Erector Spinae Plane Block as an Analgesic Intervention in Acute Rib Fractures: A Scoping Review

Introduction

Rib fractures are a common sequelae of blunt thoracic trauma and are associated with significant morbidity and mortality.¹ These injuries are more common in older, frail patients with multiple medical co-morbidities who often suffer poorer clinical outcomes. Suboptimal analgesia can lead to severe impairment of normal respiratory mechanics, with reduced tidal volumes and difficulty clearing pulmonary secretions contributing to atelectasis, hypoxia, pneumonia, and eventual respiratory failure.² This is particularly challenging in an elderly population where surgical intervention or admission to a high dependency setting for respiratory support may not be of clinical benefit. Effective analgesia reduces these risks, and to this end, a multimodal regime is often employed, with oral analgesia and intravenous opioid as first-line options, followed by administration of regional blockade.³ Each method is associated with risks, such as sedation and respiratory depression with intravenous opioids and hypotension, spinal cord injury, hematoma, infection, and local anesthetic toxicity being associated with regional anesthetic techniques.⁴ In addition, neuraxial techniques are often contraindicated in patients receiving oral anti-coagulants and in those with vertebral fractures. Neuraxial techniques can also be of minimal utility in the context of poly-trauma where positioning options are limited and hemodynamic instability may be present.⁵

Erector spinae blocks (ESB) have been proposed as an alternative first-line regional analgesia technique for use in rib fracture management. Since its inception in 2016,⁶ it has seen a wide range of applications from trauma⁷ to elective surgery which includes abdominal, thoracic, breast and orthopaedic procedures.^8–12 The erector spinae muscles are a group of stabilisers which lie between the vertebral spinous and transverse processes in the thorax, in close proximity to the dorsal rami of the intercostal nerves, along with the paravertebral space. ESB involves an injection of local anaesthetic under ultrasound guidance into the erector spinae fascial plane. The needle tip is directed at the posterior aspect of the lateral portion of the transverse process at the desired level, with subsequent injection of local anaesthetic hydrodissecting the fascial plane deep to the erector spinae muscle while remaining superficial to the vertebral transverse process. A representation of the anatomy is presented in Figure 1, rendered using 3D slicer (Version 5.2.2, 2023), an open source segmentation software and a sample CT chest dataset.¹³ The mechanism of action is thought to be related to local anaesthetic spread causing blockade of the lateral cutaneous and intercostal nerves, along with potential diffusion into the paravertebral space.^14,15 The proposed advantages of ESB are in its ease of use, and safety profile. Current blocks involve instrumenting in close proximity to neurovascular structures around the spine, and the pleural space, resulting in complications such as dural puncture, hypotension, local anaesthetic toxicity and pneumothorax.¹⁶

Figure 1 Needle placement for the erector spinae block at the level of T6 on the left, with the needle represented in grey, erector spinae muscles in green, lung in red, thoracic vertebrae and ribs in white, and the thorax in pink. Views presented are (a) posterior view from the left, (b) posterior view, (c) sagittal transection viewed from the left, (d) axial transection viewed from above, and (e) a view of the needle with the patient upright. All images created using 3D slicer (version 5.2.2, 2023) an open-source software, with the segments created using a sample CT chest dataset.

The literature surrounding ESB in rib fractures is predominantly comprised of case reports and case series, with few large-scale studies having been published. This review aims to investigate the available literature on the topic to assess clinical outcomes and safety profile, and to guide future research in the area.

Methods

This study was performed according to the Preferred Reporting Items for Systematic Reviews and Meta Analyses (PRISMA) and Joanna Briggs Institute (JBI) guidelines for scoping reviews, and registered in the Open Science Framework prior to commencement.

Search Strategy

A comprehensive literature search was performed by two reviewers (VP, MJ) to identify appropriate articles for review and inclusion in this study, with a third reviewer (BO) consulted for conflicts. Using the OVID platform, the MEDLINE and EMBASE databases were used to refine the search strategy utilising keywords and MeSH terms relating to “rib fractures”, and “erector spinae blocks” with the aid of Austin Health Library. The search strategy is shown in Appendix A. Scopus, Web of Science, and the Cochrane databases were then searched using the developed strategy.

Inclusion Criteria

All papers investigating the use of ESB as an analgesic intervention for acute rib fractures and recorded clinical outcomes were included. Studies which involved patients undergoing ESB at the time of surgical fixation were excluded due to the confounding impact of the procedure. All article types available in English except for conference abstracts were eligible for inclusion in this review.

Data Extraction

Data were extracted independently and recorded by two reviewers (MJ, VP) on a standardised excel spreadsheet. The data points recorded were as follows:

Statistical Analysis

Due to the heterogeneity of time points, measurement tools used, and outcomes recorded, statistical analysis focused on a descriptive comparison of available studies, with further quantitative analyses not feasible in this study. Variables are presented as whole numbers, or as percentages with the denominator based on the number of studies that reported the desired outcome. Weighted mean percentage change, calculated as the percentage change between two time points of the desired value with weighting proportional to the size of the investigated patient cohort in each study, was used to compare pain scores and respiratory outcomes. Conversion of median and interquartile range to mean and standard deviation was performed using the method presented by Wan et al¹⁷ to allow comparison between studies.

