CVVHD Duration: 24 Hours Per Day
CVVHD (continuous venovenous hemodialysis) is performed continuously for 24 hours per day, as defined by international consensus guidelines. 1
Definition and Duration
The First International Consensus Conference on Continuous Renal Replacement Therapy explicitly defines CRRT (which includes CVVHD) as:
- Any extracorporeal blood purification therapy intended to substitute for impaired renal function over an extended period of time
- Applied for, or aimed at being applied for, 24 hours per day 1
This distinguishes CVVHD from intermittent therapies, which are prescribed for 12 hours or less per day and include techniques like extended daily dialysis (EDD) and sustained low-efficiency dialysis (SLED) 1.
Technical Characteristics of CVVHD
CVVHD specifically involves 1:
- Driving force: External blood pump (venovenous circuit)
- Dialysate delivery: Countercurrent to blood flow at substantially slower rates than blood flow (typical dialysate flow rates are 1-2 L/hour)
- Solute removal: Primarily by diffusion
- Fluid replacement: Not routinely administered (unlike hemofiltration)
Clinical Reality
While the definition specifies 24-hour application, actual clinical practice shows that treatment may be interrupted for procedures or complications. Research confirms that 24-hour CVVH treatment on intensive care units is attainable with adequate staff instruction 2, though some modern protocols use shorter durations (10-12 hours) for specific indications 3.
Key Caveat
The "continuous" designation means the therapy is intended to run 24 hours per day, distinguishing it fundamentally from intermittent modalities. This continuous nature provides hemodynamic stability in critically ill patients, which is the primary advantage over intermittent hemodialysis 2.