“Mock before you block”: an in‐built action‐check to prevent wrong‐side anaesthetic nerve blocks

“Mock:…v. make a replica or imitation of something; adj…not authentic or real but without the intention to deceive” (Oxford English Dictionary) Whereas the seriousness of wrong-site surgery is long established, the notion of wrong-side anaesthetic nerve block as an adverse event is more recent; probably published first by Edmonds et al. in 2005 1. As a preventive measure, they suggested a ‘pre-anaesthetic check’ equivalent to the pre-operative surgical ‘time out’ 2, 3. Analyses of large data sets (> 10,000 patients) have estimated the incidence of wrong-site blocks to be ~ 4 in 10,000 (~0.04%; upper 95% CI ~0.1%, or ~1 in 1000) 4-6. Wrong-site blocks can readily occur in awake patients as the patient may believe that this is the correct way to perform the procedure 4. Since 2015, the error has been classed by NHS England as a ‘Never Event’, set aside for special consideration and used (albeit perhaps erroneously) as a marker of overall hospital safety and performance 7, 8. As a focus of regulators, prevention is rightly regarded as a priority. Contributory factors in a wrong-site block are well documented 4-6, 9 (Table 1). Hitherto, all recommendations for prevention have focused on introducing additional layers of verbal checking before conducting the block. This culminated in the Stop Before You Block initiative in 2011 10. A wonderfully catchy phrase, it was rapidly adopted by the Safe Anaesthesia Liaison Group (SALG), and the message disseminated across the UK and elsewhere (see: https://www.rcoa.ac.uk/salg). The key steps were a separate pre-anaesthetic check (similar to those suggested previously 2), and a new ‘stop’ moment immediately before needle insertion. Although logical and persuasive, Stop Before You Block has probably failed to reduce the incidence of wrong-site blocks. At its introduction, National Reporting and Learning Service (NRLS) data indicated 67 wrong-site blocks over 15 months up to November 2010 (~54 year−1) 11. In 2007, NRLS reported 33 incidents 12 and in 2009, just 27 11. In 2015, 34 errors were reported in the 9 months since April 2015 (~45 year−1) 13. The 5th National Audit Project (NAP5) Activity Survey estimated that 422,000 peripheral nerve blocks are performed annually 14; this suggests that the mean incidence has been consistently ~ 1 in 6250, with overlapping binomial 95% confidence intervals over years 15, 16. Other authors agree that the introduction of additional checklists has not reduced the incidence of wrong-site blocks 6. At least part of the reason for this is the increasingly recognised limitation of checklists themselves 17. The WHO surgical safety checklist initially produced striking results 3, but these were not confirmed in larger, more recent studies 18. A central venous catheter checklist in Michigan dramatically reduced infection rates by 66% 19 and led the NHS to adopt a ‘Matching Michigan’ initiative 20. Unfortunately and surprisingly, results were ambiguous 21. Other factors might be a failure or refusal of staff to apply checklists 22, or improved reporting (i.e. previous data were under-estimates). A more fundamental factor is rooted in neurocognitive psychology. There is a well established difference between perceptions for ‘action’ and for ‘identification’ 23. The first relates to perceptions needed to execute or complete a task (e.g. manipulate items to conduct a nerve block). The second relies on the neural system to identify a given item (e.g. recognise the correct side). The two perceptions can be readily dissociated such that, humans will actually hold and discard an item (perception for action) that they are seeking, without realising they already had it (failure of identification perception) 24. Relying upon ‘perception for identification’ alone ‘stop before you block’ is therefore predictably unlikely to influence the goal-directed ‘perception for action’ (conducting the block). The two perceptions need to be actively re-coupled by some type of in-built action check. Although verbal checklists are claimed to underlie the improved outcomes in the airline industry, Bosk et al. persuasively observe that this is true only for safe take off and landing; they have failed in ensuring baggage gets to where it should 25. Patient flows in hospitals, they argue, are more akin to the latter, where patients (like bags) come in different shapes and sizes, often in poor condition, requiring multiple, complex interventions in a pathway over time and space. These are tasks needing strong coupling of action and identification perceptions. Specifically, Bosk et al. cite wrong-site interventions as an error probably not amenable simply to introduction of a checklist: “[To say]: ‘If we just tell the workers to use checklists, we will have solved the problem…’ is simply the wrong conclusion…”. Something more than a checklist is needed. Several observations can serve as basis for developing a safer approach. First is the recognition that performing a block, especially in experienced hands, is a largely subconscious, single, confluent event conducted with fixed purpose. During training, it may be broken down into discrete components, but the very purpose of learning is to create a single, fluid movement. For any block, the process itself rarely offers a natural break in rhythm to facilitate a stop and check moment. After apparently checking the correct site and laying out the sterile tray, the anaesthetist properly regards what follows as seamless and goal-directed: putting the sterile sleeve on the ultrasound; preparing the skin; picking up the syringe; and injecting the solution (often performed with some flair, grace or speed). This commitment to action is recognised in psychology as a ‘point of no return’ 26. Introducing an interruption in the form of a verbal checklist in the midst of this process almost requires the practitioner to ‘un-learn’ the procedure and re-introduce the hesitancy or doubt that was rigorously eliminated through earlier training. Relying on assistants to introduce the necessary interruption is also not fail-safe, as assistants are also experienced and need to identify an optimum moment in what they too regard as a single movement to interrupt their anaesthetic colleague. Thus, it is important to appreciate that something needs to be built-in to the action itself in order to be effective. In terms of cognitive psychology, a safe nerve block requires both command (i.e. the strong drive to complete the task) as well as response countermand (i.e. an opportunity, integral to the action, to halt the task) 26, 27. Examples where command-countermand balance are necessary for safe task outcome are gently applying brakes when cycling downhill, or slowing and looking over your shoulder before overtaking on a motorway. The countermand slows down the primary