CRRT for ICU Nurses: Essential Knowledge Guide
What CRRT Is and Why We Use It
CRRT is a continuous (24-hour) extracorporeal blood purification therapy that replaces kidney function in critically ill patients, primarily those who are hemodynamically unstable and cannot tolerate the rapid fluid and solute shifts of intermittent hemodialysis. 1, 2
- CRRT removes excess fluid and retained solutes through diffusion, convection, ultrafiltration, and adsorption 3
- The key advantage over intermittent hemodialysis is better hemodynamic stability, slower solute shifts, and superior fluid removal tolerance 1
- CRRT is specifically indicated for patients with acute brain injury or increased intracranial pressure, as intermittent dialysis causes more dangerous ICP fluctuations 1, 4
CRRT Modalities You'll Encounter
Three Main Types
CVVH (Continuous Venovenous Hemofiltration):
- Uses convection as the primary mechanism—think of it as filtering blood like a coffee filter 5
- Produces ultrafiltrate that must be replaced with replacement solution 5
CVVHD (Continuous Venovenous Hemodialysis):
- Uses diffusion as the primary mechanism—solutes move across a concentration gradient 5, 3
- Dialysate flows countercurrent to blood at 1-2 L/hour 5, 3
- Best for hyperammonemia due to higher ammonia clearance rates 3
CVVHDF (Continuous Venovenous Hemodiafiltration):
- Combines both diffusion and convection—this is the most commonly used modality 5, 2
- Provides both dialysate flow and replacement fluid 5
Vascular Access: What You Need to Know
Site selection follows this strict hierarchy: 4, 3
- Right internal jugular vein (first choice)
- Femoral vein (acceptable, but inferior in obese patients)
- Left internal jugular vein
- Subclavian vein (LAST resort only) due to high thrombosis and stenosis risk 4, 3
Critical Access Points:
- Always use ultrasound guidance for catheter insertion 1, 4
- Use an uncuffed nontunneled dialysis catheter of adequate length to prevent recirculation 1, 4
- Obtain chest X-ray immediately after internal jugular or subclavian placement before first use 1, 4
- Catheter must be appropriate gauge and length—inadequate length causes access recirculation and malfunction 1
Anticoagulation: Your Monitoring Priorities
Regional citrate anticoagulation is first-line for patients without contraindications 1, 4, 3
Anticoagulation Algorithm:
- Assess bleeding risk first 4
- If no increased bleeding risk: Use regional citrate anticoagulation 4
- If citrate contraindicated: Use unfractionated or low-molecular-weight heparin 4
- If heparin-induced thrombocytopenia (HIT): Use direct thrombin inhibitors or Factor Xa inhibitors 4
What You Must Monitor with Citrate:
- Anticoagulant effect and filter efficacy 5
- Circuit life and complications 5
- Risk of both metabolic alkalosis and metabolic acidosis 1
CRRT Dosing: The Numbers That Matter
Target effluent volume: 20-25 mL/kg/h 1, 4, 5, 3
Critical Dosing Concepts:
- Prescribed dose ≠ delivered dose—the delivered dose frequently falls short 5
- You must frequently assess actual delivered effluent volume and adjust the prescription 1, 4
- Blood flow rate is controlled by the blood pump (unlike older arteriovenous systems) 3
- Dialysate flow rate for CVVHD: 1-2 L/hour 5, 3
Important Evidence:
- The RENAL and ATN trials showed no mortality benefit with higher intensity therapy (>25 mL/kg/h) 5
- Standard filter surface area: 0.9-1.5 m² for most adults 3
Fluid Management: What Goes In and Out
Always use bicarbonate-buffered solutions, NOT lactate 1, 4, 3
Specific Fluid Rules:
- Bicarbonate is mandatory for patients with circulatory shock 1, 4
- Bicarbonate is mandatory for patients with liver failure or lactic acidemia 1, 4, 3
- Lactate-buffered solutions worsen acidosis in these patients 1
- Avoid fluids with supra-physiologic glucose concentrations to prevent hyperglycemia 4
Fluid Balance Monitoring:
- Avoid volume overload, especially in acute lung injury patients 1, 4
- Use integrated fluid balancing systems, never adapted IV pumps (high error risk) 1, 4
- Calculate net ultrafiltration rate based on volume status and hemodynamic tolerance 3
Filter and Circuit Management
Use dialyzers with biocompatible membranes 1, 4, 3
When to Consider Pre-Dilution:
- Frequent filter clotting 1, 4
- Extracorporeal clearance limited by achievable blood flow 1, 4
- May enhance ultrafiltration rate in high-volume CVVH 1
Circuit Monitoring:
- Monitor filter performance continuously 3
- Assess for clotting, pressure alarms, and blood flow issues 6
- Pre-dilution reduces solute clearance efficiency but extends filter life 1
Medication Dosing: Critical Considerations
Therapeutic drug monitoring is essential for beta-lactam antibiotics and other dialyzable medications 5
Key Medication Principles:
- Piperacillin/tazobactam half-lives are significantly shorter with CVVHDF compared to CVVH 5
- Drug clearance varies with dialysate flow rate—higher flow = more elimination 5
- Residual kidney function significantly impacts drug clearance, especially with CrCl >50 mL/min 5
- Amino acids, proteins, vitamins, trace elements, potassium, and phosphate are lost in dialysate 1, 7
Catheter Care: Infection Prevention
Do NOT use topical antibiotics over the skin insertion site 1, 4
Do NOT use antibiotic locks for infection prevention 1, 4
- These recommendations are based on lack of efficacy and potential for resistance 1
- Standard sterile technique and proper site care are sufficient 1
Common Pitfalls and How to Avoid Them
Timing of Initiation:
- Do NOT rely on single BUN/creatinine thresholds alone—consider the broader clinical context including fluid overload, electrolyte abnormalities, and uremic complications 4
- Do NOT use diuretics to enhance kidney recovery or reduce RRT duration/frequency 4
Hemodynamic Management:
- CRRT is preferred over intermittent hemodialysis for hemodynamically unstable patients 1, 4
- Only a few critically ill AKI patients can tolerate conventional hemodialysis schedules 1
Monitoring Priorities:
- Electrolyte balance (especially calcium with citrate) 3
- Acid-base status 3
- Fluid balance—prescribed vs. actual removal 1, 4
- Filter performance and circuit pressures 3
When to Transition or Discontinue
Transition from CRRT to intermittent hemodialysis when: 1
- Vasopressor support has been stopped
- Intracranial hypertension has resolved
- Positive fluid balance can be controlled by intermittent hemodialysis
Discontinue CRRT when: 1
- Kidney function has recovered
- RRT becomes inconsistent with shared care goals
Special Situations
CRRT with ECMO:
- CRRT is the appropriate modality during extracorporeal life support due to hemodynamic instability 1
- Requires multidisciplinary coordination for circuit integration 1
- No clear evidence on optimal integration strategy—depends on local expertise 1