Modified ultrasound-guided transversus thoracic plane block: cadaveric study and preliminary clinical results in dogs undergoing median sternotomy for thoracic surgery

Objective: To describe a modified ultrasound-guided technique of the approach to the transversus thoracic plane (TTP) block, to evaluate the distribution of the injectate, and to compare the perioperative use of opioids in dogs undergoing median sternotomy between TTP block or traditional opioid-based analgesic approach. Animals and procedures In Phase I, 10 thawed mid-size adult canine cadavers were used for description of the technique and evaluation of injectate spread on computed tomography and anatomical dissection. In Phase II, 20 client-owned, adult canine dogs undergoing median sternotomy were included in this randomized, prospective, assessor-blinded, clinical study. Dogs were randomly assigned to receive a TTP block (TTPB) with bupivacaine 2 mg kg −1 ; or to the control group (CTRL) without block. Rescue intra- and postoperative analgesia consisted of fentanyl and methadone, respectively. Extra analgesia was provided with fentanyl and/or ketamine infusions when required. Postoperative pain was evaluated using the short form of the Glasgow Composite Measure Pain Scale (CMPS-SF). Results On preliminary anatomical evaluation, six pairs of intercostal nerves were stained bilaterally in the 10 cadavers. In group TTPB, 0/10 dogs required intra-operative fentanyl infusion, compared to 10/10 dogs in group CTRL, of which 9/10 required ketamine infusion. Post-operative methadone (mg/kg) required was 0.8 (0.2–1) in group TTPB and 1.4 (1.4–1.4) in group CTRL ( P < 0.001). A fentanyl infusion was required post-operatively in 6/10 dogs in CTRL group and 0/10 in TTPB group. Conclusions The TTP block approach described in this study resulted in consistent injectate distribution within the target fascial plane, with consistent staining of the intercostal nerves in the cadaveric model. In the preliminary clinical phase, its application was associated with reduced perioperative opioid consumption in dogs undergoing median sternotomy compared to a traditional opioid based analgesic approach.