A thermographic study of paravertebral analgesia

Abstract

Summary Six patients undergoing paravertebral blocks for chronically painful conditions Key wordsEquipment; thermal imaging. Anaesthetic techniques, regional; paravertebral block.Paravertebral analgesia is advocated for surgical procedures of the abdomen wherever the afferent input is predominantly unilateral e.g. nephrectomy, cholecystectomy, but it is particularly effective when used to treat the pain of posterolateral thoractomy [ 11. However, despite numerous studies showing the clinical safety and efficacy of this block [ 1-51, there appear to be some reservations which have been voiced in vague terms by some [6, 71 and more specifically by others [8]. The former include the suggestion that the technique is hazardous and ineffective and the latter that paravertebral spread rarely exceeds two dermatomes with evidence of sympathetic blockade being seen in fewer than 5% of patients. Rather than simply add further anatomical data, we undertook an objective physiological assessment of the extent of the somatic and sympathetic blockade achievable with a single percutaneous paravertebral injection. Patients and MethodsThe study was approved by the hospital ethics committee and informed consent was 'obtained from all patients. Percutaneous paravertebral blocks were perfonned in six patients presenting for treatment of chronically painful chest wall conditions (post-thoracotomy neuralgia, intercostal neuralgia and postherpetic neuralgia). Each patient underwent pre-operative automated cardiovascular data collection consisting of noninvasive pulse and blood pressures in the sitting and supine positions (Datascope 22001). Anterior, posterior and lateral thermographic control views of the naked trunk and limbs were obtained pre-operatively with a Starsight thermal imaging camera (Insight Vision Systems, Malver). Pre-operative pinprick testing was normal in all patients. The blocks were performed by a single operator experienced in this technique (J.R.) and the method used was that of Eason and Wyatt [2] supplemented with radiographic screening and the use of radio-opaque contrast medium. Following negative aspiration, 15 ml of 0.5% bupivacaine was injected over 60 s as a single bolus (with multiple aspirations) at a mean dermatomal level of T,,, with a range of T,-, to T,,,, . Postinjection data collection was undertaken by two observers (D.I. and S.P.S.C.) and consisted of pinprick mapping of the extent of the block, repeated thermographic imaging at 5min intervals until a stable image was obtained, 5min sitting and lying cardiovascular parameters and documentation of any side effects.

Placement of coiled catheters into the paravertebral space*

“…Unilateral, multi-segmental anaesthesia after singleshot paravertebral injection of local anaesthetic solution has been previously reported [11][12][13]25]. However, there are conflicting results in the literature concerning the efficacy of paravertebral catheter placement [14,16,17], possibly related to difficulties in viewing and guiding the position of the catheter tip using ultrasound [26].…”

“…In the remaining 48 cases, the mean (SD) distance from the needle tip to the catheter tip was 8.2 mm (4.9 mm). The median IQR [range]distance from the needle tip to the peak of the catheter coil was 9 (7-12 [5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20])mm. Figure 3 shows an example of a CT reconstruction, with needles and catheters placed into the paravertebral space.…”

“…Unilateral multisegmental anaesthesia after singleshot paravertebral injection of local anaesthetic is a wellestablished technique [11][12][13]. However, there are conflicting results with regard to the use of catheter-based techniques because of the variable and often limited extent of local anaesthetic spread within the paravertebral space [14][15][16][17].…”

The ultrasound-guided retrolaminar block

“…1 Injection of local anesthetic in this space typically results in unilateral block of several spinal nerves as well as variable unilateral sympathetic nerve blockade. 1,11 Analgesia and spread of local anesthetic can be inconsistent, and success rates are typically reported to be less than 90%. [12][13][14] The traditional ''blind'' approach to the paravertebral space involves tactile identification of a transverse process with the tip of the block needle and then ''walking the needle off'' in either the cephalad or caudad direction about 1 cm deeper or until a ''pop'' is felt penetrating through the costotransverse ligament (Fig.…”

The location of paravertebral catheters placed using the landmark technique

“…Thoracic paravertebral block has been shown to be a proven technique to achieve sufficient postoperative analgesia [2,3]. Unilateral thoracic anaesthesia can be achieved with a multilevel injection technique that can be used as the sole anaesthesia technique for breast surgery [4][5][6][7]. Even though a single injection technique has been shown to produce a reliable block, there are conflicting results regarding the use of paravertebral catheters.…”