SLED: advantages and disadvantages

Though so far nobody has asked any specific SAQ style questions regarding sustained low-efficiency dialysis (SLED), it will eventually happen. When it does, it may be something like "Critically evaluate SLED as a modality of renal replacement therapy in the ICU".  Question 19 from the second paper of 2008 certainly asks something like that, in the context of a comparison between SLED, IHD and CVVHF.

Those who cannot afford, or are unable to physically lift Critical Care Nephrology can find very helpful information in an older article by Mark Marshall et al (2001), or a more recent 2007 review by Tolwani et al.

Cardinal features which distinguish SLED from CRRT

Its neither IHD or CRRT; its a "hybrid" therapy.

• Employs features of both IHD and CRRT
• Runs for 6-12 hours
• Blood flow rates 100-300ml/min
• Dialysate does not come in pre-made bags: it is either generated from water that comes from a wall outlet, or it is mixed from pre-packaged electrolytes and sterile water.
• "Single-pass" machines use a dialysate generated "on-line" from reverse osmosis purified water
• "Batch" machines contain a huge tank ("batch") full of sterile water mixed with prepackaged salts.
• The dialysate flow rate is usually about 300ml/min, particularly for shorter treatments.

Advantages of SLED

From basic principles, one can establish that

• The sessions are shorter, and therefore the duration of exposure to anticoagulant is shorter.
• The patient is off-circuit for a large portion of the day. In fact, most places perform nocturnal SLED so that the patient can be mobile and active during the day.
• Haemodynamically, it is better tolerated than IHD.

Furthemore, a good pro-SLEDD review has reported several advantages of SLED over CRRT:

• Its cheaper than CRRT - up to 8 times cheaper!
• No need for any anticoagulation (much of the time saline flushes are sufficient)
• Solute removal is equivalent to CRRT.

Disadvantages of SLED

• Less efficient than IHD
• May not be tolerated by extremely unwell unstable patients.
• No difference in mortality between the different RRT modalities; thus, there is no survival advantage in using SLED - only an increased convenience and decreased cost. This was also confirmed by the SHARF study.