Background
Methodology
Hardware and devices
CRRT machine: procedures and phases of treatment
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Prescription phase: this phase consists of decisions by the prescribing clinician about the required modality and related operational parameters and includes periodic reassessment and/or change of the prescription.
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Preparation phase: this phase consists of collection of necessary disposable material, identification and checking of the disposable set, set loading (cassette tubing), connection to the filter, positioning of the tubing, and hanging of bags.
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Priming phase: priming solution is infused into the extracorporeal circuit in order to remove air and impurities remaining after sterilization of the set. When heparin anticoagulation is used, it is usually added to the priming solution. During this phase, the machine makes a general check of all components and sensors.
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Connection to the patient: this phase consists of the connection of the extracorporeal lines to the patient’s vascular access.
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Treatment phase: net ultrafiltration and diffusive and/or convective solute transport are activated (all the pumps are working) and blood purification is performed. The patient’s vital signs and circuit pressures must be monitored throughout the treatment phase.
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Special procedures: during treatment, special procedures can include replenishment of dialysate, replacement fluid, and citrate bags (when citrate anticoagulation is used), change of syringes (when using heparin anticoagulation), repositioning of the vascular access, and temporary disconnection, recirculation, and replacement of filter and kit.
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Blood return, disconnection and unload: the blood return procedure returns the blood to the patient. This is usually done by connecting a saline solution bag to the in-flow blood line and running the blood pump. When the circuit is flushed, the blood pump is stopped, the blood outflow line disconnected, and the tubing and filter unloaded.
CRRT disposables
Tubes
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Blood in-flow line (red; previously known as access or arterial line) | Segment connecting the patient’s vascular access to the filter |
Segment for pressure measurement (upstream blood pump): segment of the blood in-flow line connected to the in-flow pressure sensor | |
Pump segment line: segment inserted between the rotor and the stator of the blood pump | |
Blood in-flow air removal chamber: allows removal of light air bubbles before the blood enters the filter | |
Segment for pressure measurement (downstream blood pump): segment of the blood in-flow line connected to the pre-filter pressure sensor | |
Blood out-flow line (dark blue; previously known as return or venous line) | Segment connecting the filter to the patient’s vascular access |
Segment for pressure measurement: segment of the blood out-flow line connected to the out-flow pressure sensor | |
Blood out-flow air removal chamber: allows removal of light air bubbles before the blood returns to the patient | |
Effluent/ultrafiltrate line (yellow) | Segment that allows the flow of waste fluids from the filter |
Pump segment line: segment inserted between the rotor and the stator of the effluent/ultrafiltrate pump | |
Segment for pressure measurement: segment of the effluent line connected to the effluent/ultrafiltrate pressure sensor | |
Dialysate line (green) | Segment that allows the flow of incoming dialysate into the filter |
Pump segment line: segment inserted between the rotor and the stator of the dialysate pump | |
Segment for pressure measurement (if present): segment of the dialysate line connected to the dialysate pressure sensor | |
Heater line: segment of the dialysate line placed in contact with the heater | |
Replacement line (purple or light blue) | Segment that allows the flow of replacement fluid into the blood in-flow and/or blood out-flow lines |
Pump segment line: segment inserted between the rotor and the stator of the replacement pump | |
Segment for pressure measurement (if present): segment of the replacement line connected to the replacement pressure sensor | |
Heater line: segment of the replacement line placed in contact with the heater | |
Pre-blood line (orange) | Segment that allows the flow of specific fluids (mainly regional anticoagulants) into the blood in-flow line before the blood pump |
Pump segment line: segment inserted between the rotor and the stator of the pre-blood pump | |
Segment for pressure measurement (if present): segment of the pre-blood line connected to the pre-blood pressure sensor | |
Anticoagulant and specific antagonists line | Segments connecting the anticoagulant/specific antagonist bag or pump to the main blood circuit |
Citrate line (orange): segment for citrate infusion (i.e., pre-blood line) | |
Heparin line (white): segment connecting the heparin syringe pump to the blood in-flow line | |
Specific antagonist line (black): segment connecting the specific antagonist syringe pump to the blood out-flow line | |
Filter
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Fiber (membranes) | Every fiber, hollow and of cylindrical shape, allows the transport of fluids and solutes through their porous semi-permeable surface |
Bundle | Entire number of fibers inside the housing |
Housing | Plastic casing containing a single membrane fiber bundle |
Blood in-flow port: entrance port of blood entering into the filter | |
Blood out-flow port: exit port of blood leaving the filter | |
Dialysate in-flow port: entrance port of fresh dialysate | |
Effluent/ultrafiltrate out-flow port: exit port of waste solution | |
Potting | Polyurethane component fixing the bundle within the housing and embedding the bundle at both ends of the filter |
Volume management and fluid balance
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Gravimetric fluid balancing, using one or more scales, is most commonly used in CRRT because it is the most reliable technique during long treatment intervals. A fundamental aspect of this type of system is the continuous weighing of the effluent along with replacement fluid and/or dialysate, with weight acting as a surrogate for fluid flow rate. The machine software analyzes these scale data on an ongoing basis and any discrepancies between prescribed and actual values lead to adjustments in pump rates based on a servo-feedback mechanism. Disadvantages include limitations in scale capacity, user errors, and other disturbances of the operating environment.
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In volumetric fluid balancing, a system of balancing chambers and valves is used. During long treatments, volumetric balancing is less accurate than gravimetric balancing because of systematic, cumulative errors, as there is no continuous servo-feedback safeguard for this approach. The advantage of this system is that it eliminates the need to collect effluent and thus reduces the frequency of fluid-related interventions.
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Fluxometric fluid balancing requires the application of accurate but expensive flow meters (electromagnetic, ultrasonic and Coriolis flow meters).
Extracorporeal therapies and treatments
Continuous therapies
Slow continuous ultrafiltration
Continuous veno-venous hemofiltration
Continuous veno-venous hemodialysis
Continuous veno-venous hemodiafiltration
Continuous veno-venous high-flux hemodialysis
Intermittent therapies
Hybrid therapies
Other extracorporeal therapies
Therapeutic plasma exchange
Multiple organ support therapy
Non-cell-based systems | Intermittent, extended and continuous dialysis techniques |
Hemoperfusion techniques | |
Plasma exchange techniques | |
Plasmapheresis | |
Plasma filtration/adsorption | |
Albumin dialysis • MARS • SPAD | |
Prometheus | |
Cell-based systems (Bioartificial liver support systems) | Human hepatocytes (bioartificial liver support system) |
Porcine hepatocytes |