Clinical meaning
Continuous renal replacement therapy (CRRT) provides slow, continuous solute and fluid removal over 24 hours in hemodynamically unstable critically ill patients who cannot tolerate conventional intermittent hemodialysis (IHD). CRRT works through three mechanisms: diffusion (solutes move across a semipermeable membrane down concentration gradients -- like hemodialysis), convection (solutes are dragged across the membrane with fluid movement through solvent drag -- like hemofiltration), and ultrafiltration (hydrostatic pressure drives fluid removal). Modalities include CVVHD (continuous venovenous hemodialysis -- primarily diffusion using dialysate), CVVH (continuous venovenous hemofiltration -- primarily convection using replacement fluid), and CVVHDF (continuous venovenous hemodiafiltration -- combines both). CRRT provides superior hemodynamic stability compared to IHD because fluid and solute are removed gradually rather than in rapid 4-hour sessions.
Diagnosis & workup
Diagnostics & workup: - Labs to monitor during CRRT: BMP q6h (electrolytes, BUN, creatinine), ionized calcium (citrate anticoagulation chelates calcium), phosphorus (CRRT removes phosphorus causing hypophosphatemia), magnesium, ABG (acid-base status), CBC - Circuit monitoring: access pressures, filter pressures, transmembrane pressure (TMP -- elevated TMP indicates filter clotting), effluent appearance - Fluid balance calculation: net ultrafiltration rate = total output - total input; precise hourly fluid balance documentation - Clearance adequacy: prescribed dose 20-25 mL/kg/hr effluent rate (KDIGO recommendation); actual delivered dose often lower due to circuit downtime - Anticoagulation monitoring: if regional citrate anticoagulation: post-filter ionized calcium (target 0.25-0.35 mmol/L), systemic ionized calcium (target 1.0-1.2 mmol/L); if systemic heparin: aPTT 45-60 seconds