The candidates have been asked to compare different CRRT modalities in numerous past paper questions:
- Question 21 from the second paper of 2015 - IHD vs SLED vs CVVHDF
- Question 10 from the first paper of 2011 -CVVHD vs IHD vs SCUF
- Question 19 from the second paper of 2008 - CVVHF vs SLED vs IHD
- Question 2c from the second paper of 2001 - "List the available dialytic therapies and their associated advantages/disadvantages"
Typically, the college has expected the answers to be presented in a tabulated format. The table below makes an attempt to combine all these tables into a single reference. It has had to be split into two, so as not to induce severe strain among the eyesight-impaired readers.
| Modality | SCUF | PD | CAVH |
| Access | Vas cath | PD abdominal catheter | Arterial catheter |
| Flow rate | Low flow rate; 50-200ml/min |
nil; rather, fluid dwell time is the important feature | Arterial flow rate |
| Anticoagulation | Continuous | None | Intermittent boluses may be required |
| Fluid removal | Medium | Slow | Slow |
| Electrolyte removal | Slow; by convection |
Very slow; by diffusion alone |
Slow; by convection (mainly) |
| Efficiency of solute clearance | Very low (minimal, really) - but it is not meant for solute clearance |
Poor efficiency of fluid and electrolyte clearance | Low However, good solute clearance is ultimately achieved over a prolonged course |
| Hemodynamic impact | Very well tolerated | Tolerated by most patients | Unsuitable for hemodynamically unstable patients - arterial flow rate may be too low |
| Cost | Expensive | Cheap | Cheap |
| Advantages | Achieves good fluid removal Well tolerated unless very unstable |
Does not require anticoagulation. Patient's blood is not exposed to the circuit Intermittent, thus less labour intensive; Allows periods of mobility for the patient Well tolerated unless very unstable |
Anticoagulation may not be required; Pump may not be required |
| Disadvantages | |||
| Poor solute clearance Slow and inefficient |
Poor solute clearance Requires abdominal access Potential for peritonitis |
Requires arterial access Dependent on arterial flow rates without a pump Poor solute clearance |
| Modality | CVVHD | CVVHF | CVVHDF | IHD |
| Access | Vas cath | Vas cath | Vas cath | Vas cath or fistula |
| Flow rate | Low flow rate ; 50-200ml/min | High flow rate up to 500ml/min |
||
| Anticoagulation | Continuous | Intermittent boluses or saline flushes | ||
| Fluid removal | Slow | Rapid | ||
| Electrolyte removal | Slow; mainly diffusion |
Slow; mainly convection |
Slow; Convection and diffusion |
Rapid; by convection and diffusion |
| Efficiency of solute clearance | Low However, good solute clearance is ultimately achieved over a prolonged course |
High efficiency; however the short couse of treatment and the intermittent nature of the treatment results in less solute clearance than CVVHDF |
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| Hemodynamic impact | Well tolerated | Unsuitable for hemodynamically unstable patients | ||
| Cost | Expensive | Cheaper | ||
| Advantages | Well tolerated hemodynamically | Rapid Rarely requires anticoagulation Allows mobilization May access fistula |
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| Good clearance of small molecules Good control over electrolyte and acid-base |
Good clearance of middle molecules Good control over fluid removal and solute exchange |
Good clearance of middle molecules Good control over fluid removal and solute exchange Good control over acid-base balance |
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| Disadvantages | Expensive Requires anticoagulation Prolonged immobilization Slow and inefficient |
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| Electrolyte and acid-base control is better with CVVHDF | Electrolyte and acid-base control is faster with SLEDD and IHD | Poorly tolerated by hemodynamically unstable patients Risk of disequilibrium syndrome |
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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.