IV - Mg (dose) per Min (Unit time)

There are a lot of IV medications ordered as administer dose/unit time. The setup of the problem and the math is the same whether it's mg/min, ug/min, mg/hr, Units/hr or any of the other unit variations.  If you've looked at the single dose example, you'll find we are doing the same math problem - only the context is different. We'll go through a couple examples.

Example 1

The first example is a continuation of the Single Dose Cardizem problem.  In this example, we will calculate the maintenance drip rate. We are to run a maintenance drip at 5mg/hr. Pharmacy sends the medication in a concentration of 125mg/125ml.

We know:
Our ordered dose - 5mg/hr
Our available form - 125ml
Our available dose - 125mg

What we are going to actually give the patient is ml/unit time. And we use ml/hr because that is what we will program the pump with:

 

 

 

Again, our first factor will be the thing we know that has what we want to know in it, oriented so it is in the same position.

 

 

And multiply by the ordered dose including the ordered time :

 

 

Looking at our factors, we see all units except what we want to know will cancel, so cancel & solve:

 

 

The math in this example is trivial because of the 1:1 concentration of the medication. Let's go through another example.

Example 2

Your monitored patient suddenly develops  sternal chest pain, rating it 5 on a 10 scale. The patients vital signs are stable, they are having no difficulty breathing and are not diaphoretic. Their Pmhx includes an MI.  You inform the managing physician of the patient's pain & status and they order a stat EKG & cardiac enzymes and want the patient started on a nitroglycerine infusion at a fixed rate of 10ug/min. NTG is available in a concentration of 50mg/250ml.

We know:
Our ordered dose - 10ug/min
Our available form - 250ml
Our available dose - 50mg

What rate will we run this drip at?  As always, we begin with what we are actually going to give the patient: ml/unit time. And we use ml/hr because that is what we will program the pump with:

 

 

Again, our first factor will be the thing we know that has what we want to know in it, oriented so it is in the same position.

 

 

And multiply by the ordered dose including the ordered time. Our available dose and ordered dose have different units of weight. How do we know which way to write the factor? Remember that for purposes of setting up the problem, we can treat units of the same class as being the 'same', so we write the ordered dose weight unit  oriented opposite that of the available dose weight unit :

 

 

Looking at our factors, we see our units will not cancel. We already know our units of weight are different. And we have hours on the left side of the equation & minutes on the right & will need a conversion factor for hr<>min. Let's add that factor orienting it so the units are opposite the unit of time already in the equation :

 

 

 

 

Next add our conversion factor for ug<>mg writing it so the like unit of weight is opposite :

 

 

It might be useful to cancel the units on the right side of the equation to be sure the remaining units match what we want to know:

 

 

All our units cancel except what we want to know, so we can go ahead & finish canceling and solve:

 

 

This patient will need continuous monitoring frequent VS's while initiating the drip, typically q5min, until you are sure the patient is stable and tolerating the NTG.

To see how to calculate the dose the patient is getting from the IV rate see Dose From Rate Example 1.

 

©1997-2006 Dale Sampson, RN