Medical Dosage Calculations A Dimensional Analysis Approach Eleventh Edition Chapter 11 Flow Rates Dosage Rates for Intravenous Medications

Learning Objectives (1 of 2) 11.1 Describe intravenous (IV) medication administration. 11.2 Convert from dosage rates (drug/time) to IV rates (volume/time). 11.3 Convert from IV rates (volume/time) to dosage rates (drug/time). 11.4 Calculate infusion rates when medication must be added to the intravenous piggyback (IVPB) bag.

Learning Objectives (2 of 2) 11.5 Calculate infusion rates based on the size (weight or body surface area [BSA]) of the patient. 11.6 Calculate flow rates for IV push medications. 11.7 Calculate the duration of an IVPB infusion. 11.8 Calculate flow rates for medication requiring titration. 11.9 Construct a titration table.

Intravenous Piggyback Infusions (1 of 2) Figure 11 Intravenous Piggyback Infusions (1 of 2) Figure 11.1 Primary and secondary (IVPB) infusion setup.

Intravenous Piggyback Infusions (2 of 2) Figure 11 Intravenous Piggyback Infusions (2 of 2) Figure 11.2 Packages of secondary IV tubing: (a) 60 drops per mL, (b) 10 drops per mL. (Courtesy of Baxter Healthcare Corporation. All rights reserved. Photos by Al Dodge.)

Converting Flow Rate to Dosage Rate Example 11.1 An IV is infusing at 100 mL/h. The strength of the solution is 200 mg in 500 mL. Find the dosage rate in mg/h. Convert 100 mL/h to mg/h using the strength of the solution as the unit fraction.

Converting Flow Rate to Dosage Rate Example 11.2 (1 of 2) The patient is receiving 10 mg/min through an IVPB. The solution has a strength of 400 mg per 100 mL. Find the flow rate in mL/h.

Converting Flow Rate to Dosage Rate Example 11.2 (2 of 2) Convert mg/min to mL/h using the strength of the solution as the unit fraction.

Calculating Dosage Rates Based on the Size of the Patient A medication order might include the compound rate: “2 mg/kg/min.” This means that each minute the patient is to receive 2 milligrams of the drug for every kilogram of body weight. For computational purposes this is written as

Calculating Dosage Rates Based on the Size of the Patient Example 11 Calculating Dosage Rates Based on the Size of the Patient Example 11.3 (1 of 2) The prescriber ordered: 250 mL 5% D/W with 9 mg Aredia, 0.001 mg/kg/min IV stat. The patient weighs 80 kilograms, and the drop factor is 20 drops per milliliter. Calculate the flow rate in gtt/min. Patient’s weight: 80 kg. Order: 0.001 mg/kg/min. Solution strength: 9 mg = 250 mL. Drop factor: 20 gtt = 1 mL.

Calculating Dosage Rates Based on the Size of the Patient Example 11 Calculating Dosage Rates Based on the Size of the Patient Example 11.3 (2 of 2) Size of the Patient × Compound Order = Dosage Rate

IV Push Example 11.4 (1 of 2) 500 mg of a drug is ordered IVP over 2 min. The concentration of the drug is 100 mg/mL. How many mL will you administer? Determine the number of mL you will push during each 30-second interval.

IV Push Example 11.4 (2 of 2)

Adding Drug to an IVPB Example 11.5 (1 of 2) A patient must receive 300 mg of a drug IVPB in 100 mL NS over 60 minutes. How many mL must be added to the IV bag if the vial of the drug has strength of 75 mg/mL? At what rate should the pump be set?

Adding Drug to an IVPB Example 11.5 (2 of 2)

Chapter Summary (1 of 3) A secondary line is referred to as an IV piggyback. IV push, or bolus medications can be injected into a heplock/saline lock or directly into the vein. In a gravity system, the IV bag that is hung highest will infuse first.

Chapter Summary (2 of 3) An order containing mg/kg/min directs that each minute, the patient must receive the stated number of milligrams of medication for each kilogram of the patient’s body weight. For calculation purposes write mg/kg/min as:

Chapter Summary (3 of 3) When the size of the patient is multiplied by a compound rate, the dosage rate is obtained. When titrating medications, the dose is adjusted until the desired therapeutic effect is achieved.