Workshop Station 

Workshop Station Author: George W Kanellakos, MD, FRCPC Department of Anesthesiology, Dalhousie University Halifax, Nova Scotia, Canada [email protected] How to Make a Paravertebral Block Better than a Thoracic Epidural OBJECTIVES 1.
Understand the anatomy of the paravertebral space in order to facilitate a successful block. Discuss the insertion technique critical to the success of a paravertebral block. Discuss the advantages of a paravertebral block technique versus a thoracic epidural. Review the perioperative management of patients with paravertebral block following thoracotomy. Introduction Paravertebral blocks (PVBs) administered correctly can successfully induce unilateral thoracic analgesia(1‐7). A single injection of local anesthetic can produce analgesia and sympathetic blockade without heart rate and blood pressure changes(8,9). On average, the somatic and sympathetic block extends five and eight dermatomes, respectively. It has also been shown that a single injection is as effective as multiple injections with the obvious benefit of improved patient satisfaction(10). This block is not new(11) but has fallen out of favour in modern day practice(12). Multiple papers have been published in the past few years, reflecting a resurrection in the technique. The Procedure‐Specific Postoperative Pain Management (PROSPECT) working group has recently published recommendations for pain control specific to procedures. PVB and thoracic epidural analgesia for thoracotomy are listed as top recommendations, both based on Grade A evidence.(13) The lack of universal acceptance for PVB is difficult to ascertain but probably lies in the perceived inconsistency of adequate pain control. This perception is fueled by the numerous techniques that are all labelled “paravertebral” or “intercostal” or “pleural”. The nomenclature surrounding this block can be confusing but so is the technique itself. An intercostal catheter placed posteriorly towards the midline is predictably unsuccessful(3) and has been incorrectly given the label of failed PVB. The same comment can be made regarding “intrapleural” catheters. Local anesthetic administered in the intrapleural space has been shown to be inferior to local anesthetic in the extrapleural space(14). The paravertebral space is a difficult conceptual space within the extrapleural space, or cavity. To further complicate the literature, advocates of proper paravertebral techniques have published studies that refer to “extrapleural intercostal” blockade(15,16). Other terms used to describe PVBs are peridural(4) and interpleural(3). One is obliged to begin the discussion of paravertebral blockade with a solid understanding of anatomy. Page 1 of 11 Anatomy of Paravertebral Space The paravertebral space is a potential space in the extrapleural cavity. It contains intercostal nerves at the nerve root level, including ventral and dorsal rami and the thoracic sympathetic chain. Posteriorly it is bordered by the superior costotransverse ligament and anteriorly by the parietal pleura. The medial wall is made up of the vertebral column and the lateral border extends continuously along the intercostal space. The boney borders of the paravertebral space (PVS) are shown in Figure 1(17). Figure 1: The paravertebral space lies immediately lateral to the thoracic vertebrae. A point 2.5 cm lateral to the spinous process identifies the insertion point of the needle. Paravertebral space (PVS); spinous process (SP); thoracic process (TP). Figure 2(18), below, represents radiographic evidence of the paravertebral space. Figure 2: Left: Bilateral PVB with X‐ray contrast medium added to LA. Right: Bilateral PVB with X‐ray contrast medium added to LA. Typical and optimal contrast medium distribution is shown with the addition of some spread around the intercostal spaces on the left. Page 2 of 11 Technique The classic insertion technique for PVB is percutaneous and has been described by Eason and Wyatt(19). Similar to epidural insertion, loss of resistance is felt immediately after puncturing the superior costotransverse ligament, which represents the posterior border to the paravertebral space. Approximately 2.5 cm lateral to the midline of the spine, the transverse process is touched and a needle is directed over (commonly) or under the boney landmark no more than 1 cm and local anesthetic with or without a catheter is inserted. The skin to paravertebral distance is, on average, 5.5 cm(20). The technique is also perfectly described by Hounsell(17). Percutaneous insertion has a failure rate of 10%(21) but advances in regional anesthesia have made blind percutaneous insertion of