Modalities of Renal Replacement Therapy
| Modality | Full Name | How It Works | When Used |
| CVVH | Continuous veno-venous haemofiltration | Convection — blood driven across membrane; water and small solutes removed by pressure | Most common in ICU; haemodynamically unstable patients; continuous 24h therapy |
| CVVHD | Continuous veno-venous haemodialysis | Diffusion — solutes move down concentration gradient across membrane into dialysate | Better small solute clearance; useful for uraemia and electrolyte clearance |
| CVVHDF | Continuous veno-venous haemodiafiltration | Combination of convection and diffusion | Most comprehensive continuous modality; preferred when both fluid and solute management needed |
| IHD | Intermittent haemodialysis | Diffusion; 3–4 hour sessions, typically alternate days | Haemodynamically stable patients; better in ward/outpatient setting; faster toxin clearance |
| SLED | Sustained low-efficiency dialysis | Extended (8–12h) IHD at slower flow rates | Bridge between CVVH and IHD; haemodynamically marginal patients |
| Peritoneal dialysis | PD catheter into peritoneum; dialysate dwells and removed | Diffusion across peritoneal membrane | Rarely used in ICU; useful in paediatrics; contraindicated post-abdominal surgery |
CLINICAL PEARL The timing of RRT initiation in AKI without absolute indications (hyperkalaemia, acidosis, fluid overload) remains controversial. The STARRT-AKI trial found no difference in 90-day mortality between accelerated and standard initiation strategies. Initiate RRT when absolute indications are present; do not delay when they are, and do not initiate early without good clinical reason.