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Acute kidney injury (AKI), previously called acute renal failure (ARF), is a sudden decrease in
kidney function Assessment of kidney function occurs in different ways, using the presence of symptoms and signs, as well as measurements using urine tests, blood tests, and medical imaging. Functions of a healthy kidney include maintaining a person's fluid ...
that develops within 7 days, as shown by an increase in
serum creatinine Creatinine (; ) is a breakdown product of creatine phosphate from muscle and protein metabolism. It is released at a constant rate by the body (depending on muscle mass). Biological relevance Serum creatinine (a blood measurement) is an importa ...
or a decrease in urine output, or both. Causes of AKI are classified as either prerenal (due to decreased blood flow to the kidney), intrinsic renal (due to damage to the kidney itself), or postrenal (due to blockage of urine flow). Prerenal causes of AKI include
sepsis Sepsis, formerly known as septicemia (septicaemia in British English) or blood poisoning, is a life-threatening condition that arises when the body's response to infection causes injury to its own tissues and organs. This initial stage is follo ...
,
dehydration In physiology, dehydration is a lack of total body water, with an accompanying disruption of metabolic processes. It occurs when free water loss exceeds free water intake, usually due to exercise, disease, or high environmental temperature. Mil ...
, excessive blood loss, cardiogenic shock,
heart failure Heart failure (HF), also known as congestive heart failure (CHF), is a syndrome, a group of signs and symptoms caused by an impairment of the heart's blood pumping function. Symptoms typically include shortness of breath, excessive fatigue, a ...
,
cirrhosis Cirrhosis, also known as liver cirrhosis or hepatic cirrhosis, and end-stage liver disease, is the impaired liver function caused by the formation of scar tissue known as fibrosis due to damage caused by liver disease. Damage causes tissue repai ...
, and certain medications like
ACE inhibitor Angiotensin-converting-enzyme inhibitors (ACE inhibitors) are a class of medication used primarily for the treatment of hypertension, high blood pressure and heart failure. They work by causing relaxation of blood vessels as well as a decrease i ...
s or
NSAID Non-steroidal anti-inflammatory drugs (NSAID) are members of a therapeutic drug class which reduces pain, decreases inflammation, decreases fever, and prevents blood clots. Side effects depend on the specific drug, its dose and duration of ...
s. Intrinsic renal causes of AKI include
glomerulonephritis Glomerulonephritis (GN) is a term used to refer to several kidney diseases (usually affecting both kidneys). Many of the diseases are characterised by inflammation either of the glomeruli or of the small blood vessels in the kidneys, hence the ...
,
lupus nephritis Lupus nephritis is an inflammation of the kidneys caused by systemic lupus erythematosus (SLE), an autoimmune disease. It is a type of glomerulonephritis in which the glomeruli become inflamed. Since it is a result of SLE, this type of glomerulo ...
,
acute tubular necrosis Acute tubular necrosis (ATN) is a medical condition involving the death of tubular epithelial cells that form the renal tubules of the kidneys. Because necrosis is often not present, the term acute tubular injury (ATI) is preferred by pathologists ...
, certain antibiotics, and chemotherapeutic agents. Postrenal causes of AKI include
kidney stone Kidney stone disease, also known as nephrolithiasis or urolithiasis, is a crystallopathy where a solid piece of material (kidney stone) develops in the urinary tract. Kidney stones typically form in the kidney and leave the body in the urine s ...
s,
bladder cancer Bladder cancer is any of several types of cancer arising from the tissues of the urinary bladder. Symptoms include blood in the urine, pain with urination, and low back pain. It is caused when epithelial cells that line the bladder become mali ...
,
neurogenic bladder Neurogenic bladder dysfunction, or neurogenic bladder, refers to urinary bladder problems due to disease or injury of the central nervous system or peripheral nerves involved in the control of urination. There are multiple types of neurogenic bladde ...
, enlargement of the prostate, narrowing of the urethra, and certain medications like
anticholinergic Anticholinergics (anticholinergic agents) are substances that block the action of the neurotransmitter called acetylcholine (ACh) at synapses in the central and peripheral nervous system. These agents inhibit the parasympathetic nervous system ...
s. The diagnosis of AKI is made based on a person's signs and symptoms, along with lab tests for serum creatinine and measurement of urine output. Other tests include
urine microscopy Urinalysis, a portmanteau of the words ''urine'' and ''analysis'', is a panel of medical tests that includes physical (macroscopic) examination of the urine, chemical evaluation using urine test strips, and microscopic examination. Macroscopic ...
and
urine electrolytes Urine electrolyte levels can be measured in a medical laboratory for diagnostic purposes. The urine concentrations of sodium, chloride and potassium may be used to investigate conditions such as abnormal blood electrolyte levels, acute kidney inju ...
.
Renal ultrasound Renal ultrasonography (Renal US) is the examination of one or both kidneys using medical ultrasound. Ultrasonography of the kidneys is essential in the diagnosis and management of kidney-related diseases. The kidneys are easily examined, and most ...
can be obtained when a postrenal cause is suspected. A
kidney biopsy Renal biopsy (also kidney biopsy) is a medical procedure in which a small piece of kidney is removed from the body for examination, usually under a microscope. Microscopic examination of the tissue can provide information needed to diagnose, moni ...
may be obtained when intrinsic renal AKI is suspected and the cause is unclear. AKI is seen in 10-15% of people admitted to the hospital and in more than 50% of people admitted to the
intensive care unit 220px, Intensive care unit An intensive care unit (ICU), also known as an intensive therapy unit or intensive treatment unit (ITU) or critical care unit (CCU), is a special department of a hospital or health care facility that provides intensiv ...
(ICU). AKI may lead to a number of complications, including
metabolic acidosis Metabolic acidosis is a serious electrolyte disorder characterized by an imbalance in the body's acid-base balance. Metabolic acidosis has three main root causes: increased acid production, loss of bicarbonate, and a reduced ability of the kidneys ...
, high potassium levels,
uremia Uremia is the term for high levels of urea in the blood. Urea is one of the primary components of urine. It can be defined as an excess of amino acid and protein metabolism end products, such as urea and creatinine, in the blood that would be no ...
, changes in body
fluid balance Fluid balance is an aspect of the homeostasis of organisms in which the amount of water in the organism needs to be controlled, via osmoregulation and behavior, such that the concentrations of electrolytes ( salts in solution) in the various b ...
, effects on other
organ system An organ system is a biological system consisting of a group of organs that work together to perform one or more functions. Each organ has a specialized role in a plant or animal body, and is made up of distinct tissues. Plants Plants have ...
s, and death. People who have experienced AKI are at increased risk of developing chronic kidney disease in the future. Management includes treatment of the underlying cause and supportive care, such as
renal replacement therapy Renal replacement therapy (RRT) is therapy that replaces the normal blood-filtering function of the kidneys. It is used when the kidneys are not working well, which is called kidney failure and includes acute kidney injury and chronic kidney di ...
.


