Description of an Ultrasound-Guided Transverse Approach to the Transversus Thoracis Plane Block and Evaluation of Injectate Spread in Canine Cadavers

Abstract

Transversus thoracis plane (TTP) block has demonstrated to produce analgesia in humans undergoing median sternotomy. The objectives of the study were to describe an ultrasound-guided transverse approach to the transversus thoracis plane (t-TTP) and to evaluate the spread of two injectable volumes in canine cadavers. Two cadavers were used to describe relevant gross anatomy of the ventral thoracic area and sonoanatomy between the fifth and sixth costal cartilages. Then, eight cadavers were used to describe the ultrasound-guided injection into the TTP and were dissected to evaluate the injectate spread and the intercostal nerves staining with two different dye-lidocaine volumes: low volume (LV) 0.5 mL kg−1 and high volume (HV) 1 mL kg−1. To compare the spread between both volumes the Fisher’s exact test and Wilcoxon signed-rank test were used. The solution spread along the TTP after all injections, staining a median number (range) of 3 (2–4) and 4 (3–5) nerves with LV and HV, respectively (p = 0.014). The injection of HV versus LV increases the number of stained nerves. Ultrasound-guided t-TTP is a feasible technique that provides staining of several intercostal nerves with a single injection site, so it could be useful to provide analgesia to the ventral chest wall.

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

“…The present study demonstrates that the TTP is an identifiable plane at the third and sixth intercostal spaces, following the sonoanatomical landmarks described by the authors for the t-TTP approach [ 17 ]. Furthermore, this two-point approach performed at the third and sixth intercostal spaces enables the injection of a methylene blue and lidocaine solution in the TTP.…”

“…After that, the other hemithorax was ultrasonographically evaluated along the regions between the third and fourth and the sixth and seventh costal cartilages. The transducer was positioned on the third and the sixth intercostal spaces in a parasternal position, parallel to the longitudinal axis of the costal cartilages and slightly lateral to the sternebra, as the authors described in a previous study of the t-TTP approach [ 17 ]. The sonoanatomy of both regions was correlated with the gross anatomical findings observed during dissections to recognize the references to perform the ultrasound-guided t-TTP.…”

“…In veterinary medicine, thoracic epidural [ 6 ], thoracic paravertebral block [ 7 , 8 , 9 , 10 , 11 ], erector spinae plane block [ 12 , 13 , 14 ], intercostal blocks [ 6 , 15 ], transversus thoracis plane (TTP) block [ 16 , 17 ] and pecto-intercostal block [ 18 ] could be useful, providing analgesia to the ventral chest wall.…”

“…In dogs, sagittal [ 16 ] and transverse (t-TTP) [ 17 ] approaches for TTP block have recently been described in cadaveric studies. Although both approaches have only been reported in canine cadavers, they could enable the distal injection of an anaesthetic solution into the TTP in live dogs and block from the second to seventh intercostal nerves (T2-T7), which run through the TTP and innervate the sternum and adjacent tissues.…”

“…Although both approaches have only been reported in canine cadavers, they could enable the distal injection of an anaesthetic solution into the TTP in live dogs and block from the second to seventh intercostal nerves (T2-T7), which run through the TTP and innervate the sternum and adjacent tissues. In a previous study, the authors reported the spread of a methylene blue and lidocaine solution through the TTP and the dying of the intercostal nerves that run along this plane when it was injected into the TTP through a single injection point at the fifth intercostal space [ 17 ]. Although they observed that the spread and number of stained nerves were greater when a larger volume was administered, the higher volume (1 mL kg −1 ) did not achieve the staining of all intercostal nerves running along the TTP.…”