question about flow rates

jmqphd · May 9, 2011

What's the ml/hour? 1200 divided by 8 = 150 ml/hour.

How many hours should it have taken to get 500 ml infused? 500 ml divided by 150 = 3.33 hours So, without the precision of a pump, you're just about on time. (Trust me on this... I did it for 20 years with the tubing clamp and a second hand... OK?) You're missing the mark by 20 minutes. That's trivial.

What should the original drip rate be? I can give you a short cut. It's 25 gtts/ min.

How do I know that? 'Cuz in the old days a pedi-dripper would give you 60 gtts/ml which meant that the ml/hr was exactly the same as gtts/min.

In other words, if this were a pedi drip chamber you'd have to run it at 150 gtts/min to equal 150 ml/hour. But you have a drip chamber that is making a drop that's six times bigger than a pedi-dripper. So divide 150 by 6. You get 25.

Do you really have to adjust the drip rate to slow it down to adjust for the 20 minutes that you're flow rate is ahead????

OK Start from scratch. You don't have 1200 ml now, you have 700. You don't have 8 hours, you have 5.

How many ml/hour? 700 divided by 5 = 140. Now you're flow rate has to be 140 ml/hour. You have a dip chamber that makes a drop 6 times bigger than a pedi dripper. 140 divided by 6 = 23.33 drops/minute... which is impossible and you can see that the difference in flow rate, if you're doing it manually is trivial and and impossible to do. (Even a pump cannot give 23.33 drops/min.)

What if your drip chamber gives you 15 drops/ml. Now the drop is 4 times bigger than a pedi dripper. (Pedi-dripper = 60 gtts/ml. Adult drip chamber = 15 drops/ml. 60 divided by 15 = 4.) Suppose I have to give 150 ml/hour? Divide 150 by 4 or 37.5 gtts/min. You get it as close to that as you can. 38, 35 whatever.

I suppose there is a formula or something to do all this in one grand calculation. But I could never learn it that way. I had to do sequential (easy) operations. Just think it through step by step.

First figure ml/hour.

Then divide the gtts/ml (of your drip chamber) into 60. Whatever number you get, divide the ml/hour by that and you have your gtts/min for your particular drip chamber.

Do it about 20 times per 8 hour shift for 5 shifts/week for 20 years and you can do it all in your head.

VickyRN, MSN, DNP, RN · May 9, 2011

Moved to the Nursing Student Assistance Forum, which is more appropriate for this type of question :)