Chapter 19 Critical Care IV Calculations PowerPoint® Presentation to accompany: Math and Dosage Calculations for Healthcare Professionals Fourth Edition Booth, Whaley, Sienkiewicz, and Palmunen

Learning Outcomes 19.1 Calculate the hourly flow rate for IV infusions ordered in dosage per time (e.g. mcg/min, mg/h).

Learning Outcomes 19.2 Calculate IV flow rates for medications ordered based on body weight over a specified period of time (e.g. mg/kg/min or mcg/kg/min). 19.3 Calculate IV flow rates for titrated medications.

Key Terms Antiarrhythmic medications Dry weight Hemodynamics Titrate Vasoactive medications Antiarrhythmic medications – given to regulate the patient’s heart rate and/or rhythm Dry weight - weight if euvolemic; normal fluid status; no extra fluid weight Hemodynamics – the forces of blood flow Titrate – to adjust the dosage of medication; usually in response the patient’s vital signs or other patient indicator Vasoactive medications – medications that cause the blood vessels to dilate or constrict; used to keep the patient’s blood pressure within the normal range

Introduction Controlling vital functions in critically ill patients requires constant intervention. Constant monitoring is necessary. Medications are infused by an electronic infusion pump and include: vasoactive medications; antiarrhythmic medications; IVs administered at ordered rate. Vasoactive meds cause blood vessels to dilate or constrict. They regulate blood pressure. They affect the heart rate. The dose is titrated in response to changes in vital signs. Antiarrhythmic medications regulate heart rate/rhythm. Other meds are administered as needed by patient. They may be administered at a constant rate or titrated to patient response. If IVs infuse too fast, serious or life-threatening side effects can result. Calculations for this chapter focus on medications used in ICUs. These medications are administered in small quantities according to patient weight and/or over time.

Hourly Flow Rates – DOSAGE PER HOUR Rule 19-1 Converting dosage/h to mL/h Determine the following: D = rate of desired dose Q = dosage unit H = dose on hand A = amount to administer Use preferred method to calculate. Learning Outcome: 19.1 Calculate the hourly flow rate for IV infusions ordered in dosage per time (e.g. mcg/ min, mg/h). Rate of desired dose = mcg/h, mg/h, g/h, units/h dosage unit = mL dose on hand = total number of mcg or mg amount to administer = mL/h Methods of calculation Proportion method Dimensional analysis Formula method

Hourly Flow Rates – DOSAGE PER HOUR (cont.) Example Find the hourly flow rate. Ordered: morphine sulfate 4 mg/h On hand: morphine sulfate 10 mg/100 mL D5W Step A No conversion is needed. Learning Outcome: 19.1 Calculate the hourly flow rate for IV infusions ordered in dosage per time (e.g. mcg/ min, mg/h).

Hourly Flow Rates – DOSAGE PER HOUR (cont.) Example Step B Calculate H = 10 mg; Q = 100 mL; D = 4 mg/hr 10 mg: 100 mL = 4 mg/h : A 100 mL x 4/h = 10 x A 400 mL/h/10 = 10A / 10 A = 40 mL/h Learning Outcome: 19.1 Calculate the hourly flow rate for IV infusions ordered in dosage per time (e.g. mcg/ min, mg/h). Set up proportion. H:Q = D:A or H/Q = D/A

Hourly Flow Rates – DOSAGE PER HOUR (cont.) Example Step C Dosage strength is 1mg to 10 mL and 4 mL x 10 is 40 mL, so it is reasonable. Learning Outcome: 19.1 Calculate the hourly flow rate for IV infusions ordered in dosage per time (e.g. mcg/ min, mg/h). Problem can also be done using dimensional analysis and the formula method. See text for examples of these.

Hourly Flow Rates – DOSAGE PER MINUTE (cont.) Rule 19-2 To convert a per minute order to an hourly rate: Convert the order to mL/min. Determine: D Q H A Calculate using your chosen calculation method. Learning Outcome: 19.1 Calculate the hourly flow rate for IV infusions ordered in dosage per time (e.g. mcg/ min, mg/h). D = rate of desired dose = mg or mcg/min Q = dosage unit = mL H = dose on hand = mg or mcg A = amount to administer = mL/min Calculate using proportion method, dimensional analysis, or formula method.

