Ultrasound Guided Serratus Anterior Plane Block Versus Standard Therapy for Analgesic Relief of Rib Fractures in the Emergency Department

Background Rib fractures are a common injury encountered in the emergency department (ED) affecting an estimated 10% of all trauma patients. They are associated with significant morbidity and mortality, especially in elderly patients. Rib fractures are the leading indication for intensive care unit (ICU) admission in patients with traumatic injuries to the thorax, accounting for approximately 42% of patients who require critical care in trauma. Secondary complications from rib fractures include atelectasis, pneumonia, and acute respiratory distress syndrome. These complications are often attributed to a relative respiratory functional deficit secondary to pain which limits adequate inspiratory capacity and coughing; therefore, the management of acute rib fractures has largely been focused on controlling pain. The most common method of pain control employed in the ED has historically been the use of a multimodal analgesic approach which includes opioids, acetaminophen, and NSAIDS. Opioids confer additional risks which include respiratory depression, suppressed cough reflex, delirium, nausea, constipation, and the potential for addiction.

Ultrasound-guided serratus anterior plane block (SAPB) is an alternative method of pain control that utilizes targeted delivery of a local anesthetic agent in the serratus anterior fascial plane. This method was first described in 2013 and has been well described for the treatment of pain associated with thoracic surgical procedures, including those of the breast and chest wall. The SAPB has also been demonstrated to provide analgesic relief of pain associated with rib fractures and other blunt chest-wall traumatic injuries.

Over recent years, the SAPB technique has been gaining popularity due to its efficacy, relative ease of performance, and favorable side effect profile. This ultrasound guided technique uses a high frequency linear ultrasound transducer to identify the serratus anterior fascial planes, latissimus dorsi muscle, ribs, and pleural space. The intended target is the superficial serratus anterior fascial plane, which is bordered by the latissimus dorsi muscle posteriorly and the pectoralis muscles anteriorly. This fascial plane houses the lateral cutaneous branches of the intercostal nerves and a plane block of the superior facial plane has also been postulated to provide analgesia in the distribution of the long thoracic and thoracodorsal nerves. The block primarily works at the level of T2-T9, and previous literature has suggested that the SAPB works best for anterolateral rib fractures. The SAPB has a relatively safe side effect profile. Major complications include pneumothorax and local anesthetic systemic toxicity (LAST); however, the incidence of adverse events following SAPB performed in the ED has been low in previous studies.

Point of care ultrasound (POCUS) for procedural guidance is commonly employed by emergency physicians in daily clinical practice. Several retrospective and case-series studies have demonstrated the efficacy, feasibility, and safety of SAPB in the ED when performed by trained ED physicians. Studies like those performed by Diwan et al. and Kring et al. have demonstrated improved pain scores and decreased opioid consumption following SAPB. Despite this, to date, there has only been one published randomized controlled trial comparing the analgesic effects of SAPB versus opioid pain medication. More data is needed to further evaluate the analgesic effect of ED performed SAPB and the outcome of patients who present with acute rib fractures.

The Pain, Inspiratory capacity, and Cough (PIC) score is a tool currently utilized in blunt chest trauma cases at WellSpan York Hospital to guide inpatient management and predict the need for escalating care. This ten-point scoring tool accounts for the patient's pain level (mild/moderate/severe), inspiratory capacity (percent predicted value), and cough effort, with a goal score of >8. Inspiratory capacity and cough effort are often directly related to the level of pain a patient is experiencing, therefore, improving rib fracture pain through SAPB may improve PIC scores and help reduce the need for intensive care unit (ICU) level care. Additionally, analgesic relief with SAPB should decrease opioid consumption and its associated risks in the immediate period following rib fractures.