A Provider Increases the Epinephrine Adrenaline to 5mcgmin by Continuous Iv Infusion
Calculations
TOPICS COVERED
1. Amount of drug in a solution
2. Calculation of rate for special IV orders: units/hour; g/hour; mg/hour, mL/hour, mg/minute, milliunits/minute, mcg/minute, mcg/kg/minute
3. Use of the body surface nomogram and calculation, IV medications based on body surface area
4. Patient-controlled analgesia
5. Special types of calculation: heparin, insulin
In Chapter 6, we studied calculations for microdrip and macrodrip factors, the use of the infusion pump, and IV piggyback (IVPB) orders. In this chapter, we consider calculations for orders written in units, milliunits, milligrams, and micrograms; methods of calculating the safety of doses based on kilograms of body weight and body surface area (BSA); and the handling of orders for patient-controlled analgesia (PCA); special types of calculations in relation to continuous heparin infusion and continuous insulin infusion.
This chapter's dosage calculations are for medications mixed in IV fluids and delivered as continuous infusions. Administering these medications via infusion pumps ensures a correct rate and accuracy of dose (Fig. 7-1). Many infusion pumps can deliver rates less than 1 (e.g., 0.5 mL/hour, 0.25 mL/hour, etc.), and they also can be programmed with the amount of drug, amount of solution, patient/client's weight, and time unit (minutes or hours). Once the pump is set at an infusion rate, the pump calculates how much drug the patient/client is receiving. You, as the nurse, however, still bear the responsibility for double-checking the calculation and entering the correct information on the infusion pump. (Some hospitals require a "double-check" with two licensed staff to verify the pump is set correctly) (For this chapter, answers will be rounded to the nearest whole number. Time to run is given in hours and minutes—see Chapter 6 for conversion of hours to minutes.)
Because many of the medications that infuse via continuous infusions are very potent, small changes in the infusion rate can greatly affect the body's physiologic response. In particular, vasopressor drugs such as dopamine, epinephrine, dobutamine, and Levophed (norepinephrine) can affect the patient/client's blood pressure and heart rate, even in small doses. In most hospital settings, the pharmacy prepares medications and IV solutions.
Amount of Drug in a Solution
These calculations can be complicated. One helpful technique is reduction: Start with the entire amount of drug mixed in solution and then reduce it to the amount of the drug in only 1 mL of solution.
Here's an example:
Heparin is mixed 25,000 units in 500 mL D5W.
How much heparin is in 1 mL of fluid?
Desired dose: 1 mL
Supply: 25,000 units
Have: 500 mL
FIGURE 7-1
Infusion pump. (With permission from Evans-Smith, P. [2005]. Taylor's clinical nursing skills. Philadelphia, PA: Lippincott Williams & Wilkins.)
To solve:
Here's a simple formula you can use for this calculation, instead of the other methods:
Medications Ordered in units/hour or mg/hour
Sometimes patient/client medications are administered as continuous IVs. For these medications, a specific amount of drug is mixed in a specific amount of IV fluid. Check the guidelines (institutional or drug references) to verify dose, dilution, and rate. If any doubts exist, consult with the prescribing physician or healthcare provider.
Units/hour—Calculation of Rate
The order will indicate the amount of drug to be added to the IV fluid and also the amount to administer.
EXAMPLE
Order: heparin, infuse 800 units/hour
Available: heparin 40,000 units in 1000 mL D5W infusion pump
What is the rate?
You know the solution and the amount to administer. Because you'll be using an infusion pump, the answer will be in milliliters per hour.
Desired dose: 800 units/hour
Supply: 40,000 units
Have: 1000 mL
To solve:
FINE POINTS
Notice that the desired dose, milliliter per hour is set up as a fraction with "mL" in the numerator and "hours" in the denominator.
How many hours will the IV run?
Note: Most hospitals require changing the IV fluids every 24 hours.
EXAMPLE
Order: heparin sodium 1100 units/hour IV
Supply: infusion pump, standard solution (premixed by the pharmacy) of 25,000 units in 250 mL D5W
What is the rate?
With an infusion pump, the answer will be in milliliters per hour.
Desired dose: 1100 units/hour
Supply: 25,000 units
Have: 250 mL
To solve:
How many hours will the IV run?
EXAMPLE
Order: regular insulin 10 units/hour IV
Available: infusion pump, standard solution of 125 units regular insulin in 250 mL NS (normal saline)
What is the rate? Use on infusion pump.