Hourly Flow Rates – DOSAGE PER MINUTE (cont.) Rule 19-2 (cont.) Convert mL/min to mL/h Proportion and formula methods – multiply by 60 Dimensional analysis use the factor 60/1 as part of your equation Hourly flow rate = mL/h Learning Outcome: 19.1 Calculate the hourly flow rate for IV infusions ordered in dosage per time (e.g. mcg/ min, mg/h).

Hourly Flow Rates – DOSAGE PER MINUTE (cont.) Example Find the hourly flow rate. Ordered: 5000 mg Esmolol in 500 mL D5W at 8 mg/min via infusion pump Step A Convert mg/min to mg/h. A conversion factor or 60 min/1 hr is needed. Learning Outcome: 19.1 Calculate the hourly flow rate for IV infusions ordered in dosage per time (e.g. mcg/ min, mg/h).

Hourly Flow Rates – DOSAGE PER MINUTE (cont.) Example Step B Calculate using dimensional analysis. H = 5000 mg; Q = 500 mL; D = 8 mg/min A mL/h = 500 mL/5000 mg x 8 mg/1 min x 60 min/1 h A mL/h = 2400 mL/50 h A mL/h = 48 mL/h Learning Outcome: 19.1 Calculate the hourly flow rate for IV infusions ordered in dosage per time (e.g. mcg/ min, mg/h). Using dimensional analysis Looking for amount to administer in mL/h so A mL/ hr goes on one side of the equation First factor is dosage unit over dose on hand = 500 mL/5000 mg Second factor is desired dose = 8 mg/ min Third factor is the conversion factor for minutes to hour = 60 min/1 h Cancel units and solve the equation

Hourly Flow Rates – DOSAGE PER MINUTE (cont.) Example Step C Think!...Is It Reasonable? The concentration of 5000 mg/ 500 mL = 10 mg / mL, 8 mg/min x 60 min/h = 480 mg/h and 480  10 = 48 mL It is reasonable. Learning Outcome: 19.1 Calculate the hourly flow rate for IV infusions ordered in dosage per time (e.g. mcg/ min, mg/h). This problem can also be calculated using the proportion or formula method. See examples in text.

Practice Ordered: Procainamide 4 mg/min IV On hand: Procainamide hydrochloride 1 g/ 250 mL D5W Calculate hourly flow rate: ANSWER: 60 mL/h Learning Outcome: 19.1 Calculate the hourly flow rate for IV infusions ordered in dosage per time (e.g. mcg/ min, mg/h). Step A convert mg to grams. 1 g : 1000 mg = D : 4mg 1000 D = 4 g D = 0.004 g / min Step B A mL/h = 250 mL/ 1 g x 0.004 g/1 min x 60min/1 hr [cancel units: g and min] A mL/h = 60 mL/h Step C Since dose on hand is 1 g = 1000mg / 250 mL = 4 mg/mL, and 4 mg x 60 min = 240 and 60 mL x 4 mg/mL = 240 It is reasonable.

IV Flow Rates –BASED ON BODY WEIGHT To find the IV flow rate based upon weight: Convert the weight to kg. Determine the desired dose. Calculate the amount to administer. Calculate the flow rate. Learning Outcome: 19.2 Calculate IV flow rates for medications ordered based on body weight over a specified period of time (e.g. mg/kg/min or mcg/kg/min). Rule 18-8 can be applied to critical care IV dosage calculation. Round patient’s weight to the nearest tenth.

IV Flow Rates – BASED ON BODY WEIGHT (cont.) Example Find the hourly rate for an adult weighing 220 lb. Ordered: dopamine 5 mcg/kg/min On hand : dopamine 400 mg/250 mL NS Step A Convert wt to kg: 1 kg: 2.2 lb = ? : 220 lb 2.2 ? = 220 lb ? = 100 kg Learning Outcome: 19.2 Calculate IV flow rates for medications ordered based on body weight over a specified period of time (e.g. mg/kg/min or mcg/kg/min).

