Updated July 2026 · 11 min read

CRRT vs Hemodialysis in the ICU 2026

Part of the ICU Devices Hub — browse every related guide in one place.

Medical Disclaimer: This article is general educational information for licensed clinicians, not medical advice. Always follow your institution's protocols and provider orders. Management of renal replacement therapy requires physician/APRN direction.

Acute kidney injury (AKI) requiring renal replacement therapy (RRT) is common in the ICU, occurring in 5 to 10% of critically ill patients. The choice between continuous renal replacement therapy (CRRT) and intermittent hemodialysis (IHD) is driven by patient hemodynamics, goals of fluid management, and logistical considerations. ICU nurses manage CRRT circuits for hours to days at a time; understanding the physiology and troubleshooting the circuit is bedside-critical knowledge.

CRRT Modalities Explained

CRRT encompasses several closely related modalities, each named for the primary mechanism of solute clearance:

When to Choose CRRT Over IHD

CRRT is preferred when any of the following apply: hemodynamic instability (requiring vasopressors, MAP <65 mmHg, or labile blood pressure that would not tolerate rapid fluid shifts), fluid overload requiring aggressive volume removal beyond what IHD can achieve tolerably, elevated intracranial pressure (cerebral edema — rapid osmolarity shifts with IHD can worsen ICP), hyperammonemia requiring sustained solute removal, or any situation where 24-hour continuous fluid balance control is clinically necessary.

IHD is appropriate for: hemodynamically stable patients, those with reliable outpatient hemodialysis access returning to established ESRD regimens, situations where the patient needs to mobilize/undergo procedures during the day, or when CRRT is not available or the circuit is repeatedly clotting and the patient is stable enough for IHD.

CRRT Circuit Management — Nursing Essentials

Circuit access and setup

CRRT requires a large-bore dialysis catheter (typically a 13.5 Fr dual-lumen or triple-lumen catheter) in a large central vein — typically the internal jugular, subclavian, or femoral vein. Femoral access has the shortest circuit life in ambulatory or repositioning patients (higher rate of kinking and clotting) but is sometimes necessary. The circuit includes the blood lines, hemofilter (the semipermeable membrane), and either dialysate, replacement fluid, or both depending on the modality.

Anticoagulation

CRRT circuits clot without anticoagulation, but systemic anticoagulation carries bleeding risk in ICU patients who are often coagulopathic. Two main approaches are used:

Regional citrate anticoagulation (RCA) is the preferred method at most centers. Citrate is infused pre-filter and chelates ionized calcium (Ca²⁺), which is essential for coagulation, within the circuit. Calcium is replenished systemically in the return line. RCA achieves excellent circuit life (24-48+ hours) without systemic anticoagulation. Monitoring: check ionized calcium (iCa) in both systemic and circuit blood (the post-filter sample) per protocol. Total calcium/ionized calcium ratio >2.5 suggests citrate accumulation — a serious complication requiring circuit discontinuation and assessment.

Unfractionated heparin (UFH) is used when citrate is contraindicated (liver failure impairs citrate metabolism, making citrate accumulation likely; citrate-sensitive patients). Heparin is infused pre-filter; monitor anti-Xa levels or aPTT per protocol.

Effluent rate and dose

CRRT dose is typically prescribed as effluent volume in mL/kg/hour. Current evidence (ATN and RENAL trials) supports a dose of 20 to 25 mL/kg/hour as adequate for most patients — higher doses do not improve outcomes and increase nursing workload. Fluid balance is managed by adjusting the net ultrafiltration rate (the difference between fluid removed and replacement fluid infused). The target net fluid removal is prescribed by the clinical team and must be monitored and adjusted continuously by the bedside nurse.

Troubleshooting Circuit Clotting

Circuit clotting is the most common CRRT complication, resulting in circuit downtime, blood loss (blood remaining in the circuit when it clots is discarded), and interruption of therapy. Warning signs of impending clotting: rising transmembrane pressure (TMP), rising filter pressure, increasing pre-filter pressure, decreasing filtration fraction. When these trend upward, notify the team and consider flushing the circuit with saline, adjusting anticoagulation, or preparing for a circuit change.

Transitioning from CRRT to IHD

Most ICU AKI patients who survive and recover kidney function (or who stabilize hemodynamically) eventually transition from CRRT to IHD and ultimately to no RRT. Transition to IHD is appropriate when: the patient has been hemodynamically stable off vasopressors for 24 to 48 hours, fluid balance can be managed with intermittent sessions, and the team agrees the patient no longer needs 24-hour continuous therapy. Early involvement of nephrology in transition planning prevents unnecessary prolongation of CRRT.

Related: acute kidney injury and CRRT, ICU sepsis bundle, vasopressor titration guide.