Medical Question - Workings of an IV

[Telly]

The basic question - The introduction of air, air embolism, in the circulatory system is bad news. How is the introduction of air avoided in the IV process?

I'm sure I'm not using all the proper medical terms here, but bear with me...

The heart is a pump, and an IV is inserted into a vein in the arm, for example. The vein system is on the suction side of the pump (heart).

Is the vein system, though it is on the suction side of the heart, slightly above atmospheric pressure? Or is it below atmospheric pressure like one would assume in most closed-system mechanical pumping systems?

When the IV is initially inserted, what about the air that is in the tubing that is directly connected to the needle (the pigtail of tubing)?

When an IV bag and tubing are connected to the needle pigtail, is air first bled (um, poor word choice, but I'm thinking mechanically here!) from the tubing, to avoid air going downstream to the IV needle?

I understand the concept of the IV Drip Chamber below the bag, to prevent air going down the tubing while infusing, and as a visual indicator of rate. But what happens when the bag runs out? If one is lying in a hospital late at night in poor shape, and the infusion pump alarm goes off because the bag has emptied, what happens if nothing is done for quite a while? I'm not talking about the the lack of goodness coming from whatever was being infused, I'm focusing on the issue of air.

I was told, after the fact by someone else, "not to worry" when the infusion pump alarm goes off, it doesn't need to be handled right away. But they did not explain the mechanics of any of the IV process with regards to avoiding the introduction of air, as they were not a Nurse or Doctor. I would feel (slightly) better if I knew the mechanics of it for the next time something occurs.

 

[Silver]

The IV tubing is flushed with the IV solution in the bag prior to being connected to your IV. The IV catheter has a needle inside of it that is used to puncture the skin and enter the vein, then the needle is removed leaving the catheter in the vein. These are flushed usually with normal saline prior to insertion, along with the small connecting tubing that goes to the IV solution.

If the IV solution infuses completely, usually the solution in the tubing stays put creating a closed system so no air enters. I have seen some blood from the vein back up into the tubing a very short distance....like 1 inch. You really don't ever want an IV solution to run dry because the biggest concern is the IV clotting off and needing to start another IV. In over 35 years of nursing I have never seen any amount of air that would cause any concern enter a patient from a peripheral IV.

Central lines or arterial lines are a different story, and are treated very carefully to ensure that the infused solution never runs out, and that air is never introduced.

 

[Brett_Cameron]

Blood normally contains dissolved gases. The small amount of air introduced by IVs and flushing quickly goes into solution. Embolism occurs when gases come out of solution within the blood system in the body. It takes on the order of 100 cc of air to start injected into the bloodstream to begin the risk of embolism, IIRC, YMMV. The small bubble of air introduced by starting IVs are on the order of 1/100 of one CC, IIRC.

Edit: Blood pressure is higher than atmospheric pressure. When lying down if the lower of your two blood pressures is 60 mm as in 110/60, then your lowest blood pressure is 60 mm mercury greater than atmospheric pressure or 32 inches of water column greater. In order for fluids to be introduced via an IV then the fluid pressure at the IV entry into your arm must be greater than 32 inches of water column greater than you lower blood pressure number. This increased pressure is usually achieved by hanging the IV bag higher than your body. Many of the IV "pump"s are more of a metering device to control the flow rate into your body than to increase the IV fluid pressure. When the IV bag runs dry, the IV fluid pressure (water column height in the bag and tubing) drops until no more flow into your body is possible. The metering pumps generally don't create enough pressure to pump air into your body.

If you knock over the IV bag pole or drop the bag on the floor, you will quickly see blood being pushed out of your body into the IV tubing, so avoid doing that.

 

[Telly]

I'm learning a lot here! After all these years, I never had an IV in me, until... suddenly...

Silver - Thank you very much for the run-through! I had (wrongly) assumed that a hollow needle was used, and that it stayed in the patient, with a stub of tubing connected to the needle. Sort of like a hypodermic needle with tubing attached to it. Now I understand.

So, as long as there is some IV solution left in the tube above the actual point of entry, then clotting of the IV penetration should not occur, right?

B_C - Thanks for the info. I assumed that blood pressure systolic/diastolic was measured at an artery, and that actual pressure in a vein would be lower, since it is in the return system, and I would think (thinking as an Engineer here), that the restrictions which the heart pump needs to overcome are mostly upstream from the IV insertion point. But maybe you were giving me an in-the-ballpark model.

Regardless, so if the pressure created by water column height from point of insertion to the top of the fluid level in the bag exceeds the vein pressure, then there will be inflow. OK, got that now.

Which brings up an observation. They were running a lot of fluid through me, so much so that I had to get up to do an empty less than every 60 minutes. Which wasn't easy, to disconnect leg squeezer air lines, get up which was a job in itself, not snag tubing, move IV pole with me, while not getting IV pole wheels caught on infusion pump/monitors AC cord, not pulling cord out of wall etc. etc. Could not have done this without DW to give major help and steadying me. And often the pump/monitor would go into a No Flow alarm when I was standing moving around after a bit. At the time, I thought maybe it was the "needle" (wrong I know now) was moving around and was momentarily blocked. With this new understanding, I now wonder if my bent-elbow standing-up height versus the IV bag height was reduced to too small of a column to infuse. I'm a taller person. I was afraid at the time that maybe the thing was going to have to be pulled out and re-done

 

[MikeD]

I have had at least 500 IVs in my life. I routinely get them for infections due to a compromised immune system from immunosuppresive drugs for my kidney/pancreas transplant. One of my Drs used to be an engineer of the electrical persuasion. He told me that it takes about a pint of air to kill someone so I shouldn't worry that I had forgotten to flush the IV tubing which contained about 5 CCs of air. It was an interesting experience. I could hear the bubbles when they went by my ears! I was alarmed but figgered I shouldn't panic as it was already done, now what do I do? So I called and was reassured. My eccentric Dr told me he uses a few mL of air to check out some heart defects by listening with his stethoscope when injecting the air into a vein.

Mike D.

 

[Telly]

......so I shouldn't worry that I had forgotten to flush the IV tubing which contained about 5 CCs of air. It was an interesting experience. I could hear the bubbles when they went by my ears! I was alarmed but figgered I shouldn't panic as it was already done, now what do I do? .........
Mike D.

Even though cringing while reading this (actually, your whole post!), the science and Engineering me wonders if the bubbles were a one-pass phenomena, or did they cycle around fewer and fewer each pass, or do they mix in and get distributed all over the body so the next pass is all spread out in time and a lower amplitude sound?

It's not everyday that one hears of something like this!

 

[ls99]

Thanks for all the good info in this thread. I like learning about things.

Mike D bummer that you had to go through a lot. Yet good that you are around and kicking, even if not too high. Thanks for passing on the Engineer/Dr description.