1Department of Anaesthesia and Intensive Care, The Chinese University of Hong Kong, Prince of Wales Hospital, Shatin, Hong Kong, China. 2Department of Ophthalmology and Visual Sciences, The Chinese University of Hong Kong, Prince of Wales Hospital, Shatin, Hong Kong, China
Accepted for publication April 11, 2000
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Abstract |
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Br J Anaesth 2000; 84: 61820.
Keywords: anaesthetics local, ropivacaine; anaesthetics local, lidocaine bupivacaine
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Introduction |
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Methods and results |
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Intravenous access and standard monitoring were established, and one drop of 1% tetracaine was administered topically. Anaesthetic solutions were prepared individually immediately before injection. The investigators performing the injections (M.W.I.T.) and assessments (D.K.W.) were blinded to the solutions used. A two-injection technique was used, consisting of inferolateral and superior injections using a 22 mm, 25 gauge needle. Local anaesthetic was injected until peribulbar fullness was observed or to a maximum of 8 ml. Ocular pressure of 30 mm Hg was applied for 20 min, and was removed at 2 min intervals to assess residual ocular movement. Movement in the superior, inferior, medial and lateral directions was scored as 0 (no movement), 1 (up to 2 mm movement) or 2 (>2 mm movement); this gave a range from 0 (complete akinesia) to 8 for each assessment.3
Surgery started after 20 min. Patients were asked to grade discomfort during injection and during surgery on a 5-point ordinal scale (none, mild, moderate, severe, worst ever). The surgeon graded operating conditions on a 10 cm visual analogue scale (VAS; 0=impossible, 10=ideal).
The principal end-point was the rate of onset and the quality of ocular akinesia. Previously, successful block was defined as an ocular mobility score 4.3 Prospective power analysis showed that a sample size of 40 patients per group would have 80% power at the 0.05 level of significance to detect a 30% difference in the proportion of patients with an ocular mobility score
4 at 6 min, assuming an expected proportion of approximately 84% in the control group.3 Data were analysed using analysis of variance for repeated measures, Students t test, the
2 test and the MannWhitney U test as appropriate. Values of P<0.05 were considered statistically significant.
Patient characteristics were similar between groups. Both groups had approximately twice as many women as men, with a mean age of 76 (SD 9) yr in group 1 and 74 (8) yr in group 2. The mean volume of anaesthetic injected was similar (6.7 (0.7) ml in group 1 and 6.7 (0.8) ml in group 2).
There were no differences between groups in the rate of onset of block or the degree of akinesia achieved (P=0.34; Fig. 1). Sixty per cent of patients in group 1 and 55% in group 2 achieved akinesia scores of 4 at 6 min (P=0.5). Because of discomfort during surgery, one patient in group 1 required additional topical anaesthesia, while two patients required topical anaesthesia and two required subtenons injection in group 2. These differences were not statistically significant. Operating condition scores were similar (group 1, 7.6 (2.2) cm; group 2, 7.1 (2.9) cm; P=0.6).
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Comment |
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Before commencing our study, the only published data on peribulbar ropivacaine were comparisons of ropivacaine/lidocaine with bupivacaine/lidocaine mixtures.3 We wished to determine whether ropivacaine as the sole anaesthetic could provide satisfactory akinesia for ocular surgery, particularly as other clinical applications have demonstrated motor sparing properties.1 However, before commencing the study, our impression with 1% ropivacaine was that onset of akinesia was delayed. Previous findings demonstrate that a high concentration of hyaluronidase (300 IU ml1) in peribulbar local anaesthesia promotes the speed of onset and quality of block,2 hence we opted for a combination of 1% ropivacaine and high-dose hyaluronidase. This was compared with our standard peribulbar local anaesthetic mixture as the control.
After we had commenced our study, a number of other studies of peribulbar ropivacaine combined with hyaluronidase 075 IU ml1 were published, and they found this to be as effective as 0.75% bupivacaine or 0.5% bupivacaine/2% lidocaine mixtures.4 5 6 Differences in methods between studies make direct comparison difficult. These include site(s) of injection, akinesia scoring methods, the definition of successful block, indications for and methods of supplementation, and the type of surgery. We used a two-injection technique according to our routine practice. Our method of assessing ocular mobility was simple and semiquantitative. We felt this was more objective and reproducible than qualitative methods. Our surgeons tolerated considerable eye movement. This was largely because we studied patients undergoing phacoemulsification, which is increasingly being performed under topical anaesthesia alone. An unsuccessful block therefore related in practice to problems with analgesia rather than akinesia, with a correspondingly low supplementation rate compared with some other studies.4
Only one other study has been published using 300 IU ml1 peribulbar hyaluronidase.2 No adverse effects specifically related to hyaluronidase were reported. Although we found that adding this dose of hyaluronidase to 1% ropivacaine resulted in an effective mixture for peribulbar block, the successful use of ropivacaine alone, or with lower concentrations of hyaluronidase, has now been reported.4 5 6 Huha et al. 6 found that plasma concentrations of ropivacaine approached the reported greatest tolerated concentration in four of 11 patients using 1% ropivacaine and hyaluronidase 7.5 IU ml1. The pharmacokinetic effects of higher hyaluronidase concentrations are unknown.
In conclusion, we have found that 1% ropivacaine with hyaluronidase 300 IU ml1 is a suitable mixture for peribulbar block, with onset and quality of anaesthesia similar to those achieved with bupivacaine/lidocaine. Further work is required to determine the effect of high concentrations of hyaluronidase on plasma concentrations of ropivacaine and the duration of block.
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Acknowledgements |
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Footnotes |
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References |
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2 Dempsey GA, Barrett PJ, Kirby IJ. Hyaluronidase and peribulbar block. Br J Anaesth 1997; 78: 6714
3 Gillart T, Barrau P, Bazin JE, Roche G, Chiambaretta F, Schoeffler P. Lidocaine plus ropivacaine versus lidocaine plus bupivacaine peribulbar anaesthesia by single medial injection. Anesth Analg 1999; 89: 11926
4 Corke PJ, Baker J, Cammack R. Comparison of 1% ropivacaine and a mixture of 2% lignocaine and 0.5% bupivacaine for peribulbar anaesthesia in cataract surgery. Anaesth Intens Care 1999; 27: 24952[ISI][Medline]
5 Gioia L, Prandi E, Codenotti M, Casati A, Fanelli G, Torri TM, et al. Peribulbar anesthesia with either 0.75% ropivacaine or a 2% lidocaine and 0.5% bupivacaine mixture for vitreoretinal surgery: a double-blinded study. Anesth Analg 1999; 89: 73942
6 Huha T, Ala-Kokko TI, Salomäki T, Alahuhta S. Clinical efficacy and pharmacokinetics of 1% ropivacaine and 0.75% bupivacaine in peribulbar anaesthesia for cataract surgery. Anaesthesia 1999; 54: 13741[ISI][Medline]