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.