🫘 CRRT Mastery Guide
Continuous Renal Replacement Therapy in ICU – A Complete Journey
🖋️ Prepared for Dr. Amir Fadhel — Specialist in Anesthesiology and Critical Care
Developed with the support of AI — tailored for clinicians, residents, and ICU trainees, especially in resource-limited settings.
📘 About This Guide
Developed in collaboration with Sophia — your AI-powered clinical assistant for anesthesia, critical care, and real-world ICU decision-making.
This guide was further enriched by key insights from a lecture by Dr. Layla Ali Hakeem, Consultant in Intensive Care Medicine & Anesthesia.
Structured for ICU clinicians, anesthesia technicians, and learners at all levels, this visually rich and clinically refined guide explores CRRT in meticulous detail, with pearls, diagrams, alarms, and bedside decision support.
🎯 In this guide, you will learn to:
- ✅ Identify indications and timing for CRRT initiation
- ✅ Master all CRRT modes (CVVH, CVVHD, CVVHDF, SCUF)
- ✅ Understand machine setup, filters, access, and fluid dynamics
- ✅ Safely manage anticoagulation: Citrate, Heparin, or No-anticoag
- ✅ Detect and resolve common alarms and circuit issues
- ✅ Apply CRRT principles in low-resource ICU settings
- ✅ Analyze real clinical case scenarios
- ✅ Test your knowledge with 15 advanced MCQs
🙏 Special thanks to Dr. Layla Ali Hakeem for her contribution to advancing ICU education and for the rich lecture that helped shape the depth of this guide.
📑 Guide Outline
1️⃣ What is CRRT?
2️⃣ Understanding AKI in the ICU
3️⃣ Principles of Clearance
4️⃣ Modes of CRRT
5️⃣ CRRT Components
6️⃣ Machine Settings
7️⃣ Anticoagulation in CRRT
8️⃣ Fluid & Electrolyte Management
9️⃣ Troubleshooting & ICU Alarms
🔟 CRRT in Limited-Resource Settings
1️⃣1️⃣ Clinical Scenarios
1️⃣2️⃣ Pocket Summary
1️⃣3️⃣ Beyond CRRT – MARS, TPE, Hemoperfusion
1️⃣4️⃣ Renal Recovery, CRRT Duration & Medical Therapy Limits
1️⃣5️⃣ 15 Advanced Clinical MCQs
Section 1️⃣ What is CRRT? – Indications & Clinical Role
🔍 What is CRRT?
Continuous Renal Replacement Therapy (CRRT) is a slow and continuous extracorporeal blood purification technique used primarily in the intensive care unit (ICU) for critically ill patients with acute kidney injury (AKI) and hemodynamic instability. Unlike intermittent hemodialysis (IHD), CRRT is run 24 hours a day and allows gentle removal of fluid and solutes without causing hypotension.
🧠 Think of CRRT not just as dialysis, but as organ support therapy, allowing time for the kidneys — and the patient — to recover.
🎯 Goals of CRRT:
- ✅ Maintain fluid balance without drops in blood pressure
- ✅ Remove uremic toxins and metabolic waste
- ✅ Correct electrolyte imbalances (K⁺, Ca²⁺, phosphate, etc.)
- ✅ Restore acid-base balance
- ✅ Enable precise control of volume status
- ✅ Support failing organs (especially in sepsis or MODS)
- ✅ Modulate inflammatory cytokines in severe infections/sepsis
📌 CRRT vs. IHD – Key Comparison
| Feature | CRRT | IHD (Intermittent Hemodialysis) |
|---|---|---|
| Duration | Continuous (24h/day) | 3–4 hours/session |
| Blood flow rate | 100–250 mL/min (low) | 300–500 mL/min (high) |
| Solute clearance method | Convection, diffusion, or both | Mainly diffusion |
| Hemodynamic effect | Stable (ideal in shock) | Hypotension common |
| ICU suitability | Yes – for unstable patients | Not preferred in shock/sepsis |
| Anticoagulation need | Usually required | Sometimes not needed |
🚨 When to Start CRRT – Indications
🔹 Oliguria or anuria with volume overload
🔹 Severe fluid overload unresponsive to diuretics
🔹 Refractory hyperkalemia
🔹 Metabolic acidosis (HCO₃⁻ < 15 despite treatment)
🔹 Severe uremia (confusion, pericarditis, bleeding)
🔹 Acute intoxications with dialyzable toxins
🔹 Sepsis-induced AKI, especially in MODS
🔹 Liver failure (e.g. hepatorenal syndrome)
🔬 Clinical Judgment – Not Just Numbers
❗ CRRT initiation is not based solely on BUN/creatinine values.
It is based on dynamic clinical assessment, including:
- Fluid status
- Acid-base balance
- Electrolyte levels
- Hemodynamics
- Urine output
- Severity of illness (SOFA, APACHE II)
🧠 “Don’t wait for labs to crash when the patient is already drowning in fluid and pressors — early CRRT saves organs.”
💡 Real ICU Tip:
🔹 A patient on norepinephrine ≥ 0.1 mcg/kg/min with fluid overload, acidosis, and oliguria is a textbook candidate for CRRT — not IHD.
🧾 Evidence Note:
The KDIGO guidelines (2012) support CRRT over IHD for AKI patients who are hemodynamically unstable or at risk for cerebral edema.
📉 Common ICU Misconceptions:
❌ “Let’s try another day of diuretics first.”
➡️ Wrong. In sepsis or shock, kidneys need rest, not overloading.
❌ “We need a nephrology consult to start CRRT.”
➡️ Wrong. In many ICUs, CRRT initiation is guided by intensivists and anesthesiologists — especially when trained.
Section 2️⃣ Acute Kidney Injury (AKI) in the ICU – Diagnosis, Classification & Staging
🧠 Why It Matters
CRRT is not a therapy for renal numbers.
It is a therapy for organ dysfunction and fluid/electrolyte derangements in critical illness.
That’s why understanding how we define and stage AKI is essential before starting CRRT.
🔹 What is AKI?
Acute Kidney Injury (AKI) is a sudden decline in kidney function resulting in:
- Accumulation of nitrogenous wastes (↑ BUN/Cr)
- Inability to maintain fluid, electrolyte, and acid-base homeostasis
📌 AKI is not just oliguria. Patients may be non-oliguric with severe biochemical disturbances.
🧪 Diagnostic Criteria for AKI (per KDIGO 2012)
AKI is diagnosed if any of the following occur:
| Criteria | Threshold |
|---|---|
| ↑ SCr by ≥ 0.3 mg/dL | Within 48 hours |
| ↑ SCr to ≥ 1.5× baseline | Within 7 days |
| Urine output < 0.5 mL/kg/hr | For > 6 hours |
🔢 Staging Systems – RIFLE, AKIN, and KDIGO
Let’s break them down:
📘 1. RIFLE Classification (2004)
Developed by the ADQI group
Stages: Risk – Injury – Failure – Loss – ESRD
| Stage | SCr Criteria | UO Criteria |
|---|---|---|
| R (Risk) | ↑ SCr × 1.5 or GFR ↓25% | < 0.5 mL/kg/hr for 6 hr |
| I (Injury) | ↑ SCr × 2 or GFR ↓50% | < 0.5 mL/kg/hr for 12 hr |
| F (Failure) | ↑ SCr × 3 or Cr ≥4 mg/dL | < 0.3 mL/kg/hr for 24 hr or anuria for 12 hr |
| L (Loss) | Persistent AKI > 4 weeks | N/A |
| E (ESRD) | > 3 months | N/A |
📗 2. AKIN (Acute Kidney Injury Network)
Refined RIFLE → focused on time-based changes
Stages: 1–3
| Stage | SCr Criteria | UO Criteria |
|---|---|---|
| 1 | ↑ SCr ≥ 0.3 mg/dL or ×1.5–2 | < 0.5 mL/kg/hr for 6 hr |
| 2 | ↑ SCr ×2–3 | < 0.5 mL/kg/hr for 12 hr |
| 3 | ↑ SCr ×3 or Cr ≥4 mg/dL | < 0.3 mL/kg/hr for 24 hr or anuria 12 hr |
📕 3. KDIGO (Current Gold Standard – 2012)
KDIGO combines RIFLE + AKIN and is now the most widely used system.
