Percentages

Percentages

Percentage is a commonly used word. Sales tax is a percentage of the sale price; a final examination is a certain percentage of the final grade; interest on a home mortgage represents a percentage of the balance owed; interest on a savings account is expressed as a percentage. Health care professionals see percentages written with medications (e.g., magnesium sulfate 50%). In addition to its use with medications, percentage is also used in the assessment of burns. The size of a burn (percentage of injured skin) is determined by using the rule of nines in an adult (Figure 5-1). The basis of the rule is that the body is divided into anatomical sections, each of which represents 9% or a multiple of 9% of the total body surface area. The total body surface area (BSA) is represented by 100%. Another method used is the age-specific burn diagram or chart. Burn size is expressed as a percentage of the total BSA. In children, age-related charts are used because their body proportions differ from those of an adult and the rule of nines cannot be applied.

Figure 5-1 The rule of nines for estimating burn percentage. (From Ignatavicius D, Winkelman C, Workman M, Hausman K: Medical-surgical nursing: critical thinking for collaborative care, ed. 6, St. Louis, 2009, Saunders.)

Many health care providers use solutions that are expressed in percentages for external as well as internal use (e.g., hydrocortisone cream, lidocaine, and intravenous [IV] solutions).

In current practice, percentage solutions are prepared by the pharmacy, and people can purchase solutions or components of the solutions over the counter. Some institutions require nurses to prepare solutions in house (in the hospital) as well as in home care for clients being cared for at home. Understanding percentages provides the foundation for preparing and calculating dosages for medications that are ordered in percentages.

The term percent (%) means parts per hundred. A percentage is the same as a fraction in which the denominator is 100, and the numerator indicates the part of 100 that is being considered.

Example:

4%=4100 (4 per 100)

PERCENTAGE MEASURES

IV solutions are ordered in percentage strengths, and nurses need to be familiar with their meaning (e.g., 1,000 mL 5% dextrose and water). Percentage solution means the number of grams of solute per 100 mL of diluent.

Example 1:

1,000 mL IV of 5% dextrose and water contains 50 g (grams) of dextrose

% = g per 100 mL; therefore 5% = 5 g per 100 mL

5 g:100 mL = x g:1,000 mL

x = 50 g dextrose

Example 2:

250 mL IV of 10% dextrose contains 25 g (grams) of dextrose

% = g per 100 mL; therefore 10% = 10 g per 100 mL

10 g:100 mL = x g:250 mL

x = 25 g dextrose

In addition to encountering percentage strengths with IV solutions, the nurse may see percentages used with a variety of other medications, including eye and topical (for external use) ointments and creams. For example, Kenalog cream is available in 0.02%, 0.025%, 0.1%, 0.5%; and pilocarpine hydrochloride ophthalmic solution is available in 0.25%, 0.5%, 1%, 2%, up to 10%.

The higher the percentage strength, the stronger the solution or ointment. A misunderstanding of these numbers (%) can have serious consequences.

Example:

10% IV solution is more potent than 5%. A solution of 5% is more potent than 0.9%. Always check the percentage of IV solution prescribed.

Practice Problems

Determine the number of grams of medication and dextrose as indicated in the following solutions.

1. How many grams of medication will 500 mL of a 10% solution contain?

________________________________

2. How many grams of dextrose will 1,000 mL of a 10% solution contain?

________________________________

3. How many grams of dextrose will 250 mL of a 5% solution contain?

________________________________

4. How many grams of medication will 100 mL of a 50% solution contain?

________________________________

5. How many grams of dextrose will 150 mL of a 5% solution contain?

________________________________

Identify the strongest solution or ointment in each of the following:

6. Ophthalmic solution 0.1%, 0.5%, 1% _______________________

7. Ointment 0.025%, 0.3%, 0.5% _______________________

8. Cream 0.02%, 0.025%, 0.25% _______________________

Answers on p. 604

CHANGING PERCENTAGES TO FRACTIONS, DECIMALS, AND RATIOS

The percent sign may be used with a whole number (15%), a fraction (1/2%), a mixed number (14½%), or a decimal (0.6%).

To change a percent to a fraction, drop the percent sign, place the number over 100, and reduce to lowest terms.

Example 1:

8%=8100, reduced is 225

Example 2:

14%=14÷100=14×1100=1400

To change a percentage to a decimal, drop the percent sign, and move the decimal point two places to the left (add zeros as needed).

Example 1:

Example 2:

Example 3:

75%=75100=34 (lowest terms). Divide the numerator of the fraction (3) by the denominator (4).

Example 3 is an alternative method. Drop the percent sign. Write the remaining number as the numerator. Write “100” as the denominator. Reduce the result to lowest terms. Divide the numerator by the denominator to obtain a decimal.

To change a percentage to a ratio, change it to a fraction, and reduce to lowest terms; then place the numerator as the first term of the ratio and the denominator as the second term. Separate the two terms with a colon (:).

Example:

10%=10100=110=1:10

Tags: Calculate with Confidence

Feb 11, 2017 | Posted by admin in PHARMACY | Comments Off

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