fluid

I've never really understood what either of these measurements meant. I've memorized the units: Osmolarity = osmoles/volume of solvent Osmolality = osmoles/ Kg of solvent But can someone simply explain what each of these terms mean, and why they are important? Not a textbook definition, just...

Apologies if this is a stupid question & I know shock has various types. But what is the difference between hypotension & shock? Is hypotension exactly the same as shock? Or is shock more of a syndrome, comprising hypotension & other clinical signs?