Rhomboid intercostal block

Pectoral nerve and serratus plane blocks are methods for providing hemithoracic analgesia 1, 2, but do not block the posterior primary rami 3. We have recently investigated the potential benefits of local anaesthetic infiltration into an interfascial space on the posterior chest wall known as the triangle of auscultation (TOA). The TOA is located along the lower medial border of the scapula. It is bounded superiorly by the trapezius, inferiorly by the latissimus dorsi, and laterally by the vertebral border of the scapula. The floor of the triangle is formed by the lower part of rhomboid major, the lateral portion of the erector spinae muscle and the serratus anterior muscle, all overlying the 6th and 7th ribs and their internal and external intercostal muscles. The tissue plane between the intercostal muscles and the floor of the TOA extends: (1) laterally deep to the scapula and serratus anterior muscle, and passes the midaxillary line where the lateral cutaneous branch of each intercostal nerve pierces the internal and external intercostal muscles; and (2) medially deep to the erector spinae muscle, continuing to the thoracic transverse processes, where the dorsal rami of the thoracic intercostal nerves emerge between the tips of adjacent transverse processes and enter the erector spinae muscles, supplying them and the overlying skin 4. With the patient positioned prone and the ipsilateral arm adducted across the chest, the scapula moves laterally and opens up this space. A linear ultrasound transducer (6–12 MHz) is placed medial to the lower border of the scapula with the orientation marker directed cranially. The tissue plain between the rhomboid major and intercostal muscles is identified, and a single injection is administered at the T6-7 level. Cadaveric examination using 25 ml of methylene blue contrast dye reveals: (1) caudad and cephalad spread of the dye; (2) deep staining of the tissue plane from T2-T8 levels; (3) staining around lateral branches of the intercostal nerves T3-T8; (4) medial extension as far as the posterior primary rami near the midline; and (5) lateral extension to the clavipectoral fascia within the axilla (inferiorly to T9 along the inferior insertion of the serratus and cranially to T2 along serratus anterior). One patient with multiple rib fractures receiving 25 ml of bupivacaine 0.25% via this approach experienced symptomatic relief, with dermatomal coverage measured from T2-9 on the whole anterior hemithorax just medial from the midline, lateral from the axilla to T9, and on the posterior hemithorax T2-9 until immediately medial to the spinous processes. This result suggests rhomboid intercostal block may be useful in providing analgesia for both the anterior and posterior hemithorax, but further comparisons with previously described blocks are required.