Distribution of Local Anesthetic in Axillary Brachial Plexus Block

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Anesthesiology 2002; 96:1315–24 © 2002 American Society of Anesthesiologists, Inc. Lippincott Williams & Wilkins, Inc. Distribution of Local Anesthetic in Axillary Brachial Plexus Block A Clinical and Magnetic Resonance Imaging Study Øivind Klaastad, M.D.,* Orjan¨ Smedby, Dr.Med.Sci.,† Gale E. Thompson, M.D.,‡ Terje Tillung, R.T.,§ Per Kristian Hol, M.D.,ʈ Jan S. Røtnes, D.M.Sc.,# Per Brodal, D.M.Sc.,** Harald Breivik, D.M.Sc.,†† Karl R. Hetland, M.D.,‡‡ Erik T. Fosse, D.M.Sc.§§

Background: There is an unsettled discussion about whether injected local anesthetic, inadequate concentration of the distribution of local anesthetic is free or inhibited when the anesthetic, or unintentional movement of the needle performing brachial plexus blocks. This is the first study to use or the patient. In 1927, Labat4 proposed that the answer Downloaded from http://pubs.asahq.org/anesthesiology/article-pdf/96/6/1315/335346/0000542-200206000-00009.pdf by guest on 01 October 2021 magnetic resonance imaging (MRI) to help answer this question. could be found in an appreciation of “minute anatomy.” Methods: Thirteen patients received axillary block by a cath- He stated that a solution injected on one side of a fascia eter–nerve stimulator technique. After locating the median normally does not reach the other side of that fascia. nerve, a total dose of 50 ml local anesthetic was injected via the Thompson and Rorie5 made similar observations using catheter in four divided doses of 1, 4, 15, and 30 ml. Results of computed tomography of patients with axillary blocks sensory and motor testing were compared with the spread of local anesthetic as seen by MRI scans taken after each dose. The and histologic examination of the brachial plexus from distribution of local anesthetic was described with reference to cadavers. They concluded that fascial compartments ex- a 20-mm diameter circle around the artery. ist for each nerve of the plexus and that these fascial Results: Thirty minutes after the last dose, only two patients barriers serve to limit circumferential (cross-sectional) demonstrated analgesia or anesthesia in the areas of the radial, spread of injected local anesthetic solutions. Conse- median, and ulnar nerve. At that time, eight of the patients had incomplete spread of local anesthetic around the artery, as seen quently, they recommended injecting into multiple 6 7 by MRI. Their blocks were significantly poorer than those of the sites. Partridge et al. also studied cadavers but ques- five patients with complete filling of the circle, although incom- tioned the functional importance of these fascial complete blocks were also present in the latter group. partments based on the spread of injected methylene Conclusion: This study demonstrated that MRI is useful in blue dye. This view is similar to that of Winnie et al.,8 examining local anesthetic distribution in axillary blocks because it can show the correlation between MRI distribution who described a perivascular concept for brachial pattern and clinical effect. The cross-sectional spread of fluid plexus blocks. They claimed that only a single needle around the brachial–axillary artery was often incomplete–in- insertion is necessary because the injected solution lo- hibited, and the clinical effect often inadequate. cates the various nerves to be blocked.8 The controversy regarding whether the spread of local anesthetic is free BRACHIAL plexus blocks may often give patchy and or inhibited has still not been settled.9 Therefore, the delayed anesthesia in one or more nerves.1–3 Among the aim of the current study was to contribute to the solu- many proposed explanations are inadequate volume of tion of this question. We hoped to gain new information about the distribution of local anesthetic by taking re- Additional material related to this article can be found on the peat magnetic resonance images after injections of local ANESTHESIOLOGY Web site. Go to the following address, click on anesthetic and then correlating these images with the the Enhancements Index, and then scroll down to find the sensory and motor status of the upper extremity. appropriate article and link. http://www.anesthesiology.org.

