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Inflammatory changes after extradural anaesthesia may affect the spread of local anaesthetic within the extradural space
British Journal of Anaesthesia 1996;77:347–351
Inflammatory changes after extradural anaesthesia may affect the spread of local anaesthetic within the extradural space T. IGARASHI, Y. HIRABAYASHI, R. SHIMIZU, H. MITSUHATA, K. SAITOH, H. FUKUDA, A. KONISHI AND H. ASAHARA
Summary We have assessed cephalad spread of analgesia in 491 patients undergoing extradural anaesthesia at the L2–3 or L3–4 interspace. Patients were classified into one of three groups based on the number of previous lumbar extradural anaesthesia procedures: none (group I, n:339), one (group II, n:82), and two or more (group III, n:70). Cephalad spread of analgesia was greater in group I than in groups II and III, regardless of the puncture site. In addition, we examined the extradural space using a flexible extraduroscope in 32 patients who were excluded from the analysis of spread. Extraduroscopy showed the extradural space to be patent in patients with no history of prior lumbar extradural anaesthesia, but it was not clearly identified in patients who had received extradural anaesthesia one or more times because of aseptic inflammatory changes, including proliferation of connective tissue, adhesions between the dura mater and the ligamentum flavum, granulation and changes in the ligamentum flavum. Extradural anaesthesia may cause aseptic inflammatory changes in the extradural space which may reduce the spread of analgesia. (Br. J. Anaesth. 1996;77:347–351) Key words Anaesthetic techniques, extradural. Equipment, extradural space indicators.
Repeat extradural anaesthesia has been reported to be unreliable compared with initial extradural anaesthesia, resulting occasionally in unilateral or failed block1 2. However, the reasons for the unreliability of repeat extradural anaesthesia have not been investigated thoroughly. Extraduroscopy provides a clear view of the lumbar extradural space3 4. Therefore, we have studied the effects of repeat extradural anaesthesia on the spread of analgesia and on extraduroscopic findings.
Patients and methods The study was approved by the local Ethics Committee and informed consent was obtained from all patients. Data were obtained from 523 patients who received extradural anaesthesia for a variety of therapeutic or surgical procedures, including extra-
corporeal shock-wave lithotripsy, transurethral resection of the prostate and transurethral resection of bladder tumours. In order to estimate the effects of repeated extradural anaesthesia on the spread of analgesia, we assessed cephalad spread of analgesia in 491 patients undergoing lumbar extradural anaesthesia performed at the L2–3 or L3–4 interspace. Patients were classified into one of three groups based on the number of previous lumbar extradural anaesthesia procedures: none (group I, n:161 (L2–3), n:198 (L3–4)), one (group II, n:33 (L2–3), n:56 (L3–4)) and two or more (group III, n:26 (L2–3), n:49 (L3–4)). Patients with a history of prior extradural anaesthesia of the cervical, thoracic or sacral region were excluded. Each patient was premedicated with hydroxyzine 25–50 mg. Patients were then placed in the right lateral decubitus position on a horizontal operating table. A 17-gauge Tuohy needle was introduced at either the L2–3 or L3–4 interspace using the paramedian technique. The extradural space was identified using loss of resistance with a small amount of air. When no cerebrospinal fluid or blood flowed from the needle, 2 % mepivacaine 20 ml were injected into the extradural space via the needle over a period of 20 s. An extradural catheter (outside diameter 1 mm; Hakko, Tokyo, Japan) was inserted 5 cm in a cephalad direction into the extradural space, and the patient was placed in the supine position. Fifteen minutes after injection, the cephalad level of analgesia was determined using the pinprick test and referring to a dermatome chart5 by pre-selecting the dependent side to record. Additional local anaesthetic was administered via the catheter 15 min after the initial injection if the level of analgesia was inadequate for the planned therapeutic or surgical procedure. In order to evaluate the effects of repeated extradural anaesthesia on the extraduroscopic findings, we examined the lumbar extradural space in the other 32 patients. These patients underwent the TAKASHI IGARASHI, MD, YOSHIHIRO HIRABAYASHI, MD, REIJU SHIMIZU, MD, HIROMASA MITSUHATA, MD, KAZUHIKO SAITOH, MD, HIROKAZU FUKUDA, MD, Department of Anaesthesiology, Jichi Medical School, 3311-1 Yakushiji, Minamikawachi-machi, Kawachi-gun, Tochigi-ken 32904, Japan. AKIO KONISHI, MD, HIROZUMI ASAHARA, MD, Department of Anaesthesia, Mitsui Memorial Hospital, 1 Izumi-cho, Kanda, Chiyoda-ku, Tokyo 101, Japan. Accepted for publication: May 1, 1996. Correspondence to T.I.
