Serratus anterior plane block (SAPB)
The serratus anterior plane block (SAPB) is an ultrasound‑guided fascial plane block that provides analgesia to the lateral and anterior chest wall by bathing the lateral cutaneous branches of the thoracic intercostal nerves.
It is particularly useful in the emergency department for analgesia of lateral/anterior rib fractures to improve ventilation, facilitate physiotherapy and reduce opioid requirements (NICE NG211).
SAPB may be delivered safely in ED settings provided clinicians follow ultrasound‑guided block principles, local governance and resuscitation arrangements (NICE IPG285; RCEM).
Anatomy and mechanism
- Target: lateral cutaneous branches of the thoracic intercostal nerves (approximately T2-T9), which pierce the serratus anterior to supply the lateral/anterior chest wall.
- Plane variants:
- Superficial SAPB - injection between latissimus dorsi and serratus anterior (may cover more lateral fibres).
- Deep SAPB - injection between serratus anterior and the external intercostal muscle / rib surface (commonly used; may produce wider longitudinal spread).
- Typical dermatomal spread: often from about the 2nd-9th ribs when performed in the mid‑axillary line (commonly at the 4th-6th rib level).
Indications and clinical role
- Primary indication: analgesia for acute lateral or anterior rib fractures to enable deep breathing, coughing and physiotherapy.
- Additional indications: analgesia for pain from intercostal drains or lateral thoracic procedures; an opioid‑sparing component of multimodal analgesia (useful in elderly or opioid‑sensitive patients).