Results

A PRISMA flowchart of the search is shown in Figure 2. The final search was performed on 22 November 2022.

Figure 2 PRISMA flowchart demonstrating the search strategy.

The initial search of the literature yielded 2159 studies due to the broad nature of the search parameters. Screening of abstracts resulted in 77 papers, following which 40 studies were excluded due to incorrect block or injury, surgical fixation, or for being presented in a conference abstract format. Of the 37 studies included, 10 were case reports,^18–27 12 were case series,^28–39 5 were cohort studies,^7,40–43 2 were randomized controlled trials (RCT),^44,45 1 was a prospective interventional study,⁴⁶ and 7 were letters to the editor.^47–53 The majority of studies were published after 2020, with 29% being published in 2022. A summary of the results of the cohort studies is shown in Table 1.

Table 1 Summary of Key Findings in the Prospective and Retrospective Cohort Studies

Demographic Data

A total of 802 patients with a mean age of 60 years across 37 studies were included in this review. 72% of which were male. Each patient had a mean (standard deviation, SD) of 6 (3) rib fractures, with 87% having unilateral injury. The most common mechanisms of injury were motor vehicle accident, and falls. Additional injury was reported in 168 patients with 1 additional injury in 60 patients, 2 additional injuries reported in 27, 3 additional injuries in 14, and 4 or more injuries in 10 patients. 28% of patients had additional chest trauma, 11% with head injury, 8% with intra-abdominal injury, 19% with spinal injury, and 30% with additional limb injury.

Block Characteristics

Block technique was similarly described in all papers, with patients in the seated or lateral position with ultrasound guidance in the parasagittal plane. Whilst a majority of blocks were performed in the intensive care setting, ESBs were safely administered in multiple locations including the hospital ward, operating theatre, via fluoroscopy,²⁹ and the prehospital retrieval setting.²⁷ Local anaesthetic regimes varied between studies, with the most common agents being ropivacaine and bupivacaine. 15–100mL of 0.2–1% ropivacaine or 15–40mL of 0.25–0.5% bupivacaine were used for single shot injections, with some studies adding adrenaline or steroid. Ropivacaine 0.2% was used in 16 studies as the agent for catheter infusion in a combination of background and bolus regimes. Bupivacaine 0.125% and 0.1% ropivacaine also saw use. 80% of blocks administered were in the form of catheter insertion, with infusion duration ranging from 0.6 to 12 days.

The main indication for ESB was as an analgesic intervention either for uncontrolled pain or as a preventative measure, with 9 studies reporting usage of the technique as a rescue measure for patients in respiratory failure.^{18,20–22,24,28,33,34,47} The majority of blocks were administered within the first 48 hours of presentation.

Pain Outcomes

Twenty-eight studies reported objective changes in pain score post administration of ESB using various scoring scales including Numerical Rating Scale (NRS), Visual Analogue Scale (VAS), Defence and Veteran Pain (DVP) score, and a 4 point verbal score.^{7,18–25,27–31,33,34,36–39,42,44–49,53} Due to the heterogeneity of scales and time points used to evaluate pain, an average weighted percentage change in pain scores was calculated. The mean reduction in pain scores from pre-block baseline was approximately 40% within the first 24 hours. Six studies reported pain scores 24 to 48 hours post block, maintaining an average reduction of 21% from pre block baseline, while a further five studies reported pain scores over 72 hours post block reporting an average 43% reduction in pain score.

Opioid use within the first 24 hours post procedure showed similar results. Five studies^{7,22,24,47,53} compared pre block opioid requirements with that of the first 24 hours post block which showed a trend towards a 34% reduction in opioid requirement; however, no studies reported statistical significance for this outcome. However, most notably, five studies reported nil further analgesic requirement post administration of ESB.^{21,28,30,36,48}

Respiratory Outcomes

Eight studies reported on respiratory function testing pre- and post administration of ESB showing an overall trend of improved values post ESB.^{7,21,24,26,37,39,44,46} Adhikary et al reported an average improvement in incentive spirometry of 590mL which was maintained over the first 3 days post block.⁷ This result was reflected in the study by Syal et al³⁹ who reported a similar magnitude of improvement in their measurements of inspiratory capacity. Sharipova et al³⁷ demonstrated a slight improvement in forced vital capacity (FVC) in 2 patients from 34 to 41%, and 40 to 47% of predicted post ESB, however the remaining two patients saw no change and a slight decrease.