| Stage | SCr Criteria | UO Criteria |
|---|---|---|
| 1 | ↑ SCr ≥ 0.3 mg/dL in 48 hr or 1.5–1.9× baseline | < 0.5 mL/kg/hr for 6–12 hr |
| 2 | ↑ SCr 2.0–2.9× baseline | < 0.5 mL/kg/hr for ≥12 hr |
| 3 | ↑ SCr 3× baseline or ≥4 mg/dL OR dialysis started | < 0.3 mL/kg/hr ≥24 hr OR anuria ≥12 hr |
🧠 KDIGO is the preferred system for ICU use and research.
⚠️ Key Point:
Staging = Severity
Indication for CRRT = Clinical context
So, a KDIGO Stage 2 patient may still not need CRRT if they’re stable.
But a Stage 1 patient in septic shock with acidosis/fluid overload might.
🧠 Clinical Pearls
- Baseline creatinine unknown? Back-calculate using MDRD assuming GFR 75
- Always consider non-renal causes of oliguria (hypovolemia, RAS inhibitors)
- Avoid contrast, nephrotoxins (aminoglycosides, NSAIDs)
- Monitor daily weight, ins and outs, Cr trends
Section 3️⃣ Principles of CRRT Clearance – Diffusion, Convection, Adsorption
🧠 Why This Matters
CRRT is built on three physiologic mechanisms of solute and fluid clearance:
1️⃣ Diffusion
2️⃣ Convection
3️⃣ Adsorption
Each CRRT mode (CVVH, CVVHD, CVVHDF) is a variation on how much of each mechanism is used. Let’s explore them now in detail.
🔹 1. Diffusion – "Solute Follows the Gradient"
📌 Primary principle behind CVVHD and part of CVVHDF
- Solutes move from higher to lower concentration across a semipermeable membrane
- Small molecules like urea, creatinine, potassium, lactate diffuse easily
- Requires dialysate fluid flowing countercurrent to blood
🧪 Fick’s Law of Diffusion:
Rate ∝ (Surface Area × Concentration Gradient) / Membrane Thickness
| Feature | Description |
|---|---|
| Solute size | Small (MW < 500 Da) |
| Direction | High → low concentration |
| Flow needed | Dialysate |
| Mode example | CVVHD |
🔹 Faster when:
- Membrane is thin & large
- Concentration gradient is high
- Flow is countercurrent
🔹 2. Convection – "Solute Follows Water"
📌 Primary mechanism in CVVH and part of CVVHDF
- Solutes are dragged across the membrane with water movement (solvent drag)
- Excellent for middle-sized molecules (cytokines, myoglobin)
- Requires replacement fluid to maintain volume
🧪 Sieving Coefficient (SC):
SC = 1 means solute passes freely with water
SC = 0 means solute does not cross
| Feature | Description |
|---|---|
| Solute size | Small & middle molecules |
| Mechanism | Solvent drag |
| Flow needed | Replacement fluid |
| Mode example | CVVH |
🔹 Faster when:
- UF rate is high
- Replacement is post-filter (better clearance)
🧠 Think of convection like “pressure-washing” the blood clean.
🔹 3. Adsorption – "Sticking to the Filter"
📌 Often forgotten, but important in sepsis & cytokine storm
- Molecules stick to the membrane surface due to charge or chemical attraction
- Works for large molecules: cytokines (IL-6, TNF-α), endotoxins, even some drugs
- Temporary effect – saturates filter in hours
| Feature | Description |
|---|---|
| Molecule type | Large proteins, endotoxins |
| Mechanism | Filter surface binding |
| Duration | Short – saturates in 6–12 hrs |
| Mode example | Happens in all modes (esp. CVVHDF) |
🧠 New membranes (e.g. Oxiris, AN69, CytoSorb) are designed to maximize adsorption.
🧬 Summary Table – Clearance Mechanisms
| Mechanism | Solute Size | Fluids Used | Primary in Mode |
|---|---|---|---|
| Diffusion | Small (< 500 Da) | Dialysate | CVVHD |
| Convection | Small–Medium | Replacement Fluid | CVVH |
| Adsorption | Large proteins | — (membrane surface) | All modes (esp. CVVHDF) |
🧠 Clinical Application Tips
- In sepsis or MODS → choose CVVHDF for maximum clearance (diffusion + convection + adsorption)
- In hyperkalemia → CVVHD is fastest (dialysate clears K⁺)
- In rhabdomyolysis → CVVH helps remove myoglobin via convection
- In fluid overload → All modes help, but SCUF is fluid-only
Section 4️⃣ Modes of CRRT – CVVH, CVVHD, CVVHDF, and SCUF
🧠 Key Concept
Each mode is defined by which fluid is used (dialysate, replacement, or both) and how solutes are removed (diffusion, convection, or both).
Let’s explore each one in full clinical context.
🔹 1. CVVH – Continuous Veno-Venous Hemofiltration
Clearance via Convection (solvent drag)
Fluid: ✅ Replacement only | ❌ No dialysate
| Parameter | Details |
|---|---|
| Solute removal | By convection (middle-sized molecules) |
| Fluids used | Replacement fluid only |
| Infusion site | Pre-filter (better filter life) or Post-filter (better clearance) |
| Used for | Sepsis, rhabdomyolysis, cytokine removal |
| Mode complexity | Moderate |
🧠 “Pressure-washing” the blood across a membrane, dragging solutes with water.
🔹 2. CVVHD – Continuous Veno-Venous Hemodialysis
Clearance via Diffusion
Fluid: ✅ Dialysate only | ❌ No replacement
| Parameter | Details |
|---|---|
| Solute removal | Small molecules by diffusion |
| Fluids used | Dialysate only (runs counter to blood flow) |
| Used for | Hyperkalemia, acidosis, uremia |
| Mode complexity | Simple |
🧠 Think “standard dialysis,” done continuously and gently.
🔹 3. CVVHDF – Continuous Veno-Venous Hemodiafiltration
Clearance via BOTH Diffusion + Convection
Fluid: ✅ Dialysate + ✅ Replacement
| Parameter | Details |
|---|---|
| Solute removal | Small & medium molecules |
| Fluids used | Dialysate + Replacement |
| Best used for | Sepsis, MODS, ICU AKI |
| Mode complexity | Advanced – full-spectrum clearance |
🧠 This is the most comprehensive mode — optimal for unstable patients with complex derangements.
🔹 4. SCUF – Slow Continuous Ultrafiltration
Fluid removal ONLY — No solute clearance
Fluid: ❌ No dialysate | ❌ No replacement
| Parameter | Details |
|---|---|
| Solute removal | None – only water |
| Fluids used | None (no dialysate/replacement) |
| UF rate | 100–300 mL/hr max |
| Best used for | Congestive heart failure, fluid overload |
| Mode complexity | Simplest |
🧠 This is the CRRT version of gentle diuresis.
