Continuous Renal Replacement Therapy Modalities

Mechanism of Solute Removal

CVVHD uses diffusion as the primary mechanism of solute removal, where dialysate solution flows countercurrent to blood flow across a semipermeable membrane 1
CVVH uses convection, where ultrafiltrate is produced and replaced with replacement solution, with solute removal occurring through convective transport 1

In CVVHD, dialysate solution is delivered across the membrane at rates typically 1-2 L/hour, and fluid replacement is not routinely administered 1
In CVVH, ultrafiltrate produced is replaced with replacement solution, and ultrafiltration in excess of replacement results in patient volume loss 1

CVVH is generally more efficient at removing middle and high molecular weight solutes compared to CVVHD, though this enhanced solute removal has not been proven to influence clinical outcomes 2

When middle to large molecular weight solute removal is prioritized, such as in certain inflammatory conditions, CVVH may be preferred 2
When there may be benefits from enhanced cytokine removal, though clinical outcome benefits remain unproven, CVVH may be considered 2

Both modalities typically aim for an effluent volume of 20-25 mL/kg/h for adequate solute clearance in acute kidney injury 3
High-volume hemofiltration is a variant of CVVH that employs ultrafiltration volumes greater than 35 mL/kg/h 4
Regional citrate anticoagulation is the first choice for patients without increased bleeding risk for both modalities 3
Using subclavian veins for vascular access increases risk of thrombosis and stenosis, regardless of modality choice 3

CVVHD provides higher ammonia clearance rates than CVVH, making it preferable for hyperammonemia management, according to the American College of Nephrology 5

CVVHD is superior to conventional HD and PD in infants for maintaining hemodynamic stability by removing isotonic fluid, as recommended by the American Academy of Pediatrics 5
All CRRT modalities result in fewer cardiovascular complications compared to intermittent HD, as stated by the National Institute of Diabetes and Digestive and Kidney Diseases 5
Warmed dialysate in neonates provides added hemodynamic stability, according to the American Heart Association 5