Oliguria refers to an abnormally low production of urine by the body, that is to say a 24-hour diuresis less than 500 ml in an adult. Normal diuresis, or the volume of urinary secretion (also referred to as urinary flow), is between 800 and 1 ml per 500 hours. Certain diseases can be accompanied by an abnormality of this urinary flow. Oligo-anuria qualifies a diuresis less than 24 ml per 100 hours. These decreases in urine secretions may be linked to kidney failure, but may also be due to other causes, particularly physiological.

Oliguria, what is it?

Oliguria is a very low volume of urine produced by the body. The average normal urine output in an adult, or the volume of urine produced, is between 800 milliliters and 1 milliliters in 500 hours. When this diuresis is less than 24 milliliters, the patient is in a situation of oliguria. We will also speak of oligo-anuria when the diuresis falls below 500 milliliters per 100 hours.

How to recognize oliguria?

Oliguria can be recognized by the volume of urine produced, when it is less than 500 milliliters.

You have to be careful, because a patient who has not urinated for 24 hours is not necessarily anuric, it can also be a blockage of urination, due to urine retention. In this case, urine output exists, but no urine is coming out.

The clinical examination is therefore necessary in the region located above the pubis, by percussion, in search of a bladder ball: this is important, because an anuric or oliguric patient will be treated in a nephrological environment. , therefore due to a problem related to the kidney, while a patient with urine retention will be treated in a urological department, that is to say relating to a problem of the urinary tract. 

Risk factors

Oliguria is a common occurrence in hospitalized patients, in whom dehydration is unlikely. Oliguria may be a risk factor for the development of acute renal failure. A significant increase in the severity of oliguria is also at higher risk of in-hospital mortality.

Short oliguria is common, however, and will not lead to the development of acute kidney failure.

Glomerular filtration defect

A rapid reduction in the rate of urine secretion may reflect a precipitously decreasing glomerular filtration rate. Thus, oliguria is one of the oldest biomarkers of kidney damage. The kidneys are the organs which carry out filtration via their glomeruli, eliminating the toxic products produced by the organism and transported by the blood: these substances, useless to the organism, are toxic if they are not eliminated, via the urine. When their kidneys fail, a person has kidney failure.

The definition of oliguria as being associated with acute renal failure has been described for over 200 years, by the English physician Heberden. Moreover, a urine secretion of less than 0,5 ml / kg / h for more than 6 hours is an alternative criterion to the increase in serum creatinine level in the assessment of risk, injury, loss or failure of kidney function.

Thus, recent international guidelines consider these two criteria, oliguria and the high level of serum creatinine, of equal importance in the diagnosis of renal failure. However, while creatinine accurately reflects glomerular filtration rate, a deficit in urinary secretion may be linked to other physiological causes.

Oliguria: a physiological response

Oliguria, when it corresponds to a physiological response, is linked to an anti-diuresis due to hypovolemia, or to a significant decrease in circulating blood volume. This physiological response is linked to the release of anti-diuretic hormone (ADH), which can then lead to reductions in urinary secretion in healthy people. Oliguria may therefore also reflect a normal physiological response, or indicate a transient disturbance of blood flow. The anti-diuresis can be increased by the stimulation of the sympathetic nervous system, in particular, that is to say the nervous structures which manage the automatic activity of the visceral organs.

Other causes of oliguria

• Oliguria can also be caused by a release of the anti-diuretic hormone caused by pain, stress, nausea, instability of hemodynamics (the flow of blood in the vessels) or surgery, even a trauma.
• In addition, pelvic examinations may help to check for benign prostatic hyperplasia. If the prostate is swollen, it compresses the urethra, which then does not allow urine to pass.
• A radiological examination, which consists of an ultrasound of the urinary tract can also highlight a possible obstruction, therefore an obstacle at the level of the ureters.
• In addition, an acute occlusion of the renal artery or vein can also damage kidney function, and cause oliguria or even anuria.

One of the major complications of oliguria is the development of acute kidney failure. In such a case, it will be necessary to resort to dialysis, the main treatment for kidney failure, which consists of filtering the blood through a machine.

An essential test to define the characteristics of oliguria is the “Furosemide stress test” (FST), in patients with oliguria: it allows to determine if the renal function is intact.

• If more than 200 ml of urine is produced within two hours after the Furosemide test, kidney function is intact;
• If there is less than 200 ml produced within two hours, kidney function is damaged, and this kidney dysfunction may require dialysis, which is the main treatment for kidney failure.

The biological assessment also makes it possible to analyze the renal filtration rate, which is measured by the clearance of creatinine, carried out either by a blood test or by the 24-hour urine analysis. 

The response to the FST test in oliguria could make it possible to discriminate between patients presenting a systemic stress response resulting in anti-diuresis, from a real failing renal function.

In addition, a study carried out in children who have undergone cardiac surgery, and therefore particularly at risk of acute renal failure, has shown that treatment with aminophylline increases urine secretion and improves post-treatment outcomes. kidney surgery. In these patients, treatment with Furosemide also improves urine secretion, but the team of American researchers has demonstrated the superiority of aminophylline over Furosemide in preventing kidney failure associated with heart surgery.

Finally, it should be borne in mind that the very first primary prevention to avoid a risk of oliguria, and also of urinary tract infection, is to have good hydration: the recommended hydration levels for adults are 1,5. , 1,9 liters per day for women, and XNUMX liters per day for men. Most children are too low in hydration, so it is important to remember the importance of drinking regularly and enough water.