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Ropivacaine 0.25% is As Effective As Bupivacaine 0.25% in Providing Surgical Anaesthesia for Lumbar Plexus and Sciatic Nerve Block in High-Risk Patients: Preliminary Report

September 5, 2007

By Kocum, A Turkoz, A; Ulger, H; Sener, M; Arslan, G

SUMMARY Ropivacaine is potentially less cardiotoxic and neurotoxic than bupivacaine. The aim of this study was to compare the effectiveness of ropivacaine 0.25% and bupivacaine 0.25% for surgical anaesthesia and postoperative analgesia during lumbar plexus and sciatic nerve block in high-risk patients. We performed combined lumbar plexus and sciatic nerve blockade on 62 consecutive ASA III or IV patients undergoing unilateral hip or femur surgery. The first 30 patients received bupivacaine (Group 1) and the remaining 32 patients received ropivacaine (Group 2). Perioperative management was otherwise similar. The groups were compared for the time of onset of the block, additional analgesics and sedatives required, time from end of surgery to the first analgesic requirement and the need for rescue analgesia. Ninety percent (29/ 32) of the patients in the ropivacaine group and 86% (26/30) of the patients in the bupivacaine group reached suigical anaesthesia. The time from the end of the surgery to the first analgesic requirement was similar between the two groups (10.3+-5.2 hours for ropivacaine, 11.2+-4.6 hours for bupivacaine). There was no statistically significant difference between the two groups in any of the measured variables (P>0.05). The results of this preliminary study suggest that ropivacaine 0.25% is as effective as bupivacaine 0.25% when used for blocking lumbar plexus and sciatic nerve in high-risk patients undergoing hip or femur surgery.

Key Words: ropivacaine, bupivacaine, sciatic nerve block, lumbar plexus block, high-risk patients

Femoral fracture is common among the elderly. This patient group has increased risk for perioperative complications, especially if they have pre-existing comorbidities1-2. Peripheral nerve blocks may provide ideal perioperative analgesia for these patients because they are not associated with haemodynamic instability or depression of pulmonary function3-9.

The nerves of the lower extremity are not bundled in a single fascial sheath and therefore separate injections are needed to adequately anaesthetise all regions innervated by the lumbar plexus and the sciatic nerve. These anatomic considerations mean that relatively large volumes of local anaesthetic are required for regional blocks in the lower extremity. The multiple injections and large volumes increase the likelihood of adverse reactions.

Bupivacaine is often used for peripheral nerve blocks in procedures that require intraoperative anaesthesia and prolonged postoperative analgesia. However, there are concerns about cardiotoxicity with this agent10-11. Bupivacaine is usually used at the minimum concentration (0.25%) required for surgical anaesthesia to reduce the risk as much as possible2,8. Ropivacaine is an enantiomeric isomer of bupivacaine that has similar anaesthetic properties, but is potentially less cardiotoxic and neurotoxic11- 14. Clinical trials have shown that ropivacaine and bupivacaine have similar efficacy when used at concentrations of 0.5% or higher10- 12. The aim of this study was to compare the effectiveness of 0.25% ropivacaine and 0.25% bupivacaine for surgical anaesthesia and postoperative analgesia during lumbar plexus and sciatic nerve block in high-risk patients undergoing hip or femur surgery.

MATERIALS AND METHODS

Following local ethics committee approval, 62 consecutive ASA physical status III or IV patients who underwent unilateral femur or hip surgery with lumbar plexus and sciatic nerve blockade between September 1, 2004 and August 1, 2005 were studied. Written informed consent was obtained from all patients. ASA physical status I and II patients, and those who received additional anaesthesia modalities or who had other fractures were excluded. Data was obtained from retrospective chart review. The first 30 patients received 0.25% bupivacaine and the following 32 patients received 0.25% ropivacaine. Blockade of the lumbar plexus and sciatic nerve were performed by two experienced anaesthetists (AK, AT).

Prior to anaesthetic injection, an 18-gauge cannula was placed in a forearm peripheral vein and Ringer’s lactate solution or saline 0.9% was infused at 1 to 2 ml/kg/h. Routine monitoring was instituted as well as invasive arterial blood pressure monitoring. All patients received supplemental nasal oxygen 2 1/min during the procedure.

