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From the Department of Anesthesiology and Critical Care, University College of Medical Sciences and Guru Teg Bahadur Hospital, Shahadra, Delhi, India.
Address correspondence and reprint requests to Dr. Asha Tyagi, 103, Siddhartha Enclave, New Delhi-14. Address e-mail to drashatyagi{at}gmail.com.
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Abstract |
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 Top Abstract IntroductionMETHODSRESULTSDISCUSSIONREFERENCES |
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METHODS: Eighty-eight adult male patients scheduled for lower limb orthopedic surgery under CSE in the sitting position were randomized to four groups (n = 22 each); intrathecal injection was made with plain bupivacaine in groups plain bupivacaine (PB) and plain bupivacaine with epidural volume extension (PBE), and hyperbaric bupivacaine in groups hyperbaric bupivacaine (HB) and hyperbaric bupivacaine with epidural volume extension (HBE). Fentanyl, 25 µg, was added to the intrathecal drug in all groups. Among these four groups, epidural volume extension was performed with 10 mL normal saline only for groups PBE and HBE. The dose of spinal bupivacaine was varied using the up-and-down sequential allocation method. The first patient of each group received 10 mg bupivacaine. A successful spinal block was defined as attainment of sensory level of at least T10 along with complete motor blockade within 20 min of the intrathecal injection. The dose of bupivacaine was sequentially increased or decreased by 1 mg depending on whether spinal block was a failure or success in the previous patient.
RESULTS: The addition of epidural volume extension to plain bupivacaine, i.e., group PBE versus group PB, resulted in a significant decrease in ED50 (relative potency estimate: 1.2, 95% CI: 1.04–1.64) and increase in maximum sensory level (T6 vs T8, respectively, P < 0.05). These differences were not seen with hyperbaric bupivacaine (group HB vs HBE). Independent of the effect of epidural volume extension, the ED50 of plain bupivacaine when compared with hyperbaric bupivacaine was significantly lower (relative potency estimate of group PB vs group HB: 0.78, 95% CI: 0.54–0.93; and for group PBE vs group HBE: 0.68, 95% CI: 0.37–0.87).
CONCLUSIONS: Administered with or without epidural volume extension, plain bupivacaine appears to be more effective, requiring a smaller dose and producing a higher sensory block with an earlier onset in comparison to hyperbaric bupivacaine. Epidural volume extension, when applied to intrathecal hyperbaric bupivacaine, fails to decrease the dose or raise the level of block.
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Introduction |
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TopAbstractIntroductionMETHODSRESULTSDISCUSSIONREFERENCES |
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When CSE is performed with patients in the sitting position, the time lag between intrathecal injection and placing the patient supine may cause lower levels of subarachnoid block with hyperbaric bupivacaine compared with plain (isobaric) bupivacaine. Whether this difference in intrathecal drug distribution may influence the cephalad spread of subarachnoid block by epidural volume extension, thus reducing the intrathecal dose requirements, has also not been investigated.
The aim of this study was to determine whether epidural volume extension decreases the dose of local anesthetic in nonobstetric patients, and whether the dose-sparing effect of epidural volume extension, if any, is different for plain, versus hyperbaric, intrathecal bupivacaine when CSE is performed with patients in the sitting position.
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METHODS |
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TopAbstractIntroductionMETHODSRESULTSDISCUSSIONREFERENCES |
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Eighty-eight randomly selected, consenting, adult male patients ASA physical status I or II, with body weight between 50 and 70 kg and height between 150 and 180 cm scheduled for lower limb orthopedic surgery using CSE anesthesia were included in the study. Patients with absolute or relative contraindications to CSE, such as history of spinal disease, coagulation abnormality, or sensitivity to local anesthetic and skin infection at the site of infection were excluded.
