Dialysis Access

Dialysis Access

Blood flows on one side of membrane while dialysate flows on the other side. To ensure effective dialysis a high blood flow is required for taking blood from the body to the dialysis machine. The blood flow required is about 5ml/kg body weight /min. Usually 250 ml to as much as 500-600 ml if tolerated.

The way to achieve this is through creation of dialysis access. This may be temporary or permanent.

A temporary access is made in those patients who will require dialysis for a few days to few weeks as in acute kidney injury ( also called earlier as ARF or acute renal failure), while awaiting creation of a permanent access.

Temporary access is obtained by inserting a tube in neck veins (Int Jugular Vein) usually on right but sometimes on left side. It is uncommon nowadays to use subclavian (behind collar bone ) or upper thigh veins. The advantage of this is that it is ready to use immediately however it often gets infected and may cause clot formation in the vein in which it is placed. It should be used for less than 2 weeks and never handled by patient. Sudden dislodgement may cause bleeding. In case long term dialysis is required and AV fistula( read further on to know about AVF) is not yet ready a permanent dialysis catheter which is useful for a few months is a far better though costly choice.

The method of choice is creation of arterio-venous fistula (AVF). It is usually made in the wrist but if blood vessels are small or thrombosed it is at times made in arm near elbow. This requires surgery usuaally under local aneasthesia. The failure rates are higher if done by inexperienced surgeons (1 in 2 to 1 in 4 AVFs may fail.)

It takes 2 to 3 months to mature and hence should be made much before the need of dialysis arises. It should be checked to see that it is working. If there is stoppage of flow early treatment may make it work again but if delayed another AVF creation is required.

If injured rapid bleeding may occur. So protect these from injuries. Do not allow these to be used for drugs and samples other than in dialysis room by dialysis personnel.

A good AVF is a life line for patients. Get it made early & keep it functional !!



The heart pumps blood so that it can reach various parts of the body and supply these parts with oxygen and nutrients. The pressure generated by the heart forces the blood to go from the heart to various organs and return from there to be sent again. There is about 5 liters of blood in average adult and heart pumps about 70 ml in each heart beat. The force generated by heart results in pressure which can be measured.

Hypertension is said to occur when the recorded blood pressure is higher than expected for the particular age. Children have lower BP, it gradually rises to adult levels and continues to increase with age in most cases. BP is measured by sphygmomanometer which was earlier mercury based but are now aneroid or electronic. BP is measured as Systolic ( higher value of the two ) and diastolic (lower reading) and written as systolic/diastolic BP in mm of Hg. e.g. 120/80 mm Hg.

Blood pressure at birth is about 70 to 85 /30 to 45 , at 5 yrs 90-110/50-66 , at 10 yr 100-120/60-80. In adults blood pressure is diagnosed when it is usually more than 140/90 mm Hg.

Causes of high blood pressure.

In most cases, there is no apparent cause. Suspicion usually falls on genetic disease, high salt intake, higher weight etc. in younger patient sometimes a cause is detected. It is often due to kidney disease, hormonal disorders, blood vessel diseases or diseases disturbing immunity. It can at times be caused by drugs like steroids and analgesics.

Symptoms of high Blood pressure

Most patients have no symptoms due to high blood pressure. It is only the measurement of blood pressure which reveals the diagnosis. Some patients with high blood pressure may have headaches, dizziness, throbbing or at times shortness of breath. If blood pressure rises suddenly to very high levels it may cause emergencies. These may include vision loss, renal failure, alteration in consciousness ( drowsiness or unconsciousness), or heart failure (manifested as breathlessness worse on lying down or activity)

Clinically it is diagnosed by BP measurement, usually on more than one occasion while a person is sitting with back supported. 2 or 3 readings may be taken and the lower readings are usually more accurate. If in doubt multiple readings can be taken while the person is continuing his activities (ABPM or ambulatory BP monitoring). Eyes are checked as blood vessels can be seen in the retina, ECG and X Ray Chest may show heart enlargement.

Laboratory tests:-

Lab tests are done to find the cause of high blood pressure if any, its effects on various organ systems and complications. The usual tests done are Blood counts, urine routine examination, Blood Urea, S Creatinine, S electrolytes, Blood Sugar, Lipid profile in blood, ECG, X Ray of chest and Ultrasonography of abdomen. In special cases hormones may be measured or Doppler Ultrasound studies are done to check blood flow and vessels in different areas.

Complications of high blood pressure:-

Complications arise if the blood pressure is very high or it has been present for  a long time. Not all persons with high BP get complications. Some of the complications are :

  • Strokes (paralytic attacks due to bleeding in the brain or reduced blood supply to part of the brain)
  • Increased likelyhood of heart attacks.
  • Heart failure (not stoppage of heart beat or cardiac arrest ) but inability of heart to meet bodily demands. This is diagnosed by swelling of feet, breathlessness at night after sleeping for 2-3 hours, fatigue etc.
  • Chronic renal disease resulting in renal failure if allowed to go unchecked for long periods.
  • Decreased blood supply to other organs due to thickening of blood vessel walls and narrowing of their internal lumen (athersosclerosis of aorta, limb vessels, vessels supplying brain, kidneys, heart, eyes etc.)

