INTRAVENOUS THERAPY INSTRUCTIONAL PACKAGE WORKBOOK FOR THE CALCULATION OF FLOW RATES AND MEDICATION DOSAGES January 2014
WORKBOOK C O N T E N T S Page Professional Responsibilities 3 Methods for flowrate Determination 4 Practice Calculations 6 Conversion Factors 11 Percentages 12 Ratios 12 Units/Millilitres 13 Dosage based on patient's Weight 13 Medication dosage calculations 14 Practice Calculations 15 Workbook for the Calculation of Flow Rates & Medication Dosages C&C DHB January 2014 Page 2
PROFESSIONAL RESPONSIBILITIES Medical and nursing/midwifery practitioners and technicians are responsible for ensuring intravenous therapy is safe for the patient. The prescribing of medicines and fluids is the responsibility of the medical practitioner or midwife. In most instances the nurse/midwife/technician is responsible for the safe administration of what has been prescribed. This includes knowing the prescribed therapy is safe for the patient. THE RESPONSIBILITIES OF THE PRESCRIBER: Intravenous fluids are given always on the written instruction of the medical staff or midwife. The following must be prescribed: The type and volume of fluids The administration rate Required additives The line number if more than one line in use Intravenous fluids are reviewed and renewed every 24 hours. Intravenous medications are prescribed including the instruction for administration. In an infusion/solution In measured amounts through a burette As a single dose (bolus) THE RESPONSIBILITY OF THE ADMINISTRATOR: The nurse/midwife/technician regulates the flow rate of the infusion. This is done by calculating the number of millilitres (ml) of fluid per hour and drops per minute (dpm). THE DROP SIZE: All the set calibrations below relate to the Baxter Interlink Needleless system. The size of the drop delivered by the giving set determines how many of these drops equal 1 ml. 10 drops = 1 ml eg. some filtered giving set used for blood Therefore 10 drops/min = 1 ml/min products. Also the 's' set. 20 drops = 1 ml Standard giving set. Therefore 20 drops/min = 1ml/min 60 drops = 1 ml Burette, paediatric or mini drop set Therefore 60 drops/min = 1 ml/min (the reservoir holds 100-150 mls) Always read the literature with the infusion set to verify the number of drops that equals 1 ml. Different manufacturers use different drop sizes. Workbook for the Calculation of Flow Rates & Medication Dosages C&C DHB January 2014 Page 3
METHODS FOR FLOW RATE DETERMINATION The following information is available from the prescription: (a) (b) Total volume of fluid to be administered Time span over which the fluid must be administered Manufacturer's information provides the drop factor equivalency. The nurse/midwife's task is to calculate the flow rate for that set. Commonly, three methods are used. The three methods give you the same answer, so chose the one that best suits you! METHOD 1: Total fluid in ml x giving set calibration = drops per minute (dpm) Time in hours 60 minutes METHOD 2: Total fluid in ml x giving set calibration = drops per minute (dpm) Time in minutes 1 METHOD 3: If you have the hourly flow rate of the infusion the figures with which you calculate are smaller. Total fluid in ml = hrly amount given x giving set calibration = drops per minute (dpm) Total hours 60 minutes EXAMPLE A patient is to receive 1000 ml of IV fluid over an 8 hour period. The infusion set has a drop device that delivers 20 dpm. What would be the flow rate in dpm METHOD 1 1000 x 20 = 20000 = 41 2 /3 = 41.66 dpm = 42 dpm 8 60 480 With a calculator, key in steps sequentially: 1000 8 x 20 60 = 41.66 dpm = 42 dpm Workbook for the Calculation of Flow Rates & Medication Dosages C&C DHB January 2014 Page 4
METHOD 2 1000 = 20 = 20000 = 41 2 /3 = 41.66 dpm = 42 dpm 480 1 480 Calculator: 1000 480 x 20 = 41.66 dpm = 42 dpm METHOD 3 1000 = 125 therefore 125 x 20 = 41 2 /3 41.66 dpm = 42 dpm 8 60 60 1 Calculator: 1000 8 = 125 60 x 20 = 41.66 dpm = 42 dpm NOTE: When a calculation gives more than 0.5 eg: 41.6 this is "rounded up" to the next whole figure eg: 42, because drops cannot be divided. When a calculation gives less than 0.5 eg: 41.3 this is "rounded down" to the last whole figure eg; 41 Workbook for the Calculation of Flow Rates & Medication Dosages C&C DHB January 2014 Page 5
