Effect of anterior quadratus lumborum block on morphine consumption in minimally invasive colorectal surgery

We read with interest the article by Coppens et al. [1]. We commend their attention to detail in describing the anterior quadratus lumborum block technique and making available ultrasound images of the procedure with visualisation of local anaesthetic spread. However, we have several points we would like to discuss. First, the use of an invasive procedure with a 0.9% saline control group raises ethical considerations [2]. In this case, the placebo carries risk to the patients without potential benefit. The Serious Harm and Morbidity (SHAM) scale was developed to grade the risk in local anaesthetic block trials to patients in the control cohort [3]. Anterior quadratus lumborum block control procedures are grade 4, ‘Invasive placebo procedure with risk of major complications’ [3]. This is the highest grade on the scale and the same as transversus abdominis plane and intercostal nerve blocks. While we understand that many regional anaesthesia studies utilise saline control groups, these risks must be considered. Did the authors consider alternative control group designs that provide equally robust evidence of block efficacy without exposing the patient to a potentially harmful procedure? For example, if the procedure had been done under anaesthesia and data collected by researchers not involved in the patient's care, surely it would provide similar double-blinding for the stated primary and secondary outcomes. Also, we assume appropriate ethical approval was sought and granted; this is, however, not mentioned in this study. Second, we noted that the authors reference similar studies that showed the anterior quadratus lumborum block failed to reduce pain scores or morphine consumption [4]. The authors' study design differed from the other studies because their department used non-steroidal anti-inflammatory drugs and avoided mobilisation within the first 24 h [1]. Both of these differences would mean the authors' patient group would have lower baseline pain and morphine requirement. We are unsure if this is a strong enough reason to suspect anterior quadratus lumborum blocks would be more beneficial in the authors' group compared with the group studied by Tanggaard et al. [4]. Third, we would like to question the safety of the fixed doses of local anaesthetic. We understand that quadratus lumborum blocks are fascial plane blocks and, therefore, require high volumes of local anaesthetic. However, the maximum recommended dose of ropivacaine is 3 mg.kg-1. The fixed doses used in this study are the maximum safe dose for a 75 kg patient. The study shows a weight range of 46.3–113 kg. This means that some patients received up to 161% of the maximum safe dose of ropivacaine. Despite this, they have reported no cases of local anaesthetic systemic toxicity. We feel that patient-specific calculations and dilution of local anaesthetic should have been considered in the design of this study, to ensure patient safety. This is particularly important, considering previous studies have shown potentially neurotoxic plasma concentrations of ropivacaine even when administered at 3 mg.kg-1 [5].