Anesth Analg 2001;93:77-81
© 2001 International Anesthesia Research Society
PEDIATRIC ANESTHESIA
Spinal Anesthesia with Tetracaine in 7.5% or 0.75% Glucose in Adolescents and Adults
Shinichi Sakura, MD,
Noritaka Imamachi, MD,
Kousaku Toyota, MD,
Atsuko Shono, MD, and
Yoji Saito, MD
Department of Anesthesiology, Shimane Medical University, Izumo City, Japan
Address correspondence and reprint requests to Shinichi Sakura, MD, Associate Professor, Department of Anesthesiology, Shimane Medical University, 89-1 Enya-cho, Izumo City, 693-8501 Japan. Address e-mail to ssakura{at}shimane-med.ac.jp
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Abstract
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To examine whether adolescents and adults might develop different anesthetic distribution and hemodynamic consequences after spinal injection of 0.5% tetracaine in 7.5% or 0.75% glucose, we studied 100 ASA I or II patients who were scheduled for elective surgery to the lower limb and fulfilled the following criteria: age between 13 and 16 yr (Adolescent group, n = 40) or between 25 and 74 yr (Adult group, n = 60); height between 155 and 180 cm; and body mass index between 18 and 32 kg/m2. Patients in each group were then randomly divided into two equal subgroups to receive spinal anesthesia with 0.5% tetracaine in either 7.5% or 0.75% glucose with 0.125% phenylephrine at the L3-4 interspace. With patients in the supine horizontal position, neural block was assessed by cold, pinprick, and touch sensation and a modified Bromage scale after the injection of the study drug. The 7.5% glucose solution produced a significantly higher and faster spread of blockade in adolescents than in adults. In contrast, there were no differences in the levels of three sensory modalities between the two age groups after the 0.75% glucose solution, which produced a lower spread of blockade than the 7.5% glucose solution in either age group. Adolescents given the 0.75% glucose solution developed a smaller maximum decrease in systolic pressure than those given the heavier solution. We conclude that adolescents may develop an extensive level of blockade more easily and quickly than adults after intrathecal hyperbaric tetracaine, but that the difference may be reduced by using a less heavy solution.
Implications: The influence of age on the characteristics of spinal anesthesia is stillcontroversial. Our results show that adolescents develop blockade moreextensively and quickly than adults after spinal anesthesia with 0.5%tetracaine in 7.5% glucose but not after the 0.75% glucosesolution.
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Introduction
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The influence of age on the characteristics of spinal anesthesia is still controversial (1–7). One study (8) showed that adolescents developed a higher level of analgesia than adults when hyperbaric tetracaine was used. Because the baricity of a local anesthetic solution is thought to influence the spinal level (9–17), understanding how solutions of different baricities affect adolescents is necessary. Accordingly, this study was conducted to examine how adolescents and adults develop anesthetic distribution and hemodynamic consequences after spinal injection of 0.5% tetracaine in 7.5% or 0.75% glucose. We hypothesized that the effects of patient age on the characteristics of spinal anesthesia would be different between the two solutions.
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Methods
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After IRB approval, we studied 100 patients who were scheduled for elective surgery to the lower limb (arthroscopy) and fulfilled the following criteria: ASA physical status I or II; age between 13 and 16 yr (Adolescent group, n = 40) and between 25 and 74 yr (Adult group, n = 60); height between 155 and 180 cm; and body mass index (BMI) between 18 and 32 kg/m2. Informed written consent was obtained from all participants, as well as from the parents of all adolescents. Patients with a history of major back problems, coagulation abnormality, neurologic disease, or infections at the site of injection were excluded. In addition, patients who did not show any demonstrable sensory block after spinal anesthetic were excluded from the study.
