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REGIONAL ANESTHESIA AND PAIN MANAGEMENT

Peribulbar Anesthesia with Either 0.75% Ropivacaine or a 2% Lidocaine and 0.5% Bupivacaine Mixture for Vitreoretinal Surgery: A Double-Blinded Study

Luigi Gioia, MD^*, Edi Prandi, MD^*, Marco Codenotti, MD, Andrea Casati, MD^*, Guido Fanelli, MD^*, Tiziana Monica Torri, BS^*, Claudio Azzolini, MD, and Giorgio Torri, MD^*

Departments of *Anesthesiology and Ophthalmic Surgery, University of Milan, IRCCS H. San Raffaele, Milan, Italy

Address correspondence and reprint requests to Andrea Casati, MD, Department of Anesthesiology, IRCCS H. San Raffaele, Via Olgettina 60, 20132 Milan, Italy. Address e-mail to casati.andrea{at}hsr.it

	Abstract

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No study has evaluated the efficacy of ropivacaine in peribulbar block for ophthalmic surgery. The purpose of this prospective, randomized, double-blinded study was to compare ropivacaine and a lidocaine-bupivacaine mixture in peribulbar anesthesia. Sixty ASA physical status I or II patients scheduled for elective vitreoretinal surgery were randomized to receive a peribulbar block with 8 mL of either 0.75% ropivacaine (ropivacaine group, n = 30) or a 1:1 mixture of 2% plain lidocaine and 0.5% plain bupivacaine (lido-bupivacaine group, n = 30). Time required for onset of surgical anesthesia, quality of postoperative analgesia, incidence of side effects, and analgesic consumption were recorded. Surgical block was achieved after 8 ± 5 min in the lido-bupivacaine group and after 10 ± 5 min in the ropivacaine group (P = 0.23). A 3-mL supplemental injection 15 min after block placement was required in 6 patients in the lido-bupivacaine group (20%) and in 10 patients in the ropivacaine group (33%) due to inadequate motor block (P = 0.38). On Postoperative Day 1, 26 patients in the ropivacaine group (87%) reported no pain at the verbal rating score, compared with 18 patients in the lido-bupivacaine group (60%) (P = 0.005). We conclude that 0.75% ropivacaine may be a suitable choice when performing peribulbar anesthesia for vitreoretinal surgery.

Implications: Quick onset of block with prolonged postoperative analgesia is an important goal in regional anesthesia for ophthalmic surgery. Evaluating clinical properties of 0.75% ropivacaine and a 1:1 mixture of 2% lidocaine and 0.5% bupivacaine for peribulbar anesthesia, we demonstrated that ropivacaine has an onset similar to that of the lidocaine-bupivacaine mixture and provides a better quality of postoperative analgesia.

	Introduction

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Both retrobulbar and peribulbar blocks provide safe and effective anesthesia for ophthalmic surgery (1). Even if retrobulbar block provides faster and more reliable anesthesia than a peribulbar block, the latter is often preferred by some practitioners because of its theoretically higher safety margin (2–3). At our institution, a 1:1 mixture of bupivacaine and lidocaine is often used to obtain a fast onset of both sensory and motor blockade and to prolong postoperative analgesia.

Ropivacaine has less central nervous system and cardiac toxicity than bupivacaine (4,5). Several studies have demonstrated the efficacy of ropivacaine in different regional anesthesia techniques (6–8); however, there are no clinical investigations on ropivacaine used for peribulbar block during vitreoretinal surgery.

We therefore conducted a prospective, randomized, double-blinded study to evaluate intraoperative and postoperative clinical properties of peribulbar anesthesia performed with either 0.75% ropivacaine or a mixture of 0.5% bupivacaine and 2% lidocaine for vitreoretinal surgery.

	Methods

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The protocol was approved by the hospital ethical committee, and written, informed consent was obtained from each patient. Sixty ASA physical status I or II patients scheduled for vitreoretinal surgery (macular pucker, epiretineal fibrosis, and removal of silicon oil) with an expected duration <120 min were included in the study. Patients allergic to local anesthetic solutions; with local sepsis, serious impairment of coagulation, and orbital abnormalities; or who were unable to cooperate in maintaining a relatively motionless supine position or who refused the anesthetic technique were not included.

After a routine preoperative evaluation, all patients were premedicated with oral diazepam (0.1 mg/kg) 1 h before the surgical procedure. Using a sealed envelope technique, patients were randomly allocated to receive peribulbar anesthesia with 8 mL of either 0.75% ropivacaine (ropivacaine group, n = 30) or a 1:1 mixture of 2% plain lidocaine and 0.5% plain bupivacaine (lido-bupivacaine group, n = 30). Sterile syringes containing the local anesthetic solution were prepared in a double-blinded fashion by one of the authors not taking part in the management of patients.

