Comparison of plain with pH-adjusted bupivacaine with hyaluronidase for peribulbar block

Skin necrosis following sclerotherapy. Part 2: Risk minimisation and management strategies

Tissue necrosis is a serious but rare complication of sclerotherapy. Early detection and targeted management are essential to prevent progression and minimise serious complications. In the first instalment of this paper, we reviewed the pathogenic mechanisms of post-sclerotherapy necrosis. Here, we describe risk minimisation and management strategies.

Risk factors must be addressed to reduce the chance of necrosis following sclerotherapy. These may be treatment-related including poor choice of sclerosant type, concentration, volume or format, poor injection technique, suboptimal ultrasound visualisation and treatment of vessels in high-risk anatomical areas. Risk factors specific to individual patients should be identified and optimised pre-operatively.

Tissue necrosis is more likely to occur with extravasation of irritant sclerosants such as absolute alcohol, sodium iodide, bleomycin and hypertonic saline, whereas extravasation of foam detergent sclerosants rarely results in tissue loss. Proposed treatments for extravasation of irritant sclerosants include infiltration of an isotonic fluid and hyaluronidase. Management of inadvertent intra-arterial injections may require admission for neurovascular observation and monitoring for ischaemia, intravenous systemic steroids, anticoagulation, thrombolysis and prostanoids infusion when required. Treatment of veno-arteriolar reflex vasospasm (VAR-VAS) necrosis follows the same protocol involving systemic steroids but rarely requires hospital admission and may not require anticoagulation.

In general, treatment of post-sclerotherapy necrosis is challenging and most proposed treatment measures are not evidence-based and only supported by anecdotal personal experience of clinicians. Despite all measures, once the necrosis has set in, it is very difficult to reverse the process and all measures described here may only be useful in prevention of progression and extension of the ulceration.

Mid to long-term measures include addressing exacerbating factors, management of medical and psychosocial comorbidities, treatment of secondary infections and referrals to relevant specialists. All ulcers should be managed with compression and prescribed dressing regimes in line with the healing stage of the ulcer.

Hyaluronidase reduces local anaesthetic volumes for sub-Tenon’s anaesthesia

BACKGROUND

Volumes of local anaesthetics for sub-Tenon's anaesthesia vary. Lower volumes produce less akinesia, whereas higher volumes increase chemosis and intra-ocular pressures. Hyaluronidase is often added to local anaesthetics to improve akinesia without increasing the volume of the injection, but this is controversial. This randomized, sequential allocation study examines the addition of hyaluronidase on the minimum local anaesthetic volume (MLAV) required for a sub-Tenon's block.

METHODS

Sixty-two patients having sub-Tenon's blocks for cataract surgery were randomized into two groups. The control group (n=31) received 2% w/v lidocaine and the study group (n=31) received 2% w/v lidocaine with hyaluronidase 15 IU ml(-1). Using parallel up-down sequential allocation from a 4 ml starting volume, the volumes in both groups were changed using a testing interval of 1 ml according to the quality of globe akinesia. The median effective local anaesthetic volume (MLAV) was calculated for both groups using probit regression.

RESULTS

The groups were similar for age, sex, and ocular axial length. The MLAV in the hyaluronidase group was 2.6 ml [95% confidence interval (CI), 2.1-3.l] and 6.4 ml (95% CI, 5.1-8.1) in the control group (P<0.002).

CONCLUSIONS

Hyaluronidase permits a significant 2.4-fold (95% CI, 1.8-3.4) reduction in MLAV for sub-Tenon's anaesthesia.

Alkalinization increases penetration of lidocaine across the human cornea

PURPOSE

To test the hypothesis that corneal permeability of lidocaine complies with the principle of nonionic diffusion.

SETTING

Department of Ophthalmology and Institute of Pharmacology, Vienna, Austria.