348
British Journal of Anaesthesia
Figure 1 Photographs of the lumbar extradural space obtained by extraduroscopy in patients with no history of prior extradural anaesthesia. The views are cephalad. The extradural space in a 53-yr-old woman is observed as a patent canal (A). The upper part of the canal appears yellow and was identified as the ligamentum flavum. The lower part appears as a white membrane with associated blood vessels and was identified as the dura mater. Bleeding was induced by the introduction of the Tuohy needle in a 51-yr-old man (B). The connective tissue in a 55-yr-old woman was so fragile (C) that the extraduroscope was able to break it easily (D).
Results
same technique of extradural puncture and additional examination of the lumbar extradural space with a flexible fibrescope, either 0.5 or 0.8 mm in diameter (Olympus AF type 5 or type 8, Tokyo, Japan) immediately after identifying the extradural space. The fibrescope was connected to a television monitor system (Olympus OTV-A and CLV-A, Tokyo, Japan) and introduced into the extradural space easily through the Tuohy needle. Patients who underwent extraduroscopy were excluded from analysis of spread. Statistical analyses were performed with the StatView package version 4.02 (Abacus Concepts, CA, USA) on a Macintosh Quadra 650 (Apple Computer Inc., CA, USA). Age, weight and height are expressed as mean (SD or range), and values were compared using repeated measures analysis of variance after Dunn’s procedure. The level of analgesia is expressed as median (range), and values were compared using the Kruskal–Wallis test after Mann– Whitney’s U test. P0.05 was considered statistically significant.
Age, weight and height did not differ between the three groups of patients undergoing extradural anaesthesia at the L2–3 or L3–4 interspace (tables 1, 2). Cephalad spread of analgesia was greater in group I than in both groups II and III, regardless of the puncture site (tables 1, 2). There were no differences in cephalad spread of analgesia between groups II and III, regardless of the puncture site. Unilateral block was not observed in any of the patients examined. Figure 1 shows typical photographs obtained via the extraduroscope in patients with no history of prior extradural anaesthesia. The extradural space in a 53-yr-old woman was observed as a patent canal (fig. 1A). The upper part of the canal appeared yellow and was identified as the ligamentum flavum. The lower part appeared as a white membrane with associated blood vessels and was identified as the dura mater. The introduction of the Tuohy needle induced bleeding in a 51-yr-old man (fig. 1B). The connective tissue in a 55-yr-old woman (fig. 1C) was
Table 1 Age, height, weight and cephalad spread of analgesia in patients undergoing extradural anaesthesia at the L2–3 interspace (mean (SD or range)) or (median [range]). *P 0.05 vs group I
Table 2 Age, height, weight and cephalad spread of analgesia in patients undergoing extradural anaesthesia at the L3–4 interspace (mean (SD or range)) or (median [range]). *P 0.05 vs group I
Age (yr) Height (cm) Weight (kg) Cephalad spread
Group I (n:153)
Group II (n:30)
Group III (n:23)
50 (22–77) 161 (8) 61 (10)
52 (24–75) 162 (7) 61 (11)
54 (25–85) 161 (8) 63 (11)
T6 [T2–T11]
T7* [T4–T11] T8* [T2–T12]
Age (yr) Height (cm) Weight (kg) Cephalad spread
Group I (n:186)
Group II (n:52)
Group II (n:47)
53 (21–84) 163 (7) 61 (10)
57 (28–83) 161 (7) 62 (9)
54 (24–88) 162 (7) 64 (10)
T7 [T2–T11]
T8* [T3–T12]
T8* [T4–T12]
Effects of repeat extradural anaesthesia
349
Figure 2 Photographs of patients with a history of previous extradural anaesthesia. Connective tissue has proliferated and the extradural space cannot be identified as a patent canal in a 67-yr-old woman with a history of three prior extradural anaesthesia procedures (A). When the endoscope was withdrawn, a channel was observed (B). Adhesions are seen between the dura mater and the ligamentum flavum in a 72-yr-old man who had undergone extradural anaesthesia 1 month previously (C). Granulation is seen in a 61-yr-old man who underwent extradural anaesthesia 3 months previously (D).
