Comparison of the Efficacy of Intrathecal Isobaric Ropivacaine and Bupivacaine in Day Care Knee Arthroscopy: A Randomized Controlled Trial.

BACKGROUND: The primary goal of ambulatory anesthesia is a rapid recovery with minimal side effects. Ropivacaine, due to its property of sensory-motor dissociation, maybe a useful agent when equivalent spinal anesthesia and quicker recovery of motor function is desirable. AIM: The aim of this study is to compare the efficacy of intrathecal isobaric ropivacaine with bupivacaine and to assess their postoperative recovery profile in patients undergoing arthroscopic knee surgery. SETTING AND
DESIGN: This randomized controlled study was conducted at a tertiary care hospital.
MATERIALS AND METHODS: A total of 90 adult American Society of Anaesthesiologist physical status Classes 1 and 2 patients were randomized into two groups to receive 2 ml plain solution of either 0.5% bupivacaine (Group B) or 0.75% ropivacaine (Group R). In the intraoperative period, onset, efficacy, duration, and regression of sensory and motor block were noted in both the groups at regular intervals. Postoperatively, the groups were compared for pain score, recovery profile, analgesic requirement, and complications. STATISTICAL ANALYSIS: Data analysis was performed using Chi-square test and Student's t-test.
RESULTS: The mean onset time of sensory block at L1 was significantly less (P = 0.025) and duration of sensory and motor block was significantly more (P = 0.001) with bupivacaine as compared to ropivacaine. The analgesic requirement on the 1st postoperative day (P = 0.011) and incidence of delayed voiding of urine (P = 0.022) were significantly more with ropivacaine. The postoperative recovery profile and discharge times were similar between the groups.
CONCLUSION: Isobaric ropivacaine was associated with a longer onset and shorter duration of sensory and motor block, increased postoperative analgesic requirement, higher complication rate, and similar discharge times as compared with bupivacaine. Therefore, isobaric bupivacaine may be preferred over isobaric ropivacaine for day care knee arthroscopy, especially in cases with an anticipated longer duration of surgery.

INTRODUCTION

The changing trend of surgical practice from an inpatient to outpatient convention has urged us to modify our anesthetic technique to suit the ambulatory setting. The primary goal of ambulatory anesthesia is rapid recovery leading to early patient discharge with minimal side effects. With the availability of rapid, short-acting anesthetic, analgesic, sympatholytic and muscle relaxant drugs, as well as improved monitoring devices, it has been possible to minimize the adverse effects of anesthesia on the recovery process.[1] Elective knee arthroscopic surgery is one such procedure where the patient can be mobilized within a few hours after surgery. Spinal anesthesia and short general anesthesia (GA) are the commonly used techniques for this procedure.

Subarachnoid block (SAB) with a local anesthetic not only makes the patient insensible to the pain of tourniquet, incision, and surgery but also it makes the surgeon comfortable by providing adequate muscle relaxation. Spinal anesthesia is gradually gaining momentum over GA in arthroscopic knee surgery due to lesser postoperative morbidity and hospital stay.[2]

Ropivacaine is an amide local anesthetic with similar structure, physiochemical properties and mechanism of action as compared with bupivacaine. It produces similar sensory block at equipotent doses and a shorter duration of motor block (50%–67% that of bupivacaine).[3] Ropivacaine provides an improved safety profile due to reduced neurotoxic and cardiotoxic potential. It may, therefore, be a potentially useful agent when equivalent spinal anesthesia and quicker recovery of motor function is desirable, especially in an ambulatory setting.[4]

We hypothesized that intrathecal isobaric 0.75% ropivacaine (15 mg) would be comparable to isobaric 0.5% bupivacaine (10 mg) for the efficacy of anesthesia and analgesia, and in addition would provide a better postoperative recovery profile and readiness for discharge. The purpose of the present study, therefore, was to evaluate the efficacy of intrathecal isobaric ropivacaine with bupivacaine in patients undergoing arthroscopic knee surgery, using the duration of the sensory block as primary outcome and duration of the motor block as secondary outcome.

