RRT Without Fear: A Practical ICU Guide for Students & Residents

A simple, systems-based way to understand, order, and assess renal replacement therapy.

Many trainees walk into the ICU terrified of renal replacement therapy (RRT). Nephrology feels abstract, academic, and "black‑box." But here’s the truth:

You don’t need to be a nephrologist. You need a framework.

When a patient starts down the road of possibly needing renal support, I find teaching the basics of the "external kidney" can be complex and difficult to convey. RRT is just physiology applied through a machine: perfusion, solute load, volume status, and organ protection. This guide gives you a clear, usable structure for real ICU practice.

⭐ THE ATTENDING FRAME: 3 QUESTIONS TO ASK EVERY TIME

1. Why does this patient need dialysis?

2. How urgent is the need?

3. Which modality matches their physiology?

Everything else is details.

1️⃣ WHEN TO START RRT: AEIOU + TRAJECTORY

Before ordering anything, ask:

Is kidney failure harming the lungs, heart, or brain?

Use AEIOU as a complication checklist:

Letter	Indication	What It Means Clinically
A – Acidosis	pH ≲ 7.1–7.2 despite resuscitation	Ventilator maxed out, worsening shock
E – Electrolytes	K⁺ >6–6.5 with ECG changes or refractory	Life-threatening arrhythmia risk
I – Ingestions	Lithium, salicylates, toxic alcohols	Dialysis removes the toxin
O – Overload	Pulmonary edema despite diuretics	Most common ICU trigger
U – Uremia	Encephalopathy, pericarditis, bleeding	Organ dysfunction from toxins

Trajectory Matters

• Pre-renal AKI: may improve with shock reversal

• ATN: slower recovery, higher RRT likelihood

• Most ICU AKI: mixed (pre-renal + ATN + congestion)

Pearl: Stop chasing creatinine. Dialysis is triggered by complications, not numbers.

2️⃣ THE DIURETIC MYTH (USE THIS ON ROUNDS)

There is no renal‑sparing dose of diuretics.

✔️ Helps with volume overload

❌ Does not reverse ATN

❌ Does not prevent dialysis

Use diuretics to improve oxygenation or buy time — not to avoid RRT when it’s needed.

3️⃣ DEMYSTIFYING THE MACHINE: THINK PHYSICS, NOT MAGIC

All RRT modalities rely on three mechanisms:

1. Diffusion (Dialysis)

• Solutes move high → low concentration

• Removes small molecules (urea, K⁺)

• “Trash removal”

2. Convection (Hemofiltration)

• Solutes dragged with water

• Better for middle molecules/inflammatory mediators

3. Ultrafiltration

• Removes plasma water

• Pure volume control

Ask yourself: How much trash? How fast? How gently?

4️⃣ CHOOSING A MODALITY: MATCH IT TO PHYSIOLOGY

Modality	Best For	Watch Outs
IHD	Stable pts, rapid clearance	Hypotension, osmotic shifts
CRRT (CVVHDF)	Shock, pressors, neuro pts, severe overload	Filter clotting, downtime
SLED / PIRRT	Moderately unstable, resource-limited settings	Intermediate clearance

Pearl: If you’re escalating pressors just to tolerate IHD, CRRT is the exit ramp.

5️⃣ DAY ZERO ORDERS: BUILDING THE “EXTERNAL KIDNEY”

Think of RRT orders as constructing temporary organ support.

Core ICU RRT Order Template

1. Modality“Start CRRT (CVVHDF)” / “Start IHD”

2. Indication“Refractory hyperkalemia + volume overload in septic shock”

3. Access

• 13–15 Fr double-lumen catheter

• Right IJ preferred--you want your catheter to be as straight as possible and as close to the heart as possible

• Avoid subclavian

• Lock per protocol

4. CRRT Prescription

• Effluent dose: 20–25 mL/kg/hr

• Blood flow (Qb): 150–200 mL/min

5. Ultrafiltration Goal

• Net even / Net –1 L / Aggressive –3 L if tolerated

• Hospital net > machine net

6. Anticoagulation

• None / Citrate / Heparin

7. Dialysate Bath

• K⁺ >6 → 2K bath

• Normal K → 3–4K bath

• Bicarb ~32

8. Labs

• BMP q6–12h

• Mg/Phos daily

• Ionized Ca if citrate

6️⃣ WHAT TO LOOK FOR ON ROUNDS (THE REAL MASTERY)

Daily RRT Checklist

• Hemodynamics + pressor trends

• Net balance vs oxygenation

• Electrolytes + acid–base

• Filter pressures + downtime

• Access alarms

• Mental status (uremia vs osmotic shifts)

The Net Trap

Machine –2 L

• IV meds +3 L= Patient is still +1 L

7️⃣ TROUBLESHOOTING PATTERNS (STAY CALM)

• Frequent filter clots: access issues, low anticoagulation, UF/Qb mismatch

• Rising TMP: thick blood, impending clot

• Citrate gap: total Ca : iCa >2.5 → possible citrate accumulation

8️⃣ SPECIAL ICU SITUATIONS

Neuro patients

• Prefer CRRT/SLED

• Avoid rapid osmotic shifts

ARDS + overload

• Volume control becomes the primary indication

Rhabdomyolysis

• Minimize downtime (myoglobin clearance)

Nutrition

• RRT removes amino acids → protein 2–2.5 g/kg/day

🎯 FINAL PEARL

You don’t need to master dialysis. You need to master:

• Recognizing when kidney failure harms vital organs

• Choosing the right modality

• Writing safe initial orders

• Reassessing daily

That’s ICU competence. That’s confidence.

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