Approach affects injectate spread in ultrasound-guided thoracic paravertebral block: a cadaveric trial

Editor—Ultrasound-guided thoracic paravertebral block has made much progress, and various approaches have been developed in the past decade.¹ However, the differences in local anaesthetic distribution patterns are unknown. We adopted two patterns of injections, namely the intercostal approach (IC approach)² and the paralaminar in-plane approach (PL approach),³⁴ and compared their injectate spreading patterns in three Thiel-embalmed human cadavers using a dye injection method.⁵⁶ For the IC approach, a 6–13 MHz linear array transducer was placed at the T4, T5 and T9 intercostal levels to visualize the transverse process. An 18-gauge Tuohy needle was inserted from lateral to medial beside the probe to penetrate the internal intercostal membrane next to the tip of the transverse process. For the PL approach, the needle was inserted from medial to lateral using a 5–8 MHz microconvex array transducer to visualize the lateral edge of the vertebral lamina at the T6, T7 and T10 levels. We investigated five injections by the IC approach and four injections by the PL approach using 10 ml of dye of various colours. One injection in each group included real-time, direct observation of the distribution pattern after dissection via a pre-inserted catheter 2.5 cm beyond the needle tip. Paravertebral spread was confirmed in all procedures. In the IC approach group, dye covered the respective intercostal space and the adjacent paravertebral space (PVS) (Fig. 1A), consistent with previous reports.⁷ The injected dye in the PL approach group covered the more longitudinal and medial PVS rather than the lateral intercostal space (Fig. 1B).⁸ Real-time dye injections from the catheter showed that in the IC approach dye first spread to the respective intercostal level following PVS whereas in the PL approach dye first covered the area around the sympathetic trunk followed by the intercostal area.

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