1991 Practical Use of Algebra
DePaul School for New Learning
Foundations of New Learning
Teacher: Catherine Marienau
Practical Use of Algebra
Non-SNL Coursework
QUARTER: Winter
YEAR: 1991
COMPETENCE STATEMENT:
PW-1 Can use mathematics to describe and solve problems.
THE LEARNING EXPERIENCE:
Algebraic math was a part of my nursing education; it was incorporated into the appropriate areas and thus not labeled separately as a math course. However, this did really prepare me for the kind of math I would be using when I went to work in intensive care. This is where I really learned to use math and to see its vital importance to my patients’ care.
REFLECTIONS:
At many local community hospitals, the doctors figure out the dosages of the super-potent drugs. I had worked in two local type hospitals before going to work at Michael Reese. Here you are working with interns and residents, they come from many different medical schools and are still considered students. The nurses are NOT students. They apparently are left to learn the math required on the job, because they always asked us how to do it.
I had grown up thinking that I was terrible in math so the fact that this was going to be such a vital responsibility in my new job I was terrified.
I also soon learned that the other nurses had little patience with the fact that I felt unsure of myself using these new formulas and trying to them at the bedside of a critically ill patient. So, it made me determined to KNOW it! I went to our clinical nurse specialist and asked her to teach me. She did teach me most of what I needed, but even she did not know how some of the figures were figured out. I HAD to know that too.
GENERALIZATIONS:
An example of the math that I need to use I can best explain with a situational problem. A man comes to the coronary intensive care unit and is having a heart attack. As a result of heart damage and the inability of his heart to pump well, he loses his blood pressure. We then use drugs that will constrict his blood vessels to send blood to his vital organs, like his brain, heart, and lungs. This drug is called dopamine; the dosage of this drug determines the effect on the body, for example, if you give too high a dose you can damage the kidneys and give him more problems than he already has. This is why you must know how to calculate the dose properly.
The first thing to be considered is the concentration of the drug in the intravenous fluid. Let’s say you mix 400 mg of dopamine in 250cc(ounces) of fluid. You need to know how many micrograms of the drug are in each cc of fluid. SO……
250cc : 400mg : : 1cc : X mg
____ = _______
(400 mg divided by 250 cc = 1.6 mg/cc)
Now we know that each cc of fluid contains 1.6 mg of the drug.
We have a problem because we need to know how many micrograms are in each cc of fluid.
1.6mg 1600mcg (Because 1000 micrograms = 1 mg)
_____ X 1000 = _______
1cc 1cc
So … 1600 mcg/1cc
These drugs are so potent that they must be given on machines that will pump it into the patient at a specific rate in cc’s per hour. What we need to figure out is how many micrograms per kilogram per minute (mcg/kg/min) to give it at; this must then be put in terms of cc’s/per/hour that the pumps deliver.
The formula then looks like this………..
mcg x kg x 60 minutes (in 1 hour, which is what the pump delivers)
_____________________ =
1600 mcg per 1 cc
Let’s say we want to give 5 mcg/kg/min to this patient.
5mcg x 68kg x 60 20,400
________________ = _________ = 12.75 or 13 cc’s per hour
1600mcg/1cc 1600
We set the pump at 13cc per hour and the patient will be receiving the right dose.
If you take over a patient who is already receiving dopamine it is your responsibility to figure out if the right dose is being given. There is a shortcut that I have discovered that works well. If 1600mcg is in 1cc, if there are 60 minutes in an hour (the pump works on cc/hr) you can just divide the mcg by 60 and you get a constant factor.
So …
1600mcg
_______ = 26.6 mcg each hour
60min
So when you walk in and find the rate at 13cc/hour you can quickly figure out if it is right. The formula would look like this:
13 cc per hour x 26.6 345.8
_____________________ = _____ = 5 mcg/kg/min
68kg 68
If any of these variables change, then you must do the whole thing over. For instance, the patient’s weight, the concentration in the bag, or the amount you want to give. This is only the formula for one type of drug.
Some are given in just mcg/min and then the weight becomes irrelevant. For instance, nitroglycerine. If you have a
50mg 0.2 mg 200mcg
_____ = _______ x 1000 to find mcg = ________ divide by 60 = 250cc 1cc 1cc
A constant factor of 3.33. Then you just multiply 3.33 by the number of cc/hour to find how many mcg/min.
You then proceed to fill in the amount in mcg that you want to give, you take the patient’s weight in kilograms, let’s say 150 pounds which you would divide by 2.2 to get the weight in kilograms (2.2 kg = 1 pound), or 68 kg.
Let’s say we want to give 50mcg/min. We then divide 50 by 3.33 and set the pump accordingly – at 15cc/hour. To check your figures you can take the cc,s per hour and divide by 3.33, or 15cc multiplied by 3.33 = 49.5 mcg/min (close enough).
Sometimes we do what we call titration of these drugs according to the patient’s symptoms. If we are using dopamine for low blood pressure we increase it if the pressure is low and decrease it if it goes up to an acceptable level. With a medication like nitroglycerine, used to relieve chest pain by dilating the coronary arteries, you increase it or decrease it according to the patient’s pain. Sometimes if a person is unstable you may be changing the amounts you are giving every minute or so. You must keep checking what amount you are giving so that you prevent other side effects of the drugs.
There are many other things that critical care nurses calculate on a daily basis. If you require more I will try to explain. Some of it requires knowledge of anatomy and physiology like figuring some one’s cardiac output (how many cc’s of blood the heart pumps out per minute). There’s cardiac index which is found by taking the cardiac output and multiplying it by the person’s body surface area (we use a chart to figure this by the height and weight). We figure systemic vascular resistance (the resistance offered by the body to the blood on its way out of the left ventricle on its way to the body, which would be high with high blood pressure). These involve many formulas and many patient parameters that would require tons of explanation.
APPLICATIONS:
As a nurse who goes to a different hospital every day, I desperately need these skills to survive, to say nothing about my patient’s survival, and my not being sued. Each hospital mixes drugs in different concentrations, so you have to start from scratch each time. Some hospitals have charts to calculate the drugs, but what if they don’t? I find that I end up teaching other nurses about the constant factors at least once a month because they can’t believe there is a faster way to figure.
Doing this is making me reflect upon the past 7 years of critical care nursing – I see what I could not see while just doing what I had to do. This now illustrates to me why they are now advertising, “If caring were enough, anyone could be a nurse.”
HOW IT FULFILLS THE COMPETENCE:
I can and do use math to describe and solve problems as a part of my work every day.