Acute renal failure

Acute renal failure (ARF) is a rapid loss of renal functiondue to damage to the kidneys, resulting in retention of nitrogenous (urea and creatinine) and non-nitrogenous waste products that are normally excreted by the kidney. Depending on the severity and duration of the renal dysfunction, this accumulation is accompanied by metabolic disturbances, such as metabolic acidosis(acidification of the blood) and hyperkalaemia(elevated potassium levels), changes in body fluid balance, and effects on many other organ systems. It can be characterised by oliguriaor anuria(decrease or cessation of urine production), although nonoliguric ARF may occur. It is a serious disease and treated as a medical emergency.

Causes

Renal failure, whether chronicor acute, is usually categorised according to pre-renal, renal and post-renal causes:

• Pre-renal (causes in the blood supply):
  • hypotension(decreased blood supply), usually from shockor dehydrationand fluid loss, heart attack
  • vascular problems, such as atheroembolic diseaseand renal vein thrombosis(which in part may be secondary to loss of coagulation factorsdue to renal dysfunction)
• Renal (damage to the kidney itself):
  • infection
  • toxinsor medication(e.g. some NSAIDs, aminoglycosideantibiotics, amphotericin B, iodinated contrast, lithium)
  • rhabdomyolysis(breakdown of muscle tissue) - the resultant release of myoglobinin the blood affects the kidney; it can be caused by injury(especially crush injury and extensive blunt trauma), statins, MDMA(ecstasy) and some other drugs
  • hemolysis(breakdown of red blood cells) - the hemoglobindamages the tubules; it may be caused by various conditions such as sickle-cell disease, and lupus erythematosus
  • multiple myeloma, either due to hypercalcemiaor "cast nephropathy" (multiple myeloma can also cause chronic renal failureby a different mechanism)
  • Acute glomerulonephritiswhich may due to a variety of causes, such as anti glomerular basement membrane disease/Goodpasture's syndrome, Wegener's granulomatosisor acute lupus nephritis with systemic lupus erythematosus
• Post-renal (causes in the urinary tract):
  • urinary retention(as a side-effect of medicationor due to benign prostatic hypertrophy, kidney stones)
  • pyelonephritis
  • obstruction due to abdominal malignancy (e.g. ovarian cancer, colorectal cancer)

Diagnosis

Renal failure is generally diagnosed either when creatinineor blood urea nitrogentests are markedly elevated in an ill patient, especially when oliguria is present. Previous measurements of renal function may offer comparison, which is especially important if a patient is known to have chronic renal failureas well. If the cause is not apparent, a large amount of blood testsand examination of a urinespecimen is typically performed to elucidate the cause of acute renal failure, medical ultrasonographyof the renal tract is essential to rule out obstruction of the urinary tract.

Consensus criteria^{[{{fullurl:Template:FULLPAGENAME}}#endnote_Bellomo][{{fullurl:Template:FULLPAGENAME}}#endnote_Lameire]} for the diagnosis of ARF are:

• Risk: serum creatinine increased 1.5 times OR urine production of <0.5 ml/kg body weight for 6 hours
• Injury: creatinine 2.0 times OR urine production <0.5 ml/kg for 12 h
• Failure: creatinine 3.0 times OR creatinine >355 μmol/l (with a rise of >44) or urine output below 0.3 ml/kg for 24 h
• Loss: persistent ARF or more than four weeks complete loss of kidney function

Kidney biopsymay be performed in the setting of acute renal failure,to provide a definitive diagnosis and sometimes an idea of the prognosis, unless the cause is clear and appropriate screening investigations are reassuringly negative.

Treatment

Acute renal failure is usually reversible if treated promptly and appropriately. The main interventions are monitoring fluid intake and output as closely as possible; insertion of a urinary catheteris useful for monitoring urine output as well as relieving possible bladder outlet obstruction, such as with an enlarged prostate. In both hypovolemia and intrinsic causes (acute tubular necrosis) administering intravenous fluidsis typically the first step to improve renal function. If a central venous catheteris used, a central venous pressure of 15 cmH₂O(1.5 kPa) is often used as a target for increasing circulatory volume^{[{{fullurl:Template:FULLPAGENAME}}#endnote_Galley]}. If the cause is obstruction of the urinary tract, surgical relief of the obstruction (with a nephrostomyor suprapubic catheter) may be necessary. Metabolic acidosisand hyperkalemia, two prime complications of renal failure, may require medical treatment with sodium bicarbonateadministration and antihyperkalemic measures, respectively.

Dopamineor other inotropesmay be given to improve cardiac outputand renal perfusion, and diuretics(in particular furosemide) may be administered. If a Swan-Ganz catheteris used, a pulmonary artery occlusion pressure (PAOP) of 18 mmHg(2.4 kPa) is the target for inotropic support (Galley 2000).

Lack of improvement with fluid resuscitation, therapy-resistant hyperkalemia, metabolic acidosis or fluid overload may necessitate artificial support in the form of dialysisor hemofiltration. Depending on the cause, a proportion of patients will never regain full renal function and require lifelong dialysisor a kidney transplant.

History

Acute renal failure due to acute tubular necrosis(ATN) was recognised in the 1940sin the United Kingdom, where crush victims during the Battle of Britaindeveloped patchy necrosis of renal tubules, leading to a sudden decrease in renal function ^{[{{fullurl:Template:FULLPAGENAME}}#endnote_Bywaters]}. During the Korean and Vietnam wars, the incidence of ARF decreased due to better acute management and intravenous infusion of fluids^{[{{fullurl:Template:FULLPAGENAME}}#endnote_Schrier]}.

See also

• hepatorenal syndrome

References

1. ^ Bellomo R, Ronco C, Kellum JA, Mehta RL, Palevsky P; Acute Dialysis Quality Initiative workgroup. Acute renal failure - definition, outcome measures, animal models, fluid therapy and information technology needs: the Second International Consensus Conference of the Acute Dialysis Quality Initiative (ADQI) Group. Crit Care. 2004 Aug;8(4):R204-12. Epub 2004 May 24. PMID 15312219Full TextCriteria for ARF (Figure)
2. ^ Lameire N, Van Biesen W, Vanholder R. Acute renal failure. Lancet2005;365:417-30. PMID 15680458
3. ^  Galley HF. Can acute renal failure be prevented? J R Coll Surg Edinb 2000;45(1):44-50. PMID 10815380Fulltext
4. ^  Bywaters EG, Beall D. Crush injuries with impairment of renal function. Br Med J1941;1:427-32. Reprinted in J Am Soc Nephrol 1998;9:322-32. PMID 9527411.
5. ^  Schrier RW, Wang W, Polle B, Mitra A. Acute renal failure: definitions, diagnosis, pathogenesis, and therapy. J Clin Invest 2004;114:5-14. PMID 15232604Full textde:Akutes Nierenversagen

pt:Insuficiência Renal Aguda

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It uses material from the http://en.wikipedia.org/wiki/Acute+renal+failure Wikipedia article Acute renal failure.