Materials and Methods * Staff Anesthesiologist, Department of Anesthesiology, ‡‡ Staff Surgeon, De- partment of Hand Surgery, Oslo Orthopedic University Hospital. † Professor, The Interventional Centre, Rikshospitalet University Hospital, and Department of After obtaining approval of the protocol from the re- Radiology, University Hospital Linköping, Linköping, Sweden. ‡ Staff Anesthe- gional ethical committee (Regional Komite´ for Medisinsk siologist, Department of Anesthesiology, The Mason Clinic, Seattle, Washington. § Radiological Technologist, ʈ Staff Radiologist, # Senior Scientist, §§ Professor Forskningsetikk, Helseregion II, Oslo, Norway), 14 adult and Chairman, The Interventional Centre, †† Professor and Chairman, Depart- patients scheduled for elective hand or forearm surgery ment of Anesthesiology, Rikshospitalet University Hospital. ** Professor, De- partment of Anatomy, University of Oslo, Oslo, Norway. gave written, informed consent to participate in the Received from Oslo Orthopedic University Hospital and The Interventional study. The same investigator performed all blocks. An Centre, Rikshospitalet University Hospital, Oslo, Norway. Submitted for publica- 18-gauge cannula (Contiplex®A/D; B. Braun, Melsungen, tion September 7, 2001. Accepted for publication February 6, 2002. Support was provided solely from institutional and/or departmental sources. Presented in part Germany) with an outside short catheter (length, 45–55 at the 19th Annual Congress of the European Society of Regional Anesthesia and mm) was inserted approximately 4 cm distal to the Pain Therapy, Rome, Italy, September 22, 2000. Address reprint requests to Dr. Klaastad: Rikshospitalet University Hospital, lateral border of the pectoralis major muscle and imme- Department of Anesthesiology, Sognsvannsveien 20, 0027 Oslo, Norway. diately superior to the brachial artery, while the patients Address electronic mail to: [email protected]. Individual article reprints may be purchased through the Journal Web site, abducted the arm approximately 90° (ﬁg. 1A). The can- www.anesthesiology.org. nula–catheter was directed toward the axilla and parallel

