Oliguria is the low output of urine

Urine

Urine is a typically sterile liquid by-product of the body that is secreted by the kidneys through a process called urination and excreted through the urethra. Cellular metabolism generates numerous by-products, many rich in nitrogen, that require elimination from the bloodstream...

, It is clinically classified as an output below 300-500ml/day. The decreased output of urine may be a sign of dehydration

Dehydration

In physiology and medicine, dehydration is defined as the excessive loss of body fluid. It is literally the removal of water from an object; however, in physiological terms, it entails a deficiency of fluid within an organism...

, renal failure

Renal failure

Renal failure or kidney failure describes a medical condition in which the kidneys fail to adequately filter toxins and waste products from the blood...

, hypovolemic shock, HHNS Hyperosmolar Hyperglycemic Nonketotic Syndrome, multiple organ dysfunction syndrome

Multiple organ dysfunction syndrome

Multiple organ dysfunction syndrome ', previously known as multiple organ failure or multisystem organ failure , is altered organ function in an acutely ill patient requiring medical intervention to achieve homeostasis...

, urinary obstruction/urinary retention

Urinary retention

Urinary retention, also known as ischuria, is a lack of ability to urinate. It is a common complication of benign prostatic hyperplasia , although it can also be caused by nerve dysfunction, constipation, infection, or medications...

, and Urinary tract infection

Urinary tract infection

A urinary tract infection is a bacterial infection that affects any part of the urinary tract. Symptoms include frequent feeling and/or need to urinate, pain during urination, and cloudy urine. The main causal agent is Escherichia coli...

s.

It can be contrasted with anuria

Anuria

Anuria means nonpassage of urine, in practice is defined as passage of less than 50 milliliters of urine in a day. Anuria is often caused by failure in the function of kidneys. It may also occur because of some severe obstruction like kidney stones or tumours. It may occur with end stage renal...

, which represents an absence of urine, clinically classified as below 50ml/day.

Definition

Oliguria is defined as a urine output that is less than 1 mL/kg/h in infants, less than 0.5 mL/kg/h in children, and less than 400 mL or 500 mL in adults. In adults, this equals 17 or 21 mL/hour. For example, in an adult weighing 70kg it equals 0.24 or 0.3 ml/hour/kg. Alternatively, however, the value of 0.5 mL/kg/h is commonly used to define oliguria in adults as well.

< 500 mL in 24 h.

Olig- (or oligo-) is a Greek prefix meaning small or few.

Anuria is defined as less than 50mL urine output per day.

Pathophysiology

The pathophysiologic mechanisms causing oliguria can be categorized globally in three different categories:

• Prerenal: in response to hypoperfusion of the kidney (e.g. as a result of dehydration
  Dehydration
  In physiology and medicine, dehydration is defined as the excessive loss of body fluid. It is literally the removal of water from an object; however, in physiological terms, it entails a deficiency of fluid within an organism...
  
   by poor oral intake, cardiogenic shock
  Cardiogenic shock
  Cardiogenic shock is based upon an inadequate circulation of blood due to primary failure of the ventricles of the heart to function effectively....
  
  , diarrhea
  Diarrhea
  Diarrhea , also spelled diarrhoea, is the condition of having three or more loose or liquid bowel movements per day. It is a common cause of death in developing countries and the second most common cause of infant deaths worldwide. The loss of fluids through diarrhea can cause dehydration and...
  
  , massive bleeding
  Bleeding
  Bleeding, technically known as hemorrhaging or haemorrhaging is the loss of blood or blood escape from the circulatory system...
  
   or sepsis
  Sepsis
  Sepsis is a potentially deadly medical condition that is characterized by a whole-body inflammatory state and the presence of a known or suspected infection. The body may develop this inflammatory response by the immune system to microbes in the blood, urine, lungs, skin, or other tissues...
  
  )
• Renal: due to kidney damage (severe hypoperfusion, rhabdomyolysis
  Rhabdomyolysis
  Rhabdomyolysis is a condition in which damaged skeletal muscle tissue breaks down rapidly. Breakdown products of damaged muscle cells are released into the bloodstream; some of these, such as the protein myoglobin, are harmful to the kidneys and may lead to kidney failure...
  
  , medication
  Medication
  A pharmaceutical drug, also referred to as medicine, medication or medicament, can be loosely defined as any chemical substance intended for use in the medical diagnosis, cure, treatment, or prevention of disease.- Classification :...
  
  )
• Postrenal: as a consequence of obstruction of the urine flow (e.g. enlarged prostate, tumour compression urinary outflow, expanding hematoma
  Hematoma
  A hematoma, or haematoma, is a localized collection of blood outside the blood vessels, usually in liquid form within the tissue. This distinguishes it from an ecchymosis, which is the spread of blood under the skin in a thin layer, commonly called a bruise...
  
   or fluid collection)

Postoperative oliguria

Patients usually have decrease in urine output after a major operation that may be a normal physiological response to:

• fluid/ blood loss – decreased glomerular filtration rate secondary to hypovolemia and/or hypotension
• response of adrenal cortex to stress -increase in aldosterone
  Aldosterone
  Aldosterone is a hormone that increases the reabsorption of sodium ions and water and the release of potassium in the collecting ducts and distal convoluted tubule of the kidneys' functional unit, the nephron. This increases blood volume and, therefore, increases blood pressure. Drugs that...
  
   (Na and water retention) and antidiuretic hormone (ADH) release

Oliguria in infants

Oliguria, when defined as less than 1 mL/kg/h, in infant

Infant

A newborn or baby is the very young offspring of a human or other mammal. A newborn is an infant who is within hours, days, or up to a few weeks from birth. In medical contexts, newborn or neonate refers to an infant in the first 28 days after birth...

s is not considered to be a reliable sign of renal failure.