Acute Renal Failure (ARF)

28/04/2013 by admin | Renal
  1. Characterised by rapid decline in GFR over daysweeks with accumulation of nitrogenous waste
  2. Often noticed by rapidly rising serum creatinine and urea, accompanied by reduced urine output
  3. p/c: fluid overload, nausea, malaise, encephalopathy

 

Causes:

  1. Pre-renal:
    1. o Reduced/inadequate perfusion and inability of post-glomerular arteriole to constrict
    2. o If these two mechanisms fail = GFR falls = kidney fails
    3. o Causes: hypovolaemia (haemorrhage/severe D&V), cardiogenic shock (pump failure), sepsis, drugs (ACEi/NSAIDs), severe liver disease leading to renal failure (=’hepatorenal syndrome), burns.
    4. o Histological pattern in response to this type of injury = acute tubular necrosis (ATN) – usually recovers after several weeks. Concentrating ability of kidney lost and urinary sodium >409mmol/L
    5. o In prolonged hypotensive insults = acute cortical necrosis (less likely to recover).
  1. Renal:
    1. o Many causes = glomerulonephritis, vasculitis, nephrotoxic drugs (gentamicin, NSAIDs), rhabdomyolysis, interstitial nephritis, haemolytic/uraemic syndromes, multiple myeloma…
  2. Post-renal:
    1. o Urinary tract obstruction leading to backed up waterworks and renal failure
    2. o Common causes: BPH, carcinoma of prostate, ureteric stones, tumours of renal pelvis/ureters/bladder/cervix. External compression of ureters by tumour, retroperitoneal fibrosis. Advanced renal failure will only occur in both kidneys are obstructed.

 

Diagnostic approach:

  1. Rapid diagnosis is key as some causes are reversible.
  2. Examine bladder, prostate, look for hypovolaemia (=decreased skin turgor, tachycardia, hypotension, postural hypotension [loss of >20mmHg on standing], low CVP, fluid challenge and observe urine output).
  3. Renal USS to examine obstructions/hydronephrosis/size (big = waterlogged/malignancy/cysts. Small = chronic renal failure)/symmetry
  4. Blood tests and urinanalysis – for casts, RBCs, protein
  5. Biopsy

 

Mx:

  1. Ensure adequate oxygenation and circulation
  2. Avoid fluid overload as this will cause pulmonary oedema. If dry – fluid replete with IV fluids. If overloaded – haemodialysis/haemofiltration/peritoneal dialysis.
  3. Also be aware in ARF, risk of hyperkalaemia (K >6mmol/L) =dysrhythmias, with peaked T waves, widened QRS, absent P waves, and sine wave appearance.
  4. Tx: IV calcium, insulin, glucose, calcium resonium, dialysis
  5. Other complications: metabolic acidosis, encephalopathy, pericarditis
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