METHODS

Human corneas, mounted in an in vitro perfusion system under short-circuit conditions, were exposed on the epithelial (tear) side to lidocaine 4% in a buffered solution of pH 5 or pH 7. The endothelial bathing solutions had a constant pH of 7.4. Both solutions were adjusted to an osmolarity of 290 mOsm/L. The lidocaine permeability of the isolated corneas was assessed from the fluxes of 14C-labeled lidocaine across the tissue, measured at 15-minute intervals for 180 minutes, and corrected for the unidirectional fluxes of 3H-polyethylene glycol, a marker for the extracellular pathway. The corneal tissue content of lidocaine was estimated from the time span until the unidirectional lidocaine fluxes across the cornea reached a steady state.

RESULTS

The mean transcorneal fluxes of lidocaine in the steady state (90 to 180 minutes) were 72% higher at pH 7 than at pH 5 (101 mmol/min +/- 37 (SD) versus 59 +/- 34 nmol/min.cornea; P <.002). The corneal content of lidocaine in the steady state was 65% higher at pH 7 than at pH 5 (2.8 +/- 0.9 micromol/cornea versus 1.7 +/- 1.2 micromol/cornea; not significant).

CONCLUSIONS

A shift in solution pH from 5 to 7 significantly increased the corneal permeability of topically applied lidocaine. Alkaline pH-adjustment of topical lidocaine solutions is easy to perform by adding sodium bicarbonate. The main clinical advantages of anesthetic solutions buffered at pH 7 are increased penetration rates, effectiveness, prolonged action time, and a reduction in local irritation and lacrimation.

Comparison of pH-adjusted bupivacaine with a mixture of non-pH-adjusted bupivacaine and lignocaine in primary vitreoretinal surgery

PURPOSE

To compare the efficacy of alkalinized bupivacaine with that of a mixture of nonalkalinized bupivacaine and lignocaine for local anesthesia in primary vitreoretinal surgery.

METHODS

Through a prospective, double-blind, randomized, controlled clinical trial, 540 consecutive patients undergoing primary vitreoretinal surgery received either alkalinized 0.5% bupivacaine (group B) or a mixture of nonalkalinized 0.5% bupivacaine and 2% lignocaine (group BL), both of which were administered with hyaluronidase, for periocular anesthetic block. The periocular block involved two injections in the extraconal space-one in the lower temporal quadrant and the other in the medial periconal space. The efficacy of the block was graded from 0 to 5 depending on the adequacy of anesthesia and akinesia and the need for local supplementation.

RESULTS

Adequate anesthesia and akinesia (grade 5) were achieved in 72.2% of the patients in group B compared with 57.4% in group BL (P = 0.0003). Intraoperative supplementation was needed in 9.6% and 20.7% of the patients in groups B and BL, respectively (P = 0.0003). Postoperative analgesics were required in 7.4% of the patients in group B and in 15.2% of those in group BL (P = 0.004).

CONCLUSION

Alkalinized 0.5% bupivacaine provides better quality of anesthesia than does the mixture of nonalkalinized 0.5% bupivacaine and 2% lignocaine for patients undergoing primary vitreoretinal surgery.

Comparison of lignocaine 2% with adrenaline, bupivacaine 0.5% with or without hyaluronidase and a mixture of bupivacaine, lignocaine and hyaluronidase for peribulbar block analgesia

PURPOSE

Each of the freely available local analgesic agents may be used, alone or in combination, with or without hyaluronidase, epinephrine and sodium bicarbonate for peribulbar block analgesia (PBA). A prospective audit of four solutions was undertaken to rationalize choice of local analgesic agent for PBA.

METHODS

A randomized, prospective study on 200 middle-aged to elderly patients undergoing cataract extraction was undertaken to compare the efficacy of: (1) bupivacaine 0.5% (bup 0.5% plain); (2) bupivacaine 0.5% plus hyaluronidase 100 i.u. ml-1 (bup 0.5% hyalase); (3) lidocaine 2% plus epinephrine 1:200 000 (lido 2% epi); or (4) a mixture of lidocaine 2% and bupivacaine 0.5% (2:3 volume per volume mix) containing hyaluronidase 25 i.u. ml-1 (lido/bup/hyalase). A standardized deep peribulbar block technique, akinesia scoring system (each 5 minx4), and supplemental protocol was followed. Onset of block and supplementation rates to achieve akinesia were recorded by a blinded observer; the requirement for augmentation with topical oxybuprocaine or subconjunctival lidocaine during surgery and the time from first PBA injection to the completion of surgery (the duration of surgical access) were also recorded.

