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Chapter 8

Chapter 8. Converting Between Measurement Systems

brooke-vance
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Chapter 8

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  1. Chapter 8 Converting Between Measurement Systems Conversion within and among measurement systems is often necessary when preparing medications for administration. Discuss the steps that the allied health professional should follow to ensure that such conversions are as accurate as possible. What are the possible sources of error in conversions, and how can they be avoided through professional practice?

  2. Learning Objectives • Reading the time of day on the international standard 24-hour clock and converting to the 12-hour clock and converting between the two time standards • Reading a thermometer in Fahrenheit scale and in Celsius scale and converting measurements between the two systems. • Converting from one length unit to another within and between the metric and the household systems. • Converting from one weight or volume unit to another within and between the metric system and the household system or the metric system and the apothecary system.

  3. Learning Objectives (cont’d.) • Computing approximate equivalents between the metric and household systems. • Converting approximate equivalents between the metric and apothecary systems. • Converting approximate equivalents between the household and apothecary systems.

  4. Chapter 8 Lesson 8.1

  5. Conversion • To change from one form to another. • Necessary in medical field; no world standard. • When numbers are converted from one system to another, they will be approximately equal. • Conversions that are approximately equal may differ by as much as 10%.

  6. Time Conversions: 24-Hour Clock Figure 8-1.

  7. Standard Clock versus International Clock

  8. 4:40 AM = 0440 6:25 PM = 1825 11:02 AM = 1102 2:56 AM = 0256 10:45 PM = 2245 Check Your Understanding 8:10 PM = 2010 12:33 AM = 0033 10:00 AM = 1000 3:33 PM = 1533 7:17 AM = 0717

  9. Celsius Temperature • In the metric system, temperature is measured using the Celsius scale • 0° Celsius = 32° Fahrenheit

  10. EXAMPLE: 104°F = _____°C FORMULA: C° = 5/9 (F° – 32) SOLUTION: 5/9(104° – 32) = °C 5/9 x 72 = °C (72 x 5) ÷ 9 = °C 360 ÷ 9 = 40 104°F = 40°C (Alternative: subtract 32 from F° and divide by 1.8) Fahrenheit to Celsius

  11. Celsius to Fahrenheit FORMULA: F° =(9/5 C°) + 32 38.3°C = ______°F (9/5 x 38.3) + 32 38.3 x 9 = 344.7 344.7 ÷ 5 = 68.94 68.94 + 32 = 100.94 Round to 101.0°F 38.3°C = 101°F (May also multiply C° by 1.8 and add 32)

  12. Review of Changing Temperature • From C° to F° • Multiply C ° by 1.8 • Add 32 • From F° to C° • Subtract 32 from F ° • Divide by 1.8 • When performing temperature conversions, remember to complete the steps in the order given by first removing the parenthesis.

  13. Ratios and Proportions • Used to convert when the dosage available is not in the same measurement unit as the doctor prescribed. • Ratio: expression comparing two quantities • Proportion: comparing two equivalent fractions or ratios

  14. Solving Unknown Variables • Numerators must be of the same units. • Denominators should be of the same units. • 1 mL : 15 gtts is the same as 2 mL : 30 gtts • 1 mL/15 gtts = 2 mL/30 gtts

  15. Solving Unknown Variables (cont’d.)

  16. Using Ratio/Proportion • When setting up both ratios, be sure to label all of the terms, including x with the correct measurement to ensure that the equations are equivalents.

  17. Common Measurements Used in Conversions

  18. Volume Conversions

  19. fʒ x = ______ mL Remember, this is 10 fluid drams 4 mL = fʒi 4 mL / fʒ i = x mL / fʒx 4 x 10 = 40 1 x x= x 1 x = 4 x 10 = 40 fʒx = 40 mL Volume Conversions – Apothecary to Metric 4 mL x mL fʒx 1 fʒ 10

  20. Volume Conversions – Metric to Household • Known amounts – 1 pint = 500 ml • Insert equation in Example 9 p. 153 • Add cross multiplication • 500 x = 750 • x = 750/500 • x = 1.5 pt

  21. Conversion Clock for Liquid Volumes for Metric and Apothecary Systems

  22. Weight Measurements between Metric and Household Systems • The conversion for metric system to household system is • 2.2# = I kg • 206# = ____ kg • 2.2#/ 1 kg = 206# / x kg • 2.2 x = 206 • x = 206/2.2 • x = 93.6 kg

  23. Conversion Factors for Length Measurements – Metric to Household

  24. An abdominal cavity was opened with a 14-inch incision. Convert this measurement into cm. 2.5 cm x cm 1 in 14 in Length Conversions • 2.5 cm = 1 inch • 2.5 cm / 1 in = x cm / 14 in • 2.5 x 14 = 35 • 1 x x = x • x = 35 • 14 inches = 35 cm

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