Patients received only atropine (0.005–0.01 mg/kg) for premedication given IM approximately 1 h before anesthesia. They fasted for approximately 8 h and received no intravascular volume loading before entering an operating room. After an IV infusion of acetated Ringer’s solution was initiated at a rate of 10 mL · kg-1 · h-1, patients were placed in the lateral decubitus position, with the operative side dependent. The lumbar puncture was performed at the L3-4 interspace with a 25-gauge Quincke needle by using the midline approach. After obtaining free reflux of cerebrospinal fluid (CSF), 0.1 mL of CSF was taken for the measurement of specific gravity, and the test solution (2.2–2.8 mL on the basis of the patient height: 155–159 cm, 2.2 mL; 160–169 cm, 2.4 mL; 170–179 cm, 2.6 mL; and 180 cm, 2.8 mL) was administered at a rate of 0.1 mL/s, with the bevel of the needle oriented toward the dependent side. After injection of study solution, 0.1 mL of CSF was again aspirated and reinjected to reconfirm correct placement of the needle tip.
Patients of each age group were randomly divided into two equal subgroups to receive spinal anesthesia with 0.5% tetracaine in either 7.5% or 0.75% glucose with 0.125% phenylephrine. Thus, each subject was eventually assigned to one of four groups: Groups 1H and 1M consisted of patients between 13 and 16 yr who were given 7.5% and 0.75% glucose solutions, respectively; Groups 2H and 2M consisted of patients between 25 and 74 yr who were given 7.5% and 0.75% glucose solutions, respectively. The local anesthetic solution was prepared immediately before injection by dissolving 20 mg of crystalline tetracaine hydrochloride (Kyorin Pharmaceutical, Tokyo, Japan) in a combined solution of 3 mL of 10% or 1% glucose (Otsuka Pharmaceutical, Naruto, Japan) with 1 mL of 0.5% phenylephrine (Kowa, Nagoya, Japan). The specific gravity of each solution and CSF was measured at 37°C by a refractometer.
Patients were immediately placed supine and remained level during the rest of the study period. All variables were assessed by an investigator who was unaware of which solution had been injected. The dermatomal levels of blockade of light touch, temperature, and pinprick discrimination, as well as the degree of motor block, blood pressure, and heart rate, were measured 2, 5, 10, 15, 20, 25, and 30 min and thereafter every 30 min after intrathecal injection of the local anesthetic unless sedation or surgery prevented assessment, but at least until two-segment regression was achieved. The loss of each sensory modality was determined by the patient’s verbal response to the stimulus applied bilaterally in the midclavicular line starting caudad and moving cephalad; if there were any differences in the dermatomal levels of blockade between the left and right sides, higher levels were taken. The dull, hinged end of a sterile safety pin was used to examine light touch; an alcohol-soaked swab, for temperature; and the sharp tip of a safety pin, for pinprick. The degree of motor block was assessed by a modified Bromage scale (18) ranging from 0 to 4, where 0 = able to move hip, knee, ankle, and toes; 1 = unable to move hip, able to move knee, ankle, and toes; 2 = unable to move hip and knee, able to move ankle and toes; 3 = unable to move hip, knee and ankle, able to move toes; and 4 = unable to move hip, knee, ankle, or toes. Hypotension was treated with 5 mg ephedrine IV if systolic arterial pressure decreased by >25% of the preanesthetic value. Ephedrine was also administered when symptoms such as nausea or dizziness were reported.
Results are expressed as mean ± SD or median (10th, 90th percentiles). Continuous variables were compared with one-way analysis of variance and the Student-Newman-Keuls test. Hemodynamic values were analyzed with data that showed a maximum decrease for the first 60 min after spinal injection. The peak level of sensory block and the degree of motor block were compared by using the Kruskal-Wallis test and the Student-Newman-Keuls test. The 
2 analysis was used to compare the number of patients given ephedrine for the first 60 min after spinal injection. P < 0.05 was considered significant.