RESULTS

Groups (N=50) were comparable. Akinesia scores were similar after each agent at 5 min, better with lido 2% epi compared with bup 0.5% plain at 10 min (P<0.05), and better with bup 0.5% hyalase, lido 2% epi, and lido/bup/hyalase, than with bup 0.5% plain at 15 min (P<0.01, <0.01, <0.05, respectively) and at 20 min (P<0.05, <0.05, <0.025, respectively). The supplementation rate at 5 min was least with lido 2% epi, greater with bup 0.5% plain (P<0.01) and bup 0.5% hyalase (P<0.0005) and greatest with lido/bup/hyalase (P<0.0005), but similar in each group at 10, 15 and 20 min. Overall, those given lido 2% epi required the least number of supplemental injections to achieve globe akinesia. Mean supplemental injectate volumes, augmentation rates during surgery and the durations of surgical access provided by each agent were similar.

CONCLUSION

All four agents provided adequate analgesia during cataract extraction lasting approximately 95-100 min after PBA injection. Lido 2% epi demonstrated most rapid onset and required least number of injections to establish block. A hyaluronidase effect was evident only after 15 min in the bup 0.5% hyalase and lido/bup/hyalase groups. Bup 0.5% plain was overall the least satisfactory, and the greatest supplementation rate occurred with lido/bup/hyalase, suggesting that either lido 2% epi or bup 0.5% hyalase are the most suitable of the agents tested for this type of surgery.

Efficacy of varying concentrations of hyaluronidase in peribulbar anaesthesia

We have compared the efficacy of adding varying concentrations of hyaluronidase to a standard mixture of 2% lidocaine and 1% ropivacaine to provide peribulbar anaesthesia for cataract surgery. We used (i) the time to adequate anaesthesia for surgery and (ii) ocular and eyelid movement scores at 8 min after block as clinical endpoints. Ninety patients were randomly allocated to receive 7-10 ml of equal volumes of 2% lidocaine and 1% ropivacaine without hyaluronidase or with hyaluronidase 15 IU ml(-1) or 150 IU ml(-1). Median time at which the block was adequate for surgery was 6 min in all groups (interquartile range 4-12 min). Median eyelid movement scores were similar in all groups, but the ocular movement scores at 8 min were significantly lower in the group which received hyaluronidase 150 IU ml(-1) than in the group not given hyaluronidase (P<0.03). There were no differences between groups in the incidence of minor complications. A high concentration of hyaluronidase resulted in a statistically significantly lower ocular movement score at 8 min; the clinical relevance of this finding is uncertain.

The methodologic quality of clinical trials on regional anesthesia for cataract surgery

OBJECTIVE

To assess the methodologic quality of published randomized trials of regional anesthesia management strategies for cataract surgery.

DESIGN

Literature review and analysis.

METHOD

We performed a systematic search of the literature to identify all articles pertaining to regional anesthesia for cataract surgery on adults. Overall quality scores and scores for individual methodologic domains were based on the evaluations of two investigators experienced in methodologic research who independently reviewed all relevant articles using a quality abstraction form.

MAIN OUTCOME MEASURES

Study quality in each of five domains: representativeness, bias and confounding, intervention description, outcomes and follow-up, and statistical quality and interpretation.

RESULTS

Eighty-two randomized clinical trials were identified with a mean overall quality score of 44%. The mean domain scores ranged from 37% for representativeness to 58% for outcomes and follow-up. Forty percent or fewer studies received the maximum score for reporting the setting, the population, and the start and end dates; describing the inclusion and exclusion criteria; adequately randomizing subjects; and adequately masking individuals participating in the study. Key outcomes were often inadequately reported, including the distribution of patient-reported pain scores and the mean surgical time.

