The Red Line – Getting That Arterial Line

There are plenty of times in the land of retrieval (and in some prehospital settings) where you need a little bit more than the simple squeezy cuff gives you. An arterial line. Maybe we could share some tips that work for at least one person with the hope of encouraging people to share theirs. This post is from Dr Andrew Weatherall.

There are things in medicine that are more than a bit disconcerting. Clinical practice pretty regularly asks us to skate back and forth between degrees of uncertainty and deal with it. So you take your reassurance where you can and sometimes that is in the form of a red wiggly line – the arterial pressure waveform. Yes, I’m that sad.

Look, here is the very evocative image that flickr threw my way when I searched for “red line” under Creative Commons. Think about it.

Given the problems associated with other monitoring methodologies in retrieval medicine having a more accurate option for providing haemodynamic information is invaluable. Add in the option for easy blood sampling and moving a critically ill patient is clearly made a lot more appealing with an arterial cannula in place than without it.

They can be a bit of a bugger to get in sometimes though. Particularly in the area I spend most of my time which is paediatric anaesthesia. Now I don’t have a bazillion answers as to how to make it sure it always hits the spot but there are a bunch of things I always do to try and increase my chances of success. Now these might be things for deploying in little people but lets face it, adults are just big kids. Pathetic, large, disintegrating kids. Anyway, in no particular order here’s a few:

1. Check them all

It’s pretty rare that you need to specifically place an arterial line in one chosen artery for prehospital or retrieval work. Not all pulses were created equal though so it’s worth taking a moment to feel all the candidates to measure them up. Choose the best one for that first shot.

2. Get the position right

Whichever one you choose, it’s worth getting the position at its best for that particular artery. At the wrist I think a lot of us have been shown the wrist extended position, and that is usually pretty useful. It’s worth exploring how extended you need that position though. Sometimes when you go to extreme you can distinctly feel the pulse get a little harder to feel. And while a roll under the hips can make a femoral line just that bit easier, it’s worth doing a before and after check. . The bigger point is that you don’t want to just choose the best pulse, choose the best position for that pulse.

3. Know your kit

This is sort of a good rule for lots of prehospital and retrieval work. You need to know your kit and choose it well. Or if you’re utilising something at the place you’re picking up the patient, make sure you understand it. Different cannulae meet up to to the needle component differently. If you’re planning to have a wire as a back-up to get in (assuming it’s not an inbuilt option) you might want to double check the wire will get through the cannula. Know what you’re wielding. Plus at the same time it’s worth remembering that a smaller cannula in the artery is a lot better than a bigger one you can’t feed in. Choose the cannula you’re sure will get in.

Red dots
This also came up when I searched for “red line”. Bit of a fail there. That’s not a red line, it’s a line of red dots. It’s even called “Red Dots”. What gives flickr?

4. The Wire Bit

While I’m there, a wire can obviously be a pretty good friend. I know plenty of people who prefer the technique where you transfix the artery, come back and feed the wire up once the blood is flowing back freely. Plus get a smaller cannula in (see above) and that wire becomes the tool to dilate up to a larger bore cannula.

5. Sit Down

I know this seems really minor and maybe you feel strongly that you’re only doing it right if you’re in a moving vehicle and the family cat you brought with you to comfort the owner is sinking its claws into the back of your neck or up your nostril or something. The thing is trying to not let the environment control you is part of the gig. When you sit down you can set up your ergonomics a whole lot better and position yourself to take away muscular strain and fatigue while you’re doing it. So if the space allows it, sit down and get comfortable.

6. Side to Side and Up and Down

Now that you’ve hopefully found a comfortable position, it’s worth really mapping out that artery. Maybe other people have more sensitive fingers than me but I generally find that placing a single finger on the pulse and trying to centre it in the middle of the pad of my fingertip helps me get a sense of where it is. I then use that same finger to feel up and down the artery and figure out its course so I can mark it on the skin. It actually doesn’t matter a huge amount if the mark is perfect as long as I can go back, feel and understand where I’m feeling the artery in relation to the obvious mark I’ve made. I do this every time to help construct a picture in my head of how it all lies, even before I get onto ….

7. Use an ultrasound

If it’s available, then probably just use it. The evidence says that you’re more likely to get it in without incident and it’s unlikely to be a slower endeavour. Using the ultrasound well still demands good patient and clinician positioning as well as a scout scan up and down the artery to understand its course and any surrounding stuff. Small ultrasounds are now good enough that you should be able to pick up the tip of the cannula all the way into the middle of the vessel (and spot when you’ve still got a little bit of tissue indenting at the wall). Just use it.

8. Short, sharp, flat

It makes pretty obvious sense to approach without too steep an angle (though sometimes you can pop through the skin better with that sort of angle). A flatter approach maximises your path in the vessel which maximises your chances of staying in there. When it comes to movements I find an approach with short, sharp advances more successful than a slow steady push. At least in kids sometimes the latter seems to allow that artery to squeeze out of the way (but I’m happy to be pulled up on that one).

9. Also use local

If the patient is awake of course. Why?  I think that’s actually an obvious one.

Marco Galasso
This one, also came up on the “red line” search but really it’s about the dog. So maybe if you want to get arterial lines in, think more about puppies?

10. Be ready for success

You’re probably going to be brilliant so be ready for that not surprised. Having those tapes and connections ready so you can focus on the bit after the cannula (particularly trying to maintain a clean and dry field so everything sticks and you don’t have a bunch of stuff to clean up) lets you get on with actually using the monitor.


So there is my meagre collection of practical bits and pieces. In the prehospital and retrieval space I can’t always guarantee that I can set myself up like I can in an operating theatre. When I make the effort though it turns out I usually don’t have to compromise that much. And that effort usually makes the whole thing go a little bit smoother.

It’s also not an exhaustive list. So if you’ve got a top tip then hit up that comments section. I could use a tip to be better next time I’ve got to step up to the red line.



The main reference to read for this one would be this Cochrane review looking at success rates for arterial cannulation in kids using ultrasound. The short version is yes, do that.

All the images here were from Creative Commons posts on The first is from XoMEoX, the second is from Håkan Dahlström and the third is from Marco Galasso.





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