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Chapter 6: Disorders of the kidney 235

Table 6.3 Causes of acute renal failure Investigations
The aims are to try to distinguish acute and chronic renal
Cause Examples
failure, between prerenal, renal or postrenal causes, as
Prerenal well as the underlying cause.
Hypovolaemia Bleeding, dehydration,
Urgent urinalysis, followed by microscopy (to look for
and/or diuretics
hypotension Sepsis, cardiac failure, drugs cells and casts) and culture.
Renal ischaemia or Renal artery stenosis (acutely Urine sodium concentration. In prerenal failure, or in
congestion exacerbated by an renal failure without tubular dysfunction the kidney
ACE-inhibitor), aortic will reabsorb sodium so that urinary sodium is less
dissection, renal vein
thrombosis than 20 mmol/L (exceptions to this are in the presence
Severe liver disease Hepatorenal syndrome* of diuretics, in pre-existing chronic renal failure). If
Renal there is tubular damage, then the ability of the kidney
Acute tubular Any cause of pre-renal failure, to concentrate sodium falls, so that urinary sodium
necrosis (ATN) drugs and toxins
Acute glomeru- Primary and secondary causes rises to >40 mmol/L.
lonephritis of glomerular disease Bloods
Acute interstitial Pyelonephritis, drugs 1 Anaemia (normochromic, normocytic if underly-
nephritis ing disease or in chronic renal failure).
Cast nephropathy Myeloma 2 Raised urea, creatinine, K ,urate.
+
Diseases of Haemolytic uraemic 2+
glomerular syndrome, vasculitis, 3 Reduced Ca with increased PO 4 .
+
capillaries or systemic sclerosis, 4 Na may be high, normal or low.
small/medium accelerated phase 5 Arterial/venous blood gas shows a metabolic acido-
sized blood hypertension, sis usually with increased anion gap.
vessels pre-eclampsia 6 LFTs.
Postrenal 7 Creatine kinase (CK) – raised in myocardial infarc-
Obstruction of the Stones (bilateral), pelvic
bladder outflow malignancy, bladder tion but also very high in rhabdomyolysis (muscle
or bilateral upper outflow obstruction, breakdown).
tracts retroperitoneal disease ECG, chest X-ray.
(lymphoma, aortic Renal imaging to exclude obstruction–arenal ultra-
dissection, retroperitoneal sound should be obtained as soon as possible to look
fibrosis)
for hydronephrosis (dilated renal pelvis, calyces and
*Mechanism unclear, resolves with hepatic recovery. ureters) and for renal size.
Consider further tests for causes of ARF if diagnosis

still unclear. These include autoantibody profile, com-
It is important to assess the volume status by assess- plement levels, blood and urine tests for myeloma and
ing blood pressure, jugular venous pressure, skin turgor, possibly a renal biopsy.
ankle or sacral oedema and pulmonary oedema. Hyper-
tension may be a feature. Management
Acute renal failure is an emergency, with possible life-
threatening complications.
Complications Reversiblecausesshouldbetreatedassoonaspossible;
Hyperkalaemia may cause cardiac arrhythmias and sud- withdraw any potentially nephrotoxic drugs, treat sepsis,
den death. Fluid overload may cause cardiac failure, malignant hypertension, and relieve any obstruction.
pulmonary oedema. Gastric erosions and GI bleeding
are quite common. Uraemic pericarditis can rarely lead Fluid management
to tamponade. During recovery of ATN, there may be If volume depletion is causing renal failure then ap-
polyuria in which it is often difficult to maintain suffi- propriate fluid replacement (usually colloid, crystal-
cient water and electrolyte input. loidorblood)shouldbegiven.Fluidchallengesmaybe