Renal failure is defined as renal function inadequate to clear the waste products of metabolism despite the absence of or correction of haemodynamic or mechanical causes. Renal failure is suggested by:
• Uraemic symptoms (drowsiness, nausea, hiccough, twitching)
• Raised plasma creatinine (>200pmol/l)
• Metabolic acidosis
Persistent oliguria may be a feature of acute renal failure but non-oliguric renal failure is not uncommon; 2-3l of poor quality urine per day may occur despite an inadequate glomerular filtration rate. The prognosis is better if urine output is maintained. Clinical features may suggest the cause of renal failure and dictate further investigation. Acute tubular necrosis is a common aetiology in the critically ill (e.g. following hypovolaemia, extensive burns) but other causes must be borne in mind. In sepsis, the kidney often has a normal histological appearance. Anaemia implies chronic renal failure.
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