MATERIALS AND METHODS

The study was conducted after written informed consent from patients and after being duly approved by the Institutional Ethics Committee (Ethics/Thesis/11/3). Ninety adult patients belonging to the American Society of Anaesthesiologist physical status Classes 1 and 2, in the age group of 18–65 years, weighing between 50 and 75 kg with height ranging from 150 to 180 cm, scheduled to undergo elective knee arthroscopy under SAB were included in the study. Patients who were unable to understand the procedure and those with contraindications to regional anesthesia were excluded from the study.

After a thorough preoperative evaluation, patients were premedicated with oral alprazolam 0.25 mg at night and 2 h before surgery. In the operating room, standard monitoring was established and preoperative vital parameters (heart rate [HR], blood pressure (BP), oxygen saturation, and electrocardiogram) were recorded. Intravenous (IV) access was secured, and 500 ml of Ringer's lactate was infused as co-loading fluid. Patients were randomized to one of two groups using computer-generated random allocation chart-Group R: Ropivacaine group (n = 45) received intrathecal injection of 2 ml of 0.75% plain ropivacaine (15 mg); Group B: Bupivacaine group (n = 45) received intrathecal injection of 2 ml of 0.5% plain bupivacaine (10 mg).

Patients were placed in the lateral decubitus position with the operative side uppermost. Under all aseptic precautions, a SAB was performed in L2–L3/L3–L4 interspace using a 25G quincke spinal needle. The patients were randomly assigned to one of two groups by the second author using computer-generated random numbers which were contained in a sealed envelope. This was handed over to another anesthesiologist drawing up the study drug in an unlabeled, sterile syringe. The intrathecal procedure including administration of the drug was done by the first author who remained blinded to its contents. Patient assessment and observations were recorded by the blinded researcher in the operation theater as well as in the recovery room. Patients were placed supine immediately after the procedure, and the operating table was maintained horizontal. Time of intrathecal injection was noted, and vital parameters were monitored at 5 min intervals till the end of surgery. A fall in systolic BP <80 mmHg or 20% below the baseline was treated with fast IV fluids and ephedrine 5 mg IV, and a fall in HR <50/min was treated with atropine 0.6 mg IV. One patient had to be administered GA and was excluded from the study as the onset of the sensory block did not occur even 20 min after intrathecal injection of isobaric ropivacaine.

Sensory block was assessed by the loss of sensation to pinprick using a 25G needle along the mid-axillary line bilaterally every 2 min till two consecutive readings remained the same (i.e., when highest cephalad spread of sensory block had occurred), after which it was assessed at 10 min intervals till the end of surgery. The onset of sensory block at L1 was noted and the surgeon was allowed to start the surgery. Maximum upper level of sensory block and time required to achieve it and time to two segment regression and descent of sensory block till S2 were noted. Duration of sensory block was determined from the time of onset of block till the patient demanded the first rescue analgesic.

Motor block was assessed using Modified Bromage Scale (ranging from 1- complete motor block to 6- no weakness at all) every 2 min till two consecutive readings remained the same (i.e., the highest level of motor block was achieved), after which it was assessed every 10 min till the end of surgery.[4] Maximum degree of motor block, time to onset of the maximum degree of motor block, total duration of motor block (from initial onset until complete recovery), and total duration of complete motor block were noted.

A lower extremity tourniquet was applied in all the patients and tourniquet time and pressure were noted. Quality of motor block was assessed by the surgeon on a four-point scale (excellent - 1, good - 2, fair - 3, and bad - 4).[4] Quality of intraoperative analgesia was assessed by patient satisfaction on a two-point scale (1 – adequate analgesia, 2 – inadequate analgesia).[4]

Level of sensory and motor block were assessed postoperatively on the operating table and at regular intervals in the postanesthetic care unit (PACU) till complete recovery occurred. Readiness for discharge was assessed half hourly using Postanesthetic Discharge Scoring System (PADSS) until a score of >9 was achieved.[4] Visual analog scale (VAS) was used to assess the severity of postoperative pain at rest and during passive movements at 0, 1, 2, 4, and 6 h. Intramuscular diclofenac (75 mg) was given as a rescue analgesic whenever the VAS exceeded 4.