so fragile that the extraduroscope was able to break it easily (fig. 1D). Figures 2 and 3 show typical photographs in patients with a history of previous extradural anaesthesia. The connective tissue had proliferated and the extradural canal could not be identified clearly in a 67-yr-old woman with a history of three prior extradural anaesthesia procedures (fig. 2A). The contents were a homogeneous fat pad without fibrous septation. It was possible to advance the extraduroscope through this connective tissue without resistance. When the extraduroscope was withdrawn, a channel produced by the scope was observed in the connective tissue (fig. 2B). Other extraduroscopic findings were as follows: adhesion between the dura mater and the ligamentum flavum in a 72-yr-old man who had undergone extradural anaesthesia 1 month previously (fig. 2C), granulation in a 61-yr-old man who had undergone extradural anaesthesia 3 months previously (fig. 2D), irregularities in the ligamentum flavum in a 68-yr-old man who had undergone extradural anaesthesia 1 month previously (fig. 3A) and irregular proliferation of connective tissue and blood vessels in a 64-yr-old man who had undergone extradural anaesthesia six times within a 3-yr period, the most recent 3 months previously (fig. 3B). This proliferation of connective tissue was seen to occlude the extradural space. We encountered no accidental dural punctures and observed no signs of neurological injury in any of our patients.
Discussion We have found that cephalad spread of analgesia was reduced in patients with a history of prior lumbar extradural anaesthesia, and extraduroscopic examin-
ation revealed significant inflammatory changes occluding the extradural space in these patients. These inflammatory changes may have affected the spread of local anaesthetic within the extradural space. Similar findings were observed in patients who had undergone only one prior extradural anaesthetic procedure, and the spread of analgesia in patients who had received extradural anaesthesia only once was similar to that in patients who had received extradural anaesthesia two or more times. Repeated extradural anaesthesia has been reported to be unreliable in patients undergoing extracorporeal shock-wave lithotripsy2. In our study, we confirmed the reduction in cephalad spread of analgesia in patients undergoing repeated extradural anaesthesia. Why does repeat extradural anaesthesia become unreliable? We suggest that inflammatory changes in the extradural space, resulting from prior extradural anaesthesia, may play an important role in limiting cephalad spread of analgesia. In this study, the inflammatory changes observed included proliferation of connective tissue, adhesions between the dura mater and the ligamentum flavum, and granulation and irregularities in the extradural space. Proliferation of connective tissue, whether homogeneous or irregular, occluding the extradural space may hinder cephalad spread of anaesthetic. Adhesions between the dura mater and the ligamentum flavum may also interfere with spread. Granulation and irregularities in the extradural space may interfere with penetration of anaesthetic into the spinal nerve roots because the anaesthetic is absorbed through the connective tissue. It should be noted, however, that this reduction in cephalad spread of analgesia was not observed in all patients undergoing repeat extradural anaesthesia.
350
British Journal of Anaesthesia
Figure 3 Photographs of patients with a history of prior extradural anaesthesia. Irregularities are seen in the ligamentum flavum in a 68-yr-old man who had undergone extradural anaesthesia 1 month previously (A). Irregular proliferation of connective tissue and blood vessels is observed in a 64-yr-old man who underwent extradural anaesthesia six times in a 3-yr period, the most recent 3 months previously (B).
