Acute kidney injury

Acute kidney injury (AKI), previously called acute renal failure (ARF), is an abrupt loss of kidney function that develops within 7 days.Renal ultrasonograph of acute pyelonephritis with increased cortical echogenicity and blurred delineation of the upper pole.Renal ultrasonograph in renal failure after surgery with increased cortical echogenicity and kidney size. Biopsy showed acute tubular necrosis.Renal ultrasonograph in renal trauma with laceration of the lower pole and subcapsular fluid collection below the kidney. Acute kidney injury (AKI), previously called acute renal failure (ARF), is an abrupt loss of kidney function that develops within 7 days. Its causes are numerous. Generally it occurs because of damage to the kidney tissue caused by decreased kidney blood flow (kidney ischemia) from any cause (e.g., low blood pressure), exposure to substances harmful to the kidney, an inflammatory process in the kidney, or an obstruction of the urinary tract that impedes the flow of urine. AKI is diagnosed on the basis of characteristic laboratory findings, such as elevated blood urea nitrogen and creatinine, or inability of the kidneys to produce sufficient amounts of urine. AKI may lead to a number of complications, including metabolic acidosis, high potassium levels, uremia, changes in body fluid balance, and effects on other organ systems, including death. People who have experienced AKI may have an increased risk of chronic kidney disease in the future. Management includes treatment of the underlying cause and supportive care, such as renal replacement therapy. The clinical picture is often dominated by the underlying cause. The various symptoms of acute kidney injury result from the various disturbances of kidney function that are associated with the disease. Accumulation of urea and other nitrogen-containing substances in the bloodstream lead to a number of symptoms, such as fatigue, loss of appetite, headache, nausea and vomiting. Marked increases in the potassium level can lead to abnormal heart rhythms, which can be severe and life-threatening. Fluid balance is frequently affected, though blood pressure can be high, low or normal. Pain in the flanks may be encountered in some conditions (such as clotting of the kidneys' blood vessels or inflammation of the kidney); this is the result of stretching of the fibrous tissue capsule surrounding the kidney. If the kidney injury is the result of dehydration, there may be thirst as well as evidence of fluid depletion on physical examination. Physical examination may also provide other clues as to the underlying cause of the kidney problem, such as a rash in interstitial nephritis (or vasculitis) and a palpable bladder in obstructive nephropathy. Acute kidney injury is diagnosed on the basis of clinical history and laboratory data. A diagnosis is made when there is a rapid reduction in kidney function, as measured by serum creatinine, or based on a rapid reduction in urine output, termed oliguria (less than 400 mLs of urine per 24 hours). AKI can be caused by systemic disease (such as a manifestation of an autoimmune disease, e.g. lupus nephritis), crush injury, contrast agents, some antibiotics, and more. AKI often occurs due to multiple processes. The most common cause is dehydration and sepsis combined with nephrotoxic drugs, especially following surgery or contrast agents. The causes of acute kidney injury are commonly categorized into prerenal, intrinsic, and postrenal. Acute kidney injury occurs in up to 30% of patients following cardiac surgery.  Mortality increases by 60-80% in post-cardiopulmonary bypass patients who go on to require renal replacement therapy.  Preoperative creatinine greater than 1.2 mg/dL, combined valve and bypass procedures, emergency surgery, and preoperative intraaortic balloon pump are risk factors most strongly correlated with post-cardiopulmonary bypass acute kidney injury.  Other well-known minor risk factors include: female gender, congestive heart failure, chronic obstructive pulmonary disease, insulin-requiring diabetes, and depressed left ventricular ejection fraction.