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Results
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One-hundred patients were enrolled in the study and assigned to Groups 1H (n = 20), 1M (n = 20), 2H (n = 30), and 2M (n = 30) (Table 1). The four groups did not differ in patient characteristics except for age. No patient was given hypobaric solutions in comparison with CSF, which ranged from 1.005 to 1.008 in specific gravity at 37°C. The specific gravity of the solutions in 7.5% glucose and in 0.75% glucose was 1.037 ± 0.001 and 1.010 ± 0.001, respectively.
The 7.5% glucose solution had a tendency to produce a higher spread of blockade than the 0.75% glucose solution in both age groups (Fig. 1, Table 2). The peak dermatomal levels of sensory block to cold, pinprick, and touch were significantly higher after 7.5% glucose than after 0.75% glucose in adolescents; a significant difference between adults given different solutions was found in the peak dermatomal level of cold sensation. The 7.5% glucose solution produced a significantly higher spread of blockade in adolescents than in adults. In contrast, there were no differences in the levels of three sensory modalities between the two age groups after the 0.75% glucose solution. The mean time taken to achieve the peak dermatomal level of loss of sensation to pinprick was shorter in Group 1H than in Groups 1M and 2H. The mean time for the sensory blocks to pinprick to regress to two segments below the maximum was prolonged with the use of 0.75% glucose. Figure 2 presents the time course of the dermatomal levels of analgesia to pinprick after spinal anesthesia in adolescents. The maximum degree of motor block for the four groups was similar.
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Figure 1. Maximal cephalad sensory block to pinprick. Groups 1H and 1M consisted of patients between 13 and 16 yr who were given 7.5% and 0.75% glucose solutions, respectively; Groups 2H and 2M consisted of patients between 25 and 74 yr who were given 7.5% and 0.75% glucose solutions, respectively. The box represents the 25th–75th percentiles, and the median is represented by the solid line. Error bars above and below the box mark the 10th and 90th percentiles. *P < 0.05.
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Figure 2. Time course of sensory block to pinprick after spinal tetracaine in adolescents. Groups 1H and 1M consisted of patients between 13 and 16 yr who were given 7.5% and 0.75% glucose solutions, respectively. The box represents the 25th–75th percentiles, and the median is represented by the solid line.
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Systolic blood pressure and heart rate decreased after spinal anesthesia. The maximum decrease in systolic blood pressure was significantly smaller after the 0.75% glucose solution than after the 7.5% glucose solution in adolescents. However, the number of patients who required ephedrine for the treatment of hypotension did not statistically differ among groups. All the patients tolerated subsequent surgery well.
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Discussion
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The results of this study show that patient age may affect the characteristics of spinal anesthesia depending on the baricity of a local anesthetic solution. After spinal anesthesia with 0.5% tetracaine in 7.5% glucose, adolescents developed a higher level of blockade than adults, and the establishment of spinal anesthesia was faster in the younger group of patients than in the other. However, when 0.5% tetracaine in 0.75% glucose was administered, both age groups developed similar blockade in which heights were lower than those after the 7.5% glucose solution.
Although age has been thought to influence the characteristics of spinal anesthesia, previous studies using adults have not shown it to be a major determinant factor in the distribution of spinal anesthetic solutions (1,2,4–7). A significant increase in cephalad spread has been observed with increasing age in studies with 0.5% glucose-free bupivacaine (1,2,4). In addition, rapid development of motor blockade in older patients was reported (4). However, the age-related differences seemed small and of little clinical importance. Results obtained from studies with hyperbaric local anesthetic solutions are similar (3,5–7). Veering et al. (5) studied patients older than 19 years and demonstrated that the time to maximum cephalad spread and the upper level of analgesia slightly increased with advancing age after hyperbaric bupivacaine. Racle et al. (6) compared the level of analgesia after hyperbaric bupivacaine between patients aged 19–49 years and those aged 80–95 years and concluded that the tendency toward increasing height of block with advancing age was small as compared with large individual variation and of little significance.
