Acute Renal Failure

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eMedicine Specialties > Nephrology > Acute Kidney Failure
Acute Renal Failure
Mahendra Agraharkar, MD, MBBS, FACP, FASN, Clinical Associate Professor of Medicine, Baylor College of Medicine, President & CEO, Space City Associates of Nephrology
Rajiv Gupta, MD, Assistant Professor, Department of Medicine, Texas A & M University Health Science Center; Consulting Staff, Veterans Affairs Medical Center; Biruh T Workeneh, MD, Assistant Professor, Baylor College of Medicine


Updated: Aug 17, 2009

Introduction
Background
Acute renal failure (ARF) or acute kidney injury (AKI), as it is now referred to in the literature, is defined as an abrupt or rapid decline in renal filtration function. This condition is usually marked by a rise in serum creatinine concentration or azotemia (a rise in blood urea nitrogen [BUN] concentration). However, immediately after a kidney injury, BUN or creatinine levels may be normal, and the only sign of a kidney injury may be decreased urine production. A rise in the creatinine level can result from medications (eg, cimetidine, trimethoprim) that inhibit the kidney?s tubular secretion. A rise in the BUN level can occur without renal injury, resulting instead from such sources as GI or mucosal bleeding, steroid use, or protein loading, so a careful inventory must be taken before determining if a kidney injury is present. (See images below and Image 1.)




Photomicrograph of a renal biopsy specimen shows renal medulla, which is composed mainly of renal tubules. Patchy or diffuse denudation of the renal tubular cells is observed, suggesting acute tubular necrosis as the cause of acute renal failure.



The RIFLE system

In 2004, the Acute Dialysis Quality Initiative work group set forth a definition and classification system for acute renal failure, described by the acronym RIFLE (Risk of renal dysfunction, Injury to the kidney, Failure or Loss of kidney function, and End-stage kidney disease; see Table, below).[1 ] Investigators have since applied the RIFLE system to the clinical evaluation of AKI, although it was not originally intended for that purpose. AKI research increasingly uses RIFLE.

Table: RIFLE Classification System for Acute Kidney Injury

Stage
GFR** Criteria
Urine Output Criteria
Probability

Risk
SCreat? increased ? 1.5
or
GFR decreased >25%
UO? <0.5 mL/kg/h ? 6 h
High sensitivity (Risk >Injury >Failure)

Injury
SCreat increased ? 2
or
GFR decreased >50%
UO <0.5 mL/kg/h ? 12 h

Failure
SCreat increased ? 3
or
GFR decreased 75%
or
SCreat ?4 mg/dL; acute rise ?0.5 mg/dL
UO <0.3 mL/kg/h ? 24 h
(oliguria)
or
anuria ? 12 h

Loss
Persistent acute renal failure: complete loss of kidney function >4 wk
High specificity

ESKD*
Complete loss of kidney function >3 mo



*ESKD?end-stage kidney disease; **GFR?glomerular filtration rate; ?SCreat?serum creatinine; ?UO?urine output

Note: Patients can be classified by GFR criteria and/or UO criteria. The criteria that support the most severe classification should be used. The superimposition of acute on chronic failure is indicated with the designation RIFLE-F C ; failure is present in such cases even if the increase in SCreat is less than 3-fold, provided that the new SCreat is greater than 4.0 mg/dL (350 ? mol/L) and results from an acute increase of at least 0.5 mg/dL (44 ? mol/L).

When the failure classification is achieved by UO criteria, the designation of RIFLE-F O is used to denote oliguria. The initial stage, risk, has high sensitivity; more patients will be classified in this mild category, including some who do not actually have renal failure. Progression through the increasingly severe stages of RIFLE is marked by decreasing sensitivity and increasing specificity.

Pathophysiology
AKI may be classified into 3 general categories, as follows:



Prerenal?as an adaptive response to severe volume depletion and hypotension, with structurally intact nephrons
Intrinsic?in response to cytotoxic, ischemic, or inflammatory insults to the kidney, with structural and functional damage
Postrenal?from obstruction to the passage of urine.
While this classification is useful in establishing a differential diagnosis, many pathophysiologic features are shared among the different categories.
Patients who develop AKI can be oliguric or nonoliguric, have a rapid or slow rise in creatinine levels, and may have qualitative differences in urine solute concentrations and cellular content. This lack of a uniform clinical presentation reflects the variable nature of the injury. Classifying AKI as oliguric or nonoliguric based on daily urine excretion has prognostic value. Oliguria is defined as a daily urine volume of less than 400 mL/d and has a worse prognosis, except in prerenal failure. Anuria is defined as a urine output of less than 100 mL/d and, if abrupt in onset, suggests bilateral obstruction or catastrophic injury to both kidneys. Stratification of renal failure along these lines helps in decision-making (eg, timing of dialysis) and can be an important criterion for patient response to therapy.

