Abstract
Background
Contrast-induced acute kidney injury is a severe condition resulting from the use of radiology contrast in patients with predisposing factors.
Hypothesis
We hypothesized that a novel system including a device containing polymer resin sorbent beads and a custom-made suctioning catheter could efficiently remove contrast from an in vitro novel model of circulatory system (MOCS) mimicking the cerebral circulation.
Methods
A custom-made catheter was built and optimized for cerebral venous approach. The efficiency of a system made of a polymer resin sorbent beads column (CST 401, Cytosorbents) and this particular catheter was tested in the MOCS running a solution composed of 0.9% saline and radio-contrast. During two series of 18 cycles of first-pass experiments we assessed the catheter’s suctioning efficiency and the system’s ability to clear radio-contrast injected into the MOCS’s cerebral arterial segment. We also assessed the functioning and reliability of the MOCS.
Results
Mean suctioning efficiency of the catheter was 84% ± 24%. The polymer sorbent column contrast removal rate was initially 96% and gradually decreased with subsequent cycles in a linear fashion during an experiment lasting approximately 90 minutes. The MOCS had a reliability of 0.9946×min − 1 where 1 × min − 1 was the optimum value.
Conclusion
A system including a polymer resin sorbent beads column and a custom-made suctioning catheter had an excellent initial efficiency in quickly removing contrast from an artificial MOCS mimicking the cerebral circulation. MOCS is an inexpensive and relatively reliable custom-made system that can be used for training or testing purposes.
1
Introduction
Contrast-induced acute kidney injury (CI-AKI) is a severe condition resulting from exposure to radio-contrast agents in patients with predisposing risk factors such as impaired renal function, congestive heart failure, shock, dehydration or diabetes mellitus. CI-AKI can have grave consequences including need of dialysis and even death . The current practice encourages minimal contrast load and pre- and post-procedural hydration.
Suctioning and filtering of contrast material has been demonstrated to be possible in animal coronary arterial experiments . In this study we aim to demonstrate the use and assess the efficiency of a system designed to suction fluid mixed with contrast from the venous “cerebral circulation” of an artificial model system mimicking the blood flowing through the aorta/superior vena cava and cerebral arterial and venous circulation, followed by filtering of the fluid-contrast mixture by means of a device containing polymer resin sorbent beads – CST 401 (Cytosorbents, Monmouth Junction, NJ). The final purpose is the design of a clinically proof system for CI-AKI prevention during cerebrovascular interventions.
2
Methods
2.1
Objective
The objective of the study was to test a specially designed system made of a custom-made catheter and a polymer resin sorbent column to suction and filter a mixture of fluid and contrast injected into a model of circulatory system (MOCS). A second objective was to measure the efficiency of the contrast suctioning as well as the contrast filtering process. We also report here the design and creation of a MOCS that resembles the cerebral arterial and venous circulatory system.
2.2
Artificial model of cerebral arterial and venous system
MOCS is a system that mimics the aortic and cerebral arterial circulation in direct extension with the cerebral venous circulation, including the internal jugular veins and the superior vena cava ( Fig. 1 A, B ). For reasons of simplicity all parts of this system will be called using their anatomical designation. The segments imitated in this system were described in Fig. 1 and were sized similarly to average human vessels. At the distal end of the superior vena cava (to the pump driving the fluid inside the MOCS, labeled as the “system-pump”) a 5–11 mm Autosuture Versaport trocar (Covidien) was fitted to the tubing system in order to allow easy insertion of a 13F catheter without major fluid leakage. The distal end of the descending aorta was fitted to allow the insertion of a 5F catheter. Front and respectively side ports were produced into the distal ascending aorta (aortic inflow) and vena cava (venous outflow) to allow flow circulation from and back to the system-pump. The system was built of transparent clear vinyl plastic tubing, demonstrating enough plasticity to allow various curve shaping, cutting and perforating steps.
A system fluid (0.9% saline) was circulated through the MOCS. A total fluid volume of 4 l was run with the help of a roller-head pump (system-pump; all roller-heads used in this study were refurbished Stoeckert-Shiley pumps) at a rate of 1.5 l/min, similar with the cardiac output delivered to the head and upper extremities. The fluid was housed inside a system 5-l reservoir (“system reservoir”), placed in series fashion and included the venous part of the MOCS, followed by the system-pump that pushed the fluid into the arterial inflow, and the arterial part of the MOCS. The system fluid was then allowed to drain from the venous outflow into the system reservoir.
2.3
Veno-venous circuit
Since the system reservoir was followed by the system-pump (MOCS equivalent of the anatomical heart), it should be considered that this reservoir was part of the venous MOCS, turning the removal and return of the MOCS fluid into a veno-venous circuit.
2.4
Catheters and sorbent material
A 13F external diameter catheter (suctioning catheter) was designed and custom made for insertion through the valve situated at the distal end of the superior vena cava and the right internal jugular vein ( Fig. 1 ). In human/animal use/experiments this catheter is supposed to be inserted into a femoral vein (not replicated in our MOCS) and then threaded through the inferior and then superior vena cava respectively before reaching the jugular vein. This catheter was custom made with the purpose of being lodged into the internal jugular vein for reasons of suctioning the mixture of blood and contrast draining into the venous system ( Fig. 2 ). Full description of the catheter can be found at or in the supplemental material appendix. The distal end of the catheter (towards the suction-pump) was fitted with a fluid-contrast mix suction outlet, an inlet port for the easy insertion of a wire and dilator, and a fluid-inlet allowing the passage of a fluid bolus (air in this particular experiment) towards the balloon situated at the proximal end of the catheter. The proximal end the catheter adopts an S-shape with the suctioning holes on the concave side of the two “S” curves in order to allow high-flow suctioning unobstructed by eventual collapsing vein walls. The second catheter was a 5F JR4 Judkins commonly used in angiography procedures.