Signs and symptoms

The clinical presentation 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 Anorexia is a medical term for a loss of appetite. While the term in non-scientific publications is often used interchangeably with anorexia nervosa, many possible causes exist for a loss of appetite, some of which may be harmless, while others i ...
,
headache Headache is the symptom of pain in the face, head, or neck. It can occur as a migraine, tension-type headache, or cluster headache. There is an increased risk of depression in those with severe headaches. Headaches can occur as a result ...
,
nausea Nausea is a diffuse sensation of unease and discomfort, sometimes perceived as an urge to vomit. While not painful, it can be a debilitating symptom if prolonged and has been described as placing discomfort on the chest, abdomen, or back of the ...
, and
vomiting Vomiting (also known as emesis and throwing up) is the involuntary, forceful expulsion of the contents of one's stomach through the mouth and sometimes the Human nose, nose. Vomiting can be the result of ailments like Food-poisoning, foo ...
. Marked increases in the
potassium Potassium is the chemical element with the symbol K (from Neo-Latin ''kalium'') and atomic number19. Potassium is a silvery-white metal that is soft enough to be cut with a knife with little force. Potassium metal reacts rapidly with atmosphe ...
level can lead to abnormal heart rhythms, which can be severe and life-threatening. Fluid
balance Balance or balancing may refer to: Common meanings * Balance (ability) in biomechanics * Balance (accounting) * Balance or weighing scale * Balance as in equality or equilibrium Arts and entertainment Film * ''Balance'' (1983 film), a Bulgaria ...
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 Coagulation, also known as clotting, is the process by which blood changes from a liquid to a gel, forming a blood clot. It potentially results in hemostasis, the cessation of blood loss from a damaged vessel, followed by repair. The mechanism o ...
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 Thirst is the craving for potable fluids, resulting in the basic instinct of animals to drink. It is an essential mechanism involved in fluid balance. It arises from a lack of fluids or an increase in the concentration of certain osmolites, suc ...
as well as evidence of fluid depletion on
physical examination In a physical examination, medical examination, or clinical examination, a medical practitioner examines a patient for any possible medical signs or symptoms of a medical condition. It generally consists of a series of questions about the patien ...
. Physical examination may also provide other clues as to the underlying cause of the kidney problem, such as a
rash A rash is a change of the human skin which affects its color, appearance, or texture. A rash may be localized in one part of the body, or affect all the skin. Rashes may cause the skin to change color, itch, become warm, bumpy, chapped, dry, cr ...
in interstitial nephritis (or
vasculitis Vasculitis is a group of disorders that destroy blood vessels by inflammation. Both arteries and veins are affected. Lymphangitis (inflammation of lymphatic vessels) is sometimes considered a type of vasculitis. Vasculitis is primarily caused ...
) and a palpable
bladder The urinary bladder, or simply bladder, is a hollow organ in humans and other vertebrates that stores urine from the kidneys before disposal by urination. In humans the bladder is a distensible organ that sits on the pelvic floor. Urine enters ...
in obstructive nephropathy.


