Continuous renal replacement therapy is one of the most technically demanding skills in ICU nursing. Understanding modes, anticoagulation strategies, and how to troubleshoot alarms at 3 AM without calling the fellow first is what separates an experienced ICU nurse from a truly specialized one.
Standard hemodialysis removes solutes and fluid rapidly over 3-4 hours. For hemodynamically unstable ICU patients — septic shock, cardiogenic shock, multi-organ failure — that speed is the problem. Rapid fluid and solute shifts cause hypotension, cardiovascular stress, and cerebral edema in vulnerable patients. CRRT removes solutes and fluid slowly and continuously over 24+ hours, maintaining hemodynamic stability while providing renal support.
| Mode | Full Name | Mechanism | Primary Use |
|---|---|---|---|
| SCUF | Slow Continuous Ultrafiltration | Convection only — removes fluid | Fluid overload without significant uremia |
| CVVH | Continuous Veno-Venous Hemofiltration | Convection — removes solutes AND fluid via replacement fluid | Sepsis, toxin removal, AKI with fluid overload |
| CVVHD | Continuous Veno-Venous Hemodialysis | Diffusion — dialysate flows countercurrent | Uremia, electrolyte management |
| CVVHDF | Continuous Veno-Venous Hemodiafiltration | Both convection and diffusion | Most common in ICU — best solute and fluid removal |
Most ICU patients will be on CVVHDF. Know all four modes in case you need to understand why a mode was chosen or what changed.
The key components of the CRRT circuit from a nursing management standpoint:
Without anticoagulation, the circuit clots within hours. Two primary strategies:
| Alarm | Likely Cause | First Response |
|---|---|---|
| Access Pressure too negative (below -150 to -200 mmHg) | Catheter position, kinking, clot at tip, patient position | Reposition patient and catheter; flush catheter; check for kinking; may need to reduce blood flow rate temporarily |
| Return Pressure too positive (above +200 mmHg) | Filter clotting, kinking in return line, thrombosis | Check for kinks in return line; assess filter for clot signs; may need new circuit |
| TMP (Transmembrane Pressure) rising | Early filter clotting, high filtration fraction | Check anticoagulation; may need to reduce effluent rate; if TMP >300 mmHg, filter is clotting — replace |
| Air Detected | Loose connection, empty fluid bag, air in circuit | Check all connections immediately; clamp circuit and assess; never resume until air source identified and resolved |
| Blood Leak (in effluent) | Filter membrane rupture | Stop CRRT immediately; clamp circuit; notify physician; do not return blood in circuit — discard and replace |
| Low Blood Flow | Access problem, pump issue, low flow rate ordered | Check catheter and lines; reposition patient; if persistent, notify physician — inadequate blood flow decreases clearance |
CRRT gives you precise control over fluid balance that no other modality offers. The physician orders a net fluid removal rate — for example, "negative 100 mL/hour" — and the machine calculates total fluids in (replacement fluid + dialysate) minus total fluids out (effluent) to hit that target.
Your job is to account for every other fluid the patient receives — IV drips, blood products, flushes — so that the net balance at the end of the shift actually matches the goal. A patient on CRRT who receives 2L of unexpected blood products and fluids during a procedure but whose CRRT wasn't adjusted will end the shift with very different fluid balance than intended.
CRRT removes electrolytes along with fluid and solutes. Monitoring frequency and what to watch:
Recovery signs: urine output returning (>0.5 mL/kg/hr for 6+ hours), creatinine trending down, hemodynamics stable enough for intermittent HD, patient improving toward ICU-level step-down. The transition off CRRT typically involves a trial period of monitoring urine output with circuit off before the catheter is removed.
This guide is for educational purposes. CRRT management protocols vary by institution and machine type. Follow your facility's specific protocols and the orders of the m
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