PRACTICE CALCULATIONS (Answers on page 9) A. Calculate the flow rates in drops/minute (dpm) for administration sets with the following drop sizes:- (a) 20 drops = 1 ml (b) 60 drops = 1 ml 1. If 2000ml of fluid is to be administered over a 10 hour period, the flow rate should be: (a)... (b)... 2. If 1000 ml of fluid is to be administered over an 8 hour period, the flow rate should be: (a)... (b)... 3. If 1000 ml of fluid is to be administered over a 16 hour period, the flow rate should be: (a)... (b)... 4. A person is to receive 1000 ml over a 4 hour period. The flow rate should be: (a)... (b)... Workbook for the Calculation of Flow Rates & Medication Dosages C&C DHB January 2014 Page 6
5. The infusion rate is 120ml/hr. The flow rate should be: (a)... (b)... 6. The infusion rate is 60ml/hr. The flow rate should be: (a)... (b)... 7. The infusion rate is 90ml/hr. The flow rate should be: (a)... (b)... 8. The infusion rate is 240ml/hr. The flow rate should be: (a)... (b)... 9. The infusion rate is 2.1ml/min. The flow rate should be: (a)... (b)... 10. The infusion rate is 1.25ml/min. The flow rate should be: (a)... (b)... Workbook for the Calculation of Flow Rates & Medication Dosages C&C DHB January 2014 Page 7
B. Calculate the flow rate for the blood administration set 10 drop size = 1 ml 11. A person is to receive 300ml of blood in 3 hours. 12. A person is to receive 330ml of blood in 2 hours: C. Calculate the number of ml/hr so that a person will receive: 13. 1500ml over 12 hours 14. 1000ml over 24 hours 15. 800ml over 8 hours D Calculate the number of ml/min so that a person will receive: 16. 75ml/hr 17. 125ml/hr Workbook for the Calculation of Flow Rates & Medication Dosages C&C DHB January 2014 Page 8
ANSWERS 1a 2000 x 20 = 40000 = 10x60 1 600 66.6 = 67 7a 90 x 20 = 1800 = 60 1 60 30 1b 2000 x 60 = 120000 = 10x60 1 600 200 7b 90 x 60 = 5400 = 60 1 60 90 2a 1000 x 20 = 20000 = 8x60 1 480 41.6 = 42 8a 240 x 20 = 4800 = 60 1 60 80 2b 1000 x 60 = 60000 = 8x60 1 480 125 8b 240 x 60 = 14400 = 60 1 60 240 3a 1000 x 20 = 20000 = 960 1 960 20.8 = 21 9a 2.1 x 20 = 42 3b 1000 x 60 = 60000 = 16x60 1 960 62.5 = 63 9b 2.1 x 60 = 126 4a 1000 x 20 = 20000 = 4x60 1 240 83.3 = 83 10a 1.25 x 20 = 25 4b 1000 x 60 = 60000 = 4x60 1 240 250 10b 1.25 x 60 = 75 5a 120 x 20 = 2400 = 60 1 60 40 11 300 x 10 = 30000 = 3x60 1 180 16.6 = 17 5b 120 x 60 = 7200 = 60 1 60 120 6a 60 x 20 = 1200 = 60 1 60 20 12 330 x 20 = 3300 = 2x60 1 120 27.5 = 28 6b 60 x 60 = 3600 = 60 1 60 60 Workbook for the Calculation of Flow Rates & Medication Dosages C&C DHB January 2014 Page 9
13 1500 = 12 125ml/hr 16 75 = 60 1.25ml/min 14 1000 = 24 = 41.66 42ml/hr 17 125 = 60 2.08ml/min 15 800 = 8 = 100ml/hr Workbook for the Calculation of Flow Rates & Medication Dosages C&C DHB January 2014 Page 10
CONVERSION FACTORS Medications and intravenous solutions are expressed in terms of units as determined by the International System of Units (SI Units). The units with which we are concerned are: Weight: 1 kilogram (kg) = 1000 gram(g) 1 gram(g) = 1000 milligram(mg) 1 milligram(mg) = 1000 micrograms(mcg) Volume: 1 litre(l or L) = 1000 millilitres(ml) Note: Millilitre(ml) has supplanted the older term cubic centimetre (cc). To convert from unit to unit, the following basic procedures should be used: kg to g Multiply by 1000 g to mg Multiply by 1000 mg to mcg Multiply by 1000 g to kg Divide by 1000 mg to g Divide by 1000 mcg to mg Divide by 1000 PRACTICE CALCULATION PLEASE COVER 0.5g to mg 0.5 x 1000 = 500mg 2500g to kg 2500 1000 = 2.5kg 0.5L to ml 0.5 x 1000 = 500ml 0.01g to mg 0.01 x 1000 = 10ml 0.0007g to mg 0.0007 x 1000 = 0.7mg 0.4L to ml 0.4 x 1000 = 400ml 0.0025L to ml 0.0025 x 1000 = 2.5ml 450ml to L 450 1000 = 0.450 Workbook for the Calculation of Flow Rates & Medication Dosages C&C DHB January 2014 Page 11