Wide variations in the level of analgesia were seen in patients who underwent repeat extradural anaesthesia, and these variations were similar to those encountered in initial extradural anaesthesia. Inflammatory changes, including proliferation of connective tissue and adhesions between the dura mater and the ligamentum flavum, may play a role in limiting cephalad spread of anaesthetic. On the other hand, narrowing of the extradural space resulting from these inflammatory changes might be expected to increase cephalad spread of anaesthetic in repeat anaesthesia, as when the same volume of solution is injected into a narrower space, it might spread over a wider area. This may explain the observation that some patients with a history of prior extradural anaesthesia were found to have significant cephalad spread of analgesia. Therefore, the inflammatory changes in the extradural space alone cannot explain the variations in spread observed in patients undergoing repeat extradural anaesthesia. The specific findings observed by extraduroscopy may play an important role in determining the spread of local anaesthetics in extradural anaesthesia. The absence of any differences in the spread of analgesia between groups II and III is extremely interesting, and suggests that inflammatory changes can be induced by a single extradural anaesthesia procedure. However, the connective tissue after initial extradural anaesthesia differed from that seen after repeat anaesthesia. In the former, the connective tissue was found to be fragile and elastic, whereas in the latter case, it was dense and hard. When the extraduroscope was withdrawn, these differences were immediately obvious. The connective tissue was more easily broken in the former than in the latter. In our patients, prior extradural anaesthesia always involved introduction of a Tuohy needle and a catheter, followed by administration of local anaesthetic. Inflammatory changes induced by the introduction of an extradural catheter have been demonstrated in both animals6 7 and humans8 9. Administration of local anaesthetic alone may also cause inflammation6–10. In addition, bleeding induced by the introduction of the Tuohy needle was observed frequently in extraduroscopic examinations. The factors responsible for the inflammatory changes in the extradural space are unclear. In assessing the results of this study, we should also consider the fact that 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 cavity11 12. The introduction of air may therefore have affected our extraduroscopic findings, expanding the extradural space and stretching 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 our comparative findings. In addition, patients who underwent extraduroscopy were excluded from the analysis of spread, because extraduroscopy made channels in the extradural space and broke down the adhesions, thereby altering the spread of drug in the extradural space. The incidence of unilateral block after administration of local anaesthetic via a catheter has been reported to be higher in repeat block than in initial block1. In this study, we observed no unilateral block after administration of local anaesthetic via the needle. The laterality of the block may occur after administration of local anaesthetic via a catheter, presumably because of the misplaced catheter into the lateral side in the extradural space by aseptic inflammatory changes. Further observations are required. In summary, extradural anaesthesia caused inflammatory changes characterized by proliferation of connective tissue, adhesions and granulation, and irregularities in the extradural space. These inflammatory changes may affect the distribution of local anaesthetic within the extradural space.
References 1. Withington DE, Weeks SK. Repeat extradural analgesia and unilateral block. Canadian Journal of Anaesthesia 1994; 41: 568–571. 2. Korbon GA, Lynch C III, Arnold WP, Ross WT, Hudson SB. Repeated extradural anaesthesia for extracorporeal shockwave lithotripsy is unreliable. Anesthesia and Analgesia 1987; 66: 669–672. 3. Blomberg RG, Osson SS. The lumbar extradural space in patients examined with epiduroscopy. Anesthesia and Analgesia 1989; 68: 157–160. 4. Blomberg R. The dorsomedian connective tissue band in the lumbar extradural space of humans: An anatomical study using epiduroscopy in autopsy cases. Anesthesia and Analgesia 1986; 65: 747–752. 5. Cousins MJ, Bromage PR. Extradural neural blockade. In: Cousins MJ, Bridenbaugh PO, eds. Neural Blockade. Clinical
Effects of repeat extradural anaesthesia Anesthesia and Management of Pain, 2nd Edn. Philadelphia: JB Lippincott, 1988; 344. 6. Kyttä J, Rosenberg PH, Wahlstöm TR. Effects of continuous extradural administration of bupivacaine through a catheter in pigs. European Journal of Anaesthesiology 1986; 3: 473–480. 7. Larsen JJ, Svendsen O, Andersen HB. Microscopic extradural lesion in goats given repeated extradural injections of morphine: Use of a modified autopsy procedure. Acta Pharmacologica et Toxicologica 1986; 58: 5–10. 8. Brasseur L, Boura J, Brunet A-M, Gabriel P, Begon L, Descorps-Declere A. Failure of long-term extradural catheters. Anaesthesia 1987; 42: 557.