📊 Comparison Table – CRRT Modes
| Mode | Dialysate | Replacement | Clearance Type | Ideal Use |
|---|---|---|---|---|
| CVVH | ❌ | ✅ | Convection | Cytokine removal, sepsis |
| CVVHD | ✅ | ❌ | Diffusion | Hyperkalemia, metabolic acidosis |
| CVVHDF | ✅ | ✅ | Convection + Diffusion | Broad AKI in ICU, MODS |
| SCUF | ❌ | ❌ | Fluid only (UF) | Fluid overload in CHF, no AKI |
🧠 Clinical Selection Guide:
| Clinical Scenario | Best Mode |
|---|---|
| Severe hyperkalemia | CVVHD |
| Sepsis with AKI | CVVHDF |
| Pulmonary edema (no AKI) | SCUF |
| Rhabdomyolysis | CVVH |
| Max clearance (ICU AKI + sepsis) | CVVHDF |
Section 5️⃣ CRRT Components – Access, Filters, Fluids, Machines
🧩 The Building Blocks of CRRT
To run CRRT effectively, we must understand the hardware and consumables involved. These include:
- Vascular access
- Extracorporeal circuit
- Hemofilter / membrane
- CRRT machine
- Fluids (replacement, dialysate, anticoagulation)
🔹 1. Vascular Access
CRRT requires a double-lumen central venous catheter, typically inserted in:
| Preferred Sites | Notes |
|---|---|
| Right internal jugular | Straight path to RA – 1st choice |
| Femoral vein | Easy access, less preferred in obese |
| Left internal jugular | Longer path – higher resistance |
| Subclavian | ⚠️ Avoid due to stenosis risk |
📏 Catheter size:
- 13.5–14.5 Fr, 20–25 cm in length (adults)
- Dedicated for CRRT only — no medications or blood draws
🔹 2. Hemofilter / Membrane
Acts as the artificial kidney — responsible for:
- Removing solutes (diffusion/convection)
- Filtering fluids
- Preventing air/clot passage
| Feature | Description |
|---|---|
| Membrane type | High-flux, semi-permeable |
| Material | Polyethersulfone or AN69 |
| Surface area | 0.6–1.5 m² (adult use) |
| Lifespan | 24–72 hrs (depends on clotting, usage) |
🧠 Key tip: Monitor transmembrane pressure (TMP) and filter clotting. Rising TMP = filter clogging.
🔹 3. Tubing & Extracorporeal Circuit
- Arterial line (from patient) → pump → filter → return line
- Includes pressure sensors, air detectors, and heparin ports
🔧 Replace tubing with each new circuit or if contaminated/clotted.
🔹 4. Fluids in CRRT
CRRT fluids vary by mode. They include:
| Type | Used in | Purpose |
|---|---|---|
| Replacement fluid | CVVH, CVVHDF | Volume + solute clearance via convection |
| Dialysate fluid | CVVHD, CVVHDF | Solute clearance via diffusion |
| Anticoagulant fluid | Citrate-based circuits | Regional anticoagulation |
📦 Pre-mixed, sterile bags (commercial): Hemosol, Prismasol, NxStage
🔹 5. The CRRT Machine
Popular models include:
| Machine | Manufacturer | Features |
|---|---|---|
| Prismaflex | Baxter | Most common, modular, pediatric/adult use |
| Multifiltrate | Fresenius | Good for complex ICU circuits |
| NxStage System One | NxStage | Portable, sometimes used for IHD too |
💡 Functions of the machine:
- Blood and fluid flow control
- Pressure and air alarms
- Ultrafiltration rate adjustment
- TMP and filter lifespan monitoring
🚨 ICU Red Flags:
- High return pressure → Catheter malposition or clot
- High TMP → Filter clogging
- Air-in-line alarm → Risk of embolism
- Blood leak detection → Membrane rupture
🔍 Detailed Insight – Vascular Access for CRRT
🔹 Why It Matters
CRRT requires reliable, high-flow venous access capable of handling continuous blood flow (100–250 mL/min) without collapsing or clotting.
🛑 Compromised access = interrupted therapy = harm to patient.
1️⃣ Catheter Type – Double-Lumen Large-Bore Dialysis Catheter
- Non-tunneled, temporary use
- Double lumen: One lumen withdraws blood (arterial/red), the other returns blood (venous/blue)
- Made of soft polyurethane or silicone
- Side holes to improve flow
2️⃣ French Size and Length by Age Group
| Age Group | French Size (Fr) | Length | Site Considerations |
|---|---|---|---|
| Neonates | 6.5–8 Fr | 5–10 cm | Right IJ preferred |
| Infants (1–12 mo) | 8–9 Fr | 10–12 cm | Right IJ / femoral |
| Children (1–10 y) | 9–10 Fr | 12–15 cm | Right IJ / femoral |
| Adolescents | 10–12 Fr | 15–20 cm | Right IJ / subclavian |
| Adults | 13.5–14.5 Fr | 20–25 cm | Right IJ first choice |
🔸 Note: Shorter catheters may be used in femoral access (20 cm), longer for jugular (20–24 cm).
3️⃣ Preferred Sites of Insertion
| Site | Advantages | Cautions |
|---|---|---|
| Right IJ | Straight path to SVC → 💯 best flow | Avoid carotid puncture |
| Femoral | Easy insertion, compressible | Higher infection risk, kinking in obesity |
| Left IJ | Alternate jugular access | More angulation → lower flow |
| Subclavian | Rarely used | Risk of stenosis → avoid in CRRT patients |
4️⃣ Marker Colors & Lumen Positioning
🚨 Critical to avoid reversal!
| Color | Function | Insertion Path |
|---|---|---|
| 🔴 Red | Arterial / Draw | Tip at RA/SVC junction or IVC |
| 🔵 Blue | Venous / Return | Side holes above red tip – 1–2 cm shorter |
🔁 Reversing these lumens → high pressure, hemolysis, alarms, and poor flow
5️⃣ Correct Depth of Insertion
| Site | Target Depth (Adults) | Landmark Tips |
|---|---|---|
| Right IJ | 15–20 cm | Aim RA-SVC junction, use US + ECG tip navigation |
| Femoral | 20–25 cm | IVC ~ L2–L4 level |
| Left IJ | 18–22 cm | Requires longer path to reach SVC |
🔹 Use ultrasound to guide vein entry
🔹 Use chest X-ray or ECG tip location to confirm final tip position
Section 6️⃣ Flow Rate and Access Pressure
| Flow Rate Target | 100–250 mL/min |
|---|---|
| Arterial pressure | -50 to -150 mmHg |
| Venous pressure | < 200 mmHg |
🔧 Pressures outside these limits → suspect malposition, thrombus, kinking, or clotting
⚠️ Common Pitfalls to Avoid
- ❌ Using a multi-lumen central line instead of a proper dialysis catheter
- ❌ Reversing red/blue lines “just to make it work”
- ❌ Too short a catheter → low flows, turbulent suction
- ❌ Using access for medications — especially calcium in citrate anticoagulation!
🧠 Clinical Pearls
- 💡 Prime the catheter with saline and heparin before connection
- 💡 Keep catheter dedicated to CRRT — label it and document
- 💡 Always flush ports after disconnecting to prevent clot formation
- 💡 Use transparent dressings and inspect daily for infection
🧠 Filtration Fraction (FF%) – Preventing Filter Clotting
Filtration Fraction (FF) is the % of plasma water removed during CRRT.
If too high, it increases haemoconcentration and clotting risk.
