Dosage Help

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I am doing well with dosage calculations except for two types of problems.

One is how to tell when your infusion will finish, for example: if you have 250 mL and a flow rate of 25 get/min and set calibration of 10 get/mL.

The other is if the order is to infuse 1 liter of D5NS with 10,000 U Heparin at 20 get/min using a set calibration of 15 get/mL, how many units of Heparin is the pt receiving hourly?

I would appreciate any help! Thanks!!

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With the first problem, you need to start by figuring out how many mL per minute the infusion is running. You have a rate of 25 gtt/min and a drop factor of 10 gtt/mL. Since there are 10 drops per mL, and you know 25 drops are infusing per minute, how many mL are infusing per minute? Or in other words, if 1 mL is 10 drops, how many milliliters is 25 drops? You can set this up a couple of ways; the easiest way for me is the means/extremes method, which uses ratios. You set it up like this:

10gtt:1mL=25gtt:xmL

Written out, this means: 10gtt per 1mL is equivalent to 25gtt per x number of mL.

You then multiply the means and the extremes to get a solvable equation. The "means" are the 2 inside numbers; in this case, 1mL and 25gtt. The "extremes" are the 2 outside/end numbers; in this case, 10gtt and x mL. This gives you the following equation:

10x = 25

Divide both sides by 10, and you see that x=2.5mL. So, 25 drops is equal to 2.5mL. Since you know 25 drops are infusing per minute, this means 2.5mL are infusing per minute. The total volume to be infused is 250mL. If 2.5mL infuses in 1 minute, how many minutes does it take to infuse 250mL? You can use means & extremes again:

2.5mL:1min=250mL:x minutes

2.5x = 250

x = 100 minutes

It will take 100 minutes for the solution to infuse, or 1 hour and 40 minutes. You can divide the result by 100 if you want to get the number of hours in decimal format. This would give you 1.67 hours, rounded to the nearest hundredth.

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The other is if the order is to infuse 1 liter of D5NS with 10,000 U Heparin at 20 gtt/min using a set calibration of 15 gtt/mL, how many units of Heparin is the pt receiving hourly?

The second problem is very similar, except in addition to determining how many mL are infusing per minute based on the drop factor, you also need to determine how many units are in each mL. I would start this problem the same way as above, by determining at how many mL per minute the infusion is running. You can set up another means/extremes ratio to solve:

15gtt:1mL=20gtt:x mL

15x = 20

x = 1.33 mL (rounded to nearest hundredth)

So, the infusion is running at approximately 1.33mL per minute. To obtain the hourly volume, just multiply by 60.

1.33mL/min * 60 min = 80 mL/hour

Now, how many units of heparin are in each mL? Again, set up another means/extremes ratio.

1 liter = 1000mL

10,000 units in 1000mL

1000mL:10,000units=1mL:x units

1000x = 10,000

x = 10

So, there are 10 units of heparin in every mL of solution. Since you already know the rate is 80mL/minute, just multiply the rate by the number of units per mL to obtain the rate in units.

10 units/mL * 80mL/hour = 800 units per hour

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