Standard monitoring, including noninvasive arterial blood pressure, electrocardiogram (lead II), heart rate, and peripheral SaO₂, was used. Hemodynamic variables were recorded every 5 min until completion of surgery.

The peribulbar block was performed by one of two authors (MC and LG) with substantial expertise in regional anesthesia for ophthalmic surgery. Bloomberg's modification (9) of the Davis and Mandel technique (1,10) was used: patients were asked to maintain the eye in the primary position while an Aktinson needle (23-gauge, 3.1 cm in length) was inserted at the level of the inferior orbital rim in the inferotemporal quadrant along the inferior orbital floor to a depth of approximately 2.5 cm. Five milliliters of local anesthetic solution was injected. In the same way, 3 mL was injected at the superonasal quadrant along the superior orbital roof. During the withdrawal of the needle, 0.5 mL of local anesthetic solution was injected into the orbicularis muscle. To promote the spread of the anesthetic solution and decrease intraocular pressure (IOP), orbital mechanical compression was exerted using a Honan balloon (1). Sensory and motor blocks were assessed 5, 10, and 15 min after injection by a blinded observer. At the same time, IOP was measured using a computerized indentation tonometer. Sensory block was evaluated by touching the cornea with a cotton cigarette. Ocular globe motility was evaluated in the four quadrants using a 3-point scoring system: 0 = akinesia (ocular movement <1 mm), 1 = reduced movement (ocular movement >1 mm but <4 mm), 2 = normal movement (ocular movement >4 mm), giving a maximal aggregate score of 8 for the four muscles. A score of , reduced movements in all directions, was taken to indicate successful block. Once successful block had been achieved, no further assessments were made. If inadequate motor blockade of one or more component of ocular motion was observed 15 min after block placement, a further 3 mL of the studied anesthetic solution was injected into the involved quadrant. Additional assessments were then performed 5 min later. During the operation, oxygen was administered to the patient under sterile drapes. Postoperative analgesia consisted of ketoprofen 100 mg IV if required.

Resolution of motor block (complete recovery of normal motion in the four quadrants) was evaluated 1, 3, and 6 h after the end of surgery. At the same times and on the first postoperative day, the following variables were also recorded: degree of pain (by using a 5-points verbal rating score: 0 = no pain, 1 = mild pain, 2 = moderate pain, 3 = severe pain, 4 = unbearable pain); occurrence of nausea and vomiting, headache, and any untoward event; pain medication administration; and acceptance of the anesthetic technique (acceptance was assessed using a 2-point score: 1 = good, if necessary I will repeat it; 2 = bad, I will never repeat it again).

To calculate the required study size, we took into account the results of a previous pilot study with 15 patients per group (unpublished observations). We wished to detect a 5-min difference in the time required to achieve adequate surgical anesthesia, accepting a one-tailed error of 5% and a ß error of 5% (11). Based on these calculations, the required study size was 30 patients per group.

Statistical analysis was performed using the program Statview 2.0 (Abacus Concepts, Berkeley, CA). The anthropometric characteristics, duration of surgery, and onset of sensory and motor blocks were analyzed by using Student's t-tests. Analysis of variance for repeated measures was used to analyze changes in hemodynamic variables and oxygen saturation values over time. Resolution of sensory and motor blocks, incidence of side effects, postoperative pain control, and acceptance of anesthetic technique were analyzed by using contingency table analysis with Fisher's exact test or Pearson 2 test with Cochran's test of linear trend for correction as indicated. A value of P < 0.05 was considered significant. Continuous variables are presented as mean ± SD; ordinal data are presented as number (percentage).

	Results

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Patient characteristics and duration of surgery were similar in the two groups (Table 1). No differences in the distribution of surgical procedures, IOP, hemodynamic variables, and peripheral SaO₂ were reported between the two groups (data not presented). In one patient in the ropivacaine group, IOP increased to 50 mm Hg after block placement and required acute paracentesis; however, no further problems were observed in this patient during surgery.

Resolution of motor blockade required >6 h in 18 patients in the lido-bupivacaine group (60%) and 23 patients in the ropivacaine group (90%) (P = 0.26). The degree of pain was low in all patients but one in the ropivacaine group, who reported unbearable pain due to high IOP values and was treated with topical timolol (Fig. 1). The number of patients with no pain was always higher in the ropivacaine group (1 h: 29 [96%]; 3 h: 25 [83%]; 6 h: 26 [86%]; 24 h: 26 [86%]) than in the lido-bupivacaine group (1 h: 19 [63%]; 3 h: 14 [46%]; 6 h: 15 [50%]; 24 h: 18 [60%]) (P = 0.002, P = 0.006, P = 0.006, and P = 0.005 at 1, 3, 6, and 24 h, respectively). During the first day after surgery, 25 patients in the ropivacaine group (83%) and 20 patients in the lido-bupivacaine group (66%) did not require pain medication; however, this difference failed to reach statistical significance (P = 0.23).