🔬 Formula:
FF (%) = (UF Rate × 100) ÷ Plasma Flow Rate (Qp)
Where:
- UF Rate = in mL/min
- Qp = Qb × (1 – Hct)
→ Qb = blood flow (mL/min), Hct = hematocrit
📊 Example:
- Blood Flow (Qb): 100 mL/min
- Hematocrit (Hct): 30% → Plasma Flow (Qp) = 100 × (1 – 0.3) = 70 mL/min
- UF Rate = 21 mL/min
- FF = (21 × 100) ÷ 70 = 30%
⚠️ Target FF < 25–30%
| FF (%) | Risk Level |
|---|---|
| < 20% | ✅ Safe |
| 25–30% | ⚠️ Acceptable but watch |
| > 30% | ❌ High clot risk |
🔹 High FF = ↑ filter clotting, ↑ TMP, ↓ circuit life
🧠 Strategies to lower FF:
- Increase Qb
- Use pre-dilution
- Reduce UF rate
- Anticoagulate properly
🔄 📊 Practical CRRT-HDF Dosing Chart (35 mL/kg/hr)
At the end of this section, here is a practical bedside protocol for prescribing CRRT in Hemodiafiltration (HDF) mode at a target dose of 35 mL/kg/hr, adjusted by patient weight:
| Patient Weight | Pre-filter Replacement (PBP) | Dialysate Rate | Post-filter Replacement |
|---|---|---|---|
| 40 kg | 200 mL/hr | 1000 mL/hr | 200 mL/hr |
| 50 kg | 600 mL/hr | 1000 mL/hr | 200 mL/hr |
| 60 kg | 600 mL/hr | 1300 mL/hr | 200 mL/hr |
| 70 kg | 800 mL/hr | 1500 mL/hr | 200 mL/hr |
| 80 kg | 900 mL/hr | 1700 mL/hr | 300 mL/hr |
| 90 kg | 900 mL/hr | 1900 mL/hr | 300 mL/hr |
📝 Notes:
- ✅ Total dose = 35 mL/kg/hr (Effluent = Dialysate + Replacement + Net UF)
- ✅ Pre-filter (PBP) fluid preserves filter life
- ✅ Post-filter fluid enhances clearance
- 🩸 Blood Flow Rate (Qb) depends on filter type:
- M60 → Qb > 60 mL/min
- M100 → Qb > 80 mL/min
- M150 → Qb > 100 mL/min
- 🔁 Adjust rates based on hemodynamic stability and lab values
- 📌 This is a reference protocol — tailor for each patient
Section 7️⃣ Anticoagulation in CRRT – Citrate, Heparin, and No-Anticoagulation
🧠 Why Anticoagulation Matters
CRRT circuits are prone to clotting due to:
- Slow blood flow rates
- Long duration of therapy (24h)
- Blood contact with artificial surfaces
- Low pressure venous return
🔴 Clotting leads to:
- Interrupted therapy
- Loss of filter
- Increased cost
- Blood loss
That’s why preventing clot formation inside the circuit is a cornerstone of safe and efficient CRRT.
🧪 Anticoagulation Strategies Overview
There are three main strategies, each with advantages and limitations:
| Strategy | Type | Used in Mode(s) | Notes |
|---|---|---|---|
| Citrate | Regional anticoagulation | CVVH, CVVHD, CVVHDF | Preferred; minimal systemic effect |
| Heparin | Systemic anticoagulation | All modes | Simple but ↑ bleeding risk |
| No anticoag | None | All modes | Used in high bleeding risk |
🔹 1. Regional Citrate Anticoagulation (RCA)
Most recommended method in international guidelines (KDIGO 2012)
Especially suitable for bleeding-prone ICU patients
🧬 How Citrate Works:
- Citrate binds ionized calcium (iCa²⁺) in the blood entering the filter
- This inhibits the coagulation cascade → preventing clotting within the circuit
- Before returning blood to the patient, calcium is infused back
🧪 Citrate = anticoagulant in circuit
🧪 Calcium = procoagulant in patient
⚙️ Protocol Summary:
1️⃣ Citrate Infusion (Pre-filter):
- Dose: 3–4 mmol/L of blood flow
- Usually as trisodium citrate 4%
2️⃣ Calcium Infusion (Post-filter):
- Dose adjusted to maintain systemic iCa²⁺ = 1.1–1.3 mmol/L
- Often central line or separate IV site
3️⃣ Monitor:
- Circuit iCa²⁺: 0.25–0.35 mmol/L
- Patient iCa²⁺: 1.1–1.3 mmol/L
- Check anion gap, bicarbonate, and pH regularly
⚠️ Citrate Red Flags:
| Problem | Sign | Management |
|---|---|---|
| Citrate accumulation | High total Ca/iCa²⁺ ratio > 2.5 | ↓ citrate dose, consider heparin |
| Metabolic alkalosis | ↑ HCO₃⁻, ↑ pH | Adjust citrate/replacement fluid |
| Ionized hypocalcemia | Tetany, arrhythmias | Increase calcium infusion |
🧠 Use caution in patients with liver failure, shock, or lactic acidosis — impaired citrate metabolism.
🔹 2. Unfractionated Heparin
Traditional method, easy to use but systemic
- Given as continuous IV infusion into pre-filter blood line
- Dose: 5–10 units/kg/hr (or adjusted to APTT goal)
🔬 Monitoring:
- APTT goal: 1.5–2.0 × baseline
- Monitor for bleeding, platelet count, and signs of HIT
⚠️ Risks:
- Bleeding (especially in neurosurgical patients, trauma)
- Heparin-induced thrombocytopenia (HIT)
- Systemic anticoagulation → affects all procedures
🔹 3. No Anticoagulation
Chosen in high bleeding risk or severe coagulopathy
- Use pre-dilution strategy to reduce hemoconcentration
- Use frequent saline flushes
- Expect shorter filter life
🧠 May be temporary until safe for citrate or heparin.
📊 Anticoagulation Strategy Comparison
| Feature | Citrate | Heparin | No Anticoag |
|---|---|---|---|
| Site of action | Filter only (regional) | Systemic | None |
| Bleeding risk | Very low | Moderate–high | None |
| Filter life | Long (24–72 hrs) | Moderate | Short (8–12 hrs) |
| Monitoring burden | High (iCa²⁺, total Ca) | Moderate (APTT) | Low |
| Ideal for | ICU, sepsis, trauma, post-op | General use | Coagulopathy, surgery |
🧠 Clinical Tips
- Always label calcium and citrate lines clearly
- Avoid mixing calcium and citrate in the same lumen — they'll precipitate
- Watch for metabolic shifts (alkalosis, hypocalcemia)
- Document filter life to assess anticoag strategy effectiveness
Section 8️⃣ Fluid & Electrolyte Management – Balance & Monitoring
🧠 Why It Matters
CRRT isn’t just about “cleaning the blood.” It is also a powerful tool to:
- Correct fluid overload
- Normalize electrolytes (K⁺, Ca²⁺, Mg²⁺, PO₄³⁻)
- Maintain acid-base balance
- Prevent dangerous metabolic shifts
If poorly managed, CRRT can cause volume depletion, electrolyte crashes, or iatrogenic alkalosis/acidosis.
