Thoracic Paravertebral Block: Relationship between Injected Volume and Number of AffectedNerve Structures (Anatomical Study)

Overview

Objective:
In last decade, thoracic paravertebral blocks have been increasingly used. As we use in our hospital a singleentry continuous paravetebral block for postoperative analgesia after thoracotomic procedures, we decided to investigatewhether a linear relationship exists between injected volume and extent of influenced intervertebral spaces.Design: Anatomical study on cadavers.Setting: Charles University, 3rd Medical School, University Hospital Kralovské Vinohrady, Prague.Material and methods:We performed an anatomical study on human adult cadavers by injecting water dyed with methyleneblue bilaterally at the level of Th 4. Using a standard technique, 10 ml of solution were injected in a prone position on oneside and 20 ml on the other side of the same cadaver. After removal of thoracic and abdominal organs methylene blue couldbe seen below the parietal pleura and the number of coloured intercostal spaces was determined.Results: Although 16 cadavers were used, bilateral block could be performed only in 12 cadavers because of anatomicaland technical problems. We demonstrated a relationship between injected volume and number of coloured intercostalspaces in each cadaver (P < 0.05).We were not able to prove any relationship between injected volume and number of dyedintercostal spaces. The extent of the block using a fixed volume in various cadavers was unpredictable. Various factorscould be involved. Contrary to anaesthesiologists’ opinion, the paravertebral space is not anatomically well defined, evenin anatomical materials or NMR images, before a solution is administered. We can speculate that the paravertebral spaceappears only after insertion of a Tuohy needle and its size depends not onlyon anatomical condition but also on the pressureand velocity of the administered anaestetic. Lower compliance of tissues post mortem could explain a smaller extent of theblock compared to in vivo conditions.Conclusions: In our anatomical study we were not able to demonstrate any definite relationship between the amount ofadministered volume and numberof dyed intercostal spaces.For evaluation of the impact of this anatomical study for clinicalconditions, further examinations are needed.

Key words:
anaesthetic technique – local anaesthesia – paravertebral block – extent of block – anatomical study