Pre renal AKI

Prerenal AKI represents the most common form of kidney injury and often leads to intrinsic AKI if it is not promptly corrected. Volume loss from GI, renal, cutaneous (eg, burns), and internal or external hemorrhage can result in this syndrome. Prerenal AKI can also result from decreased renal perfusion in patients with heart failure or shock (eg, sepsis, anaphylaxis).

Special classes of medications that can induce prerenal AKI in volume-depleted states are angiotensin-converting enzyme inhibitors (ACEIs) and angiotensin receptor blockers (ARBs), which are otherwise safely tolerated and beneficial in most patients with chronic kidney disease. Arteriolar vasoconstriction leading to prerenal AKI can occur in hypercalcemic states, with the use of radiocontrast agents, nonsteroidal anti-inflammatory drugs (NSAIDs), amphotericin, calcineurin inhibitors, norepinephrine, and other pressor agents.

The hepatorenal syndrome can also be considered a form of prerenal AKI, because functional renal failure develops from diffuse vasoconstriction in vessels supplying the kidney.

Intrinsic AKI

Structural injury in the kidney is the hallmark of intrinsic AKI, and the most common form is acute tubular injury (ATN), either ischemic or cytotoxic. Frank necrosis is not prominent in most human cases of ATN and tends to be patchy. Less obvious injury includes loss of brush borders, flattening of the epithelium, detachment of cells, formation of intratubular casts, and dilatation of the lumen. Although these changes are observed predominantly in proximal tubules, injury to the distal nephron can also be demonstrated. In addition, the distal nephron may become obstructed by desquamated cells and cellular debris. (See images below and Images 2-4.)




Flattening of the renal tubular cells due to tubular dilation.





Intratubular cast formation.





Intratubular obstruction due to the denuded epithelium and cellular debris. Note that the denuded tubular epithelial cells clump together because of rearrangement of intercellular adhesion molecules.



In contrast to necrosis, the principal site of apoptotic cell death is the distal nephron. During the initial phase of ischemic injury, loss of integrity of the actin cytoskeleton leads to flattening of the epithelium, with loss of the brush border, loss of focal cell contacts, and subsequent disengagement of the cell from the underlying substratum.

Many endogenous growth factors that participate in the process of regeneration have not been identified; however, administration of growth factors exogenously has been shown to ameliorate and hasten recovery from AKI. Depletion of neutrophils and blockage of neutrophil adhesion reduce renal injury following ischemia, indicating that the inflammatory response is responsible, in part, for some features of ATN, especially in postischemic injury after transplant.

Intrarenal vasoconstriction is the dominant mechanism for the reduced glomerular filtration rate (GFR) in patients with ATN. The mediators of this vasoconstriction are unknown, but tubular injury seems to be an important concomitant finding. Urine backflow and intratubular obstruction (from sloughed cells and debris) are causes of reduced net ultrafiltration. The importance of this mechanism is highlighted by the improvement in renal function that follows relief of such intratubular obstruction. In addition, when obstruction is prolonged, intrarenal vasoconstriction is prominent in part due to the tubuloglomerular feedback mechanism, which is thought to be mediated by adenosine and activated when there is proximal tubular damage and the macula densa is presented with increased chloride load.

Apart from the increase in basal renal vascular tone, the stressed renal microvasculature is more sensitive to potentially vasoconstrictive drugs and otherwise-tolerated changes in systemic blood pressure. The vasculature of the injured kidney has an impaired vasodilatory response and loses its autoregulatory behavior. This latter phenomenon has important clinical relevance because the frequent reduction in systemic pressure during intermittent hemodialysis may provoke additional damage that can delay recovery from ATN. Often, injury results in atubular glomeruli, where the glomerular function is preserved, but the lack of tubular outflow precludes its function.

A physiologic hallmark of ATN is a failure to maximally dilute or concentrate urine (isosthenuria). This defect is not responsive to pharmacologic doses of vasopressin. The injured kidney fails to generate and maintain a high medullary solute gradient, because the accumulation of solute in the medulla depends on normal distal nephron function. Failure to excrete concentrated urine even in the presence of oliguria is a helpful diagnostic clue in distinguishing prerenal from intrinsic renal disease; in prerenal azotemia, urine osmolality is typically more than 500 mOsm/kg, whereas in intrinsic renal disease, urine osmolality is less than 300 mOsm/kg.

Glomerulonephritis can be a cause of AKI and usually falls into a class referred to as rapidly progressive glomerulonephritis (RPGN). Glomerular crescents (glomerular injury) are found in RPGN on biopsy; if more than 50% of glomeruli contain crescents, this usually results in a significant decline in renal function. Although comparatively rare, acute glomerulonephritides should be part of the diagnostic consideration in cases of AKI.

Postrenal AKI

Mechanical obstruction of the urinary collecting system, including the renal pelvis, ureters, bladder, or urethra, results in obstructive uropathy or postrenal AKI.

