Keeping our nerve: what large datasets can (and might) reveal about peri‐operative nerve injury

Support for the concept of implementing ‘a few blocks for the many’ is perhaps building [1] in both the UK and the USA where the proportion of peripheral nerve blocks being performed annually is increasing [2, 3]. Absolute numbers of peripheral nerve blocks undertaken, however, remain low, and there is still room for improvement [2, 4], not just in utilising these where appropriate but also in ensuring patients are at least offered the option of regional, rather than exclusively general, anaesthesia. Whilst there has been great enthusiasm for Plan A blocks within the regional anaesthesia community and beyond, anaesthetists are inherently risk-averse and concerns persist regarding the potential for neurological injury when performing peripheral nerve blocks [5, 6]. Anaesthesia-related litigation in the UK is now most commonly related to regional anaesthesia, with cases due to peripheral nerve blocks doubling between 2008 and 2018 [7]; although, conversely, the proportion of claims related to nerve injury in the USA, based on the most recent analysis of the ASA Closed Claims Project, has decreased over the same period [8]. Peri-operative peripheral nerve injury (PPNI) is complex and not always attributable to peripheral nerve blocks. Direct surgical injury, positioning, use of a tourniquet or other pressure-related nerve injuries may occur, with various comorbidities also potentially increasing the vulnerability to injury. Many studies have sought to quantify the risk of PPNI associated with peripheral nerve blocks, but most suffer from one or more of the following limitations: not reflecting contemporary regional anaesthesia practice; lack of comprehensive denominator data (including surgical cases in which a block was not utilised); inadequate assessment of the PPNI and determination of aetiology (i.e. to exclude patient or surgical factors); and insufficient follow-up of patients with PPNI to determine if and when the injury resolves [9, 10]. Ultimately, such studies simply reflect the data reported voluntarily to registries of regional anaesthesia or single-centre retrospective cohorts, which are subject to selection and other forms of bias. This prevents anaesthetists from providing patients with accurate, contemporary information about the risks (and benefits) of regional anaesthesia, as well as the risk of peri-operative nerve injury in general. Luo et al. report the results of a retrospective review of a large administrative database from Victoria, Australia, containing more than 5.4 million non-maternity surgical admissions between 2015 and 2025 [11]. Peri-operative peripheral nerve injury events were defined as “nerve injuries that were recorded during the admitted episode” and further separated into “all nerve injuries” and “specified nerve injuries”. An advantage of this cited dataset is an accurate case denominator value, which includes cases with and without a peripheral nerve block. Based on their analysis, the overall PPNI rate was 0.02% or 1 in 5000 during the admission period, which accounted for all potential aetiologies, including direct surgical trauma as well as other patient, anaesthetic and surgical factors. In comparison, a recent systematic review of over 100,000 peripheral nerve blocks estimated the incidence of nerve injury at 1 year, by which time the majority of early injuries have resolved, to be 0.03% or 3 in 10,000 [10]. Estimates of surgery-related PPNI vary widely, depending on the procedure and approach, with ranges of 0.08–88% quoted in hip arthroplasty [12] and < 0.1–10% in arthroscopic shoulder surgery [13]. The risks of positioning-related peripheral nerve injuries differ by site, with 0.26–0.46% reported for ulnar nerve injury [14] and 0.02% for peroneal nerve injury (prolonged motor weakness) in the lithotomy position [15]. Taking all these various estimates and the timing of the reported injury into account, the overall reported figure by Luo et al. of 0.02% for PPNI appears reassuringly low for such an early time-point in the trajectory of PPNI, particularly given that these figures included direct surgical injury [11]. In addition, the rate of PPNI appeared to decrease over time, with the rate in 2023–2024 almost half the rate of that in 2015–2016. The potential reasons for this difference are not explored intensively by Luo et al., although it is possible that improvements in the quality of peri-operative care, technical and/or educational advancements or other innovations may have played a role. Interestingly, Luo et al. also found that absolute rates of PPNI were highest in patients who received both regional and general anaesthesia, and lowest in those who received regional anaesthesia only, the reasons for which are not possible to establish from this dataset. Logistic regression showed a significant difference for specific nerve injuries, again with an increased odds ratio (OR) for combined regional and general anaesthesia techniques (OR 2.68, 95%CI 2.11–3.39, p < 0.001). The risk of PPNI also appeared to be highest in younger age groups and patients living with obesity. As a retrospective cohort study, it had limitations despite the impressive number of cases. Since the data were collected within a single national health system, the inferences may not apply to other countries where healthcare delivery and specific aspects of anaesthetic practice may differ. The database itself was designed primarily for administrative purposes and not clinical research. However, it is likely that case data are complete and accurate, especially when compared with studies that have used self-reported survey or registry data. Mean duration of hospital stay for non-day-case procedures in hospitals in Victoria is approximately 5.5 days; thus, only PPNI events reported within this time frame are likely to have been included. Since there was no standardised definition of PPNI or assessment tool, it is unclear what duration or severity threshold was required for PPNI to be documented within the clinical record and coded as an injury according to the International Statistical Classification of Diseases and Related Health Problems (Tenth Revision, Australian Modification). This could have resulted in inaccurate reports and/or underreporting of transient injuries. Conversely, from a patient care perspective, the severity of nerve injuries and, in particular, the clinical course of these injuries cannot be ascertained, and so it is unknown what proportion of these 1 in 5000 cases persisted to become permanent. Furthermore, besides the surgical specialties involved, there was no additional information provided about the type and duration of surgical procedures that were (and were not) associated with PPNI, nor could cases of nerve injury be attributed definitively to events that occurred in the operating theatre. Although injury codes were available, relevant clinical information that may have