CONCLUSIONS

Greater attention to methodologic quality and detailed reporting of study results will improve the ability of readers to interpret the results of clinical trials assessing regional anesthesia for cataract surgery.

Synthesis of the literature on the effectiveness of regional anesthesia for cataract surgery

OBJECTIVE

To synthesize the findings of the randomized trials of regional anesthesia management strategies for cataract surgery.

DESIGN

Literature review and analysis.

METHOD

The authors performed a systematic search of the literature to identify all articles pertaining to regional anesthesia during cataract surgery on adults. One investigator abstracted the content of each article onto a custom-designed form. A second investigator corroborated the findings. The evidence supporting the anesthesia approaches was graded by consensus as good, fair, poor, or insufficient.

MAIN OUTCOME MEASURES

Evidence supporting the effectiveness of different forms of regional anesthesia.

RESULTS

There was good evidence that retrobulbar and peribulbar blocks provide equivalent akinesia and pain control during cataract surgery. Additionally, sub-Tenon's blocks were at least as effective as retrobulbar and peribulbar blocks. There was good evidence that retrobulbar block provides better pain control during surgery than topical anesthesia, and there was fair evidence that peribulbar block provides better pain control than topical anesthesia.

CONCLUSIONS

This synthesis of the literature demonstrates that currently used approaches to anesthesia management provide adequate pain control for successful cataract surgery, but there is some variation in the effectiveness of the most commonly used techniques. Data are needed on patient preferences to determine the optimal strategies for anesthesia management during cataract surgery.

Pain perception with pH buffered peribulbar anaesthesia: a pilot study

AIMS

To determine the relation between pH of anaesthetic solutions and patient perception of pain with peribulbar injection of local anaesthesia.

METHODS

This prospective randomised controlled double blind pilot study involved 60 consecutive patients who received a peribulbar block with either a standard acidic local anaesthetic of 5 ml 2% lignocaine and 5 ml of 0.5% bupivacaine (solution A), or an alkalinised solution composed of the same anaesthetic agents but with a pH of 7.44 (solution B). Before surgery patients were asked to grade the pain of both the preoperative dilating drops and the peribulbar injection using a visual analogue scale.

RESULTS

The mean pain scores were similar in the two treatment groups-slightly higher (4.97) in group B who received the buffered solution, compared with group A (4.84) who received the plain solution. The small difference (-0.13, 95% confidence limits -1.6 and +1.3) was not significant. There was, however, a highly significant association between pain threshold ("drop pain") and injection pain levels (p<0.0001).

CONCLUSION

This study showed no difference in the reduction in the pain experienced by patients undergoing peribulbar anaesthesia with pH buffered local anaesthetic. The study suggests the importance of "pain threshold" as a confounder and also showed the considerable pain felt by some patients on instillation of the preoperative dilating drops.

Comparison of 0.75% levobupivacaine with 0.75% racemic bupivacaine for peribulbar anaesthesia

In a single centre, randomised, double-blind study 50 patients scheduled for intra-ocular surgery received 0.75% levobupivacaine or 0.75% racemic bupivacaine for peribulbar anaesthesia. There were no significant differences in the mean (SD) volume of levobupivacaine (11 (2.7) ml) or racemic bupivacaine (10 (2.6) ml) required, time to satisfactory block (levobupivacaine-13 (5.6) min; racemic bupivacaine-11 (4.4) min), peri-operative pain scores or frequency of adverse events between levobupivacaine and racemic bupivacaine. The safer side-effect profile of levobupivacaine may offer significant advantages in the elderly population undergoing cataract extraction in whom intercurrent disease is common.

Is hyaluronidase helpful for peribulbar anaesthesia?

