Regional anaesthesia for rib fractures: too many choices, too little evidence.

Abstract

Rib fractures are common, affecting four to eight people per 10,000 population annually 1. Depending on the extent of the injury, rib fractures are associated with a high risk of pulmonary complications, requirement for critical care admission, and mortality, especially in older patients 2. Prognosis is affected by pattern and location of injuries and outcomes are worse with multiple fractures, bilateral fractures and associated pulmonary injuries. In particular, the presence of flail chest is associated with a significant jump in mortality, and when accompanied by underlying pulmonary contusion, mortality more than doubles 3. Moreover, rib fractures may have effects on longer term outcomes, with reductions in quality of life measures demonstrated for at least 2 years after initial injury. The changing baseline characteristics of the UK trauma population mean that injuries are increasingly seen in patients aged > 65 years, with a fall from the patient's own height being the most common causative mechanism. However, the incidence of trauma in older patients has increased out of proportion to changes in population baseline characteristics; this suggests that ‘hidden' trauma cases are now being identified 4. Traditionally, rib fractures in older patients were often identified some time after admission and management on medical wards was commonplace. The increasing use of whole-body computed tomography scans has now allowed identification of rib fractures which would previously have been missed by chest radiograph alone. This, in conjunction with the development of major trauma centres, has resulted in patients with rib fractures being managed more actively, with a move towards admission on thoracic or major trauma wards and a greater focus on the provision of effective analgesia. Surgical fixation is increasingly being performed not only in non-flail segments but also in the more critically unwell subject at high risk of pulmonary complications, such as patients requiring critical care admission. In this issue of Anaesthesia, we have seen two interesting papers on regional anaesthetic strategies for traumatic rib fracture management 5, 6. Both were single-centre, retrospective studies investigating ultrasound-guided regional anaesthesia, primarily with catheters, and both found improvements in non-analgesic outcomes. Womack et al. 5 reported that paravertebral catheters were associated with a reduction in mortality, and Adhikary et al. 6 found that the erector spinae plane (ESP) block was associated with improved inspiratory reserve volumes. Both studies suffer from the common drawbacks of single-centre retrospective data and serve as a timely reminder that data such as these report association, rather than causality, and should probably not lead to immediate changes in practice. However, these two interesting studies also give us an opportunity to re-assess the evidence and techniques for regional anaesthesia for rib fracture analgesia. Historically, analgesia for rib fractures has been managed with systemic analgesia alone, with only a minority of patients receiving either thoracic epidural analgesia or thoracic paravertebral blockade 7. The presence of comorbid conditions, frailty and alterations in pharmacodynamics/pharmacokinetics in older patients often results in a higher incidence of adverse effects with systemic analgesia, especially when opioid analgesia is required. In addition, patients with rib fractures are increasingly likely to have a coagulopathy, be it trauma-induced or secondary to pharmacotherapy in older patients; thus, traditional regional anaesthetic techniques might be inappropriate. However, there are now a range of regional anaesthetic approaches that can be considered, many of which are suitable for a catheter-based strategy, as single-shot techniques are likely to provide insufficient in terms of duration of analgesia effect. However, there remains a dearth of high-quality evidence for each, in terms of both procedural safety and effect on outcome. Thoracic epidural analgesia has long been seen as the gold standard in analgesic management of traumatic rib fractures. Modern advances to this technique include the use of ultrasound guidance to improve performance of practitioners inserting thoracic epidural catheters 8. By blocking spinal nerves as they emerge from the spinal cord within the epidural space (Fig. 1), nociceptive inputs from intercostal nerves are prevented from transmitting central pain signals. Thoracic epidurals have been suggested to reduce mortality in trauma centres and have benefits on analgesia, postoperative pulmonary ventilation and duration of stay. However, thoracic epidural analgesia might not have longer term outcome benefits, and meta-analyses have now demonstrated that these effects are not as marked as once thought, questioning the utility of this technique in the setting of traumatic rib fractures 9. Moreover, epidural insertion is contraindicated patients with coagulopathy and has a number of adverse consequences (Table 1) 10, including unavoidable bilateral blockade. This technique should therefore no longer be considered the gold standard analgesic strategy for rib fractures. Indeed, for isolated rib fractures, especially if unilateral the role of thoracic epidural analgesia is perhaps best reserved for historical texts, rather than contemporary clinical practice. Paravertebral blocks are designed to deliver local anaesthetic to block both dorsal and ventral rami of spinal nerves in the paravertebral space (Fig. 1), thereby blocking rib fracture-associated pain. This technique has a long history of use in this setting, with data suggesting efficacy published for nearly a 100 years. Paravertebral blocks have the benefit of being unilateral in nature, target only the vertebral levels required for nerve block and, with the advent of ultrasound-guided approaches, may have an improved safety profile and efficacy. This strategy, although not suitable for patients who are coagulopathic, is readily amenable to insertion of catheters, which should be seen as standard practice for paravertebral blockade in the setting of rib fractures. Womack et al. have demonstrated that continuous paravertebral blockade is associated with a reduction in critical care admission and mortality, but, again, these data build upon the retrospective body of information available 5. Small randomised controlled trials with a high risk of bias have demonstrated that patients receiving paravertebral blockade have improved analgesia and functional pulmonary outcomes when compared with systemic analgesia alone 11. When compared with thoracic epidural analgesia in the peri-operative setting, little difference