NephMadness 2015: Critical Care Nephrology Region

Lakhmir S. Chawla, MD, Selection Committee, Critical Care Nephrology Region

Editor's Note: The following "Scouting Report" will help you complete your bracket in the NephMadness Tournament. Read it carefully to make your selections, and discuss your thoughts in our Comments section. This article first appeared on the AJKD BLOG.

Meet the Competitors: SLED in Sepsis vs Conventional RRT in Sepsis

In acute kidney injury (AKI) there is a moment of clarification: the moment you decide the patient needs renal replacement therapy (RRT). Not only that, you need to decide which type of RRT to use. The delicate balance between keeping a patient dry for the heart/lungs and wet for kidneys evaporates with the decision to take over the essential task of fluid and solute control with a machine rather than relying on the damaged kidneys.

Biomechanical engineers have developed novel machines dedicated for ICU patients—continuous RRT machines—but often those machines or the personnel required to use them are unavailable. In those situations, nephrologists are forced to adapt conventional dialysis machines to the unique needs and limitations of septic patients with AKI. In those situations, one can use conventional hemodialysis techniques or a specialized technique such as sustained low efficiency dialysis (SLED).

SLED in Sepsis

Also referred to as prolonged intermittent renal replacement therapy (PIRRT) —and sometimes derided as "poor man's CRRT"—SLED is a hybrid form of dialysis that takes the best parts of intermittent hemodialysis and continuous RRT. Some of the goals of this modality are:

1. Slower blood flow rates as compared with standard intermittent hemodialysis

2. Slow solute removal to prevent solute disequilibrium

3. Slow ultrafiltration to provide hemodynamic stability

4. Sustained treatment to maximize dialysis dose

5. Intermittency for convenient access to patients for out-of-unit procedures and scheduled down-time.

One of the other advantages of SLED is that it leverages the existing chronic dialysis equipment and personnel. SLED is also fairly well tolerated in hemodynamically unstable patients.

For example, MD Anderson uses a standard Fresenius 2008H K dialysis machine with the ubiquitous F16nr dialyzers. However, they program these machines completely unlike conventional dialysis. MD Anderson uses a blood flow of 200 mL/min and a dialysate flow of 100 mL/min. To avoid clotting, they run an additional 100 mL per hour of normal saline pre-filter. Three quarters of this cohort was on vasopressors and seemed to tolerate the dialysis as evidenced by a trend toward decreasing vasopressor support over time and the ability to successfully remove fluid with the technique (average of 360 mL/h). The technique also provided good solute control with an 80% reduction in pre-treatment BUN and 73% reduction in pre-treatment creatinine by 48 hours.

Berbece and Richardson looked at cost and found daily SLED was about half the cost of CRRT ($1,431/week compared with $3,089 for CRRT with citrate and $2,607 with heparin). The same study also provided urea kinetics and found higher urea clearance with SLED (weekly Kt/V of 8.4 with SLED and 7.1 with CRRT). SLED was well tolerated with no hemodynamic instability in 86% of the treatments.

CRRT has two distinct advantages over SLED that keeps CRRT near and dear to the critical care nephrologist. Because CRRT is "continuous," it allows for better volume control. Bouchard and colleagues have demonstrated that patients on CRRT are subject to less volume overload than intermittent HD.

The other advantage is drug dosing. When SLED is deployed, the patient has two distinct periods of machine-induced clearance through the day: a period of excellent drug clearance with RRT is running, and then a clearance of zero when it is off. Because of this dichotomy, drug dosing is much more complicated and in order to get drug dosing right, many drugs need to be redosed immediately after SLED. When CRRT is running, drug dosing is much simpler: dose to the clearance that the machine is providing.

SLED has also been shown to be effective in lithium and salicylate toxicity.

Source: Table reproduced from Chris Nickson, Life in the Fastlane / CC BY-SA 4.0.

Conventional RRT in Sepsis

Conventional intermittent dialysis has repeatedly been tested against the darling of critical care nephrologists, CRRT. However, despite going head to head in meta-analysis after meta-analysis, intermittent dialysis continues to hold its head up high. When CRRT and conventional intermittent dialysis were compared as initial modality for RRT, there was no significant difference in mortality or renal recovery.

These studies might all be suffering from selection bias, because they typically exclude conventional intermittent dialysis from patients too unstable to tolerate the therapy.

Additionally, a recent negative study showed that SLED combined with antimicrobial therapy failed to decrease the initial high plasma IL-6 concentrations noted in patients with sepsis, ie, high initial plasma IL-6 concentrations have been shown to be directly correlated with in-hospital mortality. However, no data was presented on whether intermittent dialysis was able to lower IL-6.

Intermittent dialysis is like Northern Iowa: a throwback to an older style of college basketball, a time where coaches would recruit players to play for 4 years and mature in the program, a time before one-and-done stars. Intermittent dialysis has loads of theoretical reasons why it should not be effective and should have inferior patient outcomes, but it just keeps plugging away, defying the predictions and matching continuous therapies outcome for outcome.

NKF © 2015  The National Kidney Foundation

Cite this: NephMadness 2015: Critical Care Nephrology Region - Medscape - Mar 02, 2015.