A Technique for Ultrasound‐guided Paravertebral Brachial Plexus Injections in Dogs

Abstract

Using cadaveric dogs, we established the ultrasonographic landmarks for performing paravertebral injections around the brachial plexus nerve roots in the dog, and assessed the accuracy and regional spread of the aliquots. A mixture of methylene blue dye and an iodinated contrast medium was used as the injectate. A 0.3 ml volume was used to assess accuracy and a 3.0 ml volume was used to assess regional spread. Accuracy and regional spread were assessed from computed tomography (CT) images acquired after injection by measuring the distance from each foramen to the nearest edge of contrast medium, and the dimensions of spread of contrast medium in each anatomic plane, respectively. The mean distance of small volume injections from each foramen was 0.9 cm (standard deviation [SD] 0.56 cm). The mean spread of contrast medium for the small volume injections measured 1.7 cm (SD 0.6 cm) cranial-to-caudal, 1.2 cm (SD 0.4 cm) dorsal-to-ventral and 7.4 cm (SD 0.4 cm) medial-to-lateral. The mean spread of contrast medium for the combined three large volume injections measured 7.4 cm (SD 1.7 cm) cranial-to-caudal, 3.1 cm (SD 0.8 cm) medial-to-lateral, and 2.8 cm (SD 0.5 cm) dorsal-to-ventral. After the CT studies, staining of each nerve root and any other regional structure was assessed grossly. Based on our results, ultrasound can be used to guide injections around the nerve roots of the brachial plexus in dogs.

Comparison of three techniques for paravertebral brachial plexus blockade in dogs

“…Similarly in cadaveric dogs, the incidence of phrenic nerve staining with US guided PBPB was 20% when 3 mL of solution was used versus 0% when 0.3 mL was injected at each nerve root (Bagshaw et al 2009). Acute phrenic nerve blockade does not seem to impair ventilation in awake or sleeping dogs when it is unilateral, but it could potentially lead to hypoxia and respiratory distress, especially in patients with limited respiratory reserve or when the block is bilateral resulting in complete diaphragmatic paralysis (Stradling at al.…”

“…In humans, the use of ultrasound guidance during regional anesthesia has improved the clinical success rates and decreased the complication rates compared to neuro-stimulator guidance (Liu et al 2005;Chan et al 2007;Koscielniak-Nielsen 2008;Abrahams et al 2009). In cadaveric dogs, the US guided technique for PBPB resulted in 100% successful staining of the nerve roots C6, C7 and C8 (Bagshaw et al 2009). This difference between studies could be due to ultrasonographer experience, ultrasound machine and /or type of probe used.…”

“…In the study by Bagshaw et al (2009) they also determined the precision and spread of US guided injections of contrast medium around the nerve roots of C6, C7 and C8 with computed tomography; however, they did not visualize or evaluate the nerve T1, which also contributes to the brachial plexus in dogs.…”

“…There are two studies in dogs that describe the ultrasonographic anatomy of the nerves that form the brachial plexus at their exit from the IVF (Guilherme & Benigni 2008, Bagshaw et al 2009). In the study by Bagshaw et al (2009) they also determined the precision and spread of US guided injections of contrast medium around the nerve roots of C6, C7 and C8 with computed tomography; however, they did not visualize or evaluate the nerve T1, which also contributes to the brachial plexus in dogs.…”

“…One study describes the ultrasonographic appearance of the brachial plexus (Guilherme & Benigni 2008). Another describes the appearance and approach for PBPB with US guidance (Bagshaw et al 2009). Another study describes the US guided technique for ABPB, femoral and sciatic nerve blocks (Campoy et al, 2010).…”