Lateral ultrasound-guided paravertebral blockade: an anatomical-based description of a new technique

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1 British Journal of Anaesthesia 105 (4): (2010) Advance Access publication 3 August doi: /bja/aeq206 REGIONAL ANAESTHESIA Lateral ultrasound-guided paravertebral blockade: an anatomical-based description of a new technique P. Marhofer 1 *, S. C. Kettner 1, L. Hajbok 1, P. Dubsky 2 and E. Fleischmann 1 1 Department of Anaesthesia, Intensive Care Medicine and Pain Therapy and 2 Department of Surgery, Medical University of Vienna, Waehringer Guertel 18-20, A-1090 Vienna, Austria * Corresponding author. peter.marhofer@meduniwien.ac.at Key points Paravertebral blockade (PVB) is a versatile regional technique that is usually performed using indirect or morphometric methods. We now describe a novel ultrasound-guided approach to PVB. This technique applied at two levels (T3 and T6) provided successful blockade in a case series of 20 subjects with no evidence of significant complications. Background. Paravertebral blockade (PVB) is a regional anaesthetic technique with a large number of indications. PVB is usually performed with landmark-based techniques or methods that rely on pressure differences between the extra- and intraparavertebral space. This consecutive case series was designed to describe the ultrasound appearance of the lateral thoracic paravertebral space (PVS) and develop an ultrasound-guided method for PVB. Methods. The PVS of 20 women undergoing breast cancer surgery was investigated with a high-frequency linear ultrasound transducer in the sitting position. After identification of the transverse process, internal intercostal membrane (IIM), and pleura at the T3 and T6 levels, the depths of the IIM and pleura, and the sagittal diameter of the PVS were determined. An out-of-plane needle guidance technique was used to perform the PVB with ropivacaine 0.75% (12 ml) at both levels. Successful blockade was determined by the ability to perform surgery under light general anaesthesia without opioids. Results. Appropriate ultrasound identification of the IIM, transverse processes, and pleura was possible in all cases. Correct placement of the tip of the needle in the PVS resulted in successful PVB. No correlations of morphometric data with ultrasound measurements of the PVS were detected. Conclusions. After ultrasound identification of the boundaries of the lateral PVS, an out-ofplane needle guidance technique facilitated successful PVB. There were no clinically relevant correlations between morphometric data and ultrasound measurements. Keywords: anaesthetic techniques, regional, paravertebral; anaesthetics local, ropivacaine; anatomy; equipment, ultrasound machines Accepted for publication: 7 June 2010 Paravertebral blockade (PVB) is a regional anaesthesia technique whereby local anaesthetic is administered inside the paravertebral space (PVS). The PVS is wedge shaped with the parietal pleura as anterolateral boundary, the posterolateral aspect of the vertebral body, the intervertebral disc and foramen as the base, and the superior costotransverse ligament (SCTL) that is located between the lower border of the transverse process above and the upper border of the transverse process below and its lateral continuation, and the internal intercostal membrane (IIM) as posterior boundary. The PVS is divided into an anterior, extrapleural, and a posterior, subendothoracic, compartment by the endothoracic fascia, which is closely applied to the ribs and fuses medial to the periost and the midpoints of the vertebral bodies. The PVS contains fatty tissue, spinal nerves, dorsal rami, rami communicantes, the sympathetic chain, and intercostal vessels. Multiple indications for PVB have been reported, including surgical anaesthesia for breast surgery, 1 4 surgical anaesthesia and postoperative analgesia during and after thoracic 5 and abdominal surgery, 6 and pain therapy for fractured ribs, 7 10 postherpetic neuralgia, hyperhydrosis, 13 and liver capsule pain after abdominal trauma. 