Introduction Continuous renal replacement therapy (CRRT) is defined as a blood purification treatment technique that continuously and slowly removes water and solutes by means of extracorporeal circulation blood purification in order to replace the kidney function. Compared with normal hemodialysis, CRRT prolongs the duration of hemodialysis treatment and reduces the efficiency of treatment per unit time, minimizes the impact of solute concentration and volume changes on the body, and uses highly permeable and biocompatible filters; it provides a vital endostatic balance for the treatment of critically ill patients. Principle There are 3 main modes of solute removal by CRRT: diffusion, convection and adsorption. Different while treatment modalities have different clearance mechanisms; hemodialysis is based on diffusive clearance, hemofiltration on convective and partial adsorptive clearance, and immunosorbent and hemoperfusion on adsorption as the main clearance modality. Different substances are also cleared in different ways, with small molecules being cleared by diffusion, while medium and large molecules are cleared by convection and adsorption. Therefore, it is necessary to choose the appropriate treatment mode and determine the treatment dose according to different clinical needs. Treatment modality 1.Continuous arteriovenous hemofiltration: CAVH uses the pressure difference between human arteries and veins as the driving pressure of extracorporeal circulation, and removes water by ultrafiltration, and removes large, medium and small molecule solutes by convection principle. It is self-limiting (ultrafiltration automatically decreases when arterial pressure drops), continuous (24h continuous), stable (low hemodynamic impact) and simple (can be performed directly at the bedside). With the use of central venous double-lumen catheters and pump-driven this approach has been largely eliminated. 2.Continuous venous hemofiltration: The principle of solute removal is the same as that of CAVH, but the difference is that a single needle double-lumen catheter is left in the central vein to establish vascular access, and pump drive is applied for extracorporeal blood circulation. CVVH blood flow can reach 100-300ml/min, and the urea removal rate can reach 36L/d with post-dilution input replacement fluid, and increase to 48-100L/d with pre-dilution method. this year, CVVH has gradually replaced CAVH and become the standard treatment mode. 3.Continuous arteriovenous hemodialysis and continuous veno-venous hemodialysis: CAVHD still uses the pressure difference between the body’s arterioles to drive blood circulation, and solute transport depends mainly on diffusion, with a small amount of convection as well. When the dialysate flow rate is 15 ml/min, all small molecules in the dialysate are saturated, thus allowing the solutes in the plasma to be removed by diffusion. When the flow rate of dialysate increases to about 50ml/min, the solute clearance rate no longer increases. cVVHD, using venous-venous vascular access, with the help of blood pump to drive blood circulation, the solute transport mechanism is the same as CAVHD. 4.Continuous arteriovenous hemodialysis filtration and continuous veno-venous hemodialysis filtration: CAVHDF is also developed on the basis of CAVH, with the addition of dialysis to make up for the shortcomings of CAVH in terms of nitrogen removal. CVVHDF is developed on the basis of CVVH, and the principle of solute removal is exactly the same as that of CAVHDF, the difference is that the vascular pathway is established by vein-vein and the blood pump is used to drive the blood circulation. 5.Slow continuous ultrafiltration: The main principle is to remove solutes by convection. It does not supplement replacement fluid and does not use dialysis fluid. It is not ideal for solute removal and cannot maintain BUN and SCr at the ideal level, and sometimes it is necessary to add dialysis treatment. At present, it is mainly used clinically for edema, refractory heart failure, especially after direct cardiac surgery, trauma or major surgical resuscitation with extracellular fluid volume load. 6, daytime continuous renal replacement therapy: daytime CRRT is mainly performed during the day, because various drugs and nutrient solutions are mainly input during the day, and need to remove excessive water during the day, to ensure that patients get enough rest during the night and reduce human consumption, more importantly, daytime CRRT, filters and lines can be reused, filters reduce clotting, increase adsorption and convective removal by removing the protein layer on the membrane The efficiency of solute, extend the use of the filter time and reduce the cost, suitable for our national conditions. 7.Continuous high throughput dialysis: compared with simple HD, it can increase the removal of large molecules, urea removal rate can reach 60L/d, inulin removal rate can reach 36L/d, so that the 24h overall water removal (K/V) ≥ 1. Continuous CHFD, the weekly KT/V index can also reach 7-10. 8.High volume hemofiltration: septic shock patients in HF enter replacement fluid The rate can reach 6L/h if CVVH is continuously performed, and 50L of replacement fluid is input daily, it is called HVHF. 9.Continuous plasma filtration adsorption: plasma is continuously separated by applying plasma filter, and the filtered plasma enters the activated carbon or resin adsorption device, and the purified treated blood is then returned to the body through the intravenous line. CPFA selectively removes inflammatory mediators, cytokines, endotoxins and activated complement components, reducing the incidence of hypotension and ultimately morbidity and mortality. Clinically, it is mainly used to remove endotoxin and pro-inflammatory mediators. 10. Endotoxin adsorption: Treatment of subjects usually meets 3 criteria: (1) endotoxemia or suspected gram-negative bacterial infection; (2) clinical manifestation of systemic inflammatory response syndrome (SIRS); (3) infectious shock requiring vasoactive drugs. 11.Plasma filtration adsorption dialysis: PFAD is a new blood purification technology that integrates 3 different blood purification treatment modes, namely filtration, adsorption and dialysis. At present, PFAD has achieved significant efficacy in the treatment of animal models of septic shock, and will be expected to be clinically used in the treatment of various critical diseases such as sepsis, systemic inflammatory response syndrome, hepatorenal syndrome, and acute decompensation of chronic liver disease.