Understanding_Osmolarity_Tonicity_IV_Fluid

Understanding_Osmolarity_Tonicity_IV_Fluid - Kidneys /...

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UNDERSTANDING OSMOLARITY, TONICITY, AND IV FLUID THERAPY Dee U. Silverthorn, Ph.D. Integrative Biology University of Texas at Austin Austin TX 78712 silverthorn@mail.utexas.edu OBJECTIVES Students completing these exercises should be able to 1. distinguish between osmolarity and tonicity 2. use ECF/ICF box diagrams to explain the effects of a solution on the body's osmolarity and compartment volumes 3. use body compartment box diagrams to calculate solute amount, compartment volume, and osmolarity of a person, and explain how those parameters change with fluid/solute gain or loss 4. use the principle of mass balance to predict how administering an IV solution would change the ECF concentration of a specific ion, such as potassium 5. explain how the volume of a cell would change over time when the cell is exposed to solutions of varying osmolarities and tonicity 1
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1. Solutions 2. Body fluid compartments: dilutions and volumes of distribution 3. Osmolarity 4. Tonicity – Whole body “box” problems – Single red blood cell problems SOLUTIONS An understanding of solutions is critical for understanding osmolarity, tonicity, and intravenous (IV) fluid therapy. Although most health care professionals will never have to make these solutions, there is always the possibility that a disaster of some type, such as Hurricane Katrina or the earthquake in Haiti, will disrupt the flow of medical supplies to a region. In that case, members of the health care team may need to prepare IV solutions from scratch instead of relying on commercially packaged fluids. This first section reviews the basic chemistry of solutions. Concentrations and Solutions You may wish to refer to a general chemistry textbook to help review molarity and solutions. Abbreviations used in this article: mol = mole M = moles/liter osmol = osmoles mosmol = milliosmoles OsM = osmoles/liter mOsM = milliosmoles/liter dL = deciliters = 100 mL Eq = equivalents Concentration refers to the amount of a substance ( solute ) dissolved in a given volume of solution. The liquid in which the solute is dissolved is called the solvent . The concentration of a solution is not the same as the amount of solute in the solution. The amount refers to the total number of particles in the given volume of solution. However, if you know both the concentration and the volume, you can calculate the amount of solute. Amount vs. concentration . ...be careful! Concentration = amount/volume Solutions that you encounter in laboratory and clinical settings have their concentrations expressed in a variety of ways. Some of the most common are: amount/volume Example: 2 gm/L or mg/dL glucose per cent solutions Example: 0.9% NaCl molar solutions Example: 1 M sucrose * In all solutions, the volume is the volume of the final solution , not the volume of water added. 2
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Understanding_Osmolarity_Tonicity_IV_Fluid - Kidneys /...

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