Second Department of Anaesthesiology, Toho University School of Medicine, 2-17-6 Ohashi, Meguro-ward, Tokyo 153-8515, Japan
Corresponding author. E-mail: atruth@oha.toho-u.ac.jp
Accepted for publication: September 26, 2002
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Abstract |
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Methods. Twenty-seven patients undergoing lumbar epidural anaesthesia with lidocaine 2%, 17 ml at L4-5 or L5-S1 were randomly divided into three groups. Plain lidocaine, lidocaine with 1:200 000 epinephrine or lidocaineepinephrinebicarbonate was administrated via an epidural catheter. The pain threshold after repeated electrical stimulation was used to assess the sensory block at the L2, S1, and S3 segments. Motor block was evaluated using the Bromage scale.
Results. Patient characteristics were comparable between the groups. The pH of lidocaine in the lidocaineepinephrinebicarbonate group was significantly higher than that in other groups. Pain thresholds at the S1 and S3 segments in the lidocaineepinephrinebicarbonate group were significantly higher than those in the lidocaineepinephrine group. However, differences in the pain threshold at the L2 segment between groups were insignificant. The time to onset of sensory block at the S1 and S3 in the lidocaineepinephrinebicarbonate group was significantly shorter than that in the lidocaine group. Pain threshold by pinprick test was approximately within the 3050 mA range.
Conclusion. A combination of lidocaine, bicarbonate, and epinephrine increases the pain threshold over the sacral segments.
Br J Anaesth 2003; 90: 1738
Keywords: anaesthetics local, lidocaine; anaesthetic techniques, epidural
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Introduction |
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It has been reported that the mean time to achieve complete sacral anaesthesia with lidocaine hydrochloride 2% was 21 min following caudal epidural block.4 If a lumbar epidural successfully blocks the sacral segments within 21 min then there is no specific requirement to perform caudal epidural block. The addition of sodium bicarbonate to local anaesthetic enhances the effects of block,58 whilst the addition of epinephrine (5 µg ml1, 1:200 000) to lidocaine hydrochloride 2% markedly affected the extradural caudal spread (L2-3).9 Therefore, the addition of sodium bicarbonate and epinephrine to lidocaine would be predicted to accelerate both the onset and caudal spread of lumbar epidural anaesthesia.
Electrical stimulation has been used to assess the degree of regional block as this method allows quantification of analgesia and induces temporal summation. Induction of temporal summation may render this test closer to clinical pain.6 10 11 Temporal summation occurs when the repetition of a peripheral stimulus causes increased and prolonged firing of dorsal horn neurones (central sensitization) thereby increasing pain perception.12 Central sensitization is likely to play an important role in the physiopathology of acute and chronic pain syndromes, including postoperative and neuropathic pain.13
We compared the clinical efficacy [onset, sensory block of cephalad (L2 segment) and caudal region (S1 and S3 segments), motor block, and sympathetic block] within 20 min following lumbar epidural anaesthesia with either: (i) lidocaine alone, (ii) lidocaineepinephrine, or (iii) lidocaineepinephrinesodium bicarbonate. We assessed analgesia using repeated electrical stimulation.
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Methods |
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After institutional review board approval and written, informed consent, patients (ASA physical status III, 1665 yr of age) undergoing elective lower abdominal surgery, lower extremity surgery, vaginal surgery, or haemorrhoidectomy with epidural anaesthesia were enrolled in this prospective double-blind study. Randomization was performed by means of sealed envelopes.
The patients were divided into three groups: (i) lidocaine, (ii) lidocaineepinephrine, and (iii) lidocaineepinephrine bicarbonate. The anaesthetic solutions were as follows: plain lidocaine (20 ml of xylocaine 2% (Astra Zeneca, Osaka, Japan) plus 2 ml of saline 0.9%); lidocaine epinephrine (20 ml of xylocaine 2% plus epinephrine (1:200 000) plus 2 ml of saline 0.9%); lidocaine epinephrinebicarbonate (20 ml of xylocaine 2%, plus epinephrine (1:200 000) plus 2 ml of sodium bicarbonate 8.4%, being added immediately before administration). All solutions were given via an epidural catheter. The anaesthetic solutions were maintained at room temperature and the operating room temperature was maintained at 2426°C.
Patients were premedicated with an i.m. injection of atropine 0.5 mg and midazolam 2 mg, 30 min before admission into the operating room. After insertion of an i.v. catheter, non-invasive arterial pressure, ECG, and arterial saturation were monitored. A pulse oximeter probe was applied to a big toe. Plethysmographic waveforms were recorded before and after epidural injection and every 5 min for 20 min (Datex AS/3TM, Helsinki, Finland). Plethysmographic waveforms reflect the changes in blood pulsation or flow at the site of measurement.15 The amplitude of pulse oximeter waveforms on the toe significantly increases after lumber epidural anaesthesia16 and the increase in the pulse amplitude from the toe may aid in the early detection of successful epidural block.16 17
All epidural punctures were performed at the L4-5 or L5-S1 interspace. The epidural space was identified while patients were in the lateral position by using an 18 G Tuohy needle with its bevel facing cranially and a loss of resistance technique using saline. A 20 G catheter was inserted 35 cm into the epidural space. After negative aspiration, 3 ml of a solution containing lidocaine 2% with epinephrine was administrated as a test dose. If after 2 min there was no evidence of intravascular or subarachnoid injection, an additional 14 ml was injected over a 1.5 min period. The time at which the study drug injection ended was termed time 0 for the purpose of subsequent patient assessment. The pH of lidocaine was determined by using a pH METER (Shimadzu, Kyoto, Japan).
