Causes of AKI

There are numerous causes of AKI which are commonly divided into the following  4 categories:

1.  Prerenal Failure, an adaptive response to severe volume depletion and hypotension, with structurally intact nephrons, affecting the flow of blood before it reaches the kidneys.

Prerenal failure is the most common type of acute renal failure (60%-70% of all cases). The kidneys do not receive enough blood to filter. Prerenal failure can be caused by the following conditions:

• Dehydration: - From vomiting, diarrhea, water pills, or blood loss
  
• Disruption of blood flow to the kidneys from a variety of cause
  
  
  • Drastic drop in blood pressure from major surgery with blood loss, severe injury infection in the bloodstream (sepsis) causing blood vessels to inappropriately relax or burns 
  • Blockage or narrowing of a blood vessel carrying blood to the kidneys
  • Heart failure or heart attacks causing low blood flow  
  • Liver failure causing changes in hormones that affect blood flow and pressure to the kidney

There is no actual damage to the kidneys early in the process with prerenal failure. With appropriate treatment, the dysfunction usually can be reversed. Prolonged decrease in the blood flow to the kidneys, for whatever reason, can however cause permanent damage to the kidney tissues

2.  Intrinsic, in response to cytotoxic, ischemic, or inflammatory insults to the kidneys, with structural and functional damage. 

3.  Postrenal Failure, from obstruction to the passage of urine, affecting the movement of urine out of the kidneys.

Postrenal failure is sometimes referred to as obstructive renal failure, since it is often caused by something blocking elimination of urine produced by the kidneys. It is the rarest cause of acute kidney failure (5%-10% of all cases). This problem can be reversed, unless the obstruction is present long enough to cause damage to kidney tissue.

Obstruction of one or both ureters can be caused by the following:

• Kidney stone: usually only on one side
  
  
• Cancer of the urinary tract organs or structures near the urinary tract that may obstruct the outflow of urine
  
  
• Medications

Obstruction at the bladder level can be caused by the following:

• Bladder stone
  
  
• Enlarged prostate (the most common cause in men)
  
  
• Blood clot
  
  
• Bladder cancer
  
  
• Neurologic disorders of the bladder impairing its ability to contract

Treatment consists of relieving the obstruction. Once the blockage is removed, the kidneys usually recover in one to two weeks if there is no infection or other problem.

4.  Renal Damage, problems with the kidney itself that prevent proper filtration of blood or production of urine.

Primary renal damage is the most complicated cause of renal failure (accounts for 25%-40% of cases). Renal causes of acute kidney failure include those affecting the filtering function of the kidney, those affecting the blood supply within the kidney, and those affecting the kidney tissue that handles salt and water processing.

Some kidney problems that can cause kidney failure include:

• Blood vessel diseases
  
  
• Blood clot in a vessel in the kidneys
  
  
• Injury to kidney tissue and cells
  
  
• Glomerulonephritis
  
  
• Acute interstitial nephritis
  
  
• Acute tubular necrosis