A Two-Point Ultrasound-Guided Injection Technique for the Transversus Thoracis Plane Block: A Canine Cadaveric Study

SIMPLE SUMMARY: The transversus thoracis plane block is a locoregional technique recently described in canine cadavers to desensitize the intercostal nerves running through this plane. In canine cadavers, a transverse approach through a single injection point at the fifth intercostal space has been described, although consistent staining of the intercostal nerves was not completely achieved. The objective of this study was twofold: (1) to evaluate if the transverse approach is feasible at the third and sixth intercostal spaces and (2) to compare, by anatomical dissection, the spread of a dye solution and the staining of the intercostal nerves when a low volume (0.5 mL kg(−1)) or a high volume (1 mL kg(−1)) was equally divided at a two-point injection in the same hemithorax. Our results showed that the injection of the high-volume dye solution, equally injected at the third and sixth intercostal spaces using the transverse approach, achieved a consistent staining of from T2 to T7 intercostal nerves. This block could achieve adequate desensitization of the ventral chest wall during sternotomy in the dog. Clinical studies in live animals are necessary to confirm the efficacy of this technique. ABSTRACT: The transversus thoracis plane (TTP) block desensitizes the intercostal nerves that run through this plane, providing analgesia to the ventral thoracic wall. Two canine cadavers were used to assess the feasibility of the transverse approach for the TTP (t-TTP) under ultrasound guidance to inject a solution at the third and sixth intercostal spaces. Eight cadavers were used to compare the spread and number of intercostal nerves that were stained when a low volume (LV) 0.5 mL kg(−1) or a high volume (HV) 1 mL kg(−1) of a dye-lidocaine solution was injected into the same hemithorax, injecting the volume equally at these intercostal spaces using the transverse approach. Fisher’s exact test and Wilcoxon signed-rank test were used to contrast the spread of the different volume solutions. The injectate spread along the TTP after all injections, dying a median number (range) of 3 (2–5) and 6 (5–6) nerves with LV and HV, respectively (p = 0.011). The two-point injection of HV, using the t-TTP approach, is a feasible technique that provides a consistent staining from T2 to T7 intercostal nerves. The injection of HV instead of LV increases the spread and enhances the number of stained intercostal nerves.