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Ropivacaine (S (-)-1-propyl-2”, 6”; pipecoloxylidide hydrochloride) a newer long-acting amide local anesthetic has various clinical and pharmacokinetic advantages over bupivacaine.
The aim of this study is to compare the onset as well as the duration of sensory block, hemodynamic variables, and postoperative analgesia with 0.5%, 0.75% ropivacaine and 0.5% bupivacaine after epidural anesthesia for lower limb orthopedic surgery.
Sixty American Society of Anesthesiologists I and II patients scheduled for lower limb orthopedic surgery were enrolled into this randomized, double-blind study. Epidural block was obtained with 15 ml of 0.5% ropivacaine (Group I), 15 ml of 0.75% ropivacaine (Group II), and 15 ml of 0.5% bupivacaine (Group III). The onset time, duration, and maximum level of sensory blockade achieved, as well as hemodynamic parameters and any side effects, were noted and treated accordingly. Postoperative monitoring for pain by visual analog scale (VAS) was done every 2 hourly for 24 h and transient neurological symptoms for 72 h.
Chi-square test for nonparametric data and ANOVA for parametric data.
Demographic characteristics were similar among groups. The onset of sensory block varied from 22.35 ± 2.74 min (mean ± standard deviation [SD]) in Group I, 16.95 ± 2.96 min (mean ± SD) in Group II, and 19.70 ± 2.25 min (mean ± SD) in Group III. The mean duration of analgesia in Group III (157 ± 14.90 min)was comparable to Group II (149 ± 16.51 min) but it was significantly more than Group I (141.5 ± 17.55 min). Postoperatively, VAS scores were higher in Group I patients who required more number of postoperative epidural top-ups with tramadol. Adverse effects were noted and treated accordingly. There was no incidence of transient neurological symptoms postoperatively.
Both ropivacaine and bupivacaine provided effective epidural anesthesia for lower limb surgery. Postoperative pain was less with 0.5% bupivacaine and 0.75% ropivacaine as compared to 0.5% ropivacaine.
Ropivacaine is a new long-acting amide local anesthetic, structurally similar to aminoamides, for example, bupivacaine and mepivacaine. Ropivacaine is a pure (S)-enantiomer while the latter two are racemic mixtures. Ropivacaine has similar pharmacodynamic and pharmacokinetic profiles resembling to that of bupivacaine. The onset and duration of sensory block and the overall clinical efficacy of anesthesia have been reported to be comparable to those seen with bupivacaine. However, the degree of motor block may be less with ropivacaine than bupivacaine when used in equal concentrations. Most importantly, ropivacaine is a pure S (−) enantiomer of bupivacaine and thereby less toxic to the cardiovascular and central nervous systems (CNSs).[1,2]
Ropivacaine is easily available in two strengths, i.e., 0.5% and 0.75% for use in epidural anesthesia. Crosby et al. showed that 0.5% ropivacaine and 0.5% bupivacaine produced equally effective sensory block for cesarean section with the median duration of sensory block varied between 1.7–4.2 h for ropivacaine and 1.8–4.4 h for bupivacaine. Among the side effects, 30% patients receiving ropivacaine experienced nausea as compared to 58% of those receiving bupivacaine. In another dose finding study, Wolff et al. compared epidural ropivacaine (0.5%, 0.75%, and 1%) and 0.5% bupivacaine in patients undergoing hip surgeries and showed that 0.5% ropivacaine and 0.5% bupivacaine were indistinguishable with regard to sensory and motor blocking characteristics while 1% ropivacaine produced a longer duration of analgesia and more intense motor block than 0.5% bupivacaine. However, many patients treated with 1% ropivacaine required treatment for hypotension and bradycardia. Brown et al. compared 0.5% ropivacaine and 0.5% bupivacaine for epidural anesthesia in 45 patients undergoing lower extremity surgery and showed that bupivacaine produced slightly longer duration of motor blockade than ropivacaine but did not find any statistical significant difference in the onset of analgesia or in highest sensory level achieved.
Casati et al. evaluated the onset time, duration of epidural anesthesia, and the quality of postoperative analgesia produced by 0.5% levobupivacaine, 0.5% bupivacaine, and 0.5% ropivacaine in 45 patients undergoing total hip replacement surgery in a randomized controlled manner and found the degree of pain relief to be similar in three groups without difference in local anesthetic consumption.
Some studies revealed similar sensory blockade characteristics of ropivacaine and bupivacaine while some revealed lesser duration of analgesia with ropivacaine at equal concentrations. As there is paucity of data on the duration of effective analgesia and postoperative pain with ropivacaine in epidural anesthesia in lower limb orthopedic surgery, the present study was designed to evaluate the quality of sensory block and postoperative analgesia achieved with 0.5% and 0.75% ropivacaine and to compare it with 0.5% bupivacaine when used in lower limb surgery.