IV Flow Rates – BASED ON BODY WEIGHT (cont.) Example Convert mg to mcg: 1000 mcg: 1 mg = ? : 400 mg ? = 400,000 mcg Concentration of dose on hand is 400,000 mcg/250 mL or 1600 mcg / 1 mL Learning Outcome: 19.2 Calculate IV flow rates for medications ordered based on body weight over a specified period of time (e.g. mg/kg/min or mcg/kg/min).

IV Flow Rates – BASED ON BODY WEIGHT (cont.) Example Step B Calculate desired dose. H = 400 mg Q = 250 mL O = 5 mcg/kg/min 5 mcg/kg = D /100 kg D = 500 mcg/min Learning Outcome: 19.2 Calculate IV flow rates for medications ordered based on body weight over a specified period of time (e.g. mg/kg/min or mcg/kg/min). Using formula method

IV Flow Rates – BASED ON BODY WEIGHT (cont.) Example Calculate amount to administer: H = 1600 mcg Q = 1 mL D = 500 mcg/min Fill in formula D/H x Q = A 500 mcg/min / 1600 mcg X 1 mL = A 0.3125 ml /min = A Find hourly rate: 0.3125 mL /1 min x 60 min/1 h 18.75 mL/h = 18.8 mL/h Learning Outcome: 19.2 Calculate IV flow rates for medications ordered based on body weight over a specified period of time (e.g. mg/kg/min or mcg/kg/min). Proportion method or dimensional analysis can also be used to calculate orders based on body weight. See examples in text.

IV Flow Rates – BASED ON BODY WEIGHT (cont.) Example Step C Think!...Is It Reasonable? Since the desired dose is approximately 1/3 of dose on hand, and 0.3125 is approximately 1/3 of the dosage unit, that is reasonable. Because there are 60 min/h and 60 x 0.3125 = 18.75, the flow rate is reasonable. Learning Outcome: 19.2 Calculate IV flow rates for medications ordered based on body weight over a specified period of time (e.g. mg/kg/min or mcg/kg/min).

IV Flow Rates – BASED ON BODY WEIGHT (cont.) Rule 19-3 If you know: the total amount of medication in the total volume of solution the volume of solution that the patient has received Learning Outcome: 19.2 Calculate IV flow rates for medications ordered based on body weight over a specified period of time (e.g. mg/kg/min or mcg/kg/min).

IV Flow Rates – BASED ON BODY WEIGHT (cont.) Rule 19-3 Then you can use a proportion to calculate the amount of medication the patient has received (dose). Learning Outcome: 19.2 Calculate IV flow rates for medications ordered based on body weight over a specified period of time (e.g. mg/kg/min or mcg/kg/min).

IV Flow Rates – BASED ON BODY WEIGHT (cont.) Example Determine the amount of dopamine the patient received after 45 minutes. Using prior example: total amount of medication = 400 mg total volume of solution = 250 mL flow rate = 18.8 mL/h Learning Outcome: 19.2 Calculate IV flow rates for medications ordered based on body weight over a specified period of time (e.g. mg/kg/min or mcg/kg/min).

IV Flow Rates – BASED ON BODY WEIGHT (cont.) Example Calculate amount received in 45 min. 18.8 mL:60 min = A : 45 min 60 x A = 18.8 mL x 45 60A/60 = 846 mL/60 A = 14.1 mL Learning Outcome: 19.2 Calculate IV flow rates for medications ordered based on body weight over a specified period of time (e.g. mg/kg/min or mcg/kg/min).

IV Flow Rates – BASED ON BODY WEIGHT (cont.) Example total amount of medication = 400 mg total volume of solution = 250 mL volume received = 14.1 mL 400 mg/250 mL = x/14.1 mL 250x/250 = 5640 mg/250 In 45 minutes the patient received 22.6 mg of dopamine. Learning Outcome: 19.2 Calculate IV flow rates for medications ordered based on body weight over a specified period of time (e.g. mg/kg/min or mcg/kg/min).