If the site of obstruction is unilateral, then a rise in the serum creatinine level may not be apparent due to contralateral renal function. Although the serum creatinine level may remain low with unilateral obstruction, a significant loss of GFR occurs, and patients with partial obstruction may develop progressive loss of GFR if the obstruction is not relieved. Causes of obstruction include stone disease; stricture; and intraluminal, extraluminal, or intramural tumors.

Bilateral obstruction is usually a result of prostate enlargement or tumors in men and urologic or gynecologic tumors in women.

Patients who develop anuria typically have obstruction at the level of the bladder or downstream to it.


Frequency
United States
Approximately 1% of patients admitted to hospitals have AKI at the time of admission, and the estimated incidence rate of AKI is 2-5% during hospitalization. AKI develops within 30 days postoperatively in approximately 1% of general surgery cases[2 ]; it develops in up to 67% of intensive care unit patients.[3 ]Approximately 95% of consultations with nephrologists are related to AKI. Feest and colleagues calculated that the appropriate nephrologist referral rate is approximately 70 cases per million population.[4 ]

Mortality/Morbidity
The mortality rate estimates for AKI vary from 25-90%. The in-hospital mortality rate is 40-50%; in intensive care settings, the rate is 70-80%. Increments of 0.3 mg/dL in serum creatinine have important prognostic significance.

On long-term followup (1-10 years), approximately 12.5% of AKI survivors are dialysis-dependent (rates range widely, from 1%-64%, depending on the patient population) and 19-31% of them have chronic kidney disease.[3 ]

Race
No racial predilection is recognized.

Clinical
History
A detailed and accurate history is crucial to aid in diagnosing the type of AKI and in determining its subsequent treatment. A detailed history and a physical examination in combination with routine laboratory tests are useful in making a correct diagnosis (see Lab Studies).


Distinguishing AKI from chronic renal failure is important, yet making the distinction can be difficult. A history of chronic symptoms ? fatigue, weight loss, anorexia, nocturia, and pruritus ? suggests chronic renal failure.
Take note of the following findings during the physical examination:
Hypotension
Volume contraction
Congestive heart failure
Nephrotoxic drug ingestion
History of trauma or unaccustomed exertion
Blood loss or transfusions
Evidence of connective tissue disorders or autoimmune diseases
Exposure to toxic substances, such as ethyl alcohol or ethylene glycol
Exposure to mercury vapors, lead, cadmium, or other heavy metals, which can be encountered in welders and miners
People with the following comorbid conditions are at a higher risk for developing AKI:
Hypertension
Congestive cardiac failure
Diabetes
Multiple myeloma
Chronic infection
Myeloproliferative disorder
Urine output history can be useful. Oliguria generally favors AKI. Abrupt anuria suggests acute urinary obstruction, acute and severe glomerulonephritis, or embolic renal artery occlusion. A gradually diminishing urine output may indicate a urethral stricture or bladder outlet obstruction due to prostate enlargement.
Because of a decrease in functioning nephrons, even a trivial nephrotoxic insult may cause AKI to be superimposed on chronic renal insufficiency.

Physical
Obtaining a thorough physical examination is extremely important when collecting evidence about the etiology of AKI.

Skin
Petechiae, purpura, ecchymosis, and livedo reticularis provide clues to inflammatory and vascular causes of AK
Infectious diseases, thrombotic thrombocytopenic purpura (TTP), disseminated intravascular coagulation (DIC), and embolic phenomena can produce typical cutaneous changes.
Eyes
Evidence of uveitis may indicate interstitial nephritis and necrotizing vasculitis.
Ocular palsy may indicate ethylene glycol poisoning or necrotizing vasculitis.
Findings suggestive of severe hypertension, atheroembolic disease, and endocarditis may be observed on careful examination of the eyes.
Cardiovascular system
The most important part of the physical examination is the assessment of cardiovascular and volume status.
The physical examination must include pulse rate and blood pressure recordings measured in both the supine position and the standing position; close inspection of the jugular venous pulse; careful examination of the heart, lungs, skin turgor, and mucous membranes; and assessment for the presence of peripheral edema.
In hospitalized patients, accurate daily records of fluid intake and urine output and daily measurements of patient weight are important.
Blood pressure recordings can be important diagnostic tools.
Hypovolemia leads to hypotension; however, hypotension may not necessarily indicate hypovolemia.
Severe congestive cardiac failure (CHF) may also cause hypotension. Although patients with CHF may have low blood pressure, volume expansion is present and effective renal perfusion is poor, which can result in AKI.
Severe hypertension with renal failure suggests renovascular disease, glomerulonephritis, vasculitis, or atheroembolic disease.
Abdomen
Abdominal examination findings can be useful to help detect obstruction at the bladder outlet as the cause of renal failure, which may be due to cancer or an enlarged prostate.
The presence of an epigastric bruit suggests renal vascular hypertension.

