Spinal anesthesia with lidocaine is widely used for outpatient procedures because of its fast onset and short duration profile; however, it is also associated with a very frequent incidence of transient neurological symptoms (1–5). For this reason small doses of long acting drugs have been suggested as possible alternatives to lidocaine for outpatient spinal anesthesia (6).
Initial reports on the use of ropivacaine for spinal anesthesia suggested that its shorter duration as compared with bupivacaine could offer anesthesiologists a good option for ambulatory patients (7–10). Spinal ropivacaine has been also demonstrated to be nearly 50% less potent than bupivacaine (11), whereas levobupivacaine has the same potency as racemic bupivacaine (12); however, comparing 8 mg intrathecal levobupivacaine with 12 mg ropivacaine for inguinal hernia repair, Moizo et al. (11) reported that, even with a 1 to 1.5 potency ratio between the 2 drugs, ropivacaine provided shorter spinal block than levobupivacaine. Little information is available in the literature directly comparing the use of small doses of hyperbaric ropivacaine or levobupivacaine to produce unilateral spinal block for lower limb outpatient procedures. To achieve more information on this indication, we conducted this prospective, randomized, double-blind study to compare the adequacy and recovery profile of unilateral spinal block produced with 7.5 mg of 0.5% hyperbaric ropivacaine and equivalent (7.5 mg) and equipotent (5 mg) doses of 0.5% hyperbaric levobupivacaine.
After the study protocol had been approved by the local ethics committee, written informed consent was obtained from 91 ASA physical status I–II patients, aged 18–83 yr, scheduled to have elective ambulatory arthroscopic surgery of the knee. Patients with respiratory or cardiac disease, diabetes, or peripheral neuropathy and patients receiving chronic analgesic therapy were excluded.
After a 20-gauge IV cannula had been inserted at the forearm, standard volume infusion of lactated Ringer’s solution (7 mL/kg) was given; then patients were premedicated with midazolam (0.05 mg/kg IV) and ketoprofen (50 mg IV).
Using a computer generated sequence of numbers and a sealed envelope technique, patients were randomly divided into 3 groups: the first group received 7.5 mg of 0.5% hyperbaric levobupivacaine (group Levo-7.5, n = 30), the second group received 5 mg of 0.5% hyperbaric levobupivacaine (group Levo-5, n = 30), and the third group received 7.5 mg of 0.5% hyperbaric ropivacaine (group Ropi-7.5, n = 31). The hyperbaric anesthetic solution was aseptically prepared immediately before injection by an anesthesiologist who was not involved in further patient care using 2.7 mL of either plain ropivacaine 0.75% or plain levobupivacaine 0.75%, 1 mL of 33% glucose, and 0.3 mL of normal saline solution, achieving a final concentration of 0.5% local anesthetic with 8.25% glucose. Spinal anesthesia was performed at the L3-4 interspace using a 25-gauge Whitacre spinal needle (Becton Dickinson, Franklin Lakes, NJ) with the patient placed in the lateral decubitus position and lying on the operated side. The anesthetic solution was injected over 30 s without further cerebrospinal fluid aspiration (the speed of intrathecal injection was approximately 0.05 mL/s). The lateral decubitus position was maintained for 15 min after injection, then patients were turned to supine before surgery started.
An investigator blinded as to the solution injected recorded the evolution of sensory and motor blocks every 3 min until readiness for surgery and then every 5 min until the maximum level was reached. The level of sensory block was evaluated by loss of pinprick sensation (20-gauge hypodermic needle), whereas motor blockade was evaluated using a modified Bromage scale (0 = no motor block; 1 = hip blocked; 2 = hip and knee blocked; 3 = hip, knee and ankle blocked). Standard monitoring was used throughout the study, including noninvasive arterial blood pressure, heart rate, and pulse oximetry. Readiness to surgery was defined as the presence of adequate motor block (Bromage’s score ≥2) and loss of pinprick sensation at T12 on the operated side. Further assessment were performed every 30 min until complete regression of spinal block and achievement of home discharge criteria.