14 Several methods of PVB have been described. A loss-of-resistance technique with the SCTL as target structure was described by Eason and Wyatt. 15 Greengrass and colleagues 16 described a technique whereby the transverse process is initially contacted by the needle with subsequent caudal advancement of the needle. A pressure measurement technique in which correct needle position within the PVS is detected by different pressure values was introduced by Richardson and colleagues 17 and an autodetect syringe was used by Mundey and colleagues. 18 These techniques rely on more or less indirect methods of identification of & The Author [2010]. Published by Oxford University Press on behalf of the British Journal of Anaesthesia. All rights reserved. For Permissions, please journals.permissions@oxfordjournal.org

2 Ultrasound-guided paravertebral blockade the PVS, with estimated failure rates of % and complication rates of 5%. Ultrasound guidance has been successfully introduced for a large spectrum of regional anaesthetic techniques, and could also be applicable for PVB to provide direct visualization of PVS puncture and the spread of local anaesthetic. Luyet and colleagues 25 recently showed in a cadaver model that direct visualization of the SCTL is possible via highresolution ultrasonography. This prospective consecutive case series was designed to describe the lateral PVS by ultrasonography and to evaluate the feasibility of ultrasoundguided PVB via an out-of-plane needle guidance technique. Pleura IIM Methods After institutional ethical committee approval and written informed consent, 20 female patients (ASA I II) undergoing unilateral breast cancer surgery were included in this prospective observational study. Infections at the site of injection for the PVB, allergy against amino-amide local anaesthetic drugs, or coagulopathies were considered as contraindications. Performance of ultrasonographic-guided PVB The PVB was performed in the preoperative area with the patient sitting. Monitoring included ECG, pulse oximetry, and non-invasive arterial pressure. I.V. access was established on the contra-lateral side of the surgical procedure and midazolam 2 mg was administered via the i.v. line. After surgical disinfection of both cervical thoracic paravertebral areas and protection of the ultrasound probe and cable with a sterile ultrasound probe cover (Safersonic Conti TM cm, Safersonic Inc., Ybbs, Austria), initial ultrasound investigation of the T3 and T6 paravertebral region at the surgical side was performed. Transportable ultrasound equipment and a 50 mm linear 15-6 MHz probe were used (SonoSite M-Turbo TM, SonoSite Inc., Bothell, WA, USA). The ultrasound investigation was performed as follows: identification of T3 and T6 spinous processes by decrement from C7 (vertebra prominens), positioning of the ultrasound probe at the spinous process of T3, lateral movement until the transverse process is visible, and oblique movement until the typical double layer of the IIM, the transverse process, and the pleura are visualized in one image (Fig. 1). The image was stored on the internal hard disc of the ultrasound machine for subsequent measurements (see below). The block was performed after skin infiltration with lidocaine 1% (1 ml). An out-of-plane needle guidance technique with the needle positioned 1 cm caudal to the ultrasound probe was performed as illustrated in Figure 2. A prefilled 22 G 80 mm facette tip needle with a 30 cm injection line (UniPlex Nanoline, Pajunk Inc., Geisingen, Germany) was used. Once the tip of the needle was in a position between the IIM and the pleura, ropivacaine 0.75% (12 ml) was administered over a period of 30 s after negative aspiration. During administration of the local anaesthetic, an anterior Fig 1 Ultrasound image of the PVS between the IIM, the transverse process (), and the pleura. The score number of the IIM in this case is 5 (excellent). Right, medial. Fig 2 Out-of-plane needle guidance technique for PVB on the right side (simulated image). The white arrow indicates cranial direction. displacement of the pleura (downward movement) was observed. The same procedure was repeated