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Small-Dose Intrathecal Lidocaine Versus Ropivacaine for Anorectal Surgery in an Ambulatory Setting

Buckenmaier, Chester C. III, MD*,; Nielsen, Karen C., MD*,; Pietrobon, Ricardo, MD*†,; Klein, Stephen M., MD*,; Martin, Aliki H., RN*,; Greengrass, Roy A., MD*,; Steele, Susan M., MD*

doi: 10.1097/00000539-200211000-00028

Spinal anesthesia with the local anesthetic lidocaine has come under scrutiny because it is associated with transient neurologic symptoms (TNS). We designed this study to prospectively compare the efficacy of ropivacaine as an alternative to lidocaine in patients undergoing elective outpatient anorectal procedures. Seventy-two patients were randomized to receive either hyperbaric lidocaine 25 mg with fentanyl 20 μg (n = 37) or hyperbaric ropivacaine 4 mg with fentanyl 20 μg (n = 35). Patients were examined for motor block, sensory block, and block duration. Patients were contacted at 24, 48, 72, and 168 h and questioned about their perceptions of pain after the spinal with specific questions designed to diagnose TNS. There were no patients with TNS in either group. There was no significant difference between the lidocaine and ropivacaine groups in any of the outcomes studied. In conclusion, intrathecal hyperbaric small-dose ropivacaine with fentanyl is an acceptable anesthetic for anorectal surgery.

Departments of *Anesthesiology and †Surgery, Duke University Medical Center, Durham, North Carolina

July 10, 2002.

Address correspondence and reprint requests to Chester C. Buckenmaier III, MD, Department of Anesthesiology, Box 3094, Duke University Medical Center, Durham, NC 27710. Address e-mail to

Spinal anesthesia with the local anesthetic lidocaine is a useful choice for anorectal procedures in the ambulatory surgery setting. Advantages of spinal lidocaine include rapid onset of sensory and motor block, predictable efficacy, and prompt regression. Despite a long history of safe and effective use, intrathecal lidocaine has come under increasing scrutiny. In 1993, Schneider et al. (1) described severe radicular back pain after hyperbaric lidocaine spinal anesthesia. Since that article, multiple prospective studies have documented this syndrome, now termed transient neurologic symptoms (TNS). The incidence of TNS with intrathecal lidocaine ranges from 0% to 37%(2–4). Despite multiple studies documenting its presence, the exact etiology of TNS is unknown (5,6). However, data suggest that limiting the total dose may be beneficial (7). Currently, few data are available examining the effects of small-dose (25 mg) hyperbaric spinal lidocaine and fentanyl.

Ropivacaine, a long-acting amide local anesthetic available as a pure levoisomer, may be an alternative to lidocaine for hyperbaric spinal anesthesia. Long-acting amide local anesthetics have the smallest incidence of TNS but frequently have an unacceptable duration or side-effect profile. Studies comparing intrathecal hyperbaric small-dose lidocaine and ropivacaine for outpatient surgery are unavailable. In this double-blinded, prospective trial, intrathecal hyperbaric small-dose lidocaine and fentanyl were compared with hyperbaric small-dose ropivacaine and fentanyl for outpatient anorectal surgery.

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The study was approved by the IRB, and written, informed patient consent was obtained. Seventy-two patients classified as ASA physical status I–III, aged 18 yr or older, and scheduled for elective outpatient anorectal procedures were enrolled. Patient exclusion criteria included peripheral neuropathy, contraindications to spinal anesthesia, and the inability to give accurate responses to questions. All patients were scheduled to receive a spinal anesthetic as their primary anesthesia technique. Simple randomization schedules were generated by computer by using a 1:1 proportion. The patient’s randomization was contained in an envelope that was given to the attending anesthesiologist before the anesthetic procedure.

Patients were assigned to one of the following groups:

  1. Lidocaine group (n = 37): received a spinal anesthetic with 25 mg of 5% lidocaine (AstraZeneca, Willmington, DE) in 0.5 mL of 10% dextrose and 25 μg of fentanyl (0.5 mL).
  2. Ropivacaine group (n = 35): received a spinal anesthetic with 4 mg of 1% ropivacaine (AstraZeneca) in 0.5 mL of 10% dextrose and 25 μg of fentanyl (0.5 mL).

Sociodemographic data and baseline verbal analog scores (VAS) were obtained for pain, nausea, and pruritus (0, no pain, nausea, or pruritus; 10, worst imaginable experience of these symptoms) for each patient before surgery. The research nurse (responsible for outcomes assessment), surgeon, and patient were unaware of the injected spinal solution. All spinal anesthetics were performed in a preoperative holding area with standard ASA monitoring. Patients were given supplemental oxygen via face mask, and an upper-extremity vein was cannulated for vascular access. No attempt was made to prehydrate patients IV before placement of the spinal. Sedation for the spinal was achieved with IV midazolam 1–5 mg and fentanyl 50–225 μg, titrated to moderate sedation. All spinal anesthetics were placed by an anesthesiologist with a 25-gauge Pencan™ spinal needle and tray (B. Braun Medical Inc., Bethlehem, PA) with the patient in a sitting position.