in clinical efficacy or safety has been demonstrated, but there remains insufficient high-quality data to truly demonstrate superiority of one technique over the other 7. Although paravertebral blocks also suffer from insufficient high-quality data, they are seen as the most appropriate evolutionary choice after epidurals by clinicians. Intercostal nerve blocks are simple to perform and directly block intercostal nerve-associated nociceptive transmission. They are therefore reliable and reproducible. However, intercostal nerve blocks are associated with a high risk of systemic absorption of local anaesthetic, require multiple injections and are limited by the duration of action of local anaesthetics. Catheter techniques are used rarely, as these are only of utility in the event of single rib fractures. The site of injection must also be carefully considered, as posterior rib fractures might require a very posterior approach. There are few high-quality data demonstrating clinical efficacy and/or safety of intercostal nerve blocks, and the primary reason for their continued use is the ease of performance, particularly without ultrasound, and presumed safety due to the relatively superficial nature of the target nerves. There are a growing number of paraspinal approaches that have been used for traumatic rib fracture analgesia. Many of these techniques have been described as ‘paravertebral by proxy' techniques, aiming to deliver local anaesthetic to the paravertebral space by means of a fascial plane or diffusion through tissue 12, thereby blocking the spinal nerves within the paravertebral space (Fig. 1). They may also be used in patients who have a coagulopathy. However, the precise mechanism of action of many of these fascial plane techniques remains unclear. The erector spinae plane (ESP) block is perhaps the most widely used of these novel techniques 13, having been employed in both peri-operative and chronic pain settings 14, 15. The data presented by Adhikary et al. in this issue of Anaesthesia suggests that the ESP block has benefits on acute pain and short-term pulmonary function 6. Several case reports have been published demonstrating the utility of the ESP block in this setting, but as there are no prospective studies published, no firm recommendations on safety or efficacy can be offered. Other paraspinal techniques such as the retrolaminar block, mid-point of the transverse process block or the rhomboid intercostal and subserratus plane block have all been used in traumatic rib fracture patients, but with little objective, prospective, high-quality data published 16-18. These remain worthwhile avenues of investigation, but well-designed studies are needed. Further laterally, the serratus plane block aims to block multi-level intercostal nerves along the angle of the rib. This technique has found its home during various chest wall surgeries, and has been used for rib fracture analgesia 19. It is a simple ultrasound-guided procedure that is amenable to performance in the supine position and in the presence of coagulopathy but will only be useful for antero-lateral rib fractures rather than posterior fractures. Unfortunately, there is limited evidence related to this block as well, with no prospective, well-designed randomised studies supporting its efficacy or safety in this setting. Overall, clinicians are taking up these fascial plane techniques with insubstantial evidence for their safety and efficacy at a pace rarely seen in the arena of evidence-based medicine, which is also reflected in other subspecialty practice 20. However, the ease of use, theoretical safety profile, ubiquity of ultrasound-guided practice, suitability for catheter insertion, and snowballing of information via social media means that fascial plane techniques are here to stay and are likely to soon become the gold standard. Which fascial plane block will triumph for the management of rib fractures remains to be seen. The need for further high-quality research studies is apparent, but it is vital that future work must focus on clinically-relevant, patient-centred outcome measures. The importance of this has been highlighted recently in airway research, where only a minority of analysed studies had such an outcome measure 21. In terms of rib fracture analgesia, assessment of pain would appear to be the obvious outcome of interest. However, rib fractures often occur in conjunction with multiple other traumatic injuries, and local anaesthetic techniques focusing on chest wall sensory innervation will be of little benefit for additional extra-thoracic injuries; as such, measurement of pain scores may be too blunt a tool. Surrogate markers of analgesic quality such as inspiratory function tests or incidence of pulmonary complications, duration of hospital stay or requirement for critical care admission may be valid alternatives. There is also a need for future studies to be prospective, with comparable, and clinically-relevant, cohort groups (i.e. the inclusion of older patients and those with cognitive impairment). Many studies investigating rib fracture analgesia have utilised a ‘before and after' intervention, comparing patients with a historical control group which has the potential to introduce bias 22, 23. The effect of immortal time bias is of particular importance when considering mortality as an outcome in patients managed within major trauma centres, as significant reductions in mortality rates have occurred due to a multitude of changes in the organisation and delivery of trauma care, that include many different elements of clinical management. A final factor to consider is the impact of rib fixation on outcomes. There is an increasing recognition of the clinical benefits of rib fixation and, as such, it is likely to be utilised with increasing frequency as part of rib fracture management protocols. The provision of safe and effective analgesia for rib fractures is a key element in the management of thoracic trauma, especially in older patients. Thoracic epidural analgesia should no longer be considered as a first-line regional anaesthetic technique in these patients. Although thoracic paravertebral catheters are probably the current standard of care, we expect that ultrasound-guided fascial plane techniques will soon supplant paravertebral blockade. However, there is an urgent need for high-quality, prospective research studies to allow us to determine the optimal regional anaesthetic technique and how precisely this can be utilised in pain management pathways for rib fractures, so we can produce meaningful improvements in patient-centred outcomes for this common, but clinically significant condition. MW is an Editor of Anaesthesia and KE is on the Editorial Board. We thank Dr A. Barron for assistance with figure production.