Causes


Prerenal

''Prerenal'' causes of AKI ("pre-renal azotemia") are those that decrease effective blood flow to the kidney and cause a decrease in the glomerular filtration rate (GFR). Both kidneys need to be affected as one kidney is still more than adequate for normal kidney function. Notable causes of prerenal AKI include
low blood volume Hypovolemia, also known as volume depletion or volume contraction, is a state of abnormally low extracellular fluid in the body. This may be due to either a loss of both salt and water or a decrease in blood volume. Hypovolemia refers to the loss ...
(e.g., dehydration),
low blood pressure Hypotension is low blood pressure. Blood pressure is the force of blood pushing against the walls of the arteries as the heart pumps out blood. Blood pressure is indicated by two numbers, the systolic blood pressure (the top number) and the di ...
,
heart failure Heart failure (HF), also known as congestive heart failure (CHF), is a syndrome, a group of signs and symptoms caused by an impairment of the heart's blood pumping function. Symptoms typically include shortness of breath, excessive fatigue, a ...
(leading to cardiorenal syndrome),
hepatorenal syndrome Hepatorenal syndrome (often abbreviated HRS) is a life-threatening medical condition that consists of rapid deterioration in kidney function in individuals with cirrhosis or fulminant liver failure. HRS is usually fatal unless a liver transpla ...
in the context of liver cirrhosis, and local changes to the blood vessels supplying the kidney. The latter include
renal artery stenosis Renal artery stenosis (RAS) is the narrowing of one or both of the renal arteries, most often caused by atherosclerosis or fibromuscular dysplasia. This narrowing of the renal artery can impede blood flow to the target kidney, resulting in renov ...
, or the narrowing of the
renal artery The renal arteries are paired arteries that supply the kidneys with blood. Each is directed across the crus of the diaphragm, so as to form nearly a right angle. The renal arteries carry a large portion of total blood flow to the kidneys. Up to a ...
which supplies the kidney with blood, and renal vein thrombosis, which is the formation of a
blood clot A thrombus (plural thrombi), colloquially called a blood clot, is the final product of the blood coagulation step in hemostasis. There are two components to a thrombus: aggregated platelets and red blood cells that form a plug, and a mesh of ...
in the
renal vein The renal veins are large-calibre veins that drain blood filtered by the kidneys into the inferior vena cava. There is one renal vein draining each kidney. Because the inferior vena cava is on the right half of the body, the left renal vein is lo ...
that drains blood from the kidney.


Intrinsic or renal

Intrinsic AKI refers to disease processes which directly damage the kidney itself. Intrinsic AKI can be due to one or more of the kidney's structures including the
glomeruli ''Glomerulus'' () is a common term used in anatomy to describe globular structures of entwined vessels, fibers, or neurons. ''Glomerulus'' is the diminutive of the Latin ''glomus'', meaning "ball of yarn". ''Glomerulus'' may refer to: * the filter ...
, kidney tubules, or the interstitium. Common causes of each are
glomerulonephritis Glomerulonephritis (GN) is a term used to refer to several kidney diseases (usually affecting both kidneys). Many of the diseases are characterised by inflammation either of the glomeruli or of the small blood vessels in the kidneys, hence the ...
,
acute tubular necrosis Acute tubular necrosis (ATN) is a medical condition involving the death of tubular epithelial cells that form the renal tubules of the kidneys. Because necrosis is often not present, the term acute tubular injury (ATI) is preferred by pathologists ...
(ATN), and
acute interstitial nephritis Interstitial nephritis, also known as tubulointerstitial nephritis, is inflammation of the area of the kidney known as the renal interstitium, which consists of a collection of cells, extracellular matrix, and fluid surrounding the renal tubules. ...
(AIN), respectively. Other causes of intrinsic AKI are rhabdomyolysis and
tumor lysis syndrome Tumor lysis syndrome (TLS) is a group of metabolic abnormalities that can occur as a complication from the treatment of cancer, where large amounts of tumor cells are killed off ( lysed) from the treatment, releasing their contents into the blood ...
. Certain medication classes such as
calcineurin inhibitor Immunosuppressive drugs, also known as immunosuppressive agents, immunosuppressants and antirejection medications, are drugs that inhibit or prevent activity of the immune system. Classification Immunosuppressive drugs can be classified into ...
s (e.g.,
tacrolimus Tacrolimus, sold under the brand name Prograf among others, is an immunosuppressive drug. After allogeneic organ transplant, the risk of organ rejection is moderate. To lower the risk of organ rejection, tacrolimus is given. The drug can also ...
) can also directly damage the tubular cells of the kidney and result in a form of intrinsic AKI.


