DIMENSIONAL ANALYSIS - FAQ

NURSING MEDICAL CALCULATIONS- DIMENSIONAL ANALYSIS APPROACH

WHAT IS DIMENSIONAL ANALYSIS?

• It is a problem solving method based on the principles of cognitive theory that learning is dependent on how information is structured, organized, and conceptualized.
• It provides a systematic way to set up problems and helps to organize and evaluate data.
• It is a method that can be used whenever two quantities are directly proportional to each other and one quantity must be converted to the other using a conversion factor or conversion relationship.

USE OF DIMENSIONAL ANALYSIS

• To determine numerical value of an equation.
• To determine the units of a variable in an equation.
• To check the correctness of an equation.

TYPES OF PROBLEMS

• One factor problem: Only one label--- Example: Converting 400 mg to kg
• Two factor problems: Two labels---Example: Questions asking for mg/kg
• Three factor problems: Three labels—Example: Questions asking for mg/kg/day

SYSTEMS OF MEASUREMENT USED FOR MEDICATION DOSAGE ADMINISTRATION

• Metric system
• Apothecary system
• Household system

Metric system

• Decimal system of weights and measurements based on units of tens.
• The basic units are gram, meter, and liter.

Weight
1 kilogram (kg) = 1000 grams (g)
1 g = 1000 milligrams (mg)
1 mg = 1000 micrograms (mcg)

Volume
1 liter  (L) = 1000 milliliters (mL)
1 mL = 1 cubic centimeter (cc)

APOTHECARY SYSTEM
System of measuring and weighing drugs and solutions in which fractions are used to  identify parts of the unit of measurement.

Weights
1 pound (lb) = 16 ounces (oz)
1 oz = 8 drams (dr)
1 dr = 60 grains (gr)

Volume
1 gallon (gal) = 4 quarts (qt) = 8 pints (pt)
1 pt = 16 fluid ounces (fl oz)
1 fl oz = 8 fluid drams (fl dr)
1 fl dr = 60 minim (M)

HOUSEHOLD SYSTEM

• 1 cup = 8 oz
• 2 tablespoons (Tbsp) = 1 oz
• 3 teaspoons (tsp)= 1 tablespoon (Tbsp)
• 1 teaspoon = 60 drops (gtt)

THE FIVE STEPS OF DIMENSIONAL ANALYSIS

• Identify the given quantity (the beginning point of the problem)
• Identify the wanted quantity (the answer to the problem)
• Establish the unit path (a series of conversions necessary to achieve the answer to the problem) from the given quantity to the wanted quantity using equivalents as the conversion factors.
• Simplifying the expression: Multiplication/division of numbers

Dimensional analysis set-up

(Given quantity) x (conversion factor for given) x (conversion factor for wanted) = Wanted quantity

Dimensional analysis unit conversion

Practice Questions On Dimensional Analysis http://home.sc.rr.com/nurdosagecal/