Coming up soon :

Treatment of high blood pressure





Swine flu and other influenzas






When the kidneys fail to maintain the body in a healthy state, the condition is called chronic renal failure. In advanced stages of chronic renal failiure, symptoms arise. These are called uremic symptoms and may consist of one or more of the following:-

Weakness, decreased appetite, nausea, vomiting, hiccups, breathlessness, swelling of the body, decreased amount of urine etc. Later on a person may develop fits or increasing drowsiness, unconsciousness, extreme weakness, muscle paralysis etc. Initially these symptoms are mild but later on they do not allow a person to live a normal life and still later they will kill a person unless treated.

The process of taking over of failed kidney functions by treatment is called Renal Replacement Therapy (RRT). This mainly comprises of Dialysis and Renal Transplant.

Dialysis is the process through which the accumulated waste products are removed. It also removes extra water salt, potassium, acid, phosphorus and molecules of middle size.  Thus it attempts to return the body to a healthy state.

Dialysis is mainly of two types:- Hemodialysis and Peritoneal dialysis.


In this a membrane called dialysis membrane is used as a filter. It is folded many times over to increase its area to about .5 sq meters to 2 sq meters (for children and adults of various sizes). This membrane allows only small molecules to move from one side to the other.

Blood flows on one side of the membrane and dial sate fluid flows on the other. The dialysate fluid is produced in the dialysis machine by diluting commercial concentrates. The composition of the dialysate is similar to Blood without cells, proteins, fats and other larger molecules.

Smaller molecules present in high concentration in blood and dialysate move across because of difference in concentration (called electrochemical gradient) from a higher concentration to lower concentration. Pressure can be applied across the membrane to create pressure to push water and salt across as well.

Functions of the Kidney

Functions of the Kidney

The main function of the kidney is the maintenance of the interior composition of the body. Due to continued digestion and utilisation of food in the body, construction and destruction of the various body tissues, waste products are generated daily.

  • Excretion of waste products

If allowed to collect in the body, the function of the body is affected. These waste products are thrown out from the body by liver and intestines, lungs, skin and kidneys.

Kidneys excrete urea, creatinine and similar products in a concentrated form in urine. The amount of excretion closely balances the amount of production of these materials.

  •  Water and salt balance

Kidneys maintain salt and water balance in the body. When healthy, a person may drink upto 10 liters of water or as low as ½ litre in a day. The kidneys increase and decrease urine appropriately to maintaine the total body water.

About 1 litre of blood flows through kidney. Of this about 180 litres of water, some salts and small particle are filtered daily in the kidney. Of this 180 litres, only 1 to 2 litre is finally excreted as urine. The rest is absorbed back to the blood from urinary tubules. Thus kidneys can dilute or concentrate urine.

The body water in humans depends to a large extent on salt content of the body. In case of reduced intake of salt , kidneys limit salt wastage in urine and similarly if intake is high , kidneys try to excrete extra salt.

Kidneys also excrete phosphate, ammonia products, urates and various drugs ingested by humans.

  • Acid balance

Urine is acidic in nature as it has to carry the daily acids produced from metabolism and activities of daily living, exercise etc. by excreting acid the pH of the body tissue and blood is maintained in a narrow range.

  • Haemoglobin production

Kidneys produce a hormone called erythropoietin or EPO in short. EPO stimulates bonemarrow to produces RBCs and hemoglobin. Lack of EPO production in the kidneys leads to anemia or decreased  hemoglobin.

  • Bone Health

Vitamin D produced from the ultraviolet radiation from sun or ingested in food is inactive. The liver and kidneys transform this inactive form to active form. Lack of activation leads to various bone abnormalities, fractures, bone pains and muscle weakness.

Structure of the Kidney

Structure of the Kidney

There are 2 kidneys in human body. Each weighs about  125 gms. These are located one on each side of the spine in abdomen. These are covered and protected in their upper part by ribs. These are bean shaped and beans are said to be kidney shaped.

Each kidney has about 1 million filtering units. These are called renal corpuscles and can be seen by microscope . The ball like portion where formation of urine begins by filtering from blood is called glomerulus. The filtered fluid gets modified while passing through tube like structures.

Kidneys are very rich in blood supply. It gets more blood per 100 gms of tissue than any other organ except heart.  About one fifth of the total blood pumped by heart goes to the kidneys.

After the urine is formed in the kidneys, it comes to the urinary bladder by two tubes called ureters. The urine can be stored in bladder till voided at will. Various valve like structures prevent urine from flowing backwards and leakage through the urethra , the final part connecting bladder to the outside.