Causes
The causes of AKI traditionally are divided into 3 main categories: prerenal, intrinsic, and postrenal.

Prerenal AKI
Volume depletion
Renal losses (diuretics, polyuria)
GI losses (vomiting, diarrhea)
Cutaneous losses (burns, Stevens-Johnson syndrome)
Hemorrhage
Pancreatitis
Decreased cardiac output
Heart failure
Pulmonary embolus
Acute myocardial infarction
Severe valvular disease
Abdominal compartment syndrome (tense ascites)
Systemic vasodilation
Sepsis
Anaphylaxis
Anesthetics
Drug overdose
Afferent arteriolar vasoconstriction
Hypercalcemia
Drugs (NSAIDs, amphotericin B, calcineurin inhibitors, norepinephrine, radiocontrast agents)
Hepatorenal syndrome
Efferent arteriolar vasodilation ? ACEIs or ARBs
Intrinsic AKI
Vascular (large and small vessel)
Renal artery obstruction (thrombosis, emboli, dissection, vasculitis)
Renal vein obstruction (thrombosis)
Microangiopathy (TTP, hemolytic uremic syndrome [HUS], DIC, preeclampsia)
Malignant hypertension
Scleroderma renal crisis
Transplant rejection
Atheroembolic disease
Glomerular
Anti?glomerular basement membrane (GBM) disease (Goodpasture syndrome)
Anti?neutrophil cytoplasmic antibody-associated glomerulonephritis (ANCA-associated GN) (Wegener granulomatosis, Churg-Strauss syndrome, microscopic polyangiitis)
Immune complex GN (lupus, postinfectious, cryoglobulinemia, primary membranoproliferative glomerulonephritis)
Tubular
Ischemic
Cytotoxic
Heme pigment (rhabdomyolysis, intravascular hemolysis)
Crystals (tumor lysis syndrome, seizures, ethylene glycol poisoning, megadose vitamin C, acyclovir, indinavir, methotrexate)
Drugs (aminoglycosides, lithium, amphotericin B, pentamidine, cisplatin, ifosfamide, radiocontrast agents)
Interstitial
Drugs (penicillins, cephalosporins, NSAIDs, proton-pump inhibitors, allopurinol, rifampin, indinavir, mesalamine, sulfonamides)
Infection (pyelonephritis, viral nephritides)
Systemic disease (Sj ? gren syndrome, sarcoid, lupus, lymphoma, leukemia, tubulonephritis, uveitis)
Postrenal AKI
Ureteric obstruction (stone disease, tumor, fibrosis, ligation during pelvic surgery)
Bladder neck obstruction (benign prostatic hypertrophy [BPH], cancer of the prostate [CA prostate or prostatic CA], neurogenic bladder, tricyclic antidepressants, ganglion blockers, bladder tumor, stone disease, hemorrhage/clot)
Urethral obstruction (strictures, tumor, phimosis)

Differential Diagnoses
Acute Tubular Necrosis
Azotemia
Chronic Renal Failure


Other Problems to Be Considered
Obstructive uropathy
GI bleeding
Protein overloading
Steroid use




Workup
Laboratory Studies
Several laboratory tests are useful for assessing the etiology of AKI, and the findings can aid in proper management. These tests include complete blood cell (CBC) count, serum biochemistries, urine analysis with microscopy, and urine electrolytes.

Blood urea nitrogen (BUN) and serum creatinine
Although increased levels of BUN and creatinine are the hallmarks of renal failure, the rate of rise is dependent on the degree of renal insult as well as protein intake with respect to BUN.
The ratio of BUN to creatinine is an important finding, because the ratio can exceed 20:1 in conditions in which enhanced reabsorption of urea is favored (eg, in volume contraction); this suggests prerenal AKI.
BUN may be elevated in patients with GI or mucosal bleeding, steroid treatment, or protein loading.
Assuming no renal function, the rise in BUN over 24 hours can be roughly predicted using the following formula: 24-hour protein intake in milligrams X 0.16 divided by total body water in mg/dL added to the BUN value.
Assuming no renal function, the rise in creatinine can be predicted using the following formulas:
For males: weight in kilograms X [28 ? 0.2(age)] divided by total body water in mg/dL added to the creatinine value
For females: weight in kilograms X [23.8 ? 0.17(age)] divided by total body water added to the creatinine value
As a general rule, if serum creatinine increases to more than 1.5 mg/dL/d, rhabdomyolysis must be ruled out.
CBC count, peripheral smear, and serology
The peripheral smear may show schistocytes in conditions such as HUS or TTP.
A finding of increased rouleaux formation suggests multiple myeloma, and the workup should be directed toward immunoelectrophoresis of serum and urine.
The presence of myoglobin or free hemoglobin, increased serum uric acid level, and other related findings may help further define the etiology of AKI.
Serologic tests for antinuclear antibody (ANA), ANCA, anti-GBM antibody, hepatitis, and antistreptolysin (ASO) and complement levels may help include and exclude glomerular disease. Although serologic tests can be informative, the costs can be prohibitive if these tests are not ordered judiciously.
Urinalysis
Findings of granular, muddy-brown casts are suggestive of tubular necrosis. (See image below and Image 5.) The presence of tubular cells or tubular cell casts also supports the diagnosis of ATN. Often, oxalate crystals are observed in cases of ATN.




