A sonographic investigation for the development of ultrasound-guided paravertebral brachial plexus block in dogs: cadaveric study.
To describe a novel in-plane ultrasound (US)-guided approach to the sixth (C6), seventh (C7), eighth (C8) cervical and to the first thoracic (T1) spinal nerves. Prospective, descriptive, experimental anatomic study. A total of seven canine Beagle cadavers. Phase 1: One cadaver was used to define bony landmarks for the C6-T1 spinal nerves using computed tomography (CT) and magnetic resonance imaging. An US transducer was positioned lateral to the C6 vertebra. Methylene blue (0.05 mL kg-1) was injected cranial and caudal to the transverse process of C6. The probe was moved caudally to identify the cranial costal fovea of T1 and 0.1 mL kg-1 of methylene blue was injected. Full cadaver dissection was performed to assess the staining of the spinal nerves. Phase 2: The technique was repeated using a 50:50 mixture of iohexol and methylene blue in six dogs. CT verified the proximity of contrast to C6, C7, C8 and T1 nerves. Mediastinal, epidural, intravascular and pleural contamination was recorded. Methylene blue staining of the phrenic nerve was assessed by dissection. Phase1: The identified bony landmarks were the lamina ventralis of C6, the transverse process of C6 and C7, T1 vertebra and the first rib. Phase 2: At all the 12 sites, the C6, C7 and C8 nerves were in contact with contrast material. Contrast was demonstrated in close proximity to the anatomical location of the T1 nerve in 11/12 sites. Mediastinal, epidural and intravascular contamination was observed in six, four and two cadavers, respectively. Pleural contamination was not observed. The phrenic nerve was stained on 2/12 of sides. In-plane US-guided blockade of the spinal roots is a feasible technique. However, because of the undesirable spreads of contrast, further research is needed to diminish the occurrence of contaminations of noble structures.