The present study was conducted on sixty patients of age 18–60 years of the American Society of Anesthesiologists (ASA) I and II undergoing lower limb surgeries after obtaining approval from the Hospital Ethics Committee. Written informed consent was taken from all patients. Following exclusion criteria were taken into consideration:
The patients selected were randomly allocated into one of the three groups of twenty each. The present study was done in a double-blind manner by making sixty coded slips. The person performing the procedure and carrying out the observation was blinded to the drug solution injected. The drug solution was prepared in three separate syringes of 15 ml each.
Preanesthetic assessment was carried out 1 day before surgery. Details pertaining to the patient's clinical history, general physical and systemic examinations, and basic routine investigations were noted.
Patients were explained in their own vernacular language about epidural anesthesia and linear visual analog score using a 10 cm line, where 0 denoted “no pain” while 10 “worst imaginable pain.” All patients were kept fasting overnight and were given tablet alprazolam 0.5 mg orally on the night before surgery.
Baseline readings of heart rate, blood pressure, and peripheral arterial oxygen saturation were taken on receiving patients in operation theater. After preloading with 500 ml of crystalloid, the back was cleaned and draped under all aseptic conditions and local infiltration with 2% lidocaine was given in L3–L4 intervertebral space. Epidural block was performed using an 18-gauge Tuohy needle in the L3–L4 interspace using a midline approach in the sitting position, and space was identified by the loss of resistance to air. Epidural catheter was inserted 3–5 cm in a cephalad direction and a test dose of 3 ml of 2% lidocaine with 15 µg of adrenaline was injected after negative aspiration for cerebrospinal fluid and blood. If there were no untoward effects, the main dose of 15 ml of study drug solution was injected over 4 min epidurally. The following observations were recorded from this time:
Sensory block was assessed by loss of sensation to pinprick in the midline using a 22-gauge blunt hypodermic needle every 5 min until no change in level occurred 5 min apart. The following sensory parameters were defined:
The degree of motor block was assessed 30 min after epidural drug administration by the modified Bromage scale.
Postoperative pain was assessed by visual analog scale (VAS) at 2 h, 4 h, 6 h, 8 h, 10 h, 12 h, 18 h, and 24 h after surgery. Whenever VAS score reached >4, tramadol 100 mg in 8 ml of normal saline was given epidurally. Time to the first dose of tramadol and the total dose required for postoperative analgesia during 24 h was noted. In addition to this, total duration of analgesia which was the time interval from administration of the drug epidurally to time of first top up was also recorded.
Postoperative monitoring for any transient neurological symptoms such as tingling (paresthesia), numbness, pain originating in the gluteal region, or radiating to lower extremities was done at 24, 48, and 72 h.
The occurrence of hypotension and bradycardia was recorded. Hypotension was defined as 20% decrease of systolic blood pressure as compared with baseline and managed by intravenous (i/v) fluids, vasopressors such as i/v mephentermine 3 mg in incremental doses. Bradycardia was considered when heart rate decreased to 20% less than the baseline and was treated with 0.4 mg atropine.
Side effects such as nausea, vomiting, and shivering were also noted and appropriately treated. After completion of the study, the results were compiled and statistically analyzed using Chi-square test for nonparametric data and ANOVA for parametric data. Post hoc students paired t-test was applied wherever indicated using SPSS Statistics for Windows, Version17.0 (Chicago: SPSS Inc.). P < 0.05 was considered statistically significant and <0.001 as highly significant.
The three groups were similar in age, gender, number of ASA Grades I and II patients, and duration of surgery [Table 1].
The onset of sensory block was 16.95 ± 2.96 min in Group II, 19.70 ± 2.25 min in Group III, and 22.35 ± 2.74 min in Group I. On statistical analysis, the difference was statistically significant (P < 0.05) when Group II was compared with Group I and Group III [Table 2].
The mean Bromage scale after 30 min of epidural drug administration was 2.35 ± 0.49 in Group I, 2.80 ± 41 in Group II, and 2.85 ± 0.37 in Group III. The intergroup statistical comparison between Group I and II as well as between Groups I and III was statistically significant (P < 0.05). Hence, it can be inferred that the patients receiving 0.5% ropivacaine achieved lesser motor blockade than those receiving 0.5% bupivacaine and 0.75% ropivacaine [Table 2].
The hemodynamic changes occurring between 10 and 40 min were seen in all the three groups and coincided with the peak effect of epidural anesthesia. There was statistically significant decrease in blood pressure and heart rate from the baseline in all the three groups after 10–15 min. However, when these groups were compared with each other, the changes were statistically insignificant [Figure 1]. On intergroup comparison, all the adverse effects were statistically comparable except for incidence of bradycardia in Group III which was significantly higher (P < 0.05) [Table 3].