CST 401 is a biocompatible polymer resin sorbent with the gross appearance of beads with a diameter of approximately 425 μm to 1000 μm with a surface area of at least 850 m 2 /g. It has been employed in human sepsis clinical trials due to its ability to efficiently remove various cytokine molecules (please see supplemental material regarding clinical use data for CST-401) .
2.5
Functioning of suction and filtering systems
The 5F JR4 catheter (injecting catheter) was inserted at the beginning of the procedure with the help of a 0.35 inch J-tip wire into the right carotid artery, after advancing through the descending aorta. Subsequently the 13F external diameter catheter was introduced though the distal Versaport valve into the superior vena cava and with the help of a guiding stylet advanced into the right internal jugular vein. The MOCS circulation was initiated after connecting the roller-head system-pump and 5-l reservoir in series fashion with the arterial and venous end of the MOCS respectively allowing the pump-driven circulation of the system fluid from the venous end to the reservoir, then to the system-pump and to the arterial end of the system.
Fig. 2 is a diagram of the suctioning and filtering systems and their connection with the MOCS. The suctioning system was made of clear vinyl tubing plus a graduated 1.5-l container (“suction container”) and it was connected to the fluid-contrast mix outlet of the 13F catheter. The tubing was threaded through the roller-head of the suction-pump that extracted fluid from the 13F catheter at a speed of 1.5 l/min – equal to the flow at the tip of the 13F suctioning catheter – and then allowed it to drain into the suction container. From here a third roller-head pump (filtration-pump) pushed the fluid through the polymer resin sorbent beads column and then into the 5-l reservoir at a speed of 200 ml/min, reintroducing thus the filtered fluid-contrast mix into the MOCS circulation. The sorbent column contained 500 g of polymer resin sorbent beads.
During each of the injection-suctioning cycles 8 cc of contrast containing 320 mg iodine/ml (Visipaque, GE Healthcare) were manually injected through the 5F JR4 catheter into the carotid artery while the system fluid was running through the MOCS. Concomitantly with the contrast injection, suctioning was initiated in the 13F catheter through the distal fluid-contrast mix outlet, and a 10 cc air bolus was deployed into the 13F catheter balloon, allowing the balloon to inflate in the superior vena cava at 3–4 s after the injection, just prior to the contrast reaching the superior vena cava. Since the balloon was inflated in the superior vena cava, contrast was adsorbed from both internal jugular veins, as illustrated in Clip 1 Frame .
The suctioned fluid-contrast mix was then relayed to the suction reservoir and subsequently through the sorbent beads column and then into the system reservoir as described above. The sorbent beads column was positioned on a vertical pole and the fluid was circulated in a gravitational direction. The suctioning time per each cycle was approximately 30 s. Each cycle was repeated at 4–5 min intervals. We performed a total of 18 injection-suctioning cycles per each column and repeated the same process for two separate columns, with results being averaged.
2.6
Assessment of suctioning efficiency and sorbent column removal rate
The sorbent column contrast removal rate was calculated as a percentage ratio of the difference between the contrast concentration in the affluent minus effluent fluid divided by the affluent concentration, where the affluent and effluent fluid were referred to in connection with the sorbent column. The affluent concentration was calculated in 1 cc aliquots of system fluid mixed with contrast from the suction container, and the effluent concentration from similar volume samples suctioned through a port of the tubing connecting the sorbent column with the 5-l system reservoir.
To assess the catheter suctioning efficiency as a first step we calculated the mass of contrast iodine filtered by sorbent as the product of the volume of system fluid suctioned during each suctioning cycle and the difference between the corrected affluent and the effluent contrast concentration. The corrected affluent contrast concentration was the difference between the affluent concentration and the contrast concentration in the system prior to the index suctioning/filtration cycle. The suctioned volume was measured by visual inspection of the suction container. The suctioning efficiency was calculated as the percentage ratio between the amount of suctioned contrast iodine and the amount injected (the latter equal to 2.56 g contrast iodine, equal to the volume of contrast 8 cc multiplied by 320 mg iodine/ml).
To calculate the efficiency of the entire system in filtrating contrast material we performed two additional series of 18 cycles, this time without suctioning and filtering the contrast (labeled as “filtration/suction-off experiments” in opposition to the “filtration/suction-on” experiments where contrast material was filtered). Contrast concentrations were measured in 1 cc samples extracted from the 5-l system reservoir 3–4 min after each injection and suctioning cycle in the filtration/suction-on experiments and after a similar amount of time following the injection of contrast material in the filtration/suction-off experiments, with the system filtering efficiency being equal to the ratio of the difference (filtration/suction-off minus filtration/suction-on) divided by the filtration/suction-off concentration values.
2.7
Contrast material concentration measurement
Iodine concentration in the samples was measured by X-ray fluorescence as previously described .
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