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Acute Kidney Injury

Acute kidney injury (AKI) is defined by a recent elevation of plasma creatinine. 30% of patients are not oliguric and some may be polyuric. The following are important aspects of the management of acute kidney injury.

• Early diagnosis to identify reversible causes and rapidly progressive disease.
• Controlling hyperkalaemia.
• Recognition and correction of dehydration.
• Recognition and relief of urinary tract obstruction.

Acute kidney injury is common in hospital. The commonest causes are effective circulating volume depletion and nephrotoxins (drugs). It is preventable by avoiding these factors especially prior to surgery and radiological contrast procedures. Ask for advice!

Causes

• Pre-renal:
  • Hypovolaemia/ hypotension related to volume depletion, pump failure or vasodilatation.
• Renal:
  • Nephrotoxins including drugs and chemicals (including radiocontrast agents).
  • Acute interstitial nephritis.
  • Acute glomerulonephritis.
  • Systemic vasculitides.
  • Haemolytic - uraemic syndrome.
  • Acute-on-chronic renal failure, e.g., in patients with polycystic disease, glomerulonephritis, diabetic nephropathy.
• Post-renal obstruction:
  • Tubular - urate or Bence Jones protein.
  • Ureteric - single kidney with calculus, bilateral uric acid sludging, retroperitoneal involvement by tumour or fibrosis. Pelvic involvement by carcinoma of bladder or cervix.
  • Prostatic hypertrophy or cancer.

Investigations

Evaluation of the state of hydration is crucial in the management of patients with AKI. Initially assess hydration by means of weight change, blood pressure (lying and standing), and jugular venous pressure or possibly central venous pressure.

• Abdominal and rectal examinations to detect a distended bladder, abdominal masses, prostatic enlargement or pelvic masses.
• Urine for microscopy, red cells including their morphology, white cells and casts. Urine culture. Urinary Na, K and creatinine concentrations and osmolality may sometimes be helpful. Nursing staff should test urine for blood, protein and glucose using a urine test strip.
• CBC + diff, Na, K, urea, creatinine, bicarbonate, Cl, and coagulation profile. The biochemical tests should be done at least daily. Plasma potassium may need checking more often. Assess pH if HCO₃ <18 mmol/L.
• ECG to assess for changes of hyperkalaemia.
• Urinary tract ultrasonography to exclude obstruction and to assess kidney size.
• If you suspect Goodpasture's Syndrome or a systemic vasculitis such as Wegener's granulomatosis - rapid serological tests for anti-GBM, antiproteinase 3 and anti-myeloperoxidase antibodies are available from Immunology. These tests should not usually be ordered out of normal working hours and the clinical problem should be discussed with a Physician (call Lab if wanted urgently).
• Urgent renal biopsy may be indicated, particularly when the urine sediment is active, i.e., red cells, casts, suggesting glomerulonephritis.

Management

• Stop any potentially nephrotoxic drugs.
• Ensure optimal hydration with appropriate fluid - blood or sodium chloride 0.9%. When the patient has been rehydrated give 600 mL plus urine output and other losses per 24 hours, either as oral fluid or 5% glucose. Replace sodium losses as sodium chloride 0.9% within this volume.
• Do not give diuretics unless the patient is volume overloaded.
• Ureteric obstruction - consult Urology team urgently.
• Bladder outlet obstruction - catheterize. Refer to Urology urgently if unable to do this - beware high sodium diuresis.
• Hyperkalaemia. This may be immediately life-threatening and should be treated according to its severity.
  • Haemolysis or delay in sample process may cause spurious hyperkalaemia. Consider a repeat sample to confirm.
  • The response to hyperkalaemia should reflect the clinical situation, and the following is a guide only. Monitor any therapy given with repeat potassium measurements.

Treatment of Hyperkalaemia

Note: Treatment of hyperkalaemia with insulin and glucose or with bicarbonate produces only temporary reduction in potassium. Salbutamol (usually given as continuous nebulizer) has a similar effect but may cause marked tachycardia and/or tremor. Routine use is not recommended.

Note: Potassium elimination occurs via kidneys, or bowel. Bowel elimination may be increased by use of sodium resonium but there are significant potential side effects. Routine use is not recommended - consult Nephrology to discuss.

• Indications for urgent dialysis - discuss with Nephrologist:
  • K >7.5 mmol/L unresponsive to above therapy - discuss.
  • Pericarditis.
  • Cardiac failure or fluid overload not responding to diuretics.
  • pH <7.1 mmol/L causing clinical consequences and unresponsive to appropriate therapy.

Note: Care should be taken with IV line insertion - veins may be required for subsequent AV fistula formation. Where possible try to use the dominant arm and avoid forearm veins. Avoid radial and brachial artery for blood gas sampling from the non-dominant arm.

Urine Chemistry in Oliguria

A high urinary sodium >20 mmol/L, in the absence of diuretic therapy, may indicate established acute tubular necrosis and predict a poor response to appropriate pressure and volume resuscitation. Similarly a urine to plasma osmolality of <1.1 may predict poor response.

Topic Code: 2735