Postrenal

''Postrenal'' AKI refers to acute kidney injury caused by disease states downstream of the kidney and most often occurs as a consequence of
urinary tract The urinary system, also known as the urinary tract or renal system, consists of the kidneys, ureters, bladder, and the urethra. The purpose of the urinary system is to eliminate waste from the body, regulate blood volume and blood pressure, c ...
obstruction. This may be related to
benign prostatic hyperplasia Benign prostatic hyperplasia (BPH), also called prostate enlargement, is a noncancerous increase in size of the prostate gland. Symptoms may include frequent urination, trouble starting to urinate, weak stream, inability to urinate, or loss o ...
,
kidney stones Kidney stone disease, also known as nephrolithiasis or urolithiasis, is a crystallopathy where a solid piece of material (kidney stone) develops in the urinary tract. Kidney stones typically form in the kidney and leave the body in the urine s ...
, obstructed
urinary catheter In urinary catheterization a latex, polyurethane, or silicone tube known as a urinary catheter is inserted into the bladder through the urethra to allow urine to drain from the bladder for collection. It may also be used to inject liquids used ...
,
bladder stone A bladder stone is a stone found in the urinary bladder. Signs and symptoms Bladder stones are small mineral deposits that can form in the bladder. In most cases bladder stones develop when the urine becomes very concentrated or when one is ...
s, or cancer of the
bladder The urinary bladder, or simply bladder, is a hollow organ in humans and other vertebrates that stores urine from the kidneys before disposal by urination. In humans the bladder is a distensible organ that sits on the pelvic floor. Urine enters ...
,
ureters The ureters are tubes made of smooth muscle that propel urine from the kidneys to the urinary bladder. In a human adult, the ureters are usually long and around in diameter. The ureter is lined by urothelial cells, a type of transitional epit ...
, or
prostate The prostate is both an Male accessory gland, accessory gland of the male reproductive system and a muscle-driven mechanical switch between urination and ejaculation. It is found only in some mammals. It differs between species anatomically, ...
.


Diagnosis


Definition

Introduced by the KDIGO in 2012, specific criteria exist for the diagnosis of AKI. AKI can be diagnosed if any one of the following is present: * Increase in SCr by ≥0.3 mg/dl (≥26.5 μmol/L) within 48 hours; or * Increase in SCr to ≥1.5 times baseline, which has occurred within the prior 7 days; or * Urine volume < 0.5 mL/kg/h for 6 hours.


Staging

The ''RIFLE criteria'', proposed by the Acute Dialysis Quality Initiative (ADQI) group, aid in assessment of the severity of a person's acute kidney injury. The acronym RIFLE is used to define the spectrum of progressive kidney injury seen in AKI: * Risk: 1.5-fold increase in the serum creatinine, or glomerular filtration rate (GFR) decrease by 25 percent, or urine output <0.5 mL/kg per hour for six hours. * Injury: Two-fold increase in the serum creatinine, or GFR decrease by 50 percent, or urine output <0.5 mL/kg per hour for 12 hours. * Failure: Three-fold increase in the serum creatinine, or GFR decrease by 75 percent, or urine output of <0.3 mL/kg per hour for 24 hours, or no urine output (anuria) for 12 hours. * Loss: Complete loss of kidney function (e.g., need for renal replacement therapy) for more than four weeks. *
End-stage kidney disease Chronic kidney disease (CKD) is a type of kidney disease in which a gradual loss of kidney function occurs over a period of months to years. Initially generally no symptoms are seen, but later symptoms may include leg swelling, feeling tired, vo ...
: Complete loss of kidney function (e.g., need for renal replacement therapy) for more than three months.