task by opposing it, and in fact becomes itself a natural and integral part of the action itself. Second – and in large part related to the first – is the observation that in many cases of wrong-site block, there has been a significant time delay between performing the ‘stop’ check and the actual injection 4-6. Probably because the procedure is a seamless event once started, most practitioners are prone to conduct the stop moment check before starting the block, rather than, as recommended, just before inserting the needle. Analyses indicate that, from the team's perspective, the ‘stop before you block’ was properly completed but nevertheless, a wrong-site injection occurred. The team simply misidentified the site from the very start (akin to failure of identification perception), or something actively distracted them during the time delay. Third, it is striking that the wrong side injection is noticed immediately (or even during the act of injecting, when it is anyway too late), rather than postoperatively days or weeks after the event 4-6. Finally, there has never been a case of two successive wrong-site blocks; a second block performed immediately after a wrong-site block is always on the correct side. Our new proposal is based on these insights. ‘Mock Before You Block’ in its purest form requires the anaesthetist to prepare an additional, empty syringe (no needle), or empty needle sheath on the sterile tray. The anaesthetist prepares the patient as normal, uses ultrasound if required, but then first picks up the empty syringe/sheath and ‘pretends’ to perform a (mock) block with it (i.e. touching the skin) and declaring: “Is the mock block on the correct side?”. This is the important integral, countermanding step to the primary action. Only after positive confirmation is the second, solution-containing syringe (with needle) used to complete the block. If the patient is awake, then the mock-block should be performed before infiltrating any subcutaneous local anaesthetic (Table 2). The mock-block serves as a action trigger, rather than the verbal trigger in Stop Before You Block, and serves to re-couple action and identification perception. It actually turns to advantage the fact that wrong-site blocks are invariably immediately recognised. Using mock-block, a wrong-site block will require two successive action errors: one at the mock block stage (estimated incidence ~ 1:6520) and one at the true block stage where again, the incorrect site is contacted (estimated incidence ~ 1:6520). Thus, the likelihood of error is ~1 in 39 million (i.e.1:65202). This is probably why successive wrong-site blocks are unknown. The mock block is itself harmless. However, it will not prevent errors caused by marking the wrong site in the first place, or in cases where there have been errors in the consent process. It is not possible to acquire controlled trial evidence to assess effectiveness, but we note that both the WHO surgery checklist 3 and the Stop Before You Block campaign 10 were introduced without any supportive evidence, but rather with consensus. We (JM and JJP) have adopted the method into our own practice. Since the vast majority of anaesthetists have not performed or witnessed a wrong-site block, most trainees assigned to us were nonplussed or mystified at the ‘mock block’ step as something they had not encountered before. Although they understood the logic, they did not assign any importance to the step, over and above identifying the correct site for block. Furthermore, when performing a block under supervision, they frequently forgot to implement the mock block. In contrast, responses from colleagues who had experienced a wrong-site block have been overwhelmingly positive, as they better understood the safety potential. We observed the dramatic effect of a wrong-site mock block. A distracted assistant and trainee failed to notice the wrong site being prepared, even after a correct ‘stop before you block’ check. However, making a mock block declaration elicited initial surprise, followed by disbelief (at their own oversight), followed by expressions of huge relief that a mock block, and not a real block, had been performed. We can anticipate suggestions to modify the mock block, but to be effective all these would have to be conducted after preliminary site identification and sterile preparation of skin, just before true injection. These might include: using a sterile gloved finger or the sterile ultrasound probe rather than empty syringe; signing the site with one's own signature (or other unique mark); or applying a sterile label/dressing to re-mark the site. All of these need careful consideration (e.g. adding extra skin marks/labels could further confuse). A recent suggestion to label the injecting syringe 26 serves only as a further visual aid, without itself interrupting the action. To be truly effective, it is essential to make the mock block step a mandatory part of all blocks, in exactly the same way as intravenous access, minimum monitoring and skin preparation are all considered prerequisites to performing any regional anaesthetic technique. We recognise that experts in regional blockade may be slow to adopt this. However, trainees can and should be taught the method from early on. In postgraduate examinations, candidates currently can only pass a question on regional anaesthesia if they begin “I will establish consent, intravenous access, monitoring etc…”. We now hope and anticipate that they must henceforth be expected also to say: “…I will then perform a mock block, which will trigger a ‘stop-before-you-block’ check.” In this manner, ‘mock before you block’ is not designed to replace ‘stop before you block’. Rather, it strengthens the check moment by introducing a natural break (countermand response/in-built action check), to encourage the ‘stop before you block’ to be performed at its correct time. Relying on ‘stop before you block’ in isolation as an audiovisual cue has not proved enough. It will be important to assess the acceptability of our proposal in clinical practice; although we have found it straightforward to adopt, there may be unforeseen problems. Testing the method in simulation will be important, particularly to investigate the psychology of team reactions to wrong-site mock block. Most importantly, we hope to stimulate debate about whether there is a better alternative suggestion for an in-built action check, which is the unique notion upon which our approach rests. Finally, we note that there may be scope to apply the general principle more widely (e.g. by way of a mock incision) to help prevent wrong-site surgery. JP is an elected Member of Council, Royal College of Anaesthetists, and Chair of SALG. He also sits on the new national Expert Panel, Patient Safety, NHS Improvement. The views expressed are his own and not of these organisations. No other funding or competing interests declared.