Patients were randomized to one of the four study groups [plain bupivacaine (PB), plain bupivacaine with epidural volume extension (PBE), hyperbaric bupivacaine (HB), hyperbaric bupivacaine with epidural volume extension (HBE)]. Intrathecal bupivacaine with 25 µg fentanyl was injected intrathecally in all groups. However, the baricity of bupivacaine and the addition of epidural volume extension defined the individual group. While groups HB and HBE received hyperbaric bupivacaine, groups PB and PBE received plain bupivacaine. Among these four groups, epidural volume extension was performed with 10 mL normal saline for groups PBE and HBE. Intrathecal drug was prepared and CSE block performed by a dedicated anesthesiologist, whereas the block characteristics were assessed by another anesthesiologist who was blinded to group allocation.
All patients were premedicated with diazepam 0.2 mg/kg orally 2 h before surgery. In the operating room, IV access was established and 10 mL/kg of lactated Ringer's solution was infused over 5–10 min. As routine protocol, ondansetron 4 mg IV and midazolam 0.03 mg/kg IV were also given.
CSE block by the median approach was performed using the needle-through-needle technique with a CSE set (CSE CureTM, Portex®). With the patient in sitting position, the epidural space was identified at the L4–5 level with a 16-gauge Tuohy needle using loss-of-resistance to air technique, limiting the total amount of air injected to <2 mL. A 26-gauge pencil-point spinal needle was advanced through the epidural needle into the subarachnoid space, and the intrathecal drug injected at a rate of 0.5–1 mL/s with the bevel facing cephalad. The spinal needle was withdrawn and an epidural catheter inserted 5 cm into the epidural space through the Tuohy needle, followed by confirmed negative aspiration for blood and cerebrospinal fluid. If the patient had been allocated to group PBE or HBE, 10 mL normal saline was injected over 10–15 s through the epidural catheter. No epidural injection was made in patients allocated to groups PB and HB. The epidural catheter was secured and the patient put in the supine position.
Assessment of the sensory and motor blockade was done every 3 min after placing the patient supine by an anesthesiologist blinded to group allocation, until adequate blockade was achieved or 20 min after intrathecal injection had passed. The outcome of block was defined as one of the following:
After the maximum sensory block (Smax) was achieved, the level of analgesia was tested every 15 min until the block started receding. In cases with adequate block, the following additional block characteristics were noted:
In case of an inadequate block, epidural injection of 0.5% plain bupivacaine in aliquots of 3 mL was given to facilitate surgery.
Sensory level of the block was assessed using absolute loss of sensation to pinprick with 25-gauge needle, and the level recorded as the highest dermatome9 with no sensation to pinprick. Motor block was graded in the normal limb as per modified Bromage score of Breen et al.,8 wherein score 1 = complete block, unable to move feet or knees; 2 = almost complete block, able to move feet only; 3 = partial block, just able to move knees; 4 = detectable weakness of hip flexion while supine, full flexion of knees; 5 = no detectable weakness of hip flexion while supine; and 6 = able to perform partial knee bend.
The dose of intrathecal bupivacaine was decided by using the up-and-down sequential allocation method of Dixon and Massey.10 While the first patient of each group received 10 mg bupivacaine, in successive patients, the dose of intrathecal bupivacaine was determined by the outcome of spinal block in the previous patient of that group (i.e., in case of the block being adequate, the dose of bupivacaine was decreased by 1 mg in the next patient and in case of an inadequate block, the dose was increased by 1 mg in the next patient).
If local anesthetic when given through the epidural catheter was not effective in providing analgesia, the patient was excluded from the study. The next patient of that group then received the same intrathecal dose as the excluded patient.
Any intraoperative episodes of hypotension, nausea and vomiting, pruritus, or shivering were noted. Hypotension was defined as a decrease in systolic blood pressure to <100 mm Hg, or more than 20% from preoperative baseline systolic blood pressure during the first 30 min after intrathecal drug deposition, and was treated using 6 mg boluses of ephedrine IV.
Statistical Analysis
Demographic data, time variables, and sensory levels among the groups were evaluated using one way analysis of variance. For comparison of mean sensory level achieved, T1 to T12 dermatomes were designated as numbers 1 to 12. 
