We previously reported an approach to ultrasound-guided thoracic paravertebral block (USG-TPVB) that used a transverse image of the thoracic paravertebral space (TPVS) and in-plane needling.1 In this technique, we aimed to position a needle tip into the lateral edge of the TPVS between the internal intercostal membrane and the parietal pleura. Successful injection is confirmed by observing the parietal pleura being pressed down ventrally by a local anesthetic. However, the steric spread of the local anesthetic in the TPVS has been unclear.
We were able to observe the thoracic cavity in real time under thoracoscopy when we injected a local anesthetic into the TPVS at the end of thoracoscopic surgery. The patient in this case was a 16-year-old man (weight, 65 kg; height, 165 cm) who underwent video-assisted thoracoscopic surgery for recurrent pneumothorax. We visualized the transverse image of the TPVS with a SonoSite M-Turbo portable ultrasound machine (Fujifilm, Bothell, WA, USA) and inserted an 18-guage Tuohy needle (Hakko, Tokyo, Japan) from the outer end of the ultrasonic linear array transducer in a lateral-to-medial direction. After the needle tip reached the TPVS, we injected 20 mL of 0.5% ropivacaine into the TPVS in increments of 5 mL after aspiration (injection speed, approx. 1 mL/s).
Initially, the parietal pleura expanded in a lateral direction along the intercostal space at the level of the local anesthetic injection. The local anesthetic then spread in a craniocaudal direction along the lateral aspects of the thoracic vertebral bodies. In addition, the local anesthetic seeped through the parietal pleura into the interpleural space (Figure 1 and video file).
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This observation is associated with two significant findings. First, when the spread of the local anesthetic is observed on ultrasonography to press down on the parietal pleura, the local anesthetic is expanding laterally along the intercostal space. This intercostal spread suggests that the local anesthetic can act most strongly at the level of injection in our technique. Second, the TPVS can communicate with the interpleural space. Although we know that the TPVS is continuous with four spaces (the intercostal space, the epidural space, the contralateral paravertebral space, and the posterior mediastinum2, 3), the fifth communicating space is newly discovered.
There is a limitation associated with our new findings. Our observation was made in the thoracic cavity on the nonventilated side during one lung ventilation. The changes in interpleural pressure in rhythm with respiration may actually affect the spread of local anesthetic. However, we observed the spread of the local anesthetic during USG-TPVB under one of the common clinical situations. Further studies are needed in order to determine a more precise use of USG-TPVB.