🔹 Fluid Balance – Precision is Key
🔄 Net Ultrafiltration (UF) = Fluid Out – Fluid In
| Term | Meaning |
|---|---|
| Fluid in | Replacement + dialysate + meds + nutrition |
| Fluid out | Ultrafiltrate + urine + other losses |
| Net UF target | Typically 50–200 mL/hr |
| Goal | Negative balance (for edema) or neutral |
🧠 Adjust UF hourly based on:
- Hemodynamics
- Vasopressors
- MAP goals
- Lactate clearance
- Cumulative fluid balance
💧 Fluid Overload Definition
Fluid Overload % =
(Fluid In – Fluid Out) ÷ Admission weight (kg) × 100
⚠️ >10% fluid overload is associated with increased mortality
🔁 Early CRRT improves outcomes if started before overload worsens
🔹 Electrolyte Monitoring – 4x Daily in ICU (or q6h)
| Electrolyte | Target Range | Management Strategy |
|---|---|---|
| K⁺ | 3.5–5.0 mmol/L | Adjust dialysate K⁺ (0, 2, or 4 mmol/L) |
| Na⁺ | 135–145 mmol/L | Use Na⁺-matched fluids to avoid shifts |
| Ca²⁺ (ionized) | 1.1–1.3 mmol/L | Titrate calcium infusion if on citrate |
| Mg²⁺ | 1.7–2.2 mg/dL | Supplement in replacement if low |
| Phosphate | 2.5–4.5 mg/dL | Add phosphate (if fluid is non-phosphate) |
| Bicarbonate | 22–26 mmol/L | Managed by dialysate/replacement buffer |
⚠️ Red Flags
| Issue | Cause | Action |
|---|---|---|
| Hypokalemia | High clearance, low K⁺ dialysate | Increase dialysate K⁺ |
| Hypophosphatemia | No phosphate in CRRT fluids | Supplement IV or use Phoxilium® |
| Hypocalcemia (iCa²⁺ < 1.0) | Citrate accumulation | Increase calcium infusion, check ratio |
| Hypernatremia / Hyponatremia | Inappropriate Na⁺ in CRRT fluid | Match fluid Na⁺ to plasma Na⁺ |
| Alkalosis (HCO₃⁻ > 30) | Excess citrate / buffer | Adjust fluid buffer, use lactate-base |
🔬 Advanced Adjustments
- K⁺ bath options: 0, 2, or 4 mmol/L — match to labs
- Phosphate-containing fluids: Phoxilium, MultiBic Phos
- Avoid citrate in severe liver failure (poor metabolism)
- Use bicarbonate-free fluids in alkalosis
💡 Clinical Pearls
- Check daily weight — it’s the most honest fluid status measure
- Balance nutrition input (especially enteral) in fluid-in calculation
- Replace magnesium and phosphate proactively, especially in sepsis and refeeding
- Never forget to chart all non-CRRT IVs in fluid-in totals
📍 Best Placement:
At the end of Section 8 – Fluid & Electrolyte Management
(just after electrolyte monitoring and clinical pearls)
🧾 Insert This Box:
💊 Drug Dosing & Nutritional Considerations in CRRT
🧠 Drug Dosing During CRRT
- Do NOT automatically reduce drug doses during CRRT — many drugs are cleared as efficiently as in patients with normal renal function
- Renally excreted medications (e.g., β-lactams, aminoglycosides, vancomycin) may require higher or more frequent dosing
- Highly protein-bound or large molecule drugs (e.g., midazolam, phenytoin) are less affected by CRRT
- Consider therapeutic drug monitoring (TDM) where available (e.g., for vancomycin, aminoglycosides)
- Be alert for filter clearance of vasoactive agents (e.g., norepinephrine, insulin, heparin infusion)
🥣 Nutrient Losses & Repletion
- CRRT removes:
- Water-soluble vitamins (B-complex, C)
- Electrolytes: K⁺, Mg²⁺, PO₄³⁻
- Trace elements (Zn, Se, Cu)
- Consider daily multivitamin and trace element supplementation
- Protein and calorie intake should be liberalized — CRRT allows full enteral nutrition
- Watch for hypophosphatemia in early refeeding or sepsis
🧠 These effects are amplified in high-volume CRRT (>35 mL/kg/hr)
Section 9️⃣ Troubleshooting & ICU Alarms – Detect, Decode, Decide
🧠 Why This Section Matters
CRRT alarms are not just beeping annoyances — they are your machine whispering about the patient, the circuit, or your setup.
Ignoring them = filter loss, therapy interruption, blood loss, or patient harm.
This section teaches how to interpret alarms and fix them, clinically and technically.
🔔 Alarm Categories in CRRT
CRRT alarms fall under 5 main categories:
1️⃣ Access pressure alarms
2️⃣ Return pressure alarms
3️⃣ Transmembrane pressure (TMP) alarms
4️⃣ Air/blood leak alarms
5️⃣ Machine safety/system alarms
Let’s decode each one.
🔴 1. Access Pressure Alarms
"The machine is struggling to pull blood from the patient"
| Alarm | Value Range | Cause | Action |
|---|---|---|---|
| High negative pressure | < -150 mmHg | Kinked line, catheter against wall, clot | Flush, reposition patient, reverse lumen |
| Low access pressure | > -30 mmHg | Disconnection, open port | Check line integrity |
📌 Ideal range: –50 to –150 mmHg
🔵 2. Return Pressure Alarms
"The machine is pushing blood back with too much force"
| Alarm | Value Range | Cause | Action |
|---|---|---|---|
| High return pressure | > 200 mmHg | Clot in return limb, kinked catheter | Check tubing, flush, reposition |
| Low return pressure | Near 0 mmHg | Disconnection or leak | Immediately pause system, inspect |
📌 Ideal range: < 180 mmHg
⚫ 3. Transmembrane Pressure (TMP) Alarms
"The filter is choking – clogging or clotting"
TMP = Pressure difference across the filter membrane
TMP = (Filter outlet pressure – Effluent pressure)
| TMP Value | Meaning | Action |
|---|---|---|
| < 100 mmHg | ✅ Normal | Continue monitoring |
| 100–200 mmHg | ⚠️ Mild resistance | Watch trend |
| > 200–250 mmHg | 🚨 Impending clot | Consider changing filter or anticoag |
| > 300 mmHg | ❌ Filter failure | Stop and change filter/circuit |
🧠 Sudden TMP rise = filter clotting or fibrin deposition
🔺 4. Blood Leak or Air Alarms
"You may be losing blood or about to air-embolize the patient"
| Alarm | Cause | Action |
|---|---|---|
| Blood leak | Rupture in filter membrane | Stop immediately, replace filter, assess patient |
| Air-in-line | Air bubble in return line | Clamp, stop blood pump, clear air manually |
🧠 These are life-threatening. Always treat as emergencies.
⚙️ 5. System Alarms (Non-pressure)
| Alarm Type | Meaning | Action |
|---|---|---|
| Effluent pump alarm | Blocked or failing pump | Check tubing, restart pump |
| Fluid balance error | Mismatch in input/output | Recalibrate scale or re-zero platform |
| Temperature out of range | Blood warmer error | Check warmer, inspect power source |
| Air detector sensitivity | Faulty sensor | Call biomedical, swap machine if needed |
🧠 Troubleshooting Algorithm (Step-by-step)
1️⃣ Check the alarm message – read, don’t guess
2️⃣ Silence alarm → DO NOT resume blindly
3️⃣ Inspect circuit visually:
- Kinks
- Bubbles
- Blood color
- Flow sluggishness
4️⃣ Check pressures in order: - Access → Return → TMP
5️⃣ Flush circuit if minor occlusion suspected
6️⃣ Reposition patient — access lines may be compressed
7️⃣ Swap filter if TMP or return remains high
8️⃣ Document clearly and notify attending
9️⃣ Never override air/blood leak alarms – these are hard stops
🩸 When to Replace the Circuit?
Replace CRRT circuit if:
- TMP > 300 mmHg persistently
- Blood-tinged effluent
- Blood leak alarm
- Poor flow despite flushes
- Filter age > 72 hours
- Visible clot or fibrin strand
- Excessive frequent alarms disrupting therapy
💡 ICU Tips from Experience
- 🔄 Rotate patient Q4h to prevent catheter wall suction
- 🔧 Keep pre-filter infusion going during troubleshooting to prevent clot
- 📋 Always label lumens clearly — citrate vs calcium ports
- 🕒 Log alarm timing — frequent alarms often predict early filter failure
Section 🔟 CRRT in Limited-Resource Settings – Strategies & Workarounds
🧠 Why This Section Matters
In many hospitals around the world — including parts of developing countries and even rural hospitals in developed countries — full access to premium CRRT machines, filters, fluids, or trained nephrologists is limited.
