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From the Department of Anesthesiology, Kitasato University School of Medicine, Sagamihara, Japan.
Address correspondence to: Dr. Akifumi Kanai, Assistant Professor, Department of Anesthesiology, Kitasato University School of Medicine, 1-15-1 Kitasato, Sagamihara 228-8555 Japan. Phone: +81-42-778-8809; Fax: +81-42-778-9781; E-mail: kanaiakifumi{at}aol.com
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Abstract |
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Methods: Forty patients, physical status ASA I–II, scheduled for gynecological abdominal surgery, were enrolled in this double blind randomized trial. A catheter was inserted 4 cm in the epidural space in the midline at L1–L2. Three minutes after a test dose of 2 mL plain 1% mepivacaine over four seconds, 8 mL were injected epidurally at a rate of 1 mL•sec–1 (fast group) or 0.05 mL•sec–1 (slow group). Sensory and motor blockade, blood pressure, and heart rate were assessed at five, ten, and 15 min after the epidural injection.
Results: There was a significant difference in the spread of sensory blockade at five minutes after the epidural injection between the two groups, but not at ten and 15 min. Blood pressure decreased at five and ten minutes, recovered at 15 min in the fast group, and remained stable in the slow group.
Conclusion: Rapid injection of mepivacaine in the epidural space produced a more rapid onset of epidural block than slow injection, but there was no difference in the final extent of the block.
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Introduction |
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A time sequence is apparent during blockade of peripheral nerve action potentials by local anesthetics.6 Sympathetic precedes sensory blockade, and leads to hypotension, tachycardia, and cutaneous warmth through extensive vasodilatation. The decrease in blood pressure can be used as an indicator of the spread of sympathetic nerve blockade. Sensory and motor nerve blockade can be evaluated by cutaneous coolness and skeletal muscle weakness, respectively.
We designed the current study to compare two rates of injection of mepivacaine into the epidural space to determine whether rate of injection affects the speed of nerve blockade.
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Methods |
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All patients received lactated Ringer’s solution at a rate of 1 mL•kg–1 for one hour before arrival in the operating room and at 10 mL•kg–1•hr–1 during the subsequent observation period. Operating room temperature was kept at 25° centigrade. The epidural puncture was performed at the L1–L2 interspace with a 17-gauge Tuohy needle using the midline approach, with patients remaining in the lateral decubitus position. The epidural space was identified using a loss of resistance to saline technique. Less than 1 mL of saline was injected after the needle had entered the epidural space. A 19-gauge epidural catheter was passed through the needle with the bevel directed cephalad. Following withdrawal of the needle, 4 cm of catheter were left in the epidural space. An injection of mepivacaine 1% at room temperature was given through the epidural catheter. Three minutes after the test dose of 2 mL over four seconds, 8 mL were injected at either rate of 1 mL•sec–1 (group F) or 0.05 mL•sec–1 (group S) with the patient in the supine position.
Sensory and motor blockade, blood pressure, and heart rate were assessed at five, ten, and 15 min after the end of injection of the main dose of mepivacaine. The sensory assessment was started in the block zone and moved towards the no block zone. Sensory block was considered to have occurred when the sensation of cold was markedly reduced or abolished. A dermatome was considered blocked only if the block could be demonstrated bilaterally. Motor blockade was assessed by recording motor function of the lower limbs (modified Bromage scale) immediately after each evaluation of sensory block: 0 = no paralysis (full flexion of knees and feet); 1 = inability to raise extended legs (able to move knees); 2 = inability to flex knees (able to flex ankle joints); 3 = inability to flex ankle joints (unable to flex ankle joints and knees). The assessments were performed by an anesthesiologist who was unaware of group assignment.
Within group comparisons were made by analysis of variance with repeated measures, and between group comparisons were made by analysis of variance with non-repeated measures. If significant differences were detected by analysis of variance, individual means were compared by using the Student-Newman-Keuls test. Differences were considered statistically significant if P < 0.05. Expecting that a clinically significant difference in the number of bilaterally blocked dermatomes is four segments and that the standard deviation of the data is 4, sample size calculation indicated that 16 patients in each group would be required to detect a difference with an 
= 0.05 and ß = 0.20.
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Results |
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).
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. Although time was measured from the point at which the epidural injection was finished, no differences were found at each assessment time between the two groups. However, mean blood pressure decreased slightly at five and ten minutes, recovered at 15 min in the fast group, whereas it remained stable in the slow group. Heart rate did not change during the observation period in the two groups.
