Chapter 4 Conversions Metric and Household Systems Copyright

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Chapter 4 Conversions: Metric and Household Systems Copyright © 2016 Cengage Learning. ALL RIGHTS

Chapter 4 Conversions: Metric and Household Systems Copyright © 2016 Cengage Learning. ALL RIGHTS RESERVED.

Conversions between Metric and Household Systems Copyright © 2016 Cengage Learning. ALL RIGHTS RESERVED.

Conversions between Metric and Household Systems Copyright © 2016 Cengage Learning. ALL RIGHTS RESERVED.

Pre-scribed Medications: • Ordered in a unit of weight measurement usually gram or milligram

Pre-scribed Medications: • Ordered in a unit of weight measurement usually gram or milligram • RN responsibility to interpret order • RN responsibility to use conversions if necessary • Administer correct amount of medication prescribed Copyright © 2016 Cengage Learning. ALL RIGHTS RESERVED.

Identifying Need for Unit Conversion • A drug order written in a unit of

Identifying Need for Unit Conversion • A drug order written in a unit of measurement different from what is supplied • Usually written in one metric size (mg) but is supplied in another metric unit (g) • Encounter apothecary or household measure • Converting a unit of measure does not change amount of ordered dosage of medication! It provides an alternate expression of dosage. Copyright © 2016 Cengage Learning. ALL RIGHTS RESERVED.

Identifying Need for Unit Conversion Medication order versus supply on hand Medication order: triazolam

Identifying Need for Unit Conversion Medication order versus supply on hand Medication order: triazolam 250 mcg orally at bedtime Supply on hand: Halcion 0. 25 mg tablets Medication order: Supply on hand: Antacid Plus ½ fl oz after meals Antacid Plus 1 fl oz (30 m. L) Copyright © 2016 Cengage Learning. ALL RIGHTS RESERVED.

Identifying Need for Unit Conversion • First example: prescribed quantity must be converted into

Identifying Need for Unit Conversion • First example: prescribed quantity must be converted into the unit of measure supplied • Second example: nurse selects correct unit of measure from 2 options provided on label before calculating ordered dose • Therefore, calculating unit conversions are the first steps in dosage calculations Copyright © 2016 Cengage Learning. ALL RIGHTS RESERVED.

RULE FOR PROPORTION/RATIO 1. Recall Equivalents 2. Set up proportion for 2 equivalent ratios

RULE FOR PROPORTION/RATIO 1. Recall Equivalents 2. Set up proportion for 2 equivalent ratios 3. Cross multiply to solve for an unknown quantity, X Copyright © 2016 Cengage Learning. ALL RIGHTS RESERVED.

Conversions • Proportions and ratios are set up for solving in the same format.

Conversions • Proportions and ratios are set up for solving in the same format. THIS IS ESSENTIAL. The like units must be across from each other. The units in the numerators match, and the units in the denominators match. Copyright © 2016 Cengage Learning. ALL RIGHTS RESERVED.

Converting Using Ratio-Proportion • Example: How many cups are equivalent to 3 quarts? 1.

Converting Using Ratio-Proportion • Example: How many cups are equivalent to 3 quarts? 1. It is known that 1 qt equals 4 cups 2. Set up proportion by expressing ratios as fractions Note: X, in the denominator, is the unknown. Copyright © 2016 Cengage Learning. ALL RIGHTS RESERVED.

Converting Using Ratio-Proportion 3. Cross-multiply Simplify: Divide both sides by number before X Copyright

Converting Using Ratio-Proportion 3. Cross-multiply Simplify: Divide both sides by number before X Copyright © 2016 Cengage Learning. ALL RIGHTS RESERVED.

In review: Using ratio-proportion method: 1. Recall known equivalent 2. Set up proportion •

In review: Using ratio-proportion method: 1. Recall known equivalent 2. Set up proportion • Ratio for known equivalent equals ratio for unknown equivalent 3. Cross-multiply to solve for unknown quantity (X) Copyright © 2016 Cengage Learning. ALL RIGHTS RESERVED.

Converting within Metric System • Most conversions are derived by multiplying or dividing by

Converting within Metric System • Most conversions are derived by multiplying or dividing by 1, 000 – Multiplying by 1, 000 • Move decimal three places to right • Used when converting from larger to smaller unit Note: Sometimes you have to add zeros to hold the places equal to the number of zeros in the equivalent. Example: 2 grams per tablet means the same as 2, 000 milligrams per tablet. 1 g = 1, 000 mg, so 2 x 1, 000 = 2, 000 mg Copyright © 2016 Cengage Learning. ALL RIGHTS RESERVED.

Converting within Metric System • Most conversions are derived by multiplying or dividing by

Converting within Metric System • Most conversions are derived by multiplying or dividing by 1, 000 – Dividing by 1, 000 • Move decimal three places to left • Used when converting from smaller to larger unit Example: Convert 20 mg to g 1 g = 1000 mg, so we divide moving decimal 3 places to left; x=0. 02 g Copyright © 2016 Cengage Learning. ALL RIGHTS RESERVED.