Desired dose: 10 units/hour
Supply: 125 units
Have: 250 mL
To solve:
How many hours will the IV run?
g/hour; mg/hour—Calculation of Rate
The order will indicate the amount of drug added to the IV fluid and the amount to administer.
EXAMPLE
Order: calcium gluconate 2 g in 100 mL
D5W; run 0.25 g/hour IV via infusion pump.
What is the rate?
Because we know the solution and the amount of drug per hour, you can solve the problem and administer the drug in milliliters per hour per infusion pump. Round the final answer to the nearest whole number.
Desired dose: 0.25 g/hour
Supply: 2 g
Have: 100 mL
To solve:
How many hours will the IV run?
EXAMPLE
Order: aminophylline 250 mg in 250 mL D5W; run 65 mg/hour IV per infusion pump.
What is the rate? Use an infusion pump.
Desired dose: 65 mg/hour
Supply: 250 mg
Have: 250 mL
To solve:
How many hours will the IV run?
SELF-TEST 1
Infusion Rates
Solve the following problems. Answers appear at the end of this chapter.
| 1. Order: | heparin sodium 800 units/hour IV |
| Supply: | infusion pump, standard solution of 25,000 units in 250 mL D5W |
a. What is the rate?
b. How many hours will the IV run?
| 2. Order: | Zovirax (acyclovir) 500 mg in 100 mL D5W IV over 1 hour |
| Supply: | infusion pump, Zovirax (acyclovir) 500 mg in 100 mL D5W |
What is the rate?
| 3. Order: | Amicar (aminocaproic acid) 24 g in 1000 mL D5W over 24 hour IV |
| Supply: | infusion pump, vials of Amicar (aminocaproic acid) labeled 5 g per 20 mL |
a. How much Amicar do you add to the IV?
b. What is the rate?
| 4. Order: | Cardizem (diltiazem) 125 mg in 100 mL D5W at 10 mg/hour IV |
| Supply: | infusion pump, vial of Cardizem (diltiazem) labeled 5 mg/mL |
a. How much diltiazem do you add to the bag?
b. What is the rate?
| 5. Order: | Lasix (furosemide) 100 mg in 100 mL D5W; infuse 4 mg/hour |
| Supply: | infusion pump, vial of Lasix (furosemide) labeled 10 mg/mL |
a. How much furosemide do you add to the IV bag?
b. What is the rate?
| 6. Order: | regular insulin 15 units/hour IV |
| Supply: | infusion pump, standard solution of 125 units in 250 mL NS |
a. What is the drip rate?
b. How many hours will this IV run?
| 7. Order: | nitroglycerin 50 mg in 250 mL D5W over 24 hour via infusion pump |
What is the drip rate?
| 8. Order: | heparin 1200 units/hour IV |
| Supply: | infusion pump, standard solution of 25,000 units in 500 mL D5W |
a. What is the rate?
b. How many hours will the IV run?
| 9. Order: | regular insulin 23 units/hour IV |
| Supply: | infusion pump, standard solution of 250 units in 250 mL NS |
a. What is the rate?
b. How many hours will the IV run?
| 10. Order: | Streptase (streptokinase) 100,000 international units/hour for 24 hour IV |
| Supply: | infusion pump, standard solution of 750,000 international units in 250 mL NS |
What is the rate?
mg/minute—Calculation of Rate
The order will indicate the amount of drug added to IV fluid and also the amount of drug to administer. These medications are administered through an IV infusion pump in milliliters per hour.
Note: The dimensional analysis method will combine all of the calculation steps into one equation.
EXAMPLE
Order: Bretylol (bretylium) 1 mg/minute IV
Supply: infusion pump, standard solution of 1 g in 500 mL D5W (1000 mg in 500 mL)
The order calls for 1 mg/minute. You need milliliters per hour for the pump.
Convert the order to milligrams per hour by multiplying the drug amount by 60 (60 minutes = 1 hour): 1 mg/minute × 60 minutes = 60 mg in 1 hour.
What is the rate?
Desired dose: 60 mg/hour
Supply: 500 mL
Have: 1 g (1000 mg)
To solve:
FINE POINTS
The conversion factors can be placed anywhere in the equation. All of the "units of measurement" in the conversion factor will be cancelled out in the equation.
How many hours will the IV run?