needles less common and today nerve stimulators have reduced the failure rate to 6%(22,23). Ultrasound has dramatically changed the way regional anesthesia is practiced and is now being used for PVB. The anatomy of the paravertebral space seen on ultrasound requires significant practice to recognize. A significant benefit of the percutaneous technique over thoracic epidurals is the acceptance of placement while the patient is anesthetized(24). The success rate of PVBs is highly dependent on the insertion technique. As mentioned, the literature is full of confusing labels for the true location of a PVB. In order to be successful at the block, local anesthetic must be deposited as close to the vertebral column as possible. If the injection is too lateral, it fails to spread cephalad‐caudad adequately and becomes similar to an intercostal block. As mentioned, intercostal blocks do not provide adequate pain relief for thoracotomy. The true insertion technique was well described by Sabanathan in 1988(25) but has since been republished in 1995(26). Catheter position is depicted in Figure 3(12). The technique is simple and is described here, word for word: “The essential steps are as follows. At the end of operation, the parietal pleura is raised from the posterior chest wall up to the vertebral bodies from two intercostal spaces above and below the thoracotomy incision, exposing the paravertebral space. A small defect is made in the extrapleural fascia into the paravertebral space using Lahey's forceps. A percutaneously inserted cannula is passed through the defect into the paravertebral space under direct vision and advanced 2 to 3 cm to lie against the costovertebral joints. The pleura is reattached, if possible, and the paravertebral space is infused for 5 days with 0.5% bupivacaine at a rate of 0.1 mL/kg body weight per hour with an on‐line bacterial filter.” (Sabaratnam Sabanathan et al, 1988) Figure 3: Optimal position of a paravertebral catheter (Published by Richardson and Lonnqvist, 1998)(12) Page 3 of 11 One recent study(27) found epidural analgesia to be far superior to PVB. The insertion technique described, however, was percutaneous using low doses of local anesthetic infusion. The solution used was 0.25% bupivacaine with 1.6mcg/mL fentanyl at 0.1mL/kg/hr. It is likely that inconsistent catheter placement coupled with low local anesthetic doses contributed to poor outcome observed for PVBs. In a similar study where 40 catheters were also placed percutaneously but 0.5% ropivacaine was used, the catheter position was confirmed with chest x‐rays after contrast medium was injected(28). All catheters were confirmed in the paravertebral space and the study found PVBs were effective. Another study published in 2011 also used a high concentration of local anesthetic (0.5% ropivacaine) that would have been expected to produce adequate pain control following thoracotomy(29) but they failed to do so. They concluded that PVB using a catheter placed by the thoracic surgeon was ineffective on postoperative pain after thoracotomy and did not confirm the analgesic effect that has been observed after percutaneous catheter placement. On further analysis, the described insertion technique did in fact vary from the Sabanathan description above, despite the authors’ claim to have followed this exact technique. These studies underscore that the location of the catheter is critical in the success rate of PVB. Catheter placement in our institution is done intraoperatively during a thoracotomy by the surgeon, in a manner similar to what Sabanathan has described above. Another problem with the PVB literature has been the heterogeneity of local anesthetic solutions used, with or without supplementary medications. Multimodal analgesic regimens have been well described and PVB should be part of a regimen(15,30,31). For each planned dermatome to be blocked, the literature supports 2mL of local anesthetic (lidocaine) injected(8,9). This results in an average single injection volume of 10 mL to block 5 dermatome levels. In an attempt to maximize pain relief but limit toxicity, bupivacaine and ropivacaine dosing regimens vary widely between institutions making comparisons very difficult. A proven local anesthetic regimen that has gained universal acceptance has not yet emerged for PVB infusions(32) with at least one study reviewing this in detail(33). Recommendations from this study advocate a minimum bupivacaine concentration of 0.25% or equivalent ropivacaine concentration of 0.3%. The authors also mention that initially higher concentrations may be required in the first 24 hours to achieve adequate pain control. Richardson