increased the risk of development of a new PPNI was missing, such as the specific regional anaesthesia technique performed (if applicable); positioning for surgery; if a tourniquet was used; and patient factors such as pre-existing peripheral neuropathy, diabetes or other comorbidities. In contrast to the study by Luo et al., a single-centre cohort study from the USA involving 9558 patients reported a higher overall incidence of 1.2% for new PPNI, with a rate of 0.9% for cases with a nerve block and 1.4% for cases without a nerve block (p = 0.053) [16]. Similar to Luo et al., patients who avoided general anaesthesia had a lower rate of PPNI compared with those who received general anaesthesia (0.6% vs. 1.4%, respectively, p = 0.003). This study used a database that was designed specifically to collect anaesthesia-related outcome measures for patients having surgery who were admitted to hospital at least overnight. The surgical procedure and type of anaesthesia, including regional block technique, were noted for each case. The assessment of PPNI was standardised, starting with the presence or absence of pre-existing neuropathy, and each patient was asked a scripted question on postoperative day 1: “Since surgery, have you noticed any areas on your body of new numbness, tingling, or weakness?”; if affirmative, the site was noted and examined with details entered into the database [16]. Patients with new PPNI were followed for up to one year after surgery. Of these patients, 82% reported resolution of PPNI by 3 months after surgery, and only one patient was left with no improvement at one year [16]. If such a trajectory was extrapolated to the 1 in 5000 rate during the admission period in the cohort studied by Luo et al., the incidence at one year of permanent PPNI in their cohort would potentially only be 1 in 575,000. Unfortunately, while the overall PPNI risk estimate from Luo et al. does seem reassuring, it remains unclear what is the exact risk of PPNI attributable to regional anaesthesia, whether or not the results from this administrative data analysis are generalisable outside Victoria, Australia, and if these figures would be different if clinical assessment tools questioning for PPNI specifically had been used. The 8th National Audit Project (NAP8) of the Royal College of Anaesthetists in the UK is due to launch in early 2026 and aims to study both major complications of regional anaesthesia and general PPNI. Utilising the methodology described previously [2], a short, intensive activity survey will be undertaken over a 1-week period, with the data extrapolated to generate an estimated annual caseload. This denominator will then be combined with the complication numerator, collected during a 1-year case registry phase, where all anaesthetists in the UK and the Republic of Ireland will be asked to report major complications secondary to central neuraxial and peripheral nerve blocks, as well as all cases of PPNI not related to direct surgical injury (Table 1) [17]. The scope will include all patients under the care of an anaesthetist where regional anaesthesia or surgical local infiltration is delivered for: acute and chronic pain in any hospital setting; peri-operative analgesia and anaesthesia in adults and children; and all obstetric practice. Based on the number of procedures in NAP7 [2], and the fact that in NAP8 the Royal College of Anaesthetists is collaborating with the College of Anaesthesiologists of Ireland (expanding numbers by approximately 15%), the estimated denominator is approximately 400,000 peripheral nerve blocks and > 400,000 central neuraxial procedures. All anonymously-reported cases of PPNI will be reviewed by a multidisciplinary panel (including neurologists, clinical neurophysiologists, peripheral nerve surgeons, neurosurgeons and anaesthetists), and only cases with persistent symptoms at 6 months will be considered permanent and included in the final analysis. Whilst the NAPs have many strengths, one limitation, unlike the work by Luo et al., is that the denominator for case volume is extrapolated from a short activity survey. This methodology has now been utilised successfully for almost 20 years but, ultimately, NAPs are a 1-year snapshot from a single country which, like the work by Luo et al., may not necessarily be generalisable elsewhere where practice may differ. Another significant risk is that of under-reporting of PPNI. The methodology of the NAPs does not involve the consent of patients and therefore dictates that patients cannot be followed up actively where this is not standard practice. Given that the majority of patients in the UK are not followed up directly by anaesthetists following discharge, NAP8 will rely on engaging relevant surgical and neurology colleagues, as well as other allied health professionals such as physiotherapists, in order to capture patients with PPNIs who present postoperatively [18]. Ideally, robust electronic national (or international) registries and automated follow-up systems would collect information on PPNI (as well as all other peri-operative complications and outcomes), but building and actually implementing such an aspiration is no simple task. Until then, we hope that the upcoming NAP8 project, the current work by Luo et al. and any other future studies will to provide patients and clinicians with contemporary information about the risk of PPNI. In the short term, perhaps a more achievable element of future work would be to standardise the definition and assessment of PPNI [16], in the same way recent attempts have been made to standardise many other peri-operative outcomes [19]. Generating evidence regarding peri-operative outcomes and the role of regional anaesthesia is important to the ongoing process of improving patient participation in clinical decision-making. We congratulate Luo et al. for contributing the results of their systemwide analysis, and we also look forward to embarking on the NAP8 project. Investigating PPNI, while not solely owned by anaesthetists, will (hopefully) catalyse changes in practice that ensure reliable and robust follow-up of all patients, particularly those who have had regional anaesthesia. As part of this, fostering multidisciplinary collaborations that extend beyond the operating theatres and the immediate postoperative period may improve overall surgical care for all patients. YL is a NAP8 Research Fellow for the Centre of Innovation and Research within the Royal College of Anaesthetists, UK. EM is a US Government employee and an Editor of Anaesthesia. KF is a US Government employee. AM is the clinical Lead for NAP8 and has received an honorarium from GE Healthcare and consultancy fees from Intelligent Ultrasound. This material is in part the result of work supported with resources and the use of facilities at the Veterans Affairs Palo Alto Health Care System (Palo Alto, CA, USA). The contents do not represent the views of the Department of Veterans Affairs or the United States Government.