++
Oliguria and anuria are defined as urine output less than 0.5 mL/kg/h and less than 50 mL/d, respectively. Frequently observed in the postoperative period, oliguria and anuria may be the initial presenting sign of acute kidney injury (AKI), a condition associated with significant perioperative morbidity. Acute renal failure (ARF) in the perioperative setting is a serious surgical complication as over 50% of acute hemodialysis patients have perioperative ARF. The mortality rate for perioperative ARF remains in the range of 20%–80% depending upon patient comorbidities. More than 90% of perioperative ARFs result from relative hypovolemia with inadequate renal perfusion. The Kidney Disease Improving Global Outcomes (KDIGO) criteria for AKI are defined in Table 90-1.
++
++
In the situation of severe renal hypoperfusion, there is a narrow window of only 30–60 minutes between the onset of oliguria and the initiation of ischemic acute tubular necrosis (ATN). The causes of oliguria can be classified as prerenal, intrarenal, or postrenal. This classification provides a useful structure for the systematic approach to therapy and is summarized in Table 90-2.
++
++
AKI is caused by decreased renal perfusion due to decreased intravascular blood volume or impaired renal hemodynamics. The causes include the following:
++
Hypovolemia—Hypovolemia is the most common cause of perioperative oliguria. Intravascular volume depletion is caused by bleeding, gastrointestinal disease such as vomiting, diarrhea or bleeding, renal losses due to diuretics or glucose osmotic diuresis, skin or respiratory losses from insensible losses, sweat or burns, and third space sequestration due to crush injury or skeletal fracture.
Hypotension—Decreased blood pressure can result from hypovolemic, myocardial, or septic shock, pharmacologic therapies, or other conditions that result in vasodilation.
Poor cardiac output—Poor cardiac output results in marked reductions in kidney perfusion that parallel the severity of the underlying disease.
Renal ischemia—Bilateral renal artery stenosis or unilateral stenosis in a solitary functioning kidney ...