Thoracic and lumbar extradural structure examined by extraduroscope

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1 British Journal of Anaesthesia 1998; 81: CLINICAL INVESTIGATIONS Thoracic and lumbar extradural structure examined by extraduroscope T. IGARASHI, Y. HIRABAYASHI, R. SHIMIZU, K. SAITOH AND H. FUKUDA Summary We examined the extradural space using a flexible extraduroscope in 113 patients undergoing extradural anaesthesia. Patients were classified into two groups to receive either thoracic or lumbar extradural anaesthesia as needed for perioperative analgesia. The extraduroscopy showed that the thoracic extradural space becomes widely patent after injecting a given amount of air and that the amount of fatty and fibrous connective tissue is less in the thoracic extradural space compared with the lumbar extradural space. We suggest that differences between the structure of these two vertebral regions may affect the spread of local anaesthetics in the extradural space. (Br. J. Anaesth. 1998; 81: ) Keywords: anaesthetic techniques, extradural; anatomy, extradural space; measurement techniques, extraduroscope Many investigators have described differences in dose requirement of local anaesthetics depending on the site of injection for extradural anaesthesia. 1 4 Several authors have reported a reduction in thoracic dose requirement compared with lumbar extradural dose requirements. 5 6 However, the reasons for this reduction in thoracic dose requirement have not been thoroughly investigated. Several factors may contribute to the different dose requirements, including the size of the underlying nerve roots, 7 8 the thickness of their coverings 5 and the negati ve intrapleural pressures. 3 Differences in the anatomy of the extradural space associated with the vertebral regions may affect the spread of local anaesthetics. Some of these factors have been assessed by magnetic resonance imaging 9 or the direct measurement of extradural pressures. 10 As extraduroscopy can provide a clear view of die extradural space, we used this technique to investigate the differences in the structure of different regions in the extradural space. Patients and methods This study was approved by our Local Ethics Committee and informed consent was obtained from all patients. We examined the extradural space with a flexible fibrescope in 115 patients undergoing extradural anaesthesia for a variety of surgical or therapeutic procedures including hysterectomy, oophorectomy, knee arthroscopy, total knee arthroplasty, total hip arthroplasty, transurethral resection of the prostate, transurethral resection of bladder tumours, thoracotomy and upper and lower abdominal surgery. Patients with a history of previous extradural anaesthesia, pregnancy, neurological disease, abnormalities of vertebral column or abdominal distension were excluded. Patients were classified into two groups according to the site of the extradural anaesthesia as needed for perioperative analgesia: the thoracic group (n 63) and the lumbar group (n 52). The extradural anaesthesia was carried out between the Th7 and Th10 in the thoracic group and L2 L3 interspace in the lumbar group. Each patient was premedicated with hydroxyzine 25 to 50 mg and atropine 0.25 to 0.5 mg. The patient was placed in the right lateral decubitus position on a horizontal operating table. A 17-gauge Tuohy needle was introduced at either the thoracic or lumbar interspace, using the paramedian technique. The extradural space was identified using the loss-ofresistance method with 5 ml of air. When no cerebrospinal fluid or blood flowed from the needle, these patients underwent examination of the lumbar extradural space with a flexible fibresccpe measuring 0.7 mm in diameter (Igarashi Ika Kogyo Co., MS-501, Tokyo, Japan) which was connected to a television monitor system (Igarashi Ika Kogyo Co., FY-2000E, Tokyo, Japan). The extraduroscope was introduced approximately 10 cm in a cephalad direction into the extradural space via the Tuohy needle. No air was injected after the insertion of the extraduroscope in each patient. If paraesthesia or resistance were noted during extraduroscope insertion, no attempt was made to advance the extraduroscope through the area of resistance. Consequently, two patients in the lumbar group in whom the extraduroscope could not be advanced more than 5 cm cephalad were excluded from the analysis. Extraduroscopic findings were continuously recorded on a video recorder during the fibrescopic examination in each patient. After the extraduroscopic examination, an extradural catheter (od, 0.85 mm, B. Brown, Bethlehem, PA, USA) was inserted 5 cm in a cephalad direction into the extradural space and the patient was then placed in the supine position. All procedures were performed by the same anaesthetist. The patients received local anaesthetics via the catheter during the planned therapeutic or surgical procedure, with or without general anaesthesia. TAKASHI IGARASHI, MD, YOSHIHIRO HIRABAYASHI, MD, REIJU SHIMIZU, MD, KAZUHIKO SAITOH, MD, HIROKAZU FUKUDA, MD, Department of Anaesthesiology, Jichi Medical School, Yakushiji, Minamikawachi-machi, Kawachi-gun, Tochigi-ken , Japan. Accepted for publication: February 24, Correspondence to T. I.

