Haemodialysis Apparatus : Dialysis System, Dialysis Machine

Dialysis System

The objectives are to transport the patient's blood to the dialyser, remove uremic toxins and fluid, and return the patient's cleansed blood. The components include an extracorporeal blood circuit, a dialyzer, a dialysis machine, and a water purification system. 

Dialysis Machine

Blood enters the machine, blood pump forces the blood into the dialyzer, fresh dialysate is injected into the extracorporeal site, used dialysate is removed, and the system detects the presence of air before the blood reaches the patient via an air trap monitor. 

Dialyser Designs 

The machine's hollow fiber portion;  Blood passes through it for dialysis to take place; Solutes and water are transferred across a semi-permeable membrane;  Dialysate and blood flow is separated and counter-current;  There are four parts to the membrane transport process: one inlet and one outlet port for dialysate and blood;  Diffusion and convection carry smaller solutes from higher to lower concentrations;  Convection carry larger solutes The hollow fiber dialyser is the most efficient design (high efficiency, low resistance).

The arterial line, which is the distal portion, is where blood enters the dialysis machine. The vein, which is located in the same fistula but is closer to the heart, enters the heart again. The extracellular circuit contains a blood circuit and a dialyzer. 

Dialysis Membranes

There are 3 types of Dialysis Membranes

• Cellulose-Low biocompatibility; flux reflects the degree of ultrafiltration; potential for convective dialysis
  directly proportional to pore size
• Semi-synthetic cellulose 
• Synthetic polymers 

Biocompatibility:- Blood reacts more and may have adverse drug reactions (ADRs) when exposed to dialyser membranes or high reactivity. 

Transport Properties   

Drags Solvent drug (bigger in size); Convection: water pushed by either hydrostatic or osmotic pressure;  Diffusion: high concentration to low concentration across a concentration gradient.

Dialyser Efficiency

Capacity to eliminate minute solutes; Removing urea is dependent on surface area (0.8-2.1 m2). Maximum urea clearance at infinite blood and dialysate flow rate is known as the KOA (mass transfer area coefficient). Low efficiency is defined as KOA < 500 ml/min; moderate efficiency is defined as KOA < 500 ml/min; high efficiency is defined as KOA < 700 ml/min. High-efficiency dialysers have larger surface areas but smaller pores, making it ineffective to clear larger molecules.

Dialyser Flux 

A dialyzer's flux is defined as its capacity to eliminate very big molecules like beta-2 microglobulin.  Big pores  High flux -> 15-20 and up to 80 m//hr/mmHg; measured using water permeability (Kuf), which is defined as ml of transmembrane ultrafiltration per hour per mmHg of transmembrane pressure.  Dialysate back-filtration into blood-quality water when a high-flow dialyser is utilized. (Very pure)

Safety Monitors

Overtly negative arterial pressure reading  decreased arterial inflow and issues with access.

The following symptoms can occur: high pressure in the dialyser inflow pressure monitor; high pressure in the dialyzer coagulation; obstruction in the venous limb; positive signal air in the system from the air detector; clamping of the venous line and stopping of the blood pump.

HD Circuit

• Divided into 3 segments 
• Pre-pump segment -Has a sampling port, Saline is infused
• P2 pump (Roller pump to venous line)-Anticoagulation is to be done 
• P3 (venous)-Air detector, +ve pressure , Pressure drop between the dialyzer and venous 

Dialysate Pathway

The pH level should be approximately 7.2. If any of the parameters are out of the ordinary, the clamp will activate, causing the dialyzer to flow through without passing through the bloodstream. 

Anti-Coagulation

Heparin, low molecular weight, unfractionated;  RCA, saline flushes, prostacyclin, argatroban, lepirudin;  Heparin, unfractionated;  Bolus: first 4000 IU, then 1000–2000 IU after two hours;  Infusion: first 2000 IU, then 800-1200 IU/hr to conclude 30–60 minutes prior to session.

Contraindication for Heparin

Recent surgical procedures; bleeding; pericarditis; cardiac tamponade resulting from hemopericardium; coagulopathies/thrombocytopenia; active bleeding; adverse effects of heparin; thrombocytopenia generated by heparin; pruritus; rapidly progressing osteoporosis; alopecia.

