Radiological Evaluation of Thoracic Paravertebral Catheters: A Prospective Clinical Trial

Background

The paravertebral block is a regional anaesthetic technique which can be used for analgesia after thoracic, cardiac, breast surgery, upper abdominal surgery or for pain therapy. Thoracic paravertebral blockade is performed by injecting a local anaesthetic solution into the paravertebral space, which contains the thoracic nerves, their branches and the sympathetic trunk. This space is a wedge-shaped area sandwiched between the heads and necks of the ribs. The posterior wall is formed by the superior costo-transverse ligament, the antero-lateral wall is the parietal pleura with the endothoracic fascia and the medial wall is the lateral surface of the vertebral body and disc. Also medially, there is communication with the epidural space via the intervertebral foramen. It has been shown, that each space communicates inferiorly and superiorly across the heads and necks of the ribs. Thus injecting local anaesthetic in the paravertebral space should results to an analgesia corresponding to a unilateral epidural anaesthesia.

Unilateral multisegmental anaesthesia after single-shot paravertebral injection of local anaesthetics is well established. On the other hand, a variety of different studies on volunteers, patients and cadavers showed conflicting results regarding the vertical spread over several adjacent segments after paravertebral injection leading to the recommendation of some authors to use a multi-injection technique to achieve a multilevel somatic nerve blockade, specially described during breast surgery using paravertebral block alone.

Can we explain these different contradictory reports and recommendations? Available radiologic and anatomic studies show many different patterns of contrast dye spread after single shot paravertebral contrast dye injection. One study even reports different distribution of dye even after several paravertebral single shots of the same operator in the same patient. Some radiological studies report cloud-like contrast dye accumulation without significant cranio-caudal spread. This could be due to the restricted intercostal spread or to subpleural spread or even to injection of the contrast dye into the autochthonic muscles of the back.

The spread of local anesthetics (or contrast dye as substitute) is affected by nuances of differences in the needle placement because of the fine membranes like the endothoracica fascia. This might be the major problem during the insertion of catheters. The final location of catheter tip is hard to predict. Catheters might dissect during the insertion and possibly the difference is only a more medial or more lateral puncture. The placement of catheters into the paravertebral space leading to a clear cranio-caudal spread of local anaesthetics resulting in multisegmental spread of anaesthesia is the goal of a catheter for paravertebral analgesia but it seems not easy to be achieved - despite of an uncontestable clinical benefit of paravertebral catheters for pain relief.