This is Part 4 of the Acid Base saga. In this episode, I discuss the acid base effects of fluids and when and how to use sodium bicarbonate.
If you haven’t checked out the previous episodes, you should definitely do that first:
- Part I lays out the background of the quantitative approach
- Part II puts it in mathematical terms to allow calculation of acid base status
- Part III takes you through some real world examples
You may need the EMCrit Acid Base Sheet to follow along
The Acid Base of Fluids
Crystalloids will have acid-base effects by their SID and the dilution of extracellular Atot
“Balanced Fluids” are fluids with a SID just low enough to balance the dilution of the weak acid, albumin (SID of 24-28)
For the effects on a patient with altered pH, any fluid with a SID the same as the pt’s bicarb will keep the patient at the same pH. If the SID is greater than the pt’s bicarb, then the fluid will be alkalotic and if less than the pt’s bicarb–acidotic (Intens Care Med 2011;37:461).
Hypertonic fluids are even more acidifying b/c they draw pure water into the extracellular space
If not stored in glass, bicarb containing solutions leech CO2 and become not so much bicarbonate.
If given at all, should be given slowly by push over 5-10 minutes or by drip; never by rapid push
In hyperkalemia, NaBicarb isotonic is essentially a potassium-free, non-acidic fluid that dilutes down the potassium.
NaBicarb can be used as a substitute for hypertonic saline in increased ICP (Neurocrit Care 2010;13:24). They used 85 ml of 8.4% sodium bicarb infused over 30 minutes.
Balanced solutions (p-lyte) led to lower Cl and higher bicarb (Am J Emerg Med. 2011 Jul;29(6):670-4)
Another incredible review on fluids including the rec. that we use 3 amps of bicarb (J Intens Care Med 2010;25(5):271)
Also of interest may be the previous episode on intubating the patient with the severe metabolic acidosis