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Medication Calculations

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  • 1. In Critical Care Nursing, often medications are ordered as IV continuous drips. These medications are potent and the nurse must maintain constant monitoring to assess for desired effect and potential side effects. The physician may order to “titrate” an IV medicated drip. To “titrate” a drip is to increase or decrease a drip to achieve the desired effect. Such drugs may be 1) Lasix, 2) Dopamine, 3) Dobutamine, 4) Nipride, 5) Nitroglycerin, 6) Heparin, and 7) Insulin. As an example, the nurse may “titrate” an Insulin drip and increase the rate to bring the serum blood glucose levels down to the normal range. Once this range is met, the nurse may then maintain that rate or decrease the rate to prevent hypoglycemia. Many drugs are administered IV route in the Critical Care Unit. Medications may be ordered in: “mg/hr”: Lasix, Cardizem , Aminophylline “units/hr”: Heparin and Insulin “mcg/min”: Nitroglycerin “mcg/kg/min”: Dopamine and Dobutamine “mg/min”: Lidocaine Two Formulas can be used: “Formula Method” D x V = flow rate (ml/hr) H “Ratio – Proportion” (D) osage on hand = Dosage prescribed (Q) (H) Solution on hand X (ml/hr we are solving for)
  • 2. MEDICATONS IN “MG/HR” …. CASE STUDY: Mrs. Wilma Wetlung has been admitted with CHF and requires a Lasix drip. The MD has ordered Lasix @ 6mg/hr. You receive a Lasix IV bag of 200mg in 100ml of 0.9% NaCl. How many ml/hr will you infuse the drip at? Formula Method: 6mg/hr X 100ml = flow rate (ml/hr) 200mg ANSWER: 3 ml/hr Ratio – Proportion Method: 200mg X 6mg/hr = 200x=600 x = 3ml/hr 100ml X MEDICATIONS IN “UNITS/HR” …. CASE STUDY: Mr. D. V. Tee came into the ER c/o shortness of breath and was found to have a pulmonary embolism. He was started on a Heparin drip. The MD ordered for Heparin 25,000units in 500ml of 0.9% NaCl to infuse at 1200 units/hr. What will be the rate in ml/hr? Formula Method: 1200 units/hr X 500ml = flow rate (ml/hr) 25,000 units ANSWER: 24 ml/hr Ratio – Proportion Method: 25,000 units X 1200units/hr = 25,000x = 600,000 x=24ml/hr 500 ml X MEDICATIONS IN “MCG/MIN” …. These medication calculations add one extra step. This step is to multiply by 60 at the end because your order is “per minute” and your IV pump infuses “per hour”.
  • 3. CASE STUDY: Mr. O. Klusion came into the ER with chest pain. The patient is admitted to the CCU and placed on a Nitroglycerin IV drip to titrate for chest pain and to maintain a SBP >90<140. The MD orders to start it at 20mcg/min. You hang a bottle of 50mg in 250ml D5W. How many ml/hr will it be infused? Formula Method: (Ordered) 20mcg/min x 250ml (On Hand) 50mg Next: Convert 50mg to mcg ….. 20mcg/min x 250ml = 0.1ml/min 50,000mcg Finally: Multiply x 60minutes …. 0.1ml/min x 60min = 6ml/hr Ratio – Proportion Method: 50mg X 20mcg/min = 250ml X Next: Convert 50mg to mcg … 50,000mcg X 20mcg/min = 50,000x = 5,000 x=0.1ml/min 250ml X Finally: Multiply x 60mintes … 0.1ml/min x 60min = 6ml/hr MEDICATIONS IN MCG / KG / MIN … These formulas are the same except that you must also multiply by the patient’s weight in kg. If the patient’s weight is provided in pounds, then you must convert it to kg by dividing by “2.2”.
  • 4. Common medications ordered this way are Dopamine and Dobutamine. Let’s try one. Dobutamine to infuse at 5mcg/kg/min. The drug is supplied in 500mg in 250ml of 0.9% NaCl. The patient weighs 80kg. Formula Method: 5mcg/kg/min X 250ml = 500mg Next, convert 500mg to mcg … 5mcg/kg/min X 250ml = 0.0025 ml/min (per kg) 500,000mcg Next, multiply by kg … 0.0025ml/min X 80kg = 0.2ml/min Lastly, multiply by 60minutes to give your hourly rate …. 0.2ml/min X 60 = 12ml/hr (final answer) NOW, YOU TRY ONE! CASE STUDY: Your patient in the CCU who endured an MI is having decreased cardiac output. The vital signs and urine output are decreasing. The Cardiologist wants to start the patient on Dobutamine drip and orders it to start at 5mcg/kg/min. You have a bag of 800mg/250ml NS. The morning weight was 110kg. Calculate your rate (ml/hr) for the IV pump. GO AHEAD NOW …. ANSWER SHOULD BE: 10.3ml/hr
  • 5. 1) Cardizem 250mg in 250ml of 0.9% NaCl to infuse at 10mg/hr 2) Heparin 25,000 units in 500ml 0.9% NaCl to infuse at 1150units/hr 3) Insulin 200 units in 100ml of 0.9% NaCl to infuse at 4units/hr 4) Lasix 200mg in 100ml of 0.9% NaCl to infuse at 2mg/hr 5) Dopamine 800mg in 250ml of D5%W to infuse at 10mcg/kg/min. The patient weighs 83kg. 6) Dobutamine 250mg in 250ml of D5%W to infuse at 10mcg/kg/min. The patient weighs 62kg. 7) Lidocaine 1G in 250ml of D5%W to infuse at 2mg/min 8) Nitroglycerine 50mg in 250ml D5%W to infuse at 10mcg/min ANSWERS: 1) Cardizem @ 10ml/hr 2) Heparin @ 23ml/hr 3) Insulin @ 2ml/hr 4) Lasix @ 1ml/hr 5) Dopamine @ 15.6ml/hr 6) Dobutamine @ 37.2ml.hr 7) Lidocaine @ 30ml/hr 8) Nitroglycerine @ 3ml/hr BACK TO N240 HOMEPAGE