CVVHD vs HD: Key Differences
CVVHD (Continuous Venovenous Hemodialysis) is a continuous therapy running 24 hours per day using diffusion for solute removal, while HD (Hemodialysis) is an intermittent therapy typically running ≤12 hours using the same diffusive mechanism but at higher intensity. 1
Fundamental Operational Differences
Duration and Delivery
- CVVHD: Continuous therapy intended for 24-hour application, using an external pump to drive blood through a venovenous circuit 1
- HD: Intermittent therapy prescribed for ≤12 hours, typically 3-4 hours per session 1
Mechanism of Solute Removal
Both modalities use diffusion as their primary mechanism 1. Dialysate flows countercurrent to blood at rates of 1-2 L/hour in CVVHD (much slower than blood flow), while HD uses higher dialysate flow rates during shorter treatment periods 1.
Hemodynamic Tolerance
CVVHD is specifically designed for hemodynamically unstable patients 2. The continuous, gentle nature of fluid and solute removal makes it superior in critically ill patients with cardiovascular instability 3, 2. In contrast, intermittent HD can cause rapid fluid shifts that unstable patients cannot tolerate 2.
Clinical Application Context
Patient Selection
- CVVHD: Reserved for critically ill ICU patients with acute renal failure who are hemodynamically unstable, often requiring vasopressors 4
- HD: Used in more stable patients or those with less severe illness 4
Mortality and Outcomes
The evidence shows nuanced findings:
- When CVVHD patients appear to have higher crude mortality, this reflects selection bias—CVVHD is applied to sicker patients with higher APACHE scores and more organ failures 4, 5
- After adjusting for illness severity, CVVHD shows survival benefit in patients with intermediate severity (APACHE II 24-29) and those with 2-4 failing organs 6
- In patients with APACHE III scores >103, CVVHD provides survival opportunity where HD shows 0% survival 4
Practical Considerations
Resource Utilization
- CVVHD is significantly less expensive: Daily treatment costs of $775 vs $1,813 for CVVH (a related continuous modality) 7
- CVVHD requires continuous ICU nursing presence but causes fewer complications (1 vs 18 complications in one study) 6
Specific Clinical Scenarios
Use CVVHD when:
- Systolic blood pressure <90 mmHg
- Multiple organ failure (≥3 organs)
- Severe hemodynamic instability requiring vasopressors
- Need for continuous fluid management in acute lung injury
- Subdural hematoma with ESRD (lower expansion risk with CVVHD) 8
Use HD when:
- Patient is hemodynamically stable
- Fewer organ failures
- Outpatient or chronic dialysis setting
- Need for rapid, high-efficiency solute removal in stable patients
Dosing Differences
- HD: Minimum Kt/V of 1.2 delivered three times weekly 1
- CVVHD: Dose measured by continuous clearance; no direct Kt/V equivalent but provides steady-state solute control 1
Common Pitfalls
- Don't use HD in hemodynamically unstable patients—this is the primary indication for CVVHD 2
- Don't assume CVVHD has worse outcomes—crude mortality differences reflect patient selection, not treatment efficacy 5
- Don't overlook the cost-effectiveness of CVVHD compared to other continuous modalities 7
The choice between CVVHD and HD fundamentally depends on hemodynamic stability and illness severity, not on theoretical advantages in solute clearance, as both use diffusion with similar efficiency for low-molecular-weight solutes 1.