351 9. Brems-Dalgaard E, Just SL, Pedersen H. Encapsulated extradural catheter: CT findings. Neuroradiology 1991; 33: 81–82. 10. Steiness E, Rasmussen F, Svendsen O, Nielsen P. A comparative study of serum creatine phosphokinase (CPK) activity in rabbits, pigs and humans after intramuscular injection of local damaging drugs. Acta Pharmacologica et Toxicologica 1978; 42: 357–364. 11. Parkin IG, Harrison GR. The topographical anatomy of the lumbar extradural space. Journal of Anatomy 1985; 141: 211– 217. 12. Harrison GR. The extradural space. Anaesthesia 1989; 44: 361–362.
Inflammatory changes after extradural anaesthesia may affect the spread of local anaesthetic within the extradural space T. IGARASHI, Y. HIRABAYASHI, R. SHIMIZU, H. MITSUHATA, K. SAITOH, H. FUKUDA, A. KONISHI AND H. ASAHARA
Summary We have assessed cephalad spread of analgesia in 491 patients undergoing extradural anaesthesia at the L2–3 or L3–4 interspace. Patients were classified into one of three groups based on the number of previous lumbar extradural anaesthesia procedures: none (group I, n:339), one (group II, n:82), and two or more (group III, n:70). Cephalad spread of analgesia was greater in group I than in groups II and III, regardless of the puncture site. In addition, we examined the extradural space using a flexible extraduroscope in 32 patients who were excluded from the analysis of spread. Extraduroscopy showed the extradural space to be patent in patients with no history of prior lumbar extradural anaesthesia, but it was not clearly identified in patients who had received extradural anaesthesia one or more times because of aseptic inflammatory changes, including proliferation of connective tissue, adhesions between the dura mater and the ligamentum flavum, granulation and changes in the ligamentum flavum. Extradural anaesthesia may cause aseptic inflammatory changes in the extradural space which may reduce the spread of analgesia. (Br. J. Anaesth. 1996;77:347–351) Key words Anaesthetic techniques, extradural. Equipment, extradural space indicators.
Repeat extradural anaesthesia has been reported to be unreliable compared with initial extradural anaesthesia, resulting occasionally in unilateral or failed block1 2. However, the reasons for the unreliability of repeat extradural anaesthesia have not been investigated thoroughly. Extraduroscopy provides a clear view of the lumbar extradural space3 4. Therefore, we have studied the effects of repeat extradural anaesthesia on the spread of analgesia and on extraduroscopic findings.
