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nbme23/Block 3/Question#29

A 50-kg (110-lb) experimental animal receives 1 L ...

Intracellular volume: decreased;
Intracellular osmolality: increased;
Extracellular volume: increased;
Extracellular osmolality: increased

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submitted by aladar50(17),

I’m not the best at the calculations of ICF/ECF, but basically you are infusing a hypertonic solution into the animal. Initially, this is all going to go into the extracellular space, as any IV infusion will do. Since it is higher than isotonic solution, water is going to go from the intracellular space to the extracellular space to try to balance it out, so the intracellular space will have decreased volume and increased osmolality (since only water is leaving, making it more concentrated).

So you know for sure ICF volume is decreased and osmolality increased, and the extracellular volume will be increased. I think the osmolality of the extracellular space is the tricky part and the part where maybe someone else can help with the calculations but basically it’s hypertonic enough that the osmolality will still be increased.

btl_nyc  Since hypertonic solution was added, osmolality has to go up. The degree of the hypertonicity doesn't really matter. The fluid flowing out of the ICF will increase ICF osmolality. Since water follows salt, the water's gonna flow only until the ECF and ICF have the same tonicity. So if the ICF osmolality went up, the ECF osmolality also had to go up, because they both need to be equal after the water is done equilibrating. +5  
krewfoo99  ECF fluid is hypertonic because we infused an hypertonic solution. ECF volume is going to go up because A) we added more volume via injection B) Sodium attracts water, and since hypertonic solution was given water goes from ICF to ECF ICF volume decreases because the water is going to ECF. This causes an increase in Intracellular osmolarity, since you have more solutes compared to water (Less water to dilute it) +