122 British Journal of Anaesthesia The extraduroscopic findings in our 113 patients were analysed by two independent investigators who did not have access to the patients medical histories.

2 122 British Journal of Anaesthesia The extraduroscopic findings in our 113 patients were analysed by two independent investigators who did not have access to the patients medical histories. Furthermore, they were unaware as to whether the extraduroscopy was in the lumbar or thoracic space. The extraduroscopic findings were divided into five categories for analysis: patency of the extradural space after injecting air, amount of fatty tissue, amount of fibrous connective tissue, degree of pulsation and degree of vascularity. The patency of the extradural space was scored using the following grading system: 1 very narrow, 2 patent and 3 widely patent. The other four areas of analysis were scored using the following grading system: 1 none, 2 moderate and 3 considerable. To reach consensus when a discrepancy between two observers in each finding was noted, the difference was resolved by a third experienced investigator. The third investigator was required for 17 patients to give an opinion for the patency of the extradural space, for 20 patients for the amount of fatty tissue, for 25 patients for the amount of fibrous connective tissue, for 15 patients for the degree of pulsation and for 27 patients for the degree of vascularity, all within a total group of 113 patients. Statistical analyses were carried out using a statistical software package (StatView V4.02, Abacus Concepts, CA, USA) on a personal computer (Macintosh Quadra 650, Apple Computer Inc., CA, USA). Mean (SD) values for age, weight, height, body mass index and body surface area, and median (range) values for each extraduroscopic finding between the lumbar and the thoracic groups were compared using the Mann-Whitney U test. A P value less than 0.05 was considered statistically significant. Results Age, height and weight were comparable between the thoracic and lumbar groups (table 1). Extraduroscopic examination (fig. 1) revealed that patency of the extradural space after injecting air was greater (P ), the amount of fatty (P ) and fibrous connective tissue (P ) was less and the degree of pulsation was more remarkable (P ) in the thoracic group than in the lumbar group. No significant differences were detected between the groups in the findings of vascularity. Figure 2 shows typical findings of the thoracic extradural space. The thoracic extradural space in a 55-yr-old man was observed as a widely patent canal owing to the injected air (fig. 2A). The upper part appeared as a gray membrane and was identified as the dura mater associated with blood vessels, while the lower part of the canal was identified as the ligamentum flavum and the periosteal layer. The few stretched fibrous connective tissues were scattered among the patent canal in the same patient (fig. 2B). Beyond the fibrous connective tissues, fatty tissue was also seen to be thinly spaced. Figure 3 shows typical findings of the lumbar extradural space. The narrow extradural space made by the injected air was seen in the upper part of the photograph in a 57-yr-old man (fig. 3A).The upper part of the canal that appeared as a grey membrane was identified as the dura mater. The lower part of the photograph appeared as a white membrane and was identified as the periosteal layer. The fibrous connective tissues joined together and formed a membranous structure between the dura mater and the periosteal layer. As the extraduroscope was Table 1 Patient characteristics. Mean (SD) [range] Thoracic group (n 63) Lumbar group (n 50) P Age (yr) 60 (10) [41 74] 56 (12) [40 73] NS Height (cm) 157 (8) [ ] 155 (8) [ ] NS Weight (kg) 56 (8) [38 79] 56 (7) [41 75] NS Body mass index (kg m 2 ) 23 (3) [18 30] 23 (3) [18 31] NS Body surface area (m 2 ) 1.56 (0.18) [ ] 1.53 (0.17) [ ] NS Figure 1 Extraduroscopic findings in the thoracic and lumbar groups. Open bars indicate score 1, solid bars indicate score 2 and shaded bars indicate score 3. Significant differences between the groups were found in the median values for patency of the extradural space after injecting air (P ), amount of fatty tissue (P ), amount of fibrous tissue (P ) and degree of pulsation (P ). No significant differences between the groups were found with respect to the median values for degree of vascularity.