Patients and methods The study was approved by the local Ethics Committee and informed consent was obtained from all patients. Data were obtained from 523 patients who received extradural anaesthesia for a variety of therapeutic or surgical procedures, including extra-
corporeal shock-wave lithotripsy, transurethral resection of the prostate and transurethral resection of bladder tumours. In order to estimate the effects of repeated extradural anaesthesia on the spread of analgesia, we assessed cephalad spread of analgesia in 491 patients undergoing lumbar extradural anaesthesia performed at the L2–3 or L3–4 interspace. Patients were classified into one of three groups based on the number of previous lumbar extradural anaesthesia procedures: none (group I, n:161 (L2–3), n:198 (L3–4)), one (group II, n:33 (L2–3), n:56 (L3–4)) and two or more (group III, n:26 (L2–3), n:49 (L3–4)). Patients with a history of prior extradural anaesthesia of the cervical, thoracic or sacral region were excluded. Each patient was premedicated with hydroxyzine 25–50 mg. Patients were then placed in the right lateral decubitus position on a horizontal operating table. A 17-gauge Tuohy needle was introduced at either the L2–3 or L3–4 interspace using the paramedian technique. The extradural space was identified using loss of resistance with a small amount of air. When no cerebrospinal fluid or blood flowed from the needle, 2 % mepivacaine 20 ml were injected into the extradural space via the needle over a period of 20 s. An extradural catheter (outside diameter 1 mm; Hakko, Tokyo, Japan) was inserted 5 cm in a cephalad direction into the extradural space, and the patient was placed in the supine position. Fifteen minutes after injection, the cephalad level of analgesia was determined using the pinprick test and referring to a dermatome chart5 by pre-selecting the dependent side to record. Additional local anaesthetic was administered via the catheter 15 min after the initial injection if the level of analgesia was inadequate for the planned therapeutic or surgical procedure. In order to evaluate the effects of repeated extradural anaesthesia on the extraduroscopic findings, we examined the lumbar extradural space in the other 32 patients. These patients underwent the TAKASHI IGARASHI, MD, YOSHIHIRO HIRABAYASHI, MD, REIJU SHIMIZU, MD, HIROMASA MITSUHATA, MD, KAZUHIKO SAITOH, MD, HIROKAZU FUKUDA, MD, Department of Anaesthesiology, Jichi Medical School, 3311-1 Yakushiji, Minamikawachi-machi, Kawachi-gun, Tochigi-ken 32904, Japan. AKIO KONISHI, MD, HIROZUMI ASAHARA, MD, Department of Anaesthesia, Mitsui Memorial Hospital, 1 Izumi-cho, Kanda, Chiyoda-ku, Tokyo 101, Japan. Accepted for publication: May 1, 1996. Correspondence to T.I.
348
British Journal of Anaesthesia
Figure 1 Photographs of the lumbar extradural space obtained by extraduroscopy in patients with no history of prior extradural anaesthesia. The views are cephalad. The extradural space in a 53-yr-old woman is observed as a patent canal (A). The upper part of the canal appears yellow and was identified as the ligamentum flavum. The lower part appears as a white membrane with associated blood vessels and was identified as the dura mater. Bleeding was induced by the introduction of the Tuohy needle in a 51-yr-old man (B). The connective tissue in a 55-yr-old woman was so fragile (C) that the extraduroscope was able to break it easily (D).
Results
same technique of extradural puncture and additional examination of the lumbar extradural space with a flexible fibrescope, either 0.5 or 0.8 mm in diameter (Olympus AF type 5 or type 8, Tokyo, Japan) immediately after identifying the extradural space. The fibrescope was connected to a television monitor system (Olympus OTV-A and CLV-A, Tokyo, Japan) and introduced into the extradural space easily through the Tuohy needle. Patients who underwent extraduroscopy were excluded from analysis of spread. Statistical analyses were performed with the StatView package version 4.02 (Abacus Concepts, CA, USA) on a Macintosh Quadra 650 (Apple Computer Inc., CA, USA). Age, weight and height are expressed as mean (SD or range), and values were compared using repeated measures analysis of variance after Dunn’s procedure. The level of analgesia is expressed as median (range), and values were compared using the Kruskal–Wallis test after Mann– Whitney’s U test. P0.05 was considered statistically significant.
