Pathophysiology

Rib fractures are associated with multiple complications including pneumonia, acute respiratory distress syndrome, atelectasis and lung collapse. Pain from rib fractures causes hypoventilation and increased pulmonary complications. Patients with multiple rib fractures often require critical care admission.1

Image 1 – Cutaneous distribution of thoracic nerves. (Testut.)

SAPB was first developed as an analgesic option in breast and thoracic surgery. The block has since been described in case reports3 for rib fracture and intercostal drain analgesia in the emergency department and in a recent feasibility study.4 There remains limited evidence for performing the block. The addition of a SAPB to standard rib fracture care is reported to improve pain scores and reduce in-hospital opioid requirements.12

Serratus anterior:

  • Originates on the anterior surface of ribs 1-8 and inserts onto the medial border of the scapula.
  • Lies between latissimus dorsi above, and the ribs and pleura below.
  • The thoracic intercostal nerves pierce serratus anterior.
  • A potential space exists superficial and deep to serratus anterior.
  • Within this space run the intercostal nerves (lateral cutaneous branches), long thoracic nerve and thoracodorsal nerve. The thoracodorsal artery runs along with the thoracodorsal nerve.
Image 2 – Diagram of the course and branches of a typical intercostal nerve.

These nerves can be blocked in the superficial or deep space to provide analgesia from ribs one to nine. They are ideal for anterior or lateral fractures. More posterior fractures may be better suited to a more posterior nerve block such as an erector spinae (ESP) block, paravertebral block, or neuraxial technique if suitable. Nevertheless, in those where the lateral or sitting position to allow more posterior nerve block techniques is not possible (pain, concomitant injury, spinal precautions), an SAPB, which is able to be performed in the supine position, will likely provide analgesia for more posterior fractures.12

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