Sloughing of cells, which is responsible for the formation of granular casts, is a feature of acute tubular necrosis.



Reddish brown or cola-colored urine suggests the presence of myoglobin or hemoglobin, especially in the setting of a positive dipstick for heme and no RBCs on the microscopic examination.
The dipstick assay may reveal significant proteinuria, which would suggest glomerular or interstitial disease.
The presence of RBCs in the urine is always pathologic. Eumorphic RBCs suggest bleeding along the collecting system. Dysmorphic RBCs or RBC casts indicate glomerular inflammation, suggesting glomerulonephritis is present.
The presence of WBCs or WBC casts suggests pyelonephritis or acute interstitial nephritis. The presence of urine eosinophils is helpful in establishing a diagnosis but is not necessary for allergic interstitial nephritis to be present.
The presence of eosinophils, as visualized with Wright stain or Hansel stain, suggests interstitial nephritis but can also be seen in urinary tract infections, glomerulonephritis, and atheroembolic disease.
The presence of uric acid crystals may represent ATN associated with uric acid nephropathy.
Calcium oxalate crystals are usually present in cases of ethylene glycol poisoning.
Urine electrolytes
Urine electrolyte findings also can serve as valuable indicators of functioning renal tubules.
The fractional excretion of sodium (FENa) is the commonly used indicator. However, the interpretation of results from patients in nonoliguric states, those with glomerulonephritis, and those receiving or ingesting diuretics can lead to an erroneous diagnosis. FENa can be a valuable test for helping to detect extreme renal avidity for sodium in conditions such as hepatorenal syndrome. The formula for calculating the FENa is as follows:
FENa = (UNa/PNa) / (UCr/PCr) X 100
Calculating the FENa is useful in AKI only in the presence of oliguria.
In patients with prerenal azotemia, the FENa is usually less than 1%. In ATN, the FENa is greater than 1%. Exceptions to this rule are ATN caused by radiocontrast nephropathy, severe burns, acute glomerulonephritis, and rhabdomyolysis.
In the presence of liver disease, FENa can be less than 1% in the presence of ATN. On the other hand, because administration of diuretics may cause the FENa to be greater than 1%, these findings cannot be used as the sole indicators in AKI.
In patients who are receiving diuretics, a fractional excretion of urea (FEUrea) can be obtained, since urea transport is not affected by diuretics. The formula for calculating the FEUrea is as follows: FEUrea = (Uurea/Purea) / (UCr/PCr) X 100
FEUrea of less than 35% is suggestive of a prerenal state.

Imaging Studies
In some cases, renal imaging is useful, especially if renal failure is secondary to obstruction. The American College of Radiology recommends ultrasonography, preferably with Doppler methods, as the most appropriate imaging method in AKI.[5 ]



Ultrasonography

Renal ultrasonography is useful for evaluating existing renal disease and obstruction of the urinary collecting system. The degree of hydronephrosis does not necessarily correlate with the degree of obstruction. Mild hydronephrosis may be observed with complete obstruction if found early.
Obtaining images of the kidneys can be technically difficult in patients who are obese or in those with abdominal distension due to ascites, gas, or retroperitoneal fluid collection.
Ultrasonographic scans or other imaging studies showing small kidneys suggest chronic renal failure.
Doppler ultrasonography
Doppler scans are useful for detecting the presence and nature of renal blood flow.
Because renal blood flow is reduced in prerenal or intrarenal AKI, test findings are of little use in the diagnosis of AKI.
Doppler scans can be quite useful in the diagnosis of thromboembolic or renovascular disease.
Increased resistive indices can be observed in patients with hepatorenal syndrome.
Nuclear scans
Radionuclide imaging with technetium-99m-mercaptoacetyltriglycine (99m Tc-MAG3),99m Tc-diethylenetriamine pentaacetic acid (99m Tc-DTPA), or iodine-131 (131 I)?hippurate can be used to assess renal blood flow and tubular functions.
Because of a marked delay in tubular excretion of radionuclide in prerenal disease and intrarenal disease, the value of these scans is limited.
Aortorenal angiography can be helpful in establishing the diagnosis of renal vascular diseases, including renal artery stenosis, renal atheroembolic disease, atherosclerosis with aortorenal occlusion, and in certain cases of necrotizing vasculitis (eg, polyarteritis nodosa).