Age, weight and height did not differ between the three groups of patients undergoing extradural anaesthesia at the L2–3 or L3–4 interspace (tables 1, 2). Cephalad spread of analgesia was greater in group I than in both groups II and III, regardless of the puncture site (tables 1, 2). There were no differences in cephalad spread of analgesia between groups II and III, regardless of the puncture site. Unilateral block was not observed in any of the patients examined. Figure 1 shows typical photographs obtained via the extraduroscope in patients with no history of prior extradural anaesthesia. The extradural space in a 53-yr-old woman was observed as a patent canal (fig. 1A). The upper part of the canal appeared yellow and was identified as the ligamentum flavum. The lower part appeared as a white membrane with associated blood vessels and was identified as the dura mater. The introduction of the Tuohy needle induced bleeding in a 51-yr-old man (fig. 1B). The connective tissue in a 55-yr-old woman (fig. 1C) was
Table 1 Age, height, weight and cephalad spread of analgesia in patients undergoing extradural anaesthesia at the L2–3 interspace (mean (SD or range)) or (median [range]). *P 0.05 vs group I
Table 2 Age, height, weight and cephalad spread of analgesia in patients undergoing extradural anaesthesia at the L3–4 interspace (mean (SD or range)) or (median [range]). *P 0.05 vs group I
Age (yr) Height (cm) Weight (kg) Cephalad spread
Group I (n:153)
Group II (n:30)
Group III (n:23)
50 (22–77) 161 (8) 61 (10)
52 (24–75) 162 (7) 61 (11)
54 (25–85) 161 (8) 63 (11)
T6 [T2–T11]
T7* [T4–T11] T8* [T2–T12]
Age (yr) Height (cm) Weight (kg) Cephalad spread
Group I (n:186)
Group II (n:52)
Group II (n:47)
53 (21–84) 163 (7) 61 (10)
57 (28–83) 161 (7) 62 (9)
54 (24–88) 162 (7) 64 (10)
T7 [T2–T11]
T8* [T3–T12]
T8* [T4–T12]
Effects of repeat extradural anaesthesia
349
Figure 2 Photographs of patients with a history of previous extradural anaesthesia. Connective tissue has proliferated and the extradural space cannot be identified as a patent canal in a 67-yr-old woman with a history of three prior extradural anaesthesia procedures (A). When the endoscope was withdrawn, a channel was observed (B). Adhesions are seen between the dura mater and the ligamentum flavum in a 72-yr-old man who had undergone extradural anaesthesia 1 month previously (C). Granulation is seen in a 61-yr-old man who underwent extradural anaesthesia 3 months previously (D).
so fragile that the extraduroscope was able to break it easily (fig. 1D). Figures 2 and 3 show typical photographs in patients with a history of previous extradural anaesthesia. The connective tissue had proliferated and the extradural canal could not be identified clearly in a 67-yr-old woman with a history of three prior extradural anaesthesia procedures (fig. 2A). The contents were a homogeneous fat pad without fibrous septation. It was possible to advance the extraduroscope through this connective tissue without resistance. When the extraduroscope was withdrawn, a channel produced by the scope was observed in the connective tissue (fig. 2B). Other extraduroscopic findings were as follows: adhesion between the dura mater and the ligamentum flavum in a 72-yr-old man who had undergone extradural anaesthesia 1 month previously (fig. 2C), granulation in a 61-yr-old man who had undergone extradural anaesthesia 3 months previously (fig. 2D), irregularities in the ligamentum flavum in a 68-yr-old man who had undergone extradural anaesthesia 1 month previously (fig. 3A) and irregular proliferation of connective tissue and blood vessels in a 64-yr-old man who had undergone extradural anaesthesia six times within a 3-yr period, the most recent 3 months previously (fig. 3B). This proliferation of connective tissue was seen to occlude the extradural space. We encountered no accidental dural punctures and observed no signs of neurological injury in any of our patients.