Yet critically ill patients still arrive:
- In shock
- In renal failure
- With no urine output
- Drowning in fluid
So we adapt, innovate, and save lives.
This section empowers ICU teams to deliver safe, modified CRRT using the tools available.
🔹 Common Limitations
| Challenge | Impact |
|---|---|
| No Prismaflex / Multifiltrate | No automated CRRT delivery |
| No pre-mixed dialysate | Risk of error, delays |
| No phosphate/citrate fluids | Electrolyte imbalance, clotting |
| No trained dialysis nurse | Setup delays, poor troubleshooting |
| Limited filter or tubing supply | Early circuit loss, reuse pressures |
🔧 Adapted Strategies
🔸 1. Use IHD machines in CRRT-like fashion
- Low-flow intermittent dialysis over 8–10 hours
- Adjust flow rate: 100–150 mL/min
- Use larger dialysate volumes at slower rates
- Avoid rapid shifts (especially in brain injury, children)
🧠 This is not true CRRT — but it's better than no support at all.
🔸 2. DIY Fluids When Premixed Not Available
- Use normal saline or Ringer’s as base
- Add sodium bicarbonate, potassium chloride, glucose, calcium, and magnesium as needed
- Label every bag clearly
- Use double-check system for every custom mix
📌 Follow standard CRRT fluid recipes used in humanitarian/dialysis relief missions
🔸 3. Use SCUF for Gentle Fluid Removal
- When machines are basic or patient can't tolerate solute shifts
- Remove 100–200 mL/hr fluid via basic hemofilter setup
- No dialysate or replacement fluid needed
- Prevents worsening pulmonary edema
🔸 4. Prevent Circuit Loss
- Use pre-filter replacement when citrate or heparin is unavailable
- Flush every 1–2 hours with saline + heparin (if safe)
- Rotate access site positions frequently
- Train staff to recognize early signs of filter clotting
🔸 5. Train Non-nephrology ICU Staff
- Nurses, anesthesiologists, ICU doctors can all manage CRRT
- Create quick-reference visual protocols
- Record and replay your own video demonstrations using real equipment
- Use simulation scenarios for troubleshooting training
📘 Ethical & Practical Principles
| Rule | Application in Crisis |
|---|---|
| “Some dialysis is better than none” | Slow low-efficiency treatment is better than waiting |
| “Start before drowning” | Don’t wait for >10% fluid overload |
| “Reuse when absolutely safe” | If filter reuse is done, it must follow disinfection and flushing protocols |
| “Simplify to save lives” | Focus on fluid, K⁺, and urea — ignore fine-tuning if unavailable |
🧠 CRRT Triage in Scarce Settings
Use a prioritization approach when filters or machines are limited:
| Priority Group | Example |
|---|---|
| ✅ High Priority | Sepsis with AKI, refractory acidosis |
| ⚠️ Medium | Oliguria with hyperkalemia |
| ⛔ Delay / Monitor | Mild AKI, stable, making urine |
💡 ICU Pearls for Limited Settings
- Label all lines with color-coded tape if multi-purpose
- Flush calcium lines before reuse to avoid citrate precipitation
- Use shared machine shifts — rotate 2 patients on 12h/12h cycles
- Make one recovery bag to salvage blood from clotted circuits (if policy permits)
- Never let fear of perfection delay care — adapted therapy is therapy
Section 1️⃣1️⃣ – Clinical Scenarios – Real ICU Cases, Triggers & Decisions
🧠 Why This Section Matters
CRRT isn’t started by lab numbers — it’s started by recognizing critical bedside patterns.
Here, we apply everything you've learned so far in practical, life-saving ICU cases.
Each case includes:
- The clinical trigger
- The CRRT mode & setup
- A decision framework
- 🔺 Red flags
- 💡 Key takeaways
🩸 Case 1 – Septic Shock + Rising Lactate + Oliguria
Patient: 55-year-old male, septic from perforated bowel, MAP 58 mmHg on norepinephrine 0.15 mcg/kg/min, lactate 4.8, UO < 0.3 mL/kg/hr
Labs: Creatinine 2.4 → 3.6 in 24 hr, pH 7.21, HCO₃⁻ 15, K⁺ 5.7
🔹 Trigger: Oliguria + worsening AKI + acidemia in septic shock
🔹 CRRT Plan:
- Mode: CVVHDF
- Blood flow: 120 mL/min
- Dialysate: 1300 mL/hr
- Replacement: 200 pre + 200 post
- UF: 50 mL/hr (fluid-neutral in first 6 hr)
- Anticoagulation: Citrate (high bleeding risk)
🔺 Red Flag: Don’t wait for creatinine to peak — act on trend + perfusion failure
💡 Pearl: Septic AKI needs early solute and volume stabilization, not just pressors
💀 Case 2 – Hyperkalemia with Rhabdomyolysis
Patient: 30-year-old male post-crush injury, serum K⁺ 6.8, CPK 20,000, UO 200 mL/day
Vitals: Stable, MAP 75 without vasopressors
🔹 Trigger: Hyperkalemia + pigment nephropathy risk
🔹 CRRT Plan:
- Mode: CVVH (convection removes myoglobin)
- Blood flow: 150 mL/min
- Replacement: 1800 mL/hr pre + 200 post
- Dialysate: 0
- UF: 100 mL/hr
- Anticoagulation: Heparin
🔺 Red Flag: Myoglobin not cleared by diffusion — convection is key
💡 Pearl: Don’t overload these patients with fluids — monitor Ca²⁺ and urine pH
💨 Case 3 – Pulmonary Edema in CHF, Still Making Urine
Patient: 78-year-old woman with EF 25%, bibasilar crackles, SpO₂ 89% on 6L O₂, UO ~600 mL/day
🔹 Trigger: Fluid overload not resolving with diuretics
🔹 CRRT Plan:
- Mode: SCUF
- Blood flow: 100 mL/min
- UF: 150 mL/hr
- No dialysate or replacement
- Anticoagulation: None (coagulopathy)
🔺 Red Flag: Do not use full CVVH if renal function is intact and solutes are stable
💡 Pearl: SCUF is perfect when the problem is volume, not uremia
🧠 Case 4 – Liver Failure with Hepatorenal Syndrome
Patient: 60-year-old with cirrhosis, Cr 4.0, INR 2.5, total bilirubin 15, UO < 200 mL/day
🔹 Trigger: Fluid overload + rising Cr in setting of multiorgan dysfunction
🔹 CRRT Plan:
- Mode: CVVHD
- Blood flow: 100 mL/min
- Dialysate: 1500 mL/hr
- Replacement: 0
- UF: 75 mL/hr
- Anticoagulation: No anticoagulation (high bleeding risk)
🔺 Red Flag: Avoid citrate in severe liver failure — risk of accumulation
💡 Pearl: Focus on slow clearance; don’t chase “normal” numbers in dying liver
🚨 Case 5 – Pediatric Septic AKI in 5-Year-Old
Weight: 20 kg, post-appendiceal rupture, MAP 55 mmHg, rising BUN/Cr, fluid overload >10%
🔹 Trigger: Pediatric septic AKI + fluid overload
🔹 CRRT Plan:
- Mode: CVVHDF
- Blood flow: 50 mL/min
- Dialysate: 500 mL/hr
- Replacement: 300 pre + 100 post
- UF: 40 mL/hr
- Anticoagulation: Regional citrate
🔺 Red Flag: Children develop faster metabolic shifts — monitor Na⁺, PO₄³⁻, and Ca²⁺ closely
💡 Pearl: Use low-flow settings, soft UF goals, and adjust fluids every 2–4 hrs
🔷 Special Focus – CRRT in Sepsis & Cytokine Storm
🧠 Why CRRT is Crucial in Sepsis
Sepsis triggers:
- Massive cytokine release (IL-6, TNF-α, IL-1β)
- Capillary leak, fluid overload, and metabolic acidosis
- Rapid AKI → ↑ lactate, ↓ urine, ↑ potassium
CRRT becomes both a renal support and an immunomodulatory therapy.