Converting within Metric System • Example: Convert 0. 3 g to equivalent number of

Converting within Metric System • Example: Convert 0. 3 g to equivalent number of mg 1. Recall known equivalent – Equivalent is: 1 g = 1, 000 mg 2. Set up equivalent ratios Copyright © 2016 Cengage Learning. ALL RIGHTS RESERVED.

Converting within Metric System 3. Cross-multiply Answer: Copyright © 2016 Cengage Learning. ALL RIGHTS

Converting within Metric System 3. Cross-multiply Answer: Copyright © 2016 Cengage Learning. ALL RIGHTS RESERVED.

Converting within Metric System • Example: Convert 50 m. L to L 1. Recall

Converting within Metric System • Example: Convert 50 m. L to L 1. Recall known equivalent – Equivalent is: 1 L = 1, 000 m. L 2. Set up equivalent ratios Copyright © 2016 Cengage Learning. ALL RIGHTS RESERVED.

Converting within Metric System 3. Cross-multiply Simplify Copyright © 2016 Cengage Learning. ALL RIGHTS

Converting within Metric System 3. Cross-multiply Simplify Copyright © 2016 Cengage Learning. ALL RIGHTS RESERVED.

Remember: When converting from a larger to a smaller unit of measure, the number

Remember: When converting from a larger to a smaller unit of measure, the number of smaller units should be greater than original number of larger units Conversely, When converting from a smaller to a larger unit of measure, the number of larger units should be less than the original number of small units Copyright © 2016 Cengage Learning. ALL RIGHTS RESERVED.

Conversion Slide • Use this diagram when converting dosages within metric system • See

Conversion Slide • Use this diagram when converting dosages within metric system • See which way the arrow points then: Move decimal three places to left for each step kg g mg mcg Move decimal three places to right for each step • 1 mcg = 0. 001 mg (moved decimal point to the left 3 places) • 2 g = 2, 000 mg (moved decimal point to the right 3 places) Copyright © 2016 Cengage Learning. ALL RIGHTS RESERVED.

Approximate Equivalents • • 1 t = 5 m. L 1 T = 3

Approximate Equivalents • • 1 t = 5 m. L 1 T = 3 t = 15 m. L = fl oz 1 fl oz = 30 m. L = 6 t = 2 T 1 L = 1 qt = 32 fl oz = 2 pt = 4 cups 1 pt = 500 m. L = 16 fl oz = 2 cups 1 cup = 250 m. L = 8 fl oz 1 kg = 2. 2 lb 1 inches (in) = 2. 5 cm need to know! Copyright © 2016 Cengage Learning. ALL RIGHTS RESERVED.

Converting Between Systems of Measurement • Use ratio-proportion method • Same steps as when

Converting Between Systems of Measurement • Use ratio-proportion method • Same steps as when converting within same system of measurement Copyright © 2016 Cengage Learning. ALL RIGHTS RESERVED.

Converting Between Systems of Measurement • Convert 2 fl oz to m. L -converting

Converting Between Systems of Measurement • Convert 2 fl oz to m. L -converting from a larger to smaller unit 1. Recall equivalent – Equivalent is: 1 fl oz = 30 m. L 2. Set up equivalent ratio 3. Cross-multiply Copyright © 2016 Cengage Learning. ALL RIGHTS RESERVED.

Converting Between Systems of Measurement • Example: Convert 45 m. L to t –

Converting Between Systems of Measurement • Example: Convert 45 m. L to t – Converting from smaller to larger unit 1. Recall equivalent – Equivalent is: 1 t = 5 m. L 2. Set up equivalent ratio Copyright © 2016 Cengage Learning. ALL RIGHTS RESERVED.

Converting Between Systems of Measurement 3. Cross-multiply Simplify Copyright © 2016 Cengage Learning. ALL

Converting Between Systems of Measurement 3. Cross-multiply Simplify Copyright © 2016 Cengage Learning. ALL RIGHTS RESERVED.

Converting Between Systems of Measurement • Approximate equivalent: 1 kg = 2. 2 lb

Converting Between Systems of Measurement • Approximate equivalent: 1 kg = 2. 2 lb (so our weight in kg is about half of our weight in pounds) Copyright © 2016 Cengage Learning. ALL RIGHTS RESERVED.

Converting Between Systems of Measurement • When converting from a smaller to a larger

Converting Between Systems of Measurement • When converting from a smaller to a larger unit of measure, the resulting number of larger units will be less than the original number of smaller units. • When converting from a larger unit of measure to a smaller unit of measure, the resulting number of smaller units should be greater than the original number of larger units. • Always look at your answer and ask yourself if it makes sense. Copyright © 2016 Cengage Learning. ALL RIGHTS RESERVED.

Quick Review • Steps for using ratio-proportion method to convert within or between systems

Quick Review • Steps for using ratio-proportion method to convert within or between systems of measure: 1. 2. 3. 4. 5. Recall known equivalent Set up proportion ratio Label and match units in numerators and denominators Cross-multiply to find value of x Label units in answer to match unknown x Copyright © 2016 Cengage Learning. ALL RIGHTS RESERVED.

Copyright © 2016 Cengage Learning. ALL RIGHTS RESERVED.

Copyright © 2016 Cengage Learning. ALL RIGHTS RESERVED.