PCA Pump problem. There has got to be an easier way!

0May 26, '12 by Java MamaHi Everyone,
So...I am in my 3rd semester (just started last week), and I am trying to stay ahead of the game. I'm pretty good with the math, but I'll tell you, I have been sitting here trying to figure out how the heck they get these answers to the PCA pump questions. Is there something I'm missing? Here is an example problem:
Morphine Sulfate: basal rate=2mg/hr
PCA dose=2mg with a lockout of 6 minutes
(possible dose every 6 minutes for 4 hours)
2mg/hr x 4 hours=8 mg in 4 hrs. from IV
2 mg every 6 minutes (a dose every 6 minutes=60 minutes divided by 6=10 doses/hr)= 2mg x 10 doses=20 mg in 60 min. x 4 hrs=80 mg in 4 hrs
8 mg + 80 mg= 88 mg maximum in 4 hours
This is exactly how the sample problem is presented. Where are they getting 88 mg in 4 hours, if it is 2 mg/hr? I am lost! I am used to dimensional analysis (if it can be figured out that way). Please tell me what I am missing. I've tried finding some websites to help, but I can't find anything like this. Thanks again, I appreciate the help. 
1May 26, '12 by GrnTea, BSN, MSN, RNit's the 8mg in the first four hours, from the basal rate,
plus
the 80mg from the 2mg x 10 doses per hour x 4 hours.
don't overthink this. it's really two dimensional analysis problems, plus one small bit of regular old vanilla addition.:d
in real life not everyone will use that much. the question you are answering here is, "what is the maximum dose the pt can get if it's set this way?"
if you are confused as to the terms, the basal rate is what infuses all the time. in your example, that's the 2 mg/hr.
the pca part, the patientcontrolled analgesia part, are the doses that the patient gets when s/he pushes a button, and the pump delivers the preset dose. that's the 2mg every 6 minutes part. the next preset dose won't be delivered until the lockout period is past, even if the button is pressed a lot in that time. your example calculates the most the patient can get on those settings. does that help?
psu_213 likes this. 
0May 28, '12 by Java MamaThanks Grntea. I guess I am looking at the 2mg per hour and thinking THAT is the max per hour that they could get. I am practicing more of the problems and would appreciate if you could take a look at this one and tell me if I got it right. Thanks
Basal Rate=5mg/hr
Demand (PCA) Dose=2mg
Lockout every 12 minutes
*5mg/hr x 1 hr = 5mg in 1 hour
*2mg every 12 minutes (a dose every 12 minutes=60 min divided by 12 = 5 doses in 1 hour).
*2mg x 5 doses/hr = 10 mg/hr
*10 mg max in 1 hour 
0May 28, '12 by Esme12, BSN, RN Senior ModeratorQuote from Java MamaBut if you are getting a solid 5 mg per hour no matter what and the patient gets all 5 of the PCA dose (10mg)...how many mg in one hour total would that be?Thanks Grntea. I guess I am looking at the 2mg per hour and thinking THAT is the max per hour that they could get. I am practicing more of the problems and would appreciate if you could take a look at this one and tell me if I got it right. Thanks
Basal Rate=5mg/hr
Demand (PCA) Dose=2mg
Lockout every 12 minutes
*5mg/hr x 1 hr = 5mg in 1 hour
*2mg every 12 minutes (a dose every 12 minutes=60 min divided by 12 = 5 doses in 1 hour).
*2mg x 5 doses/hr = 10 mg/hr
*10 mg max in 1 hour
This is a great site.
DosageHelp.com  Helping Nursing Students Learn Dosage Calculations 
0May 28, '12 by GrnTea, BSN, MSN, RN"*5mg/hr x 1 hr = 5mg in 1 hour
yes
*2mg every 12 minutes (a dose every 12 minutes=60 min divided by 12 = 5 doses in 1 hour).
*2mg x 5 doses/hr = 10 mg/hr
yes
*10 mg max in 1 hour "
nope. you forgot the addition part. the max amount per hour is the amount from the basal rate plus the amount from the patientcontrolled rate. basal rate, 5m/hr; max possible patientcontrolled rate, 10mg/hr, total, 15mg/hr. 
0May 28, '12 by KelRN215, BSN, RNQuote from Java MamaRemember how a PCA works. If it is set up as PCA and continuous, the continuous rate is given no matter what. The demand doses are in addition to the continuous dose. This patient is going to get 5 mg/hr regardless of whether or not he pushes the button. If he pushes his demand button every 12 minutes, he'd get an additional 10 mg in an hour on top of the 5 mg he's already getting as a continuous infusion.Thanks Grntea. I guess I am looking at the 2mg per hour and thinking THAT is the max per hour that they could get. I am practicing more of the problems and would appreciate if you could take a look at this one and tell me if I got it right. Thanks
Basal Rate=5mg/hr
Demand (PCA) Dose=2mg
Lockout every 12 minutes
*5mg/hr x 1 hr = 5mg in 1 hour
*2mg every 12 minutes (a dose every 12 minutes=60 min divided by 12 = 5 doses in 1 hour).
*2mg x 5 doses/hr = 10 mg/hr
*10 mg max in 1 hour 
0May 29, '12 by Java MamaOkay...starting to make more sense. Here is another problem to see if I got it
Basal Rate=400 mcg/hr
Demand (PCA) Dose=250 mcg
Lockout=every 15 minutes
*Basal Rate=400 mcg/hr
*250 mcg every 15 minutes (60 divided by 15= 4 doses/hr)
*250 mcg x 4 =1,000 mcg/hr
*1,000 mcg + 250 mcg= 1,250 mcg/hr as the "maximum" dose a patient can get in 1 hour. 
0May 29, '12 by Esme12, BSN, RN Senior ModeratorQuote from java mamano, watch what numbers you are plugging in.okay...starting to make more sense. here is another problem to see if i got it
basal rate=400 mcg/hr
demand (pca) dose=250 mcg
lockout=every 15 minutes
*basal rate=400 mcg/hr
*250 mcg every 15 minutes (60 divided by 15= 4 doses/hr)
*250 mcg x 4 =1,000 mcg/hr
*1,000 mcg + 250 mcg= 1,250 mcg/hr as the "maximum" dose a patient can get in 1 hour.
your basal (continuous) rate per hour is 400mcg.
the patient can get 250mcg every 15 minutes. there are 4 doses of 250 mcgs that can be given totaling 1,000mcg per hour.
if the patient can deliver 1,000mcg total per hour on demand and the pump delivers 400mcg totalper hour continuously........
how much total will the patient get per hour if all the drug (1,000mcg/hr per the patient and 400mcg/hr per the pump) is administered?
1,000mcg/hr + 400mcg/hr = ?mcg/hr total