Oliguria

The pathological processes involved are either pre-renal, renal or post-renal. Prerenal problems account for approximately 70% of outpatient cases of ARF and up to 60% of hospital-based cases. ¹ Oliguria is rarely found in chronic renal failure.

• Pre-renal causes include:
  • Dehydration
  • Vascular collapse
  • Low cardiac output
• Renal problems are associated with structural renal damage e.g. acute tubular necrosis, primary glomerular diseases, or vascular lesions.
• Postrenal failure is secondary to a mechanical or functional obstruction to the flow of urine. The commonest cause is a blocked catheter.² This usually responds to release of the obstruction.

• Excessive fluid loss e.g. diarrhoea, vomiting.
• Drug use e.g. gentamicin, non-steroidal anti-inflammatories.
• Children may give a history of gross haematuria and oedema suggesting glomerular disease. Previous streptococcal infection may suggest a postinfectious glomerulonephritis. A history of bloody diarrhoea may precede the haemolytic uraemic syndrome.
• Symptoms of urinary tract obstruction e.g. complete failure to pass urine. This is ANURIA; it is a medical emergency and should be investigated with an ultrasound scan, arranged urgently.

Findings will vary according to the cause. The patient may be very unwell; extremely breathless, pale, clammy and shut down peripherally with an unrecordable blood pressure. ²

• There may be signs due to ARF e.g. oedema, anaemia.
• Signs of congestive heart failure e.g. gallop rhythm and hepatomegaly.
• Hypertension
• Signs of the underlying disease e.g. a butterfly rash on the face and joint swelling suggest systemic lupus erythematosus.

• MSU dipstick:
  • In prerenal failure few hyaline and fine granular casts are observed. There is little protein, haem or red cells.
  • In intrinsic renal failure, haematuria and proteinuria are prominent. Broad brown granular casts are found in ischaemic or toxic acute tubular necrosis. Red cell casts are usually observed in acute glomerulonephritis. The urine in acute interstitial nephritis has white cells.
• Urinary electrolytes
• Serum electrolytes
• Serum creatinine; in prerenal failure the ratio of urinary to plasma creatinine is high- > 40. The urinary sodium concentration is low - < 20 mEq/L. In intrinsic renal failure the findings are opposite.
• Full blood count - anaemia results from dilution and decreased erythropoiesis.
• Arterial blood gases - for acid-base status and pA O₂.
• Renal ultrasound with doppler.
• Initially kidney biopsy is not necessary. If prerenal and postrenal causes have been ruled out and an intrinsic renal disease is suspected, renal biopsy may be valuable in establishing diagnosis.

• Restoration of intravascular volume.
• Treatment of any reversible causes.
• Strict fluid balance and correction of electrolyte abnormality or metabolic acidosis.
• Input and output records, daily weights, physical examination, and serum sodium are used to determine ongoing therapy.
• Emergency treatment of hyperkalaemia is indicated when serum potassium exceeds 6.5 mEq/L .
• Potassium administration is contraindicated until urine flow is established.
• Dialysis may be required until the kidneys recover. ³ The general goal of dialysis is to remove endogenous and exogenous toxins and to maintain the fluid, electrolyte, and acid-base balance. There are no absolute indications for acute dialysis. The decision depends on the onset, duration, and severity of the abnormality to be corrected.

Surgical

Patients with oliguria secondary to obstruction, frequently require urological surgery.

Renal failure that results from nephrotoxic injury, interstitial nephritis, and neonatal asphyxia is frequently of the nonoliguric type. It is related to a less severe renal injury, and has a better prognosis.
Mortality rates in oliguric ARF vary according to the underlying cause and associated medical condition. It may be 5% for patients with community-acquired ARF, but as high as 80% in multi-organ failure patients in intensive care.¹The most common causes of death are sepsis, heart and lung failure and withdrawal of life support.

• Cardiovascular complications because of fluid and sodium retention e.g. hypertension, congestive heart failure, and pulmonary oedema.
• Gastrointestinal e.g. anorexia, nausea, vomiting and ileus.
• Haematological e.g. anaemia and platelet dysfunction.
• Hyperkalaemia produces ECG abnormalities and arrhythmias.
• Infections; there may be impaired immunity secondary to uraemia.
• Neurological e.g. confusion, sleepiness and seizures