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Fig. 1. (A) Illustration of the point of needle insertion. The patient is in a supine position with the right arm abducted 90° and maximally rotated externally, exposing the medial surface of the arm. The cannula with an outside catheter was inserted immediately superior to the brachial artery, approximately 4 cm distal to the lateral border of the pectoralis major muscle. It was directed toward the axilla, parallel to the artery. The initial cannula angle to the skin was 30–40°. After fascial click, the cannula–catheter was advanced (aided by a nerve stimulator) with a flat angle to the skin. The catheter was taped in median nerve–stimulating position. Subsequently, the cannula was withdrawn and a flexible extension tube was connected to the catheter for later injections of local anesthetic. (B) Schematic cross-sectional drawing from the right arm illustrating the quadrant system around the brachial artery and the common position of the four terminal nerves. The musculocutaneous nerve is usually found in the deep superior quadrant (Q1), the median nerve in the superficial superior quadrant (Q2), the ulnar nerve in the superficial inferior quadrant (Q3), and the radial nerve in the deep inferior quadrant (Q4). The terms deep and superficial refer to the medial surface of the arm. to the artery with an initial needle angle to the skin of local anesthetic injection. Scanning and clinical testing 30–40°. After “fascial click,”10 the cannula–catheter was were also repeated 10, 20, and 30 min after the last dose advanced with a flat angle to the skin, aided by a periph- and at a variable time after the end of surgery. eral nerve stimulator (Stimuplex®DIG/HNS11; B. Braun). Giving the total dose of local anesthetic in divided Continuous suction (using a syringe) was applied to the doses, with MRI performed between each dose, was cannula to detect inadvertent intravascular position of its expected to yield a better dynamic impression of the tip. Muscle twitches distinctive for median nerve stimu- local anesthetic distribution than after a single large lation were sought with a maximum current of 0.5 mA bolus dose. In particular, the position of the 1-ml dose in and an impulse width of 0.1 ms. The catheter was fixed the cross-sectional MRI plane would indicate if the cath- in this nerve-stimulating position, the cannula was with- eter tip had an appropriate position in this plane, close drawn, and the catheter was connected to a flexible to the brachial–axillary artery. extension tube for later injection of local anesthetic. The Imaging was performed with an open 0.5 T GE Signa extension tube had a dead space of 0.5 ml and was SP scanner (GE Medical, Milwaukee, WI). Twenty-two prefilled with local anesthetic solution. sagittal images, covering the lateral part of the clavicle as Subsequently, the patients entered the magnetic reso- well as the proximal part of the abducted arm, were nance imaging (MRI) scanner. Its open design allowed acquired with a T2-weighted fast-spin echo sequence the patients to be supine with the arm abducted 90°. The (repetition time, 7,700 ms; effective echo time, 95 ms; local anesthetic was injected in divided doses (1, 4, 15, slice thickness, 4 mm; slice interval, 4 mm; matrix, and 30 ml) at a speed of approximately 0.5 ml/s and with 128 ϫ 256; field of view, 32 ϫ 24 cm). The images were 10 min between each dose. The total volume was always evaluated by the radiology team, who were blinded to 50 ml, usually as 1% lidocaine with 5 ␮g/ml epinephrine. the clinical effect. In case of longer operations, allowance was made for The local anesthetic distribution was studied in sagittal replacing some of the lidocaine with 0.5% bupivacaine. MRI slices, giving cross-sectional views of the neurovas- No contrast agent was added. To limit distal spread, cular bundle with the brachial plexus. A circle was digital compression was applied at the insertion site drawn in the images with a diameter of 20 mm and during and for 1 min after the injection of the second, center in the midaxis of the brachial–axillary artery (fig. third, and fourth dose. 1B). The circle was divided into four quadrants. With A sequence of MRI scanning and block assessment reference to the 90° abducted arm, the quadrants were (sensory and motor testing) was performed after each named according to the terminology of Thompson and

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Fig. 2. (A–I) Cross-sectional images from the proximal right arm of patient no. 11 showing complete spread of 1% lidocaine with 5 ␮g/ml epinephrine. Scans were taken before the first dose; after each of the four local anesthetic injections (10 min apart); 10, 20, and 30 min after the Downloaded from http://pubs.asahq.org/anesthesiology/article-pdf/96/6/1315/335346/0000542-200206000-00009.pdf by guest on 01 October 2021 last dose; and once postoperatively (134 min after the last dose). In (A) and (H), a 20-mm diameter circle with center in the midaxis of the artery was drawn, showing the four quadrants (Q1,Q2,Q3,Q4). The first dose (1 ml) contacted the artery in Q2 and Q3. After the last dose, all quadrants were completely filled. Thirty minutes after the last dose, the patient had anesthesia of all main terminal nerves except for the axillary nerve, as at the time of the postoperative scan. She un- derwent surgery for a trigger finger (thumb) without pain.