All patients were maintained in the sitting position with knees flexed after the spinal injection. The number of needle insertions needed to enter the intrathecal space, the vertebral interspace level (L2-3, L3-4, or L4-5), and the perceived difficulty of the spinal (easy, moderate, or difficult) were recorded by the anesthesiologist.

The block was then evaluated by a research nurse at 5 and 10 min after local anesthetic injection. By using a toothpick and alcohol swab, loss of sensation to pinprick and temperature was evaluated to determine the upper and lower dermatomal spread of the sensory and sympathetic block. Motor block was also assessed with a modified Bromage scale (mBS; 0, full movement; 1, loss of hip flexors; 2, loss of knee extension; 3, loss of plantar flexion/extension), and the highest value in either limb was recorded. After sitting upright for at least 10 min, all patients were placed prone in the jackknife position for surgery. During surgery, the quality of the spinal block was assessed as adequate for surgery or inadequate, requiring conversion to general anesthesia. The need for increased IV fluids or vasopressor administration (ephedrine, phenylephrine, or atropine) was at the discretion of the anesthesiologist and was documented as an adverse event.

After arrival in the postanesthesia care unit (PACU), additional sensory, sympathetic (temperature), and motor data were collected as described every 15 min for 1 h. Times (minutes) from spinal injection to resolution of the motor block, to unassisted ambulation, to first void, and to meet PACU discharge criteria were also recorded. Pain, nausea or vomiting, and pruritus VAS scores on PACU arrival and discharge were also obtained.

Study patients were contacted by the research nurse via telephone at 24, 48, 72, and 168 h and questioned concerning their perceptions of pain after the spinal anesthetic with specific questions designed to diagnose TNS (Appendix 1). Patients who responded positively to Questions 5 and 6 on the outpatient follow-up questionnaire were considered to have TNS (back pain with radicular symptoms). Patient satisfaction with the spinal anesthetic was evaluated by the response to Question 12.

All data analysis was performed with an intent-to-treat principle that included all randomized patients. For continuous demographic and clinical data, parametric and nonparametric analysis of variance was used to analyze baseline differences between treatment groups (lidocaine versus ropivacaine). Stratified contingency table analysis and χ2 tests were used to analyze baseline differences in categorical patient variables. Analysis of covariance adjusted for baseline symptom scores was used to compare outcomes between the two treatment groups in the PACU and again at 24, 48, 72, and 168 h after surgery. All tests were two tailed, with a significance set at 0.05.

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Demographic data and type of surgery for the two groups are provided in Table 1. The two treatment groups were similar in sex, ASA status, age, and body mass index (kg/m2). Baseline median values for pain, nausea, and pruritus were 0. There was no significant difference between the lidocaine and ropivacaine groups with respect to number of attempts to enter the intrathecal space (no more than three attempts;Table 2), lumbar level of insertion (P = 0.10), or perceived difficulty of the spinal (P = 0.60). Adequate intraoperative anesthesia was achieved in all patients in both groups. Errors in the administration of the anesthetic protocol or technical complications with the spinal resulted in five patients (two ropivacaine and three lidocaine) being removed from data analysis. No adverse hemodynamic events were observed in any of the patients.

Table 1

Table 1

Table 2

Table 2

The cephalad extent of sensory block was the same for both groups (mean level, L5;P = 0.75). Motor block was minimal for both groups. There was no difference between groups in the extent of motor block after spinal placement (10 min after the block, 10 ropivacaine and 14 lidocaine patients had an mBS of ≥1). Motor block (mBS 3) persisted in the PACU in one patient receiving lidocaine and one receiving ropivacaine (P = 0.90). There was no significant difference between the lidocaine and ropivacaine groups in any of the variables studied (Table 2).

Mild back pain was reported in 10% of lidocaine patients and 11% of ropivacaine patients (P = 0.91) at 24 h. The incidence of back pain increased in both groups at 48 h but then decreased over the ensuing week. One patient from the lidocaine group had persistent back pain at 7 days (Table 2). No patients had back pain with radicular symptoms consistent with a diagnosis of TNS during the 1-wk follow-up period after either of the spinal anesthetics. Patient satisfaction with the spinal anesthetic was not different between the two treatment groups (P = 0.85), with 94% of the ropivacaine and 95% of the lidocaine patients being satisfied or very satisfied.