at the T6 level. All PVB procedures were performed by one anaesthesiologist (P.M.). PVS measurements The following measurements were made at the T3 and T6 levels (Fig. 3): (i) ultrasound appearance of the IIM in per cent visibility from the transverse process in a lateral direction: 1, none (no visibility); 2, poor (,25% visibility); 3, moderate (26 50% visibility); 4, good (51 75% visibility); 5, excellent (.75% visibility); (ii) skin IIM distance in millimetres at the level of the lateral border of the transverse process (a); (iii) skin pleura distance in millimetres at the same level where the skin IIM distance was measured (b); (iv) sagittal diameter in millimetres of the PVS (b2a) (c). 527

3 Marhofer et al. a b c with target values between 35 and 50 to provide adequate depth of anaesthesia. Fluid management was performed by administration of lactated Ringer s solution 5 ml kg 21 h 21. Surgical incision was performed 10 min after admittance to the operation theatre. Once surgery was finished, continuous propofol infusion was discontinued and the laryngeal mask was removed. Subjects were transferred to the recovery room for immediate postoperative observation including standard monitoring and 2 h later to the ward. Subjects received acetaminophen 1 g i.v. after admission to the recovery room and 6, 12, and 24 h after surgery. The entire intra- and postoperative procedure was supervised by one anaesthesiologist (E.F.). Fig 3 Ultrasound image of the PVS lateral to the. a, distance skin IIM; b, distance skin pleura; c, diameter of the PVS. In addition to the measurements above, the estimated puncture depth (d) was calculated with the assumption of a needle insertion site 10 mm caudal to the ultrasound probe and a position of the tip of the needle in the middle of the PVS: ( d = a + c ) 2 2 The calculated puncture depth is more precise than the directly measured puncture depth using the 1 cm markers of the needle. The following correlations of morphometric data (BMI) and PVS measurements were calculated: BMI visibility IIM T3; BMI visibility IIM T6; BMI depth IIM T3; BMI depth IIM T6; BMI depth pleura T3; BMI depth pleura T6. The correlation between depth and visibility of the IIM was also calculated at both puncture levels. The PVB were deemed successful if the subject did not require opioid administration during the entire perioperative period. Intra- and postoperative anaesthesia management Subjects were transferred from the preoperative area to the operation theatre 10 min after performance of the PVB. In addition to standard monitoring (ECG, pulse oximetry, and non-invasive arterial pressure), bispectral index monitoring (BIS TM, Philips Inc., Eindhoven, The Netherlands) was used for measurement of adequate depth of anaesthesia. General anaesthesia was induced with propofol 2 4 mg kg 21, and a laryngeal mask was inserted to allow supported or spontaneous ventilation with oxygen/air (FI O2 ¼0.3) and E CO 2 was maintained between 4.7 and 5.4 kpa. A continuous propofol infusion was adjusted according to BIS monitoring Rescue and emergency management A decrease in arterial pressure or heart rate of.30% from initial values was treated with repetitive bolus administration of etilephrine or atropine, respectively. An intraoperative increase in arterial pressure or heart rate of.30% was assessed as insufficient analgesia and treated with repetitive bolus administration of fentanyl 2 mg kg 21 until baseline values were achieved. Postoperative pain was assessed by visual analogue scale (VAS) at 1 h intervals during the first 12 postoperative hours and thereafter by verbal contact. Subjects were treated with piritramid 3 mg if VAS was 3 during the first 12 postoperative hours and thereafter if they reported episodes of pain. Nausea and vomiting was treated with ondansetron 8 mg i.v. The studyrelated postoperative observation ended 24 h after surgery. Postoperative observation The puncture areas were investigated to detect local infection or haematoma 24 h after performance of the PVB. Statistical analysis Pearson s correlation was performed to determine the correlation of BMI with the visibility and depth of the IIM. Data are presented as median (range). Results Twenty consecutive patients were included in this study; pertinent data are shown in Table 1. The following surgical procedures were performed: excisional biopsy and sentinel Table 1 Pertinent subject data. Data are presented as median (range) except n and side Patient variable Patient data n 20 Side (left/right) 9/11 Age (yr) 58 (41, 74) Weight (kg) 66 (46, 105) Height (cm) 163 (157, 174) BMI (kg m 22 ) 24.8 (18.4, 36.3) 528