6 Brown : the deep superior quadrant (Q1), the superficial the fifth metacarpal. To avoid metal disturbance in the superior quadrant (Q2), the superficial inferior quadrant scanner, a pinprick test was performed using a sharp- ϭ (Q3), and the deep inferior quadrant (Q4), at both the ened toothpick, repeatedly touching the skin (0 nor- brachial and axillary artery levels. For each quadrant, we mal; 1 ϭ hypalgesia, patient felt sharp touch but less recorded whether the fluid filled the quadrant area in- than normal; 2 ϭ analgesia, patient felt touch but not side the circle (not considering the area of the artery and sharp; 3 ϭ anesthesia, patient did not feel touch). Motor muscle tissue) completely (score 2) or partially (score 1), tests of the corresponding nerves were abduction of the or whether fluid was not present (score 0). Two groups arm, flexion of the elbow, extension of the fingers–wrist, of patients were defined according to the cross-sectional flexion of the second finger, and abduction of the fin- distribution of local anesthetic 30 min after the last dose. gers. The motor power was scored as follows: 0 ϭ Patients in the complete-spread group had all quadrants normal power, 1 ϭ slightly reduced power, 2 ϭ moder- filled, determined by counting quadrants in the same ately or strongly reduced power, 3 ϭ no power (paral- slice or filled quadrants from all anatomic levels imaged ysis). To avoid change of arm position in the preopera- (fig. 2). Patients in the incomplete-spread group lacked tive scanning period, no motor test was performed on complete filling of one or more quadrants, even when all the axillary and musculocutaneous nerves until the last slices were considered (figs. 3 and 4). Longitudinally, the preoperative scan had been made. A correlation test was most proximal and most distal slices containing local performed based on the status 30 min after the last dose anesthetic fluid were determined. The distance between of local anesthetic, comparing the local anesthetic dis- these images was the longitudinal extension of the fluid. tribution as seen by MRI and its sensory–motor effect. A Clinical assessment included sensory and motor func- complete spread of local anesthetic (filling of all quad- tion of the axillary, musculocutaneous, radial, median, rants) was expected to result in block of all the main and ulnar nerves. The sensory testing points were as terminal nerves, whereas incomplete spread would be follows: laterally and in the middle of the proximal half associated with an incomplete block. of the arm, over the brachioradial muscle (5 cm distal to the elbow joint), between the first and second metacar- Statistic Analysis pals on the dorsal side, between the second and third Descriptive data are presented as mean, range, and metacarpals on the volar side, and on the medial side of standard deviation. The spread of the fluid in the MRI

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Fig. 3. (A–I) Sagittal images of the right infraclavicular region of patient no. 8 showing imcomplete spread of 1% lidocaine with 5 ␮g/ml epinephrine. The ﬁrst dose was not convincingly seen at the given anatomic level. Subsequent doses

filled Q2 but not the other three quad- Downloaded from http://pubs.asahq.org/anesthesiology/article-pdf/96/6/1315/335346/0000542-200206000-00009.pdf by guest on 01 October 2021 rants. However, Q3 and Q4 were filled at other anatomic levels. Only Q1 was not filled in any image. Thirty minutes after the last dose, the patient had analgesia of the musculocutaneous, median, and ulnar nerves, but there was no effect on the radial and axillary nerves. The block was sufficient for excision of the nail of the fifth finger. At the time of the postoperative scan (112 min after the last dose), the block had progressed to anesthesia of all main terminal nerves except for the axillary nerve.

scans was analyzed by studying the maximum spread eter tip was calculated to end, on average, 7 mm prox- among all slices and comparing the four quadrants at imal to the lateral border of this muscle (range, 25 mm each time point with the Friedman test, computed with distal to 45 mm proximal to this reference). The nerve StatView 5.0 (SAS Institute Inc., Cary, NC). The sensory stimulator technique was abandoned in two patients effect in the five nerves of the arm (as well as the motor (nos. 12 and 13) because of difficulties finding an appro- effect in the three distal nerves) was also compared priate motor response. Instead, the “fascial click” tech- at each time point with the Friedman test. The clinical nique was applied. In the remaining 11 patients, the effect in the groups with complete and incomplete median nerve was stimulated in all cases by an average of spread of the fluid 30 min after the last dose was com- 0.24 mA (range, 0.15–0.50 mA). Three patients (nos. 4, pared with an unpaired Wilcoxon test and computed 9, and 13) had an unintended arterial puncture. There with JMP 3.1 (SAS Institute Inc.). Results were consid- were no signs of catheter dislocation from clinical in- ered significant at P Ͻ 0.05. spection. Ten patients received the local anesthetic as 50 ml of 1% lidocaine with 5 ␮g/ml epinephrine. The remaining three patients (nos. 2, 3, and 4) were given a Results 50-ml mixture of 200 mg bupivacaine, 100 mg lidocaine, The patient population included 11 men and 3 and 50 ␮g epinephrine. Only patient no. 1 had a supple- women, with an American Society of Anesthesiologists mentary dose given via the catheter, immediately before physical status I or II. A technical breakdown of the MRI start of surgery. scanner caused one of the women (no. 10) to be ex- The local anesthetic was distinctly seen on MRI scans cluded from further analysis. The age, height, and weight and did not obliterate arteries or nerves (figs. 2–4). The of the remaining 13 patients were 51 Ϯ 13 yr (range, fluid demarcation tended to be irregular in outline. In the 30–73 yr), 176 Ϯ 10 cm (range, 156–191 cm), and reference images (before the injection of the 1-ml dose), 82 Ϯ 16 kg (range, 61–105 kg), respectively. The hand extravasated blood or hematoma could not be definitely surgery lasted 47 Ϯ 44 min (range, 14–155 min). The discerned, even in the three patients in whom an arterial point of needle insertion was superior to the artery and, puncture occurred. Of the 22 images acquired in each on average, was 38 mm (range, 10–50 mm) distal to the MRI scan, an average of 17 (range, 13–22) were of good lateral border of the pectoralis major muscle. The cath- enough quality for scoring the fluid in the cross-sectional

