To the Editor:—
We read with interest the article by Ripart et al. 1that provides clinical evidence to conclude that single-injection, high-volume medial canthus episcleral anesthesia is an efficient and safer alternative to peribulbar anesthesia. The salient features of their method are the injection of a relatively high volume (8–10 ml) of anesthetic solution and the use of adjuncts, such as clonidine premedication and propofol sedation. The high volume of the injected fluid is in contrast with the low volumes (less than 4 ml) normally injected into the episcleral space. The high-volume injection provides good motor blockade, including akinesia of the lids, in addition to sensory block.
We would like to share our experiences at Moorfield Eye Hospital, London, during the period of training in the module of ophthalmic anesthesia. The method used for induction of block is basically the same as described by Stevens 2and Guise. 3A volume of 2.5–4 ml local anesthetic was injected. In patients in whom akinesia was deemed to be inadequate, a 1–1.5-ml top-up was administered at the original sub-Tenon site. Digital palpation was used to assess intraocular pressure, and digital compression was applied for a few minutes with a view to aid the diffusion of the injectate. We performed nearly 200 blocks, with only 10% of the patients being topped-up. The akinesia produced was regarded as adequate by the surgeons. No complications attributable to the block were noted.
The reports regarding the variation of intraocular pressure with the volume of the fluid injected into the episcleral space are scanty. Bowman et al. 4reported an immediate mean pressure increase of 11.4 mmHg after injection of 10 ml fluid in the peribulbar space. Preliminary results of the study conducted by Ripart et al. 5did not show a large increase above baseline after injection of a large volume of local anesthetic, probably because of the decrease produced by the previously mentioned adjuncts. Incidentally, fears that a large volume injection may cause a sustained increase in intraocular pressure, jeopardizing the retinal blood supply and impairing the surgical field, have not been confirmed. 6Use of clonidine and propofol can be hazardous, especially for elderly patients. As per our experience, explanation of the procedure and assurance renders sedation unnecessary. The presence of a sympathetic nurse, a relative, or an interpreter helps the patient to relax and cooperate. We believe that more reliable data on the variation of intraocular pressure with the volume of injectate needs to be generated. This will help in fine-tuning the technique based on high-volume injection by way of determining the optimal volume and the ways of minimizing its adverse effects.