2 test was used for comparison of incidence of adverse effects. A P value <0.05 was considered statistically significant. The up-and-down sequences were analyzed using the formula of Dixon and Massey which enabled ED50 with 95% CI to be calculated. Data were also subjected to probit regression as a back-up sensitivity test for calculating ED50 and estimates of relative median potency along with their 95% CI for intergroup comparisons. A CI that does not include the value of 1 indicates statistically different doses (SPSS software version 10).
Sample Size Determination
Sample size was calculated on an assumed standard deviation of 1.0 mg, being one-fifth of the range of the bupivacaine dose used for routine CSE practice in orthopedic surgeries of the lower limbs (7.5–12.5 mg). To detect a difference of 1 mg bupivacaine among groups, at a power of 0.9 and P value of 0.05, 21 patients were required in each group.
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RESULTS |
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TopAbstractIntroductionMETHODSRESULTSDISCUSSIONREFERENCES |
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The sequences of doses for adequate and inadequate blocks in the four groups are shown in Figures 1 and 2. Figure 1A and B display sequences for plain bupivacaine groups, whereas Figure 2A and B depict the same for hyperbaric bupivacaine.
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A dose-sparing effect of epidural volume extension was seen with plain (group PB vs PBE: relative potency estimate 1.2), but not with hyperbaric bupivacaine (group HB vs HBE: relative potency estimate 1.04) (Tables 2 and 3). Also, the ED50 of plain bupivacaine was significantly less than that of hyperbaric bupivacaine, whether used with or without epidural volume extension (relative median potency estimate for group PB vs HB: 0.78, and for group PBE vs HBE: 0.68, Tables 2 and 3). For patients developing adequate block, Smax, Tmax, Time10, and Tadeq were compared among the groups (Table 4).
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The effects of epidural volume extension were analyzed by comparing groups PB versus PBE, and group HB versus HBE, whereas effects due to altered intrathecal baricity independent of epidural volume extension were projected by comparing group PB versus HB and group PBE versus HBE. Epidural volume extension increased the mean Smax significantly with plain but not hyperbaric bupivacaine (P < 0.05, Table 4). Such a difference in Smax was absent between groups HB and HBE. Plain bupivacaine showed significantly higher Smax whether used with or without epidural volume extension (P < 0.05). The Tmax was statistically similar among all groups (Table 4).
Epidural volume extension did not alter Time10, the onset to level T10 being statistically similar between groups PB and PBE, and groups HB and HBE (Table 4). However, the Time10 varied with baricity of the intrathecal drug, being significantly less in group PB than in group HB (P < 0.05), and in group PBE compared with group HBE (P < 0.05).
The addition of epidural volume extension significantly decreased the Tadeq for hyperbaric bupivacaine (P < 0.05, Table 4). In contrast, epidural volume extension failed to significantly alter Tadeq when added to plain bupivacaine (Table 4).
With both groups using plain bupivacaine, almost all cases of inadequate blocks were due to failure to achieve complete motor blockade (group PB: 9 of 10, group PBE: 9 of 9). In contrast, the majority of inadequate blocks with hyperbaric bupivacaine were due to failure to achieve both adequate sensory and motor blockade (group HB: 10 of 11 and group HBE: 8 of 10).
The incidence of intraoperative adverse effects in patients with adequate block, i.e., hypotension, nausea and vomiting, shivering and pruritus was statistically similar in the four groups. Hypotension occurred in 4, 6, 2, and 5 patients of groups PB, PBE, HB, and HBE, respectively.
Six patients had to be excluded from the study and were duly repeated as per the methodology. Four exclusions were due to accidental dural punctures and two patients were excluded due to nonfunctioning epidural catheters.
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DISCUSSION |
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TopAbstractIntroductionMETHODSRESULTSDISCUSSIONREFERENCES |
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An adequate block in this study was defined as a sensory level of T10 along with modified Bromage Score of 1, attained within 20 min11 of intrathecal drug deposition, since although orthopedic lower limb surgeries do not require levels higher than T10, complete motor blockade is considered essential.
