Outline the way in which you would evaluate and treat oliguria which has developed in a 36-year-old patient who has been admitted to your Intensive Care Unit with severe community acquired pneumonia.
Oliguria in the critically ill may well be an appropriate physiological response to relative volume depletion and circulating stress hormones (including ADH). In that scenario, there would be no evidence of renal failure per se (eg. increase in serum creatinine, decreased creatinine clearance), appropriate urinary concentration would occur (elevated urinary specific gravity and osmolality andlow urinary sodium <20 mmol/L), and an increase in urine output would be expected with fluid loading and/or diuretic administration. If instead signs/investigations suggest renal failure is developing, this would be traditionally divided into pre-renal, renal and post-renal causes. History (e.g. deliberate fluid restriction, associated medical conditions, past history of abdominal surgery, muscle damage, administration of nephrotoxic drugs [e.g. NSAIDs] etc.) and examination (confirmation of diagnosis [e.g. palpation, catheterisation, bladder scan], dehydrated, abdominal distension with increased intra-abdominal pressure, blocked/misplaced urinary catheter, etc.) will obviously help in the diagnosis. Urinalysis is also helpful (e.g. granular or epithelial cell casts with acute tubular necrosis, active sediment with glomerulonephritis, heavy proteinuria with nephritic syndrome. Further monitoring may be required if the haemodynamic status is considered inadequate, and specific investigations to assess renal blood flow or exclude obstruction may be clinically indicated.
Specific treatment will depend on the cause (e.g. optimise pre-renal state with hydration and/or haemodynamic supports, adequate treatment of infection, relieve obstruction, remove nephrotoxins), but in general there are no specific therapies that have been demonstrated to improve long-term outcome. Treatment options that could be considered include diuretics to enhance urine output, alkalinisation of urine for rhabdomyolysis, and CRRT rather than intermittent haemodialysis if indications for dialysis have been met.
An excellent article on evaluation of oliguria in the ICU is presented by RN Sladen.
A systematic aproach to oliguria is summarised elsewhere.
Briefly, an approach to this specific scenario would resemble the following:
1) Confirm oliguria.
2) Discriminate between renal success and renal failure.
3) Discriminate between causes of renal failure
Sladen, Robert N. "Oliguria in the ICU: systematic approach to diagnosis and treatment." Anesthesiology Clinics of North America 18.4 (2000): 739-752. This article is perfect for this question, but is not available as free full-text.
Lesko, Janene, and James R. Johnston. "Oliguria." AACN Advanced Critical Care 8.3 (1997): 459-468.
Dujovny, Nadav. "Oliguria." Common Surgical Diseases. Springer New York, 2008. 367-369.
Zaloga, Gary P., and Steven S. Hughes. "Oliguria in patients with normal renal function." Anesthesiology 72.4 (1990): 598-602.