Pathophysiology
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.