This is a "dilutional" hyponatremia. Essentially, it is the result of water moving into the extracellular fluid to dilute whatever extraneous osmotically active agent is present there.
Historically, such hyponatremia has not yet appeared in the CICM fellowship exam. However, HONK makes numerous appearances, and on occasion the candidates have been asked to calculate the corrected sodium (eg. in Question 19 from the second paper of 2010).
The resulting expansion of the extracellular compartment produces a dilution of the remaining electrolytes.
Observe. Let us take a cylinder model of human fluid physiology, and give it a massive dose of undiluted intravenous glucose syrup. And lets prevent the body from disposing of it properly by killing the kidneys and impairing the cellular uptake of glucose. Lets cook up a HONK.
Let us say that we have given 100g of glucose, which is about 556mmol. Without functioning GLUT transporters, this syrup will distribute into the extracellular fluid alone.
Voila. Hyponatremia. Without getting rid of any sodium, we have produced a low serum sodium, and the serum osmolarity is significantly higher than it should be, owing to the presence of 36mmol/L of glucose.
There is a famous equation which describes the "correction" of sodium.
Does it fit our model? According to the above equation, the sodium should drop by 10.2mmol/L. The model predicts a drop of 11.6mmol/L. So the model is not wildly incorrect.
The "corrected" sodium is what one will be left with after one gets rid of all the glucose. It is useful to be able to predict this, because without fluid deficit correction a severe hypernatremia may result during the management of a HONK state. However, one should not be fooled by the use of the term "corrected sodium" to assume that the sodium from the lab results is somehow "incorrect". The sodium concentration reported by the lab is the accurate concentration of sodium in the body fluids. And all the other ions in the body fluids are diluted to the same extent. Thus, one should use the "uncorrected" sodium to calculate the anion gap (this issue is discussed with greater detail in the chapter on anion gap calculation)
Just about any extracellular osmolar load.
The common ones are: