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Med Math The basics use like units use common sense find a formula/system that works for you

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Making weight.. 1 kilogram (kg) = 2.2 pounds (lb) Actual conversion Wt: 220 lb 220 divided by 2.2 = 100kg 10% or Midnight rule Half of 220 = 110 10% of 110 = 11 Subtract 11 from 110 = 99kg

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Metric conversions 1 gram (g) = 1000 milligrams (mg) 1 mg = 1000 micrograms (mcg) 1 liter (L) = 1000 milliliters (ml) You need to give 500 mcg. How many mg? Mg - move decimal 3 places to the left = 0.5 mg OR 500 = half of 1000 so half of 1 =.5 mg You need to give 100 mg. How many mcg? How many g? mcg - move decimal point 3 places to the right = 100,000 mcg g - move decimal point 3 places to the left = 0.1 g

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Basic calculations Desired dose (D) Known dose on hand (H) x Unit of measure or volume on hand (Q) = volume or unit of measure to be administered (X) D X Q = X H

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Example 1 You are ordered to give 5 mg Valium IV. The label states there is 10 mg in 2cc (10mg/2cc). How many ccs will you give? DD= 5mg Concentration = 10 mg Volume on hand = 2 cc Wight conversion need = no Unit to be given= cc Formula #1 Desired Dose X Volume on Hand = ___ml to be given Concentration 5 mg X 2 cc = 1 cc You will give 1cc! 10 mg

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Example 2 You are to give 0.5 mg/kg IV push. Your patient weighs 80 kg. The drug comes packaged: 100mg/10cc. How many mg will you give? How many ccs will you deliver? Your equation to determine mg will look like this: 0.5 mg/kg x 80 kg = 40 mg to be given Your equation to determine cc will look like this: DD= 0.5mg / kg Concentration = 100 mg Volume on hand = 10 cc Wight conversion need = yes 0.5 mg/kg x 80 kg = 40 mg to be given Unit to be given= cc Formula #1 Desired Dose X Volume on Hand = ___ml to be given Concentration 40 mg x 10 cc = 4cc 100 mg

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Drip calculations Clock method (used only for 4:1 ratio) 4 3 1 60 15 30 45 2 If your dose is 1 mg/min, your drip rate is 15 gtt/min. If the order is greater than 4 mg/min, add them together. A dose of 6 mg/min is 90 gtt/min (4 + 2 =6 so 60 + 30 = 90)

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Drip calculations example 3 Formula 2 : IV bag volume (ml) Desired Dose Admin Setup (gtt) ---------------------- --- X --------------- ------ X ---------------------- = gtt/min Concentration of Drug 1 min 1ml The order is for 5 mg/min. You have a 500 cc bag of NS, a 60 gtt/cc administration set, and 2 g of drug on hand. How many gtt/min will you administer? DD= 5mg Concentration = 2 g = 2000 mg Volume on hand = 500 cc Wight conversion need = no Unit to be given= gtt / min 5 mg x 500 cc (ml) x 60 gtt/cc = 75 gtt/min 2000 mg x 1 min x I ml Note: If the dose is weight based, determine the total dose prior to beginning the equation or multiply everything by the number of kg.

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Questions

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To calculate drip rates / transfusion rates example 4 To calculate the drip rate (drops / minute) Formula 3 # Drip Rate gtt = Volume to be infused (ml) x Drop Factor (gtt/ml) min infusion Time (minutes) 1 unit of blood is approximately 400ml in volume E.g. A unit of blood is prescribed to run over 2 hours; The giving set has a drop factor of 20 gtt /ml. What is the drip rate (drops /min)?

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Calculate the Transfusion rate example 5 E.g. A unit of blood is prescribed to run over 4 hours; The giving set has a drop factor of 20 gtt /ml. What is the drip rate (drops /min) ? Formula 3 # Drip Rate gtt = Volume to be infused (ml) x Drop Factor (gtt/ml) min infusion Time (minutes) Drip rate = 400 ml x 20 gtt Drip Rate is drops 4 hour x1ml Thus Drip Rate = 400ml x 20 gtt x 1 hour 4 hour x 1 ml x 60 minutes By multidimensional analysis units are correct (drops / minute) Drip Rate = 100 / 3 = 33 drops / minute

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Drop rate is rounded up or down to the nearest drop In the clinical setting to be able to count drops / minute it is sensible to have a number divisible by 4 - Thus you would set this drip at 32 drops per minute

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Converting drip rate (gtt /min) to ml /hour Example 6. What is the transfusion rate in ml /hour of a blood transfusion being run at 40 drops / minute through a giving set with drop factor of 20 gtt / ml?

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Formula 3 # Drip Rate gtt/ min = Volume to be infused (ml) x Drop Factor (gtt/ml) infusion Time (minutes) 40gtt/min = volume to be infused x 20 gtt /ml 60 min 40 gtt x 60 min = volume to be infused x 20 gtt/ ml min Volume to be infused = 40 gtt x 60 min = 120ml /hr min x 20gtt/ml

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exampl 7 : You are asked to run an intravenous infusion of 1litre of D5W over 6 hours. What drop rate will you set the infusion at if the giving set has a drop factor of 10 gtt/ml? Volume to be infused X IV Drip Set (gtt) = ____ gtt/min Time in (min) 1ml =1000ml x 10 gtt 6 hours X 60 (mins) X 1ml = 1000 = 27.8 drops / min 36 Since we always round up or down to the nearest drop the actual rate will be 28 drops / minute

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Questions

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example 8: You are asked to set up a 1litre normal saline infusion to run over 10 hours. The giving set has a drop factor of 20 gtt / ml. what rate will you set the drip at in drops/minute? Volume to be infused X IV Drip Set (gtt) = ____ gtt/min Time in (min) 1ml = 1000ml x 20 gtt-------------- 10 hr X (60 min) X 1 ml = 100 = 33 drops / minute 3

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example 9 : A 750ml infusion of 5% dextrose is infusing at 65gtt/min. The drop factor of the giving set is 60 gtt/ml. How long will the infusion take? Volume to be infused X IV Drip Set (gtt) = ____ gtt/min Time in (min) 1ml 65 gtt/min = 750ml x 60 gtt X hr x(60min)x 1ml X = 750 x 60 x 1 65 x 60 X = 11.5 hours

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example 10 : A litre of normal saline is meant to be running over 8 hours. The drip is set at 83gtt/min,the giving set has a drop factor of 20gtt/ml. Volume to be infused X IV Drip Set (gtt) = ____ gtt/mi Time in (min) 1ml 83 drops = 1000ml x 20 gtt min X hr x (60min)x 1 ml X hr = 20,000 = 20,000 = 4 hours 83 x 60 4980 Thus you need to halve the drops /min to 42 drops / minute

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example 11 : A litre of 5% dextrose is running at 80 gtt/min. The drop factor is 60 gtt/ml. What will the pump be set at in ml/Hr.

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Formula 3 : 1000ml X 60 gtt =80 gtt /min time (?) 1ml Time = 1000 ml X 60 gtt/ml = 750 min = 750/60 = 12.5 hrs 80 gtt /min 1000 ml will be run in 12.5 hrs 1000 ml / 12.5 hrs = 80 ml / hr

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example 12 : A heparin infusion is prescribed to run at 5000 units / Hr. The infusion is made up of 25,000 units in 500ml 5% dextrose. What rate in ml/hr will you set the pump? Answer = 100ml/1 hr

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Questions