Prerenal
Intrinsic renal
Postrenal
▪Hypotension after anesthesia induction
▪Insufficient intraoperative hydration
▪High nasogastric (NG) tube output
▪Increased vascular permeability (“third spacing”)
▪Surgical site bleeding/drain output
▪Abdominal compartment syndrome
▪Gastrointestinal bleeding
▪Retroperitoneal bleeding
▪Acute tubular necrosis (ATN) related to intra- or postoperative hypotension
▪Rhabdomyolysis related to positioning/prolonged surgery
▪Embolism (or microemboli) with vascular surgery or CPB
▪Acute interstitial nephritis (AIN) related to antibiotics or diuretics
▪Contrast nephropathy
▪Prolonged cross-clamping in vascular surgery
▪Ureteral damage or compression
▪Bladder outlet obstruction/urinary retention
Review operative and anesthesia records: specifically assess for hypotension, blood transfusions, use of diuretics, use of contrast, use of CPB, length of cross-clamp time, urine output, and any operative complications.
Evaluate the patient for intravascular volume status (orthostatic vital signs, jugular venous pressure) and abdominopelvic surgical drain output (increased clear drain output that has a creatinine level greater than serum creatinine level may signify urinary leak).
Review patient chart for recent contrast studies, ongoing and immediate postoperative urine output, surgical drain output, and nasogastric tube output.
Urine analysis: muddy brown granular and epithelial cell casts suggest ATN; hematuria may suggest nephrolithiasis, ureteral trauma, or intrinsic renal insult; eosinophiluria may indicate interstitial nephritis; rhabdomyolysis is indicated by urine myoglobin without red blood cells in urinalysis.
Urine labs: high urinary specific gravity, low urinary sodium, and <1 % fractional excretion of sodium (FENa) support the diagnosis of a prerenal etiology.
Serum labs: CBC and metabolic panel.
Studies to consider: bladder scan for post-void residual (perform in and out catheterization if bladder scan values are suspect), retroperitoneal ultrasound (US), or computed tomography (CT) scan (to assess for hydronephrosis, fluid collections).
Principles of Management
The treatment and further workup is predicated on the working diagnosis. Nephrology consultation may be required if establishing euvolemia or relieving urinary tract obstruction does not result in improvement. Of course, a nephrologist should be involved if renal replacement therapy is needed—for example, if the patient has acidosis, volume overload compromising organ function, significant hyperkalemia, or uremia. Key points in management include:
For all patients, if urine output is difficult to quantify, place a urinary catheter – but remove this as soon as possible.
In case of intravascular volume depletion, aggressive intravenous fluids (IVF) either with Lactated Ringers (LR) or normal saline (NS) with frequent clinical reassessment of volume status and UO.
Volume overload and CHF: diurese in the usual fashion; work up for myocardial infarction if CHF is new for the patient.
If there is obstruction which is not relieved by a urinary catheter, this usually merits rapid surgical or percutaneous intervention.
References
1.
Biteker M, et al. Incidence, risk factors, and outcomes of perioperative acute kidney injury in noncardiac and nonvascular surgery. Am J Surg. 2014;207(1):53–9.PubMedCrossRef
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