THE kidneys are two bean-shaped organs located on either side of the spine, in the space behind the abdominal cavity, which also contains the stomach, intestines, liver, spleen, and female genital organs.
The kidneys get its blood supply from the aorta through the renal arteries, which become progressively smaller in size. The smallest blood vessels, called arterioles, form groups of microscopic vessels called capillaries, each group of which is called a glomerulus. The blood leaves each glomerulus through an arteriole, which joins a small vein. The small veins join to form a large vein, which transports blood out of the kidney.
Each kidney has about a mil-lion nephrons, which are microscopic units that filter blood, producing urine in the process. Each nephron comprises a glomerulus and a tiny tubule that drains fluid from the glomerulus. The fluid becomes urine by the time it reaches a collecting duct.
There are numerous collecting ducts that lead to cup-like structures (calyces). Each kidney has many calyces, which all drain into a single large chamber-like structure (renal pelvis) from which the urine drains into another tube-like structure (ureter).
The two ureters from both kidneys join the bladder, from which the urine leaves the body through the urethra via the vulva in females and the penis in males.
The kidneys continuously produce urine, which is composed of excess water, salts, and waste products. Urine does not usually contain organisms or substances like glucose, proteins, ketones, blood etc.
The kidneys' main function is to filter blood to get rid of waste products, toxins, and excess water and electrolytes from the body, whilst reabsorbing useful chemicals.
Many medicines are excreted by the kidneys. The kidneys help in the regulation of blood pressure and also produce hormones which help regulate the production of red blood cells, and the growth and maintenance of bones.
The kidneys enable a person to consume various food, medicines, fluids and substances without toxic by-products reaching harmful levels in the body.
The functions of both kidneys can be performed sufficiently by one kidney. That is why it is possible for a person to donate a kidney to another person.
Kidney (renal) failure occurs when the kidneys are unable to perform their functions, leading to accumulation of toxic substances in the body, and consequent harm to health.
Renal failure can be acute or chronic. The former occurs rapidly, and the latter, gradually over many years, during which the kidneys are destroyed slowly.
It is estimated that about 5% of hospitalised patients develop acute renal failure, with a higher incidence in patients in the intensive care unit.
The causes of acute renal failure are usually categorised into:
- Pre-renal: causes that affect the blood flow to the kidneys.
- Post-renal: causes that affect the flow of urine out of the kidneys.
- Renal: causes in the kidney itself that affect blood filtration and urine formation.
Pre-renal causes account for more than half of the causes of acute renal failure. The causes include dehydration, from vomiting, diarrhea, blood loss and diuretics; and reduced blood flow to the kidneys, from bleeding, severe injuries or burns, infections of the blood (septicaemia), heart attack or heart failure, blockage or narrowing of blood vessel supplying the kidneys and liver failure, which affects hormones regulating blood flow and pressure to the kidneys.
As the kidneys are not damaged by the pre-renal causes, the situation can be reversed with appropriate treatment. However, delayed or inadequate treatment can lead to permanent renal damage.
Post-renal causes are the least common causes of acute renal failure. The causes include obstruction of the ureters by stones or cancer of the urinary tract or adjacent structures; and obstruction at the bladder by stones, enlarged prostate in men, blood clots, bladder cancer and neurological conditions affecting the bladder's ability to contract.
The situation is remedied by removal of the blockage, with the kidneys usually recovering its function within a week or two provided there is no infection. However, delayed or inadequate treatment can lead to permanent kidney damage.
Renal causes account for a quarter to half of all causes of acute renal failure. They may affect filtration, blood supply within the kidney, and the handling of salt and water. Although there are several renal conditions, the most common is acute tubular necrosis, a condition in which the tubules are damaged, leading to impairment of the kidney's filtration function. The causes of this condition include shock, medicines, especially antibiotics, chemotherapeutic agents and poisons.
Glomerulonephritis is a condition in which the glomeruli are damaged by various causes, one of the most common being a streptococcal bacterial infection of the throat.
Acute interstitial nephritis is a condition in which there is inflammation of kidney tissue that deals with salt and water balance. The causes include medicines like antibiotics, painkillers and diuretics.
There may be no symptoms, especially in the early stages of acute renal failure or the symptoms may be non-specific. The symptoms include decreased passage of urine, swelling of the body, abdominal discomfort, lethargy, fatigue, poor concentration and confusion. Fits and coma may occur in severe acute renal failure.
The findings on physical examination are usually few.
A diagnosis is often made from laboratory investigations of the blood or urine. These tests may be done because the patient is generally unwell or hospitalised for another reason, or as part of screening tests.
The blood levels of urea and creatinine are raised when the causes are pre-renal. The serum electrolyte levels may be very high or low when there are filtration problems. A low haemoglobin count is present when there is severe renal failure or it is prolonged.
There may be inappropriate excretion of protein and other substances in the urine. The urine may be darkened by creatinine and other substances.
Microscopic examination of the urine may reveal blood, pus and casts, which are solid materials. The retention of urine in the bladder after passing urine is indicative of a post-renal cause, which is usually an enlarged prostate in men.
An ultrasound examination of the kidneys and bladder may reveal evidence of specific causes of the renal failure. Sometimes, a kidney biopsy may be done to obtain tissue samples of the kidneys for microscopic examination.
The management of acute renal failure depends on the cause and its severity. The condition is usually managed by a kidney specialist (nephrologist) or a physician, if there is no nephrologist available.
The objectives of management are to identify and remove the cause of the failure, and to determine the extent to which the body is affected by the failure.
Dehydration will be corrected with intravenous fluids. If the body's excess fluids are not adequately removed by the kidneys, fluid intake should be limited. If the blood flow to the kidneys is reduced, measures will be taken to improve cardiac function and increase blood pressure. Electrolyte abnormalities will be corrected so that other bodily functions will not be impaired.
A review of the patient's medicines and food intake will be made. The compounds that are harmful to the kidneys will be removed or their dosages reduced.
If there is no response to the management measures and renal function does not return to normal, renal dialysis will be carried out. There are two types of dialysis, i.e. through the blood vessels (haemodialysis) or through the abdominal cavity (peritoneal dialysis). The body's waste products are removed by circulating the blood through an artificial kidney machine in the former, and through a catheter inserted into the abdominal cavity in the latter.
The majority of patients do not require dialysis if the cause is identified and removed or treated. This is particularly so if the cause is not due to kidney damage, when there is usually restoration of normal renal function.
However, there are instances where there may be residual kidney damage resulting in only partial restoration of function. Although such patients may not need dialysis, many have to take medicines to handle the loss of function.
Several measures can be taken to prevent acute renal failure. Adequate fluid consumption will ensure proper functioning of the kidneys. The avoidance of medicines that can damage the kidneys would be very helpful. This is one of the reasons why doctors hold the view that self-medication should be done only with the advice of the doctor.
When one is unsure or does not know the side-effects of medicines, it is prudent to seek advice from the doctor or the pharmacist.
Annual medical examinations will provide information about the health status of the kidneys and urinary tract.
Patients at increased risk of chronic renal disease should be aware of the need for early medical attention, particularly when they have urinary symptoms or notice changes in the urine. They also have need for more frequent medical check-ups and tests of renal function.
Dr Milton Lum is a member of the board of Medical Defence Malaysia. This article is not intended to replace, dictate or define evaluation by a qualified doctor. The views expressed do not represent that of any organisation the writer is associated with.