Time of first voiding of urine and presence of any other side effects in the postoperative period were noted. All patients were asked about any persistent symptoms such as pain, vomiting, headache, backache, hypotension, delayed voiding, and transient neurologic symptoms on the day following surgery and again after 1 week of the anesthetic procedure.

Statistical analysis

Analysis was performed with SPSS software version 15, using the duration of the sensory block as the primary outcome and duration of the motor block as secondary outcome. A sample of 30 patients per group was required to detect a difference of 15% in duration of the sensory block between the two groups with 94.72% power and two-sided alpha error of 0.05. Chi-square test or Fisher's exact test was used to compare categorical variables such as sensory block, motor block, the maximum level of sensory and motor block, and unpaired t-test was used for quantitative variables such as HR and BP. Frequency distribution and their percentage were applied for some categorical variables like the maximum degree of sensory and motor block and requirement of postoperative analgesics. Values of P < 0.05 was considered to be statistically significant.

RESULTS

The demographic profile of patients was comparable between the groups. Duration of surgery and tourniquet time were also found to be similar [Table 1].

Table 1

Patient characteristics and duration of surgery

On comparing the hemodynamic parameters, no significant difference in mean HR was found between the groups. Mean systolic BP was significantly less at 50 (P = 0.004), 90 (P = 0.006), and 100 (P = 0.023) minutes; and mean diastolic BP was significantly less at 70 min (P = 0.049) after intrathecal injection in Group B as compared to Group R [Figure 1].

Figure 1

Hemodynamic parameters including HR, SBP, DBP. Dark blue line represents HR for Group R patients, brown line represents HR for Group B patients, purple line represents SBP for Group R patients, sky blue line represents SBP for Group B patients, light blue line represents DBP for Group R patients, pink line represents DBP for Group B patients. There was no clinically significant change in hemodynamic parameters after intrathecal injection, both within and between the groups. HR = Heart rate (beats/min), SBP = Systolic blood pressure (mmHg), DBP = Diastolic blood pressure (mmHg). Group R = Ropivacaine group, Group B = Bupivacaine group

Meantime of onset of sensory block at L1 was significantly shorter (Group B - 4.04 ± 3.12 min, Group R - 6.14 ± 5.09 min; P = 0.025) and duration of sensory block was significantly longer (Group B - 284.64 ± 32.33 min, Group R - 257.57 ± 39.12 min; P = 0.001) with bupivacaine. The mode and median of maximum upper level of sensory block were at T8 in both the groups and the number of patients who attained this block was significantly more with bupivacaine (37.4%) as compared to ropivacaine (22%) (P = 0.017). There was no significant difference between groups in the meantime to onset of the maximum sensory block, time for two segment regression and time for the descent of sensory block till S2 [Table 2].

Table 2

Characteristics of sensory block

A greater number of patients in the bupivacaine group had a better degree of motor block at 2 min (P = 0.01), 4 min (P ≤ 0.001), 10 min (P ≤ 0.001), and 20 min (P = 0.006) after intrathecal injection. Duration of motor block was significantly longer with bupivacaine as compared to ropivacaine (250.07 ± 34.81 min vs. 222.11 ± 41.78 min; P = 0.001). There was no significant difference in the number of patients who attained maximum motor block, time to onset of the maximum motor block and total duration of the complete motor block between the groups [Table 3]. Quality of motor block as assessed by the surgeon and the quality of intraoperative analgesia as assessed by the patient was adequate, and there was no statistically significant difference between the groups.

Table 3

Characteristics of motor block

Postoperatively, VAS score was significantly more in Group R at 1 h (P = 0.039) and 6 h (P = 0.011) at rest and in Group B at 4 h both at rest (P = 0.001) and on movement (P ≤ 0.001). A significantly greater number of patients in Group R needed 2 analgesic doses on the first postoperative day (33.33% vs. 11.11%; P = 0.011) [Table 4].