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This study demonstrates that intrathecal small-dose hyperbaric lidocaine 25 mg and ropivacaine 4 mg provide similar levels of block and duration. Both local anesthetics, when combined with 25 μg of fentanyl, provide acceptable conditions for anorectal surgery. There were no significant differences between the two spinal anesthetics in regression of sensory block to S2, pain, or nausea, as well as time to void, walk, and meet discharge criteria. Motor block was minimal in both groups and was likely of equal duration, as suggested by the similar time to ambulation for both groups. This is the first prospective trial comparing small-dose hyperbaric lidocaine with ropivacaine for outpatient anorectal procedures.

There is compelling evidence associating spinal lidocaine with TNS; as a result, research has been undertaken to find an alternative anesthetic (8,9). All local anesthetics used in the United States have been associated with TNS, although the incidence is smallest when the long-acting amide local anesthetics bupivacaine and ropivacaine are used (8,10–13). This study protocol was designed to compare lidocaine with ropivacaine and determine whether ropivacaine could be used as a substitute anesthetic. As a long-acting amide anesthetic, ropivacaine would ideally provide extended sensory blockade for improved analgesia with a small incidence of TNS.

The fact that both local anesthetics yielded similar results suggests that this ultra-small dose of ropivacaine 4 mg is similar to lidocaine 25 mg in providing acceptable surgical anesthesia for anorectal surgery in an ambulatory setting. In this protocol, patient positioning and local anesthetic doses were delivered to achieve isolated sacral anesthesia while attempting to avoid lower-extremity weakness. Larger doses of local anesthetic or supine positioning may have demonstrated a more prolonged motor blockade with ropivacaine that was not confirmed with this model. One advantage related to the minimal motor blockade observed with both local anesthetics was the ability of most patients to position themselves on the operating room table after the spinal. Spinals using larger local anesthetic doses typically produce increased motor block, requiring operating room personnel to assist in patient positioning. Interestingly, the lack of a difference in VAS scores, time to first void, and time to ambulation may be related to the fact that both groups received intrathecal fentanyl 25 μg, which likely provided analgesia longer than either small-dose local anesthetic could have achieved if used alone. The time to reach discharge criteria was significantly longer than the times reported by Li et al. (14) for local and spinal anesthesia for anorectal procedures. The dissimilar spinal anesthetic recovery likely represents institutional PACU differences. Although local anesthesia with sedation is a viable alternative to spinal anesthesia for anorectal surgery, many anesthesiologists and surgeons prefer an anesthetic that does not involve tissue manipulation within the surgical field.

The link between TNS and lidocaine spinal anesthesia has been investigated, but debate remains over the physiologic mechanisms that are involved in its development. Animal studies have demonstrated irreversible conduction block with clinically relevant concentrations of tetracaine and lidocaine (3,15). However, clinical trials that varied the concentration (but not the total dose) of intrathecal lidocaine failed to demonstrate a concentration effect in the incidence of TNS (5,6,16).

The small incidence of TNS in both groups in this study is likely related to the small dose of local anesthetic used. Morisaki et al. (17) demonstrated this point by using 3% lidocaine and dosages between 30 and 45 mg for anorectal surgery. This resulted in an incidence of TNS of only 0.4%, much smaller than previous studies involving larger dosages. Ben-David et al. (7) also demonstrated a dramatic difference with large-dose (33% incidence of TNS) and small-dose (3.6%) hypobaric lidocaine for knee surgery, further supporting the role that dose may have played in our study.

Another factor that may have contributed to the lack of TNS in our study was the use of the jackknife position. Other authors have also suggested that positioning for surgery may contribute to TNS, particularly when the lithotomy position and knee surgery positions (similar to lithotomy) are used (18,19). Interestingly, all of the patients in Morisaki et al.’s study were also positioned in the jackknife position for surgery, as was the case for our study. Studies involving larger total spinal lidocaine doses (70–80 mg) in patients placed in the supine or jackknife positions have also noted a significantly decreased incidence of TNS compared with studies that involve patients in high-risk positions (20,21).

Although patients in both the lidocaine and ropivacaine groups did have back pain, no patient met our criteria for TNS. Failing to detect a small incidence of TNS is one of the potential limitations of this study. The study population size was selected to determine equivalency of the anesthetics and was probably too small to detect a very infrequent incidence of TNS.

In conclusion, despite being a long-acting amide local anesthetic, small-dose ropivacaine 4 mg combined with fentanyl is an acceptable anesthetic for anorectal procedures in the ambulatory setting. Prolonged motor and sensory block typically associated with long-acting local anesthetics is not produced in the intrathecal space when ultra-small dosages are used. Adequate surgical conditions for anorectal surgery are produced with these small doses when the local anesthetics are combined with the opioid adjunct fentanyl. Intrathecal hyperbaric small-dose ropivacaine with fentanyl was as effective as small-dose lidocaine with fentanyl for ambulatory anorectal procedures.

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Appendix 1. 24 Hour Follow-Up Questionnaire




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