Medication Calculations PDF

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Activity 6: Medication safety Access: Alternative resources: You will also find medication calculations required for this course available at several web sites and in other texts. For example http://nursing.flinders.edu.au/students/studyaids/drugcalculations/ Revision calculations from Teaching and Learning are also available in Medication Calculations folder in Blackboard. Dosage Calculation Revision: Complete the following medication calculations that will be checked in tutorial class. Amount required = Dose ordered x Volume of dose available Dose available 1. Mr. Fraser is ordered Ramipril 5mg daily. You have in stock Ramipril 2.5 mg tablets. How many tablets will you give for his dose? a. 5 x 2.5 = 12.5/5 = 2 tablets daily 2. Mr. Fraser takes Panadol Osteo 2 tablets twice a day. Each tablet contains 665 mg paracetamol. a. How many mg is in each dose? = 1330mg per dose. b. How many grams in each dose? 1.33mg 3. On arrival in theatre Mr. Fraser is ordered IVI Gentamycin 240 mg stat. Gentamycin ampoules contain 80mg /2mL. How many mL of Gentamycin will you draw up for the required dose? Dose to be given/stock strength X stock volume/1 240/80 x 2 = 3x2 = 6mL

Activity 4: IV Fluid management Calculations Access: Gatford & Phillips Chapter 4 - Intravenous infusion pages 85-96 Key formulas for IV fluid volumes and drip rates and example questions: Read the explanations and formulas and answer the following questions. Calculators are permitted, but students are advised to attempt simple calculation without, as this helps with understanding. 1. Amount of fluid over time = Hourly rate x number of hours. Example: An intravenous infusion running at 80 mL/h. How much fluid will be received in (a) 3h = 240mL (b) 8h = 640mL (c) 12h = 960mL 2. Length of infusion time = Total volume to be infused divided by hourly rate. Time for an infusion to run: Time in hrs = Volume in ml Rate in hrs Example: One litre of IV fluid running at a rate of 80 mL/h. How long will it take to administer the litre of fluid? Give you answer in hours and minutes. ● 12 hours and 30 minutes

3. When setting an electronic infusion pump, the pump is set by dialing the rate in mL/hr, and the volume to be infused. If an infusion is ordered over a number of hours rather than by an hourly rate, calculate the hourly rate as shown. Hourly rate in mL: Rate in mL/hr = Volume in mL Time in hrs Example: IV 1 litre to run over 8 hours, how many mL/hr will you give? ● 1000/8 = 125mL/hr 4. When fluid is ordered over a number of minutes, you need to enter that into the above formula as a fraction or decimal of the time in hours, or use the formula below. Hourly rate if time given in minutes: Rate in mL/hr = Volume in mL x 60 Time in minutes Example: A fluid challenge of 300 mL is to run over 30 minutes. Calculate the required hourly rate. ● 600mL/hr 5. When on electronic infusion pump is not available or in use, the nurse needs to calculate a drip rate to manually adjust and count the number of drops to give the fluid at the required rate. The standard adult giving set currently in use delivers 20 drop/ mL of fluid. Flow rate in drops per minute if time given in hours: Rate (drops /minute) = Volume in mL x Drop factor (drops /mL of giving set) Time in hours x 60 Note quick tip: 20 divided by 60 equals one third, so the drip rate for a standard adult giving set is one third of the ordered hourly rate. Example: Intravenous infusion (IV) is ordered at 80mL/hr, however an IV pump is not available. The IV administration set being used delivers 20 drops/mL Calculate the required drip rate in drops per minute. Give the answer to the nearest whole number. ● 27

Activity 6: Medication Safety PCA dose calculations: Refer to Gatford and Phillips pages 103- 105 When administering infusions containing an amount of medication the nurse needs to understand the concentration of the medication contained in the infusion fluid, so they can calculate the dose of medication being administer either at a regular infusion rate or, in the case of PCA, each time the patient presses the button. Calculating strength of a solution: Strength of solution in units of measurement (mg, micro or units)/mL = Dosage added Volume of solution in mL

Examples: 1. A patient-controlled analgesia infusion (PCA) infusion contains morphine 100mg in a total volume of 100mL IV fluid. The PCA machine has been set, to deliver a bolus of 2mL fluid each time the button is pressed. a. What is the concentration of the morphine in mg/mL?