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Fig. 4. (A–I) Cross-sectional images from the proximal right arm of patient no. 1 showing extraordinary incomplete spread of 1% lidocaine with 5 ␮g/ml epinephrine. The first dose is seen in Q3, not contacting, but still close to the artery. Subsequent doses were located very superficially. Thirty minutes after the last dose, only Q3 was completely filled, and Downloaded from http://pubs.asahq.org/anesthesiology/article-pdf/96/6/1315/335346/0000542-200206000-00009.pdf by guest on 01 October 2021 there was no fluid in Q1, even when considering all anatomic levels. At that time, there was analgesia only of the ulnar nerve. At 60 and 80 min after the last dose, the median and musculocutaneous nerves demonstrated analgesia. At the start of surgery (95 min after the last dose), 29 ml of 1% lidocaine with 1.6 ␮g/ml epinephrine was given via the catheter to pro- long and possibly enhance the block. Ex- cept for some light tourniquet pain, the block was satisfactory for the 80-min pal- mar surgery. (I) At the time this image was taken, 125 min after the top-up dose, the block had progressed to anesthesia of the median nerve, but still without analgesia of the radial nerve.

plane. For patient no. 4, images were not obtained length of longitudinal spread inside the circle was 10 min after the last dose (technical reason) and post- 92 mm (range, 32–128 mm). operatively (the patient was too sedated). The degree of cross-sectional spread also increased The initial 1-ml dose of local anesthetic spread over after each dose and remained unchanged during the several levels (longitudinally) and usually engaged more 30 min after the last dose (fig. 6). Thirty minutes after the than one quadrant (cross-sectionally), both inside (fig. 5) last dose, all but one patient (no. 1) had some fluid in all and outside the circle. In one of the patients (no. 9), the quadrants. Five patients had all quadrants completely filled 1-ml dose could not be recognized, and in another (no. (complete-spread group), whereas eight lacked complete 1), the lateral border was outside the scanned area. filling of at least one quadrant (incomplete-spread group)

Among the remaining 11 patients, the longitudinal (figs. 2–5). In general, the two superficial quadrants (Q2 spread of the 1-ml dose inside the circle was, on and Q3) had a higher degree of fluid filling than the two average, 36 mm (range, 24– 64 mm). Except for pa- deep quadrants (Q1 and Q4). The difference between quad- tient nos. 1 and 8, the 1-ml dose touched the artery in rants was significant after the two last doses but did not all patients. approach significance 10 min or more after the end of After administration of each of the subsequent three injection (fig. 6). Postoperative scans taken at 155 min doses, the longitudinal local anesthetic spread increased (range, 110–226 min) after the last dose still showed con- until the last dose had been given and stayed unchanged siderable volumes of fluid surrounding the artery. for the next 30 min. Thirty minutes after the last dose, Figure 7 shows that, 30 min after the last dose, a higher the proximal border of the fluid was outside the scanned degree of analgesia or anesthesia was found for the area in one patient (no. 12). In the remaining 12 patients, median and ulnar nerves (92 and 69%, respectively) than the proximal border was, on average, 8 mm proximal to for the axillary, musculocutaneous, and radial nerves (0, the humeral head (range, 32 mm proximal to 16 mm 38, and 38%). Significant differences between the nerves distal to this reference). The distal border of the fluid were present at all times except for after the first two was definable only in three patients, either because it doses (1 and 4 ml). Only one of 13 patients (no. 11, in was outside the scanned area or because of poor image the complete-spread group) demonstrated surgical anes- quality. With this uncertainty, the average measured thesia (analgesia or anesthesia) in the areas of the mus-