Practice Determine the amount to administer and flow rate for a patient weighing 175 lb. Ordered: Nitroprusside 0.5 mcg/kg/min IV On hand: Nitroprusside 50mg/ 250 mL D5W Patient’s weight in kg? Desired dose? Flow Rate? 79.5 kg Learning Outcome: 19.2 Calculate IV flow rates for medications ordered based on body weight over a specified period of time (e.g. mg/kg/min or mcg/kg/min). Step A – Convert weight. 1 kg: 2.2 lb = x : 175 lb [cancel units – lb] x = 175 / 2.2lb = 79.5 kg Step B Calculate desired dose: 0.5 mcg/kg = ?/79.5 kg x = 0.5 mcg x 79.5 = 39.75 mcg /min = 39.8 mcg/min Calculate amount to administer: A mL/h = 1 mg/1000 mcg x 250 mL/50 mg x 39.8 mcg/1 min x 60 min/1h [cancel units – mcg, min] A mL/h = 597,000 mg / 50,000 h A mL/h = 11.9 mL / h Step C Dose ordered is approximately 1/5 of dose on hand and 60 x 1/5 = 12, so it is reasonable. 39.8 mcg/min 11.9 mL/h

IV Flow Rates for Titrated Medications (cont.) Goal – to administer the least amount of medication to obtain desired effect Titration is used to adjust rate to the effect on the patient’s hemodynamics. Constant monitoring Frequent adjustment Titration table Learning Outcome: 19.3 Calculate IV flow rates for titrated medications. Monitor patient’s response to medication. Rates must be adjusted quickly and accurately. AP will order the drug, dosage range, and desired effect. AP may add a limitation that would stop an increased dose even if desired effect has not been achieved. Titration table has dosages at different rates within the order range.

IV Flow Rates for Titrated Medications (cont.) Rule 19-4 For safe titration: Calculate starting rate. Calculate minimum allowable rate. Calculate maximum allowable rate. Begin infusion at starting rate. Titrate dosage based on patient response. Learning Outcome: 19.3 Calculate IV flow rates for titrated medications.

IV Flow Rates for Titrated Medications (cont.) Rule 19-4 (cont.) Do not exceed maximal rate. If the patient's response exceeds the prescribed parameters at the minimal dose, discontinue the infusion and notify AP. Learning Outcome: 19.3 Calculate IV flow rates for titrated medications. Call AP for new order if the patient does not have the desired response at maximal dose.

Error Alert The patient’s weight may fluctuate frequently due to changes in volume status. Base calculations on the patient’s “dry weight” when titrating IV rates. Learning Outcome: 19.3 Calculate IV flow rates for titrated medications. Sometimes can be determined by noting patient’s weight when discharged from last hospital stay.

IV Flow Rates for Titrated Medications (cont.) Example Ordered: Dopamine 400 mg/500 mL NS, to infuse at 5 to 20 mcg/kg/min IV to maintain systolic BP greater than 90 mm Hg. Keep HR less than 100. Start at 5 mcg/kg/min and titrate to effect. Use titration table on next slide. Learning Outcome: 19.3 Calculate IV flow rates for titrated medications.

IV Flow Rates for Titrated Medications (cont.) Example Dopamine dosage (mcg/100kg) IV rate (ml/h) 1600 mcg/1 mL 5 mcg/kg/min 18.8 mL/h 10 mcg/kg/min 37.5 mL/h 15 mcg/kg/min 56.3 mL/h 20 mcg/kg/min 75 mL/h Learning Outcome: 19.3 Calculate IV flow rates for titrated medications. If table is not available, calculate each following Rule 19-5 and 18-8, using proportion method, dimensional analysis, or formula method. What is minimum rate? What is maximum rate? What is starting rate? 18.8 mL/h 75 mL/h 18.8 mL/h

