Robert C. Hamilton

Comparison of 4 topical anesthetic agents for effect and corneal toxicity in rabbits

PURPOSE To compare the onset time, duration of action, corneal toxicity, and corneal epithelial healing time of 4 topical anesthetic agents in rabbits. SETTING Faculty of Medicine, University of Calgary, Calgary, Alberta, Canada. METHOD Fifty-six rabbits were treated with 4 topical anesthetics (bupivacaine, lidocaine, procaine, and benzocaine) at different concentrations and different pH of solutions. Corneal sensation, corneal toxicity, and corneal epithelial healing time were measured. RESULTS The onset time of all 4 anesthetic agents was within 1 minute; however, bupivacaine and lidocaine produced significantly longer action than procaine or benzocaine (P < .05). Buffered bupivacaine and lidocaine had a significantly longer anesthetic effect than that of the nonbuffered solutions (P < .05). No significant effect on corneal epithelial healing time or corneal toxicity was observed. CONCLUSION Topical bupivacaine and lidocaine had a longer anesthetic effect, particularly in buffered solutions. No significant corneal toxicity was observed.

Periocular local anesthesia: Medial orbital as an alternative to superior nasal injection

Abstract We developed a new technique, the medial orbital pericone local anesthetic block, that surgeons can use as a secondary block when inferotemporal retrobulbar or peribulbar/periocular injection of local anesthetics results in incomplete anesthesia. Unlike secondary local injections placed in the superonasal quadrant of the orbit, our technique injects the anesthetic into the fat compartment of the nasal side of the globe, a site that is relatively avascular and lacks vital anatomic structures. In more than 15,000 patients, this method proved an effective, safe means of secondary block and promoted orbicularis oculi muscle akinesia.

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

Fifty patients scheduled for cataract surgery under peribulbar block were randomised to receive either plain (pH 5.4) or pH-adjusted (pH 6.8 range 6.7–6.9) 0.75% bupivacaine. Hyaluronidase was added to both solutions prior to peribulbar block. The time of onset of akinesia of the globe and the need for supplementary injections were recorded by an independent observer. Patients who returned for surgery to the second eye received the alternative local anaesthetic solution for the second peribulbar block. The relative efficacy of the different anaesthetic solutions was compared in patients who underwent unilateral surgery (Group A, n = 50). In 12 patients (Group B) who underwent bilateral surgery, direct comparisons between eyes in the same patient were possible. In both groups of patients, eyes receiving peribulbar block with the pH-adjusted solution showed a shorter time to partial akinesia of the globe (P < 0.05). However, there was no difference between the solutions in the time to complete akinesia of the globe, but the number of supplementary injections required for an effective block with the pH-adjusted solution was increased. Onset time to akinesia of the lateral and superior rectus muscles was shortened in patients receiving the pH-adjusted solution but there were minimal effects on the medial and inferior recti.RésuméCinquante patients devant subir une extraction de cataracte sous anesthésie régionale rétrobulbaire participent à cette étude. Le choix de l’agent anesthésique utilisé se fait au hasard et comporte la bupivacaine 0,75% avec pH á 5,4 (formule commerciale) ou bupivacaïne 0,75% avec pH corrigé à 6,8 (valeurs variant entre 6,7 et 6,9). Quand un patient revient pour une chirurgie de l’autre oeil, le choix de l’anethésique local est alterné. Dans tous les cas, de l’hyaluronidase est ajoutée à l’anesthésique local. Un observateur non informé de l’agent utilisé note le temps nécessaire pour obtenir une akinésie de l’oeil, ainsique le besoin d’injections supplémentaires. L’efficacité des deux solutions anesthésiques est comparée entre les patients soumis à une seule chirurgie (Groupe A, n = 50). Chez 12 patients subissant deux interventions (Groupe B), des comparaisons entre les yeux du même patient sont faites. Dans les deux groupes de comparaisons, la solution avec pH corrigé permet un début plus rapide d’akinésie partielle du globe oculaire (P < 0,05). Cependant, le temps nécessaire pour obtenir une akinésie complète est comparable avec une solution ou l’autre. L’utilisation de la solution à pH corrigé entraîne un plus grand nombre d’injections suppleméntaires. Elle permet un début plus rapide d’akinesie des muscles droits supérieur et latéral, mais a peu d’effets sur les muscles droits interne et inférieur.

Retrobulbar block revisited and revised

Abstract In recent years, the traditional Atkinson retrobulbar block anesthesia technique has been modified to reduce the risk of certain complications. Technique modifications described in this paper eliminated anesthesia‐induced postoperative extraocular muscle malfunction in a series of 8500 procedures.

Modified retrobulbar block

To the Editor: We read with interest the recently published article by Drs. Wong, Koehrer and Sutton I introducing a modified retrobulbar block for eye surgery. A technique of ophthalmic regional anaesthesia should be based on sound anatomical principles, especially in the selection of a needle path and depth of insertion that will avoid structures such as important blood vessels, extraocular muscles and the optic nerve. In addition, it should include precise instruction as to direction of needle insertion. We have analysed the technique described in the article and suggest that it falls short in several of these areas and may be prone to the production of serious complications, such as globe perforation, optic nerve trauma, intraorbital haemorrhage or injection into one of the extraocular muscles with resultant local anaesthetic myotoxity. It is argued that, if a retrobulbar needle can be placed in a straight line rather than with redirection after partial orbital insertion, perforation of the globe is less likely. Since the globe is closer to the orbit roof than its floor 2 there is more reason for needle redirection with performing retrobulbar injection from above rather than from below the globe. In the described modified retrobulbar technique the needle is advanced in the sagittal plane but no instruction is given regarding the angle of insertion. From illustration C, the needle path appears to be on the medial side of the superior rectus/levator palpebae complex yet on the lateral side of the optic nerve. This is anatomically impossible for a needle advancing in a sagittal plane. With the description of the needle path and insertion to 32-33 mm it is possible to be in line with the optic nerve which is a more medial orbital structure than is commonly realized, particularly towards the orbit apex. We believe selection of a superomedial needle entry point is ill-advised not only because of the trochlear complex, although it may well be lateral to the described path, but also because this quadrant is the most vascular part of the anterior orbit, containing the end arteries of the ophthalmic arterial system. In addition, the superior ophthalmic vein, the largest venous channel of the orbit, courses anteromedially to posterolaterally, in the orbit between the superior rectus muscle and the optic nerve, across the described path of the needle. Furthermore, we are concerned that the needle avoid the medial rectus and superior oblique muscles along the pathway described. Finally, the depth of needle entry into the orbit described both for the standard retrobulbar and the modified retrobulbar blocks are in excess of the 31 mm amount recommended as maximum orbit penetration by Katsev et al. in their extensive analysis of safe practice based on bony anatomy. 3