IV Gauge for CT

Odelle · Feb 9, 2011

Hi there! I'm a CT tech considering going into nursing.

Since I don't know what this doctor was looking for, I can't say for sure whether an 18g was really necessary. Usually when CT techs ask about the IV they are doing some kind of CT angiogram to look at blood vessels. So for a PE, we do a CTA of the chest, and the reason for a large gauge is because we are using a machine called a power injector to inject our contrast. It gets a nice, even bolus for the imaging, and you can't do this by hand.

You can usually get a great CT with a 20g in the AC. Sometimes, if we get a 22g or it's more distal, like in the forearm, we can get away with injecting more slowly if the patient isn't obese, or we can use different contrast (which is more expensive, and can be contraindicated if the patient's BUN/creatinine aren't good). But neither of those will guarantee this, meaning that we charge the patient for an exam that was inconclusive.

18g is great because there's much less chance of infiltration, but a 20g is usually sufficient. I don't know what your ER doctor is talking about, that was probably the protocol at wherever he came from.

PS We hate infiltrating contrast, I'm told it can eat at the patient's muscles, and it's extremely painful to have 80cc or whatever in your arm. I would much rather scan for a PE with a weird 20g in the upper arm, or the shoulder even, than risk blowing a vein down towards the wrist. Hand/wrist IVs are unacceptable for CT angiograms... it can be a PITA on little old ladies with no veins, but it's better than that poor LOL bruised up with infiltrated iodine.

Also, if the patient is obese and all you can get is a 22 in the lower forearm, we can try because the doctor is insistent that the scan gets done, but more than likely the report will say "Evaluation of the pulmonary vessels limited by suboptimal IV" or something like that.

MesaRN · Feb 9, 2011

We are required to have 18G in a great vein (AC or better) for R/O PE (which I assume was the reason for the chest CT). This rule is so ingrained that even if you have a 20 in the AC they will not take it and require a central if no 18 can be established. Typically we do deep brachial with Ultrasound guidance as a last resort. This is due to the pressure necessary for CT angio of head/neck/chest as it must reach the organs at the same time as the scan. For abd ct and gauge will do.

Our go to IV size is 18 or greater. Only time we use a smaller guage is if we just can't get an 18.

jossjjojo · Feb 9, 2011

I've been told that they have to have a 20 gauge above the wrist. The will refuse anything less and it's because the vein will not hold up to their power injectors.

GM2RN · Feb 9, 2011

Ridiculous! I would have come unglued. Despite his opinion about the size of IV needed, he shouldn't speak to you in a rude manner, which I assume he did by snapping at you. I would have also insisted he explain it to the pt. I also can't believe a 20 yoa cp gets worked up in your ED. He would've needed a hx in mine. Our requirement for contrast is a twenty. Also, if he was so concerned about this pt and thought he was so ill to require larger IV access, why d/c the existing, functioning 20? This just doesn't make sense to me. Sounds like he's going to be a challenge to break in.

We had a 21 yo male with a STEMI in the ED a few weeks ago.

Odelle · Feb 9, 2011

Unfortunately, lots of young people with chest pain (due to anxiety, obesity, etc) come in and get worked up. My old facility, everyone with CP had to have a PE protocol done, lots of unecessary radiation to these patients. But then, you have the random 2 or 3 people a year that are walkie-talkie, no apparent distress other than chest pain, and they end up having B/L PEs.

I really wish there was a more cut-and-dry way to decide "This patient may have have a PE, or may have a mass or a subdural bleed in their brain", but by the way ER doctors order it doesn't seem like it. They radiate patients like water. I'm just glad my new facility seems to be much less unlikely to order CT Chest on pregnant patients, for a while I was scanning 2, 3, 4 ladies a month and of course, the scan would be negative. I wonder if somebody got sued at that ER because that 1:1,000,000 patient happened to have a PE and they didn't do a CT.

BrnEyedGirl, BSN, MSN, RN, APRN · Feb 9, 2011

Were I work an 18g in the AC is required for a PE study.

alem-tsahai · Feb 9, 2011

At my old job the protocol was an 18g. This was at a small community hospital and they were absolutely inflexible about that rule. It was very annoying, since the majority of our patients were from nursing homes.

At my new gig, a large level one trauma center, a 20g is completely acceptable. Go figure.

