Ultrasound-guided serratus plane injection using superficial and deep approaches in cat cadavers: anatomical and dye spread study.

This study aims to describe the anatomy and sonoanatomy of the lateral thoracic wall of cat cadavers and compare the spread of a bupivacaine-dye solution into the superficial (SSP) or deep (DSP) planes of the serratus ventralis thoracis (SVT) muscle. One formalin-fixed and sixteen frozen-thawed feline cadavers (32 hemithoraces) were used and randomly assigned to receive either a SSP or DSP ultrasound-guided injection. With cadavers in lateral recumbency, a linear transducer was transversely placed between the fourth and fifth ribs, at the level of the scapulohumeral joint and a 22-gauge Tuohy needle was inserted in-plane, in a caudocranial direction, until the tip was in the desired fascial plane. Bupivacaine-dye solution (0.3 mL/kg) was injected. Injectate placement and number of stained nerves were assessed by dissection. Differences were considered when p ≤ 0.05. The intercostobrachial nerve (nIC), lateral cutaneous branches of intercostal nerves 3 to 9 in SSP, and lateral cutaneous branches of intercostal nerves 3 to 7 in DSP were identified. Injection success was 93.75% (SSP) and 100% (DSP). In the SSP group, the nIC and the lateral cutaneous branches of intercostal nerves 3 to 7 were stained in 26.6; 66.6; 93.3; 86.6; 26.6 and 6.6% of cases and 31.2; 68.7; 87.5; 75.0; 56.2 and 18.7% in the DSP group, respectively. The sonoanatomy and landmarks for SSP and DSP plane injections have been successfully described in cats. Both approaches stained nerves involved in thoracic wall sensory innervation and appear feasible for regional analgesia. Clinical studies are warranted to assess their efficacy.