At the same observation times hemodynamic variables were also recorded. Clinically relevant hypotension was defined as a decrease in systolic arterial blood pressure by 30% or more from baseline values, and it was initially treated with a rapid IV infusion of 200 mL lactated Ringer’s solution; if this proved to be ineffective, an IV bolus of etilefrine (5 mg) was given. Clinically relevant bradycardia was defined as heart rate decrease to less than 45 bpm, and it was treated with 0.5 mg IV atropine.
The quality of spinal block was judged according to the need for supplementary IV analgesics and sedation: adequate spinal block = neither sedation nor analgesics were required to complete surgery; inadequate spinal block = need for additional analgesia (0.01 mg IV bolus of fentanyl) required to complete surgery; failed spinal block = general anesthesia required to complete surgery.
The time from local anesthetic injection to readiness for surgery and the spread of sensory block on both sides were recorded. Similarly, the time from local anesthetic injection to complete resolution of sensory and motor blocks, urination, unassisted ambulation, and readiness for home discharge, as well as recovery room complications, need for bladder catheterization, and pain treatments were also recorded. Standard criteria for home discharge were used, including hemodynamic stability, resolution of sensory and motor blocks, recovery of spontaneous voiding, unassisted ambulation with crutches, pain, nausea controlled with oral medication, and tolerance of oral fluids.
Postoperative analgesia consisted of 50 mg oral ketoprofen every 8 h on the operation day, and rescue analgesia with oral tramadol (50 mg) if the patient asked for more analgesics. The need for rescue tramadol during the first 24 h after surgery was also recorded. Postoperative follow-up was performed the day after surgery by phone, and 1 wk after surgery during a routine orthopedic visit by asking the patient about postoperative pain, headache, and paresthesias in the buttocks, thighs, or lower limbs.
The calculation of the required sample size was based on mean and standard deviation of complete regression of spinal block after anesthesia with ropivacaine and levobupivacaine reported in previous investigations (10–12): 30 patients per group were required to detect a 20-min difference in time for complete regression of spinal anesthesia with an expected effect size to standard deviation ratio of 0.9 accepting a two-tailed α error of 5% and a β error of 20% (13).
Statistical analysis was performed using the program Systat 7.0 (SPSS Inc., Chicago, IL). Data distribution was first evaluated using the Kolmogorov-Smirnov test. Anthropometric data, onset time of surgical block, and recovery times were analyzed with the Kruskal-Wallis test. The Mann-Whitney U-test with the Bonferroni’s correction was used for the post hoc comparisons. Changes over time were analyzed with a two-way analysis of variance for repeated measures with the Dunnett’s and Scheffé’s tests for post hoc comparisons. The Bonferroni’s correction was used for multiple comparisons. Categorical variables were analyzed using the contingency tables analysis and the χ2 test with the appropriate corrections. A P value ≤5% was considered as significant. Continuous variables are presented as mean ± sd or as median (range); categorical data are presented as number (%).
No differences in anthropometric variables and duration of surgery were reported among the three groups (Table 1). The median (range) time required to achieve readiness to surgery was 11 (10–16) min in group Levo-7.5, 10 (9–12) min in group Levo-5, and 10 (9–13) min in group Ropi-7.5 (P = 0.33). The median (range) maximum sensory level on the operated side was T8 (T7–9) in group Levo-7.5, T10 (T7–10) in group Levo-5, and T9 (T8–L1) in group Ropi-7.5 (P = 0.84). In all three groups there was a significant difference in height of sensory level between the operated and non-operated side; however, no differences were reported among the three groups. Figure 1 shows the evolution of sensory block on both the operated and non-operated sides during the first 30 min after injection. No differences in the evolution of sensory block on both sides were reported among the three groups. A strictly unilateral sensory block 30 min after injection was observed in 15 patients of group Levo-7.5 (50%), 18 patients of group Levo-5 (61%), and 22 patients of the group Ropi-7.5 (73%) (P = 0.40); whereas strictly unilateral motor block was observed in 28 patients of group Levo-7.5 (93%), 25 patients of group Levo-5 (83%), and 29 patients of group Ropi-7.5 (94%) (P = 0.31).
