Ultrasound-guided subscalene approach for the brachial plexus in dogs: a descriptive cadaveric study
Santiago E. Fuensalida, Lisa Tarragona, Alfredo Díaz, Nicolas H. Giansanti, Angela Briganti, Diego A. Portela, Pablo E. Otero
Background:
Effective regional anesthesia of the thoracic limb in dogs requires reliable techniques for brachial plexus (BP) blockade. The subscalene approach, although utilized, lacked detailed anatomical validation. This study aimed to describe the sonoanatomy of the subscalene groove, assess the feasibility of an ultrasound-guided subscalene in-plane approach to the BP, and compare one-point versus two-point injection techniques in canine cadavers. The hypothesis posited that two injection points would be necessary for complete nerve staining.
Methods:
A prospective, randomized, descriptive anatomical study was conducted using 19 thawed adult canine cadavers. Phase I involved sonoanatomy evaluation and dissection in two cadavers. Phase II assessed injectate spread following ultrasound-guided subscalene injections in 17 cadavers. Group 1 received a single injection cranial to C8; Group 2 received two injections (cranial to C8 and C7). Success was defined as circumferential staining of C6–T1 spinal nerves (>1 cm).
Results:
Sonoanatomy reliably matched dissection findings. Successful staining of all BP components occurred in 88% of Group 2 versus 41% of Group 1 cadavers (p = 0.0104). Median stained nerves were 3 (Group 1) and 4 (Group 2). Staining of the phrenic nerve branches was consistent across all specimens. Accidental staining of the vagosympathetic trunk and recurrent laryngeal nerve occurred only with prevertebral fascia laceration.
Limitations:
As a cadaveric study, results may not fully extrapolate to live animals due to tissue condition differences. All procedures were performed by a single experienced operator, potentially limiting generalizability. Additionally, injectate behavior could differ in vivo due to physiological variables.
Conclusions:
The ultrasound-guided subscalene approach is anatomically precise and feasible for identifying and accessing the BP in dogs. A two-point injection method significantly improves success rates in nerve staining compared to a single injection. While effective, the risk of phrenic nerve involvement necessitates caution and supports the need for clinical evaluation in live animals.
(a) Ultrasound image of the subscalene groove of a dog cadaver obtained with a linear transducer oriented parallel to the longitudinal
axis of the subscalene muscles, immediately cranial to the first rib. (b) Schematic representation of C6, C7, C8 (ventral branches of the last three
cervical spinal nerves) and T1 (first thoracic spinal nerve). Cd, caudal; Cr, cranial; L, lateral; M, medial; R, first rib.
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