View larger version (15K): [in this window] [in a new window]   Figure 1. Verbal rating scale score measured 1, 3, 6, and 24 h after surgery in patients receiving peribulbar anesthesia with either 0.75% ropivacaine (ropivacaine group, n = 30) or a 1:1 mixture of 2% lidocaine and 0.5% bupivacaine (lido-bupivacaine group, n = 30).

	Discussion

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The most interesting finding in this prospective, randomized, double-blinded study is that, when performing peribulbar block for vitreoretinal surgery, 0.75% ropivacaine provided a short and predictable onset time of surgical anesthesia similar to that provided by a 1:1 mixture of 2% plain lidocaine and 0.5% plain bupivacaine, with better control of postoperative pain relief.

Bupivacaine alone might seem more appropriate as a control drug than the lidocaine-bupivacaine mixture; however, the lidocaine-bupivacaine mixture is currently used at our institution for peribulbar block, combining lidocaine's onset time and the long postoperative pain relief of bupivacaine (1–3).

Our findings regarding the onset of peribulbar block are consistent with results of those of Dopfmer et al. (12), who evaluated the clinical properties of either 3% prilocaine or a 1:1 mixture of 2% lidocaine and 0.5% bupivacaine and observed a median time at which the peribulbar block was considered adequate for surgery of approximately 12 minutes with the lidocaine-bupivacaine mixture and 10 minutes with the short-acting prilocaine (13). Other studies evaluating the effects of adding hyaluronidase to a lidocaine-bupivacaine mixture on the onset time of peribulbar block reported successful block after a time ranging between 10 and 15 minutes (14,15). Similar observations regarding the onset times of surgical block have also been reported when using 0.75% ropivacaine for different peripheral nerve blocks, in which 0.75% ropivacaine provided an onset time of surgical anesthesia shorter than that provided by 0.5% bupivacaine and similar to that provided by 2% mepivacaine (7,8,16), which has pharmacological properties similar to those of lidocaine (13). In fact, the lower potential for systemic toxicity of ropivacaine compared with bupivacaine (5,6,17) enables it to be used for surgical anesthesia in concentrations up to 1%; this higher concentration may facilitate diffusion of local anesthetic molecules into peripheral nervous tissue, improving the onset of nerve blockade.

Results on the duration of postoperative analgesia are not surprising because patients in the ropivacaine group received 3 times as much ropivacaine compared with the amount of bupivacaine administered in the lido-bupivacaine group; however, this observation may have clinical relevance when deciding which is the better local anesthetic solution to be used when performing vitreoretinal surgery with peribulbar block.

The use of regional anesthesia for ophthalmic surgery has become increasingly popular over the last years because it is associated with fewer respiratory and hemodynamic untoward events than general anesthesia (1). Moreover, postoperative pain relief and the incidence of nausea and vomiting are better controlled after regional anesthesia than after general anesthesia (1). Retrobulbar anesthesia is associated with rare but severe complications (such as ocular perforation, direct optic nerve injury, extraocular muscle paresis, severe retrobulbar hemorrhage, retinal vascular occlusion, contralateral amaurosis, and systemic local anesthetic toxicity). To reduce the morbidity risks associated with retrobulbar anesthesia, Davis and Mandel (10) developed peribulbar block, which seems to be associated with fewer complications than retrobulbar anesthesia (18). For this reason, peribulbar anesthesia is now considered a safe and effective technique for vitreoretinal surgery. The only complication observed in the present study was a sustained increase in IOP observed in one patient despite the use of a relatively small injected volume. This complication was easily and effectively treated by the ophthalmic surgeon and was probably produced by an incomplete dispersal of the local anesthetic solution within the periocular compartment. However, no other untoward events were reported in any patient.

Because we compared 0.75% ropivacaine with a mixture of 2% lidocaine and 0.5% bupivacaine, the results of this investigation are relevant only to this solution. However, we conclude that 0.75% ropivacaine alone is a suitable choice when performing peribulbar anesthesia for vitreoretinal surgery.

	Acknowledgments

 
This study was supported in part by a grant from the IRCCS H. San Raffaele, Milan, Italy.

We thank the anesthesia and ophthalmic surgery nurses, without whose help and cooperation this study would not have been possible.

	References

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