Procedures
Renal biopsy
A renal biopsy can be useful in establishing the diagnosis of intrarenal causes of AKI and can be justified if it will change management (eg, initiation of immunosuppressive medications). A renal biopsy may also be indicated when renal function does not return for a prolonged period and a prognosis is required to develop long-term management.
In as many as 40% of cases, renal biopsy results reveal an unexpected diagnosis.
Acute cellular or humoral rejection in a transplanted kidney can be definitively diagnosed only by performing a renal biopsy.
Treatment
Medical Care
The mortality rate for patients in the intensive care unit (ICU) is higher in those who have AKI, especially when AKI is severe enough to require dialysis treatment. In addition, evidence suggests that the relative risk of death is 4.9 in patients in the ICU who have renal failure that is not severe enough to require dialysis. This reflects that the high mortality rate in patients with AKI who require dialysis may not be related to the dialysis procedure or accompanying comorbidities and that AKI alone may be an independent indicator of mortality.

Aggressive treatment should begin at the earliest indication of renal dysfunction. A large proportion of the renal mass is damaged before any biochemical evidence of renal dysfunction is appreciated because the relationship between the GFR and the serum creatinine level is exponential, not linear. The rise of serum creatinine may not be evident before 50% of the GFR is lost.
At this point, recognizing the presence of AKI and promptly initiating therapy aimed at minimizing the damage to the remaining functional renal mass are important considerations. This may also aid in reversing the renal damage that has already occurred. Reversing renal damage can be accomplished only by identifying the underlying cause and directing the appropriate therapy.
Maintenance of volume homeostasis and correction of biochemical abnormalities remain the primary goals of treatment. Furosemide can be used to correct volume overload when the patients are still responsive to it. Furosemide plays no role in converting an oliguric AKI to a nonoliguric AKI or to increase urine output when a patient is not hypervolemic. However, the response to furosemide can be taken as a good prognostic sign. At this stage, the kidneys remain vulnerable to the toxic effects of various chemicals. All nephrotoxic agents (eg, radiocontrast agents, antibiotics with nephrotoxic potential, heavy metal preparations, cancer chemotherapeutic agents, NSAIDs) are either avoided or used with extreme caution. Similarly, all medications cleared by renal excretion should be avoided or their doses should be adjusted appropriately.
Correcting acidosis with bicarbonate administration is important. It cannot be overstated that the current treatment of AKI is mainly supportive in nature and no therapeutic modalities to date have shown efficacy in treating the condition. Therapeutic agents, such as dopamine, fenoldopam, and mannitol, are not indicated in the management of AKI and may be harmful for the patient.
Hyperkalemia, which can be life-threatening, should be treated by decreasing the intake of potassium, delaying the absorption of potassium, exchanging potassium across the gut lumen using potassium-binding resins, controlling intracellular shifts, and instituting dialysis, as outlined in the eMedicine article Hyperkalemia.
Correcting hematologic abnormalities (eg, anemia, platelet dysfunction) warrants appropriate measures, including transfusions and administration of desmopressin or estrogens.

Diet
Dietary modulation is an important facet of the treatment of AKI. Diet and fluid restriction become crucial in the management of oliguric renal failure, wherein the kidneys do not adequately excrete either toxins or fluids.
Because potassium and phosphorus are not excreted optimally in patients with AKI, blood levels of these electrolytes tend to be high. Frequent measurements are mandatory to achieve acceptable blood levels by modification of the diet or by intravenous supplementation.
In the polyuric phase of AKI, potassium and phosphorus may be depleted and patients require dietary supplementation and intravenous fluids.
Calculation of the nitrogen balance can be challenging, especially in the presence of volume contraction, hypercatabolic states, gastrointestinal bleeding, and diarrheal disease.
Medication

Pharmacologic treatment of AKI has been attempted on an empiric basis, with varying success rates. Several promising experimental therapies in animal models are awaiting human trials. Experimental therapies include growth factors, vasoactive peptides, adhesion molecules, endothelin inhibitors, and bioartificial kidneys. Aminophylline has also been used experimentally for prophylaxis against renal failure.

A prophylactic strategy shown to decrease the incidence of contrast nephropathy is the IV administration of fluids. Although controversy exists regarding the ideal fluid, normal saline and isotonic NaHCO 3 have proven to be effective. Normal saline solution of 1 mL/kg/h administered 12 hours before the procedure and then 12 hours after the procedure is recommended. In patients who are at high risk for volume overload, isotonic NaHCO 3 solution should be administered before and after the procedure. It can be prepared by mixing 3 ampules of NaHCO 3 in a liter of D5W and can be given at a rate of 3 mL/kg/h for 1 hour prior to the procedure; 1 mL/kg/h during the procedure; and for 6 hours afterward.

Another prophylactic agent, used with varying success, is N -acetylcysteine at a dosage of 1200 mg PO q12h. This is administered to high-risk patients the day before a contrast study is performed and is continued the day of the procedure. Diuretics, NSAIDs, and possibly ACEIs should be withheld near the time of the procedure.