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Fig. 5. Magnetic resonance imaging quadrant scores. The diagram describes the magnetic resonance imaging distribution of local anesthetic for each patient (nos. P01–P14) at 10-min intervals (from the ﬁrst dose until 30 min after the last dose) and at a variable postoperative time. When considering all anatomic levels,

the best ﬂuid score of each quadrant (Q1, Q2,Q3,Q4) is recorded. Patient nos. 4, 7, 9, 11, and 14 belong to the complete- spread group of patients (all quadrants ﬁlled 30 min after the last dose).

culocutaneous, median, ulnar, and radial nerves. Surgery block than the incomplete-spread group 30 min after the was allowed after supplementary peripheral blocks in last dose (table 1). Nevertheless, blocks were insufficient five patients (nos. 3, 4, 5, 9, and 13) and general anes- in the complete-spread group (fig. 7). The motor block thesia in one patient (no. 12, who also had supplemen- developed similarly to the sensory block. Only when tary peripheral blocks). considering the three distal nerves was the motor block Comparing MRI distribution and clinical effect, the significantly better in the complete-spread group than in complete-spread group had a significantly better sensory the incomplete-spread group (table 1). The proximal

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musculocutaneous nerves, our results are comparable to those of several recent studies on axillary blocks with injection into a single site.1–3,12 Because the axillary and musculocutaneous nerves leave the neurovascular bundle proximally, we primarily assumed that the poor effect on these nerves was caused by the short proximal spread in our study, e.g., compared with results of Ya- momoto et al.12 The short proximal fluid spread observed in our study was a result of the distal catheter tip position and probably the reduced proximal thrust of local anesthetic injection (slow injection rate, local anesthetic not given as a bolus dose). On the other hand, Downloaded from http://pubs.asahq.org/anesthesiology/article-pdf/96/6/1315/335346/0000542-200206000-00009.pdf by guest on 01 October 2021 Fig. 6. Maximum fluid score (0, 1, or 2) over all anatomic levels for each quadrant and each point in time; means for all pa- we found no correlation between the proximal spread tients. Significance levels for the difference between quadrants and the sensory–motor effect of any nerve studied, in- are indicated at all times. cluding the axillary and musculocutaneous nerves. Al- though Yamomoto et al.12 confirmed that the proximal spread did not correlate to the sensory or motor effect spread is inhibited by 90° arm abduction during injec- on any nerve. tion compared with 0° abduction, arm position had no Additional information regarding this is available on the impact on the sensory block of any of the brachial ANESTHESIOLOGY Web site at http://www.anesthesiology.org. plexus nerves in their study, as also found by Koscielniak-Nielsen et al.13 Discussion In the cross-sectional plane, the low current sufficient for stimulating the median nerve indicated that the cath- The current study was undertaken to help determine eter tips were very close to this nerve initially. Although whether the distribution of local anesthetic is free or there was a risk of catheter dislocation by arm movements inhibited when using axillary blocks. On patients receiv- on entering the scanner, in most cases the 1-ml dose was ing such blocks, we repeatedly compared the clinical found by MRI to contact the brachial–axillary artery. Thus, effect of divided doses of local anesthetic injected into a the catheter tips most likely maintained an appropriate single site with its spread as seen by MRI. cross-sectional position during the injections. A cross-sectional view at our approximate average in- To our knowledge, the current study is the first to use jection site (the lateral border of the pectoralis major MRI to investigate local anesthetic distribution by a bra- muscle) should show the three distal brachial plexus chial plexus block technique. We wanted to determine nerves (the radial, median, and