WHAT CAN WE GIVE?
Crystalloids and colloids are the two categories of fluids used in fluid therapy. Crys- sodium-based electrolyte solutions or solutions of glucose in water that are commonly used to replace lost fluid and electrolytes. The composition is similar to plasma fluid. Crystalloids are further described by their tonicity and are categorized as isotonic, hypotonic, hypertonic Tonicity is based on a measurement called osmolality. Recall that osmolality is the osmotic pressure of a solution based on the number of particles per kilogram of solution. pressure is the ability of solutes(particles) to attract water(caus osmosis). Not all particles contribute to osmolality. Sodium and glucose provide most of the particles to determine osmotic pressure. Normal osmolality of blood extracellular fluid is 290 to 310 mosm/kg. The osmolality of isotonic solutions is the same as blood and extracellular water; thus isotonic solutions produce no significant changes in the blood. Hypotonic solutions have osmolality lower than that of blood and can cause the red blood cells to swell. However, in proper concentrations hypo- tonic solutions can shift fluid out of the intravascular space without swelling the red blood cells. The osmolality of hypertonic solutions is greater than that of blood and can cause the red blood cells to shrink. However, in proper concentrations hyper tonic solutions can shift fluid into the intravascular space without shrinking the red blood cells. Figure 19-1 summarizes solution tonicity