Peripheral nerve blocks for hip fracture analgesia: addressing methodological challenges beyond technique selection. A reply

We read with interest the comments by Wang et al. [1] and Çelebioğlu [2] on our article [3]. In both letters, the authors suggest that the control intervention in our study should have been the supra-inguinal fascia iliaca block, which is known to provide more reliable and effective analgesia as compared with the infra-inguinal approach [1, 2]. Our study was initially conceived as a dual-centre trial, involving another emergency department in the UK. The decision to use the infra-inguinal fascia iliaca block as control was dictated by the fact that, in the UK, this technique is the most used across emergency departments, as per national guidance [4]. Therefore, we decided to compare the newer PENG block with the standard care of emergency departments, which is – at least in the UK setting – different from the standard of care delivered in operating theatres by anaesthetists. Future trials, conducted in settings where emergency physicians are familiar with the supra-inguinal fascia iliaca block, should compare this approach with the PENG block. Concerning the choice of outcomes, early pain relief is a key patient-reported outcome as it enables patient comfort during investigations, personal hygiene and transferring between the emergency department and inpatient bed. Similarly, capturing the duration of nerve block analgesia is paramount, especially considering that many patients experience significant delays to surgery due to worsening operating capacity at many centres [5]. Due to the limited resources, we lacked the capacity to reassess pain at time intervals such as at 6-, 12- or 24-h post-block, or at arrival in the operating theatre. Therefore, we decided to focus our efforts on obtaining an accurate measurement of the acute analgesic effect of both interventions. Future adequately funded studies should investigate the effects of blocks in the overall pre-operative time, including important patient-centred outcomes such as the incidence of delirium and the quality of life measured using validated scales. As Wang et al. suggest, the verbal rating scale should be preferred to the visual analogue scale, as the former is a more reliable tool when assessing pain in the older population [1]. Wang et al. also raise concerns about the use of different volumes and concentrations in the two groups of our trial. The choice of the volume is block-specific and based on previous literature. Fascia iliaca block is volume-dependent, requiring an injectate of at least 30 ml, whereas almost all previous trials on the PENG block used 20 ml of injectate, in line with the initial description of the technique. This implies that when comparing these two blocks (or any blocks requiring different volumes), the use of an identical concentration of anaesthetic will result in a different total dose between the two groups. Conversely, the use of an identical dose will result in a different concentration of the anaesthetic. Researchers committed to designing similar trials will inevitably confront themselves with this conundrum. Other investigators opted for an identical local anaesthetic concentration [6], whereas we decided to use an identical dose (75 mg of levobupivacaine) [3]. From a safety perspective, clinicians typically calculate the total dose of local anaesthetic before performing a peripheral nerve block, ensuring it does not exceed the maximum dose allowed for the chosen drug. Therefore, with a pragmatic approach in mind, our trial tried to establish which of the two interventions with a similar risk profile could provide better analgesia. Our findings are not generalisable to a scenario where the PENG block and fascia iliaca block are performed with identical concentrations. When interpreting the results of our trial, clinicians or researchers should expect to replicate the same effect only if the identical methodology is used, including techniques, volumes, doses and concentration of local anaesthetics and use of adjuvants (dexamethasone).