Compare Continuous Venovenous  Haemofiltration (CVVHF) , Sustained Low Efficiency Dialysis (SLED) and Intermittent hemodialysis  (IHD) with respect to

a)  mechanism of solute clearance
b)  advantages and
c)  disadvantages

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College Answer

            CVVH

SLED

IHD

            Mechanism of solute clearance

 Solvent removal occurs as a consequence of a pressure gradient across a semi permeable membrane. Solute removal occurs only by convection (solvent drag).

Solute removal occurs predominantly by diffusion down a concentration gradient created by dialysate fluid on the other side of the semi permeable membrane.

 Solute clearance by diffusion

            Advantages

Achieves better clearance of middle molecules (< 15 Kd) than CVVHD/IHD, fluid management easier and flexible, lesser hemodynamic instability as compared to IHD.

 Can be done at night so patient can be mobilized during the day. Period of anticoagulation reduced. Possible cost savings by using online water and ability for one
machine to deliver 2 treatment episodes per day.

shortest treatment time, anticoagulation often not required, cost  savings by using online water

            Limitations

 Patient immobilized , need for continuous anticoagulation  , higher nursing requirement

 inferior clearance of middle molecules, reduced fluid management flexibility. Higher risk of disequilibrium syndrome

 least clearance of middle molecules, least flexible fluid management, highest risk of disequilibrium syndrome. Possible greater

Discussion

CVVHDF, IHD and SCUF are discussed in this fashion in Question 10 from the first paper of 2011.

Thus, the same table can be reproduced here, mutatis mutandis.

An even more expansive table of comparison between all conceivable RRT modalities is available in the Required reading section.

Modality CVVHF SLED IHD
Access Vas cath Vas cath Vas cath or fistula
Flow rate Low flow rate Low flow rate High flow rate
Anticoagulation Continuous May be continuous or intermittent Intermittent boluses
Fluid removal Slow Medium Rapid
Electrolyte removal Slow;
by convection (mainly) and diffusion
Medium rate Rapid;
by convection and diffusion
Efficiency of solute clearance Low
However, good solute clearance is ultimately achieved over a prolonged course
Medium clearance efficacy High efficiency;
however the short couse of treatment and the intermittent nature of the treatment results in less solute clearance than CVVHDF
Hemodynamic impact Well tolerated Tolerated by most patients Unsuitable for hemodynamically unstable patients
Cost Expensive Cheap Cheapest
Advantages

Good clearance of middle molecules

Well tolerated hemodynamically

Good control over fluid removal and solute exchange

Intermittent, thus less labour intensive;

Anticoagulation may not be required;

Intermittent, allowing periods of mobility for the patient

Well tolerated unless very unstable

Less labour intensive;

Anticoagulation may not be required;

Intermittent, allowing periods of mobility for the patient

Disadvantages

Expensive

Requires anticoagulation

Prolonged immobilization

Poorly tolerated by very hemodynamically unstable patients;

Requires reverse osmosis facilities;

Poor fluid management

Limited clearance of middle molecules

Poorly tolerated by hemodynamically unstable patients;

and then there is the risk of disequilibrium syndrome.

References

References

D'Intini, Vincent, et al. "Renal replacement therapy in acute renal failure." Best Practice & research clinical anaesthesiology 18.1 (2004): 145-157.

O'Reilly, Philip, and Ashita Tolwani. "Renal Replacement Therapy III: IHD, CRRT, SLED." Critical care clinics 21.2 (2005): 367-378.

Wei, S. S., W. T. Lee, and K. T. Woo. "Slow continuous ultrafiltration (SCUF)--the safe and efficient treatment for patients with cardiac failure and fluid overload." Singapore medical journal 36.3 (1995): 276-277.

Kanno, Yoshihiko, and Hiromichi Suzuki. "Selection of modality in continuous renal replacement therapy." (2010): 167-172. -This seems to be an entire issue of Contributions to Nephrology (Vol. 166) by Claudio Ronco.