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

Abstract

Editor—Ultrasound-guided thoracic paravertebral block has made much progress, and various approaches have been developed in the past decade.1Krediet AC Moayeri N Van Geffen GJ et al.Different approaches to ultrasound-guided thoracic paravertebral block: an illustrated review.Anesthesiology. 2015; 123: 459-474Crossref PubMed Scopus (141) Google Scholar However, the differences in local anaesthetic distribution patterns are unknown. We adopted two patterns of injections, namely the intercostal approach (IC approach)2Shibata Y Nishiwaki K Ultrasound-guided intercostal approach to thoracic paravertebral block.Anesth Analg. 2009; 109: 996-997Crossref PubMed Scopus (73) Google Scholar and the paralaminar in-plane approach (PL approach),3Taketa Y Fujitani T A novel paralaminar in-plane approach for ultrasound-guided continuous thoracic paravertebral block using microconvex array transducer.Reg Anesth Pain Med. 2015; 40: 390Crossref PubMed Scopus (8) Google Scholar4Taketa Y Fujitani T Irisawa Y Sudo S Takaishi K Ultrasound-guided thoracic paravertebral block by the paralaminar in-plane approach using a microconvex array transducer: methodological utility based on anatomical structures.J Anesth. 2017; 31: 271-277Crossref PubMed Scopus (11) Google Scholar and compared their injectate spreading patterns in three Thiel-embalmed human cadavers using a dye injection method.5Carline L McLeod GA Lamb C A cadaver study comparing spread of dye and nerve involvement after three different quadratus lumborum blocks.Br J Anaesth. 2016; 117: 387-394Abstract Full Text Full Text PDF PubMed Scopus (135) Google Scholar6Munirama S Eisma R Columb M Corner GA McLeod GA Physical properties and functional alignment of soft-embalmed Thiel human cadaver when used as a simulator for ultrasound-guided regional anaesthesia.Br J Anaesth. 2016; 116: 699-707Abstract Full Text Full Text PDF PubMed Scopus (25) Google Scholar 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.7Paraskeuopoulos T Saranteas T Kouladouros K et al.Thoracic paravertebral spread using two different ultrasound-guided intercostal injection techniques in human cadavers.Clin Anat. 2010; 23: 840-847Crossref PubMed Scopus (19) Google Scholar The injected dye in the PL approach group covered the more longitudinal and medial PVS rather than the lateral intercostal space (Fig. 1B).8Takeda Y Ishikawa S Nakamoto T 3D Anatomy Project in Okayama. 3D Anatomy project in Okayama University, Okayama, Okayama2016Google Scholar 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. These findings are based on the anatomical features of the endothoracic fascia (ETF), which lines and clings to the parietal pleura in the intercostal area. Apart from the parietal pleura, the ETF tends to cover the vertebral body from the inner side of the transverse process.9Karmakar MK Chung DC Variability of a thoracic paravertebral block. Are we ignoring the endothoracic fascia?.Reg Anesth Pain Med. 2000; 25: 325-327Crossref PubMed Scopus (44) Google Scholar Thus, dye injected by the medial approach would be more likely to penetrate the ETF and spread in the medial direction around the vertebral body. Although this was a small-scale trial, our findings suggest that there is a difference in injectate distribution between the lateral and medial approaches of ultrasound-guided thoracic paravertebral block in human cadavers, and that the medial approach could produce a greater sympathetic blocking effect than the lateral approach. None declared.