SMART Trial - Balanced Crystalloids vs NS in Critically Ill Adults

Written by Alex Chen, MD

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In patients admitted to the ICU, use of balanced fluids resulted in a lower rate of major acute kidney events (MAKE) at 30 days compared to normal saline (14.3% vs 15.4%). This is a NNT of 94 to avoid one MAKE.

Why does this matter?
Saline has historically been the most commonly administered IV fluid. There has been evidence to suggest that it is associated with hyperchloremic metabolic acidosis, AKI, and death. Previous observational data has been inconsistent, while previous pilot trials have been underpowered to detect differences in clinical outcome.

“The old lower-the-chloride-to-save-the-kidneys trick. That's the second time I've covered that this week.” – Maxwell SMART
This was a pragmatic, cluster-randomized, multiple-crossover trial conducted in 5 ICUs at a single academic medical center.  15,802 patients received either balanced crystalloids (LR or Plasma-Lyte A) or normal saline depending on the month.  Primary outcome of this study was major adverse kidney event, which was a composite end point of death from any cause within 30 days, new renal-replacement therapy, or persistent renal dysfunction at 30 days.  Secondary outcomes included in-hospital death, ICU-free days, ventilator-free days, vasopressor-free days, and RRT-free days. 

In terms of the primary outcome, the balanced crystalloid group had fewer events compared to saline (14.3% vs 15.4%).  This was primarily driven by lower mortality rates.  The two groups did not differ significantly in their secondary outcomes.  Interestingly, in the subgroup analyses, there was a clear dose-response relationship.  This likely explains why those with sepsis had fewer events when they were given balanced crystalloids vs saline (33.8% vs 38.9% with a 4.2% absolute risk reduction for mortality).  While the nature of being a single center study may limit generalizability, the study had a large sample size and took all-comers to the ICU.  This study also does not differentiate between Plasma-Lyte A and LR.  Overall, it takes something as simple as changing the type of fluid a patient receives to change outcomes on a larger scale.

Source
Balanced Crystalloids versus Saline in Critically Ill Adults.  N Engl J Med. 2018 Mar 1;378(9):829-839. doi: 10.1056/NEJMoa1711584. Epub 2018 Feb 27.

Another Spoonful
There is a FOAM-fest on the SALT-ED and SMART trials.

Peer reviewed by Thomas Davis and Clay Smith.

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