The dose of bupivacaine in the first patient of each group was 10 mg, since earlier studies regarding block characteristics after epidural volume extension in orthopedic patients have used similar doses of bupivacaine.12,13 Also, in our usual clinical practice, the minimum dose of intrathecal bupivacaine during CSE is 10 mg.
For epidural volume extension in groups PBE and HBE, 10 mL normal saline was injected through the epidural catheter over 10–15 s. This volume has been proven effective for increasing the level of sensory block12–17 during epidural volume extension, which is a time-dependent phenomenon7,15 with maximum benefits if performed early. The epidural injection was hence performed immediately after block completion and before turning the patient supine. In our study, the addition of epidural volume extension did not show any dose sparing effect with hyperbaric bupivacaine. In contrast, the addition of epidural volume extension to plain bupivacaine resulted in a significant decrease in ED50 and increase in Smax. The effect of gravity would have led to caudad pooling of hyperbaric bupivacaine. The time lag between intrathecal injection and epidural instillation, demanded by the needle-through-needle technique of CSE, would compound differential intrathecal drug distribution, and hence the effect of epidural volume extension.
Although there is no study that elaborates the role of intrathecal drug baricity for the dose-sparing effect of epidural volume extension, Mardirosoff et al.15 observed failure of epidural volume extension in augmenting sensory block when patients were asked to sit for 5 min after intrathecal deposition of hyperbaric bupivacaine. The authors attributed failure of block augmentation to the restricted spread of local anesthetic to lumbar and sacral roots. Yamazaki et al.18 studied the role of intrathecal drug baricity in affecting cephalad augmentation of spinal block after epidural volume extension, and reported no difference by altering baricity of intrathecal tetracaine. However, in this investigation, the authors performed epidural volume extension with the patients in the lateral position, and that too 20 min after the intrathecal injection. With the patient in lateral position, spread of hyperbaric local anesthetic would not be confined to caudad spaces. Epidural volume extension performed 20 min after the subarachnoid injection may not be effective, since it is a time-dependent phenomenon.7 Thus, their results cannot be extrapolated to our study, wherein epidural volume extension was performed immediately after CSE block with the patient in the sitting position.
Independent of the addition of epidural volume extension, a comparison of group PB with HB, and group PBE with HBE revealed lower ED50, higher Smax, and earlier Time10 for plain bupivacaine. These results may all have been due to the differences in the drug baricity of the two solutions and its interplay with gravity. The caudad fixation of hyperbaric bupivacaine in the sitting position is evident from significantly lower Smax (P < 0.05) in group HB versus group PB (Table 4).
Plain bupivacaine resulted in a higher incidence of failed motor blockade, despite adequate sensory analgesia. This may have been due to the difference in baricity of the intrathecal bupivacaine. Delayed onset of motor blockade with plain bupivacaine has also been noted in earlier studies, when comparing plain and hyperbaric bupivacaine in identical concentrations for central neuraxial block in nonobstetric patients in the sitting position.19,20 In our study, the time limitation imposed for observing development of adequate motor block may have also contributed to more patients with inadequate motor block in groups PB and PBE.
Based on the above findings, there is no clinical utility of epidural volume extension application to intrathecal hyperbaric bupivacaine, since it failed to decrease the dose or raise the level of block, when CSE was performed in the sitting position. Whether used with or without epidural volume extension, plain bupivacaine appears to be more effective, requiring a smaller dose and producing higher sensory block with an earlier onset in comparison to hyperbaric bupivacaine. The ED50 of intrathecal plain bupivacaine with 25 µg fentanyl, for lower limb surgery with CSE performed in the sitting position, with and without epidural volume extension, is 6.5 and 7.8 mg, respectively. The addition of epidural volume extension to plain bupivacaine under these circumstances should be expected to raise the sensory level significantly as a consequence of its baricity.
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Footnotes |
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REFERENCES |
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TopAbstractIntroductionMETHODSRESULTSDISCUSSIONREFERENCES |
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