What are the causes of postoperative oliguria (oliguria is a condition characterized by decreased urine output)?

From the Guidelines

Postoperative oliguria is often caused by hypovolemia, decreased cardiac output, or direct renal injury from hypoperfusion, nephrotoxic medications, or inflammatory mediators released during surgery, and should be managed by assessing volume status and identifying the cause, rather than immediately triggering fluid therapy 1. The causes of postoperative oliguria can be multifactorial, including:

• Hypovolemia due to inadequate fluid intake or excessive fluid loss
• Decreased cardiac output resulting from anesthesia, blood loss, or pre-existing cardiac conditions
• Direct renal injury from hypoperfusion, nephrotoxic medications, or inflammatory mediators released during surgery
• Mechanical obstruction, such as a kinked or blocked urinary catheter
• Electrolyte imbalances, such as hyperkalemia or hyponatremia According to the most recent and highest quality study, a near-zero fluid balance is recommended to avoid complications associated with fluid overload or deficit 1. Key points to consider in managing postoperative oliguria include:
• Assessing volume status and identifying the cause of oliguria
• Avoiding excessive fluid administration, which can lead to fluid overload and complications such as pulmonary edema or abdominal compartment syndrome
• Using vasopressors to maintain adequate blood pressure, if necessary, to ensure renal perfusion
• Monitoring urine output, electrolytes, and renal function to guide management decisions
• Considering the use of diuretics, such as furosemide, in patients with persistent oliguria and signs of fluid overload 1. It is essential to note that the use of 0.9% saline should be avoided due to the risk of salt and fluid overload 1, and instead, balanced crystalloids such as Ringer’s lactate should be used. Additionally, postoperative fluid management should aim to maintain a near-zero fluid balance, with a focus on avoiding fluid overload or deficit 1.

From the FDA Drug Label

Although urine flow is apparently one of the better diagnostic signs for monitoring vital organ perfusion, the physician also should observe the patient for signs of reversal of mental confusion or coma. However, it has been observed that in some oliguric or anuric patients, administration of the drug has produced an increase in urine flow which may reach normal levels.

The causes of postoperative oliguria are not directly stated in the drug label. Key points about oliguria include:

• Oliguria is a condition characterized by decreased urine output
• The label discusses the use of dopamine to increase urine flow in patients with oliguria, but does not specify the causes of oliguria
• The label mentions that poor perfusion of vital organs can lead to decreased urine flow, but this is not explicitly stated as a cause of postoperative oliguria 2

From the Research

Causes of Postoperative Oliguria

• Postoperative oliguria can be caused by various factors, including:
  • Intravascular volume depletion, which elicits a kidney response consisting of augmented sodium retention at Henle's loop and water at the collecting tubules 3
  • Hypovolaemia, which can lead to decreased renal perfusion and subsequent oliguria 4
  • Vasopressor requirement at admission, non-elective procedures, male sex, and baseline serum creatinine, which were found to be higher among oliguric patients 5
  • Perioperative fluid restriction, which can lead to hypovolaemia and subsequent oliguria, although the evidence is insufficient to associate restrictive fluid management with an increase in oliguria 4
• Other possible causes of postoperative oliguria include:
  • Acute pulmonary oedema, which can complicate the clinical picture and require invasive therapies such as renal replacement therapies (RRT) 3
  • Electrolyte imbalances, such as potassium ion imbalance, which can occur in the presence of large amounts of drainage from wounds or abscess cavities, nasogastric suction, or intestinal fistulae 6
  • Postoperative complications, such as acute kidney injury (AKI), which can be related to oliguria, although oliguria was largely unrelated to kidney dysfunction measured by serum creatinine in one study 5

Management of Postoperative Oliguria

• The management of postoperative oliguria includes:
  • Assessment of volemic status and risk-benefit of fluid challenge or furosemide stress test 7
  • Investigation of possible perioperative complications 7
  • Use of diuretics, such as furosemide or mannitol, to improve diuresis and water loss, although the effectiveness of these diuretics can depend on the underlying cause of oliguria 3
  • Consideration of invasive therapies, such as RRT, in patients who do not respond to less invasive measures 3