suprahepatic IVC control was established. Vital signs, arterial blood gases, and lactate were monitored until death. Primary end points were blood loss and time to death. Lactate, pH, and vital signs were secondary end points. Groups were compared using the χ and the Student t test with significance at p < 0.05.

RESULTS

Intervention group's time to death was significantly prolonged: 59.3 ± 1.6 versus 33.4 ± 12.0 minutes (p = 0.001); and total blood loss was significantly reduced: 333 ± 122 vs 1,701 ± 358 mL (p = 0.001). In the intervention group, five of the six swine (83.3%) were alive at 1 hour compared to zero of seven (0%) in the control group (p = 0.002). There was a trend toward worsening acidosis, hypothermia, elevated lactate, and hemodynamic instability in the control group.

CONCLUSIONS

Resuscitative balloon occlusion of the IVC demonstrates superior hemorrhage control and prolonged time to death in a swine model of liver hemorrhage. This technique may be considered as an adjunct to total hepatic vascular isolation in severe liver hemorrhage and could provide additional time needed for definitive repair.

LEVEL OF EVIDENCE

Therapeutic study, level II.

Original Research: Porcine model for observing changes due to ischemia/reperfusion injury secondary to intra-abdominal endovascular balloon occlusion

Compared with conventional aortic cross-clamping, endovascular balloon occlusion (EBO) is a valuable strategy in unstable ruptured abdominal aorta aneurysm patients; however, it is unclear how long the balloon may remain safely inflated. Using a porcine model, we evaluated the influence of different EBO time periods on intra-abdominal pressure (IAP) and the association between various pathophysiologic indicators and reperfusion time. Twelve healthy three-month-old domestic piglets were subjected to ischemia/reperfusion injury using EBO within the abdominal aorta. Animals were grouped as A, B, and C based on 30, 60, or 120 min of ischemic time, respectively. Changes in IAP, hemodynamic data, respiratory and renal function, and histology after reperfusion were compared with baseline measurements. All pigs gradually developed intra-abdominal hypertension after ischemia/reperfusion injury. IAP increased significantly after 4 h of reperfusion in all three groups (all P < 0.001) with maximal IAP reaching > 22 mmHg in 10 pigs. However, no significant intergroup differences were found. Cardiac output remained stable, but mixed venous oxygen saturation decreased significantly at 4 h after reperfusion (P < 0.05). The pH decreased significantly at 10 min in all three groups (all P < 0.001). Histological changes in the small intestine, lung, and kidney occurred secondary to aortic ischemia; however, no significant differences were noted between groups (P > 0.05). EBO within the abdominal aorta induced ischemia/reperfusion injury which led to intra-abdominal hypertension, pathological changes within multiple organs, and decreased mixed venous oxygen saturation after only 30 min of abdominal aortic ischemia.

Design of a synthetic simulator for pediatric lumbar spine pathologies

OBJECT

Simulation has become an important tool in neurosurgical education as part of the complex process of improving residents' technical expertise while preserving patient safety. Although different simulators have already been designed for a variety of neurosurgical procedures, spine simulators are still in their infancy and, at present, there is no available simulator for lumbar spine pathologies in pediatric neurosurgery. In this paper the authors describe the peculiarities and challenges involved in developing a synthetic simulator for pediatric lumbar spine pathologies, including tethered spinal cord syndrome and open neural tube defects.

METHODS

The Department of Neurosurgery of the University of Illinois at Peoria, in a joint program with the Mechanical Engineering Department of Bradley University, designed and developed a general synthetic model for simulating pediatric neurosurgical interventions on the lumbar spine. The model was designed to be composed of several sequential layers, so that each layer might closely mimic the tensile properties of the natural tissues under simulation. Additionally, a system for pressure monitoring was developed to enable precise measurements of the degree of manipulation of the spinal cord.

RESULTS

The designed prototype successfully simulated several scenarios commonly found in pediatric neurosurgery, such as tethered spinal cord, retethered spinal cord, and fatty terminal filum, as well as meningocele, myelomeningocele, and lipomyelomeningocele. Additionally, the formulated grading system was able to account for several variables involved in the qualitative evaluation of the technical performance during the training sessions and, in association with an expert qualitative analysis of the recorded sessions, proved to be a useful feedback tool for the trainees.

CONCLUSIONS

Designing and building a synthetic simulator for pediatric lumbar spine pathologies poses a wide variety of unique challenges. According to the authors' experience, a modular system composed of separable layers that can be independently replaced significantly enhances the applicability of such a model, enabling its individualization to distinctive but interrelated pathologies. Moreover, the design of a system for pressure monitoring (as well as a general score that may be able to account for the overall technical quality of the trainee's performance) may further enhance the educational applications of a simulator of this kind so that it can be further incorporated into the neurosurgical residency curriculum for training and evaluation purposes.