You did an Allen test, didn’t you!? Rethinking pre-procedural assessment for arterial line placement
Shawn Jackson, Ethan Sanford, and Justin Lockman
The Allen test (or the very similar “modified Allen test”) is a bedside clinical assessment used to evaluate the adequacy of the ulnar artery/palmar arch collateral circulation before radial artery puncture or cannulation. It seeks to answer the question, “Will this hand be at risk of ischemic injury if I injure or obstruct the radial artery?” We imagine that every reader of the Pediatric Anesthesia Article of the Day has been told, at some point, the importance of the Allen test and the potential for catastrophe if it is forgone. But what is the evidence for this practice? And is it still necessary in the era of ultrasound? Today’s PAAD looks back at two publications over the past 3-years to help address this question!1,2
Original article
Gleich SJ, Wong AV, Handlogten KS, Thum DE, Nemergut ME. Major Short-term Complications of Arterial Cannulation for Monitoring in Children. Anesthesiology. 2021 Jan 1;134(1):26-34. doi: 10.1097/ALN.0000000000003594. PMID: 33079134.
Original article
Abbasi RK, Packiasabapathy S, Hamilton M, Walker SG, Mazurek M, Dierdorf S. Ipsilateral double arterial puncture in children. Paediatr Anaesth. 2022 Apr;32(4):581-582. doi: 10.1111/pan.14413. Epub 2022 Feb 18. PMID: 35150182.
First, it is worth mentioning that a prospective assessment of the value of the Allen test in predicting clinical complications has never been performed in children, and likely will never be. There have been numerous studies in adults showing that the test is, at best, controversial. One of the first dates back to 1983 which revealed that 16 patients with an abnormal Allen test went on to have their radial artery cannulated without any complications3. A more recent publication demonstrated that an abnormal Allen test failed to predict complications when the radial artery was harvested for a flap (for the hand or the flap)4 – and we think that is pretty definitive obstruction to radial flow!
So, what DO we know regarding safe cannulation strategies for pediatric arterial lines? First and foremost, it is remarkably safe. In the Gleich et al article highlighted above, data from 5,142 arterial cannulations were analyzed, and the authors found an overall low risk of complications (0.2%). When the radial artery accounted for 66% of lines (3395 cannulations!) there was not a single major complication. In fact, the only site which was associated with any complications was the femoral artery1. It is worth noting that an Allen test was not a requirement for this study or included in procedural documentation.
The safety of distal upper extremity cannulation was further highlighted by the Abbasi et al publication, which provides data on what to do when presented with the fairly common conundrum of “ipsilateral puncture – or not?”. Here is the scenario: you (or your trainee) have just attempted an ultrasound guided arterial line in the radial or ulnar artery and it was unsuccessful. Is it safe to cannulate the other artery ON THE SAME HAND?! It turns out, in the 58 patients who had subsequent attempts at cannulation in the other ipsilateral artery (either radial after ulnar or ulnar after radial), not one had major complications and only four had transient pallor or coolness that improved while the cannula was still in place.2
There remain some limitations here. For example, we don’t know whether or not the use of ultrasound has changed the risk profile of this procedure in a way that decreases the risk of vascular compromise to the hand. We also don’t know whether simple arterial puncture (as for arterial blood gas analysis) poses more or less risk, although we suspect less risk. Certainly, several “single arterial punctures” commonly occur prior to definitive arterial cannulation, and the lack of large numbers of reports of injury after this procedure seem compelling. It’s also worth noting that while instances of patient harm are not reported in the literature, it’s possible that a signal could be present.
While several major health organizations (including the WHO) still advocate for the continued use of the Allen or modified Allen test, many clinicians no longer consider this part of their routine practice. The AHA no longer recommends it during transradial coronary procedures, stating “application of the Allen or Barbeau test is not a useful triage strategy, and an abnormal test should not preclude TRA (transradial artery access).5”
Personally, we don’t bother doing an Allen test and we don’t think there is reason to document anything about it. We can imagine the medical/legal advocates raising their voices in objection, but we don’t think performing the test prevents injury, and we don’t think the data are strong enough to protect us legally if there is injury and we had performed the test. We shouldn’t engage in performative acts for the sake of unknown legal risk in the absence of clinical benefit. The data indicate the Allen test is roughly as informative and impactful as rubbing a lucky rabbit’s foot, we also don’t advocate for killing rabbits to avoid legal risk.
What is your practice? Do you routinely perform an Allen test as part of your practice? Feel free to vote in the poll below and email any thoughts (or alternatives!) to Myron at myasterster@gmail.com for further discussion in the Friday Reader Response.
References:
1. Gleich SJ, Wong AV, Handlogten KS, Thum DE, Nemergut ME. Major Short-term Complications of Arterial Cannulation for Monitoring in Children. Anesthesiology 2021;134(1):26-34. DOI: 10.1097/ALN.0000000000003594.
2. Abbasi RK, Packiasabapathy S, Hamilton M, Walker SG, Mazurek M, Dierdorf S. Ipsilateral double arterial puncture in children. Paediatr Anaesth 2022;32(4):581-582. DOI: 10.1111/pan.14413.
3. Slogoff S, Keats AS, Arlund C. On the safety of radial artery cannulation. Anesthesiology 1983;59(1):42-7. DOI: 10.1097/00000542-198307000-00008.
4. Miller TJ, Safa B, Watt AJ, Chen ML, Lin WC. An abnormal clinical Allen's Test is not a contraindication for free radial forearm flap. Clin Case Rep 2020;8(11):2191-2194. DOI: 10.1002/ccr3.3093.
5. Mason PJ, Shah B, Tamis-Holland JE, et al. An Update on Radial Artery Access and Best Practices for Transradial Coronary Angiography and Intervention in Acute Coronary Syndrome: A Scientific Statement From the American Heart Association. Circ Cardiovasc Interv 2018;11(9):e000035. DOI: 10.1161/HCV.0000000000000035.