Oliguria in ICU 

 Definition

Oliguria = Urine output < 0.5 mL/kg/hour

 Exam pearl: Oliguria may precede rise in creatinine by 24–48 hours.

 Why Oliguria Matters in ICU?

Oliguria is:

• Earliest sign of renal hypoperfusion
• Marker of shock
• Predictor of mortality
• Often reversible if detected early

In ICU, urine output is a real-time organ perfusion monitor.

Minimum Urine Output

• Adults: 0.5 mL/kg/h
• Children: 1 mL/kg/h
• Neonates: 1–2 mL/kg/h

 Causes of Oliguria – Structured Approach

1️⃣ Pre-Renal (Most Common in ICU)

Due to ↓ renal perfusion.

Causes:

• Hypovolemia (bleeding, diarrhea, burns)
• Septic shock
• Cardiogenic shock
• Hepatorenal syndrome
• Increased intra-abdominal pressure
• Severe vasodilation

Pathophysiology:

↓ Perfusion → RAAS activation → Na+ retention → Concentrated urine

Lab Clues:

2️⃣ Intrinsic Renal Causes

A. Acute Tubular Necrosis (ATN)

Most common intrinsic cause in ICU.

Causes:

• Prolonged shock
• Sepsis
• Nephrotoxins (aminoglycosides, contrast)
• Rhabdomyolysis

B. Acute Interstitial Nephritis

• Drug induced (NSAIDs, PPIs, antibiotics)
• Eosinophilia
• WBC casts

C. Glomerulonephritis

• RBC casts
• Proteinuria
• Hypertension

3️⃣ Post-Renal (Always Rule Out first)

Mechanical obstruction.

Causes:

• BPH
• Clots
• Stones
• Foley catheter blockage
• Neurogenic bladder

Immediate Step:

✔️ Check catheter patency
✔️ Bladder scan
✔️ Ultrasound KUB

 Stepwise ICU Approach to Oliguria

 STEP 1 – Confirm True Oliguria

• Check catheter
• Ensure no kinking
• Flush catheter
• Bladder scan

 Never treat before confirming patency.

 STEP 2 – Assess Hemodynamics

• MAP (<65?)
• Lactate
• Capillary refill
• IVC ultrasound
• Passive leg raise

 STEP 3 – Volume Status Assessment

Clinical Signs:

• JVP
• Skin turgor
• Edema
• Lung crackles

Ultrasound:

• IVC collapsibility
• LV function
• Venous congestion (VExUS score)

 STEP 4 – Labs

• Serum creatinine
• BUN
• Electrolytes
• ABG
• Urine routine
• Urine sodium
• FENa
• FEUrea (if diuretics used)

 Fluid Challenge – When & How?

Indicated if:

• Suspected hypovolemia
• No signs of overload

Protocol:

• 250–500 mL balanced crystalloid
• Reassess in 15–30 min

 Stop if:

• No increase in UO
• Rising CVP
• Lung B lines

 Role of Diuretics in Oliguria

Important Exam Point:

❌ Diuretics DO NOT treat AKI
✔️ Used only for volume overload

Furosemide stress test:

• 1–1.5 mg/kg IV
• <200 mL urine in 2 hrs → predicts severe AKI

Indications for Renal Replacement Therapy (RRT)

Absolute Indications (AEIOU)

 Biomarkers in Oliguria

Emerging markers:

• NGAL
• KIM-1
• Cystatin C

Not routine yet in India.

 Important ICU Concepts

1️⃣ Oliguria ≠ Always AKI

Post-op oliguria:

• Stress response
• ADH surge
• Pain-induced vasoconstriction

2️⃣ Transient Oliguria in Shock

Short episodes (<6 hrs) may not cause permanent damage.

3️⃣ Permissive Oliguria?

Seen in:

• Fluid restriction strategy
• ARDS patients
• De-resuscitation phase

Must monitor:

• Lactate
• Creatinine
• Electrolytes