Each patient received midazolam 1 to 3 mg IV and fentanyl 50 to 100 [mu]g IV before the block procedure to reduce pain during positioning. Each patient was placed in lateral decubitus position with the side to be operated uppermost. Lumbar plexus blockade was achieved using Winnie’s posterior approach15. The lumbar plexus was located using an insulated stimulation needle (Stimuplex D 10 cm, B.Braun, Melsungen AG, Germany) connected to a stimulator. Contraction of the quadriceps femoris muscle in response to a current less than 0.5 mA at 1 Hz confirmed that the desired lumbar plexus injection site had been reached. After this block was completed, the same technique and needle were used to block the sciatic nerve using the posterior approach described by Labat3. Plantar flexion of the foot with a current less than 0.5 mA at 1 Hz while performing peripheral nerve block was obtained in all 62 patients and thus confirmed that the desired sciatic nerve injection site had been reached. At each injection site, a 5 ml test dose of the local anaesthetic with adrenaline (1/400 000 dilution) was given. If no sign of intravascular or subarachnoid injection was noted within three minutes, the remainder of the drug without adrenaline was administered slowly in increments. The total volumes injected were 30 ml at the lumbar plexus and 20 ml at the sciatic nerve. The patient was then turned to the supine position and an iliac crest block with 10 ml of either local anaesthetic was performed16.

The time from the last injection to readiness for surgery and time needed for the surgical procedure were recorded. The time to readiness for surgery was determined by assessing for sufficient sensory and motor blockade every three minutes. Pinprick testing was used to assess sensation. Pain testing was done during passive movement of the blocked leg. Inability to flex the hip joint, extend the knee joint and dorsiflex or plantarflex the foot was taken to indicate successful motor blockade. The latter applied only to patients who had neither hemiparesis nor hemiplegia in their past medical history.

When the blocks were assessed as complete, the patient was taken to the operating room. Oxygen was delivered by face mask and the individual was sedated with a propofol infusion (10 to 50^g/kg/ min). The quality of the nerve blocks was judged by need for supplementary sedative and analgesics during the surgical procedure. The blockade was considered unsuccessful if a patient required a total dose of IV fentanyl exceeding 150 [mu]g and propofol infusion exceeding 50 [mu]g/kg/min. Blood pressure, heart rate and oxygen saturation levels were recorded throughout the operation. If the systolic blood pressure fell below 90 mmHg, IV ephedrine 2.5 mg was administered. If the heart rate was less than 45 beats/min, atropine 0.5 mg IV was administered.

After surgery, patients were transported to either the intensive care unit (ICU) or the orthopaedic ward, depending on their clinical condition. Nurses recorded pain assessments and analgesic requirements every hour from the end of surgery to 24 hours postoperatively. As a routine, patients received acetaminophen (paracetamol) 1 g six hourly until discharge, except those with chronic liver disease. Patients with normal renal function who required rescue analgesia were given intramuscular (IM) diclofenac 75 mg. Those who had impaired renal function or did not respond adequately to diclofenac received pethidine 25 to 50 mg IM.

The following additional data were collected from each patient’s medical records; duration of the operation, total amount of analgesics and sedatives required during the block and surgical procedure, time from end of surgery to the first analgesic requirement, need for rescue analgesia, which is reflected by the number of patients who required rescue analgesic in three intervals after surgery (first six, 12 and 24 hours), total amount (mg) of rescue analgesic required.

Statistical analyses were performed using SPSS for Windows (version 11.0; SPSS, Inc., Chicago, IL, U.S.A.). A power analysis was performed on the basis of the success rate of the peripheral nerve block. The appropriate sample size was calculated taking into account the results of a previous study on peripheral nerve block with 0.25% ropivacaine or 0.25% bupivacaine”. A sample size of 30 for each group was determined for a power of 80% at an a of 0.05. Differences between the two groups were compared using independent Student t-tests or its nonparametric counterpart, the Mann-Whitney U test. Contingency table analysis and the chi-square tests were used to compare categorical variables. Homogeneity of variances was assessed using Levene’s test and the Lillefor’s significance correction test. Values are presented as mean +- standard deviation. P values