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. The spread of sensory blockade in the fast group was rapid, showing no difference between the ten and 15 min time points. In the slow group, the spread increased gradually, resulting in a significant difference between any two assessment times. At five minutes, significantly more dermatomes were blocked in the fast injection group compared with the slow group (P < 0.01), but at ten and 15 min there were no significant differences between the groups. Table IV shows the number of patients in whom perineal blockade was present at five, ten and 15 min. At the five-minute assessment time, perineal blockade with bilateral block of the second to fourth sacral dermatomes occurred in 13 patients in group F and three patients in group S (P < 0.05, Chi squared test).
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Discussion |
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Injecting a constant volume of anesthetic solution epidurally produces an instantaneous increase in epidural pressure with a subsequent return toward preinjection values. Characteristically, the curve of epidural pressure vs time exhibits three successive components: the peak, the descent, and the residual values.12 The first part of the epidural pressure curve has been known as the forced response curve, derived from expansion of the epidural space induced by the administration of a given volume of anesthetic. The second part of the curve constitutes the free response curve, based on intrinsic properties of the epidural space such as compliance and resistance. Finally, the higher the residual epidural pressure, the more extensive the anesthetic blockade, but higher peak epidural pressures do not change the extent of blockade. The peak epidural pressure correlates directly with the speed of injection of anesthetic solution, not with its volume, whereas the residual epidural pressure correlates directly with its volume and not with the speed of injection.7 Therefore, the speed of epidural injection does not influence the final extent of sensory blockade. Although in the present study the observation period was only 15 min, the two groups studied showed similar spread of anesthesia at 15 min. However, our results suggest a more rapid spread of mepivacaine in the epidural space and earlier establishment of block following a fast injection. A rapid epidural injection of mepivacaine will more reliably produce perineal blockade at five minutes. When early onset of analgesia and sacral blockade are required for intra- and postoperative pain control, our results suggest that a rapid injection of local anesthetic is indicated. A larger dose injected slowly might be expected to produce a similar result in the short term,1,9 but the epidural blockade will progress to include more segments than necessary, possibly resulting in severe hypotension and skeletal muscle relaxation.
In conclusion, a faster lumbar epidural infusion of mepivacaine leads to more rapid spread of sensory blockade, in the absence of clinically significant hypotension. Although no difference could be found in the final level of the block, the speed of the epidural infusion of mepivacaine is considered important when rapid analgesia is required.
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Footnotes |
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References |
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2 Galindo A, Benavides O, De Munos SO, Bonilla O, Pena R. Comparison of anesthetic solutions used in lumbar and caudal peridural anesthesia. Anesth Analg 1978; 57: 175–9.
3 Janes EF, McCrory JW. The loading dose in continuous infusion extradural analgesia in obstetrics. Br J Anaesth 1991; 67: 323–5.
4 Clark V, McGrady E, Sugden C, Dickson J, McLeod G. Speed of onset of sensory block for elective extradural caesarean section: choice of agent and temperature of injectate. Br J Anaesth 1994; 72: 221–3.
5 Capogna G, Celleno D, Tagariello V. The effect of pH adjustment of 2% mepivacaine on epidural anesthesia. Reg Anesth 1989; 14: 121–3.[Medline]
6 Fink BR. Mechanisms of differential axial blockade in epidural and subarachnoid anesthesia. Anesthesiology 1989; 70: 851–8.[Medline]
7 Cardoso MM, Carvalho JC. Epidural pressures and spread of 2% lidocaine in the epidural space: influence of volume and speed of injection of the local anesthetic solution. Reg Anesth Pain Med 1998; 23: 14–9.[Medline]
8 Terai T, Yukioka H, Fujimori M. A double-blind comparison of lidocaine and mepivacaine during epidural anaesthesia. Acta Anaesthesiol Scand 1993; 37: 607–10.[Medline]
9 Concepcion M, Covino BG. Rational use of local anaesthetics. Drugs 1984; 27: 256–70.[Medline]
10 Rosenberg PH, Saramies L, Alila A. Lumbar epidural anaesthesia with bupivacaine in old patients: effect of speed and direction of injection. Acta Anaesthesiol Scand 1981; 25: 270–4.[Medline]
11 Blanco D, Mazo V, Ortiz M, Fernandez-Llamazares J, Vidal F. Spread of local anesthetic into the epidural caudal space for two rates of injection in children. Reg Anesth 1996; 21: 442–5.[Medline]
12 Usubiaga JE, Wikinski JA, Usubiaga LE. Epidural pressure and its relation to spread of anesthetic solutions in epidural space. Anesth Analg 1967; 46: 440–6.
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