4 Ultrasound-guided paravertebral blockade HR (beats min 1 ) or MAP (mm Hg) Before block After block Skin incision 15 min 30 min 45 min 60 min 75 min 90 min 105 min 120 min HR MAP Fig 4 Haemodynamic measurements before and after the performance of PVB. Table 2 Ultrasound measurements at the T3 and T6 levels. Values are expressed as median (range). IIM, internal intercostal membrane; PVS, paravertebral space Table 3 Correlation of morphometric data with ultrasound measurements. BMI, body mass index; IIM, internal intercostal membrane Variable Ultrasound measurement Correlation Pearson s coefficient Visibility IIM T3 4 (3, 5) Depth IIM T3 (mm) 24 (17, 33) Visibility IIM T6 4 (2, 5) Depth IIM T6 (mm) 25 (18, 45) Diameter PVS T3 (mm) 7 (4, 13) Diameter PVS T6 (mm) 7 (4, 12) Depth pleura T3 (mm) 31 (24, 46) Depth pleura T6 (mm) 32 (24, 49) BMI visibility IIM T BMI visibility IIM T BMI depth IIM T BMI depth IIM T BMI depth pleura T BMI depth pleura T Depth IIM T3 visibility IIM T Depth IIM T6 visibility IIM T lymph node resection (n¼4), quadrant resection (n¼7), quadrant resection and sentinel lymph node resection (n¼6), second look resection (n¼1), and ablation and axillary dissection (n¼2). Appropriate ultrasound identification of the spinous and transverse processes, the IIM, and the pleura was possible at both levels (T3 and T6) in all subjects. Thus, correct placement of the tip of the needle was possible in all cases, resulting in successful blocks in all subjects. Puncture depth was calculated as 30 (23 41) mm for the T3 level and 30 (23 48) mm for the T6 level. All surgical procedures, as described above, were possible with the combination of ultrasound-guided PVB at the T3 and T6 levels and continuous propofol administration during surgery. No patient required opioids intraoperatively or after operation. After performance of the PVB, the mean arterial pressure (MAP) decreased by 25% from initial values (Fig. 4). One patient received atropine 0.5 mg due to intraoperative bradycardia, whereas 12/20 patients received etilephrine 2 5 mg. All episodes of hypotension occurred up to 45 min after performance of the block. We did not detect any episodes of nausea and vomiting in the postoperative period. Ultrasound measurements of the IIM, PVS, and pleura are illustrated in Table 2. The depths of the IIM and pleura were similar at the T3 and T6 levels. No differences in ultrasound measurements were detected between the T3 and T6 levels. We did not detect positive correlations between the BMI and the depth or visibility of the IIM. Only weak correlations were found between the BMI and the depth of the IIM or pleura (Table 3). No local infections or haematomata were detected at the puncture sites 24 h after performance of the block. Discussion This consecutive observational study is the first clinical description of a novel approach to ultrasound-guided PVB. We used a lateral approach to the PVS, which is localized between the transverse process, IIM, and pleura. These anatomical structures were easily detectable by high-resolution ultrasound, and an out-of-plane needle guidance technique was applicable for successful performance of PVB. The clinical use of PVB has a long history. Sellheim of Leipzig described PVB in 1905 for analgesia after abdominal surgery, 26 and Eason and Wyatt 15 introduced PVB in