Rapid intravascular volume expansion to treat clinical hypotension was required in 4 patients of group Levo-5 (13%) and 2 patients of group Ropi-7.5 (6.5%) (P = 0.08). All these patients also required IV etilefrine administration. Bradycardia was observed in one patient of group Levo-7.5 and one patient of group Levo-5 (P = 0.33). Inadequate spinal block (0.1 mg fentanyl IV required to complete surgery) was observed in one patient of group Ropi-7.5 (3%) and one patient of group Levo-5 (3%) (P = 0.42). Failed spinal block was observed in only one patient of group Ropi-7.5 (P = 0.95); this patient received general anesthesia and was then considered for further statistical analysis according to an intention-to-treat basis.
Median (range) times for resolution of sensory and motor nerve blocks, unassisted ambulation, first micturition, and fulfillment of home discharge criteria are shown in Table 1. Resolution of spinal block and time to voiding and home discharge were shorter in group Ropi-7.5 than in group Levo-7.5; whereas no differences were reported as compared to group Levo-5. Most of the time home discharge criteria were met after the patient voided.
Postoperative pain relief was adequate in all studied patients and none of them required rescue tramadol administration during the first 24 h after surgery. No serious perioperative complications were reported in the 91 studied patients. One patient of group Levo-7.5 reported postdural puncture headache the day after surgery, requiring readmission to the hospital (P = 0.20). Standard treatment with nonsteroidal antiinflammatory drugs and IV fluid administration was given with complete resolution. No bladder catheterization was required in the three groups. No complaints of low back pain or dysesthesias in the lower limbs other than pain on the operated knee were reported at the 1-wk postoperative follow-up.
Lidocaine has been the most widely used local anesthetic for spinal anesthesia in day-case procedures because of its fast onset/short duration characteristics. It was considered an ideal choice for outpatient knee arthroscopy until transient neurologic symptoms were consistently reported after lidocaine spinal block (1–5). Furthermore, it has also been reported that outpatient status and knee arthroscopy position represent other relevant and independent risk factors for developing transient neurological symptoms after spinal anesthesia (5). For this reason, small doses of long-acting local anesthetics have been proposed to produce short-lasting spinal anesthesia (6). Ropivacaine and levobupivacaine are increasingly used for spinal anesthesia, but little information is available regarding their use to produce unilateral spinal block for lower limb outpatient procedures. Results of this prospective, randomized, double-blind study show that doses as small as 7.5 mg hyperbaric ropivacaine or 5 mg hyperbaric levobupivacaine provide a similarly adequate and restricted spinal block for outpatient knee arthroscopy, enabling patient discharge within <3.5 hours after spinal injection, whereas 7.5 mg of 0.5% hyperbaric levobupivacaine resulted in a 20% longer hospital stay.
Malinovsky et al. (8) reported that 15 mg of plain ropivacaine is less potent than 10 mg of plain bupivacaine; in fact, 16% of their patients had inadequate spinal anesthesia for urologic endoscopic surgery with ropivacaine. Khaw et al. (14) compared isobaric and hyperbaric intrathecal ropivacaine for cesarean delivery and reported that hyperbaric ropivacaine produced a more rapid and predictable block with faster recovery as compared with plain ropivacaine. Breebaart et al. (10) compared 15 mg intrathecal ropivacaine and 10 mg levobupivacaine with 60 mg lidocaine for outpatient knee arthroscopy and concluded that the three local anesthetics behave similarly with respect to the quality of anesthesia and degree of motor block but that voiding and discharge occurred significantly earlier with lidocaine than with the other two drugs. The authors considered a relative potency ratio of 1 to 1.5 between levobupivacaine and ropivacaine but used plain solutions and larger doses of local anesthetic as compared with the present study.