and Sabanathan have done extensive work in this area and routinely use 0.5% bupivacaine at 0.1 mL/kg/hr. Launcelott, a pain specialist in our institution utilized multiple local anesthetic regimens using lidocaine, bupivacaine or ropivacaine with varying concentrations. Although a proper dose finding study is necessary, the following perioperative analgesic regimen has been found to be highly successful: Preoperative medication: gabapentin 200 – 600 mg PO (patient age, health dependent) acetaminophen 975 mg PO celecoxib 200 mg PO Intraoperative bolus: 0.5% bupivacaine with epinephrine (5 mL boluses, 20 mL total) Postoperative infusion: 0.375% ropivacaine at 12 mL/hr Postoperative medications: celecoxib 200 mg PO BID or 400 mg PO OD acetaminophen 975 mg PO q6h hydromorphone 1 mg SC q3h prn or 2‐6 mg PO q4h prn PCA hydromorphone IV PRN (rarely used) Page 4 of 11 According to the product monograph, the dosage guideline for prolonged epidural infusions of ropivacaine is 28mg/hr over a 72 hour period. It should be stressed that this is for epidural administration, not the paravertebral space. When calculating the infusion dosage of ropivacaine in our regimen, one might expect to observe toxic symptoms. This was indeed observed when high infusion rates of lidocaine and bupivacaine were administered, particularly on postoperative day 1, but to date not one case of observed toxicity has been found while using ropivacaine in this manner. This has now been supported by hundreds of cases over a two year period. Published studies demonstrate ropivacaine administered at high doses by long term epidural infusion does not result in toxic plasma levels(28,33) even after 120 hours(34). Extrapolating these findings to our infusion rate, predicted free plasma concentrations of ropivacaine would still be well below the published toxic threshold(35). Paradoxically, plasma concentrations have even been observed to drop after 70 hours of infusion(34,36). To further support this controversial practice, a literature review of bilateral PVBs where high doses of local anesthetics were used also failed to find evidence of local anesthetic toxicity(18). The stated rate of 12 mL/hr was not developed quickly, with many patients starting at 6 or 8 mL/hr. It was observed that all patients eventually required increases to their infusion with the end result being 12mL/hr. Initially lower concentrations (0.2% local anesthetic) with lower infusion rates were used but this evolved to the current concentration at a higher infusion rate. Eventually it was decided to start all patients at this rate enabling adequate comfort levels to be achieved more quickly. Pain control is considered adequate when patients are able to sit up, cough, turn over and ambulate without difficulty. It appears that in order to achieve this level of pain control, not only does it require a minimum concentration but total volume is also critical. Clinical Efficacy and Indications PVBs have been successfully used in numerous procedures. The literature is now full of studies that support PVB as at least equal to or more efficacious than epidurals(1‐7,37). Any surgical procedure that is unilateral in nature to pain has been successfully treated with PVB. PVB is also being used for non‐
surgical pain, including rib fractures(38,39), to minimize morbidity secondary to pain and improve outcomes. Recently support for bilateral PVB for midline laparotomy has been suggested(18). Surgical indications suited for PVB are listed in Table 1. Table 1: Surgical Indications/Contraindications Suitable for Paravertebral Block Clinical Indications Thoracotomy VATS procedures Chest tubes Rib fractures Mastectomy Open cholecystectomy Nephrectomy Inguinal hernia repair Clinical Contraindications Sternotomy Midline laparotomy Local anesthetic allergy or toxicity Thoracic spine deformity Anticoagulation (for percutaneous insertions) (relative contraindication) Sepsis (local or systemic) Page 5 of 11 Two recent studies, including a meta‐analysis that reviewed 10 studies and 520 patients(4) and an extensive “best evidence review”(6), compared paravertebral to epidural continuous infusions for post‐
