You have a patient
in the ER in septic shock. You are about to administer resuscitation
fluid but notice that the patient is severely hyponatremic. You
don't want to correct too rapidly and risk osmotic myelinolysis.
What do you do? I've seen this situation many times. This problem
is addressed in a post at Academic Life in Emergency Medicine
and some references provided.
One thing you could
do, says the author, is use lactated ringers which is hypotonic to
normal saline (though it may still be hypertonic to a patient with
severe hyponatremia). After all, there's been a shift toward lactated ringers in sepsis resuscitation for entirely different reasons anyway so why not?
If you do the math
(a link to a calculator is provided) you find that, all other things
being equal, lactated ringers raises sodium in a severely
hyponatremic patient a lot less than saline. And, using the
calculator, you can reliably predict how fast the sodium will rise
with a given rate of fluid resuscitation, right? Wrong. Because all
other things are not equal. You can bet that patient is pouring out
vasopressin, driven by non-osmotic stimuli (volume receptor
mediated). When you replete the patient's volume you will turn off
that signal and a water diuresis may ensue. That is a variable that
cannot be anticipated in the calculation. The only way I know to
deal with that situation is to recheck the patient's chemistries
frequently, pay attention to the urine output and urine osm in order
to catch any trend toward overcorrection early, then deal with it
however your sound clinical judgement may dictate.
That is not to take
away from the point that lactated ringers may be preferable.
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