In a dose-effect study comparing hyperbaric levobupivacaine and racemic bupivacaine on volunteers, Alley et al. (12) reported that levobupivacaine and racemic bupivacaine have a nearly equivalent clinical profile, and similar results have been reported by Glaser et al. (15) in patients undergoing total hip replacement. On the contrary, when comparing the dose/effect relationship of hyperbaric ropivacaine and bupivacaine, McDonald et al. (7) reported a nearly 50% lower potency with ropivacaine than bupivacaine. However, Moizo et al. (11) recently reported that 8 mg hyperbaric levobupivacaine or 12 mg hyperbaric ropivacaine are acceptable alternatives to 8 mg hyperbaric bupivacaine when limiting spinal anesthesia at the operative side for inguinal hernia repair, but the use of a 1.5 to 1 equipotency ratio between ropivacaine and levobupivacaine resulted in a shorter duration of spinal anesthesia with ropivacaine, even if this was not associated with faster home discharge. Similar results have been also reported by Danelli et al. (16) during spinal anesthesia for cesarean delivery. For this reason we considered both an equivalent and a supposed equipotent dose of levobupivacaine as compared to 7.5 mg ropivacaine, and the results of this study seem to confirm the validity of the 1 to 1.5 equipotency ratio between levobupivacaine and ropivacaine.
Interestingly, the use of such small doses of either ropivacaine or levobupivacaine provided very fast recovery of voiding and home discharge. Urmey et al. (17) reported first micturition within 170 to 198 minutes after 60 mg of 2% plain lidocaine for outpatient knee arthroscopy. These results are not clinically different from our present findings, where spinal block with 7.5 mg ropivacaine or 5 mg levobupivacaine allowed recovery of sensory block within 135 and 150 minutes, respectively, and spontaneous micturition within 190 minutes for both groups.
In the present investigation we did not report any case of urinary retention requiring bladder catheterization, whereas in a previous investigation we observed an incidence of urinary retention as frequent as 6% in patients receiving 8 mg hyperbaric bupivacaine (18). The limiting factor to fulfill home discharge criteria was most commonly the recovery of spontaneous voiding. Interestingly, Mulroy et al. (19) suggested a relaxation of the requirements for voiding before home discharge in outpatients receiving spinal block with short-duration drugs (or <7 mg of hyperbaric bupivacaine) and undergoing surgical procedures at low risk of urinary retention. Such an aggressive approach to home discharge after outpatient procedures could further reduce the time required before the patient is sent home; however, further studies are required to confirm the safety of this practice in a large population.
The main problem with ropivacaine and levobupivacaine is that hyperbaric formulations are not available on the market, and therefore the physician has to dilute them. This could potentially reduce the safety of spinal injection. Moreover, the final density of the anesthetic solution may be less predictable than that of the commercially available specific hyperbaric formulations. However, in a laboratory investigation, McLeod (20) recently determined the density of levobupivacaine and ropivacaine with and without the addition of 8% dextrose at 23°C and 37°C. He reported a mean (± 3 sd) density of 1.030 (± 0.0011) for 0.5% levobupivacaine with 8% dextrose and 1.029 (± 0.0006) for 0.5% ropivacaine with 8% dextrose. Accordingly, although we did not directly measure the density of the local anesthetic solution in each patient, it can be assumed that no clinically relevant differences in density were present between the two drugs.
The final concern is the need to wait for up to 15 min before starting surgery after spinal injection to facilitate the lateral distribution of the local anesthetic solution. This may be considered a problem in a busy operating room. However, this disadvantage seems much more theoretical than practical: comparing preparation times (time from spinal injection to readiness to surgery) of either unilateral or conventional bilateral spinal block with the same small dose of bupivacaine resulted in a 5-min difference—statistically significant but clinically negligible (18). Moreover, this small disadvantage is also related to our organization of the operating room: it has been clearly demonstrated that placing all our regional anesthetics outside the operating room in a properly designed block room markedly improves efficiency (21,22).
In conclusion, the results of this study show that doses as small as 7.5 mg of 0.5% hyperbaric ropivacaine or 5 mg of 0.5% hyperbaric levobupivacaine are adequate for short-lasting spinal block for outpatient knee arthroscopy with a faster home discharge as compared with 7.5 mg of 0.5% hyperbaric levobupivacaine.
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© 2005 International Anesthesia Research Society
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