thoracotomy pain control. The findings support equivalent pain control with less observed side effects, leading to the recommendation that paravertebral blockade can be used for major thoracic surgery. The catheter insertion techniques in this meta‐analysis were a combination of percutaneous and open insertion by the surgeon. Percutaneous insertions inherently have a higher rate of incomplete or failed block and their inclusion in the study did not lower the overall success rate but rather they found PVB failed less often than epidurals . Epidurals have been shown to have a failure rate ranging from 1%(40) to 12% (41). It is important to note that additional pain modalities were employed in the paravertebral groups, ranging from PCA morphine to IM ketorolac. One potential limitation of the meta‐analysis that may favour epidural catheters is that a subset of the studies included only used local anesthetic in the epidural space without the addition of opioids. When an opioid (hydromorphone) is added to epidural infusions, a new prospective RCT published in 2012 found that epidurals may provide enhanced analgesia over PVB(42). In this study, Group 1 was given a common epidural infusion of bupivacaine 0.25% with hydromorphone 0.01mg/mL, Group 2 was given 0.25% bupivacaine alone by epidural and Group 3 was given 0.25% bupivacaine by paravertebral catheter. They found that Group 1 had superior pain control over Groups 2 and 3, which were found to be equivalent when compared head to head. Minor side effects were observed in the epidural groups but these were minimal and easily managed. The magnitude of effect was a lower visual analogue score in favour of epidurals of approximately 1 point from approximately 3.4 to 2.4. This new study helps address an important gap in the literature. However, the paravertebral infusion used was 0.25% bupivacaine at 8mL/hr with little or no multimodal pain adjuncts used. Five patients reportedly required PCA supplementation. As described above, the paravertebral regimen developed in our institution is dramatically different from this regimen and it may provide additional pain relief. This finding underscores the need for a dose finding study for paravertebral catheter infusions. When comparing PVBs to thoracic epidurals, not only is quality of pain control an outcome measure, but side effects profiles and complications need to be considered. Problems with epidurals are well known, including hypotension, urinary retention, pruritus, nausea and vomiting, respiratory depression, headache, incomplete block, infection, nerve injury and rarely spinal cord injury secondary to needle trauma or hematoma(43). Modern day use of novel anticoagulants, especially low molecular weight heparins, has introduced uncertainty and complicated the care associated with epidurals. These side effects pale in comparison to PVB side effects, which include intercostal or nerve root injury, inadvertent epidural or spinal anesthesia, infection, pneumothorax and local anesthetic toxicity. Perhaps the most serious and often feared complication is pneumothorax, which has been reported to have an incidence of 1.1%(21). It is also important to note these side effects are predominantly a result of percutaneous insertions, similar to epidurals. However, in thoracotomy procedures, catheter placement in the intraoperative field eliminates these risks. Although this may be true for open thoracotomy insertions of PVB, it is recommended that percutaneous insertions be avoided in anticoagulated patients and treatment should be similar to neuraxial techniques(44). Therefore, even if a patient is anticoagulated, open paravertebral insertion is indicated over a percutaneous technique, although this has been suggested only as a relative contraindication(37). Table 2 is a summary of the side effects for each technique. Page 6 of 11 Table 2: Side Effect Profile for Epidural and Paravertebral Catheters Epidural Paravertebral Hypotension Intercostal or nerve root injury Urinary retention Inadvertent epidural or spinal Pruritus Infection Nausea and vomiting Pneumothorax Respiratory depression Incomplete block Headache Local anesthetic toxicity Incomplete block Infection Spinal cord injury (hematoma) Surgical techniques are constantly changing and in thoracic surgery VATS procedures are gaining momentum. Even though patients are spared a large thoracotomy incision, they are still subject to the development of chronic pain at an alarmingly high incidence(45,46). Some advocate VATS procedures should receive preoperative thoracic epidurals, especially if the risk of conversion to open thoracotomy is high(47). A PVB inserted intraoperatively is well suited to be placed in these patients, effectively removing the unnecessary risks associated with prophylactic epidural insertion. Physiologic Effects Studies have shown that a successful PVB with 5 dermatomes of somatic analgesia has an extra 3 dermatomes of sympathetic block and causes minimal heart rate and blood pressure changes(8,9). In one study(8), hypertension was observed without a change in heart rate. The authors speculated that unilateral vasodilation resulted in a compensatory increase in vascular resistance in the non‐blocked areas. The support for this hypothesis was based on the observed decrease in temperature of the non‐