PERCENTAGES Sometimes drugs are available in a form where the concentration is expressed as a percentage (%). The term percent means "in a hundred". It is a method of expressing strength, eg: (a) 1% lignocaine. This means 1 gram of lignocaine in 100ml of fluid (b) 50% dextrose solution means 50 grams of dextrose in each 100ml of fluid. To convert a decimal to a percentage Multiply by 100 or move the decimal point two places to the right. To convert a percentage to a decimal Divide by 100 or move the decimal point two places to the left. EXAMPLE : The doctor prescribes 5% Dextrose 1000mls to be infused over 10 hours. How much Dextrose will the patient receive each hour? Calculation : Hourly rate of infusion - 1000 = 100 ml/hour 10 5% translates to 5grams per 100mls, therefore the patient will receive 5 grams of Dextrose per hour. Answer : 5 grams. RATIOS The concentration of a drug may also be expressed as a ratio. eg: (a) Adrenaline 1 : 1000 solution This means there is 1 gram of adrenaline in each 1000ml of fluid (b) Isoprenaline 1 : 5000 solution This means there is 1 gram of isoprenaline in each 5000ml of fluid. Workbook for the Calculation of Flow Rates & Medication Dosages C&C DHB January 2014 Page 12
UNITS/MILLILITRES Concentration may also be expressed as units/millilitres (u/ml) or international units/millilitres (iu/ml) eg: Heparin 25,000iu/5ml Therefore each ml contains 5,000iu of Heparin. DOSAGE BASED ON PATIENT'S WEIGHT The amount of a medication or solution is often based on the patient's weight and is prescribed as milligram/kilogram(mg/kg). The prescribed mg dose in multiplied by the kg weight of the patient. EXAMPLE: The prescribed dose is 25mg/kg. The patient weights 66.0kg What is the dose required for the patient? Calculation: 25mg x 66.0kg = 1650mg To convert to grams(g) move decimal point three places to the left or divide by 1000. Answer: 1.65g PRACTICE CALCULATIONS PLEASE COVER Prescribed dose = 50mg/kg Weight of patient = 79kg What is the dose required for the patient? 50mg x 79kg = 3950mg 1000 = 3.95g Prescribed dose = 35mg/kg Weight of patient = 62.5kg What is the dose required for the patient? 35mg x 62.5kg = 2187mg 1000 = 2.187g Workbook for the Calculation of Flow Rates & Medication Dosages C&C DHB January 2014 Page 13
MEDICINE DOSAGE CALCULATIONS There are several methods used to calculate medication dosages. The preferred option is the fraction method. Mathematically this method is easy, but it requires perfect recall of the formula or ready access to it when needed. It is insufficient to rely on memory alone. However, a mental approximation can be made as a check to avoid gross error. EXAMPLE 1 Voltaren comes in 3ml ampoules containing 75mg of the drug. How many ml will you administer for a 60mg IM dose? Approximation: We know that 60 is more than 2 / 3 of 75. Therefore your answer will be more than half the amount in a 3ml ampoule. THE FRACTION METHOD Calculation Formula Amount you want x Volume you have Amount you have 1 The formula gives the fraction of the available solution you require. This can be greater than 1. You want to administer 60mg. The 3ml solution contains 75mg. Amount you want = 60 You must give 60 of the 3 ml solution 75 75 Remember "of" means multiply so 60 of 3 ml is 60 x 3 75 75 1 Therefore: 60 x 3 = 180 75 = 2 2 / 5 = 2.4ml With a calculator: 60 75 x 3 = 2.4 Check this agrees with the approximation Answer = 2.4ml will give you 60mg of Voltaren Note: You do not round up or round down when administering medications. Dosages smaller than 1 ml are measurable on a syringe. Workbook for the Calculation of Flow Rates & Medication Dosages C&C DHB January 2014 Page 14