Any protective effect of N -acetylcysteine would appear to be limited to patients receiving radiocontrast. A meta-analysis of patients undergoing major surgery found no evidence that N -acetylcysteine used perioperatively can alter mortality or renal outcomes when radiocontrast is not used.[6 ]Similarly, a review of randomized, controlled trials of other measures used to protect renal function perioperatively (eg, the administration of dopamine, diuretics, calcium-channel blockers, ACEIs, or hydration fluids) found no reliable evidence that these interventions are effective.[7 ]


Diuretics
Although diuretics seem to have no effect on the outcome of established AKI, they appear useful in fluid homeostasis and are used extensively. The use of isotonic sodium chloride solution in conjunction with diuretics is debatable. The only therapeutic or preventive intervention that has an established beneficial effect in the management of AKI is administration of isotonic sodium chloride solution to keep the patient euvolemic or even hypervolemic.



Furosemide (Lasix)
Increases excretion of water by interfering with chloride-binding cotransport system, which, in turn, inhibits sodium and chloride reabsorption in the thick ascending loop of Henle and the distal renal tubule. Potent and rapid-acting agent with peak action at 60 min and lasting 6-8 h.
In renal failure, higher doses must be used for greater diuretic effects. Doses as high as 600 mg/d may be needed under monitored conditions.
Frequently, IV doses are needed in AKI to maintain urine output. IV infusions are often helpful in ICU settings, in which larger doses are necessary. This method promotes a sustained natriuresis with reduced ototoxicity compared to conventional intermittent bolus dosing.

Dosing
Adult
20-40 mg PO qd initially

Pediatric
Not established

Interactions
Metformin decreases concentrations; interferes with hypoglycemic effect of antidiabetic agents and antagonizes muscle-relaxing effect of tubocurarine; auditory toxicity appears to be increased with coadministration of aminoglycosides or ethacrynic acid; hearing loss of varying degrees may occur; anticoagulant activity of warfarin may be enhanced when taken concurrently; increased plasma lithium levels and toxicity are possible when taken concurrently

Contraindications
Documented hypersensitivity; hepatic coma, anuria, and states of severe electrolyte depletion

Precautions
Pregnancy
C - Fetal risk revealed in studies in animals but not established or not studied in humans; may use if benefits outweigh risk to fetus

Precautions
Perform frequent serum electrolyte, carbon dioxide, glucose, creatinine, uric acid, calcium, and BUN determinations during first few months of therapy and periodically thereafter; avoid using other nephrotoxic agents if possible

Vasodilators
Dopamine in small doses (eg, 1-5 mcg/kg/min) causes selective dilatation of the renal vasculature, enhancing renal perfusion. Dopamine also reduces sodium absorption, thereby decreasing the energy requirement of the damaged tubules. This enhances urine flow, which, in turn, helps prevent tubular cast obstruction. Most clinical studies have failed to establish this beneficial role of renal-dose dopamine infusion.



Dopamine (Intropin)
Stimulates both adrenergic and dopaminergic receptors. Hemodynamic effect is dose-dependent. Lower doses predominantly stimulate dopaminergic receptors, which, in turn, produce renal and mesenteric vasodilation. Cardiac stimulation and renal vasodilation produced by higher doses.

Dosing
Adult
1-5 mcg/kg/min IV

Pediatric
Administer as in adults

Interactions
Phenytoin, alpha-adrenergic and beta-adrenergic blockers, general anesthesia, and MAOIs increase and prolong effects

Contraindications
Documented hypersensitivity; pheochromocytoma or ventricular fibrillation

Precautions
Pregnancy
C - Fetal risk revealed in studies in animals but not established or not studied in humans; may use if benefits outweigh risk to fetus

Precautions
Caution in hypertension, CVA, coronary heart disease, and dysrhythmias; closely monitor urine flow, cardiac output, pulmonary wedge pressure, and blood pressure during infusion; before infusion, correct hypovolemia with either whole blood or plasma, as indicated; monitoring central venous pressure or left ventricular filling pressure may be helpful in detecting and treating hypovolemia

Calcium channel blockers
Effective in animal models but efficacy not proven in humans. Effects are believed to be mediated through vasodilation, and calcium channel blockers increasingly are used to enhance the function of transplanted kidneys.



Nifedipine (Adalat, Procardia)
Relaxes smooth muscle and produces vasodilation, which, in turn, improves blood flow and oxygen delivery.