Evaluation

The deterioration of kidney function may be signaled by a measurable decrease in urine output. Often, it is diagnosed on the basis of
blood test A blood test is a laboratory analysis performed on a blood sample that is usually extracted from a vein in the arm using a hypodermic needle, or via fingerprick. Multiple tests for specific blood components, such as a glucose test or a cholester ...
s for substances normally eliminated by the kidney:
urea Urea, also known as carbamide, is an organic compound with chemical formula . This amide has two amino groups (–) joined by a carbonyl functional group (–C(=O)–). It is thus the simplest amide of carbamic acid. Urea serves an important r ...
and
creatinine Creatinine (; ) is a breakdown product of creatine phosphate from muscle and protein metabolism. It is released at a constant rate by the body (depending on muscle mass). Biological relevance Serum creatinine (a blood measurement) is an importa ...
. Additionally, the ratio of BUN to creatinine is used to evaluate kidney injury. Both tests have their disadvantages. For instance, it takes about 24 hours for the creatinine level to rise, even if both kidneys have ceased to function. A number of alternative markers have been proposed (such as NGAL,
KIM-1 The KIM-1, short for ''Keyboard Input Monitor'', is a small 6502-based single-board computer developed and produced by MOS Technology, Inc. and launched in 1976. It was very successful in that period, due to its low price (thanks to the inexp ...
, IL18 and cystatin C), but none of them are established enough as of 2018 to replace creatinine as a marker of kidney function. Once the diagnosis of AKI is made, further testing is often required to determine the underlying cause. It is useful to perform a bladder scan or a post void residual to rule out urinary retention. In post void residual, a catheter is inserted into the urinary tract immediately after urinating to measure fluid still in the bladder. 50–100 mL suggests
neurogenic bladder dysfunction Neurogenic bladder dysfunction, or neurogenic bladder, refers to urinary bladder problems due to disease or injury of the central nervous system or peripheral nerves involved in the control of urination. There are multiple types of neurogenic bladde ...
. These may include urine sediment analysis,
renal ultrasound Renal ultrasonography (Renal US) is the examination of one or both kidneys using medical ultrasound. Ultrasonography of the kidneys is essential in the diagnosis and management of kidney-related diseases. The kidneys are easily examined, and most ...
and/or
kidney biopsy Renal biopsy (also kidney biopsy) is a medical procedure in which a small piece of kidney is removed from the body for examination, usually under a microscope. Microscopic examination of the tissue can provide information needed to diagnose, moni ...
. Indications for kidney biopsy in the setting of AKI include the following: # Unexplained AKI, in a patient with two non-obstructed normal sized kidneys. # AKI in the presence of the
nephritic syndrome Nephritic syndrome is a syndrome comprising signs of nephritis, which is kidney disease involving inflammation. It often occurs in the glomerulus, where it is called glomerulonephritis. Glomerulonephritis is characterized by inflammation and t ...
. # Systemic disease associated with AKI. # Kidney transplant dysfunction. In
medical imaging Medical imaging is the technique and process of imaging the interior of a body for clinical analysis and medical intervention, as well as visual representation of the function of some organs or tissues (physiology). Medical imaging seeks to rev ...
, the acute changes in the kidney are often examined with
renal ultrasonography Renal ultrasonography (Renal US) is the examination of one or both kidneys using medical ultrasound. Ultrasonography of the kidneys is essential in the diagnosis and management of kidney-related diseases. The kidneys are easily examined, and most ...
as the first-line modality, where CT scan and magnetic resonance imaging (MRI) are used for the follow-up examinations and when US fails to demonstrate abnormalities. In evaluation of the acute changes in the kidney, the echogenicity of the renal structures, the delineation of the kidney, the renal vascularity, kidney size and focal abnormalities are observed.Content initially copied from:
(CC-BY 4.0)
CT is preferred in renal traumas, but US is used for follow-up, especially in the patients suspected for the formation of
urinoma Extravasation of urine refers to the condition where an interruption of the urethra leads to a collection of urine in other cavities, such as the scrotum or the penis in males. It can be associated with a calculus. Mechanism An injury to the ureth ...
s. A CT scan of the abdomen will also demonstrate bladder distension or hydronephrosis. File:Ultrasonography of acute pyelonephritis.jpg, Renal ultrasonograph of acute
pyelonephritis Pyelonephritis is inflammation of the kidney, typically due to a bacterial infection. Symptoms most often include fever and flank tenderness. Other symptoms may include nausea, burning with urination, and frequent urination. Complications may ...
with increased cortical echogenicity and blurred delineation of the upper pole. File:Ultrasonography of postoperative renal failure.jpg, Renal ultrasonograph in renal failure after surgery with increased cortical echogenicity and kidney size. Biopsy showed acute tubular necrosis. File:Ultrasonography of renal trauma with laceration.jpg, Renal ultrasonograph in renal trauma with laceration of the lower pole and subcapsular fluid collection below the kidney.


