# Comparison of injectate spread following transverse vs. sagittal in-plane ultrasound-guided thoracic paravertebral block: a cadaveric study

## TL;DR

This study compares two ultrasound-guided injection techniques for thoracic paravertebral blocks in cadavers, finding similar dye spread patterns between the approaches.

## Contribution

The study provides empirical evidence on injectate spread patterns in thoracic paravertebral blocks using two ultrasound-guided approaches.

## Key findings

- Both transverse and sagittal in-plane approaches reliably target the paravertebral space with similar staining outcomes.
- Dye spread was predominantly cephalad, with no significant differences in stained segments or sympathetic chain staining between approaches.
- Significant associations were found between stained paravertebral segments and sympathetic chain staining.

## Abstract

Thoracic paravertebral block (TPVB) is a clinically valuable regional anesthesia and analgesia technique for managing postoperative acute pain and certain chronic pain conditions. There are several approaches for ultrasound-guided TPVB. However, currently it is hard to provide an evidence-based recommendation on the choice between approaches. Comparisons of injectate distribution patterns among different approaches are limited. This observational cadaveric study compared dye distribution following TPVB using transverse in-plane (TI) and sagittal in-plane (SI) ultrasound-guidance.

Ten paravertebral injections at the T6-7 were performed on five cadavers. Left side received injections with TI approach, and right side with SI approach. All injections consisted of 20 mL of 0.02% methylene blue. The cadavers were dissected to evaluate dye distribution. The ChAracteristics of Cadaver Training and sUrgical Studies (CACTUS) guideline was adhered to conduct and report this study.

All paravertebral injections resulted in dye staining in paravertebral space (PVS). On average, 3 [IQR (3, 3)] PVS segments were stained with TI approach, and 2 [IQR (1, 2)] with SI approach (p = 0.26). Median intercostal staining area was 55.1 [IQR (30.1, 76.0)] cm2 with TI and 38.3 [IQR (7.8, 82.6)] cm2 with SI approach (p = 0.50). Sympathetic chain staining was observed in 80% (TI) and 40% (SI) of cadavers (p = 0.50). Regardless of injection approach, (1) the cephalad and caudal dye distribution was 1 [(IQR (0, 2)] and 0 [IQR (0, 1)] segment separately (p = 0.04); (2) a significantly higher odds of PVS staining, and a significantly longer distance of intercostal space stained were observed at T6-7 (p < 0.001, p < 0.01) and T5-6 level (p = 0.001, p < 0.01); (3) a positive association was observed between the number of PVS segments stained and sympathetic chain staining (p = 0.003).

Both TI and SI ultrasound-guided TPVB approaches reliably target PVS. A predominantly cephalad distribution was noted with two approaches. No significant differences were observed between two approaches regarding the number of PVS segments stained, intercostal spread area, and the percentage of sympathetic chain stained. This study adds knowledge to the spread pattern of TPVB.