Dosing
Adult
10-30 mg IR cap PO tid; not to exceed 120-180 mg/d
30-60 mg SR tab PO qd; not to exceed 90-120 mg/d

Pediatric
0.25-0.5 mg/kg/dose PO tid/qid prn

Interactions
Caution with coadministration of any agent that can lower BP, including beta-blockers and opioids; H2 blockers (eg, cimetidine) may increase toxicity

Contraindications
Documented hypersensitivity

Precautions
Pregnancy
C - Fetal risk revealed in studies in animals but not established or not studied in humans; may use if benefits outweigh risk to fetus

Precautions
May cause lower extremity edema; allergic hepatitis has occurred rarely

N-acetylcysteine
Used for prevention of contrast toxicity in susceptible individuals such as those with diabetes mellitus.



N-acetylcysteine (Mucosil, Mucomyst)
May provide substrate for conjugation with toxic metabolites.

Dosing
Adult
For prevention of nephrotoxicity: 600 mg PO bid on day preceding and day of procedure

Pediatric
Not established

Interactions
None reported

Contraindications
Documented hypersensitivity

Precautions
Pregnancy
B - Fetal risk not confirmed in studies in humans but has been shown in some studies in animals

Precautions
GI distress may occur

Follow-up
Further Outpatient Care
Always keep in mind that renal recovery in most cases is not complete and the kidneys remain vulnerable to nephrotoxic effects of all therapeutic agents. Therefore, agents with nephrotoxic potential are best avoided.
Prognosis
The prognosis of patients with AKI is directly related to the cause of renal failure and, to a great extent, to the duration of renal failure prior to therapeutic intervention. If AKI is defined by a sudden increment of serum creatinine of 0.5-1 mg/dL and is associated with a mild to moderate rise in creatinine, the prognosis tends to be worse. However, even if renal failure is mild, the mortality rate is 30-60%. If these patients need dialytic therapy, the mortality rate is 50-90%.
The mortality rate is 31% in patients with normal urine sediment test results and is 74% in patients with abnormal urine sediment test results.
The survival rate is nearly 0% among patients with AKI who have an Acute Physiology and Chronic Health Evaluation II (APACHE II) score higher than 40; the survival rate is 40% in patients with APACHE II scores of 10-19.
Other prognostic factors include the following:
Older age
Multiorgan failure (ie, the more organs that fail, the worse the prognosis)
Oliguria
Hypotension
Vasopressor support
Number of transfusions
Noncavitary surgery
Prerenal azotemia due to volume contraction is treated with volume expansion; if left untreated for a prolonged duration, tubular necrosis may result and may not be reversible.
Postrenal AKI, if left untreated for a long time, may result in irreversible renal damage. Procedures such as catheter placement, lithotripsy, prostatectomy, stent placement, and percutaneous nephrostomy can help to prevent permanent renal damage.
Timely identification of pyelonephritis, proper treatment, and further prevention using prophylactic antibiotics may improve the prognosis, especially in females.
Early diagnosis of crescentic glomerulonephritis via renal biopsy and other appropriate tests may enhance early renal recovery because appropriate therapy can be initiated promptly and aggressively.
The number of crescents, the type of crescents (ie, cellular vs fibrous), and the serum creatinine level at the time of presentation may dictate prognosis for renal recovery in this subgroup of patients.
Patient Education
Educating patients about the nephrotoxic potential of common therapeutic agents is always helpful. A good example is NSAIDs; most patients are unaware of their nephrotoxicity, and their universal availability makes them a constant concern.
For excellent patient education resources, see eMedicine's Diabetes Center. Also, visit eMedicine's patient education article Acute Kidney Failure.
Miscellaneous
Medicolegal Pitfalls
Although AKI potentially is a reversible condition, it can occur in patients with chronic renal failure. Every effort should be made to identify reversibility, even if improvement in renal function is marginal. The best way to identify reversibility is by tracking the rate of deterioration of renal function. If the rate of worsening renal function accelerates, the cause should be sought and treated.
Renal recovery is usually observed within the first 2 weeks, and many nephrologists tend to diagnose patients with end-stage (ie, irreversible) renal failure 6-8 weeks after onset of AKI. It is always better to check these patients periodically because some patients may regain renal function much later.
Special Concerns
Great controversy exists regarding the timing of dialysis. Dialysis, especially hemodialysis, may delay the recovery of patients with AKI. Most authorities prefer using biocompatible membrane dialyzers for hemodialysis. There seems to be no difference in outcome between the use of intermittent hemodialysis and continuous renal replacement therapy (CRRT), but this is currently under investigation. However, CCRT may have a role in patients who are hemodynamically unstable and who have had prolonged renal failure after a stroke or liver failure. Such patients may not tolerate the rapid shift of fluid and electrolytes caused during conventional hemodialysis. Although not frequently used, peritoneal dialysis can also technically be used in acute cases and probably is tolerated better hemodynamically than conventional hemodialysis.
Indications for dialysis in patients with AKI are as follows:
Volume expansion that cannot be managed with diuretics
Hyperkalemia refractory to medical therapy
Correction of severe acid-base disturbances that are refractory to medical therapy
Severe azotemia (BUN >80-100)
Uremia