Continuous Renal Replacement Therapy

Continuous renal replacement therapy (CRRT) treats acute kidney injury by gradually removing uremic toxins and excess fluids over 24 hours while maintaining acid-base balance and stabilizing electrolytes. Unlike faster intermittent hemodialysis, CRRT provides a gentler approach that closely mimics natural kidney function, making it particularly suitable for hemodynamically unstable patients who cannot tolerate rapid fluid shifts.

Continuous venovenous hemofiltration (CVVH) uses ultrafiltration to remove excess fluid and solutes, making it ideal for patients with fluid overload and unstable blood pressure. Continuous venovenous hemodialysis (CVVHD) incorporates a dialysate solution that enhances toxin removal through diffusion, allowing solutes to move from blood into the dialysate. CVVHD provides more comprehensive solute removal than CVVH alone.

The hemofilter contains hollow fibers that extract plasma water and solutes using hydrostatic and osmotic pressure. Blood is pumped through the hemofilter, where this pressure gradient generates an ultrafiltrate containing waste products and excess fluid. The ultrafiltrate drains into a collection device while filtered blood is reinfused into the patient, completing the continuous filtration cycle.

CRRT requires a double-lumen catheter, typically placed in the jugular, femoral, or subclavian vein. This catheter allows simultaneous blood withdrawal and reinfusion through separate lumens. The double-lumen design enables continuous blood circulation through the CRRT circuit without interruption, maintaining steady filtration and solute removal throughout the 24-hour treatment period.

Nursing management involves daily monitoring of patient weight, lab values, and fluid balance to ensure proper electrolyte management. Hourly assessments of hemodynamic stability, intake and output, and catheter patency are crucial for preventing complications. A clear yellow ultrafiltrate indicates proper function, while blood-tinged ultrafiltrate suggests filter membrane rupture, requiring immediate cessation of therapy to prevent blood loss.

Replacement fluids are infused before (pre-filter) or after (post-filter) the hemofilter to maintain the patient's fluid and electrolyte balance. Pre-filter infusion reduces filter clotting risk, while post-filter infusion helps dilute remaining solutes like urea and creatinine. The ultrafiltration rate is typically set between 0 and 500 mL per hour and adjusted based on the patient's fluid balance needs and electrolyte status.

CRRT may continue for weeks depending on the patient's condition and kidney function recovery. The hemofilter requires replacement every 24 to 48 hours to ensure efficient filtration and reduce clotting risk. Once acute kidney injury resolves or CRRT is no longer clinically indicated, therapy is discontinued and the double-lumen catheter is removed from the patient.