drip volume always constant

I am not entirely sure what you are asking, and I am still a student myself so I am far from an expert. The gtts/mL depends on the size of the tubing being used, and will be listed on the packaging of the tubing. Gtts/min will vary based on how much fluid is to be administered over how many hours. As for the valves you asked about, this is the reason you fill the drip chamber up about 2/3 of the way when you are priming your tubing. In reality, you would probably be using a pump, and you would therefore be entering your rate as mL/hr and the pump would regulate the drips per minute.

the question is asking you to recalculate based on the new volume of 500mL.

The drip rate, once set, should remain constant and does not vary by the amount remaining to infuse. But if you are allowing gravity to infuse the bag there are many reasons that the rate may vary --- crimp in the line, the angiocath could be positional and has moved, the angiocath may have become bent as when a patient bends their arm with an AC line, human error setting the drip rate the begin with, etc..

Jenn makes some valid points that if this infusion was on the pump the issues would have been become evident earlier or not at all with pump alarms.. But the question simply wants to find out if you know the math to recalculate the drip rate.

Thank you Jenn and Bravo. I think we agree on my second calculation.

By definition the rate of a gravity infusion controlled by drip rate will always change over the course of the infusion since the drip rate is the balance of upstream pressure vs downstream resistance. The downstream resistance may remain the same, but as the bag empties the upstream pressure changes drastically. How much it changes may not always be noticeable however.

Thank you very much, Muno. That really clarifies it for me. It makes good sense. We simplify our calculation as if drip rate were constant; then, we follow up later on to adjust the drip rate to target the desired duration over which to administer the total volume. I noticed that some facilities limit the drip-rate adjustment to 25% of the initial rate (don't want the change too large).

Dare I ask: Is the drip-volume constant, or can that too vary with the pressure changes? Maybe drip volume physics are more complex than drip rates. (?) I am just curious and can agree that the matter may be beyond the scope of what we need to determine for safe and accurate IV med administration. Also, as others have said, we are using more electronic pumps for med admin now.

The size of the drop will be constant. A 15 gtt set will have 15gtts/ml all the time. There may be some very slight variability if you shake the drip chamber, but as long as that remains relatively unperturbed, the volume per drop will be fairly constant. IV line problems can happen in real life, so it's good to check those lines from time to time. You should have a pretty good idea how much fluid should remain in the bag as time goes along so you can figure out if the line is running faster or slower than expected. Doing problems like this will help you figure out how to recalculate a drip rate should something not go as planned.