What causes acute kidney failure?
What is acute kidney failure?
What are the potential repercussions of acute kidney failure?

The kidneys play an important role in maintaining the body's water, electrolyte and acid-base balance, discharging metabolic end products and toxins. Both kidneys are situated in the retroperitoneal space. Each receives blood via a large artery (arteria renalis) and a large vein (vena renalis).
At the microscopic level, a kidney consists of nephrons each of which comprises a glomerulus and a tubular system. Every glomerulus is made up of a capillary tuft, an efferent artery and an enclosing capsule named Bowman capsule. Located between the Bowman capsule and the glomerulus is a space into which the primary urine from the capillaries is pressed out by the blood pressure (glomerular filtration).
The composition of primary urine is similar to plasma water.
It contains all substances capable of passing through the glomerular filter (< approximately 60 kDaA).

Substances are resorbed (removed from) or secreted (added to) in the primary urine as it travels through the tubular system in a selective process, which determines the substances which the body is to recover or discharge. Body water is recovered in quantities that ensure a beneficial water balance for the body. At the end of the tubular system, the final urine reaches the pelvis of the ureter (pelvis renalis) from where it is discharged via the ureter and bladder. In addition to discharging uremic toxins (excretory function), the kidneys also play a vital role in regulating electrolyte (potassium, sodium, calcium, etc.), acid-base balance (bicarbonate, H+ ions), and water metabolism.

In combination with other metabolic functions, these kidney functions ultimately also serve to regulate blood pressure. Furthermore, kidneys are responsible for producing and activating important hormones like erythropoietin for haematosis and vitamin D for bone metabolism (endocrine function).

What causes acute kidney failure?
Acute kidney failure can have a variety of causes differing in terms of location. Causes can be prerenal e.g. circulatory shock, intrarenal e.g. inflammation, diabetes, high blood pressure, or postrenal e.g. blockage of urinary channels through kidney stones. In the event of acute kidney failure, renal functions deteriorate rapidly. The most common causes of acute kidney failure are prerenal. Acute kidney failure usually occurs in patients undergoing intensive care for disorders of the liver, heart, lungs or other organs (multi-organ failure).

What is acute kidney failure?
Acute kidney failure is a sudden and persistent, but basically reversible deterioration in renal functions. It typically occurs in 4 phases:

1. Damage (occurring over a few minutes to several days) resulting in a sharp drop in urine discharge and rise in the proportion of substances in blood which need to be excreted via urine   (creatinine, urea).
2. Oliguria/anuria (lasting up to 10 weeks). In this phase, the patient discharges very little (oliguria < 500 ml/d) or no urine (anuria <100 ml/d).
3. Polyuria (1-2 weeks) involving a notable resurgence in urine production (> 2000 ml/d).
4. Restoration (after several months).

What are the potential repercussions of acute kidney failure?
Though the chances of restoring renal functions are high, the mortality rates of such usually gravely ill patients at intensive care wards lie between 50% and 70%. These patients frequently expire due to other complications, e.g. multiple organ failure or infection (pneumonia, sepsis). Furthermore, acute kidney failure can lead to chronic renal insufficiency requiring dialysis (in roughly 5% of cases).