EXAMPLE
Order: lidocaine 3 mg/minute IV
Supply: infusion pump, standard solution of 2 g in 500 mL D5W (2000 mg in 500 mL)
The order calls for 3 mg/minute. We need mL/hour for the pump.
Convert the order to milligrams per hour: Multiply 3 mg/minute × 60 = 180 mg/hour
What is the rate?
Desired dose: 180 mg/hour
Supply: 500 mL
Have: 2 g (2000 mg)
To solve:
Set pump at 45 mL/hour.
How many hours will the IV run?
SELF-TEST 2
Infusion Rates for Drugs Ordered in mg/minute
Solve the following problems. Answers appear at the end of the chapter.
| 1. Order: | lidocaine 1 mg/minute IV |
| Supply: | 2 g in 250 mL D5W, infusion pump |
a. What is the drip rate?
b. How many hours will the IV run?
| 2. Order: | Trandate (labetalol) 2 mg/minute IV |
| Supply: | Trandate (labetalol) 300 mg in 300 mL D5W, infusion pump |
a. What is the drip rate?
b. How many hours will the IV run?
| 3. Order: | Bretylol (bretylium) 2 mg/minute IV |
| Supply: | Bretylol (bretylium) 1 g in 500 mL D5W, infusion pump |
a. What is the drip rate?
b. How many hours will the IV run?
| 4. Order: | Cordarone (amiodarone) 1 mg/minute for 6 hours |
| Supply: | Cordarone (amiodarone) 450 mg in 250 mL D5W, infusion pump |
What is the drip rate?
| 5. Order: | Ativan (lorazepam) 1 mg/minute |
| Supply: | Ativan (lorazepam) 80 mg in 250 mL NS, infusion pump |
a. What is the drip rate?
b. How many hours will the IV run?
Medications Ordered in mcg/minute, mcg/kg/minute, or milliunits/minute—Calculation of Rate
Intensive care units administer powerful drugs in extremely small amounts called micrograms (1 mg = 1000 mcg). The orders for these drugs often use the patient/client's weight as a determinant, because these drugs are so potent.
EXAMPLE
Order: renal dose dopamine 2 mcg/kg/minute
Order: titrate Levophed to maintain arterial mean pressure above 65 mm Hg and below 95 mm Hg
This section shows how to calculate doses in micrograms and in milliunits, and how to use kilograms in determining doses. Most infusion pumps used in hospitals allow you to program these drugs and the pump will calculate the rate for you. However, it is still important to know how to calculate the rate.
mcg/minute—Calculation
Drugs ordered in micrograms per minute are standardized solutions prepared by a pharmacist. They are administered using infusion pumps that deliver medication in milliliters per hour.
To calculate drugs ordered in micrograms per minute, first determine how much of the drug is in 1 mL of solution (see beginning of this chapter). If the drug is supplied in milligrams, convert it to micrograms; then divide that amount by 60 to get micrograms per minute. The final number tells you how much of the drug is in 1 mL of fluid. You can then use one of the three methods to solve for the infusion rate, on the basis of the ordered dosage. The dimensional analysis method will combine all the steps into one equation.
Solving micrograms per minute requires four steps:
1. Reduce the numbers in the standard solution to milligrams per milliliter.
2. Change milligrams to micrograms.
3. Divide by 60 to get micrograms per minute.
4. Use either the formula, ratio, or proportion method to solve for milliliters per hour.
EXAMPLE
Order: Intropin (dopamine) 400 micrograms per minute IV
Supply: infusion pump, standard solution 400 mg in 250 mL D5W
Step 1. Reduce the numbers in the standard solution.
Step 2. Change milligrams to micrograms.
1.6 mg × 1000 = 1600 mcg/1 mL
Step 3. Divide by 60 to get micrograms per minute.
Step 4. Solve for milliliters per hour (Round to nearest whole number).
Step 5. Set the infusion pump; program the milliliters per hour and volume to be infused.
Step 6. To set the infusion pump, program the following
• Total number of milliliters ordered = 250 mL
• Milliliters per hour to run = 15 mL/hour $ hour to run = 15 mL/hour hour to run = 15 mL/hour hour to run = 15 mL/hour hour to run = 15 mL/hour hour to run = 15 mL/hour
EXAMPLE
Order: Aramine (metaraminol) 60 mcg/minute IV
Supply: infusion pump, standard solution 50 mg in 250 mL D5W
Step 1. Reduce the numbers in the standard solution.
