Consult Rounds: Hyponatremia and AKI- need CRRT- what do we do??

 

Hyponatremia correction is challenging but manageable.
Offering and prescribing CRRT in the ICU is also doable by most nephrologists.

Here comes the challenge.

You are called, “ anuric patient, Na 110, K 5.4, BUN 90, Crt 6.0mg/dl) and altered mental status”
Now you are confronted with correcting the Na slowly and providing good dialytic clearance as well given anuria and hyperkalemia.

CRRT has advantages in its ability to correct plasma sodium values in a predictable and slow manner. Compared with standard hemodialysis machines, where the lowest dialysate sodium concentration is 130 mEq/l, CRRT solutions can be customized to any desired sodium level, allowing for personalized therapy. 

To act on these advantages and prescribe CRRT to target an increase in serum sodium no >6 mEq/L per day, there are three options: either (1) customize the CRRT circuit or (2) customize CRRT solutions. (3) add D5W infusion separate line with standard CRRT

So how is this rate calculated if we were to use Method 3( the easiest of the 3 options)

If D5W rate will be used – the formula is (140 -- target Na value)/( 140 X clearance)
So if we take 110 meq/L as the starting Na value and goal is in 24 hours to be 118. Given the patient was symptomatic, using 3% saline bolus- we get him to 112-113meq/L range. Then if we do 30cc/kg/hour clearance of CVVHDF, that would be roughly 2.4 liters/hour and hence the rate of D5W would need be 375cc/hour. If we use clearance of 25cc/kg/hour- then around 300cc/hr of D5W would be needed.

In an article by Rosner et al, in CJASN, method 1 is well discussed using this figure- changing the post filter fluid or replacement fluid to sterile water( d5W) and rate calculated similarly as stated above.

For method 2: Adding sterile water to commercial dialysis solutions to achieve a desired final sodium concentration would be next way. For instance, if a 5-L bag of replacement solution has a sodium concentration of 140 mEq/L, then the addition of 1 L of water would result in a final sodium solution of the replacement solution of 116.7 mEq/L. 

An important caveat, once desired Na is reached, D5W needs to be changed back to standard replacement fluids and or D5W drip discontinued.