Guide — Critical Care
CRRT Basics for Nurses
What continuous renal replacement therapy is, why it is used in the ICU instead of standard dialysis, how each modality works, and what nurses monitor throughout therapy.
12 min read · Critical Care
Educational use only. CRRT management is a complex clinical skill requiring institutional training and physician/advanced practice orders. This content is for learning purposes only. Follow your institution's CRRT protocols for all patient care decisions. This material supports nursing education and exam review. It is not medical advice and is not a substitute for clinical judgment, institutional policy, or medical direction. Always follow facility protocols and current provider orders.
What Is CRRT and Why Use It?
Continuous renal replacement therapy (CRRT) is a slow, continuous form of renal replacement therapy performed 24 hours a day. Unlike conventional intermittent hemodialysis (IHD), which removes large amounts of fluid and solutes rapidly over 3–4 hours, CRRT removes them gradually and continuously.
Why CRRT in the ICU? Critically ill patients are often hemodynamically unstable. Rapid fluid and solute shifts during conventional HD cause hypotension in patients who cannot tolerate it. CRRT avoids these shifts by operating slowly — making it the preferred modality for hemodynamically unstable patients with acute kidney injury.
Indications for CRRT
How CRRT Cleans the Blood: Convection vs. Diffusion
Convection (Solvent Drag)
Fluid is pushed across a semipermeable membrane under pressure, carrying solutes with it — like squeezing water through a screen. Larger molecules (middle molecules) are cleared effectively. Requires replacement fluid to maintain volume balance.
Diffusion (Dialysis)
Solutes move across a membrane from an area of high concentration (blood) to low concentration (dialysate flowing countercurrent). Highly effective for small molecules (urea, creatinine, potassium). Does not require replacement fluid.
CRRT Modalities
CVVH — Continuous Veno-Venous Hemofiltration
CVVHD — Continuous Veno-Venous Hemodialysis
CVVHDF — Continuous Veno-Venous Hemodiafiltration
Anticoagulation in CRRT
The extracorporeal circuit triggers the clotting cascade. Anticoagulation is required to maintain filter patency and extend circuit life (target: 24–72 hours per filter).
| Agent | Mechanism | Monitoring | Notes |
|---|---|---|---|
| Systemic Heparin | Systemic anticoagulation via antithrombin III | aPTT 45–60 sec; anti-Xa levels at some centers | Simple; increased bleeding risk; contraindicated in HIT |
| Regional Citrate | Chelates ionized calcium in circuit (Ca2+ required for coagulation) | Ionized Ca2+ in circuit (0.25–0.35 mmol/L), systemic ionized Ca2+ (1.12–1.35 mmol/L) | Preferred when bleeding risk is high; extends filter life; requires calcium replacement infusion |
| Argatroban | Direct thrombin inhibitor; no platelet involvement | aPTT or ACT per protocol | Use when heparin contraindicated (HIT); hepatically metabolized — adjust in liver failure |
| No Anticoagulation | N/A | Visual circuit inspection; filter pressure monitoring | Used when systemic anticoagulation risk is unacceptably high; shorter circuit life expected |
Fluid Management and Net Fluid Removal
CRRT allows precise hourly fluid balance management. The key concept is net ultrafiltration (net UF) — the difference between what is removed (effluent) and what is replaced (replacement fluid + dialysate).
The physician sets a net fluid removal goal (e.g., “remove 100 mL/hr net”). The nurse monitors the cumulative fluid balance and makes adjustments to maintain the prescribed net removal rate, accounting for all other fluid inputs and outputs.
Hypotension is the most common complication of overly aggressive net fluid removal in hemodynamically unstable patients. Monitor BP continuously and notify the provider if MAP drops below target during therapy.
Nursing Monitoring Priorities
NCLEX / CCRN Pearls
- ›CRRT is preferred over intermittent HD in hemodynamically unstable ICU patients because it avoids rapid fluid and solute shifts.
- ›CVVH uses convection only; CVVHD uses diffusion only; CVVHDF uses both — CVVHDF is most common in ICUs.
- ›Regional citrate anticoagulation chelates calcium in the circuit — systemic calcium replacement is always required alongside it.
- ›CRRT can cause profound hypokalemia, hypophosphatemia, and hypothermia — all require active monitoring and correction.
- ›Hypotension during CRRT is usually from overly aggressive net fluid removal; reduce the net UF rate and notify the provider.
- ›Rising transmembrane pressure (TMP) indicates filter clotting — assess anticoagulation adequacy and prepare for filter change.
Related Resources
Standards & sources
Fact-checked Jun 20, 2026This page is written to align with Society of Critical Care Medicine (SCCM) · Surviving Sepsis Campaign · American Association of Critical-Care Nurses (AACN). It is an educational summary, not a citation of any single document — always verify specific doses, values, and protocols against current guidelines and your facility policy. How we source content →