5 Marhofer et al. A B Fig 5 Ultrasound illustration of the PVS (between the arrows) before (A) and after administration (B) of 12 ml of local anaesthetic. into modern clinical practice. During the past two decades, Karmakar, Lönnqvist, and Richardson have significantly contributed to the popularity of PVB The practical performance of PVB is still based on pure morphometric and indirect methods of identification of the PVS, such as loss-of-resistance, 15 bone contact, 16 and pressure measurement In order to estimate the site and depth of puncture, formulae such as ( weight in kg) and ( weight in kg) have been developed. 36 The major drawback of these indirect methods is a more or less unreliable final needle position and subsequent unpredictable site of administration of the local anaesthetic. Despite a number of publications reporting relatively high success and low complication rates of PVB, an evaluation of the exact percentages regarding this issue is problematic and does not reflect routine clinical practice. Despite a lack of evidence-based outcome data, direct visualization of anatomical structures via ultrasound has been shown to be beneficial for a large number of regional anaesthetic techniques The PVB is perfectly suitable for ultrasound guidance due to the superficial position of the anatomical landmarks. In order to avoid impaired visibility of the SCTL and pleura, we developed an approach lateral to the transverse process, in which ultrasound visualization of the transverse process, the lateral continuation of the SCTL which is described as the IIM and the pleura was possible in all cases. The lateral approach via landmark-based guidance methods or ultrasound-guided via an in-plane needle guidance technique for the catheter advancement to the thoracic PVS has been described recently Renes and colleagues 40 recently described an in-plane technique to advance catheters to the PVS via ultrasound. Despite their encouraging results of correct catheter position, data from Luyet and colleagues 25 indicate an unreliable catheter position in the thoracic PVS in cadavers. These results are consistent with our clinical observation of insufficient surgical analgesia after placement of paravertebral catheters. Therefore, we decided to perform two single punctures at the T3 and T6 levels with a total of 24 ml of local anaesthetic. One single puncture at the T4 or T5 level with 20 ml is an alternative to the double-puncture technique but might be associated with an unpredictable cranial spread of local anaesthetic. The number of dermatomes covered by one single injection in the PVS varies from 1 to 10, 41 and therefore analgesia for breast and axilla surgery might be unpredictable after one single puncture. Recommended volumes of local anaesthetic for PVB vary. Single-site injection of ml is reported as equieffective compared with multiple-site injection of 3 4 ml per level We decided to administer ropivacaine 0.75% (12 ml) at two levels, and the clinical data of surgery without the use of opioids support this management. We decided to perform PVB with an out-of-plane technique (Fig. 2), our preferred method for superficial regional blocks, which is associated with lower needle penetration depth compared with in-plane needle guidance. The range of the calculated puncture depth was mm, where direct visualization of the needle tip is unproblematic. Once the needle tip penetrates the IIM and the local anaesthetic is administered, spread of local anaesthetic can be confirmed by anterior movement of the pleura (Fig. 5). In addition, patients report a slight feeling of pressure during injection probably due to displacement of the pleura. We did not perform an additional loss-of-resistance technique because of possible gaps between the lateral and medial portion of the SCTL and the IIM, and the impossibility to detect penetration of the needle through the SCTL or IIM. 25 In addition, we have previously observed that facette tip needles provide almost painless puncture procedures and allow exact placement of the tip of the needle, whereas blunt needles, which are required for a loss-of-resistance technique, are associated with more pain during puncture and less exact needle guidance. We performed no sensory tests to confirm block quality, which might be interpreted as a limitation. Women undergoing breast cancer surgery are under enormous 530