Respiratory complication was not consistently reported throughout the studies. Mladenovic et al⁴¹ reported an incidence of respiratory complication of 19% with pneumonia being the most common presentation. 5.5% of this cohort experienced respiratory failure, with the key finding in this study being that ESB delivered after 48hrs post admission being associated with higher rates of complication and increased ICU LOS. Four studies reported patients being rapidly weaned from respiratory supports, including one patient being extubated successfully post ESB despite previous failure due to inadequate analgesia.^21,22,33,34

Block Safety

No studies included in this review reported a major adverse event following ESB. Three studies^42,43,50 reported complications in the form of block failure (n = 25), infection (n = 3), and haematoma (n = 2); however, none required any further intervention. Of note, no cases of hypotension, local anaesthetic toxicity, dural puncture, or pneumothorax were reported. Elawamy et al⁴⁵ in a comparative RCT demonstrated 6 cases of hypotension, 2 cases of bradycardia, and 3 vascular punctures in a cohort of 30 patients receiving thoracic paravertebral blocks (TPVB), with no complication demonstrated in the ESB cohort. Seven studies^{19,20,25,33,35,40,43} included patients on prophylactic/therapeutic anticoagulation or had ESB administered in the setting of coagulopathy. Three papers,^38,44,45 including both RCTs, excluded this patient cohort. A cohort of 249 patients investigated by Dultz et al and White et al,^40,43 including 89 patients receiving anticoagulation or with concurrent coagulopathy revealed only 4 patients complicated by haematoma or infection. None of these patients required further intervention. Five further studies included patients with anticoagulation with only 1 further case of infection arising from them. No reports of dural puncture, local anaesthetic toxicity, hypotension, or pneumothorax were reported.

Discussion

The available data suggests that ESB is an effective analgesic technique which is safe despite the fact that it is used in high-risk patients. However, it lacks large scale, prospective data to support its use.

A multitude of trials and meta-analyses have shown the efficacy of ESB as an analgesic adjunct in thoracic, abdominal, breast, orthopaedic, and cardiac surgery.^54,55 These studies demonstrate a reduction in pain scores post operatively with associated reductions in opioid use and opiate-induced nausea and vomiting. These findings are also seen when ESB is applied as analgesia for rib fracture with improvements in pain scores, opioid use, and respiratory parameters being consistently demonstrated. Its effectiveness in the setting of multi trauma is also demonstrated with multiple studies reporting improved pain scores in the presence of further injury in close proximity to the chest wall. Early administration of ESB in this context may also reduce the incidence of respiratory deterioration as suggested by Mladenovic et al.⁴¹ The clinical significance of this should be highlighted as rib fractures are often seen in older, frailer patients in whom escalation of invasive ventilation and prolonged ICU admission may not provide long-term benefit. Furthermore, the ability to successfully administer ESB within a number of environments from the operating theatre to the emergency department and even a prehospital²⁷ setting reflect its versatility and ease of use.

The current literature on ESB in rib fractures suggests that ESB is at least comparable to current techniques, with an improved safety profile. Randomised control trials conducted by El Malla et al⁴⁴ and Elawamy et al⁴⁵ demonstrated that ESB is as effective as serratus anterior block (SAB) and TPVB respectively, with comparable pain outcomes. This is supported by data published by Murray et al⁴² and Riley et al^50,51 comparing ESB to TPVB, SAB, and opioid analgesia in retrospective matched cohort studies. In terms of block safety, no complications from administration of ESB with systemic consequences were reported. A 2% complication rate of infection and haematoma was demonstrated in the two largest cohort studies investigating safety,^40,43 while Elawamy et al⁴⁵ demonstrated a higher complication rate in TPVB compared to ESB. Studies conducted by Dultz et al⁴⁰ and White et al⁴³ also suggest that use of ESB in patients on anticoagulant medication, or concurrent coagulopathy, a contraindication to many available neuraxial techniques, is safe. This reflects research in other specialties in which ESB has been successfully utilized without complication in patients with thrombocytopenia,^56,57 coagulopathy,^58–60 therapeutic anticoagulation,⁶¹ or antiplatelet therapy.⁶² For example, Adhikary et al demonstrated no haemorrhagic complications in a case series of 5 patients receiving ESB while on intravenous heparin therapy post thoracotomy and left ventricular assist device implantation.⁶³ The ability to continue anticoagulation peri-block also confers clinical advantages in the trauma setting, where missed doses of venous thromboembolism prophylaxis increases the risk of thrombotic events.^64,65

While this scoping review demonstrates favourable qualitative analysis of ESB, there remain many domains in which data is lacking. The ultimate goal of analgesic regimes in the conservative management of rib fractures is to prevent respiratory deterioration, an outcome which was sparsely reported within the current studies. Further, there have been only 3 prospective studies,^44–46 two of which compared ESB to another regional technique. The majority of remaining studies are retrospective cohort studies or case series without a comparator group. As such, extrapolating the clinical efficacy of ESB versus the current gold standard remains difficult. The optimal timing, local anaesthetic regime, and the cohort of patients in which ESB would provide the most benefit are also yet to be fully explored.

Conclusion

In conclusion, while the current results show promise, the heterogeneity of reported outcomes and lack of large scale prospective trials preclude a firm recommendation of best practice for ESB use in rib fracture management. ESB has demonstrated benefits of ease of use being applied in a variety of settings and has comparable efficacy compared to TPVB and SAB. Moreover, ESB has an improved complication profile. Future studies should aim to determine the impact of ESB on respiratory complications, the optimal timing of administration, the optimal regime for administration and the safety of this regional technique.