I’ve been in the hospital for the past few months (I’m paraplegic with no sensation at or below my behind and idiot me let a decubitus ulcer on my behind get so bad it was infected down to the bone because damn fool that I am I kept “hoping it would get better”) and have only been browsing a little bit because the best that I can manage in here is a dial-up modem; however I have a question that has been puzzling me almost as long as I’ve been in here, so I decided to ask.
I’ve been on IV antibiotics for the duration, so except for when there is a big enough gap that they disconnect me there is always a large bag of saline dripping slowly. When it’s time for the antibiotics, the nurse hangs a little bag and it drips INSTEAD of the large bag until it runs out, then the large bag starts dripping again all on its own.
What is the physics of that? The important part seems to be that the little bag needs to be higher, but I can’t figure out why that would completely stop the large one from dripping until the small one runs out. The tubing joins in a Y just before the pump, so only one tube goes through the pump (in any case I’m sure I remember back before pumps that I had IVs in a similar configuration). Why doesn’t the large one just drip more slowly while the small one is dripping?
Hope you’re on the road to recovery ulcerwise. Is that a word?
If the little bag is higher, wouldn’t the pressure in it’s line be higher than the pressure in the line from from the saline bag. So no fluid would flow from the saline line, or virtually none anyway, until the pressure in the line from the little bag is diminished by it’s being empty.
That’s my guess anyway.
My Mom was recently hospitalized overnight and had a saline drip as well as a medicine drip. Each one was through it’s own pump. In that case the pumps would control the dosage regardless of bag height.
Critical care nurse checking in.
The drip setup you have is called a piggyback. The large volume bag (usually 1000cc) is hung lower than the small volume bag (usually 50, 100 or 250cc, depending on the medication). When the small bag empties, the large bag takes over. Most tubing has a tiny valve above the y-site where the piggyback plugs in. If the system is on a pump, as they are in the ICU where I work, the main fluid has one readout, and there’s a second one for the piggyback. Program in the rate and volume of the small bag, and when it is competed the program for the large volume takes over.
If you ask me, the true horror is that he’s had to stay in the Hospital the whole time instead of some more comfortable place (with highspeed internet access).