Discussion We have found that cephalad spread of analgesia was reduced in patients with a history of prior lumbar extradural anaesthesia, and extraduroscopic examin-
ation revealed significant inflammatory changes occluding the extradural space in these patients. These inflammatory changes may have affected the spread of local anaesthetic within the extradural space. Similar findings were observed in patients who had undergone only one prior extradural anaesthetic procedure, and the spread of analgesia in patients who had received extradural anaesthesia only once was similar to that in patients who had received extradural anaesthesia two or more times. Repeated extradural anaesthesia has been reported to be unreliable in patients undergoing extracorporeal shock-wave lithotripsy2. In our study, we confirmed the reduction in cephalad spread of analgesia in patients undergoing repeated extradural anaesthesia. Why does repeat extradural anaesthesia become unreliable? We suggest that inflammatory changes in the extradural space, resulting from prior extradural anaesthesia, may play an important role in limiting cephalad spread of analgesia. In this study, the inflammatory changes observed included proliferation of connective tissue, adhesions between the dura mater and the ligamentum flavum, and granulation and irregularities in the extradural space. Proliferation of connective tissue, whether homogeneous or irregular, occluding the extradural space may hinder cephalad spread of anaesthetic. Adhesions between the dura mater and the ligamentum flavum may also interfere with spread. Granulation and irregularities in the extradural space may interfere with penetration of anaesthetic into the spinal nerve roots because the anaesthetic is absorbed through the connective tissue. It should be noted, however, that this reduction in cephalad spread of analgesia was not observed in all patients undergoing repeat extradural anaesthesia.
350
British Journal of Anaesthesia
Figure 3 Photographs of patients with a history of prior extradural anaesthesia. Irregularities are seen in the ligamentum flavum in a 68-yr-old man who had undergone extradural anaesthesia 1 month previously (A). Irregular proliferation of connective tissue and blood vessels is observed in a 64-yr-old man who underwent extradural anaesthesia six times in a 3-yr period, the most recent 3 months previously (B).
Wide variations in the level of analgesia were seen in patients who underwent repeat extradural anaesthesia, and these variations were similar to those encountered in initial extradural anaesthesia. Inflammatory changes, including proliferation of connective tissue and adhesions between the dura mater and the ligamentum flavum, may play a role in limiting cephalad spread of anaesthetic. On the other hand, narrowing of the extradural space resulting from these inflammatory changes might be expected to increase cephalad spread of anaesthetic in repeat anaesthesia, as when the same volume of solution is injected into a narrower space, it might spread over a wider area. This may explain the observation that some patients with a history of prior extradural anaesthesia were found to have significant cephalad spread of analgesia. Therefore, the inflammatory changes in the extradural space alone cannot explain the variations in spread observed in patients undergoing repeat extradural anaesthesia. The specific findings observed by extraduroscopy may play an important role in determining the spread of local anaesthetics in extradural anaesthesia. The absence of any differences in the spread of analgesia between groups II and III is extremely interesting, and suggests that inflammatory changes can be induced by a single extradural anaesthesia procedure. However, the connective tissue after initial extradural anaesthesia differed from that seen after repeat anaesthesia. In the former, the connective tissue was found to be fragile and elastic, whereas in the latter case, it was dense and hard. When the extraduroscope was withdrawn, these differences were immediately obvious. The connective tissue was more easily broken in the former than in the latter. In our patients, prior extradural anaesthesia always involved introduction of a Tuohy needle and a catheter, followed by administration of local anaesthetic. Inflammatory changes induced by the introduction of an extradural catheter have been demonstrated in both animals6 7 and humans8 9. Administration of local anaesthetic alone may also cause inflammation6–10. In addition, bleeding induced by the introduction of the Tuohy needle was observed frequently in extraduroscopic examinations. The factors responsible for the inflammatory changes in the extradural space are unclear. In assessing the results of this study, we should also consider the fact that 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 cavity11 12. The introduction of air may therefore have affected our extraduroscopic findings, expanding the extradural space and stretching 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 our comparative findings. In addition, patients who underwent extraduroscopy were excluded from the analysis of spread, because extraduroscopy made channels in the extradural space and broke down the adhesions, thereby altering the spread of drug in the extradural space. The incidence of unilateral block after administration of local anaesthetic via a catheter has been reported to be higher in repeat block than in initial block1. In this study, we observed no unilateral block after administration of local anaesthetic via the needle. The laterality of the block may occur after administration of local anaesthetic via a catheter, presumably because of the misplaced catheter into the lateral side in the extradural space by aseptic inflammatory changes. Further observations are required. In summary, extradural anaesthesia caused inflammatory changes characterized by proliferation of connective tissue, adhesions and granulation, and irregularities in the extradural space. These inflammatory changes may affect the distribution of local anaesthetic within the extradural space.
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