Classification

Acute kidney injury is diagnosed on the basis of
clinical history The medical history, case history, or anamnesis (from Greek: ἀνά, ''aná'', "open", and μνήσις, ''mnesis'', "memory") of a patient is information gained by a physician by asking specific questions, either to the patient or to other peo ...
and laboratory data. A diagnosis is made when there is a rapid reduction in
kidney function Assessment of kidney function occurs in different ways, using the presence of symptoms and signs, as well as measurements using urine tests, blood tests, and medical imaging. Functions of a healthy kidney include maintaining a person's fluid ...
, as measured by serum
creatinine Creatinine (; ) is a breakdown product of creatine phosphate from muscle and protein metabolism. It is released at a constant rate by the body (depending on muscle mass). Biological relevance Serum creatinine (a blood measurement) is an importa ...
, or based on a rapid reduction in urine output, termed
oliguria Oliguria or hypouresis is the low output of urine specifically more than 80 ml/day but less than 400ml/day.Boon et al, Davidson's Principles & Practice of Medicine (20th Ed), p475 The decreased output of urine may be a sign of dehydration, kidney ...
(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 Lupus nephritis is an inflammation of the kidneys caused by systemic lupus erythematosus (SLE), an autoimmune disease. It is a type of glomerulonephritis in which the glomeruli become inflamed. Since it is a result of SLE, this type of glomerulo ...
),
crush injury A crush injury is injury by an object that causes compression of the body. This form of injury is rare in normal civilian practice, but common following a natural disaster. Other causes include industrial accidents, road traffic collisions, build ...
,
contrast agents A contrast agent (or contrast medium) is a substance used to increase the contrast of structures or fluids within the body in medical imaging. Contrast agents absorb or alter external electromagnetism or ultrasound, which is different from radiop ...
, 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 A contrast agent (or contrast medium) is a substance used to increase the contrast of structures or fluids within the body in medical imaging. Contrast agents absorb or alter external electromagnetism or ultrasound, which is different from radiop ...
. 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 intra-aortic 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. Volatile anesthetic agents have been shown to increase renal sympathetic nerve activity (RSNA), which causes retention of salts and water, diminished renal blood flow (RBF) and an increase in serum renin levels, but not in antidiuretic hormone (ADH).


Treatment

The management of AKI hinges on identification and treatment of the underlying cause. The main objectives of initial management are to prevent cardiovascular collapse and death and to call for specialist advice from a
nephrologist Nephrology (from Greek'' nephros'' "kidney", combined with the suffix ''-logy'', "the study of") is a specialty of adult internal medicine and pediatric medicine that concerns the study of the kidneys, specifically normal kidney function ( ...
. In addition to treatment of the underlying disorder, management of AKI routinely includes the avoidance of substances that are toxic to the kidneys, called
nephrotoxin Nephrotoxicity is toxicity in the kidneys. It is a poisonous effect of some substances, both toxic chemicals and medications, on kidney function. There are various forms, and some drugs may affect kidney function in more than one way. Nephrotoxin ...
s. These include
NSAID Non-steroidal anti-inflammatory drugs (NSAID) are members of a therapeutic drug class which reduces pain, decreases inflammation, decreases fever, and prevents blood clots. Side effects depend on the specific drug, its dose and duration of ...
s such as ibuprofen or
naproxen Naproxen is a nonsteroidal anti-inflammatory drug (NSAID) used to treat pain, menstrual cramps, inflammatory diseases such as rheumatoid arthritis, gout and fever. It is taken orally. It is available in immediate and delayed release formulat ...
,
iodinated contrast Iodinated contrast is a form of intravenous radiocontrast agent containing iodine, which enhances the visibility of vascular structures and organs during radiographic procedures. Some pathologies, such as cancer, have particularly improved visib ...
s such as those used for CT scans, many
antibiotics An antibiotic is a type of antimicrobial substance active against bacteria. It is the most important type of antibacterial agent for fighting bacterial infections, and antibiotic medications are widely used in the treatment and prevention o ...
such as
gentamicin Gentamicin is an antibiotic used to treat several types of bacterial infections. This may include bone infections, endocarditis, pelvic inflammatory disease, meningitis, pneumonia, urinary tract infections, and sepsis among others. It is not e ...
, and a range of other substances. Monitoring of kidney function, by serial serum creatinine measurements and monitoring of urine output, is routinely performed. In the hospital, insertion of a
urinary catheter In urinary catheterization a latex, polyurethane, or silicone tube known as a urinary catheter is inserted into the bladder through the urethra to allow urine to drain from the bladder for collection. It may also be used to inject liquids used ...
helps monitor urine output and relieves possible bladder outlet obstruction, such as with an enlarged prostate.