The upper part appeared as a gray membrane and was identified as the dura mater with associated blood vessels, while the lower part of the canal was identified as the ligamentum flavum and the

3 Thoracic and lumbar extradural structure 123 Figure 2 Photographs obtained via the thoracic extraduroscope in a 55-yr-old man. The thoracic extradural space was observed as a widely patent canal owing to the injected air (A). The upper part appeared as a gray membrane and was identified as the dura mater with associated blood vessels, while the lower part of the canal was identified as the ligamentum flavum and the periosteal layer. The few stretched fibrous connective tissues were scattered among the patent canal in the same patient (B). Beyond the fibrous connective tissues, fatty tissue was also seen to be thinly spaced. In this patient, patency of the extradural space after injecting air, amount of fatty tissue, fibrous connective tissue, degree of pulsation and vascularity were scored as 3, 2, 2, 3, and 2 respectively. Figure 3 Photographs obtained via the lumbar extraduroscope in a 57-yr-old man. The narrow extradural space made by the injected air was seen in the upper part of the photograph (A). The upper part of the canal that appeared as a gray membrane was identified as the dura mater. The lower part of the photograph appeared as a white membrane and was identified as the periosteal layer. The fibrous connective tissues joined together and formed a membranous structure between the dura mater and the periosteal layer. A large amount of fatty tissue was seen to be under tension and tightly adherent to the dura mater and the periosteal layer as the extraduroscope was advanced (B). The extradural canal appeared to be very short and narrow because of the presence of a large amount of fatty and fibrous connective tissue. In this patient, patency of the extradural space after injecting air, amount of fatty tissue, fibrous connective tissue, degree of pulsation and vascularity were scored as 1, 3, 3, 1, and 2 respectively. advanced, a large amount of fatty tissue was seen to be under tension and tightly adherent to the dura mater and the periosteal layer (fig. 3B). The extradural space appeared to be very short and narrow because of the presence of a large amount of fatty and fibrous connective tissues. We encountered no accidental dural punctures and observed no signs of persistent neurological injury in any of our patients. Discussion In this study, extraduroscopic examination showed that the patency of extradural space after injecting air was more and the amount of fatty and fibrous connective tissue was less in the thoracic extradural space than in the lumbar extradural space. We suggest that the amount of fatty and fibrous connective tissue in the extradural space may play an important role in determining the patency of the extradural space after injecting air, thereby affecting the longitudinal spread of anaesthetic solution in the different sites of the extradural space. 5 6 We found that the patency of the extradural space, which was made by 5 ml of air injected into the space, was greater in the thoracic region than in the lumbar region. This difference in the patency of the extradural space after injecting a given amount of air between these two vertebral regions may be influenced by the negative intrapleural and positive intraabdominal pressures. Because the extradural pressure is lower in the thoracic region than in the lumbar region, 14 thoracic extradural space may be easier to enlarge after the injection of air compared with the lumbar extradural space. In addition, the thoracic vertebral canal is smaller than the lumbar vertebral canal in transverse size. 15 A given amount of air may presumably produce a longer canal in the thoracic extradural space, rather than in the lumbar extradural space. Therefore, the longitudinal spread of local anaesthetics may be related to the findings of the patency of the extradural space after injecting air, as well as the size of the vertebral canal. In this study, the amount of fatty tissue observed in the extradural space was less in the thoracic than in the lumbar region. The lumbar extradural space is reported to be packed tightly with rigid fat. 16 Because the lumbar vertebrae are able to move by large ranges of flexion, extension and rotation, 17 the large amount of fatty tissue in the lumbar extradural space serves as a cushion for the spinal cord and this may hinder the spread of local anaesthetics. In addition, the amount of fatty tissue in each vertebral region may be a possible reason for the ranges of patency of the extradural space after injecting air. It is reported that a catheter is easily inserted for a longer distance without kinking in the thoracic than in the lumbar extradural space. 18 Increasing amounts of fatty tissue in the lumbar extradural space may simultaneously increase the power of adhesion between fatty tissue and other tissue such as the dura mater and the ligamentum flavum. Therefore, the thoracic extradural space becomes more compliant and less resistant, and patency of the extradural space after injecting air alters according to the vertebral region. Other connective tissues except for fatty tissue were observed as strands or membranes in the extradural space and we defined them as fibrous connective tissue in this study. These fibrous connective tissues exist among fatty tissue, the dura mater and the periosteal layer, and the amount of fibrous connective tissue revealed a statistically significant difference between thoracic and lumbar extradural space. The fibrous connective tissues joined together and formed a membranous structure in the lumbar extradural space, while in the thoracic extradural space they remained as a strand structure. In some cases, the thin and fragile membrane structures were observed as an incomplete partition in the lumbar extradural space. Along with the amount of fatty tissue, a large amount of fibrous connective tissue in the lumbar extradural space may decrease the longitudinal