Our results, together with those of Hirabayashi et al. (8), have indicated that there seem to be significant age-related differences when adolescents are involved. In addition to confirming the previous findings of a higher cephalad spread of spinal analgesia with hyperbaric tetracaine in adolescents, this study demonstrated faster establishment of anesthesia in these patients for the first time. It is interesting to note that the relationship between age and the above characteristics observed in these two studies is completely opposite to that demonstrated in studies that used only adults, in which older patients developed higher blockade and faster onset of motor blockade. Thus, it is highly likely that factors that influence the differences between adolescents and adults in the spinal characteristics after the 7.5% glucose solution are different from those that influence the differences among adults.
Although patients who had similar body height, weight, and BMI were enrolled, there might have been other factors that were different between adolescents and adults, influencing the spinal spread. Among them, the anatomic configuration of the spine may offer the most plausible explanation for the different anesthetic spread between the two age groups. When adolescents lie in the supine horizontal position, the degree of the thoracic kyphotic curvature seems to decrease, probably because of the flexibility of their vertebral columns. Sagittal midline magnetic resonance images of the vertebral column of healthy adolescent volunteers showed that the vertebral column becomes straighter at the upper part of the thoracic vertebrae as compared with that of adults (8). Thus, elimination of the inclination of an upward slope may allow hyperbaric tetracaine (the 7.5% glucose solution) to rise easily to higher dermatomal levels.
In contrast, the 0.75% glucose solution, which is marginally hyperbaric, seemed to behave differently. The effect of baricity of a local anesthetic solution on the spread of spinal anesthesia has previously been demonstrated in adults (9–17). Brown et al. (13) found that the hyperbaric tetracaine solution produced higher sensory levels than did the isobaric or the hypobaric solutions. We previously found that 0.5% tetracaine in a 0.75% glucose solution produced a less cephalad level of analgesia than the 7.5% glucose solution (17,19). These results have added that the same rule concerning the effects of baricity can be applied to adolescents. The solution, with specific gravity only slightly in excess of that of CSF, can only move slowly down the slope created by the lumbar lordosis in the supine, but in horizontal patients, less extensive blocks are produced. Thus, even if the anatomic configuration of the thoracic spine in adolescents differs from that in adults, the difference may not have had any effect on the spread of the 0.75% glucose solution between the two age groups.
It was not surprising to observe hemodynamic stability after spinal anesthesia with the 0.75% glucose solution in adolescents, in view of its less extensive and slower anesthetic spread. It is likely that sympathetic blockade was also more restricted and of slower onset with the less heavy solution; thus, significantly less hemodynamic change resulted.
There is a concern that sex might have affected the present results, because a larger percentage of male patients was enrolled in the adult groups than in the younger groups, despite no statistical difference in male/female ratio among the four study groups. However, the sex of a patient has been thought to have no direct effect on anesthetic distribution in CSF (13). In addition, further comparisons of our data between female and male patients in each group were conducted, revealing no statistical difference.
There are limitations to this study. First, although the investigator who made the assessment of the development of spinal anesthesia was not informed of the group assignment, it is highly likely that he could easily distinguish adolescents from the other group of patients through verbal communication with them. To reduce bias, however, the investigator did not care for the patient, perform spinal anesthesia, or collect outcome data. Second, the physique of patients who entered the study was limited. Patients usually have a wider range of height and weight than the criteria set in this study. Because patient height, weight, and BMI may affect the volume of CSF and the level of spinal anesthesia with isobaric bupivacaine (20,21), it is possible that a patient whose physique is beyond our criteria may develop different blockade from that observed, especially after the 0.75% glucose solution.
In conclusion, these results suggest that adolescents develop an extensive level of blockade more easily and quickly than adults after intrathecal hyperbaric tetracaine but that the difference may be reduced by using a less heavy solution.
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Footnotes
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Presented in part at the annual meeting of the American Society of Anesthesiologists, San Francisco, CA, October 14–18, 2000.
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References
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Accepted for publication February 14, 2001.
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Abstract
Introduction