Prerenal

In prerenal AKI without
fluid overload Hypervolemia, also known as fluid overload, is the medical condition where there is too much fluid in the blood. The opposite condition is hypovolemia, which is too little fluid volume in the blood. Fluid volume excess in the intravascular comp ...
, administration of
intravenous fluid Intravenous therapy (abbreviated as IV therapy) is a medical technique that administers fluids, medications and nutrients directly into a person's vein. The intravenous route of administration is commonly used for rehydration or to provide nutrie ...
s is typically the first step to improving kidney function. Volume status may be monitored with the use of a
central venous catheter A central venous catheter (CVC), also known as a central line(c-line), central venous line, or central venous access catheter, is a catheter placed into a large vein. It is a form of venous access. Placement of larger catheters in more central ...
to avoid over- or under-replacement of fluid. If
low blood pressure Hypotension is low blood pressure. Blood pressure is the force of blood pushing against the walls of the arteries as the heart pumps out blood. Blood pressure is indicated by two numbers, the systolic blood pressure (the top number) and the di ...
persists despite providing a person with adequate amounts of intravenous fluid, medications that increase blood pressure ( vasopressors) such as
norepinephrine Norepinephrine (NE), also called noradrenaline (NA) or noradrenalin, is an organic chemical in the catecholamine family that functions in the brain and body as both a hormone and neurotransmitter. The name "noradrenaline" (from Latin '' ad'', ...
, and in certain circumstances medications that improve the heart's ability to pump (known as
inotrope An inotrope is an agent that alters the force or energy of muscular contractions. Negatively inotropic agents weaken the force of muscular contractions. Positively inotropic agents increase the strength of muscular contraction. The term ''inot ...
s) such as
dobutamine Dobutamine is a medication used in the treatment of cardiogenic shock (as a result of inadequate tissue perfusion) and severe heart failure. It may also be used in certain types of cardiac stress tests. It is given by IV only, as an injection in ...
may be given to improve blood flow to the kidney. While a useful vasopressor, there is no evidence to suggest that
dopamine Dopamine (DA, a contraction of 3,4-dihydroxyphenethylamine) is a neuromodulatory molecule that plays several important roles in cells. It is an organic compound, organic chemical of the catecholamine and phenethylamine families. Dopamine const ...
is of any specific benefit and may in fact be harmful.


Intrinsic

The myriad causes of intrinsic AKI require specific therapies. For example, intrinsic AKI due to vasculitis or glomerulonephritis may respond to
steroid A steroid is a biologically active organic compound with four rings arranged in a specific molecular configuration. Steroids have two principal biological functions: as important components of cell membranes that alter membrane fluidity; and a ...
medication,
cyclophosphamide Cyclophosphamide (CP), also known as cytophosphane among other names, is a medication used as chemotherapy and to suppress the immune system. As chemotherapy it is used to treat lymphoma, multiple myeloma, leukemia, ovarian cancer, breast cancer ...
, and (in some cases) plasma exchange. Toxin-induced prerenal AKI often responds to discontinuation of the offending agent, such as ACE inhibitors, ARB antagonists,
aminoglycosides Aminoglycoside is a medicinal and bacteriologic category of traditional Gram-negative antibacterial medications that inhibit protein synthesis and contain as a portion of the molecule an amino-modified glycoside ( sugar). The term can also refer ...
,
penicillins Penicillins (P, PCN or PEN) are a group of β-lactam antibiotics originally obtained from ''Penicillium'' moulds, principally '' P. chrysogenum'' and '' P. rubens''. Most penicillins in clinical use are synthesised by P. chrysogenum using ...
, NSAIDs, or paracetamol. The use of diuretics such as furosemide, is widespread and sometimes convenient in improving fluid overload. It is not associated with higher mortality (risk of death), nor with any reduced mortality or length of
intensive care unit 220px, Intensive care unit An intensive care unit (ICU), also known as an intensive therapy unit or intensive treatment unit (ITU) or critical care unit (CCU), is a special department of a hospital or health care facility that provides intensiv ...
or hospital stay.


Postrenal

If the cause is obstruction of the urinary tract, relief of the obstruction (with a nephrostomy or
urinary catheter In urinary catheterization a latex, polyurethane, or silicone tube known as a urinary catheter is inserted into the bladder through the urethra to allow urine to drain from the bladder for collection. It may also be used to inject liquids used ...
) may be necessary.


Renal replacement therapy

Renal replacement therapy, such as with hemodialysis, may be instituted in some cases of AKI. Renal replacement therapy can be applied intermittently (IRRT) and continuously (CRRT). Study results regarding differences in outcomes between IRRT and CRRT are inconsistent. A systematic review of the literature in 2008 demonstrated no difference in outcomes between the use of intermittent hemodialysis and continuous venovenous hemofiltration (CVVH) (a type of continuous hemodialysis). Among critically ill patients, intensive renal replacement therapy with CVVH does not appear to improve outcomes compared to less intensive intermittent hemodialysis. However, other clinical and health economic studies demonstrated that, initiation of CRRT is associated with a lower likelihood of chronic dialysis and was cost-effective compared with IRRT in patients with acute kidney injury.


Complications

Metabolic acidosis, hyperkalemia, and pulmonary edema may require medical treatment with sodium bicarbonate, antihyperkalemic measures, and diuretics. Lack of improvement with Fluid replacement, fluid resuscitation, therapy-resistant hyperkalemia, metabolic acidosis, or fluid overload may necessitate renal replacement therapy, artificial support in the form of Kidney dialysis, dialysis or hemofiltration. However, oliguria during anesthesia may predict AKI, but the effect of a fluid load is highly variable. Striving toward a predefined urine output target to prevent AKI is futile.


