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Continuous renal replacement therapy (CRRT) set-ups

Different options as standard therapies for acute kidney injury

  • Continuous Veno-Venous Hemodialysis (CVVHD)
  • Continuous Veno-Venous Hemofiltration (CVVH)
  • Continuous Veno-Venous Hemodiafiltration (CVVHDF)
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CRRT at a glance

Continuous Renal Replacement Therapy (CRRT)
Controls the patient’s fluid status, by enabling gentle fluid removal
Cleans the patient’s blood with an electrolyte solution
Removes uremic toxins
Corrects electrolyte and acid base abnormalities
Requires extracorporeal blood circuit (“veno-venous access”)
Normally a continuous therapy, but may be unavoidably interrupted – for example, due to bag and filter changes, surgery, CT scans etc.

Advantageous CRRT variants: CVVHD and post-dilution CVVHDF

  • CVVHD and post CVVHDF enable efficient use of CRRT-fluid. Any predilution would dilute uremic toxins and reduce efficacy of CRRT-fluid usage.
  • Minimal or limited hemoconcentration with CVVHD and post CVVHDF contributes to better filter potency. Pure post CVVH would require high blood flows to limit hemoconcentration, which practically can be difficult to realize.
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multiFiltrate Ci-Ca® EMiC®2

When Ci-Ca® and EMiC®2 are combined the patient benefits from an established Ci-Ca CVVHD protocol as well as an increased middle-molecule clearance. For more details see:

EMiC®2 filter 

Continuous Veno-Venous Hemodialysis (CVVHD)

CVVHD is a diffusion based therapy. Blood is pumped through the blood compartment of the filter and dialysate flows counter-currently. The counter-current flow optimizes the diffusion gradient and, thus the resulting clearances. Practically with CVVHD, dialysate flow is clearly smaller than the blood flow, corresponding to clearances closely related to dialysate flow.

 
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Continuous Veno-Venous Hemodialysis (CVVHD)

 

Continuous Veno-Venous Hemofiltration (CVVH)

CVVH is a convection based therapy. Blood is pumped through the blood compartment of the filter and a significant filtrate flow is produced by action of the filtrate pump. This filtrate flow requires compensation by infusion of a substitution fluid to the blood flow pre- or post-filter. This way, high filtrate flows can be generated which enhances solute removal.

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Continuous Veno-Venous Hemofiltration in post-dilution (Post-CVVH)

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Continuous Veno-Venous Hemofiltration in pre-dilution (Pre-CVVH)

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Continuous Veno-Venous Hemofiltration in pre-and postdilution (Pre-Post CVVH)

 

Continuous Veno-Venous Hemodiafiltration (CVVHDF)

CVVHDF combines the use of both, diffusion and convection therapies. Blood is pumped through the blood compartment of the filter and dialysate flows counter-currently. The counter-current flow optimizes the diffusion gradient and, thus, the resulting diffusive clearances. In addition, a substitution fluid is infused into the blood flow either pre- or post-filter. This is paralleled by filtration of plasma water across the membrane resulting in convective clearance.

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Continuous Veno-Venous Hemodiafiltration in predilution (Pre-CVVHDF)

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Continuous Veno-Venous Hemodiafiltration in postdilution (Post-CVVHDF)

CRRT vs. iHD

Renal replacement therapy (RRT) for the treatment of acute kidney injury (AKI) is mostly realized as extracorporeal blood purification.

Among the extracorporeal blood purification methods, mainly CRRT and intermittent hemodialysis (iHD) are used to treat AKI. Intermittent hemodialysis means application of RRT as it is otherwise applied in chronic dialysis patients with treatment duration of, e.g., 4 hours.

SLEDD

In addition to CRRT and iHD, hybrid therapies are also used in some centers.

These hybrid therapies are characterized by:

  • Longer therapy duration (e.g., 8 to 12 hours per session) which allows for lower blood and dialysate flows.
  • Daily application (or almost daily). 

One hybrid therapy is SLEDD (Slow Extended Daily Dialysis), which is used to describe slow (meaning relatively low blood and dialysate flows), extended (meaning duration clearly exceeding the typical 4 – 5 hours of iHD) dialysis treatments being applied daily.

From point of both efficacy and patient tolerability, these therapy forms can be considered as in-between CRRT and iHD.

 

The advantages of CRRT and iHD

  • CRRT therapy is steadier and gentler
  • iHD therapy is quicker resulting in faster changes in the patient
  • Renal recovery has been shown to be better with CRRT, including more likely avoidance of chronic dialysis dependency after AKI
  • With respect to mortality, no difference could so far be proven
Advantages of CRRT Advantages of iHD

  • Slow fluid removal possible

    • Better hemodynamic stability

    • No need to restrict infusions / parenteral nutrition

  • Slower, more gentle metabolic / osmotic fluctuations

    • Lower risk for cerebral edema

  • Higher treatment dose possible due to continuous clearance

  • Better recovery of renal function 

  • Faster detoxification, e.g., faster correction of hyperkalemia 

  • Patient immobilized only for a few hours

  • Limited duration of anticoagulation, maybe treatment feasible without anticoagulation 

Multiple large studies from different continents have demonstrated better renal recovery when CRRT was used.1,2,3 Summarizing the results of these and many further studies, Schneider et al. concluded in a meta-analysis, that patients starting treatment of AKI with an intermittent RRT modality “had a 1.7 times increased risk of remaining dialysis dependent as compared with those who initially received CRRT”.4

More recently, Wald et al. published the results of the so far largest study comparing outcome after use of CRRT and iHD.5  This study clearly shows that starting the treatment of AKI with CRRT is associated with significantly better recovery of renal function and a lower incidence of chronic dialysis dependence.

As costs of subsequently needed chronic dialysis have a huge economic impact, Bellomo and Schneider conclude in an accompanying editorial: “The economic case for using conventional IHD [iHD instead of CRRT] collapses as the real cost of IHD is revealed by the study by Wald et al”.6 

In addition to pure economic evaluations, avoiding chronic dialysis after an AKI episode is an important medical and ethical goal given the high burden for the patient associated with chronic dialysis, further supporting the choice of CRRT as initial treatment modality in AKI.

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1 Bell M et al., Intensive Care Medicine (2007); 33: 773-780

2 Uchino et al, The International journal of Artificial Organs (2007); 30: 281-292

3 Lin YF et al, The American Journal of Surgery (2009); 198: 325-332

4 Schneider AG et al., Intensive Care Medicine (2013); 39: 987-997

5 Wald R et al., Critical Care Medicine (2014); 42: 868-876

6 Bellomo R & Schneider AG, Critical Care Medicine (2014); 42: 990-991