Review about ultrasounds in paravertebral blocks

Paravertebral block was introduced by Hugo Sellheim in 1905 as a unilateral block preventing the hemodynamic side effects of spinal anaesthesia, but was almost forgotten in the middle of the last century. Eason and Wyatt revitalized the technique in 1979. Ultrasound guidance was first described for vessel cannulation, and gained widespread clinical use in regional anaesthesia. However, anatomical knowledge is a prerequisite for use of ultrasound. The paravertebral region is a wedge-shaped space bounded anteriorly by the parietal pleura, medially by the postero-lateral aspect of the vertebra, the intervertebral foramen, and the intervertebral disc, and posteriorly by the superior costotransverse ligament. Paravertebral block has been reported to be highly efficient for perioperative and chronic pain management, but with reduced adverse effects compared with central neural block. Techniques to reach the paravertebral space include the landmark method, nerve stimulation, the intercostal approach, and placement under direct visualization. Two difficulties of the classic approach have to be considered: (1) the distances from the skin to anatomical landmarks are highly variable and (2) loss of resistance to saline injection may often be overlooked. Several studies have yielded high success rates for ultrasound-guided paravertebral needle placement, without any signs of pleural puncture. However, anatomical data showed that paravertebral catheters inserted through ultrasound-guided, correctly placed needles were often misplaced. In conclusion, there is strong evidence that ultrasound guidance may enhance efficacy and safety of single-shot paravertebral block. However, data concerning ultrasound-guided paravertebral catheterization are conflicting, and further refinements are required to improve continuous paravertebral regional anaesthesia as well.