Diffusion and clearance of ropivacaine after serratus anterior plane block by CT imaging: a prospective, single-arm trial

OBJECTIVE: CT-based visualisation and quantification of local anaesthetic distribution and clearance within the fascial plane following a single-injection serratus anterior plane block (SAPB). METHODS: A total of 16 participants received an ultrasound-guided SAPB with 40 ml of 0.375% ropivacaine. Computed tomography (CT) scans were performed at 30 and 60 min post-injection. The primary outcome was the clearance rate of ropivacaine from the fascial space between 30 and 60 min. Secondary outcomes included the three-dimensional diffusion range of injectate. RESULTS: CT-based volumetric analysis showed that the volume of the ropivacaine within the fascial plane was 29.1 (28.3, 29.4) ml at 30 min post-injection and decreased to 26.0 (25.2, 26.9) ml at 60 min after a single 40 ml injection of 0.375% ropivacaine, resulting in a clearance rate of 6.4 ± 1.5 ml/h. CT imaging revealed that the injectate was primarily located within the deep serratus anterior plane, showing craniocaudal and anteroposterior spread along the thoracic wall. In the absence of postural restrictions, the injectate exhibited a tendency to migrate caudally over time. CONCLUSIONS: This study demonstrates that CT imaging can directly visualise the distribution pattern and quantitatively assess the clearance of local anaesthetic within the fascial plane after a single-injection SAPB.