By Kent R. Spitler, MSEd, RN, NREMT-P EMS Educator Charlotte, North Carolina Introduction Medication calculations can cause frustration for EMS providers. Math and pharmacology can make it difficult to succeed on course exams, in the clinical setting, and in the field. There is a solution to make medication calculations easier. The answer to this problem is simple by showing students how to perform calculations using a simple process. While there are plenty of good drug and solution textbooks, study guides, and presentations available showing the methods of medication calculations, It seems that it much of it causes mathematical confusion often called “math mental blocks” for many EMS providers. There are only a few drug calculations necessary in the prehospital setting. These calculations include IV drip rates, IV piggyback infusion, IM and Subcutaneous injection. A good review of the metric system is in order here since medicine is based on this measurement system. It is necessary to practice drug calculations on a regular basis to gain a comfort level with the methods. The best way to achieve this comfort level is to practice medication calculations 30 minutes a day for six months and it will come natural after while. Common abbreviations are used in medication administration for all medical fields. Below is a list of some abbreviations that are found in drug calculations used in the prehospital setting: Gram = Meter = Liter = Gm = Gtts = Hr = IVPB = Mcg = Mass Length Volume Grams Drops Hour Intravenous Piggyback Micrograms 5 cc = 15 cc = 30 cc = 30 cc = 60 mg = 1 Gram = X= x= 1 tsp 1 TBS or 3 tsp 1 ounce 2 TBS 1 Grain 15 Grains Multiply Unknown answer / = Per or Each = Divide - = Minus gtts/ml = Drops per milliliter gtts/min = Drops per minute Conversion
Min = Minute Mg = Milligrams Ml = Milliliters
Convert grams to milligrams: multiply X 1000 Convert liters to milliliters: multiply X 1000 Convert milligrams to grams: divide by 1000 Convert milliliters to liters: multiply X 1000 Don’t forget where to place the decimal
It is assumed that the reader has an understanding of general mathematics. It also assumed that the reader has a general understanding of the metric system as it relates to medicine and drug calculations.
IV Drip Rate Calculations IV calculations are easier than they appear. There are four common drip sets in two categories: minidrip set which includes microdrip or pediatric set, and regular drip set which include macrodrip or adult sets. The various drip sets are as follows: 1
60 gtts/ml 10 gtts/ml 15 gtts/ml 20 gtts/ml
minidrip drip set regular drip set regular drip set regular drip set (this set is sometimes used, but it’s not as popular)
Next, think about where these numbers came from for use in medicine. Since there are 60 minutes in one hour and 60 seconds in one minute, it appears natural to calculate drip rates based on the clock. There is one (1) 60 minute period in one hour There are six (6) 10 minute periods in one hour There are four (4) 15 minute periods in one hour There are three (3) 20 minute periods in one hour It makes sense doesn’t it? When calculating IV drip rates all that needs to be done is divide the amount to be infused over one (1) hour by how many time periods the drip set has in one (1) hour based on the clock. 60 gtts/ml set If infusing 60 ml/hr using a 10 gtts/ml set 60 divide 60 by 6 (6 - 10 minute periods) which 50 10 10 gtts/ml set is 10 or 10 gtts/min. If infusing 60 ml/hr using a 60 gtts/ml set divide 60 by 1 (1 60 minute 45 15 15 gtts/ml set period) which is 60 or 60 If infusing 60 ml/hr gtts/min. using a 15 gtts/ml set divide 60 by 4 (4 - 15 40 minute periods) which 20 20 gtts/ml set is 15 or 15 gtts/min. 30 The calculations are based on the following formula: If infusing 60 ml/hr using a 20 gtts/ml set Amount to be infused X drip set = x gtts/min divide 60 by 3 (3 - 20 Time (in minutes)...