Medication administration - Intravenous critical care: Nursing pharmacology

Medications used in critical care settings have significant physiologic effects; are typically administered intravenously, or IV; and they are usually administered by titrating, or adjusting, the infusion rate according to the health care provider’s order until the desired therapeutic effect is reached.

Many of these medications are high alert medications, meaning they may cause significant harm to the patient if administered incorrectly, so these medications are always delivered through an IV pump to ensure accuracy.

As the nurse, you’ll calculate volumes per unit of time, and dosages based on body weight. To calculate a dose using the Dimensional Analysis, or DA method, the three components you need are D, for the Desired dose, or dose ordered by the health care provider; H, for Have, or the dosage you have available; and V, for Vehicle or the form and amount in which the medication comes, like tablets or liquid.

Now let’s calculate an infusion rate using Dimensional Analysis. First, you’ll read the order, which is: heparin 1300 units/hr IV continuous infusion.

Then, check the medication label. Since the available dose is 25,000 units per 500 mL, you will calculate how many milliliters per hour to administer to achieve the Desired dose.

To do this, first identify your components, Desired, Have, and Vehicle. And since there’s a time component, we also have T, for Time.

In this case, D is 1300 units, which was obtained from the health care provider’s order; H is 25000 units, which was obtained from the medication label; V is 500 mL, which was also obtained from the medication label; and T is 1 hour, which was also obtained from the health care provider’s order.

Next, you’ll determine if a conversion factor is required. To determine this, compare the units of D with the units of H.

They’re the same, so no conversion factor is needed. Likewise, since T is in hours and the infusion rate you’re calculating is in mL/hr, no conversion factor is needed.

Now, set up the equation, where X is the rate in milliliters per hour, written out like this. X number of milliliters per hour equals Vehicle over Have multiplied by Desired dose over Time.

X mL/hr = V x D / H x T Now, plug in the components. This gives you 1 mL multiplied by 1300 units divided by 50 units multiplied by 1 hr.

X = 1 mL x 1300 units / 50 units x 1 hr Remember, you can cross out the units of the numerator that match the units of the denominator, because they cancel out.

X = 1 mL x 1300 units / 50 units x 1 hr Then, you’ll multiply the numbers in the numerator and then the numbers in the denominator to get 1300 mL divided by 50 hrs.

X = 1300 mL / 50 hours Next, divide 1300 mL by 50 hrs to solve for X. X = 26 mL/hr The answer is 26 mL per hour, meaning you'll program the IV pump to infuse heparin at 26 mL/hr to achieve the ordered dose of 1300 units per hour.

Before starting the infusion, remember to ask another nurse to check the order, IV bag, your calculation, and the IV pump setting.

Now, often you’ll administer a medication that’s dosed based on the patient’s body weight. Let’s calculate the infusion rate for a dose based on your patient’s body weight using the Dimensional Analysis method.

First, you’ll read the order, which is: nitroprusside 0.3 mcg/kg/min continuous IV infusion. Then, check the medication label.

Since the medication available is 50 mg in 250 mL 5% dextrose, you will calculate how many milliliters per hour to administer to achieve the Desired dose.

Now, identify your components, D, H, and V. So, in this case, D is 0.3 mcg/kg/min, which was obtained from the health care provider’s order; H is 50 mg, which was obtained from the medication label; and V is 250 mL, which was also obtained from the medication label.

You also need to know the patient’s weight, which is 85 kg. Next, you’ll determine if a conversion factor is required.

To determine this, compare the units of D with the units of H. Because D is in micrograms and H is in milligrams, a conversion factor is needed.

Use the following conversion factor for micrograms to milligrams: 1000 micrograms = 1 milligram Likewise, because the Desired dose is in minutes, and the infusion rate you’re calculating is in mL/hr, a conversion factor is needed.

Use the following conversion factor for minutes to hours: 60 minutes = 1 hour Now, set up the equation, where X is the infusion rate you’ll administer, written out like this.

X number of milliliters per hour equals Vehicle over Have multiplied by Dose multiplied by weight in kilograms multiplied by the conversion factors.

X mL/hr = V x D x Weight in kg x Conversion factor for minutes x Conversion factor for grams / H x Conversion factor for hours x Conversion factor for micrograms Now, plug in the values for the components.

Since D is in mcg/kg/min, the kilograms per minute goes into the denominator to get 250 mL multiplied by 0.3 micrograms multiplied by 85 kilograms multiplied by 60 minutes multiplied by 1 milligram; divided by 50 milligrams multiplied by 1 kilogram per minute multiplied by one hour multiplied by 1000 micrograms.

Remember, you can cross out the units of the numerator that match the units of the denominator, because they cancel out.

Then, you’ll multiply the numbers in the numerator and then the numbers in the denominator to get 382500 mL divided by 50000 hours.

X = 382500 mL / 50000 hrs Next, divide 382500 mL by 50000 hrs to solve for X. X = 7.65 mL/hr This gives you the final answer of 7.65 mL per hour.

Now, if your IV pump is calibrated by whole numbers, you'll round up to the nearest whole number and program your pump to 8 mL per hour.

But if your pump is calibrated by tenths, you’ll round up to the nearest tenth and program the IV pump at 7.7 mL/hr. Before starting the infusion, remember to ask a second nurse to double check your order, IV bag, calculation, and IV pump.

Alright, as a quick recap...In critical care settings,