The mean duration of analgesia was calculated as time interval from the epidural drug administration to the time of first tramadol top up. It was significantly prolonged in Group III when compared to Group I. However, when concentration of ropivacaine was increased to 0.75%, the duration increased and the Group II and III were comparable. The postoperative pain VAS scores were higher in Group I patients throughout the study period than Group II and III; statistically all the groups were comparable except at 18 h when pain scores were clinically as well as statistically higher in patients receiving 0.5% ropivacaine as compared to 0.75% ropivacaine and 0.5% bupivacaine [Figure 1]. As shown in Table 2, tramadol requirement was more in Group I as compared to other two groups. Transient neurological symptoms were not observed in any group at 24 h, 48 h, and 72 h postoperative follow-up period.
Ropivacaine is a long-acting regional anesthetic that has come up recently into practice. It has been extensively studied after animal studies indicated that it is less cardiotoxic than equivalent doses of bupivacaine. However, the replacement of widely used bupivacaine with ropivacaine will depend on relative cardiotoxicity and relative anesthetic potency of ropivacaine in humans.
In our study, the mean onset of sensory block was faster in patients receiving 0.75% ropivacaine as compared to 0.5% bupivacaine and 0.5% ropivacaine. This difference was statistically significant but clinically insignificant. Similar results were shown by Finucane et al. in comparison of three doses of ropivacaine (0.5%, 0.75%, and 1%) with 0.5% bupivacaine in patients undergoing hysterectomy. However, studies by Wolff et al., Brown et al., Brockway et al., and Chandran et al. showed comparable onset of analgesia at all dermatomal levels.[4,5,8,9]
The duration of sensory blockade (time to two segment regression) was significantly longer with 0.75% ropivacaine than 0.5% ropivacaine and 0.5% bupivacaine which was in accordance with the study by Concepcion et al.
Our study indicated that 0.5% ropivacaine produced significantly lesser motor block than 0.75% ropivacaine and 0.5% bupivacaine. However, the motor block produced by 0.75% ropivacaine and 0.5% bupivacaine was comparable. Our result corresponds to other studies by Brown et al., Brockway et al., and Muldoon et al. which proved that bupivacaine produced more motor blockade than ropivacaine at equal concentration.[5,8,11] But, McGlade et al., failed to demonstrate any difference in motor block characteristics of the two drugs.
This greater degree of differential block with ropivacaine at low concentrations has a clinical advantage in providing analgesia with minimal motor block. This property of ropivacaine holds definitive advantage in situations such as labor analgesia and postoperative pain management where early ambulation is desirable. However, higher concentrations are needed when abdominal muscle relaxation or complete motor blockade of lower limbs is necessary.
The hemodynamic changes occurring between 10 and 40 min were seen in all the three groups and coincided with the peak effect of epidural anesthesia. There was decrease in blood pressure and heart rate from the baseline in all the three groups after 10–15 min. However, on intergroup comparison, the groups were comparable with each other except incidence of bradycardia which was significant in 0.5% bupivacaine group.
The difference between 0.5% bupivacaine and 0.5% ropivacaine group was significant statistically when duration of analgesia was assessed, whereas 0.75% ropivacaine and 0.5% bupivacaine were comparable. The above results correspond to those of Brown et al., who demonstrated prolonged sensory analgesia with 0.5% bupivacaine than 0.5% ropivacaine. Similar results have been seen in an intradrug comparison study of three concentrations of ropivacaine (0.5%, 0.75%, and 1%) by Zaric et al., and Sandler et al., who showed least duration of analgesia with 0.5% ropivacaine and maximum with 1% ropivacaine.[13,14] However, in comparison of 0.75% ropivacaine and 0.5% bupivacaine for epidural anesthesia in lower extremity orthopedic surgeries, Chandran et al. observed relatively longer duration of postoperative analgesia with ropivacaine while there were no significant differences in other block parameters.
The relatively lesser duration of analgesia in all the groups of our study in comparison to the previous studies could be attributed to the lesser volume of drug used. The total number of top-ups and the tramadol requirement in 24 h was also noted which revealed highest requirement in 0.5% ropivacaine group than in 0.5% bupivacaine and least in 0.75% ropivacaine group.
Both ropivacaine and bupivacaine were effective for epidural block in patients undergoing lower limb surgeries. The duration of postoperative analgesia was less with 0.5% ropivacaine while 0.75% ropivacaine and 0.5% bupivacaine were comparable. Keeping in view the better safety profile of ropivacaine, it can replace bupivacaine in regional techniques where larger amounts of local anesthetics are required.
There are no conflicts of interest.