British Journal of Anaesthesia 1995; 74: 41-45 Spread of subarachnoid hyperbaric amethocaine in adolescents Y. HIRABAYASHI, R. SHIMIZU, K. SAITOH, H. FUKUDA Summary We have compared the spread of subarachnoid hyperbaric amethocaine in adolescents with that in adults. Amethocaine 8 mg in 2 ml of 10% glucose was injected through a 25-gauge spinal needle inserted at the L3-4 interspace in 21 adolescents aged 12-16 yr and in 111 adults aged 17-82yr. Although we found no differences in height, weight or body mass index between the adolescents and adults, maximum spread of analgesia was significantly higher in the adolescents (median T3 (range C5)) than in the adults (T4 (T9-C7)). We conclude that subarachnoid injection of hyperbaric amethocaine produces an unexpectedly higher level of analgesia in adolescents than in adults. (Br. J. Anaesth. 1995; 74: 41-45) Key words Anaesthetic techniques, subarachnoid amethocaine. Anaesthetics local, Although the influence of age, height, weight and body mass index on the spread of spinal anaesthesia with hyperbaric amethocaine has been reported in adults [1], there are no objective data on the correlation between these variables and the spread of spinal anaesthesia with hyperbaric amethocaine in adolescents. We experienced several instances during which subarachnoid injection of hyperbaric amethocaine produced an unexpectedly higher level of analgesia in adolescents. This study was conducted, therefore, to see if subarachnoid injection of a uniform dose of hyperbaric amethocaine produced a higher level of analgesia in adolescents than in adults. Patients and methods We studied 132 patients, ASA I II, undergoing minor orthopaedic or lower abdominal surgery. After approval by the Hospital thics Committee, informed consent was obtained from the patients or parents. The patients were allocated to two s according to age: adolescent (12-16 yr, n = 21) and adult (17-82 yr, n = 111). All patients were devoid of known neurological or spinal disease and had no contraindications to spinal anaesthesia. None of the patients was premedicated. Patients were placed in the lateral position on a horizontal operating table. Under aseptic conditions lumbar puncture was performed at the L3 4 interspace with a 25-gauge uincke needle using a median approach. The needle was inserted with its bevel oriented parallel to the dural fibres and then rotated 90 to direct the bevel cephalad. The correct position of the needle was confirmed by aspiration and re-injection of 0.1 ml of CSF before and after administration of the drug. Amethocaine 8 mg in 2 ml of 10 % glucose was given over 40 s. Immediately after subarachnoid injection, the patients were gently turned to the supine horizontal position. No attempt was made to influence the level of sensory block by manipulating the operating table. The level of analgesia to pinprick was determined bilaterally 5, 10, 15, 20, and 60 min after subarachnoid injection according to a dermatomal chart [2]. If the levels of analgesia obtained differed, the average value was used for analysis. Motor block was assessed by a modified Bromage score (0 = ability to raise the extended legs; 1 = inability to raise the extended legs; 2 = inability to flex the knee; 3 = inability toflex the ankle) at the same time intervals. Statistical analyses were performed with the StatView package version 4.0 (Abacus Concepts, CA, USA) on a Macintosh LC575 (Apple Computer Inc., CA, USA). The adolescent and adult s were compared by Student's unpaired t test for parametric data and the Mann-Whitney U test for non-parametric data. Correlation between height, weight or body mass index and maximum spread of analgesia was evaluated by the Spearman rank correlation coefficient. A regression curve of the number of analgesic segments was calculated by polynomial regression model. P < 0.05 was considered to be significant. Results There were no differences in height and weight between the two s (table 1). The adolescents had reached their full height but not yet gained full body mass, while no statistical difference in body mass index was found between the two s (P = 0.0581). Subarachnoid injection of hyperbaric amethocaine 8 mg produced a higher level of analgesia in the adolescent than in the adult at each assessment YOSHIHIRO HIRABAYASHI, MD, RIJU SHIMIZU, MD, KAZUHIKO SAITOH, MD, HIROKAZU FUKUDA, MD, Department of Anaesthesiology, Jichi Medical School, Tochigi, 329-04 Japan. Accepted for publication: July 22, 1994. Correspondence to Y.H.
British Journal of Anaesthesia 42 Table 1 Mean (SD and range) patient characteristics in the adolescent and adult s Age (yr) Height (cm) Weight (kg) Body mass index (kg m-2) Sex (M/F) Adolescent Adult 14.1 (12-16) 162 (9.7) (143-178) 56 (10.7) (-79) 21.1 (2.4) (16.8-25.4) 13/8 37.3 (17-82) 162(9.1) (141-185) 60(12.3) (40-99) 22.7 (3.6) (16.2-36.8) 56/55 C4-j C6C8- I T2^ to T6T8T10 1.3 (T4.5-( o a 1.6 1.7 Height (m) 1.8 1.9 C8T2<T9-C8)<T9.5-C7.5] (T10-T2) T5- CD 1.5 C6- (C5) T3-1.4 t C4- T1 -i <D t.t 03 T7 T9T11 T6- '3! T8- (L2-T3) 5 T10 10 15 20 60 Time (min) Figure 1 Median (range) spread of analgesia after subarachnoid injection of amethocaine 8 mg in 2 ml of 10% glucose at each assessment time in the adolescent (O) and adult ( ) s. *P = 0.0001, -(-P = 0.0002 between s. 50 C 70 Weight (kg) 110 90 o o 0 C6- o C8T2-0 oc Table 2 Maximum spread of analgesia, times from subarachnoid injection of amethocaine to maximum spread of analgesia and to total motor block in the legs in the adolescent and adult s (median (range) or mean (SD)). ***P = 0.0001 Maximum spread of analgesia Time to max. spread (min) Time to total motor block (min) Adolescent Adult T3 (C5)*** T4(T9-C7) 19(7.8) 21 (10) 9 (3.9) 10(5.8) time (fig. 1). Maximum spread of analgesia was higher in the adolescent than in the adult (P = 0.0001) (table 2). The times from subarachnoid injection to maximum spread of analgesia and to total motor block in the legs did not differ between s (table 2). The maximum spread of analgesia in both the adolescent and adult s was plotted against height, weight and body mass index (fig. 2). There was no correlation between height, weight or body mass index and level of analgesia in any of the s. Maximum spread of analgesia was plotted against age (fig. 3). In adolescents, subarachnoid injection of hyperbaric amethocaine 8 mg produced higher levels T6 T8T1010 15 20 * 25 35 40 BMI (kg Figure 2 Maximum spread of analgesia in the adolescent (O) and adult ( # ) s vs height (A), weight (B) and body mass index (BMI) (c). Maximum spread of analgesia in adolescents did not correlate with height (p = -0.28), weight (p = -0.36) or body mass index (p = 0.29). Maximum spread of analgesia in adults did not relate to height (p = 0.04), weight (p = -0.10) or body mass index (p = -0.09). of analgesia. In adults, it provided mid-thoracic levels of analgesia, irrespective of age. Discussion We have shown that subarachnoid injection of hyperbaric amethocaine unexpectedly produced a higher level of analgesia in adolescents than in adults. If adolescents had a significantly smaller height, weight and body mass index compared with adults, this finding would not be surprising. However, in this study, adolescents had the same height, weight and body mass index as adults. The most extended spread of analgesia (C5 level) occurred in two boys: a 13-yr-old boy was 168 cm tall, weighed 64 kg
43 Spinal anaesthesia in adolescents C4-, C6C8- T4T6T8T10 0 10 20 40 50 Age (yr) 60 70 80 90 Figure 3 Maximum spread of analgesia vs age. A regression curve of the number of analgesic segments: y = 25.384 O ^ ^ + O.OOTx^-O.OOOOlx3, r2 = 0.35, P = 0.0001. and had a body mass index of 22.7 kg m~2 ; and a 14yr-old boy, 170 cm, 60 kg and body mass index 20.8 kg m~2. This suggests that a more important factor than height, weight and body mass index may influence the spread of subarachnoid hyperbaric amethocaine in adolescents. We propose three potential mechanisms that may influence the spread of subarachnoid hyperbaric amethocaine, particularly in adolescents. One is related closely to the anatomical configuration of the vertebral column in the supine horizontal position. When the patient lies in the supine horizontal position, hyperbaric amethocaine injected at the apex of the lumbar curvature spreads in both cephalad and caudad directions under the influence of gravity [3, 4]. In a cephalad direction, it pools in the lower pan of the thoracic hollow [5, 6]. It was reported recently that the lower part of the thoracic hollow is not at T5-6, but at T8 [7]. Hyperbaric amethocaine, therefore, pools in the vicinity of T8. xaggeration or elimination of the thoracic kyphotic curvature affects the distribution of this pool in the thoracic hollow. Particularly at the upper thoracic region, the inclination of an upward slope may determine the maximum cephalad spread of hyperbaric amethocaine. When adolescents lie in the supine horizontal position, the degree of the thoracic kyphotic curvature decreases because of the flexibility of their vertebral column. The vertebral column becomes straighter at the upper part of the thoracic vertebrae (fig. 4 shows the typical anatomical configuration of the vertebral column in adolescents and adults). limination of the inclination of an upward slope may allow hyperbaric amethocaine to rise easily to higher dermatomal levels (fig. 5). A second potential mechanism affecting the spread of subarachnoid block in adolescents is the amount of CSF surrounding the spinal cord. It is widely accepted that a given dose of local anaesthetic injected into a decreased volume of spinal CSF may produce a higher dermatomal level of block. If adolescents had a smaller CSF volume, this might be a determinant of spread of subarachnoid hyperbaric amethocaine. However, there are no data on the effect of age on volume of spinal CSF. The third mechanism that potentially modifies the spread of subarachnoid solution in adolescents is the Figure 4 Sagittal midline magnetic resonance images of the vertebral column of healthy volunteers. The examinations were performed while the volunteers lay in the supine horizontal position. The legs were extended and a headrest (1 cm in thickness) was placed under the volunteer's head. A: A 16-yr-old, 57-kg, 167-cm adolescent, B: A 39-yr-old, 65-kg, 170-cm adult. In the adolescent (A), elimination of the inclination of an upward slope is seen particularly at the upper part of the thoracic vertebrae; a decrease in anterior-posterior diameter allows the thoraco-cervical vertebral column to become straighter. The spinal cord ends at LI both in the adolescent (A) and in the adult (B).
British Journal of Anaesthesia 44 A Site of injection (L3-4) Site of injection (L3-4) Figure 5 Distribution of hyperbaric local anaesthetic solutions within the subarachnoid space in adolescents (A) and adults (B). In adolescents, elimination of the inclination of an upward slope allows hyperbaric amethocaine to rise easily to higher dermatomal levels. rate of growth of the vertebral canal relative to the spinal cord. It is well known that in young children the spinal cord is close to the sacral canal, and that as they grow, the end of the cord and the dermatomal segments of the cord retract cephalad relative to the vertebral canal. The end of the cord is thought to assume its adult position at the end of the second decade of life [8]. Although our sagittal magnetic resonance images showed no difference in the level of the end of the cord between the adolescent and adult volunteers, further studies are required to clarify this question. There is disagreement on the effect of advancing age on the spread of spinal anaesthesia in adults. Veering, Burm and Spierdijk [9] demonstrated a moderate correlation (r = 0.74) between age and level of analgesia with bupivacaine 15 mg in 8% glucose. Cameron and colleagues [10] found a small but statistically significant (r = 0.5) correlation between age and level of analgesia with 20 mg of isobaric bupivacaine. Pitkanen and colleagues [11] also found a small but significant (r = 0.227) correlation between age and level of analgesia with isobaric bupivacaine 15 mg. In each of these studies the overall range of analgesia at all ages was so wide that this statistical correlation is of little predictive help in clinical practice. In contrast, Tuominen and colleagues [1] studied the spread of spinal anaesthesia with hyperbaric amethocaine 15 mg in patients aged 17-82 yr and found a relatively high level of analgesia (T4 level), irrespective of age. In common with Tuominen and colleagues, we found that hyperbaric amethocaine 8 mg produced a mid-thoracic level of analgesia in adults, irrespective of age. With subarachnoid injection of hyperbaric bupivacaine 15 mg, Racle and colleagues [12] compared the level of analgesia between younger (less than 50 yr) and older (more than 80 yr) patients and concluded that the effect of advancing age on the spread of spinal anaesthesia was small. Thus patient age plays a small part in determining the spread of hyperbaric spinal anaesthetic solutions in adults. Body mass is thought to influence the level of analgesia with isobaric bupivacaine [13, 14]. However, the influence of body mass has been denied for hyperbaric solutions of bupivacaine [15, 16] or amethocaine [1]. We did not find a significant correlation between weight or body mass index and level of analgesia in either in this study. Unlike weight and body mass index, height is thought to influence the level of analgesia after subarachnoid injection of local anaesthetics. Greene [3] argued that taller patients have longer and larger subarachnoid spaces with more CSF volume. Local anaesthetics should reach lower dermatomal levels after travelling the same distance from the site of injection in taller patients than in shorter patients. However, clinical data on this subject are conflicting. Pitkanen [14] found a significant effect of height (153-193 cm) on the level of analgesia in 20 patients receiving 0.5% hyperbaric bupivacaine (r = 0.48) and in 70 patients receiving 0.5 % isobaric bupivacaine (r = 0.35). In contrast, several investigators found that the spread of spinal anaesthesia correlated poorly with the height of the patient. Norris [15, 16] demonstrated that height (146178 cm) did not correlate with the level of analgesia with hyperbaric bupivacaine 12 or 15 mg in parturients. Brown and colleagues [17] noted that men and women receiving 10 or 15 mg of hyperbaric amethocaine developed similar levels of analgesia (T8-9) despite the greater height of men (173 cm) compared with women (160 cm). In our study, the height of the patients was 143-178 cm and 141 185 cm in the adolescent and adult s, respectively, and there was no correlation between height and level of analgesia. The role of height in determining level of analgesia would be clinically important if spinal anaesthesia was used in children [3]. Although we demonstrated a higher cephalad spread of spinal anaesthesia with hyperbaric amethocaine in adolescents, these results are not necessarily applicable to other local anaesthetic drugs or solutions. Another limitation is the physique of the patients. Although we could not find a significant difference in body mass index between the s, we cannot exclude the possibility that adolescents have a smaller body mass index. However, this does not affect our conclusions because a smaller body mass index in adolescents is associated with a short anterior-posterior thoracic diameter and furthermore, body mass index itself has no direct effect on the spread of hyperbaric spinal anaesthetic solutions [1,15, 16]. A third limitation is the fact that we defined adolescents as patients aged 12-16 yr. Adolescent populations have a very wide range of height and weight, and it is possible that there are ethnic differences in growth of the body. The range of height and weight of our adolescents may not encompass all adolescents. If amethocaine 8 mg was injected into the subarachnoid space in adolescents with smaller heights and weights than those of our, unnecessarily high and potentially dangerous levels of block may ensue. Finally, this study could not be carried out by blinded observers. However, all observations were performed by one of the authors
Spinal anaesthesia in adolescents 45 or by trainees under the direct supervision of the same investigator and therefore we believe that these data are valid. References 1. Tuominen M, Pitkanen M, Doepel M, Rosenberg PH. Spinal anaesthesia with hyperbaric tetracaine: ffect of age and body mass. Acta Anaesthesiologica Scandinavica 1987; 31: 474-478. 2. Cousins MJ, Bridenbaugh PO. Neural blockade. In: Clinical Anesthesia and Management of Pain, 2nd edn. Philadelphia: JB Lippincott, 1988; 344. 3. Greene NM. Distribution of local anaesthetic solutions within the subarachnoid space. Anesthesia and Analgesia 1985; 64: 715-7. 4. Wildsmith JAW. Baricity and spinal anesthesia: What solution when? Anesthesiology Clinics of North America 1992; 10: 31-43. 5. Kitahara T, Kuri S, Yoshida J. The spread of drugs used for spinal anesthesia. Anesthesiology 1956; 17: 205-208. 6. Norris MC. Spinal anesthesia for cesarean section. In: Norris MC, ed. Obstetric Anesthesia. Philadelphia: JB Lippincott, 1993; 439. 7. Hirabayashi Y, Shimizu R, Saitoh K, Fukuda H. Reevaluation of physiologic curvature of the thoracolumbar spinal column in the supine position. Anesthesiology 1994; 81: 266-267. 8. Murphy TM. Spinal and epidural anesthesia. In: Miller RD, ed. Anesthesia. New York: Churchill Livingstone, 1981; 637. 9. Veering BT, Burm AGL, Spierdijk J. Spinal anaesthesia with hyperbaric bupivacaine: ffects of age on neural blockade and pharmacokinetics. British Journal of Anaesthesia 1988; 60: 187-194. 10. Cameron A, Arnold RW, Ghoris MW, Jamieson V. Spinal analgesia using bupivacaine 0.5% plain: Variation in the extent of the block with patient age. Anaesthesia 1981; 36: 318-322. 11. Pitkanen M, Haapaniemi L, Tuominen M, Rosenberg PH. Influence of age on spinal anaesthesia with isobaric 0.5 % bupivacaine. British Journal of Anaesthesia 1984; 56: 279-284. 12. Racle JP, Benkhadra A, Poy JY, Gleizal B. Spinal analgesia with hyperbaric bupivacaine: Influence of age. British Journal of Anaesthesia 1988; 60: 508-514. 13. McCulloch WJD, Littlewood DG. Influence of obesity on spinal analgesia with isobaric 0.5% bupivacaine. British Journal of Anaesthesia 1986; 58: 610-614. 14. Pitkanen MT. Body mass and spread of spinal anesthesia with bupivacaine. Anesthesia and Analgesia 1987; 66: 127-131. 15. Norris MC. Height, weight, and the spread of subarachnoid hyperbaric bupivacaine in the term parturient. Anesthesia and Analgesia 1988; 67: 555-558. 16. Norris MC. Patient variables and the subarachnoid spread of hyperbaric bupivacaine in the term parturient. Anesthesiology 1990; 72: 478-482. 17. Brown DT, Wildsmith JAW, Covino BG, Scon DB. ffect of baricity on spinal anaesthesia with amethocaine. British Journal of Anaesthesia 1980; 52: 589-596.