RESULTS

A total of 62 patients were included in the study (30 bupivacaine, 32 ropivacaine). The patients in both groups were comparable with respect to demographic variables (Table 1). Seven patients in the ropivacaine group and seven patients in the bupivacaine group had hemiparesis or hemiplegia on the same side and one patient in the ropivacaine group had hemiparesis or hemiplegia on the other side of the fracture in their past medical history. Two patients in the ropivacaine group and four in the bupivacaine group required supplemental analgesics during surgery. There was no significant difference in the number of patients who required additional analgesics during the operation. One patient in the ropivacaine group developed bilateral blockade reaching the level of T4, which was most likely due to epidural spread. The regional block was considered unsuccessful in these seven cases and all data for these patients were excluded from the analysis. Only the data from the remaining 55 was analysed.

The mean time from last injection to readiness for surgery was 13.6+-4. 1 minutes in the ropivacaine group and 14.6+-2.9 minutes in the bupivacaine group (P= 0.39). The success rate of blockade providing surgical anaesthesia was 90% for ropivacaine (29 patients) and 86% (26 patients) for bupivacaine. There was no significant difference between the groups with respect to success rate of blockade-provided surgical anaesthesia.

There were no significant differences between the ropivacaine and bupivacaine groups with respect to the length of the operation, total amount of analgesics and sedatives required during the blockade and surgical procedure (Table 2).

In the postoperative period, probably due to the effect of intraoperative sedation, two patients in the ropivacaine group and one patient in the bupivacaine group were not fully cooperative and it was difficult to accurately assess pain in these three patients. These three patients were not taken into account during the final analysis of the mean time from end of the surgery to first analgesic requirement and rescue analgesic requirement. There were no significant differences between the ropivacaine and bupivacaine groups with respect to number of patients who required rescue analgesic in each of the three intervals after surgery (first six, 12 and 24 hours following the end of the surgical procedure) (Table 3). The mean time from end of surgery to first analgesic requirement was 10.5+-5.3 hours in the ropivacaine group and 1 1.3+-4.7 hours in the bupivacaine group (P= 0.60). The mean amounts of rescue analgesics required postoperatively in the ropivacaine and bupivacaine groups were as follows: IM diclofenac 77.7+-64.0 mg vs. 60.0+-61.2 mg respectively (P=0.31) and IM pethidine 32.9+- 41.4 mg vs. 55.0+-47.8 mg respectively (P=0.08). There was no intraoperative or postoperative clinically significant adverse event or complication in either group.

DISCUSSION

In this study, the lumbar plexus and sciatic nerve blocks achieved with the 0.25% formulations of ropivacaine and bupivacaine provided adequate surgical anaesthesia. Further, the blockade achieved by either drug was of similar quality and provided similar duration of postoperative analgesia. This is the first clinical study to have demonstrated that 0.25% ropivacaine and 0.25% bupivacaine provide comparable quality of surgical anaesthesia for hip or femur repair in high-risk patients.

It has been previously reported that 0.25% bupivacaine can provide sufficient surgical anaesthesia with combined lumbar plexus and sciatic nerve block818. Chudinov et al18 investigated continuous lumbar plexus block with 0.25% bupivacaine for anaesthesia and perioperative analgesia in 20 patients with hip fracture. The continuous lumbar plexus blocks were successful in all cases, but surgical anaesthesia was achieved in only 15% (3/20) of the cases. The authors suggest that the reason that surgical anaesthesia was not achieved was that the anaesthetic drug did not reach the region of sciatic nerve root (which is mandatory for the surgical anaesthesia of this region), rather than the low concentration of bupivacaine. Of the remaining 17 patients who required additional anaesthesia for surgery, five received sciatic nerve blockade and all these patients subsequently achieved surgical anaesthesia. Asao et al8 also gave anecdotal accounts of the efficacy of 0.25% bupivacaine for providing surgical anaesthesia via lumbar and sciatic blockade in four high-risk patients.

