Indications for Starting Furosemide (Lasix) in Severe LV Dysfunction (HFrEF) with AKI

The Central Principle: AKI Type Determines Whether to Diurese

Indications to Start/Continue Furosemide Despite AKI

• Elevated JVP, peripheral edema, ascites, orthopnea, PND
• Pulmonary rales, chest X-ray showing pulmonary vascular congestion, pleural effusions
• Elevated BNP/NT-proBNP

• The NKF Primer states: "The most evidence-based treatment of CRS is the relief of venous congestion. Numerous observations show a direct correlation between effective measures to reduce volume overload and improved outcomes in patients with CRS." - National Kidney Foundation Primer on Kidney Diseases, 8e, p. 331
• In this context, the AKI itself is an indication to decongestion, not a contraindication.

• A mild/moderate rise in creatinine during active decongestion (so-called "worsening renal function" or WRF) is often acceptable and even expected.
• Studies have shown that patients who achieve adequate decongestion - even if they develop transient WRF - have better long-term outcomes than those with preserved creatinine but inadequate decongestion.

• Severe dyspnea, hypoxemia, or inability to maintain oxygen saturation - diuresis is urgently indicated regardless of creatinine.

Practical Decision Framework

Severe HFrEF + AKI
       |
Is the patient volume overloaded (congested)?
       |
   YES                              NO (or low output state)
   |                                |
Start IV furosemide             Assess CO/hemodynamics
(double home oral dose           Consider inotropes first
or 1-2.5x home dose IV)         Cautious or no diuresis
       |
Monitor response at 6-12h:
- Urine output target: ≥100-150 mL/h
- Urine sodium in first void (>50 mEq/L = adequate response)
- Daily weight, net fluid balance
       |
Inadequate response?
       |
Add thiazide (metolazone) - "dual nephron blockade"

Dosing Guidance

• IV route is mandatory in acute decompensation (oral furosemide has variable bioavailability of 10-90%, mean 50%)
• Starting dose: Double the patient's home oral dose and give intravenously
  • Equivalency: furosemide 80 mg oral = furosemide 40 mg IV = torsemide 20 mg oral = bumetanide 1 mg oral/IV
• Bolus vs. continuous infusion: The DOSE trial showed no significant efficacy difference - either is acceptable
• GFR <30 mL/min: Consider bumetanide over furosemide as its excretion is minimally affected by reduced kidney function, and it has lower risk of ototoxicity

When NOT to Diurese (Relative Contraindications)

• Cardiogenic shock / systolic BP <90 mmHg without vasopressors
• Clinically volume-depleted (dry patient - elevated urea:creatinine ratio, flat JVP, dry mucous membranes)
• AKI clearly from a non-congestion cause (e.g., nephrotoxin, obstruction, intrinsic renal disease)
• Severe hypokalemia or hyponatremia requiring correction first

If Furosemide Resistance Develops

1. Add metolazone 2.5-5 mg oral 30 min before IV furosemide (dual nephron blockade) - watch for hypokalemia and hypomagnesemia
2. Increase furosemide dose before switching strategies
3. Consider ultrafiltration as a last resort (note: CARESS-HF trial showed no benefit over aggressive pharmacologic diuresis)
4. Dopamine low-dose may be tried in refractory CRS not responding to first-line decongestion - but routine use is not recommended (ROSE and DAD-HF trials were negative)
5. Inotropes (dobutamine, milrinone) if co-existing low-output state is confirmed

Key Take-Home Points

• The AKI of congested HFrEF is often the indication FOR furosemide, not against it.
• The pathophysiology is backward pressure (renal venous hypertension) → ↓GFR; decongesting the venous circuit relieves this.
• Accept a small rise in creatinine if the patient is decongesting effectively (weight coming down, urine output adequate).
• Use IV furosemide, dose adequately (do not under-dose out of fear of creatinine), and monitor response at 6-12 hours.
• Stop or reduce only if: hemodynamic compromise appears, patient becomes clinically volume-depleted, or severe electrolyte derangement occurs.

• National Kidney Foundation Primer on Kidney Diseases, 8e, pp. 331-332 (Therapeutic Strategies for Cardiorenal Syndrome)
• Harrison's Principles of Internal Medicine 22E, pp. 2025, 2036 (Cardiorenal interactions; ADHF management)

Assessing Response to Furosemide and When to Uptitrate

1. Traditional Markers (24-Hour Assessment)

Daily Weight

• Target weight loss: 0.5-1.0 kg/day (up to 1.5 kg/day in severe congestion)
• Weighed at the same time each day (morning, after voiding, before eating)
• Limitation: Requires 24 hours before a dose-adjustment decision can be made, delaying decongestion therapy. Also an imperfect surrogate because venous capacitance can shift without actual weight change.

Net Fluid Balance (Ins and Outs)

• Strict hourly urine output measurement
• Target: negative net balance of 500-1000 mL/day in most patients
• Minimum urine output threshold: If output is <0.5 mL/kg/h or <30 mL/h several hours after the dose, this suggests inadequate response
• Same limitation as weight: decisions often delayed until end-of-day review

Clinical Decongestion Signs (Serial Examination)

• Falling JVP
• Reduction in peripheral edema, ascites
• Improvement in dyspnea, orthopnea
• Improving oxygen saturation / reduction in supplemental O2 requirement
• Clearing of pulmonary rales (less reliable than JVP)

2. Urine Chemistry - The Early Decision Tool (2-6 Hour Window)

Spot Urine Sodium at 2 Hours Post-Dose

• The Siddiqi et al. 2024 review summarises observational data linking low urine sodium excretion after IV furosemide to worse outcomes in ADHF, and multiple RCTs (ESCALATE, DECONGEST) have been designed around urine sodium-guided titration.

Fractional Excretion of Sodium (FENa) / Urine Creatinine Ratio

• FENa >0.2-0.3% after a furosemide dose suggests adequate tubular response
• Urine Na:Cr ratio (spot) also used in some protocols

3. When to Uptitrate the Dose

• Urine output <100-150 mL/h
• Net fluid balance still positive
• Spot urine Na <50 mEq/L at 2 hours
• No appreciable symptomatic improvement
• Weight not falling

Step 1: IV furosemide at 2.5x home oral dose (or 40-80 mg IV if diuretic-naive)
         ↓
         Check urine Na at 2h, urine output at 6h
         ↓
Not responding? → Double the dose (logarithmic curve)
         ↓
Still not responding? (diuretic resistance)
         ↓
Step 2: Add metolazone 2.5-5 mg PO 30 min before next furosemide dose
        ("dual nephron blockade" - distal tubule blockade)
        → Monitor electrolytes closely (K, Mg)
         ↓
Still inadequate?
         ↓
Step 3: Add MRA (spironolactone) for proximal aldosterone-driven sodium retention
         ↓
Step 4: Consider SGLT2 inhibitor (emerging data for proximal nephron blockade in acute CRS)
         ↓
Step 5: Consider low-dose dopamine in refractory CRS (inconsistent evidence)
         ↓
Step 6: Ultrafiltration (last resort - no superiority shown over pharmacologic diuresis in CARESS-HF)

4. Biomarkers to Track During Diuresis

5. Assessing Adequacy of Overall Decongestion (Discharge Target)

• JVP normalised (<4 cm above sternal angle)
• No orthopnoea, no peripheral oedema (or minimal)
• Target weight achieved (often 2-4 kg below admission weight)
• Spot urine Na improving
• BNP/NT-proBNP trending down (though not a hard cut-off)
• Stable or improving creatinine

The CRS Pathophysiology Context

- Comprehensive Clinical Nephrology, 7e, Fig. 75.8