6 Ultrasound-guided paravertebral blockade psychological pressure and data regarding sensory testing immediately before surgery can be unreliable. Nevertheless, all surgical procedures were performed under opioid-free anaesthesia, which provides evidence for successful PVB. In addition, we observed a significant decrease in MAP after blockade due to sufficient sympathetic blockade which might serve as another sign of successful blockade. Only weak correlations between morphometric data and ultrasound measurements were observed. The IIM is visible by ultrasound independent of the depth or the BMI, which might be advantageous in obese patients. Correlations between BMI and the depth of the SCTL or IIM and the pleura were also weak. Therefore, published formulae calculating the depth of the PVS based on morphometric data should not be used in adults. In summary, ultrasound-guided PVB, in which local anaesthetic is administered between the transverse process, the IIM, and the pleura via an out-of-plane approach, is an effective regional anaesthetic technique for breast surgery. The lack of correlations between morphometric data and ultrasound measurements of the PVS supports the use of ultrasound guidance for PVB. Conflict of interest None declared. Funding This study was supported by the Austrian National Bank Fund (Vienna, Austria). References 1 Hara K, Sakura S, Nomura T, Saito Y. Ultrasound guided thoracic paravertebral block in breast surgery. Anaesthesia 2009; 64: Kemper M, Fernandez A, Candau A, Valladares G. Paravertebral block for breast surgery. Rev Esp Anestesiol Reanim 2009; 56: Klein SM, Bergh A, Steele SM, Georgiade GS, Greengrass RA. Thoracic paravertebral block for breast surgery. Anesth Analg 2000; 90: Terheggen MA, Wille F, Borel Rinkes IH, Ionescu TI, Knape JT. Paravertebral blockade for minor breast surgery. Anesth Analg 2002; 94: 355 9, table of contents 5 Garutti I, Olmedilla L, Perez-Pena JM, et al. Hemodynamic effects of lidocaine in the thoracic paravertebral space during one-lung ventilation for thoracic surgery. J Cardiothorac Vasc Anesth 2006; 20: Serpetinis I, Bassiakou E, Xanthos T, Baltatzi L, Kouta A. Paravertebral block for open cholecystectomy in patients with cardiopulmonary pathology. Acta Anaesthesiol Scand 2008; 52: Gil S, Pascual J, Villazala R, Madrazo M, Gonzalez F, Bernal G. Continuous perfusion of ropivacaine plus fentanyl for nerve-stimulator-guided paravertebral thoracic block to manage pain for a man with multiple rib fractures. Rev Esp Anestesiol Reanim 2009; 56: Karmakar MK, Chui PT, Joynt GM, Ho AM. Thoracic paravertebral block for management of pain associated with multiple fractured ribs in patients with concomitant lumbar spinal trauma. Reg Anesth Pain Med 2001; 26: Karmakar MK, Ho AM. Acute pain management of patients with multiple fractured ribs. J Trauma 2003; 54: Mohta M, Verma P, Saxena AK, Sethi AK, Tyagi A, Girotra G. Prospective, randomized comparison of continuous thoracic epidural and thoracic paravertebral infusion in patients with unilateral multiple fractured ribs a pilot study. J Trauma 2009; 66: Ji G, Niu J, Shi Y, Hou L, Lu Y, Xiong L. The effectiveness of repetitive paravertebral injections with local anesthetics and steroids for the prevention of postherpetic neuralgia in patients with acute herpes zoster. Anesth Analg 2009; 109: Naja ZM, Maaliki H, Al-Tannir MA, El-Rajab M, Ziade F, Zeidan A. Repetitive paravertebral nerve block using a catheter technique for pain relief in post-herpetic neuralgia. Br J Anaesth 2006; 96: Ohseto K. Efficacy of thoracic sympathetic ganglion block and prediction of complications: clinical evaluation of the anterior paratracheal and posterior paravertebral approaches in 234 patients. J Anesth 1992; 6: Hall H, Leach A. Paravertebral block in the management of liver capsule pain after blunt trauma. Br J Anaesth 1999; 83: Eason MJ, Wyatt R. Paravertebral thoracic block a reappraisal. Anaesthesia 1979; 34: Greengrass R, O Brien F, Lyerly K, et al. Paravertebral block for breast cancer surgery. Can J Anaesth 1996; 43: Richardson J, Cheema SP, Hawkins J, Sabanathan