When a person does not have normal kidney functioning, he is given a treatment. Dialysis is the medical treatment given for kidney failures. It helps to collect the waste products from blood and removes it. It also restores the normal pH value of blood with help of artificial kidney machine. Three important process in dialysis are Diffusion, Osmosis and Ultrafiltration.
There are two types of dialysis

  1. Extra Corporeal Dialysis (Hemodialysis)
  2. Intra Corporeal Dialysis (Peritoneal Cavity Dialysis)

Extra Corporeal Dialysis (Hemodialysis)

Proportioning Pump

Pure water is mixed with dialysate. It maintains a Ratio of 34:1. Two types of pumps are available.

  1. Fixed Ratio Type: Here always a fixed ratio of 34:1 is maintained
  2. Variable Ration Type: In this type a variation of ± 5% changes occur in the ration of 34:1

The output from the pump goes to the heater.

Dialysate Temperature Control

When performing dialysis, a specific range of temperature is maintained and controlled. The nominal temperature acceptable for a human body is 40oC. If the range of value increases the blood, components are damaged. Therefore, for the safety purpose the heater should be turned off beyond 43oC. In a person, an increase in temperature leads to Hyperthermia.

Conductivity Measurement

A conducting cell is used to continuously monitor the changes in conductivity of blood. It helps to decide the proportionate ratio and its accuracy. The result is displayed in terms of percentage as how it is deviated from the reference reading

Dialysate Flow Meter

The normal flow rate is set to 500 ml/minute at downstream of the dialyzer. When there is leakage of blood, it will be indicated with a colour change in the fluid.

Dialysate Pressure Control

A pressure gauge is used to indicate the pressure. The algebraic sum of dialysate pressure and venous blood pressure gives the membrane pressure. When the pressure exceeds the normal level, pump that creates negative pressure is turned off automatically. The dialysate solution is then passed to the drain.

Blood Leakage Detector

A photoelectric transducer is used to detect the blood leakage across the dialyzer membrane. Usually there will be around 25 mg of Hb/litre blood leakage. If blood leakage occurs, again the dialysate is by-passed to drain.

Bubble Trap

Air embolism is the presence air bubbles in blood flow path. It is a serious hazard in dialysis. So, recently ultrasound techniques are used to detect the presence of air in the path.

Heparin Pump

It is used to inject medicines to the patient.

Ultra Filtration Circuit

This monitors the amount of fluid coming out of the patient body

Ultra Filtration rate = Total Fluid Removed in Litres / Time Taken for the treatment


This is the most important part of dialysis machine. It has two compartments. In one part, the blood flows and in another compartment dialysate solutions flows in. Three types of dialyzers namely parallel plate dialyzer, coil dialyzer and hollow fiber types are available. The blood flows in at a rate of 200ml/minute. The time taken for dialysate to flow is 500 ml/minute. This dialyzer has to be cleaned and reused for each dialysis.
kaemodialysis machine

About Vidya Muthukrishnan

Ms M.Vidya has been teaching professionally for the past 5 years, and is currently employed as an Assistant Professor in the Department of Instrumentation and Control Engineering at the Sri Krishna College of Technology. She has completed her B.Tech Electronics and Instrumentation from SASTRA University and M.Tech in Biomedical Engineering from VIT University Vellore.

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