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Chapter 52 Measurement Systems, Basic Mathematics, and Dosage Calculations Copyright ©2012 Delmar, Cengage Learning. All rights reserved. The Metric System • Primary system of measurement in medicine • Three basic units: – Gram (g), which measures mass (weight) – Liter (L), which measures volume (liquid) – Meter (m), which measures length (size) Copyright ©2012 Delmar, Cengage Learning. All rights reserved. The Metric System • Based on multiples of 10 – Add prefixes to the basic units to indicate the value (multiple or submultiple) of the unit – Kilo = 1000 – Kilo+gram = 1000 grams Copyright ©2012 Delmar, Cengage Learning. All rights reserved. The Metric System Prefix Unit Decimal Value Micro- 1/1,000,000 of a unit 0.000001 Milli- 1/1,000 of a unit 0.001 Centi- 1/100 of a unit 0.01 Deci- 1/10 of a unit 0.1 No prefix 1 unit 1 Deka- 10 units 10 Hecto- 100 units 100 Kilo- 1,000 units 1,000 Copyright ©2012 Delmar, Cengage Learning. All rights reserved. Household Measures • Patients at home typically use household measurements • You may need to use these measurements to explain to patients how to take their medications after discharge Copyright ©2012 Delmar, Cengage Learning. All rights reserved. Household Measures • • • • • Drop (gtt) Teaspoon (t or tsp) Tablespoon (T or tbs) Ounce (fluid) (fl oz) Cup • • • • Pint (pt) Quart (qt) Ounce (weight) (oz) Pound (lb) Copyright ©2012 Delmar, Cengage Learning. All rights reserved. Household Measures 60 gtt = 1 tsp 3t=1T 2 T = 1 fl oz 1 cup = 8 fl oz 1 pt = 2 cups 1 qt = 4 cups (2 pt) 1 lb = 16 oz Copyright ©2012 Delmar, Cengage Learning. All rights reserved. The Apothecary System • The first system of medication measurement, but not commonly used today • Basic units: – Grain (gr) – Quart (qt) – Pint (pt) – Ounce or fluid ounce (oz) – Dram – Minim Copyright ©2012 Delmar, Cengage Learning. All rights reserved. Review of Basic Math • Basic math skills are necessary for accurately calculating and verifying medication dosages to ensure patient safety before administering any medication Copyright ©2012 Delmar, Cengage Learning. All rights reserved. Review of Basic Math • A fraction indicates a part of a whole number – Numerator: top of fraction – Denominator: bottom of fraction • A percentage expresses a value that is part of 100 Example >> 35% is 35/100 (or 0.35) Copyright ©2012 Delmar, Cengage Learning. All rights reserved. Review of Basic Math • A ratio expresses a relationship between two components – It is another way to express a fraction Example >> 1 : 5 is the same as 1/5 Copyright ©2012 Delmar, Cengage Learning. All rights reserved. Review of Basic Math • A proportion expresses the relationship between two ratios Example >> 3 : 5 = 600 : 1000 – Means: 5 and 600 – Extremes: 3 and 1000 – The product of the means always equals the product of the extremes – You can solve for X if you know the other 3 values Copyright ©2012 Delmar, Cengage Learning. All rights reserved. Dosage Calculations • Calculating the right dose of medication is a responsibility not to be taken lightly • The wrong dose of any medication can have profound adverse consequences Copyright ©2012 Delmar, Cengage Learning. All rights reserved. Basic Formula • (Needed/Available) x Vehicle = Dose – Needed > Amount prescribed by provider – Available > Supply on hand – Vehicle > Form and amount of supply Copyright ©2012 Delmar, Cengage Learning. All rights reserved. Ratio and Proportion Method • Dosage on hand : amount on hand = Dosage desired : amount desired (x) • When using this method, you may need to convert between units of measurement Copyright ©2012 Delmar, Cengage Learning. All rights reserved. Converting Between Units of Measurement • Identify the equivalent • Set up a proportion of two equivalent ratios • Solve for x • Calculating dosage by weight – Conversion factor: 1 kg = 2.2 lbs Copyright ©2012 Delmar, Cengage Learning. All rights reserved.