EXAMPLE: 2 Approximation: The concentration of Amoxil syrup is 125mg per 5ml. How many ml will you administer for a 50mg dose? We know that 50 is less than half of 125. Therefore your answer will be less than half of 5 ml. CALCULATION Formula Amount you want x Volume you have Amount you have 1 50 x 5 = 205 = 2ml 125 1 125 With a calculator: 50 125 x 5 = 2 Answer: Administer 2ml syrup to give 50mg Amoxil Try these following calculations: 1 The doctor has ordered Morphine Sulphate 8mg to be given IM. The vial is labelled 1ml = 10mg Please Cover 8 x 1 = 0.8ml 10 1 The patient will receive ml 2 The doctor has ordered Atropine Sulphate 0.4mg for the patient. 0.4mg = 400mcg The vial of Atropine is labelled 600mcg in 1ml. The patient will receive ml. 400 x 1 = 0.66ml 600 1 3 The doctor has ordered Vitamin B12 1.6mg IM. The vial is labelled Neo-cytamen 1000mcg in 1ml. You will administer ml. 4 The doctor has ordered Aminophylline 380mg IV. The vial is labelled 250mg in 10ml. The patient will receive ml 1.6mg = 1600mcg 1600 x 1 = 1.6ml 1000 1 380 x 10 = 380 250 1 25 = 15.2ml Workbook for the Calculation of Flow Rates & Medication Dosages C&C DHB January 2014 Page 15
PRACTICE CALCULATIONS (Continued) Please Cover 5 The doctor has ordered Gentamicin Sulphate 60mg IV. The vial is labelled 80mg/2ml. 60 x 2 = 120 = 1.5ml 80 1 80 You will administer ml 6 The doctor has ordered Frusemide 25mg IV. The vial is labelled 20mg/2ml (to be added to 100ml sodium chloride 0.9%). 25 x 2 = 50 = 2.5ml 20 1 20 You will add ml to the infusion 7 The doctor has ordered Cefoxitin 800mg every 12 hours. You have a 1g vial labelled "Add 2ml of diluent to provide a total solution of 2.5ml" 800 x 2.5 = 20 2ml 1000 1 10 You will administer ml to the patient 8 The doctor asks you to check with him/her Isuprel 1.5mg to be added to 500ml of Dextrose 5% in water. The vial is labelled 1:5000 (0.2mg/ml) The doctor will draw up Isuprel to be added to 500ml of Dextrose 5% in water 1.5 x 1 = 7.5ml 0.2 1 or 1500 x 1 = 7.5ml 200 1 9 The doctor has ordered Xylocaine 500mg to be added to 1000ml of Dextrose 5% in water. The vial is labelled 1g/25ml. 500 x 25 = 125 =12.5ml 1000 1 10 You are asked to check the amount Xylocaine ml will be added to the infusion 10 The doctor has ordered Ranitidine 20mg to be added to 100ml sodium chloride 0.9% in a burette. The vial is labelled 50mg/2ml. 20 x 2 40 = 4 = 0.8ml 50 1 50 5 You will add ml Ranitidine to the infusion Workbook for the Calculation of Flow Rates & Medication Dosages C&C DHB January 2014 Page 16
PRACTICE CALCULATIONS 1 A 1000ml bag of 0.9% sodium chloride has 40mmol of KC1 added. The infusion is discontinued when 600ml of the infusion has been administered. How much KC1 has been infused when discontinued? 2 The physician has ordered 1600ml of IV fluid over an 8 hour period. The infusion set delivers 20 drops/ml. What will be the flow rate? 3 Ward stock of an antibiotic is 500mg. The diluent is 7.5ml of water to provide a total solution of 10ml. You are required to administer 225mg of antibiotic to your patient. What volume of fluid will you administer? 4 What flow rate must be maintained, using an administration set delivering 20drops/ml, to give 1 litre of IV fluid over 12 hours? 5 A dose of 75mg of Pethidine has been ordered. It is available in ampoules of 100mg in 2ml. What volume is to be administered? 6 Ward stock of an IV antibiotic is 1g. You are required to administer 750mg to your patient. The diluent is 7.5ml of water to provide a total solution of 10ml. How much will you give your patient? 7 Ward stock of a drug is 200mg in 5ml. You are required to administer 95mg. What volume will you administer 8 Your patient is to receive 80ml/hour of IV fluid. The infusion is administered through the Standard administration set that delivers 20 drops/ml. What should be the flow rate? 9 You are required to add 15mmol of KC1 to a 500ml bag of IV fluid. Ward stock of KC1 is 10mmol per 10ml. How much will you add? Workbook for the Calculation of Flow Rates & Medication Dosages C&C DHB January 2014 Page 17
PRACTICE CALCULATIONS - ANSWERS 1 600ml x 40mmol = 2400 = 24 = 1000 1000 1 24mmol 2 1600 = 200ml/hr = 200ml x 20 = 8 hrs 60 1 66.6 = 67dpm 3 225mg x 10ml = 2250 = 4½ = 500mg 1 500 4.5ml 4 1000ml = 83.3ml/h = 83.3ml x 20 = 12 60 1 27.7 = 28dpm 5 75mg x 2ml = 150 = 3 = 1½ = 100 1 100 2 1.5ml 6 750mg x 10ml = 7500 = 15 = 7½ = 1000ml 1 1000 2 7.5ml 7 95mg x 5ml = 475 = 19 = 2 3 / 8 = 200mg 1 200 8 2.37ml 8 80ml x 20 = 1600 = 80 = 26 2 / 3 = 60mins 1 60 3 26.6 = 27dpm 9 15mmol x 10mmol = 150 = 15 = 10mmol 1 10 1 15ml Workbook for the Calculation of Flow Rates & Medication Dosages C&C DHB January 2014 Page 18