Practice Ordered: Xylocaine 1 g in 250 mL D5W; start IV infusion at 2 mg/min and titrate to absence of ventricular dysrhythmia; dosage range 1 mg/min – 4 mg/min. Calculate the minimum dose. Calculate the maximum dose. Calculate the starting dose 15 mL/h Learning Outcome: 19.3 Calculate IV flow rates for titrated medications. Calculate starting dose Step A Convert mg to g. 2 mg/min x 60 min/h = 120 mg/h 1 g:1000 mg = D : 120mg/h D = 0.12 g Step B H – 1 g Q – 250 mL D – 0.12 g Max dose 0.12g/h / 1g x 250 mL = A [cancel units – g] 4 mg/min x 60 min/h = 240 mg/h 30 mL/h = A = starting dose 1000 mg: 1g = D: 240 mg/h Calculate minimum dose: [cancel units – g] 1 mg /min x 60 min/h = 60 mg/h D = 0.24 g/h 1g:1000 mg = D:60 mg/h 0.24 g/h/1 g x 250 mL = Max D = 0.06g/h [cancel units –g] 0.06 g/h/1g x250 mL = minimum dose maximum dose = 60 mL/h [cancel units – g] 15 mL / h = minimum dose Step C Minimum dose is half starting dose, and 15 ml x 2 = 30 15 mL ; max dose is 4 times minimum dose, and 4 x 15 = 60, so it is reasonable. 60 mL/h 30 mL/h

In Summary In this chapter you have learned to calculate the hourly flow rate for IV infusions ordered in dosage per time (e.g. mcg/ min, mg/h); calculate IV flow rates for medications ordered based on body weight over a specified period of time (e.g. mg/kg/min or mcg/kg/min). Convert to like units. Calculate the amount to administer (mL/min). Calculate the flow rate (mL/h). Refer to Rule 19-3 to calculate how much medication the patient has received over a given time when the flow rate and the supply dose is known. Dose on hand (H)/ dosage unit (Q) = Dose of medication received (D)/ volume of solution administered (A) Refer to Rule 18-8. Calculate the desired dose (per minute). Calculate the flow rate (mL/ h).

In Summary In this chapter you have learned to calculate IV flow rates for titrated medications. Refer to Rule 19-4 For safe titration: Calculate the starting rate. Calculate the maximum allowable rate. Calculate the minimum allowable rate. Begin infusion at the starting rate. Titrate (adjust) dosage based on patient response. Do not exceed maximal rate (call AP for new order if the patient does not have the desired response at the maximal rate). If the patient’s response exceeds the prescribed parameters at the minimal dose, discontinue the infusion and notify the AP. Refer to Rule 18-8 Convert to like units Calculate the desired dose (per minute) Calculate the amount to administer (mL/min) Calculate the flow rate (mL/ h)

Apply Your Knowledge True or False: Vasoactive medications regulate the heart rate and rhythm. Medications can be titrated to achieve a specific effect. To be administered by electronic infusion pump, IVs must be calculated in mL/min. F They are administered to keep blood pressure within normal range T Learning Outcome: 19.1 Calculate the hourly flow rate for IV infusions ordered in dosage per time (e.g. mcg/ min, mg/h). F mL/h

Apply Your Knowledge Complete the formula: Volume of solution received Total amount of medication = amount of medication received Total volume of solution ? Volume of solution received Learning Outcome: 19.2 Calculate IV flow rates for medications ordered based on body weight over a specified period of time (e.g. mg/kg/min or mcg/kg/min).

Apply Your Knowledge Dopamine Dosage IV Rate (mL/h) 1000 mcg/1 mL A 5 mcg/kg/min 11.7 mL/h B 10 mcg/kg/min 23.4 mL/h C 15 mcg/kg/min 35.1 mL/h D 20 mcg/kg/min 46.9 mL/h Learning Outcome: 19.3 Calculate IV flow rates for titrated medications. At which point(s) would you call the AP? If the desired response did not occur by the maximum rate of 46.9 mL/h or it it exceeded parameters at minimum dose.

End of Chapter 19 Great works are performed not by strength but by perseverance. ~ Samuel Johnson