S. Thoracic paravertebral space location. A new method using pressure measurement. Anaesthesia 1996; 51: Mundey DA, Buckenmaier CC III, Plunkett AR. Loss of resistance technique for paravertebral nerve blockade using the Episure Autodetect Syringe a case report. Pain Med 2009; 10: Coveney E, Weltz CR, Greengrass R, et al. Use of paravertebral block anesthesia in the surgical management of breast cancer: experience in 156 cases. Ann Surg 1998; 227: Lonnqvist PA, MacKenzie J, Soni AK, Conacher ID. Paravertebral blockade. Failure rate and complications. Anaesthesia 1995; 50: Richardson J, Lonnqvist PA. Thoracic paravertebral block. Br J Anaesth 1998; 81: Richardson J, Sabanathan S. Thoracic paravertebral analgesia. Acta Anaesthesiol Scand 1995; 39: Marhofer P, Harrop-Griffiths W, Kettner SC, Kirchmair L. Fifteen years of ultrasound guidance in regional anaesthesia: Part 1. Br J Anaesth 2010; 104: Marhofer P, Harrop-Griffiths W, Willschke H, Kirchmair L. Fifteen years of ultrasound guidance in regional anaesthesia: Part 2 recent developments in block techniques. Br J Anaesth 2010; 104: Luyet C, Eichenberger U, Greif R, Vogt A, Szucs Farkas Z, Moriggl B. Ultrasound-guided paravertebral puncture and placement of catheters in human cadavers: an imaging study. Br J Anaesth 2009; 102: Bonica J. The management of pain with analgesic block. The Management of Pain. London: Henry Kimpton, 1953; Karmakar MK. Thoracic paravertebral block. Anesthesiology 2001; 95: Karmakar MK, Booker PD, Franks R, Pozzi M. Continuous extrapleural paravertebral infusion of bupivacaine for postthoracotomy analgesia in young infants. Br J Anaesth 1996; 76:

7 Marhofer et al. 29 Karmakar MK, Chung DC. Variability of a thoracic paravertebral block. Are we ignoring the endothoracic fascia? Reg Anesth Pain Med 2000; 25: Karmakar MK, Critchley LA, Ho AM, Gin T, Lee TW, Yim AP. Continuous thoracic paravertebral infusion of bupivacaine for pain management in patients with multiple fractured ribs. Chest 2003; 123: Karmakar MK, Gin T, Ho AM. Ipsilateral thoraco-lumbar anaesthesia and paravertebral spread after low thoracic paravertebral injection. Br J Anaesth 2001; 87: Karmakar MK, Ho AM, Law BK, Wong AS, Shafer SL, Gin T. Arterial and venous pharmacokinetics of ropivacaine with and without epinephrine after thoracic paravertebral block. Anesthesiology 2005; 103: Lonnqvist PA. Pre-emptive analgesia with thoracic paravertebral blockade? Br J Anaesth 2005; 95: Lonnqvist PA, Hildingsson U. The caudal boundary of the thoracic paravertebral space. A study in human cadavers. Anaesthesia 1992; 47: Richardson J, Sabanathan S, Rogers C. Thoracotomy wound exploration in a single lung transplant recipient under extrapleural paravertebral nerve blockade. Eur J Anaesthesiol 1993; 10: Lonnqvist PA, Hesser U. Depth from the skin to the thoracic paravertebral space in infants and children. Paediatr Anaesth 1994; 4: Tenicela R, Pollan SB. Paravertebral-peridural block technique: a unilateral thoracic block. Clin J Pain 1990; 6: Marhofer P, Chan VW. Ultrasound-guided regional anesthesia: current concepts and future trends. Anesth Analg 2007; 104: , tables of contents 39 Burns DA, Ben-David B, Chelly JE, Greensmith JE. Intercostally placed paravertebral catheterization: an alternative approach to continuous paravertebral blockade. Anesth Analg 2008; 107: Renes SH, Bruhn J, Gielen MJ, Scheffer GJ, van Geffen GJ. In-plane ultrasound-guided thoracic paravertebral block: a preliminary report of 36 cases with radiologic confirmation of catheter position. Reg Anesth Pain Med 2010; 35: Cheema SP, Ilsley D, Richardson J, Sabanathan S. A thermographic study of paravertebral analgesia. Anaesthesia 1995; 50: Pusch F, Wildling E, Klimscha W, Weinstabl C. Sonographic measurement of needle insertion depth in paravertebral blocks in women. Br J Anaesth 2000; 85: Weltz CR, Greengrass RA, Lyerly HK. Ambulatory surgical management of breast carcinoma using paravertebral block. Ann Surg 1995; 222: Kapral S, Greher M, Huber G, et al. Ultrasonographic guidance improves the success rate of interscalene brachial plexus blockade. Reg Anesth Pain Med 2008; 33: