British Journal of Anaesthesia 1992; 68: 136-138
PREDICTION OF THE SPREAD OF REPEATED SPINAL ANAESTHESIA WITH BUPIVACAINE M. TUOMINEN, M. PITKANEN, T. TAIVAINEN AND P. H. ROSENBERG SUMMARY
KEY WORDS Anaesthetic techniques: spinal. Anaesthetics, local: bupivacaine.
Although the spread of a spinal block with plain 0.5% bupivacaine is difficult to predict [1,2], a repeated block in an individual patient, using exactly the same method, results in a block similar to the first [3, 4]. Some factors, such as position of the patient during injection [5] or warming the anaesthetic solution before injection [6] may affect the level of block. It has been shown also that the spread of the block is reduced when plain 0.5% bupivacaine 3 ml is injected at the L4-5 interspace instead of L2-3 or L3-^ [7, 8]. We have examined the effect of changing the anaesthetic technique and solution used for successive spinal blocks in the same patient. PATIENTS AND METHODS
After approval by the Ethics Committee, we carried out a prospective study in orthopaedic patients undergoing spinal block with plain 0.5% bupivacaine according to our usual techniques: (1) Interspace L3-4 is used most frequently with the patient in a lateral horizontal position [9]. (2) Interspace L4-5 is used with the patient in a lateral horizontal position when a low block is required [7, 8]. (3) Injection of local anaesthetic is made at in-
TABLE I. Patient characteristics {mean (SD) [range]). For definitions of groups, see text
No. of patients Age (yr) Height (cm) Weight (kg) Body mass index (kgm-2) Interspace used for first block (No. patients) L2-3 L3^
L4-5 Time between anaesthetics (months)
Group 1
Group 2
17
23
41 [14-68] 169 (7) 68 (12) 23.8(3.1) [15.9-29.8]
51[17-81] 169 (8) 75 (15) 25.9(4.1) [19.1-34.6]
Group 3 16
37 [14-58] 177 (8) 75 (14) 23.8 (3.4) [19.2-32.4]
1 9 7
2 21 —
— 15 1
8[0-21]
10 [0-33]
13 [0-25]
M . TUOMINEN, M.D.J M . PlTKANEN, M.D. J T . TAIVAINEN, M.D.J
P. H. ROSENBERG, M.D. ; Department of Anaesthesia, Surgical Hospital, Helsinki University Central Hospital, Kasarmikatu 11-13, 00130 Helsinki, Finland. Accepted for Publication: August 2, 1991.
Downloaded from http://bja.oxfordjournals.org/ at Karolinska Institutet on June 2, 2015
We have studied in 56 patients the predictability of spread of repeated spinal anaesthesia in the same patient on the basis of a previous block. With plain 0.5% bupivacaine, prediction of the second block was accurate. A significantly higher or lower spread of analgesia than in the previous block was achieved when plain 0.5% bupivacaine was administered using a modified technique—sitting position or lower interspace, respectively. When hyperbaric 0.5% bupivacaine was injected instead of plain solution for the second block using a similar technique, no baricity-related correlation was found between the first and second blocks. Change in technique did not reduce interindividual variation in the spread of analgesia. We conclude that individual anatomical properties may play a more important role than, for example, baricity in subarachnoid distribution of a local anaesthetic solution.
terspace L3-4 with the patient in a sitting position for 2.5 min, if a high block is required [5]. (4) Interspace L2-3 is used rarely [9]. Data were collected for injection technique and spread of analgesia in all patients having spinal block with plain 0.5% bupivacaine. In 56 of these patients (ASA I—II), two blocks were performed for surgery on the lower extremities during the prospective period (table I). Thus these patients served as their own controls. According to the spread of analgesia during the first block, patients were allocated to three groups for the subsequent block as follows: Group 1 included 17 patients who had a block to T10 or below, during the first spinal anaesthetic. For the second spinal anaesthetic, the injection technique was changed and included interspace L3-4 (one patient L2-3) with the patient in a sitting position during injection and for 2.5 min thereafter, in order to obtain a higher block. Group 2 included 23 patients who had a block to T9 or higher during the first spinal anaesthetic. For the second spinal anaesthetic the injection technique was changed to interspace L4-5 with the patient in a lateral horizontal position in order to produce a lower block. Group 3 included 16 patients who received hyperbaric 0.5% bupivacaine instead of plain sol-
REPEATED SPINAL ANAESTHESIA
137
RESULTS
In groups 1 and 2, the difference in maximal cephalad spread of sensory block between the first and second spinal anaesthetic was significant {P < 0.001) (fig. 1, table II). In group 1 the mean level of analgesia increased from T i l (range L2-T10) to T7 (range T11-T3) when the technique was changed for the second block. In group 2 the mean level of analgesia decreased from T6 (range T9-T1) to T10 (range L2-T4). In group 3, there was no correlation between the blocks when the first spinal anaesthetic was with plain bupivacaine and the second one was with hyperbaric solution (fig. 1). Eight patients had a higher, three patients a lower and five patients the same spread of analgesia during the repeated block compared with the first. The difference between the first and second blocks was 1.3 (3.7) segments. Anaesthesia was adequate for surgery of the lower extremities in all patients and there were no complications.
T3-,
T5-
g
T7-I
< 0.001 between first ( • ) and second (E2) block). In group 3, hyperbaric 0.5% bupivacaine was injected instead of plain solution using the same standardized technique.
DISCUSSION
The results of this study confirm earlier observations that the use of the sitting position of the patient maintained during injection and for a subsequent 2.5 min increased the level of spinal block compared with a lateral horizontal position [5]. In addition, injection at L4-5 interspace instead of L3-^l or L2-3 resulted in a lower level of anaesthesia [7, 8] when plain 0.5% bupivacaine was used. Interindividual variation in the spread of sensory block was considerable in this study. In all patients, irrespective of technique, the variation in spread of analgesia was 13 segments, ranging from L2 to T l . In group 1 the variation was four segments for the first anaesthetic (segmental level T10 or lower) but eight segments in the second block. In group 2, the variation was eight segments for the first block (segmental level T9 or higher) and 10 segments for the second. Change of the method of injection did not reduce interindividual variability, possibly because BMI was not standardized. Extensive spread of analgesia has been demonstrated in patients with high BMI values in several studies [8, 11, 12]. Some of our patients also had BMI values outside the normal range, and this may also have contributed to the large interindividual variation. The only exception in group 2 was a patient with a relatively
TABLE II. Characteristics of the spinal blocks (mean (SD) [range]). For definitions of groups, see text
First anaesthetic Spread No. segments blocked Second anaesthetic Spread No. segments blocked Difference between first and second anaesthetic (No. segments)
Group 3
Group 1
Group 2
Group 3
T i l [L2-T10] 11.7(1.5)
T6 [T9-T1] 17.2(2.7)
T9 [L1-T4] 13.7(3.1)
T7[T11-T3] 15.6(2.9)
T10 [L2-T4] 12.8 (2.9)
T8 [T12-T2] 15.1(3.2)
3.9 (2.8)
4.4(2.6)
1.3(3.7)
Downloaded from http://bja.oxfordjournals.org/ at Karolinska Institutet on June 2, 2015
ution for the second spinal anaesthetic, irrespective of the height of the first block. The injection technique (interspace, position of the patient, volume of solution (3 ml) and speed of the injection) was the same as during the first spinal block. Subarachnoid blocks were performed using 25-, 26- or 27-gauge spinal needles and a standard midline approach. The needle size was unchanged for the second block. All injections of local anaesthetic were made over 15 s. In groups 1 and 2 the same volume (mean 3.1 ml, range 2.8-4.0 ml) of plain 0.5% bupivacaine was used for both blocks. The segmental spread of analgesia was studied by pinprick (27-gauge needle) at 15-min intervals by an anaesthetist who was unaware of the outcome of the first anaesthetic. Analgesia was defined as inability to appreciate sharp pinprick. Assessments made 60 min after the injection of plain bupivacaine were considered to indicate maximal spread of analgesia. If the block was not symmetrical, the higher level of block was recorded. Body mass index (BMI) (kg m~2) was calculated from the formula weight/(height)2. The normal values for Finnish adults are 20.2-24.6 kg m~2 for females and 21.1-25.9kg nr 2 for males [10]. Data were analysed using Student's t test. P < 0.05 was considered statistically significant. Results are expressed as mean (SD).
BRITISH JOURNAL OF ANAESTHESIA
138
ACKNOWLEDGEMENT The study was supported by a grant from the Sigrid Juselius Foundation (P.H.R.).
REFERENCES 1. Logan MR, McClure JH, Wildsmith JAW. Plain bupivacaine: an unpredictable spinal anaesthesia agent. British Journal of Anaesthesia 1986; 58: 292-296.
2. Wildsmith JAW. Predicting the spread of spinal anaesthesia. British Journal of Anaesthesia 1989; 62: 353-354. 3. Tuominen M, Kuulasmaa K, Taivainen T, Rosenberg PH. Individual predictability of repeated spinal anaesthesia with isobaric bupivacaine. Ada Anaesthesiologica Scandinavica 1989; 33: 13-14. 4. Taivainen T, Tuominen M, Kuulasmaa K, Rosenberg PH. A prospective study on reproducibility of the spread of spinal anesthesia using plain 0.5% bupivacaine. Regional Anesthesia 1990; IS: 12-14. 5. Tuominen M, Kalso E, Rosenberg PH. Effects of posture on the spread of spinal anaesthesia with isobaric 0.75% or 0.5% bupivacaine. British Journal of Anaesthesia 1982; 54: 313-318. 6. Stienstra R, van Poorten JF. The temperature of bupivacaine 0.5% affects sensory level of spinal anesthesia. Anesthesia and Analgesia 1988; 67: 272-276. 7. Tuominen M, Taivainen T, Rosenberg PH. Spread of spinal anaesthesia with plain 0.5% bupivacaine: influence of the vertebral interspace used for injection. British Journal of Anaesthesia 1989; 62: 358-361. 8. Taivainen T, Tuominen M, Rosenberg PH. Influence of obesity on the spread of spinal analgesia after injection of plain 0.5% bupivacaine at the L3-4 or L4-5 interspace. British Journal of Anaesthesia 1990; 64: 542-546. 9. Greene NM. Distribution of local anesthetic solutions within the subarachnoid space. Anesthesia and Analgesia 1985; 64: 715-730. 10. Heliovaara M, Aromaa A. Height, Weight and Obesity of Finnish Adults. Helsinki: Publications of the Social Insurance Institution, Finland, ML: 19, 1980; 91-92. 11. McCulloch WJD, Littlewood DG. Influence of obesity on spinal anaesthesia with isobaric 0.5% bupivacaine. British Journal of Anaesthesia 1986; 58: 610-614. 12. Pitkanen M. Body mass and spread of spinal anesthesia with bupivacaine. Anesthesia and Analgesia 1987; 66: 127-131. 13. Chambers WA, Edstrom HH, Scott DB. Effect of baricity on spinal anaesthesia with bupivacaine. British Journal of Anaesthesia 1981; 53: 279-282. 14. Chambers WA, Littlewood DG, Edstrom HH, Scott DB. Spinal anaesthesia with hyperbaric bupivacaine: effects of concentration and volume administered. British Journal of Anaesthesia 1982; 54: 75-79. 15. Cummings GC, Bamber DB, Edstrom HH, Rubin AP. Subarachnoid blockade with bupivacaine. A comparison with cinchocaine. British Journal of Anaesthesia 1984; 56: 573-579. 16. Moller IW, Fernandes A, Edstrom HH. Subarachnoid anaesthesia with 0.5% bupivacaine: effects of density. British Journal of Anaesthesia 1984; 56: 1191-1195. 17. Stienstra R, van Poorten JF. Plain or hyperbaric bupivacaine for spinal anesthesia. Anesthesia and Analgesia 1987; 66: 171-176. 18. Mitchell RWD, Bowler GMR, Scott DB, Edstrom HH. Effects of posture and baricity on spinal anaesthesia with 0.5% bupivacaine 5 ml. British Journal of Anaesthesia 1988; 61: 139-143. 19. Stienstra R, Greene NM. Factors affecting the subarachnoid spread of local anesthetic solutions. Regional Anesthesia 1991; 16: 1-6.
Downloaded from http://bja.oxfordjournals.org/ at Karolinska Institutet on June 2, 2015
high BMI (32 kg m"2). Difficulty in identification of lumbar interspaces in such an obese patient may account for the unexpected spread of anaesthesia. Two patients in whom a higher block was not reached in the second anaesthetic had normal BMI values. It has been shown that, when hyperbaric 0.5% bupivacaine is injected with the patient in the horizontal position, the height of block is increased in comparison with the same dose of plain bupivacaine [13—16]. However, our data do not support these findings. Recent studies by other investigators support our results; there were no differences between spinal blocks with plain and hyperbaric 0.5% bupivacaine when the injections were made with the patients in the lateral or sitting positions [17, 18]. Individual anatomical properties may play a more important role than expected in the subarachnoid spread of local anaesthetic. This view is supported by three findings, namely: spread of a block with plain bupivacaine may be predicted well on basis of a previous block in the same patient; lack of a systematic correlation between the effects of plain and hyperbaric solutions; and great interindividual variation in the spread of block. The anatomical configuration of the spinal cord with individual variations in extent of lumbar lordosis, the variable extent of the spinal cord, the volume of cerebrospinal fluid and other physical properties of the patient, such as obesity, are mainly responsible for the initial distribution of a local anaesthetic within CSF and for the great interindividual variability in extent of block produced by spinal anaesthesia. The extent of block is affected also by the baricity of the solution in relation with the position of the patient [19].
PREDICTION OF THE SPREAD OF REPEATED SPINAL ANAESTHESIA WITH BUPIVACAINE M. TUOMINEN, M. PITKANEN, T. TAIVAINEN AND P. H. ROSENBERG SUMMARY
KEY WORDS Anaesthetic techniques: spinal. Anaesthetics, local: bupivacaine.
Although the spread of a spinal block with plain 0.5% bupivacaine is difficult to predict [1,2], a repeated block in an individual patient, using exactly the same method, results in a block similar to the first [3, 4]. Some factors, such as position of the patient during injection [5] or warming the anaesthetic solution before injection [6] may affect the level of block. It has been shown also that the spread of the block is reduced when plain 0.5% bupivacaine 3 ml is injected at the L4-5 interspace instead of L2-3 or L3-^ [7, 8]. We have examined the effect of changing the anaesthetic technique and solution used for successive spinal blocks in the same patient. PATIENTS AND METHODS
After approval by the Ethics Committee, we carried out a prospective study in orthopaedic patients undergoing spinal block with plain 0.5% bupivacaine according to our usual techniques: (1) Interspace L3-4 is used most frequently with the patient in a lateral horizontal position [9]. (2) Interspace L4-5 is used with the patient in a lateral horizontal position when a low block is required [7, 8]. (3) Injection of local anaesthetic is made at in-
TABLE I. Patient characteristics {mean (SD) [range]). For definitions of groups, see text
No. of patients Age (yr) Height (cm) Weight (kg) Body mass index (kgm-2) Interspace used for first block (No. patients) L2-3 L3^
L4-5 Time between anaesthetics (months)
Group 1
Group 2
17
23
41 [14-68] 169 (7) 68 (12) 23.8(3.1) [15.9-29.8]
51[17-81] 169 (8) 75 (15) 25.9(4.1) [19.1-34.6]
Group 3 16
37 [14-58] 177 (8) 75 (14) 23.8 (3.4) [19.2-32.4]
1 9 7
2 21 —
— 15 1
8[0-21]
10 [0-33]
13 [0-25]
M . TUOMINEN, M.D.J M . PlTKANEN, M.D. J T . TAIVAINEN, M.D.J
P. H. ROSENBERG, M.D. ; Department of Anaesthesia, Surgical Hospital, Helsinki University Central Hospital, Kasarmikatu 11-13, 00130 Helsinki, Finland. Accepted for Publication: August 2, 1991.
Downloaded from http://bja.oxfordjournals.org/ at Karolinska Institutet on June 2, 2015
We have studied in 56 patients the predictability of spread of repeated spinal anaesthesia in the same patient on the basis of a previous block. With plain 0.5% bupivacaine, prediction of the second block was accurate. A significantly higher or lower spread of analgesia than in the previous block was achieved when plain 0.5% bupivacaine was administered using a modified technique—sitting position or lower interspace, respectively. When hyperbaric 0.5% bupivacaine was injected instead of plain solution for the second block using a similar technique, no baricity-related correlation was found between the first and second blocks. Change in technique did not reduce interindividual variation in the spread of analgesia. We conclude that individual anatomical properties may play a more important role than, for example, baricity in subarachnoid distribution of a local anaesthetic solution.
terspace L3-4 with the patient in a sitting position for 2.5 min, if a high block is required [5]. (4) Interspace L2-3 is used rarely [9]. Data were collected for injection technique and spread of analgesia in all patients having spinal block with plain 0.5% bupivacaine. In 56 of these patients (ASA I—II), two blocks were performed for surgery on the lower extremities during the prospective period (table I). Thus these patients served as their own controls. According to the spread of analgesia during the first block, patients were allocated to three groups for the subsequent block as follows: Group 1 included 17 patients who had a block to T10 or below, during the first spinal anaesthetic. For the second spinal anaesthetic, the injection technique was changed and included interspace L3-4 (one patient L2-3) with the patient in a sitting position during injection and for 2.5 min thereafter, in order to obtain a higher block. Group 2 included 23 patients who had a block to T9 or higher during the first spinal anaesthetic. For the second spinal anaesthetic the injection technique was changed to interspace L4-5 with the patient in a lateral horizontal position in order to produce a lower block. Group 3 included 16 patients who received hyperbaric 0.5% bupivacaine instead of plain sol-
REPEATED SPINAL ANAESTHESIA
137
RESULTS
In groups 1 and 2, the difference in maximal cephalad spread of sensory block between the first and second spinal anaesthetic was significant {P < 0.001) (fig. 1, table II). In group 1 the mean level of analgesia increased from T i l (range L2-T10) to T7 (range T11-T3) when the technique was changed for the second block. In group 2 the mean level of analgesia decreased from T6 (range T9-T1) to T10 (range L2-T4). In group 3, there was no correlation between the blocks when the first spinal anaesthetic was with plain bupivacaine and the second one was with hyperbaric solution (fig. 1). Eight patients had a higher, three patients a lower and five patients the same spread of analgesia during the repeated block compared with the first. The difference between the first and second blocks was 1.3 (3.7) segments. Anaesthesia was adequate for surgery of the lower extremities in all patients and there were no complications.
T3-,
T5-
g
T7-I
< 0.001 between first ( • ) and second (E2) block). In group 3, hyperbaric 0.5% bupivacaine was injected instead of plain solution using the same standardized technique.
DISCUSSION
The results of this study confirm earlier observations that the use of the sitting position of the patient maintained during injection and for a subsequent 2.5 min increased the level of spinal block compared with a lateral horizontal position [5]. In addition, injection at L4-5 interspace instead of L3-^l or L2-3 resulted in a lower level of anaesthesia [7, 8] when plain 0.5% bupivacaine was used. Interindividual variation in the spread of sensory block was considerable in this study. In all patients, irrespective of technique, the variation in spread of analgesia was 13 segments, ranging from L2 to T l . In group 1 the variation was four segments for the first anaesthetic (segmental level T10 or lower) but eight segments in the second block. In group 2, the variation was eight segments for the first block (segmental level T9 or higher) and 10 segments for the second. Change of the method of injection did not reduce interindividual variability, possibly because BMI was not standardized. Extensive spread of analgesia has been demonstrated in patients with high BMI values in several studies [8, 11, 12]. Some of our patients also had BMI values outside the normal range, and this may also have contributed to the large interindividual variation. The only exception in group 2 was a patient with a relatively
TABLE II. Characteristics of the spinal blocks (mean (SD) [range]). For definitions of groups, see text
First anaesthetic Spread No. segments blocked Second anaesthetic Spread No. segments blocked Difference between first and second anaesthetic (No. segments)
Group 3
Group 1
Group 2
Group 3
T i l [L2-T10] 11.7(1.5)
T6 [T9-T1] 17.2(2.7)
T9 [L1-T4] 13.7(3.1)
T7[T11-T3] 15.6(2.9)
T10 [L2-T4] 12.8 (2.9)
T8 [T12-T2] 15.1(3.2)
3.9 (2.8)
4.4(2.6)
1.3(3.7)
Downloaded from http://bja.oxfordjournals.org/ at Karolinska Institutet on June 2, 2015
ution for the second spinal anaesthetic, irrespective of the height of the first block. The injection technique (interspace, position of the patient, volume of solution (3 ml) and speed of the injection) was the same as during the first spinal block. Subarachnoid blocks were performed using 25-, 26- or 27-gauge spinal needles and a standard midline approach. The needle size was unchanged for the second block. All injections of local anaesthetic were made over 15 s. In groups 1 and 2 the same volume (mean 3.1 ml, range 2.8-4.0 ml) of plain 0.5% bupivacaine was used for both blocks. The segmental spread of analgesia was studied by pinprick (27-gauge needle) at 15-min intervals by an anaesthetist who was unaware of the outcome of the first anaesthetic. Analgesia was defined as inability to appreciate sharp pinprick. Assessments made 60 min after the injection of plain bupivacaine were considered to indicate maximal spread of analgesia. If the block was not symmetrical, the higher level of block was recorded. Body mass index (BMI) (kg m~2) was calculated from the formula weight/(height)2. The normal values for Finnish adults are 20.2-24.6 kg m~2 for females and 21.1-25.9kg nr 2 for males [10]. Data were analysed using Student's t test. P < 0.05 was considered statistically significant. Results are expressed as mean (SD).
BRITISH JOURNAL OF ANAESTHESIA
138
ACKNOWLEDGEMENT The study was supported by a grant from the Sigrid Juselius Foundation (P.H.R.).
REFERENCES 1. Logan MR, McClure JH, Wildsmith JAW. Plain bupivacaine: an unpredictable spinal anaesthesia agent. British Journal of Anaesthesia 1986; 58: 292-296.
2. Wildsmith JAW. Predicting the spread of spinal anaesthesia. British Journal of Anaesthesia 1989; 62: 353-354. 3. Tuominen M, Kuulasmaa K, Taivainen T, Rosenberg PH. Individual predictability of repeated spinal anaesthesia with isobaric bupivacaine. Ada Anaesthesiologica Scandinavica 1989; 33: 13-14. 4. Taivainen T, Tuominen M, Kuulasmaa K, Rosenberg PH. A prospective study on reproducibility of the spread of spinal anesthesia using plain 0.5% bupivacaine. Regional Anesthesia 1990; IS: 12-14. 5. Tuominen M, Kalso E, Rosenberg PH. Effects of posture on the spread of spinal anaesthesia with isobaric 0.75% or 0.5% bupivacaine. British Journal of Anaesthesia 1982; 54: 313-318. 6. Stienstra R, van Poorten JF. The temperature of bupivacaine 0.5% affects sensory level of spinal anesthesia. Anesthesia and Analgesia 1988; 67: 272-276. 7. Tuominen M, Taivainen T, Rosenberg PH. Spread of spinal anaesthesia with plain 0.5% bupivacaine: influence of the vertebral interspace used for injection. British Journal of Anaesthesia 1989; 62: 358-361. 8. Taivainen T, Tuominen M, Rosenberg PH. Influence of obesity on the spread of spinal analgesia after injection of plain 0.5% bupivacaine at the L3-4 or L4-5 interspace. British Journal of Anaesthesia 1990; 64: 542-546. 9. Greene NM. Distribution of local anesthetic solutions within the subarachnoid space. Anesthesia and Analgesia 1985; 64: 715-730. 10. Heliovaara M, Aromaa A. Height, Weight and Obesity of Finnish Adults. Helsinki: Publications of the Social Insurance Institution, Finland, ML: 19, 1980; 91-92. 11. McCulloch WJD, Littlewood DG. Influence of obesity on spinal anaesthesia with isobaric 0.5% bupivacaine. British Journal of Anaesthesia 1986; 58: 610-614. 12. Pitkanen M. Body mass and spread of spinal anesthesia with bupivacaine. Anesthesia and Analgesia 1987; 66: 127-131. 13. Chambers WA, Edstrom HH, Scott DB. Effect of baricity on spinal anaesthesia with bupivacaine. British Journal of Anaesthesia 1981; 53: 279-282. 14. Chambers WA, Littlewood DG, Edstrom HH, Scott DB. Spinal anaesthesia with hyperbaric bupivacaine: effects of concentration and volume administered. British Journal of Anaesthesia 1982; 54: 75-79. 15. Cummings GC, Bamber DB, Edstrom HH, Rubin AP. Subarachnoid blockade with bupivacaine. A comparison with cinchocaine. British Journal of Anaesthesia 1984; 56: 573-579. 16. Moller IW, Fernandes A, Edstrom HH. Subarachnoid anaesthesia with 0.5% bupivacaine: effects of density. British Journal of Anaesthesia 1984; 56: 1191-1195. 17. Stienstra R, van Poorten JF. Plain or hyperbaric bupivacaine for spinal anesthesia. Anesthesia and Analgesia 1987; 66: 171-176. 18. Mitchell RWD, Bowler GMR, Scott DB, Edstrom HH. Effects of posture and baricity on spinal anaesthesia with 0.5% bupivacaine 5 ml. British Journal of Anaesthesia 1988; 61: 139-143. 19. Stienstra R, Greene NM. Factors affecting the subarachnoid spread of local anesthetic solutions. Regional Anesthesia 1991; 16: 1-6.
Downloaded from http://bja.oxfordjournals.org/ at Karolinska Institutet on June 2, 2015
high BMI (32 kg m"2). Difficulty in identification of lumbar interspaces in such an obese patient may account for the unexpected spread of anaesthesia. Two patients in whom a higher block was not reached in the second anaesthetic had normal BMI values. It has been shown that, when hyperbaric 0.5% bupivacaine is injected with the patient in the horizontal position, the height of block is increased in comparison with the same dose of plain bupivacaine [13—16]. However, our data do not support these findings. Recent studies by other investigators support our results; there were no differences between spinal blocks with plain and hyperbaric 0.5% bupivacaine when the injections were made with the patients in the lateral or sitting positions [17, 18]. Individual anatomical properties may play a more important role than expected in the subarachnoid spread of local anaesthetic. This view is supported by three findings, namely: spread of a block with plain bupivacaine may be predicted well on basis of a previous block in the same patient; lack of a systematic correlation between the effects of plain and hyperbaric solutions; and great interindividual variation in the spread of block. The anatomical configuration of the spinal cord with individual variations in extent of lumbar lordosis, the variable extent of the spinal cord, the volume of cerebrospinal fluid and other physical properties of the patient, such as obesity, are mainly responsible for the initial distribution of a local anaesthetic within CSF and for the great interindividual variability in extent of block produced by spinal anaesthesia. The extent of block is affected also by the baricity of the solution in relation with the position of the patient [19].
