Understanding the fundamental principles of continuous venovenous hemofiltration (CVVH), how it differs from hemodialysis, and its use in the critically ill patient is essential for all intensivists.
CVVH should be the intensivist’s first choice as renal replacement therapy for any intensive care unit (ICU) patient with hemodynamic instability.
Continuous renal replacement therapy (CRRT) is most often prescribed based on body weight to an effluent flow rate target of 20 to 25 mL/kg/h. Effluent flow rates higher than 25 mL/kg/h do not improve outcomes in ICU patients.
Anticoagulation is generally recommended, as the clotting cascades are activated when the blood interfaces with the nonendothelial surfaces of the tubing and filter.
Administration of replacement fluid (RF) maintains fluid balance and lowers the plasma concentration of solute by dilution. Typical RF rates are 1000 to 2000 mL/h.
CVVH is a form of CRRT that has a slower rate of solute or fluid removal per unit of time. It is generally better tolerated than conventional intermittent hemodialysis as many of the complications of hemodialysis are related to the rapid rate of solute and fluid loss as well as complement-induced hypotension. Acute kidney injury (AKI) occurs in up to 70% of patients admitted to the ICU and is associated with an increased mortality rate.1 CRRT is the treatment of choice in critically ill septic patients in the ICU.2,3 Sepsis leads to renal hypoperfusion and subsequent volume resuscitation that cannot be autoregulated by the already insufficient kidney. This is further compounded by the numerous nephrotoxic medications and contrast agents used in diagnosis and treatment. Mortality from AKI is commonly the result of multiorgan system failure (MOSF). Growing evidence suggests that AKI may also damage the lungs, brain, heart, or liver. Some forms of renal replacement therapy (RRT) may prevent MOSF.4 There is also evidence that fluid overload increases mortality and that volume control can improve outcomes.5,6,7 This has shifted the trend toward more aggressive and earlier RRT.
THE RIFLE AND ACUTE KIDNEY INJURY NETWORK CLASSIFICATIONS OF ACUTE KIDNEY INJURY
The acute dialysis quality initiative (ADQI) developed the following classification of AKI to foster uniformity in both research and clinical practice (Tables 99–1 and 99–2).
Table 99–1RIFLE classification. |Favorite Table|Download (.pdf) Table 99–1 RIFLE classification.
| ||GFR Criteria ||Urine Output Criteria |
|Risk ||Increased serum creatinine × 1.5 or GFR decrease > 25% ||UO < 0.5 mL/kg/h × 6 h |
|Injury ||Increased serum creatinine × 2 or GFR decrease > 50% ||UO < 0.5 mL/kg/h × 12 h |
|Failure ||Increased serum creatinine × 3, GFR decrease > 75% or serum creatinine > 4 mg/dL (acute rise > 0.5 mg/dL) ||UO < 0.3 mL/kg/h × 24 h or anuria × 12 h |
|Loss ||Persistent AKI: complete loss of kidney function > 4 wk || |
|ESKD ||End-stage kidney disease: complete loss of kidney function > 3 mo || |
|AKIN 1 ||Increased serum creatinine by 1.5-2× above baseline or by 0.3 mg/dL ||UO < 0.5 mL/kg/h × 6 h |