Preparing the pump apparatus
A decommissioned perfusion roller pump (COBE Laboratories, Arvada, CO) was used. An acrylic basin to contain the kidney was prepared by drilling two holes into the side of the basin, to accommodate insertion of the arterial and venous tubing from the pump into the basin. Using a Y connector, the venous inflow tubing was divided into 2 segments: one for cannulation to the renal vein and one free end of inflow tubing for aspiration of water from the basin. A small puncture was made along the large outflow tubing to insert a 7Fr vascular sheath (Terumo, Somerset, NJ) to provide intra-vascular access.
Kidney preparation/cannulation
Adult bovine kidneys were harvested within 4 h from a local slaughterhouse (Wiatrek Processing Plant, Poth, TX) and transported to our laboratory on ice and stored at − 20 °C until further use. A total of six kidneys were collected, five left and one right. Left kidneys were preferred, as it was easier to cannulate them given the longer renal veins. Kidneys were not frozen more than 1 week, and all were thawed 24 h prior to experiments. A 16Fr Foley catheter (McKesson, Grapevine, TX) was used to cannulate the renal vein and secured by inflating the Foley balloon followed by purse string suture and a zip tie around the outer wall of the vein. The renal artery was cannulated with a piece of 15Fr stiff tube and secured with a purse string suture and two zip ties.
Initiating kidney perfusion
The cannulated kidney was submerged in tap water inside the basin. The free end of the now cannulated Foley catheter was connected to the venous tubing with a Y-connector submerged in water. The basin was filled with 25 °C tap water to submerge the kidney and the free aspirating end of the Y connector. The system was purged of air by activating the pump at a flow rate of 0.40 L/min prior to attaching the arterial inflow connection to the renal artery. Once air bubbles were purged out of the tubing, the pump was deactivated. The proximal end of the 15Fr arterial cannula was connected to the arterial outflow tubing. Then, the pump was activated to a flow rate of approximately 0.49 L/min based on our pilot test. The assembled flow model is depicted in Fig. 1.
Delivery of embolic materials
Angiography was conducted via a Siemens Arcadis C arm provided by our institution’s Department of Laboratory Animal Resources. This study involved the evaluation of three embolic materials: Tornado embolization coils (Cook Medical, Bloomington, IN), Gelfoam (Pfizer, New York, NY), and a glue mixture of Histoacryl (B Braun, Bethlehem, Pennsylvania) + Lipiodol (Guerbert, Princeton, NJ). Angiography and embolization for each kidney were attempted individually by a first-year diagnostic radiology resident and two medical students under the supervision of an interventional radiologist with 23 years of experience in vascular interventions. Each of the embolic materials were delivered to one of three segmental arterial branches in a single kidney (Fig. 2). A 5Fr cobra catheter (Boston Scientific, Marlborough, MA) with a Glidewire (Terumo, Somerset, NJ) was used for selection of segmental arteries and delivery of embolic materials. Once the catheter was placed in the renal artery, digital subtraction angiography (DSA) road mapping with Omnipaque contrast media (GE Healthcare, Wood Dale, IL) was conducted to outline arterial anatomy, assess for any intraparenchymal or extraparenchymal extravasation, and assist in selection of segmental branches for deploying the various embolic agents. For coil embolization, 3–4 mm 0,035-in. pushable coils were deployed using a Benston wire (Cook Medical, Bloomington, IN). Gelfoam particles were prepared by forcefully mixing a 2 cm X 2 cm piece of Gelfoam in a syringe filled with 5 mL of contrast media using a 3-way stopcock until a slurry was created. The Gelfoam slurry was slowly deployed with pulsatile boluses under fluoroscopy until stasis was observed. The volume of Gelfoam required to achieve stasis was recorded. For the deployment of glue, a mixture of 2 mL of lipiodol and 1 mL of Histoacryl was injected at a slow continuous rate until a cast of glue and subsequent stasis was visualized in the targeted segmental arteries. Glue infusion was preceded and succeeded with a 3 mL flush of the catheter with D5W.
Data acquisition/analysis
Kidney weight upon delivery to the lab was recorded. Approximate freeze time was recorded to assess an effect on kidney tissue quality, feasibility of angiography, and arterial segmental selection. Cannulation time was collected to assess the reproducibility and difficulty of constructing the model. A pre-embolic DSA was performed to assess the variability in vascular anatomical architecture. The success rate of segmental artery selection was reported to determine whether it was feasible to execute at minimum three embolic experiments within individual segments of each single kidney. The success rate of embolic agent deployment was recorded to assess the model’s ability to serve as an embolic deployment mimic. Post-embolic nonselective DSA images were performed and interpreted to assess the embolic effect of the agents. Total operational time and fluoroscopy dose were recorded to assess the feasibility, practicality, and safety of the experiment. Additionally, the above data points were collected for a single right kidney for direct comparison to left kidney procedural outcomes.