blocked areas. Serum cortisol and glucose concentrations have been suggested to be measures of perioperative neuroendocrine stress response to surgery. Multiple studies have shown that PVB is associated with lower serum cortisol and glucose concentrations when compared to epidural analgesia(1,15,48). This has been shown both in thoracic and abdominal procedures. PVBs are unique in that they successfully block the sympathetic chain in the paravertebral space, which represents a possible mechanism for the reduced stress response observed. Summary The evidence is increasing showing PVBs are at least equal or superior to thoracic epidural blocks for post‐thoracotomy pain control. PVBs have a superior side effect and complication profile compared to epidurals. Despite this resurgence in the literature, many practitioners are doubtful of their efficacy, probably due to the confusion around what a true paravertebral block is. The percutaneous and open Page 7 of 11 insertion techniques have been well described in the literature and are relatively easy to learn. Studies that fail to show PVB benefit are likely inserting the block incorrectly or using too low a concentration of local anesthetic. The success of a PVB is also dependent on a complete multimodal therapy regimen that offers excellent pain relief while minimizing narcotic use. To date, PVB is considered a good block for unilateral incisions or conditions but in the future they may provide adequate pain control for midline incisions as well. Page 8 of 11 References 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. Richardson J, Sabanathan S, Jones J, Shah RD, Cheema S, Mearns AJ. A prospective, randomized comparison of preoperative and continuous balanced epidural or paravertebral bupivacaine on post‐thoracotomy pain, pulmonary function and stress responses. British journal of anaesthesia 1999;83:387‐92. Kaiser AM, Zollinger A, De Lorenzi D, Largiader F, Weder W. Prospective, randomized comparison of extrapleural versus epidural analgesia for postthoracotomy pain. The Annals of thoracic surgery 1998;66:367‐72. Joshi GP, Bonnet F, Shah R, Wilkinson RC, Camu F, Fischer B, Neugebauer EA, Rawal N, Schug SA, Simanski C, Kehlet H. A systematic review of randomized trials evaluating regional techniques for postthoracotomy analgesia. Anesthesia and analgesia 2008;107:1026‐40. Davies RG, Myles PS, Graham JM. A comparison of the analgesic efficacy and side‐effects of paravertebral vs epidural blockade for thoracotomy‐‐a systematic review and meta‐analysis of randomized trials. British journal of anaesthesia 2006;96:418‐26. Elsayed H, McKevith J, McShane J, Scawn N. Thoracic epidural or paravertebral catheter for analgesia after lung resection: is the outcome different? Journal of cardiothoracic and vascular anesthesia 2012;26:78‐82. Scarci M, Joshi A, Attia R. In patients undergoing thoracic surgery is paravertebral block as effective as epidural analgesia for pain management? Interactive cardiovascular and thoracic surgery 2010;10:92‐6. Karmakar MK. Thoracic paravertebral block. Anesthesiology 2001;95:771‐80. Saito T, Den S, Cheema SP, Tanuma K, Carney E, Carlsson C, Richardson J. A single‐injection, multi‐segmental paravertebral block‐extension of somatosensory and sympathetic block in volunteers. Acta anaesthesiologica Scandinavica 2001;45:30‐3. Cheema SP, Ilsley D, Richardson J, Sabanathan S. A thermographic study of paravertebral analgesia. Anaesthesia 1995;50:118‐21. Kaya FN, Turker G, Mogol EB, Bayraktar S. Thoracic paravertebral block for video‐assisted thoracoscopic surgery: single injection versus multiple injections. Journal of cardiothoracic and vascular anesthesia 2012;26:90‐4. Bonica JJ. Management of intractable pain with analgesic blocks. Journal of the American Medical Association 1952;150:1581‐6. Richardson J, Lonnqvist PA. Thoracic paravertebral block. British journal of anaesthesia 1998;81:230‐8. Kehlet H, Wilkinson RC, Fischer HB, Camu F, Prospect Working G. PROSPECT: evidence‐based, procedure‐specific postoperative pain management. Best practice & research Clinical anaesthesiology 2007;21:149‐59. Alaya M, Auffray JP, Alouini T, Bruguerolles B, Romdhani N, Said R, Ennabli K. [Comparison of extrapleural and intrapleural analgesia with bupivacaine after thoracotomy]. Annales francaises d'anesthesie et de reanimation 1995;14:249‐55. Richardson J, Sabanathan S, Mearns AJ, Evans CS, Bembridge J, Fairbrass M. Efficacy of pre‐
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