In order to evaluate the pain threshold, we used four stimuli at 2 Hz (i.e. train-of-four) with TOF GUARDTM (Biometer International, Odense, Denmark), which was originally used to evaluated the neuromuscular block. These stimuli evoke temporal summation.14 18 Bipolar surface AgAgCl electrodes were placed at the dermatomes L2 (ventral femoral region) as an index of cephalad spread, S1 (the lateral malleolus for stimulation of the sacral nerve) and S3 (gluteal region at the left paravertebral line) as an index of caudal spread.
Subjective pain thresholds were recorded as follows. A 200 µs, square wave impulse was used as a single stimulus. In order to determine the threshold for temporal summation, the single stimulus was repeated four times at 2 Hz and current intensity was increased from 5 mA in steps of 15 mA until summation (perception of the last stimulus being perceived as painful) was observed or a maximum current of 60 mA was reached in which case threshold was defined as 60 mA. The test was repeated at dermatomes L2, S1, and S3 at 5, 10, 15, and 20 min following administration of lumbar epidural anaesthesia.
Sensitivity to pinprick was tested at L2, S1, and S3 dermatomes 2 cm from the sites of electrical stimulation. The pinprick test was performed by pricking the skin twice with a 26 G needle at an interval of approximately 0.3 s. Cold sensitivity was tested with a gel bag that was kept in a freezer and applied to a 5 cm diameter area for 3 s. The pinprick test was repeated at the dermatomes L2, S1, and S3 for 5, 10, 15, and 20 min following administration of lumbar epidural anaesthesia. The onset of sensory block was defined as the time from time 0 to the abolition of the pinprick response. The level of anaesthesia was assessed in the anterior mid-sagittal line at 20 min by loss of cold sensation as described above.
Motor block was recorded using the Bromage scale (0=full flexion of feet and knees, 1=just able to move knees, 2=able to move feet only, and 3=unable to move feet or knees) with assessments performed at 5, 10, 15, and 20 min following administration of lumbar epidural anaesthesia. Each patient was hydrated with acetate Ringers solution 10 ml kg1 during the first hour.
Analysis of patient characteristics was by the KruskalWallis test. Wilcoxons signed-rank test was used for differences of haemodynamic data within the groups. The pain threshold response was compared using the repeated measures, one-way analysis of variance (ANOVA). The amplitude of plethysmographic waveforms and Bromage scale values were compared using the KruskalWallis test. A Bonferroni adjustment was made for multiple comparisons if significant results were obtained. Statistical analysis for the onset of sensory block was performed by utilization of survival analysis (KaplanMeier curves). The log rank test was used for comparisons among the groups. A P-value <0.05 was considered statistically significant. All data except the level of anaesthesia are presented as mean (SD). The level of anaesthesia is represented as median and range.
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Results |
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Discussion |
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Block of the S1 segment in the lidocaine and lidocaine epinephrine groups was delayed in this study. Our results indicate that the block of S3 is easier than that of S1 whilst the S3 segment is blocked as rapidly as the L2 segment. The data indicate that, with the exception of the S1 segment, the caudal spread of lumbar epidural anaesthesia using a catheter technique at L4/5 or L5/S1 is comparable with cephalad spread. Lumbar epidural anaesthesia produced sufficient block of the sacral segments except S1. The delayed block of S1 may be explained by the large size of this nerve root compared with those of other segments.1 2 These results stress that particular attention must be paid to the block of the S1 segment during the evaluation block of sacral segments. The S4 and S5 segments were not examined in our study because Axelsson and colleagues22 reported that the S3 segment could be blocked just as rapidly as both the S4 and S5 segments.
In previous reports, anaesthetic level was usually evaluated by pinprick or cold testing. The information obtained by these tests is usually limited to two responses, that is the presence or absence of sensation.6 The stimulation provided by pinprick or cold may be weaker than that of surgery. It has been reported these tests do not necessarily predict pain-free skin incision.23 Quantification of analgesia is needed in order to evaluate the block more accurately. It may be possible to quantitively assess the degree of sensory block by measuring the threshold of pain sensation by our repeated electrical stimulation. We believe that repeated electrical stimulation might be a more reliable method than pinprick or cold testing. Our results indicated that absence of pinprick sensation corresponded to a pain threshold of approximately 3050 mA.
It is not clear why the addition of epinephrine to lidocaine did not enhance the epidural block in this study. Murphy and colleagues9 reported that the caudal spread of analgesia was improved with an epinephrine-containing solution. In their report, the complete block of sacral segments may have required 36 min. Curatolo and colleagues21 have reported that epidural epinephrine produces segmental hypoalgesia. Evaluation was performed 30 min after the administration of the solution in their study. These reports suggest that epinephrine might produce an enhancement of the block over a period of 30 min. However, we assessed the extent of the block only to 20 min after administration of the local anaesthetic and this may explain why we did not detect a significant difference.
We conclude that a combination of lidocaine, bicarbonate, and epinephrine increases the pain threshold of the sacral segments. We must pay particular attention to the block of the S1 segment during evaluation. Lumbar epidural anaesthesia with the lidocaineepinephrinebicarbonate combination provides an acceptable alternative in cases where caudal epidural anaesthesia is difficult to perform.
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References |
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