Response to 1L of PlasmaLyte 148

What am I giving?

Plasma-Lyte 148 is a cocktail of electrolytes described elsewhere.

Change to the initial conditions: distribution of volume

The water distributes rapidly (within about 15 minutes) from the intravascular to the interstitial compartment, and becomes trapped there. All the electrolytes in it (except for the acetate and gluconate) end up trapped in the extracellular space, and the water has nowhere to go. The acetate disappears into the cells and the gluconate… well, who knows.

The bicarbonate precursors, being ineffective osmoles, vanish from our calculations. What remains is a hypoosmolar soup (244 mOsm/L).

So, in fact we have diluted the concentration of electrolytes in the body fluid compartments with Plasma-Lyte.

Changes in initial conditions: distribution of the major electrolytes

61 mOsm of the electolytes end up in the intravascular flud, and 183 in the extravascular.

If we consider that the sodium concentraton is initially 140, then it will rise by 0.8 mmol/L.  

If the chloride was initially 100, it will rise by 0.4 mmol/L.

Osmoreceptor response

Since the osmolality of the compartments decreases by only 10.8 mOsm/L, there is some minimal osmoreceptor response (this represents a slightly more than 3% change).

Baroreceptor response

The intravascular compartment volume increases by 228ml – from 5000ml to 5228ml. The increase in intravascular volume is 4.5% - outside the volume receptor sensitivity threshold.

Glomerulotubular balance response

This is explained in detail elsewhere.

Has anybody ever infused Plasma-Lyte into healthy volunteers?

But of course. The great guru of applied fluid physiology, Dr Lobo, is a co-author of this recently published paper.

Following the infusion of 2 L of Plasmalyte 148, an initial increase of plasma volume of 29% was observed; at the end of 4 hours only 14% remained. (that would be 7% with 1 litre, or 245mls in our model). As predicted, hyperchloraemia did not occur.