A prospective, randomised controlled study was performed to investigate whether hyaluronidase improved the efficacy of peribulbar anaesthesia. Ninety-two patients undergoing peribulbar anaesthesia for intraocular surgery all received 10 ml of an anaesthetic solution consisting of a 50:50 mixture of 2% lignocaine with 1 in 200,000 adrenaline and 0.5% bupivacaine. Patients were randomised to a hyaluronidase group which received 150 IU/ml hyaluronidase in this anaesthetic solution (a higher concentration than previous studies) or a control group which received no hyaluronidase. There were 44 patients in the hyaluronidase group and 48 patients in the control group. All anaesthetic injections were administered by an experienced ophthalmologist and no supplementary injections were required in any case. The mean time interval between administration of the block and commencement of surgery was 22 minutes. No statistically significant difference was found between the two groups for pre-operative akinesia (p = 0.16), intraoperative akinesia (p = 0.25), eyelid paralysis (p = 0.72), objective analgesia (p = 0.23) or subjective analgesia (p = 0.60). The majority of patients in both groups achieved excellent akinesia, eyelid paralysis and analgesia. The reasons for these findings in the light of previously conflicting reports on the value of hyaluronidase in peribulbar anaesthesia are discussed.

Topical anesthesia with pH-adjusted versus standard lidocaine 4% for clear corneal cataract surgery

PURPOSE

To evaluate and compare the efficacy of a sodium-bicarbonate-adjusted preparation of lidocaine 4% (pH = 7.2) and standard lidocaine (pH = 5.2) for topical anesthesia in clear corneal cataract surgery.

SETTING

Department of Ophthalmology, University of Vienna, Austria.

METHODS

In a prospective, randomized, double-blind clinical trial, clear corneal cataract surgery was performed under topical anesthesia in 44 eyes of 34 patients. In 22 eyes, pH-adjusted lidocaine 4% was administered; in the other 22, standard lidocaine 4%. Aqueous and serum concentrations of lidocaine were measured by high-performance liquid chromatography and ultraviolet detection. Subjective pain was assessed using a visual analog scale of no pain (0%) to worst imaginable pain (100%). On the first postoperative day, visual acuity, intraocular pressure, and corneal staining with fluorescein were examined.

RESULTS

In the pH-adjusted lidocaine group, significantly higher lidocaine concentrations were found in the aqueous humor (15.06 microg/mL +/- 8.2 [SD] versus 4.75 +/- 3.5 microg/mL; P < .0001). In all samples (n = 8), serum lidocaine concentrations were below a minimum detectable level of 0.02 microg/mL. Subjective pain ratings were similar in the pH-adjusted and standard lidocaine groups (mean 9.73 +/- 10.4% and 10.0 +/- 15.4%, respectively). There was no significant between-group difference in intraoperative and postoperative outcomes.

CONCLUSIONS

In this study, pH-adjusted lidocaine 4% was a safe, effective topical anesthetic for clear corneal surgery and had minimal local and systemic toxicity. Administration of pH-adjusted lidocaine 4% resulted in significantly higher aqueous humor lidocaine concentrations than administration of standard lidocaine 4%.

Intravenous sedation prior to peribulbar anaesthesia for cataract surgery in elderly patients

PURPOSE

To investigate if pre-block iv sedation using midazolam, alfentanil, or a midazolam-alfentanil combination minimizes pain, reduces pain recall, and attenuates haemodynamic responses to peribulbar block; and to determine other factors influencing oxygen saturation (SpO2) following iv sedation.

METHODS

In a randomized, double-blind, placebo-controlled study, 120 patients, mean age 73 yr, having cataract surgery with peribular anaesthesia, were randomized to receive either normal saline, 1 mg midazolam, 500 micrograms alfentanil, or 0.5 mg midazolam plus 250 micrograms alfentanil. Blood pressure (BP), heart rate (HR) and pulse oximetry readings were recorded before injection of the study drugs, immediately after completion of the peribulbar block, and 10 min after the block. Pain from the anaesthetic block was assessed immediately after the block and after surgery using a visual analog scale, and recall of pain was assessed by telephone on the day after surgery.

