N104: Essentials of Nursing Care - Health Safety

N104: Essentials of Nursing Care – Health Safety Study Guide

Dosage Calculations Dosage calculations are necessary when the dose on the medication label differs from the dose ordered. There are several methods for calculating doses. The most common method is the ratio- proportion or formula method. The following basic equation can be applied when preparing solid or liquid forms of the medication: • The dose ordered is the amount of the medication prescribed. • The dose on hand is the weight or volume of the medication available in the units supplied by the pharmacy. • The amount on hand is the basic unit or quantity of the medication that contains the dose on hand. For solid medications, the amount on hand may be one capsule or one tablet. For liquids, the amount may be 1 mL or 1 L, depending on the container. • The amount to administer is the actual amount the nurse will administer. For example, the prescriber orders morphine sulfate 2 mg IV. The dose ordered is 2 mg. The medication is available in a vial containing 10 mg per milliliter. The dose on hand is 10 mg in an amount on hand of 1 mL. Intravenous Flow Rates Intravenous (IV) fluid must be given at a specific rate, neither too fast nor too slow. The specific rate may be measured as ml/hour, L/hour, or drops/min. To control or adjust the flow rate, only drops per minute are used. The IV delivery system contains a needle or plastic dropper, which gives the number of drops per ml (the drop factor). A number of different drop factors are available (determined by the length and diameter of the needle). Common drop factors are: 10 drops/ml (blood set), 15 drops/ml (regular set), and 60 drops/ml (microdrip set). To measure the infusion rate, the nurse must know: • The number of drops • Time in minutes • The formula for calculating flow rates: Volume (mL) × drop factor (gtt/mL) Time (min) = gtts/min(flow rate) Example The physician orders 1500 ml IV saline to be infused over 12 hours. Using a drop factor of 15

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