Emergency RN · Feb 9, 2011

in the er today i had a 20 y/o "chest pain." of course the pt received the full cardiac workup as well as a ct of the chest. prior to taking my pt to ct the md asked me what size iv i put in the patient and i replied 20 g. in my opinion, i felt this size iv was sufficient. however, the md, who is newly off residency, snapped back and said i want an 18 g in this patient. i proceded to question why and he said that he could (not sure why he said he bc it is the radiologist who does this) could read the scan better. i had my doubts but let the fight rest because for one i had no time for this and two i knew it would get me no where, fast. he put in an order for the 20 g to be dc'd and an 18 g lac placed. i spoke to a few seasoned nurses as well as rad tech's who have never heard that the size 20 or 18 g made a difference on the scan. anyone knowledgeable in this area??

this is a question related to physics.

the 18 ga is preferred in some institutions, mandated in others.

the size ga is meaningless in terms of final quality of the image. despite what many people believe, the quality of the image depends more on the rate of injection, and not the size of the catheter. this is because the injector machine is insensitive to resistance; it will smoothly power inject the same volume over a unit time (for example say, ...5 ml over one second) regardless of the catheter size. hence, if a study called for 10 ml of contrast to be injected over 2 seconds, the machine will inject 10 ml of contrast over 2 seconds regardless of the size of the catheter. so the final image quality between two different sized iv's will be identical as the rate of injection (determined by the study protocol) remained the same. the exact same 10 ml got into the patient in the time required, regardless of catheter size.

but... (and respondent odelle brushed upon this)

...the amount of pressure during the injection will be vastly different. if you use say, ...a 24 ga catheter, just imagine the amounts of pressure required to push 10 ml within 2 seconds, through it; would it be high or low? answer; it would be strikingly high. would the machine still be able to do it? of course it could; it is an unthinking machine that is geared to delivery that volume over that set time, regardless of the pressure that it generates. so what would happen to the vein that is on the other side of that catheter? almost immediate rupture.

now since that first iv was in the antecubital vein, and most patient's only come to the hospital with two; you've just ruined one. so... if you want to do the study, you can only get one more try. hence, the larger the catheter, the less pressure there is at the injection site, and less pressure means less likelihood of vein rupture or infiltration which indirectly allows them to complete the study at the prescribed protocol rate.

btw, great question :up:

as for the md being nasty to you? well, aside from clinical rationales, some people are just plain ill tempered regardless of their stripe. don't let it get to you.

XingtheBBB, BSN, RN · Feb 9, 2011

We had a 21 yo male with a STEMI in the ED a few weeks ago.

We recently had one end up on a balloon pump because no-one (including him and his wife) really thought about MI when the CP started. Work-up is costly but is costs less than a law suit. Don't underestimate how fast hearts are aging in this day of frequent fast food, high stress, and computer recreation.

Editorial Team / Moderator · Feb 9, 2011

Our radiologists prefer an 18g, a 20g will suffice, but it needs to be as close to the AC as possible. We once did a PE study/CT angio with a 20g in a pt's wrist, though. After that worked successfully, I got kinda skeptical about the whole OMG MUST BE IN THE AC attitude.

XingtheBBB, BSN, RN · Feb 9, 2011

Oh, and I do see the value in a large vein and agree for going for the AC however, I think a 20 is sufficient. I will say, I would never accept and order for "D/C IV. Sorry, it's the nurses not the MD's business if there is an extra IV. Tape over it if he's so concerned that CT will use it, write "not for CT" but why pull it? If he gets admitted to ICU or stepdown, even tele in some places, he'll have to have two accesses anyway.

Emergency RN · Feb 9, 2011

oh, and i do see the value in a large vein and agree for going for the ac however, i think a 20 is sufficient. i will say, i would never accept and order for "d/c iv. sorry, it's the nurses not the md's business if there is an extra iv. tape over it if he's so concerned that ct will use it, write "not for ct" but why pull it? if he gets admitted to icu or stepdown, even tele in some places, he'll have to have two accesses anyway.

i beg your pardon, but an invasive procedure such as an iv insertion absolutely requires a doctor's order. if the doctor says to d/c it, it is a medical, and not a nursing judgment.

"...sorry, it's the nurses not the md's business if there is an extra iv"

i would like to see you go to your state bon with that line of thinking; they'll pull your license so fast your head would spin.