Step 2. Change milligrams to micrograms.
0.2 mg = 200 mcg/1 mL
Step 3. Divide by 60 to get mcg/minute.
3.33 mcg/minute
Round to hundredths.
Step 4. Solve. Round to the nearest whole number.
Step 5. Set the pump: total number of milliliters = 250 (standard solutions); milliliters per hour = 18.
mcg/kg/minute—Calculation
EXAMPLE
Order: Intropin (dopamine) 2 mcg/kg/minute
Supply: infusion pump, standard solution 200 mg in 250 mL D5W; client weighs 176 lb
Note that this order is somewhat different. You are to give 2 mcg/kg body weight. First you weigh the patient/client and then convert pounds to kilograms (if the weight is already in kilograms, no conversion is necessary); then multiply the number of kilograms by 2 mcg. Once you have determined this answer, follow the steps described earlier.
The patient/client weighs 176 lb.
(Dimensional analysis will combine all the steps, including weight conversion, into one equation.)
1. Reduce the numbers in the standard solution.
2. Change milligrams to micrograms.
0.8 = 800 mcg/mL
3. Divide by 60 to get mcg/kg/minute.
Round to hundredths.
4. Solve. Round to the nearest whole number.
FINE POINTS
The order "2 mcg/kg/minute" is written as 
The denominator "kg/minute" is a shortened version of the fraction; both "kg" and "minutes" need to be cancelled.
5. Set the pump: total number of milliliters = 250 (standard solution); milliliters per hour = 12.
Milliunits/minute—Calculation
In obstetrics, a Pitocin (oxytocin) drip can initiate labor. The standard solution is 15 units in 250 mL. Because 1 unit = 1000 milliunits, you solve these problems in the same way as micrograms per minute.
EXAMPLE
Order: Pitocin (oxytocin) drip 2 milliunits/minute IV
Supply: infusion pump, standard solution 15 units in NS 250 mL
1. Reduce the numbers in the standard solution
2. Change units of pitocin to milliunits
1 unit = 1000 milliunits
0.06 × 1000 = 60 milliunits/mL
3. Divide by 60 to get milliunits per minute
4. Solve. Round to the nearest whole number.
5. Set the pump: total number of milliliters = 250; milliliters per hour = 2.
SELF-TEST 3
Infusion Rates for Drugs Ordered in mcg/minute, mcg/kg/minute, and milliunits/minute
Calculate the number of milliliters to infuse and the rate of infusion. Answers appear at the end of the chapter.
| 1. Order: | Intropin (dopamine) double strength, 800 mcg/minute IV |
| Supply: | standard solution of 800 mg in 250 mL D5W, infusion pump |
| 2. Order: | Levophed (norepinephrine), 12 mcg/minute IV |
| Supply: | standard solution of 4 mg in 250 mL D5W, infusion pump |
| 3. Order: | Dobutrex (dobutamine) 5 mcg/kg/minute IV |
| Supply: | patient/client weight, 220 lb; standard solution of 1 g in 250 mL D5W, infusion pump |
| 4. Order: | Dobutrex (dobutamine) 7 mcg/kg/minute IV |
| Supply: | patient/client weight, 70 kg; standard solution of 500 mg in 250 mL D5W, infusion pump |
| 5. Order: | nitroglycerin 10 mcg/minute IV |
| Supply: | standard solution of 50 mg in 250 mL D5W, infusion pump |
| 6. Order: | Pitocin (oxytocin) 1 milliunit/minute IV |
| Supply: | standard solution of 15 units in 250 mL NS, infusion pump |
| 7. Order: | Isuprel (isoproterenol) titrated at 4 mcg/minute IV |
| Supply: | solution of 2 mg in 250 mL D5W, infusion pump |
| 8. Order: | Brevibloc (esmolol) 50 mcg/kg/minute IV |
| Supply: | 2.5 g in 250 mL D5W; weight, 58 kg, infusion pump |
| 9. Order: | Nipride (nitroprusside) 2 mcg/kg/minute IV |
| Supply: | patient/client weight, 80 kg; nipride 50 mg in 250 mL D5W, infusion pump |
| 10. Order: | Inocor (amrinone) 200 mcg/minute |
| Supply: | Inocor (amrinone) 0.1 g in 100 mL NS, infusion pump |
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