b. How much morphine is delivered each time the button is pressed? c. If the button has been pressed 5 times in one hour, how much total morphine has been received that hour? 2. A patient-controlled analgesia infusion (PCA) infusion contains hydromorphone 20mg in a total volume of 100mL IV fluid. The PCA machine has been set, to deliver a bolus of 1mL fluid each time the button is pressed. a) What is the concentration (micrograms/mL) of the infusion solution? (Note mg to microgram conversion needed) b) How much hydromorphone is in each bolus dose? c) If the patient has five bolus doses in an hour, how much hydromorphone will he have received that hour? 3. A patient has a PCA with Fentanyl 500 microgram in total 50mL Normal Saline the PCA machine is set to deliver 1 mL each time the button is pressed. a. What is the concentration of Fentanyl in microgram/mL? b. How much Fentanyl is given in each dose? c.

If the patient has pressed the button 7 times in 2 hours, how much Fentanyl received?

Activity 8: Paediatric Medication Calculations Access: Gatford & Phillips Chapter 5 Paediatric dosages pages 110-120. Apply your learning as you complete the following questions. Calculators are permitted. Notes: Children can vary significantly in size and weight at the same age, depending on their individual genetic make-up and pattern of growth, as well as health relate issues. In ordering medications for children doctors most commonly base the dosage order on recommendation of dosage per kilogram child’s body weight. This information is sometimes provided in dose/kg/single dose OR dose/kg/day (to be divided by the number of doses daily) Calculating recommended dose by child’s weight: Recommended dose = Dose per kg x weight in kg Example: 1. a. The recommended paracetamol dose for children is 15mg/kg per dose up to 4th hourly with a maximum of 4 doses in 24 hours. Calculate the correct dose of paracetamol for a child who weighs 10 kg. b. What volume of paracetamol elixir will you administer to give the above dose if the available stock strength is 100 mg/5mL? (use dosage calculation) Give you answer correct to 1 decimal point. Calculating recommended individual dose from daily dose recommendation: Recommended daily dose divided by number of doses per day Examples: 2. Cephalothin, 60 mg/kg/day, 4 doses per day a. What is the daily dose for a child weighing 10kg? b. What is the individual dose? 3. Amoxicillin, 45 mg/kg/day, 4 doses per day for a child weighing 20kg? a. What is the daily dose? b. What is the individual dose?

IV Fluids: Flow rate in drops per minute if time given in hours using a paediatric or micro drip set with drop factor of 60: Rate (drops /minute) = Volume in mL x Drop factor (drops /mL of giving set) Time in hours x 60 Example: 4. Give IV fluid at rate of 50mL/hr using a micro giving set with drop factor of 60 drops per mL Note quick tip: 60 cancels to 0 60 Therefore, drip rate is the same as the hourly rate when using a micro giving set.

Activity 6: Medication Calculations Complete the following calculations and bring your answers to class. Note: When administering insulin, a specific insulin syringe marked in units should be used. This is a NSW Health policy to try to reduce medication error with insulin administration. However, students still need to understand conceptually that most vial concentrations are 100units/mL, and the implication for volume to be drawn up. Check insulin syringes in clinical laboratories or see Gatford & Philips page 81. Once insulin is further diluted (as for an IV insulin infusion), the nurse must understand the concentration of the solution, and implication for dose given.

1. Your patient is ordered a stat dose of 6 units of Actrapid insulin. The vial contains 100units per mL. How much volume do you need to draw up to give the required dose? a) Dosage formula = 6/100 = 0.06 2. You are preparing an insulin infusion of 50 units of Actrapid insulin in Normal Saline with a total volume of 50 mL Note: This is a standard strength for an IV insulin infusion for adults. a) 50 units/50mL = 1 Refer to dosage algorithm for children in Blackboard > Course Materials> Tutorial 5 > Paediatric DKA Management Guidelines a. What volume of Actrapid do you need to draw up? i. b. What size/type of syringe would you use to ensure as accurate a dose as possible? i. c.

You add the Actrapid to a 50 mL syringe contain normal saline. How much normal saline do you need to make a total volume of 50mL? i.

d.

How many units of insulin are there per mL of this solution? i.

e. To give three (3) units per hour, what hourly rate will you set the syringe pump? i....