RESULTS

Pain scores were low in all four groups. Midazolam-alfentanil reduced pain perception, and all iv sedation used reduced pain recall. Midazolam reduced systolic BP; alfentanil +/- midazolam reduced HR. All iv sedation reduced SpO2 more than did saline, but not usually to a clinically important level. Nine patients had a SpO2 < or = 90%; all had received alfentanil with or without midazolam. It was not possible to predict oxygen saturation levels by any factors other than iv sedation and baseline SpO2 levels.

CONCLUSION

Intravenous sedation with midazolam or alfentanil or in combination reduced pain perception, pain recall, and haemodynamic responses from peribulbar anaesthesia. Fifteen percent of patients given alfentanil developed clinically important oxygen desaturation. The use of fine gauge needles combined with slow injection of anaesthetic solution causes minimal discomfort, and routine iv sedation may be unnecessary.

Re-evaluation of hyaluronidase in peribulbar anaesthesia

AIMS/BACKGROUND

Hyaluronidase can augment the actions of local anaesthetics in peribulbar anaesthesia. However, evidence suggests satisfactory anaesthesia can be achieved using mixtures without hyaluronidase. A randomised double blind study was conducted on 50 patients, undergoing peribulbar anaesthesia, to validate this observation.

METHODS

Patients received a standard mixture of local anaesthetic (0.5% bupivacaine and 2% lignocaine in a 1:1 ratio) with or without hyaluronidase (25 IU/ml of mixture), pH values 5.16 and 5.24 respectively. Time taken to establish satisfactory anaesthesia to allow surgery was noted.

RESULTS

The onset time to globe akinesia in the control group ranged from 2 to 15 minutes (mean 5.64 and median 4 minutes) and in the hyaluronidase group from 2 to 12 minutes (mean 4.64 and median 4 minutes). The volume of local anaesthetic injected to achieve satisfactory anaesthesia ranged from 8 to 16 ml (mean 10.96, SD 1.95) in the control group and 10 to 18 ml (mean 11.64, SD 2.8) in the hyaluronidase group. A Mann-Whitney test to compare onset times to globe akinesia between groups gave a p value = 0.6 and 95% confidence interval (-1 to 2 minutes).

CONCLUSION

Addition of 25 IU/ml of hyaluronidase to a standard pH unadjusted local anaesthetic mixture does not significantly reduce the time to the onset of satisfactory globe akinesia.

The role of hyaluronidase on lidocaine and bupivacaine pharmacokinetics after peribulbar blockade

Orbital regional anesthesia is the only circumstance where hyaluronidase is routinely added to local anesthetics to accelerate the onset of the block. The aim of this study was to compare the pharmacokinetics of lidocaine and bupivacaine with or without hyaluronidase for peribulbar blockade. Twenty-one patients scheduled for cataract surgery with lens implantation were included in this prospective randomized study. Peribulbar blocks were achieved with plain bupivacaine 0.5% (5.5 mL), lidocaine 2% (5.5 mL), and hyaluronidase (100 IU = 2 mL) (n = 10) ir sterile water (2 mL) (n = 11). Plasma bupivacaine and lidocaine concentrations were measured by high-performance liquid chromatography at regular intervals from the end of the local anesthetic injection until the 360th minute. Maximum plasma concentration (Cmax) and time to reach Cmax (Tmax) were obtained for all the patients except one who needed a supplementary injection and was excluded from the study. The time to onset and duration of the analgesia and akinesia were monitored at the times of sampling. Motor blockade was incomplete in two patients in each group without affecting surgery. The Tmax and absorption half-life (t1/2a) of lidocaine and bupivacaine were not different within each group (P > 0.05). The Tmax of lidocaine was shorter in the presence of hyaluronidase (17.1 +/- 2.6 min vs 32.7 +/- 6.0 min) as well as the Tmax of bupivacaine (16.8 +/- 3.0 min vs 26.5 +/- 4.4 min). The Cmax of lidocaine and bupivacaine were not modified by the addition of hyaluronidase. The clearance, terminal half-life, and volume of distribution were not different between groups. The absorption of lidocaine and bupivacaine from the peribulbar space are hastened by the addition of hyaluronidase. The Tmax of lidocaine is not different from that of bupivacaine within each group suggesting that the absorption of local anesthetics is minimally influenced by the liposolubility of the drugs. Moreover, hyaluronidase influences the absorption kinetics of both lidocaine and bupivacaine in the same manner.