✅ CRRT Strategy for Sepsis in ICU
| Parameter | Recommendation |
|---|---|
| Timing | Start early (Stage 2 KDIGO or rising lactate + oligo) |
| Mode | CVVHDF (best for small & middle molecule clearance) |
| Clearance types | Diffusion + Convection + Adsorption |
| Replacement fluid | Use pre + post if possible |
| Dialysate | Potassium-adjusted (K⁺ 0 or 2 mmol/L if hyperkalemic) |
| UF target | Start neutral or mild negative (50–100 mL/hr) |
| Anticoagulation | Regional citrate preferred (unless liver failure) |
| Filter choice | If available, use adsorptive membranes: |
- **Oxiris®**
- **CytoSorb®**
- **AN69 ST membrane**
| Blood flow (Qb) | 150–200 mL/min for adults | | Dose | 25–35 mL/kg/hr (can go up to 40 in cytokine storm) |
🔺 Red Flags
| Situation | Action |
|---|---|
| Liver dysfunction (↑ INR, ammonia) | Avoid citrate; consider no anticoagulation |
| Refractory lactic acidosis | Start CRRT even without oliguria |
| Persistent hypotension | Reduce UF; keep volume neutral |
| Rapid circuit clotting | Check catheter position + anticoagulation dose |
💡 Clinical Pearls
- CRRT in sepsis = organ support + cytokine clearance
- Don’t wait for creatinine alone — follow trend + perfusion markers
- Monitor phosphate and calcium closely — septic patients deplete fast
- Keep CRRT running >20 hours/day for effective cytokine clearance
- Evaluate CRRT success by urine recovery + lactate drop + pressor tapering
Section 1️⃣2️⃣ – Pocket Summary & 15 Advanced MCQs for CRRT Mastery
📌 CRRT Pocket Summary – Clinical Quick Guide
| Category | Key Point |
|---|---|
| Indications | AKI with hemodynamic instability, fluid overload, acidosis, hyperkalemia |
| Start Early If | Urine output ↓ + lactate ↑ + rising creatinine |
| Best Mode | CVVHDF – combined convection + diffusion |
| Flow Rates | Qb: 100–200 mL/min; Dialysate + Replacement = 20–35 mL/kg/hr total |
| UF Goal | 50–200 mL/hr (adjust by fluid balance, MAP, and pressors) |
| Access Site | Right IJ preferred; 13.5–14.5 Fr dual lumen catheter |
| Anticoagulation | Citrate (best); Heparin (monitor APTT); or None if bleeding |
| Electrolyte Risks | Hypokalemia, hypophosphatemia, alkalosis, hypocalcemia |
| Red Alarms | Blood leak, air-in-line, high TMP → stop & change filter |
| Filter Life | 24–72 hrs max; shorter if no anticoag or access issue |
📍 Suggested Placement:
As an appendix at the end of the guide, after Section 1️⃣2️⃣ (MCQs)
Titled:
🧠 Beyond CRRT – Advanced Extracorporeal Therapies
📘Section 1️⃣3️⃣ Appendix – Beyond CRRT: MARS, TPE, and Hemoperfusion
🩺 1. MARS – Molecular Adsorbent Recirculating System
A liver support system combining dialysis + adsorption via albumin
🔹 Use in:
- Acute-on-chronic liver failure
- Hepatic encephalopathy
- Post-transplant graft dysfunction
- Drug-induced liver injury
- Intractable pruritus in cholestasis
🔹 Removes:
- Albumin-bound toxins (bilirubin, bile acids, aromatic AAs)
- Ammonia, urea, copper, tryptophan
- Some drugs (diazepam, phenytoin)
🔹 Technology:
- Blood passes through an albumin circuit
- Toxins bind → cleared via charcoal and ion-exchange cartridges
- MARS flux membrane enables protein-bound solute clearance
💉 2. TPE – Therapeutic Plasma Exchange
Removes patient’s plasma and replaces with FFP/albumin
🔹 Use in:
- TTP, myasthenia gravis
- Guillain-Barré
- Goodpasture’s syndrome
- Catastrophic antiphospholipid syndrome
- Refractory sepsis with autoimmune storm
🔹 Mechanism:
- Removes harmful antibodies, cytokines, and immune complexes
- Replaces with donor plasma or albumin
🧲 3. Hemoperfusion
Blood is passed through an adsorptive filter (e.g., activated charcoal)
🔹 Use in:
- Toxin ingestion/overdose (e.g., theophylline, paraquat, phenobarbital)
- Endotoxin removal in septic shock (with polymyxin-B columns)
🔹 Not for: Protein-bound drugs with high molecular weight
🔹 Limitations: Cost, availability, risk of thrombocytopenia
📌 Clinical Notes
- These therapies are not a replacement for CRRT but can be used alongside or after
- Require specialized equipment, filters, and trained personnel
- Often used in liver ICUs, neuro ICUs, or immunology-linked critical care
Section 1️⃣4️⃣ – CRRT Duration, Recovery, and the Limits of Medical Therapy
📘 When to Start. How Long to Continue. And When to Stop.
🔁 Part 1 – How Long Should CRRT Continue?
✅ CRRT is not about “sessions” — it’s continuous, individualized, and re-evaluated daily.
| Parameter | Typical Practice |
|---|---|
| CRRT Duration | 2–14 days (average) |
| Filter Changes | Every 24–72 hrs (based on clotting, alarms, TMP) |
| CRRT dose | 20–25 mL/kg/hr (effluent rate) |
| Start weaning | When renal recovery signs appear |
| Discontinue | If irreversible, switch to IHD or palliative |
🧠 What guides continuation of CRRT?
- Persistent oliguria/anuria
- Uncontrolled hyperkalemia or acidosis
- Ongoing fluid overload
- Multiorgan dysfunction with unstable MAP
- Ongoing nephrotoxic exposures
🧪 Key daily labs to assess during CRRT:
- BUN, Cr, K⁺, HCO₃⁻, pH
- Ca²⁺ (ionized & total)
- Phosphate, magnesium
- Urine output trend
- Lactate, MAP, and vasopressor use
🔄 Part 2 – Recognizing Renal Recovery: When Are the Kidneys Waking Up?