In our study, the success rate of a combination of lumbar plexus and sciatic nerve blockade providing surgical anaesthesia with 0.25% ropivacaine or 0.25% bupivacaine was achieved in 90% and 86% of patients respectively. Two possible factors in this high success rate are the advanced age of our subjects and the high prevalence of co-morbidities in the group. A clinical study by Paqueron et al’” and electrophysiological research by Benzon et al2″ reported that smaller doses of local anaesthetic (compared to doses required for surgical anaesthesia in younger people) are adequate for regional blocks in elderly patients. This is possibly because of altered nerve electrophysiology and increased peripheral-nerve sensitivity to local anaesthetic agents in this age group. Studies have also shown that co-morbidity can affect results. Data from research on diabetes mellitus suggest that the impaired nerve conduction in this disease results in less anaesthetic agent requirement to achieve surgical anaesthesia21. The mean age of our study population was higher than 75 years of age and nearly half of the patients were diabetic. Also, nearly 25% of our patients had a previous cerebrovascular accident resulting in paresis or paralysis in their past medical history. All these factors that may affect neural function were present in both groups. We believe that these factors are possibly the reasons why we achieved such good success with respect to surgical anaesthesia with the low concentrations.

The equipotency issue between ropivacaine and bupivacaine has gained a great deal of attention. Bupivacaine seems to have slightly greater potency than ropivacaine. However, although statistically significant, the observed differences may not be clinically relevant in terms of success rate of surgical anaesthesia22. In the study conducted by Bertini et al21, they found that ropivacaine had a shorter anaesthesia onset time and a lower need for intraoperative fentanyl requirement in equal concentrations when compared with bupivacaine. However, we did not find any difference regarding these variables. Several studies have investigated the duration of postoperative analgesia when ropivacaine or bupivacaine are administered10,11. Greengrass et al10 compared 0.5% ropivacaine or 0.5% bupivacaine for lumbar plexus and sciatic nerve blockade during knee arthroplasty. They observed significantly longer duration of postoperative analgesia with bupivacaine than with ropivacaine (17 vs. 13 hours). However, McNamee et al11 found no significant difference between these drugs’ mean analgesia durations (13 vs. 15 hours respectively). Our findings are more consistent with the latter study. We also noted similar findings for types and amounts of rescue analgesics used postoperatively in the two groups. Overall, these findings suggest that use of either 0.25% ropivacaine or 0.25% bupivacaine for lumbar plexus and sciatic nerve block during hip and femur surgery in high risk patients can provide adequate early postoperative analgesia.

The limitations of the current study include a relatively small sample. In addition, co-morbid conditions in some of the patients such as hemiplegia made it impossible to accurately assess motor block. The use of ultrasound may eventually become a standard of care for regional anaesthesia but we were not able to use this facility. Other obvious limitations of our study are the lack of randomisation and blinding, the lack of a control group, the sequential nature of the groupings and the retrospective nature of the data collection. However, we believe that our study still provides useful information on the effectiveness of lumbar plexus and sciatic nerve block using of 0.25% ropivacaine or 0.25% bupivacaine for surgical anaesthesia and postoperative analgesia in high-risk cases undergoing hip surgery.

When elderly patients with co-morbid conditions require femur or hip surgery, the lowest required dose of anaesthetic agent should be used for peripheral nerve blockade. Our results suggest that 0.25% ropivacaine provides adequate anaesthesia and postoperative analgesia in this patient group and it is as effective as the same concentration of bupivacaine.

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A. KOCUM*, A. TURKOZ[dagger], H. ULGER*, M. SENER[double dagger] G. ARSLAN[section]

Department of Anesthesiology and Reanimation, Baskent University Faculty of Medicine, Ankara, Turkey

* M.D., Anesthesiology Specialist.

[dagger] M.D.. Associate Professor.

[double dagger] M.D., Asistant Professor.

[section] M.D., Professor, Director.

Address for reprints: Dr. A. Kocum, Baskent University Hospital. Dadaloglu Mah. 39. Sok. No:6 Yuregir, Adana, Turkey.

Accepted for publication on February 12, 2007.

Copyright Australian Society of Anaesthetists Aug 2007

(c) 2007 Anaesthesia and Intensive Care. Provided by ProQuest Information and Learning. All rights Reserved.