During a viral pandemic which presents predominantly with hypoxaemia, a significant number of patients need careful monitoring of oxygen therapy and ventilatory requirements. As such, performing ABGs are becoming much more necessary and commonplace in A+E and on the wards.
I used to really hate taking ABGs. I can still feel the scrape of the needle on bone and the yelp of pain that a blindly digging needle causes while searching for that elusive flashback of pulsating bright red blood, and the disappointment when it doesn’t.
Compounded further by the confidence of a fellow foundation doctor who had just finished a respiratory job and had spent four months solely performing early morning gases on COPD and sleep apnoea patients who swan in and triumphantly gets it the first time. But this procedure does not have to be such an ordeal, with a few minor alterations to your technique and some practise you will soon become A.B.G. - A Boss Gass-er.
Preparation and positioning
- Get someone to show you the equipment in use in your hospital locally before approaching a dyspnoeic patient. In true N.H.S. fashion, these will undoubtedly be different from the ones you have practised within the medical school and the simulation centre. The most important question is “does the container self-fill?.” My hospital has recently moved from self-filling to manually retractable plungers. If this is the case then just have a practice pulling back on the plunger while keeping the needle still with your other hand, as it can be a bit fiddly.
- Try and have a look at the patients clotting function, platelets and drug chart for anticoagulants before entering. Although not absolute contra-indications, derangements in these guide how much gauze I have at the ready and length of time I spend tamponading. It is also good practice to get in the habit of doing this before you start doing more invasive procedures like drains.
- As you are likely to be going into rooms with P.P.E. on, make sure you bring in 2 or 3 of each item, you need. I’ve already had to do the whole rigmarole of doffing and re-donning just to get an extra gauze or some tape that I had forgotten to bring in.
- Don’t be afraid to get comfortable. When I have found an excellent palpable radial pulse, I will make sure the bed is at a good height, have a pillow underneath the wrist to keep it flexed at 45 degrees and find a chair to sit in while performing the procedure. Using these moments to not be on your feet with a hunched back not only maximises success but you’ll be thankful for the rest later in the shift.
- Having started doing arterial lines using ultrasound, I am beginning to notice the disparities in the depth of radial arteries between patients. This will correlate to how palpable the pulse is underneath your fingers. The average radial artery depth is surprisingly superficial, at 3mm from the skin (1). If the pulse is easily palpable it is probably even closer, and if it’s faint it could be either that it is a deeper artery or your patient is peripherally shut down (a quick feel of the hands and a cap refill can rule this out for you).
- If it is close to the surface, it is easy to go through the other side of the artery. Slightly reduce your puncture angle to 30 degrees and if you don’t get a flashback, slowly withdraw towards the surface, until you do.
- When you enter the skin, do not forget to picture how deep you are in the wrist continuously! Very easy to do, and all of a sudden you’re in no-mans-land and will have no idea how much to push further or retract.
The importance of local anaesthetic
- I’m sure you will all be able to perform a modified Allen’s test - a prerequisite for top marks in OSCEs but often foregone in real practice. However, it has been shown time and time again that doctors do not follow British Thoracic Society mandatory guidance to offer local anaesthetic when performing ABGs (except obviously in medical emergencies or unconscious patients) (2, 3). I was the same up until about six months ago when a colleague made an impassioned argument that fear of the pain of previous ABGs culminated in the late presentation of a sick asthmatic patient he was looking after. It was only really out of laziness and not feeling comfortable giving local anaesthetic that I wasn’t doing it myself. But since I have been, it has been pretty transformative for my practice.
- Just distal to where you have identified the pulse, use a small orange (25G) needle, to inject a small subcutaneous bleb (1-2ml) of 1% lidocaine. Ensure that you drawback on the syringe to check you are not in a blood vessel. Then leave the anaesthetic for a minute or two before attempting the ABG.
- Doing this has massively improved my success rate. The reduced pain and potential flinching cuts stress for both provider and patient. It could even reduce a delayed presentation next time.
- Here is an excellent review of the literature - which cites multiple studies which find reduced levels of reported pain for patients and increased success rates for doctors.
Knowing when to stop
- If it doesn’t quite happen after 2 or 3 attempts, then I would give the patient rest and get some fresh eyes on the situation. I have seen respiratory registrars who have done 1000s of them miss ABGs, so of course, you or I will. Knowing when to get some help is an essential part of being a safe junior doctor, and when it is about performing a painful procedure, it is also the most humane thing to do.
I hope that was helpful! I’ve got some awesome blogs with insights and tips to make sure you feel supported and are ready to manage COVID patients. Subscribe to my blogs below to get an email update when I publish the next one.
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