Table 4

Postoperative pain, complications and discharge scores

The incidence of delayed voiding of urine was significantly more with ropivacaine (13.33% vs. 0; P = 0.022), whereas the mean time taken for first voiding of urine was significantly longer with bupivacaine (270.23 min vs. 255.34 min; P = 0.028). No other significant complications were noted. There was no significant difference in the time taken to achieve readiness for discharge from PACU between the groups (Group B - 208.19 ± 30.36 min, Group R - 189.00 ± 34.10 min; P = 0.591) [Table 4].

DISCUSSION

Anesthesia for ambulatory surgery involves a multi-component integrated approach which requires good preoperative evaluation, appropriate intraoperative management, and early postoperative mobilization.[1] Of the various types of anesthesia that have been successfully used for knee arthroscopy including general, neuraxial, peripheral nerve blocks and local anesthesia, spinal anesthesia offers many advantages. Bupivacaine and ropivacaine have been widely used for this purpose, as have other newer local anesthetic agents like levobupivacaine.[5] Due to its better hemodynamic profile and shorter duration of the motor block, ropivacaine enables early mobilization in the postoperative ward, a fact which makes it suitable for shorter procedures conducted in daycare settings.[6]

In our study, we compared the efficacy of intrathecal isobaric ropivacaine with isobaric bupivacaine in patients undergoing knee arthroscopy. Isobaric ropivacaine was associated with a longer onset, shorter duration of sensory and motor block and lesser degree of the motor block as compared with bupivacaine. On the postoperative period, ropivacaine group had increased analgesic requirement, higher complication rate and similar discharge time as compared with bupivacaine.

There was no clinically significant change in hemodynamic parameters after intrathecal injection, both within and between the groups. Sympatholysis is less pronounced with an isobaric anesthetic, where baricity contributes to less extensive spread and indirectly a smaller reduction in BP as compared with a hyperbaric solution.[7] Many other clinical studies have found no difference in the hemodynamic profile between isobaric bupivacaine and ropivacaine.[8910] In contrast to our study in which none of the patients required treatment for intraoperative bradycardia or hypotension, three patients received atropine for bradycardia and two patients received ephedrine for intraoperative hypotension in Gautier et al.'s study, even though they had used lesser doses of both the drugs.[4] McNamee et al. found the incidence of intraoperative hypotension requiring treatment with IV ephedrine to be 12% and 26% with isobaric ropivacaine and bupivacaine, respectively. Two patients in their ropivacaine group required atropine for the treatment of bradycardia compared with none in the bupivacaine group.[11]

As compared to other studies, the duration of sensory and motor block was found to be longer in both our study groups.[41112] Despite using higher doses of drugs (17.5 mg), McNamee et al. found the duration of sensory block to be 3.5 h and 3 h, as compared with 4.74 h and 4.29 h found in our study, using isobaric bupivacaine and ropivacaine, respectively.[11] Demographic differences in the patient population as well as different doses of drugs used in other studies may have contributed to this difference.

When identical doses of isobaric ropivacaine and bupivacaine were compared, ropivacaine was found to have almost similar efficacy, but a shorter duration of sensory (257.57 vs. 284.64 min, P = 0.001) and motor (222.11 vs. 250.07 min, P = 0.001) block. This is corroborated by many authors.[611131415] Similar to our study motor recovery was faster with ropivacaine in a study conducted by Jagtap et al.[16] In another study, the duration of motor block was found to be shorter with ropivacaine, as in our study, though the duration of sensory block was similar between the groups. This could be due to the addition of fentanyl in both the groups.[17] In contrast, Boztuğ et al. found similar duration of motor block between isobaric ropivacaine (15 mg) and bupivacaine (7.5 mg) in patients undergoing arthroscopic knee surgery.[18] A lesser dose of bupivacaine used in their study as compared to ours, may have led to a similar duration of action between the groups. A longer duration of sensory block and shorter duration of motor block with 0.75% isobaric ropivacaine as compared to 0.5% isobaric bupivacaine has also been reported.[19]