4 124 British Journal of Anaesthesia spread of anaesthetic solution by increasing the power of adhesion among the dura mater, the ligamentum flavum and fatty tissue. The pulsation of the dural sac may reflect the cerebrospinal fluid pulse wave. The pulse wave is composed of spinal vascular (arterial and venous) pulsation and the intracranial pulse wave transmitted through the spinal canal from the intracranial space to lumbar level. 19 Because the pulse wave of the cerebrospinal fluid is less at lower vertebral levels, 19 the pulsation of the dural sac was more significant in the thoracic than in the lumbar extradural space. A marked pulsation of the thoracic dural sac may, at least in part, support the findings of the great patency of the thoracic extradural space after injecting air because the thoracic dural sac may become more movable by separating from the fatty and the fibrous connective tissues after this injection. Several factors may have influenced our results. The extradural space was observed after introducing a small amount of air. The extradural space is sometimes described as a potential space, rather than a true cavity The introduction of air might have expanded the extradural space and stretched the connective tissues. However, in our study, all patients received identical extradural punctures and the effects of the air introduced into the extradural space should have been similar in all cases. Therefore, we believe that this factor had no influence on a comparative study. We found fatty tissue existed like segmental parts in the extradural space as the fibrescope was introduced in a cephalad direction. Sagittal mid-line magnetic resonance imaging 22 and cryomicrotomy 23 have shown that the extradural fatty tissue is divided into segments by the interposing laminae in the lower thoracic and lumbar regions. In this study, extradural structures could be observed mainly from the point where fatty tissue did not exist. Nevertheless the patency of the extradural space after injecting air was similar regardless of whether or not fatty tissue was present. In this study, thoracic extradural anaesthesia was performed at one point within the Th7 10 interspace, and the extraduroscope was introduced approximately 10 cm in a cephalad direction from the Tuohy needle tip. In the patients of the lumbar group, the tip of the fibrescope could reach the level a little less than Th12 when the extraduroscope was introduced 10 cm in a cephalad direction from the L2 3 interspace. Therefore, we compared anatomical differences between the middle thoracic and upper lumbar extradural space. In the lower thoracic and lumbar segments, the extradural space has been suggested to be transversely divided into three compartments: anterior, dorsal and dorsolateral The extraduroscope may have advanced through the dorsal compartment into other compartments in the two patients who were excluded from this analysis. Nerve irritations during the extraduroscopic procedures may be closely associated with the fact that the extraduroscope touched the nerve roots after the passage of the extraduroscope through the dorsal compartment into the other compartments. In this study, the tip of the Tuohy needle was introduced into the extradural space as precisely in the midline as possible and no evidence was detected that the extraduroscope advanced into the other compartments in any patients, so the findings were presumably of the dorsal compartment within the extradural space. Before beginning this study, we considered whether air might be an appropriate injectate in the extradural space. We could not obtain a clear view of the extradural space using the loss-of-resistance method with saline because the saline adhered to the tip of the fibrescope. Therefore, we used air for the loss-of-resistance method and minimized its amount to 5 ml in this study. The extraduroscopic findings would have had more rigour if some objective measurements, such as a ratio of the object s area to the visible area, had been made. However, because of the characteristics of the magnifying lens, the ratio could change according to the portion of the visible area or the distance between the tip of the fibrescope and the objects. Therefore we opted for semiquantitative analysis with the arbitrary type of scoring rather than precise measurements. To ensure objectivity, the extraduroscopic findings were reviewed by independent investigators who did not have access to the patients medical histories. Finally, the patients were classified into two groups according to the site of the extradural anaesthesia as needed for perioperative analgesia. Although we should consider the possibility that non-randomization of the two groups of patients could have influenced the outcome of this study, it is unlikely to have any bearing on the extraduroscopic findings. In summary, extraduroscopy showed that the thoracic extradural space becomes widely patent after injecting a given amount of air and that the amount of fatty and fibrous connective tissue diminishes in the thoracic extradural space compared with the lumbar extradural space. We suggest that the differences in the structure between these two vertebral regions may affect the spread of local anaesthetics in the extradural space. References 1. Frumin MJ, Schwartz H, Burns JJ, Brodie BB, Papper EM. Site of sensory during segmental spinal and segmental peridural anesthesia in man. Anesthesiology 1953; 14: Foldes FF, Colavincenzo JW, Birch JH. Epidural anesthesia: reappraisal. Anesthesia and Analgesia 1956; 35: Bromage PR. Mechanism of action of extradural analgesia. British Journal of Anaesthesia 1975; 47: Park WY. Factors influencing distribution of local anesthetics in the epidural space. Regional Anesthesia 1988; 13: Bromage PR. Mechanism of action. In: Bromage PR, eds. Epidural Analgesia. Philadelphia: WB Saunders, 1978; Bernards CM. Epidural and spinal anesthesia. In: Barash P, Cullen B, Stoelting R, eds. Clinical Anesthesia. 3rd Edn. Philadelphia: Lippincott-Raven, 1996; Bonica JJ, Backup PH, Anderson CE, Hadfield D, Crepps WF, Monk BF. Peridural block; an analysis of 3637 cases and a review. Anesthesiology 1957; 18: Bromage PR. Physiology and pharmacology of epidural anesthesia. Anesthesiology 1967; 28: Hirabayashi Y, Saitoh K, Fukuda H, Igarashi T, Shimizu R, Seo N. Magnetic resonance imaging of the extradural space of the thoracic spine. British Journal of Anaesthesia 1997; 79: Hirabayashi Y, Shimizu R, Matsuda I, Inoue S. Effect of extradural compliance and resistance on spread of extradural analgesia. British Journal of Anaesthesia 1990; 65:

5 Thoracic and lumbar extradural structure Blomberg R. The dorsomedian connective tissue band in the lumbar epidural space of humans: An anatomical study using epiduroscopy in autopsy cases. Anesthesia and Analgesia 1986; 65: Blomberg RG, Olsson SS. The lumbar epidural space in patients examined with epiduroscopy. Anesthesia and Analgesia 1989; 68: Igarashi T, Hirabayashi Y, Shimizu R, Saitoh K, Fukuda H, Mistuhata H. The lumbar extradural structure changes with increasing age. British Journal of Anaesthesia 1997; 78: Usubiaga JE, Wikinski JA, Usubiaga LE. Epidural pressure and its relation to spread of anesthetic solutions in epidural space. Anesthesia and Analgesia 1967; 46: Cheng PA. Anatomical and clinical aspects of epidural anesthesia. Anesthesia and Analgesia 1963; 42: Southworth JL, Hingson RA, Pitkin WM. Conduction Anesthesia. 2nd Edn. Philadelphia: JB Lippincott, 1953; Epstein BS. The normal spine. In: Epstein BS, ed. The spine; a radiological text and atlas, 3rd Edn. Philadelphia: Lea and Febiger, 1969; Muneyuki M, Shirai K, Inamoto A. Roentgenographic analysis of the positions of catheters in the epidural space. Anesthesiology 1970; 33: Urayama K. Origin of lumbar cerebrospinal fluid pulse wave. Spine 1994; 19: Harrison GR. The epidural space. [Letter]. Anaesthesia 1989; 44: Parkin IG, Harrison GR. The topographical anatomy of the lumbar epidural space. Journal of Anatomy 1985; 141: Westbrook JL, Renowden SA, Carrie LES. Study of the extradural region using magnetic resonance imaging. British Journal of Anaesthesia 1993; 71: Hogan QH. Epidural anatomy examined by cryomicrotome section. Regional Anesthesia 1996; 21: Seeling W, Tomczak R, Merk J, Mrakovcic N. Comparison of conventional and computed tomographic epidurography with contrast medium using thoracic epidural catheters. Anaesthesist 1995; 44: Savolaine E, Pandya J, Greenblatt S, Conover S. Anatomy of the human lumbar epidural space: New insights using CT-epidurography. Anesthesiology 1988; 68:

Materials and Methods. t Lecturer. i. Professor and Chair.

Materials and Methods. t Lecturer. i. Professor and Chair. ~~ Downloaded From: http://anesthesiology.pubs.asahq.org/pdfaccess.ashx?url=/data/journals/jasa/931792/ on 09/15/2018 1631 Anesthesiology 2000; 921631-6 0 2000 American Society of Anesthesiologists, Inc