📈 Timeline of Expected Recovery by Etiology
| Cause | Expected Recovery Window | Notes |
|---|---|---|
| Ischemic ATN | 5–21 days | May go through oliguric → diuretic phase |
| Sepsis-AKI | 5–14 days | Can recover with hemodynamic support |
| Rhabdomyolysis | 10–30 days | Myoglobin blocks tubules → late polyuria |
| Drug-induced AKI | 7–30 days | Depends on inflammation vs direct toxicity |
| Multiorgan Failure | Unpredictable | Often ends in irreversible damage |
| Pre-existing CKD (Stage 3–5) | Rare full recovery | May transition to ESRD |
🔬 Reliable Markers of Renal Recovery
| Marker | Interpretation |
|---|---|
| ↑ Spontaneous urine output > 400–500 mL/day | First clinical clue – may be dilute polyuria |
| ↓ BUN/Creatinine trend | Must accompany clinical improvement |
| ↓ CRRT fluid/electrolyte needs | Kidneys resume homeostasis |
| Stable MAP without vasopressors | Perfusion improves → kidney perfusion improves |
| No need for bicarbonate or phosphate | Suggests tubular recovery |
💧 Polyuric phase may precede full recovery — monitor for electrolyte depletion (K⁺, Mg²⁺, PO₄³⁻)
🛑 Don’t stop CRRT too early:
- If patient is still acidotic, oliguric, or hyperkalemic
- If diuretics are needed to maintain urine flow
- If rebound azotemia or acidosis occurs after pause
🚫 Part 3 – Why Medical Therapy Alone Often Fails in Severe AKI
🔬 Structural vs Functional AKI
| Type | Can Medical Rx Help? | Explanation |
|---|---|---|
| Pre-renal | ✅ Yes | Fluid-responsive, reversible |
| Intrinsic AKI (ATN, nephritis) | ❌ Often No | Tubular damage, inflammation, obstruction |
| Post-renal | ✅ With decompression | Obstruction relief = recovery possible |
⚠️ Real-World Mechanisms That Limit Medical Therapy:
| Mechanism | Medical Rx Failure Point |
|---|---|
| Ischemic ATN | Tubular cell death → cast formation |
| Sepsis AKI | Inflammatory vasoconstriction, microthrombi |
| Rhabdomyolysis | Myoglobin is nephrotoxic and obstructive |
| Nephrotoxic drugs | Cytotoxic → interstitial inflammation |
| Abdominal Compartment Syndrome | ↑ IAP → ↓ renal vein return → ↑ congestion |
| ECMO or CPB circuits | Hemolysis, non-pulsatile flow, embolic risk |
🧪 CRRT Is Needed Because:
- Diuretics fail in complete ATN
- Bicarbonate just masks acidosis
- Potassium binders can’t keep pace with ongoing release
- Vasopressors may support MAP but don’t fix the tubules
- Kidney perfusion and filtration are decoupled in MODS
🎯 Part 4 – Clinical Philosophy: CRRT is a Bridge, Not a Cure
“CRRT buys time for recovery — but you must still fix the underlying fire.”
👨⚕️ The ICU Clinician’s Job During CRRT:
✅ Treat sepsis
✅ Stabilize MAP
✅ Support oxygenation
✅ Stop nephrotoxic meds
✅ Drain any obstruction or source
✅ Maintain gentle, steady CRRT
✅ Watch for spontaneous improvement
🧠 Outcomes to Anticipate:
| Scenario | Interpretation |
|---|---|
| ↑ Urine + ↓ Cr | Consider trial off CRRT |
| Still oliguric + stable | Continue 24–48 hrs more |
| Recurrent uremia on pause | Resume CRRT or move to IHD |
| MODS + no renal recovery + poor GCS | Discuss goals of care, possible withdrawal |
🩺 ICU Teaching Analogy:
“The filter doesn’t heal the kidney. You do.
It just keeps the patient alive long enough for your treatments to work.”
Section 1️⃣5️⃣ Advanced Clinical MCQs for CRRT Mastery
Q1. A 60 kg patient is started on CRRT using CVVHDF. What is the minimum total effluent dose required to meet KDIGO standards?
A. 600 mL/hr
B. 1000 mL/hr
C. 1500 mL/hr
D. 2000 mL/hr
✅ Answer: D – 60 kg × 35 mL/kg/hr = 2100 mL/hr (target >2000 mL/hr)
Q2. A CRRT circuit alarms for high return pressure. The return pressure is 220 mmHg. What is the most likely cause?
A. Filter clotting
B. Air-in-line
C. Catheter malposition
D. Dialysate mismatch
✅ Answer: C – High return pressure = obstruction/kink in return line
Q3. Which statement about citrate anticoagulation is true?
A. It works by directly inhibiting thrombin
B. It increases systemic bleeding risk
C. It binds calcium to prevent clotting in circuit
D. It causes acidosis in all patients
✅ Answer: C – Citrate chelates calcium locally; systemic Ca²⁺ is replaced
Q4. What does a rising transmembrane pressure (TMP) most likely indicate?
A. Hypotension
B. Clotting of filter
C. Air embolism
D. Citrate toxicity
✅ Answer: B – TMP rise = filter clogging or clotting
Q5. Which of the following is most removed via convection?
A. Urea
B. Potassium
C. IL-6 (cytokines)
D. Ammonia
✅ Answer: C – Middle-sized molecules like cytokines follow water via convection
Q6. A patient develops total Ca²⁺ to ionized Ca²⁺ ratio >2.5 while on citrate. What does this suggest?
A. Normal metabolism
B. Citrate underdose
C. Citrate accumulation
D. Hypercalcemia
✅ Answer: C – High total:ionized Ca²⁺ = citrate accumulating
Q7. Which mode offers the best combined solute clearance for sepsis?
A. CVVH
B. CVVHD
C. CVVHDF
D. SCUF
✅ Answer: C – CVVHDF uses both convection and diffusion
Q8. What is the typical lifespan of a CRRT filter under ideal conditions?
A. 6–8 hours
B. 12–24 hours
C. 24–72 hours
D. 5 days
✅ Answer: C – Most filters are designed for 24–72 hours
Q9. In which condition is citrate anticoagulation contraindicated?
A. Trauma
B. Liver failure
C. Sepsis
D. Hypokalemia
✅ Answer: B – Citrate is metabolized in the liver
Q10. Which alarm mandates immediate stop of CRRT?
A. High TMP
B. High return pressure
C. Blood leak
D. Low access pressure
✅ Answer: C – Blood leak = filter membrane rupture
Q11. A patient on SCUF is having UF of 200 mL/hr. What is the purpose?
A. Remove potassium
B. Remove urea
C. Control acidosis
D. Remove excess fluid
✅ Answer: D – SCUF is for volume removal only
Q12. Your ICU lacks phosphate-containing fluids. What is the most likely risk?
A. Alkalosis
B. Hypophosphatemia
C. Hyperkalemia
D. Anemia
✅ Answer: B – CRRT removes phosphate → supplementation needed
Q13. Which of the following supports adsorption in CRRT?
A. SCUF
B. CytoSorb filter
C. High UF rate
D. Dialysate with phosphate
✅ Answer: B – CytoSorb is designed for cytokine adsorption
Q14. Patient has MAP 60 mmHg, norepinephrine 0.2 mcg/kg/min, lactate 5.2. Cr is 2.1 → 3.4 in 24h. What's your move?
A. Observe
B. Start IHD
C. Start CRRT
D. Give diuretics
✅ Answer: C – Meets criteria for early CRRT in septic shock
Q15. Which site is least ideal for long-term CRRT access?
A. Right IJ
B. Femoral vein
C. Subclavian vein
D. Left IJ
✅ Answer: C – Subclavian increases risk of central venous stenosis
🖋️ Final Words
This guide reflects a dedication to clinical excellence, collaboration, and the pursuit of life-saving precision in critical care.
Combining advanced ICU strategies with practical solutions for limited-resource settings, this work aims to empower clinicians, trainees, and anesthesia teams with the clarity and confidence needed to deliver safe and effective CRRT at the bedside.
With deep gratitude to Dr. Layla Ali Hakeem for her invaluable academic contribution, and to all those committed to better patient outcomes through education and continuous learning.
Stay committed. Stay curious. Stay kind.
—
Explore the full collection of completed guides at:
🔗 Mastery Guide Series: https://justpaste.it/jkd89
Prepared by Dr. Amir Fadhel
Board-Certified Anesthesiologist & Intensivist
In collaboration with Sophia, your AI-powered clinical assistant 💙
📅 Date Created: 31/05/2025
🛠️ Last Edited: 03/09/2025