Thoracic paravertebral blockade.

Abstract

We read with interest the article by Naja and colleagues (Anaesthesia 2004; 59: 459–63). Little is known of the factors that influence the spread of local anaesthetic solution within the thoracic paravertebral space [1]. The authors describe a novel method of facilitating spread that, if correct, could be clinically useful. We have concerns, however, regarding the anatomical validity of the authors' interpretation of this fascial layer and its relations within the paravertebral space. The authors suggest that the endothoracic fascia divides the paravertebral space into potential anterior (extrapleural) and posterior (subendothoracic) compartments. However, their interpretation of the previous literature they cite seems unorthodox. Radiological studies indicate that the spinal nerve lies in the posterior segment of the paravertebral space [2]. This is behind the endothoracic fascia, which fuses with the periosteum at the midpoint of the vertebral body [3, 4]. While the authors' results are encouraging, the conclusions may not be valid due to possible misinterpretation of anatomical structures in this area. We also have concerns about the amplitude of the current used (2.5 mA). Such currents may cause patient discomfort. Experience is limited regarding nerve stimulation in the paravertebral space, making the parameters employed unclear. Patient comfort must remain a priority, and failure to recognise this remains a concern. Finally, the title ‘Varying anatomical injection points within the thoracic paravertebral space: effect on spread of solution and nerve blockade’ is unfortunate. X-ray images of contrast spread do not, by themselves, correlate with adequate clinical nerve blockade. Outcome measures such as dermatomal level of block are more useful. The recognised advantages over the past 25 years regarding the usefulness of paravertebral blockade in both the acute and chronic pain setting are well recognised [5], and it behoves anaesthetists to be cognizant of the relevant anatomy. We read with interest the comments by Drs Fitzgerald and Harmon with regard to our manuscript reporting on factors influencing spread of local anaesthetic solution within the thoracic paravertebral space. We agree with their description of the guided paravertebral technique using a nerve stimulator as a novel method. It has been used for many surgical interventions at our institution since 1998 [1, 2, 3]. The paravertebral injection of radio-opaque dye was directed by the use of a nerve stimulator. Injections made at a stimulating current of 2.5 mA with appropriate intercostal and abdominal muscle response resulted in limited distribution only over the adjacent segments. The injection was made in the more dorsal part of the thoracic paravertebral space, supposedly posterior to the endothoracic fascia. Injections made at 0.5 mA, with the appropriate muscle response, resulted in a multisegmental longitudinal spreading pattern. These injections were made into the more ventral part of the thoracic paravertebral space, anterior to the endothoracic fascia, in order to cover the spinal nerve, rami communicans, the origin of the dorsal nerve and the sympathetic chain. The true functional anatomy of the paravertebral space is currently unknown. Whether the position of the endothoracic fascia is indeed adequately described in previous texts is doubtful since anatomical dissection in this area is very difficult and older textbook drawings are not always reliable. Thus, we agree that there may be factors other than the endothoracic fascia responsible for the different pattern of spread seen in our study. However, our results clearly show that injection in the anterior part of the thoracic paravertebral space does result in the more desirable longitudinal spreading pattern compared with injection made immediately upon entering the paravertebral space. As Drs Fitzgerald and Harmon point out, some patients experience discomfort at a current of 2.5 mA. From our experience the muscle response resulting from applying a current of 2.5 mA into the thoracic paravertebral space is similar in intensity to that obtained when used for other types of regional anaesthesia techniques such as brachial plexus and lumbar plexus blockade. The discomfort can be eliminated with light sedation given prior to the paravertebral block. For further details regarding the verification of adequate clinical nerve blockade, which was not our interest in the current study, readers are referred to our previous publications using the guided paravertebral blockade as a sole anaesthetic technique [1, 2]. We believe that guided paravertebral blocks are effective and safe, with fewer complications and a greater success rate than conventional paravertebral blockade [4, 5]. Z. Naja and Makassed General Hospital Beirut, Lebanon E-mail: zouhnaja@yahoo.comP.A. LönnqvistKS/Astrid Lindrens Children's Hospital Stockholm, Sweden