converting within and between systems

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After reviewing this chapter, you should be

able to:1. Convert a unit of measure to its

equivalent within the same system2. Convert approximate equivalents

between the metric, apothecary, and household systems of measure

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Equivalents are not exact Several tables are available and may

vary› For example, gr i = 60-65 mg› 60 mg is used in most cases, but 65 mg is

best for aspirin conversions Memorization of equivalents (Table 8-1)

is essential for proficiency and communication with clients about medication administration

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Changing from one form to another Within same system (e.g., mg to mcg) Between systems (e.g., oz to mL) Result is approximate, but continuity

exists

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1. Memorization is essential2. Think of equivalents as ratios

› 1 g = 1,000 mg is a ratio 1 g : 1,000 mg or 1:1,000

3. Follow basic math rules for all systems

4. Express answers using specific rules related to system to which conversion is being done (e.g., decimals for metric)

5. THINK CRITICALLY—use appropriate equivalents

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Previously discussed in Chapter 6 Cannot be applied in apothecary or

household systems Smaller to larger—move decimal to left

350 mg = 0.35 g

Larger to smaller—move decimal to right

0.850 L = 850 mL

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Refer to Chapter 41. State known equivalent first

(memorized)2. Add incomplete ratio on other side of

equals sign—both sides mirrored › Example: mg : g = mg : g (L:R as L:R)

3. Label all terms in the proportion, including x, when problem is first set up

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4. Solve the problem using the principles of ratio and proportion

› Product of the means = product of the extremes

5. Final answer for x should be labeled with correct unit of measure

Note: Carry division at least two decimal places to ensure accuracy

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8 mg = ____ g1,000 mg : 1 g = 8 mg : g

(known equivalent) (unknown)1,000 = 8

1,000 8 =

1,000 1,000 = 0.008 g

x

x

x

x

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1,000 8 =

1 1,000 8

= 1,000 1,000

= 0.008 g

mg mgg x g

x

x

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All measurements must be in the same system

Movement of decimals is limited to metric

› 0.6 mg = ____ mcg 0.600 mg = 600 mcg

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Dimensional Analysis› Used in chemistry and other sciences

Steps1.Identify the unit to which you are converting2.Write down conversion factor with desired

unit in denominator, and write the next numerator to match the previous denominator unit of measure

3.Cancel the alternate denominator/numerator units to leave the desired unit (being calculated)

4.Perform the mathematics

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0.12 kg to g (both metric)1,000 g

g = 0.12 kg1 kg

1,000 gCancel the units: g = 0.12 kg

1 kg1,000 0.12 = 120 g

= 120 g

x

x

x

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Larger to smaller› Multiply by the conversion factor

(apothecary) (metric) gr 1/100 = ____ mg (large) (small)

› Equivalent: gr 1 = 60 mg Conversion factor = 60

› Multiply 1/100 by 60—convert to decimal› Answer: 0.6 mg

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Smaller to larger› Divide by the conversion factor

(metric) (apothecary) 150 mg = gr ____

(small) (large)

› Equivalent: gr 1 = 60 mg Conversion factor = 60

› Divide 150 by 60 – convert to fraction› Answer: gr 2½

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Conversion Factor Method: pounds to kg› Divide by the conversion factor

(apothecary) (metric) 110 lb = ____ kg

(small) (large)

› Equivalent: 1 kg = 2.2 lb (Conversion factor = 2.2)

› Divide 110 by 2.2 › Answer: 50 kg

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Ratio and Proportion: pounds to kg

1 kg : 2.2 lb = kg : 110 lb2.2 110

= 2.2 2.2

50 kg

x

x

x

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Abbreviated as I&O Used to monitor fluids consumed,

injected, and excreted Includes intake of “pseudo” solids that

become liquid at room temperature—Jello, popsicles

Includes liquids that exit the body—diarrhea, urine, vomitus, gastric suction, chest drainage

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Preferred method is milliliters (mL) NOT cc

May require conversion—household to metric

Recorded during the hour within which the fluid is consumed, injected, or excreted

Totaled every 24 hours

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I&O record usually has key for conversions (e.g., 6 oz coffee cup = 180 mL)

After conversions, items are added for totals

1/3 glass apple juice (1 glass = 6 oz) = 60 mL1/2 cup coffee (1 cup = 8 oz) = 120 mL1/2 pint milk (1 pint = 500 mL) = 250 mL

430 mL

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Figure 8-1  Sample I&O flow sheet

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Record intravenous (IV) fluid intake Method of recording varies with

institutions Urine is sometimes recorded hourly

› Adult hourly output should be 30 mL or more

› To find average, add up total urine and divide by number of hours being recorded

Check institution policies to comply with charting requirements on I&O record