Dialysate Fluid

Water and water treatment: 120- 160 L of water in a 4 hr HD session.

Water distribution system 

Effect of Toxins

Risks And No Risks Of Bacterial Growth And Endotoxin

Bacteriological Standards

Ultrapure dialysate is used in high flux and HDF

Dialysis Solution

Two components of the concentration. Acid lowers pH<7.2; calcium and magnesium do not precipitate with bicarbonate; liquid/dry concentrates; base concentrate; sodium bicarbonate; sodium chloride; acidic concentrate; chloride salts of sodium, calcium, magnesium, and potassium; glucose monohydrate; 1:1.72:42.48 (acid concentrate-base concentrate-water)

Composition of Dialysate

Advantages and Disadvantages of modification in Dialysate component 

Biocompatibility 

Blood contact with some lines and membranes can cause an inflammatory response;  Biocompatible membranes do not cause an inflammatory response; Cellulose;  Synthetic and reusable membranes;  Greater biocompatibility.  Complement activation peaks after 15 minutes and lasts for up to 90 minutes.  Increased biocompatibility;  Reprocessing dialyzers with peracetic acid in RCA 

Mechanism of Dialysis Membrane Incompatibility

Hemofiltration

Convective technique.

High hydrostatic pressure causes water and compounds with molecular weights of up to around 20 kD to move across the membrane, whereas blood under pressure travels down one side of a highly permeable membrane without the need for dialysate.  Replacement fluid: pre- and post-dilution 

Hemodiafiltration

Dialysis combined with hemofiltration in a high flux membrane; strong convective transport of substances; high diffusion transport rate of low molecular weight solutes; continuous/intermittent therapy; advantages
Reduced oxidative stress and inflammation; enhanced lipid profiles; enhanced calcium phosphate product; ultrapure dialysate serves as a replacement fluid; types.

High volume HDF: 20% convection volume;  Online HDF: infinite manufacture of Ultrapure dialysate online  30% lower risk of all-cause death; 33% lower risk of cardiovascular mortality; 55% lower infection risk; high flux HD versus hemodiafiltration.  Using high-flux HD in hemodiafiltration results in greater mortality benefits.

Circuit for Hemodiafiltration 

Modes of HF and HDF

Site about the dialyzer, through which replacement fluid is infused into the patient’s blood.

• Predilution: High filtration, high convection and reduced diffusion
• Post Dilution: Reduced filtration, increased diffusion 

Uremic Toxins and their removal by Haemodialysis

•  Classification is based on molecular weight and binding properties 
• Low molecular weight water soluble 
• Low molecular weight protein bound 
• Middle molecules 

Additional Devices And Technologies

Relative Blood Volume Monitoring 

Continuous measurement of plasma protein by ultrasound/hematocrit; • Non-invasive monitoring of relative blood volume changes; • A decline in relative blood monitoring prioritises intradialytic hypotension 

Ultrafiltration Profiling 

Fluid-overloaded patients may tolerate high UF in the early stages of the condition; ultrafiltration during dialysis can be altered in a pre-programmed way; two thirds of the ultrafiltration volume in the first half of HD; and the initial high plasma refilling rate 

Sodium profiling 

Prevents intradialytic hypotension;  During the course of the treatment, there are dynamic changes in the sodium concentration of the dialysate; The initial sodium concentration is high and subsequently lower; 

Online clearance monitoring 

The notion that urea and salt have the same clearance can be used to calculate urea clearance. After the volume is input, kt/v is computed. 

Blood temperature monitoring and dialysate cooling

Intradialytic hypotension is prevented by cool dialysate. 

Home HD

HD apparatus.  Portal of entry: AV fistula > catheterized tunnel
Buttonhole more infectious than a step ladder is cannulation. 

Advantages of Home HD

Improved fertility;  Enhanced LV shape and blood pressure regulation;  Better phosphate balance; Better patient autonomy; 

Wearable Artificial Kidney

It is compact, lightweight, and ergonomic. It can be worn as a belt. The dialysate is filtered through a cartridge that contains charcoal, zirconium, resin, and coal. Dialysate is reusable; 400 milliliters are needed 

Bacteriological Standards 

Effect of Toxins

Also Read: High-Yield NEET SS Medicine Nephrology Questions

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