Thread by @Thind888

1/
I've heard this argument before that "an amp of sodium bicarb raises blood pressure as it is hyperosmolar". I thought it'd be a good idea to quantify its effects:

Let's consider an average 70kg adult with TBW = 42L, ICFV = 25L (60%), and ECFV = 17L (40%), osmolality = 280.

https://twitter.com/emily_fri/status/1327695873837502464

2/
1 amp of bicarb=50 meq of Na and 50 meq HCO3 --> a total of 100 mosm of solutes are added. A key point is that all new osmoles remain in ECF-->ECF osmoles increase to 4860 mosm

To predict changes after equilibration, we have to look at changes in total body solutes and water.

3/
Total body solutes now increase to 11860 mosm from 11760 mosm. TBW increases only by 50cc (the volume of 1 amp).
So after equilibration, new osmolality should be 11860/42.05 = 282.05 mosm/L

Now let's see how the 2 compartments would settle after equilibration (figure)

4/
So after equilibration, ECFV is increased by ~230cc. I would imagine this equilibration does not occur instantly but takes some time (?few minutes). One may thus think of 1amp NaHCO3 as equivalent to 230cc of a slow NS bolus

Augmentation of intrasvascular volume would be ~25%

5/ Hence, the projected increase in intravascular volume = 230/4 = 57.5cc (over a few minutes). This may be lower in pathological states (leaky capillaries etc)

Besides, this argument assumes that the patient is preload responsive, which is true for only a fraction of the cases.

Overall doesn't look like it should have a drastic hemodynamic effect.

Am I missing something here? Would love to hear what #NephroTwitter thinks.

@NephroGuy @kidney_boy @ArgaizR @mahrukhrizvi_MD @NephroMD @VelezNephHepato @ansakhuja