Objective: In last decade, thoracic paravertebral blocks have been increasingly used. As we use in our hospital a single entry continuous paravetebral block for postoperative analgesia after thoracotomic procedures, we decided to investigate whether 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 methylene blue bilaterally at the level of Th 4. Using a standard technique, 10 ml of solution were injected in a prone position on one side and 20 ml on the other side of the same cadaver. After removal of thoracic and abdominal organs methylene blue could be 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 anatomical and technical problems. We demonstrated a relationship between injected volume and number of coloured intercostal spaces in each cadaver (P < 0.05).We were not able to prove any relationship between injected volume and number of dyed intercostal spaces. The extent of the block using a fixed volume in various cadavers was unpredictable. Various factors could be involved. Contrary to anaesthesiologists’ opinion, the paravertebral space is not anatomically well defined, even in anatomical materials or NMR images, before a solution is administered. We can speculate that the paravertebral space appears only after insertion of a Tuohy needle and its size depends not onlyon anatomical condition but also on the pressure and velocity of the administered anaestetic. Lower compliance of tissues post mortem could explain a smaller extent of the block compared to in vivo conditions. Conclusions: In our anatomical study we were not able to demonstrate any definite relationship between the amount of administered volume and numberof dyed intercostal spaces.For evaluation of the impact of this anatomical study for clinical conditions, further examinations are needed.

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