Meantime of onset of sensory block was significantly less and maximum sensory level of T8 was attained by significantly more patients receiving isobaric bupivacaine. In contrast to our study, onset of sensory block was found to be similar or less with isobaric ropivacaine as compared to bupivacaine.[131819] While Gautier et al. found the median peak dermatomal level to be T8 with both isobaric ropivacaine and bupivacaine, another study found the median peak dermatomal level at T7, with no significant difference between groups in the number of patients achieving this level.[26]

Although we found a better degree of motor block at various time intervals with bupivacaine, there was no significant difference in the number of patients who attained maximum motor block. Ropivacaine being less lipophilic than bupivacaine, is less likely to penetrate large myelinated motor fibres, thus resulting in a relatively reduced motor block.[20]

Similar to other studies, we found no difference between groups in the time to onset of maximum sensory and motor block, time for 2 segment regression and regression till S2 and duration of complete motor block.[613] On the contrary, in a study conducted by Verma and Mehrotra the time for onset of maximum motor block and time for regression till S1 was shorter with bupivacaine as compared to ropivacaine.[18] There was no significant difference in the quality of motor block, as assessed by the surgeon and quality of intraoperative analgesia as assessed by patients. This complies with Gautier et al.'s study.[4]

Incidence of pain was significantly more with ropivacaine on the first postoperative day, as 33% patients required two analgesic doses as compared with 11% in the bupivacaine group. In patients undergoing major orthopedic surgery, analgesic requirement was found to be more with isobaric ropivacaine as compared to bupivacaine.[9] The incidence of postoperative pain can be effectively decreased by prolonging the sensory block and thus providing better postoperative analgesia by addition of adjuvants such as fentanyl to ropivacaine as found in a study conducted by Seetharam and Bhat[21] There are few other methods to reduce postoperative pain like the one used in a study done by Senapati et al. where they compared intraarticular ropivacaine and levobupivacaine with clonidine as adjuvant in both the groups, and found better postoperative analgesia with levobupivacaine as compared with ropivacaine.[22]

Patients given intrathecal ropivacaine had a significantly higher incidence of delayed voiding of urine, though the mean time taken for first voiding of urine was longer with bupivacaine. In contrast, time taken to void was not found to be significantly different between ropivacaine and bupivacaine and there was no incidence of urinary retention in other studies.[413]

Ropivacaine was introduced with a major advantage over bupivacaine in day care surgery, as it was expected to lead to early mobilization and discharge due to decreased motor blockade.[8] However, we did not find any significant difference in time taken for achieving readiness for discharge from PACU between the groups, as assessed by PADSS ≥9. McNamee et al. had concluded that ropivacaine offers a reliable motor block for major orthopedic surgery, with predictable and rapid return of motor function after surgery. However, many other studies comply with our finding of similar discharge times between isobaric ropivacaine and bupivacaine.[613]

In a systematic review of spinal anaesthesia using bupivacaine for ambulatory knee arthroscopy by Nair et al., it was found that though recovery from motor and sensory block was shorter with ropivacaine than with bupivacaine or levobupivacaine, this did not change the time to home discharge.[23]

Since ropivacaine is commercially available as an isobaric preparation, we compared it with isobaric bupivacaine, a drug which is not as commonly used clinically as its hyperbaric counterpart. The comparison therefore may not reflect the effects of hyperbaric bupivacaine and ropivacaine, both of which are known to provide a more predictable spread and better quality of sensory and motor block.[24] This maybe one of the limitations of our study. It may also be worthwhile to compare bupivacaine with a higher dose of ropivacaine than what we have used in our study.

CONCLUSION

Isobaric ropivacaine provides a longer onset and shorter duration of sensory and motor block, with a higher complication rate and greater postoperative analgesic requirement as compared to isobaric bupivacaine. Since both have similar discharge times, ropivacaine does not seem to offer any advantage over bupivacaine. Therefore, isobaric bupivacaine may be preferred over isobaric ropivacaine in knee arthroscopy, especially in cases of an anticipated longer duration of surgery.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.