Early recovery of AKI

AKI recovery can be classified into three stages 1–3 on the basis of the inverse of the AKI KDIGO serum
creatinine Creatinine (; ) is a breakdown product of creatine phosphate from muscle and protein metabolism. It is released at a constant rate by the body (depending on muscle mass). Biological relevance Serum creatinine (a blood measurement) is an importa ...
criteria.


Prognosis


Mortality

Mortality after AKI remains high. AKI has a death rate as high as 20%, which may reach up to 50% in the
intensive care unit 220px, Intensive care unit An intensive care unit (ICU), also known as an intensive therapy unit or intensive treatment unit (ITU) or critical care unit (CCU), is a special department of a hospital or health care facility that provides intensiv ...
(ICU). Each year, around two million people die of AKI worldwide. AKI develops in 5% to 30% of patients who undergo cardiothoracic surgery, depending on the definition used for AKI. If AKI develops after major abdominal surgery (13.4% of all people who have undergone major abdominal surgery) the risk of death is markedly increased (over 12-fold).


Kidney function

Depending on the cause, a proportion of patients (5–10%) will never regain full kidney function, thus entering end-stage kidney failure and requiring lifelong dialysis or a kidney transplant. Patients with AKI are more likely to die prematurely after being discharged from hospital, even if their kidney function has recovered. The risk of developing chronic kidney disease is increased (8.8-fold).


Epidemiology

New cases of AKI are unusual but not rare, affecting approximately 0.1% of the UK population per year (2000 ppm/year), 20x incidence of new ESKD (end-stage kidney disease). AKI requiring dialysis (10% of these) is rare (200 ppm/year), 2x incidence of new ESKD. There is an increased incidence of AKI in agricultural workers because of occupational hazards such as dehydration and heat illness. No other traditional risk factors, including age, BMI, diabetes, or hypertension, were associated with incident AKI. Acute kidney injury is common among hospitalized patients. It affects some 3–7% of patients admitted to the hospital and approximately 25–30% of patients in the
intensive care unit 220px, Intensive care unit An intensive care unit (ICU), also known as an intensive therapy unit or intensive treatment unit (ITU) or critical care unit (CCU), is a special department of a hospital or health care facility that provides intensiv ...
. Acute kidney injury was one of the most expensive conditions seen in U.S. hospitals in 2011, with an aggregated cost of nearly $4.7 billion for approximately 498,000 hospital stays. This was a 346% increase in hospitalizations from 1997, when there were 98,000 acute kidney injury stays. According to a review article of 2015, there has been an increase in cases of acute kidney injury in the last 20 years which cannot be explained solely by changes to the manner of reporting.


History

Before the advancement of modern medicine, acute kidney injury was referred to as ''uremic poisoning'' while
uremia Uremia is the term for high levels of urea in the blood. Urea is one of the primary components of urine. It can be defined as an excess of amino acid and protein metabolism end products, such as urea and creatinine, in the blood that would be no ...
was contamination of the blood with urine. Starting around 1847, ''uremia'' came to be used for reduced urine output, a condition now called
oliguria Oliguria or hypouresis is the low output of urine specifically more than 80 ml/day but less than 400ml/day.Boon et al, Davidson's Principles & Practice of Medicine (20th Ed), p475 The decreased output of urine may be a sign of dehydration, kidney ...
, which was thought to be caused by the urine's mixing with the blood instead of being voided through the urethra. Acute kidney injury due to
acute tubular necrosis Acute tubular necrosis (ATN) is a medical condition involving the death of tubular epithelial cells that form the renal tubules of the kidneys. Because necrosis is often not present, the term acute tubular injury (ATI) is preferred by pathologists ...
(ATN) was recognized in the 1940s in United Kingdom, the United Kingdom, where Crush syndrome, crush injury victims during the London Blitz developed patchy necrosis of kidney tubules, leading to a sudden decrease in kidney function. During the Korean War, Korean and Vietnam War, Vietnam wars, the incidence of AKI decreased due to better acute management and administration of
intravenous fluid Intravenous therapy (abbreviated as IV therapy) is a medical technique that administers fluids, medications and nutrients directly into a person's vein. The intravenous route of administration is commonly used for rehydration or to provide nutrie ...
s.


See also

* BUN-to-creatinine ratio * Chronic kidney disease * Kidney dialysis, Dialysis * Genitourinary tract injury * Kidney failure * Rhabdomyolysis * Contrast-induced nephropathy * Ischemia-reperfusion injury of the appendicular musculoskeletal system * Kidney Ischemia


References


External links

{{Authority control Medical emergencies Kidney diseases Organ failure Causes of death