Handling a Sudden Drop in Urine Output in a Postoperative Patient

Scenario

A postoperative abdominal surgery patient with a Foley catheter has urine output of only 10 mL over the past hour.
Their BP is 88/50 mmHg, HR 112 bpm, SpO₂ 94%, and IV fluids are running at 75 mL/hr.

Question: What are your immediate actions, and how do you differentiate between prerenal, renal, and postrenal causes?

Best Practice Answer

1. Recognize Oliguria as an Early Warning Sign:
   Urine output < 30 mL/hr indicates potential renal hypoperfusion or early acute kidney injury (AKI).
   In post-op patients, it is often caused by fluid deficit, hypotension, or obstruction — act immediately.

2. Initial Nursing Actions:

   • Check the Foley system: Ensure tubing is not kinked, dependent loops are cleared, and the bag is below bladder level.
   • Assess bladder fullness: Palpate or use a bladder scanner to rule out retention (postrenal cause).
   • Measure total fluid intake/output and compare to previous hours.
   • Assess hemodynamics: note hypotension (BP < 90/60) and tachycardia, indicating possible hypovolemia or shock.
   • Increase O₂ if SpO₂ < 94% to improve tissue perfusion.

3. Collaborate and Escalate:

   • Notify the provider promptly with objective data (vitals, urine output trend, assessment).
   • Anticipate orders for:
     • Fluid bolus (e.g., 500 mL NS or LR) if hypovolemia suspected.
     • Lab work: BUN, creatinine, electrolytes, urine specific gravity.
     • Bladder scan or renal ultrasound if obstruction suspected.
   • If fluids fail to improve output, anticipate nephrology consult for possible intrinsic renal injury.

4. Differentiate Likely Causes:

   • Prerenal (most common): Low BP, dry mucosa, high urine specific gravity (>1.020) → dehydration or shock.
   • Renal (intrinsic): Elevated BUN/Cr ratio < 15, urine Na⁺ > 40 mEq/L → nephrotoxic injury.
   • Postrenal: Palpable bladder, catheter obstruction, or new anuria → mechanical blockage.

5. Documentation and Monitoring:

   • Record all vital signs, urine output trends, interventions, and provider notifications.
   • Reassess urine output every 30–60 minutes after intervention.
   • Document response to fluids or other corrective measures.

Real-World Application

This question assesses your ability to recognize early renal compromise and intervene before permanent damage occurs.
Interviewers look for your understanding of:

• Normal urine output thresholds (> 0.5 mL/kg/hr)
• Early fluid management
• Recognition of shock and renal perfusion priorities

It’s highly relevant for post-op, telemetry, and critical-care roles, where fluid balance is a daily nursing responsibility.

Tip: In interviews, summarize decisively —
“If urine drops suddenly, I first check the Foley for obstruction, assess perfusion, and notify the provider with full data — treating it as a potential renal perfusion issue until ruled out.”
This conveys clinical urgency, systematic assessment, and sound prioritization.