ulnar) closely surround- whether the local anesthetic reached or surrounded the ing the artery. The axillary nerve (regularly) and the brachial plexus nerves. Because, in a preliminary inves- musculocutaneous nerve (in approximately half the tigation, we found that the terminal nerves were often cases) leave the neurovascular bundle more proximal- indistinguishable from small vessels, we had to make this ly.11 If the cross-sectional distribution of local anesthetic description differently. Given the known proximity of were free, one would therefore expect the 50-ml local the axillary–brachial artery and the brachial plexus anesthetic deposit to readily block the median, ulnar, nerves, we expected all or most of the nerves to be and radial nerves (none of them demanding a proximal found inside a small circle concentrically around the spread). But of the 13 patients in our study, only two had artery. The literature gives few clues for an appropriately the median, ulnar, and radial nerves sufficiently blocked sized circle. De Jong14 described the brachial plexus for surgery 30 min after the last dose. Only the median sheath at the axillary level with a diameter of 2–3cm.A nerve, toward which the local anesthetic was primarily circle with a 30-mm diameter included disproportion- intended, showed satisfactory effect. This alone suggests ately more muscle tissue in our images. We decided to an inhibited cross-sectional spread. The MRI results cor- use a circle with a 20-mm diameter because it gave a roborate this impression. Although the first dose (1 ml) better MRI fit and agreed with our impression from was on target (touching or close to the artery), in the dissection of human cadavers. With free cross-sectional majority of the patients the full dose did not completely spread of local anesthetic, the 50-ml dose should fill all surround the axillary–brachial artery 30 min after the quadrants of such a circle in one or more images and last dose. These patients showed a significantly poorer give a complete block at least of the three distal nerves. clinical effect than the smaller group of patients with On the contrary, inhibited spread would give incom- local anesthetic completely surrounding the artery. plete circle filling and incomplete block. The clinical effect of the method used in this study may It is noteworthy that patients with complete filling of at first appear surprisingly poor. However, except for the circle demonstrated incomplete blocks. This could the lacking and inconsistent effect on the axillary and indicate that our circle was too small to regularly em-

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Fig. 7. Sensory block effect. The diagram shows the sensory block effect of each patient (nos. P01–P14) over time. Nerves tested were the axillary (Ax), musculocutaneous (MC), median (Med), ulnar (Uln), and radial (Rad). Postoperative sensory scores for patient nos. 3, 4, 5, 9, 12, and 13 cannot be related to magnetic resonance imaging scores at this time because these patients received supplementary peripheral blocks (after the last preoperative scan). Patient nos. 4, 7, 9, 11, and 14 belong to the complete-spread group.

brace all relevant nerves or that some structure inhibited bundle: The fascial compartment surrounding a nerve sufﬁcient local anesthetic access to the nerves. When impeded local anesthetic contact with the nerve. Ex- Thompson and Rorie5 made the same observation in tending this view, one may speculate that, if a needle or their computed tomography study—that nerves could catheter is located on the inside (nerve side) of a fascial stay unblocked although the local anesthetic totally compartment, e.g., with ambitious use of a nerve stimu- surrounded the artery—they considered this a sign of lator at minimal amperage, such a position would facili- the non-unicompartmental nature of the neurovascular tate the block of that nerve but hamper the local anes-

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Table 1. Comparing Magnetic Resonance Imaging Spread and Clinical Effect

All Patients Complete Spread Incomplete Spread (n ϭ 13) (n ϭ 5) (n ϭ 8) Wilcoxon Test

