To maintain some level of attachment to core syllabus topics, this chapter should have been at least vaguely relevant to Section G6(ii) of the 2023 CICM Primary Syllabus, which asks the exam candidate to "describe the invasive and non-invasive measurement of blood pressure, including limitations, potential sources of error and the need for calibration". At this stage there have been no attempts to introduce arterial cannulation technique into SAQs, viva stations or CICM workplace competency assessments. It is not inconceivable that the college will at some stage demand it as one of their training objectives, and it seems reasonable to futureproof against this possibility.
There is a satisfactory amount of literature dealing with this topic. The best references include "Chapter 3: Arterial line placement and care" in Irwin and Rippe's Intensive Care Medicine, and the 2012 article by Tiru et al.
The notes attempt to remain site-agnostic, as Seldinger techinque does not vary substantially between sites and because specific site-related instructions are carried on in the chapters which answer CICM Syllabus Section X(ii), "describe the anatomy relevant to the insertion of an arterial line into a
brachial, axillary, posterior tibial, dorsalis pedis, radial or femoral artery." However, it is difficult not to acknowledge the fact that the radial artery is the most used site, and so a certain radio-centric bias can be felt throughout the text.
Irwin and Rippe (Ch.3) recommend that
“The catheter over the needle approach (e.g., radial or brachial site) necessitates cap, mask, sterile gloves and a small fenestrated drape; whereas, the Seldinger technique (i.e., femoral approach) requires maximum barrier precautions.”
No references is offered to explain where they got this, but it certainly seems reflective of what happens in real life theatres and ICUs. However, if one digs deep enough one can discover that in fact this "small fenestrated drape" recommendation is derived from the CDC Guidelines for the Prevention of Intravascular Catheter-Related Infections (O'Grady et al, 2011). The CDC suggest that "a minimum of a cap, mask, sterile gloves and a small sterile fenestrated drape should be used during peripheral arterial catheter insertion".
The reader is again subjected to self-indulgent abuse of Adobe Illustrator:
In short, the process is as follows:
There is a modification of this , known generally as the "transfixation" technique. It is usually used with “cannula over needle” kits, and involves intentionally puncturing both walls of the artery, skewering it “through and through”.
Surprisingly there does not appear to be any major difference between thrombotic complication rates for either technique (Jones et al, 1981). Or rather, the thrombotic complication rate with radial punctures is already high (almost 20% end up having Doppler evidence of occlusion) which could mean that about 20% of the time the posterior wall of the vessel ends up being lacerated to some extent anyway.
Generally, beyond a certain level of skill most junior doctors will have little difficulty hitting the pulse with a needle. The most common reason for "hey boss, can you give me a hand here" is the failure of the guidewire to advance beyond the needle tip. Classically, the guidewire comes out of the puncture looking like a dog's breakfast. They've clearly been at it for a while.
This could be happening for a variety of reasons:
There are a few recommendations one can make to help prevent problems when arterial line insertion gets tricky:
Ultrasound-guided insertion of arterial lines has not been popularised to the same extent as central lines, because there is a lower rate of insertion-related complications with arterial lines, and the pulse makes a convenient palpable landmark.
The use of ultrasound guidance does not obviate the need for a sound knowledge of anatomy, or protect inexperienced practitioners from the risk of complications. If you don't know what you are doing, stabbing mindlessly at the pulsatile object on the screen will yield only self-doubt and disappointment. However, ultrasound guidance has been demonstrated to increase the success rate, decrease the number of “passes” and decrease procedure time for practitioners who are already proficient with the palpation method (Shiver et al, 2006). It has also been demonstrated to improve radial arterial access chances in situations where it is being used as a rescue technique, after failed “blind” attempts (Sandhu et al, 2006).
How many do you have to do before you're good at this? An old study by Konrad et al (1988) plotted learning curves for anaesthesia trainees, and found that after 5-7 attempts you have a better than 50% success rate. The competence seems to plateau after 20-30 attempts. The fact that the curve trends down towards failure once one becomes experienced suggests that either some of us become overconfident, or pick the difficult cases (leaving bounding pulses for the novices).