[Alkalinization of local anesthetics: theoretically justified but clinically useless]

PURPOSE

In vitro studies have demonstrated the potential advantages of alkalinization on anaesthetic activity, by decreasing the ratio of ionized to nonionized molecules, there by permitting more rapid penetration of local anaesthetic through biological membranes, thus decreasing the onset time. The proportion of each form depends on the pKa of the agent and the ultimate pH of the solution. When NaHCO3 is mixed with local anaesthetics, CO2 is produced. Carbon dioxide has been reported to enhance local anaesthetic action by diffusion trapping of the cationic form in pH gradient combined with a direct depressant action of CO2. The purpose of this study was to examine if clinical studies confirmed the in vitro action of alkalinisation.

SOURCE

The literature pertinent to alkalinization of local anaesthetics published in the major anaesthesia and pharmacology journals of North America and Europe.

PRINCIPAL FINDINGS

While in vitro studies have demonstrated potential advantages for alkalinization on anaesthetic activity, clinical studies have shown that alkalinization of local anaesthetics produces inconsistent results. For bupivacaine and etidocaine, alkalinization of local anaesthetic solution can produce precipitation, thus limiting the feasibility of increasing the pH.

CONCLUSIONS

On the basis of this review, routine alkalinization of local anaesthetics is not recommended.

Improved peribulbar anaesthesia with alkalinization and hyaluronidase

A prospective double-blind randomized study was carried out to determine the effect of pH and the addition of hyaluronidase to a mixture of lidocaine and bupivacaine on the efficacy of peribulbar anaesthesia. One hundred patients were assigned to one of five groups. All groups received a solution of two parts bupivacaine (0.75%) and one part lidocaine (2%) (with 1:100,000 adrenaline) as the base components of their anaesthesia. Group 1 received only the bupivacaine-lidocaine mixture, pH 3.9. Group 2 received a solution supplemented with hyaluronidase (ten units.ml-1), pH of 5.1. Group 3 received the bupivacaine-lidocaine mixture alkalinized with sodium bicarbonate to a pH of 5.1, the same as solution 2. Group 4 received the mixture with hyaluronidase alkalinized to pH of 6.7. Group 5 received the bupivacaine-lidocaine mixture alkalinized to a pH of 6.7. Efficacy of each block was graded according to the degree of residual movement 30 min following injection, as described by House et al. The solution containing hyaluronidase and pH adjusted to 6.7 was found to be the most effective (P < 0.025). The presence of hyaluronidase without alkalinization did not improve the efficacy of the mixture; and similarly, alkalinization in the absence of hyaluronidase was ineffective. These results reflected the pH- and temperature-dependent thermodynamic properties of local anaesthetics, and the pH-dependent activity of hyaluronidase.

Regional anaesthesia for intraocular surgery

The role of anaesthetists in providing local anaesthesia for intraocular surgery has changed over the past decade. No longer confined to the interested few, more and more anaesthetists are involved in monitored care and/or are performing eye block anaesthesia. This review summarizes the information related to eye block anaesthesia. The salient features of the orbital anatomy important for safe conduct of eye block anaesthesia are described. The techniques for retrobulbar and peribulbar anaesthesia, including facial nerve blocks, anaesthetic mixture, types of needles, and softening the eye are presented. Complications such as retrobulbar haemorrhage, globe penetration/perforation, visual impairment, brainstem anaesthesia, muscle injury, and oculocardiac reflex are explored. The implications of anticoagulant therapy are examined. The choice between retrobulbar and peribulbar blocks and the role of anaesthetists are discussed.