Sensory score (ﬁve nerves) 7.4 8.8 6.5 P Ͻ 0.05 Sensory score (three nerves) 5.7 7.0 4.9 P Ͻ 0.05 Motor score (ﬁve nerves) 6.7 9.4 5.0 ns Motor score (three nerves) 4.9 6.8 3.8 P Ͻ 0.05

The table shows sensory and motor scores of three groups of patients (all patients, the complete spread group, and the incomplete spread group) with regard to five nerves (axillary, musculocutaneous, median, ulnar, and radial) and three nerves (median, ulnar, and radial). A four-graded scale (0, 1, 2, 3) was used for both the sensory and the motor scores. With five and three nerves tested, the highest possible scores were 15 and 9, respectively. The Wilcoxon test demonstrated that the complete spread group had a significantly better sensory score than the incomplete spread group. The motor blocking effect was

significantly better in the complete spread group only when considering the three distal nerves (median, ulnar, and radial). Downloaded from http://pubs.asahq.org/anesthesiology/article-pdf/96/6/1315/335346/0000542-200206000-00009.pdf by guest on 01 October 2021 thetic spread to the other nerves. This could be an (median, ulnar, and radial), although not always to the explanation for our sometimes surprising finding of an- same degree. Therefore, connections between the com- esthesia only in the area of the stimulated median nerve. partments of the neurovascular bundle were postulated In the 30-min period of local anesthetic injections, as not inhibiting the distribution of local anesthetic, and there was more fluid in the superficial than in the deep multiple injections were judged unnecessary for per- quadrants. This fits with our better clinical effect on forming axillary blocks. Considering the rapid spreading median and ulnar nerves (both usually superficially lo- capacity of methylene blue, we believe that there may be cated) than on the radial (usually deeper located). Dur- little correlation between the spread of methylene blue ing the 10–30 min after the last dose and postopera- in cadavers and local anesthetics in patients. In our tively, no significant difference between superficial and study, the results of limited spread determined by MRI deep fluid filling was seen. This indicates that some agree with limited clinical effect in the same patients. cross-sectional spread must have taken place. However, The remarkable large and irregular area of local anes- the clinical effect on the radial nerve remained poor, thetic in our cross-sectional images questions the con- possibly because of delayed distribution. Taken to- cept of a sturdy, tubular brachial plexus sheath, confin- gether, these findings suggest that inhibited cross-sec- ing the fluid injected inside of it.14 The fate and rate of tional spread remains the most likely explanation for absorption of the pooled solution is also of great intrigue insufficient clinical effect on the radial nerve. because much of the anesthetic volume seems to be Limitations of our study include the lack of a stringent “unused” or unnecessary in producing the block. Future protocol in performing the block: the position of the studies would benefit from MRI scanners that could catheter tip varied, in two patients the fascial click was delineate terminal nerves17 and their inclusion or exclu- used instead of the nerve stimulator, and three patients sion from the pooled anesthetic. The ability to correlate received a mixture of two local anesthetics in stead of images with clinical effect is essential for further under- the standard local anesthetic. However, the duration of standing of why different brachial plexus blocks may all local anesthetics used was long enough to cover the vary in efficiency. 30-min postinjection scan. Furthermore, there is an un- In conclusion, the current combined clinical and MRI certainty about how well our circle in the MRI scans study demonstrated that MRI is useful for the study of embraces all the nerves of interest. Finally, the small local anesthetic distribution in axillary blocks, showing number of patients in our study and the known variabil- correlation between MRI distribution pattern and clini- ity of nerve positions around the artery15 did not allow a cal effect. The cross-sectional spread of fluid around the more detailed study of the relation between the filling of brachial–axillary artery was often incomplete–inhibited, separate quadrants and clinical effect on the individual and the clinical effect was often inadequate. nerves. Our study agrees with the findings and conclusions of The authors thank Kari Ruud (Technician, Department of Anatomy, University of Oslo, Oslo, Norway) for preparing figures 1A and B. Thompson and Rorie.5 In their computed tomography study, in which injections were made into multiple sites, the local anesthetic tended to stay in isolated pockets. References

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