Ophthalmic regional anaesthesia

Inflammatory signal transduction pathways induced by prilocaine toxicity in cultured ARPE-19 cells

Prilocaine (PRL) is a common local anesthetic. Despite the successful use of regional anesthesia for intraocular surgery, there are associated side effects that may affect the retina in case of accidental intravitreal injection. This study examined the signal transduction pathways activated by PRL toxicity and determined the protective role of nitric oxide synthase-2 (NOS2) inhibition in cultured human-derived retinal pigment epithelial cells (ARPE-19). Toxicity analysis was performed using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide assay to detect the toxic dose of PRL and protective effectiveness of asperglaucide (ASP), an NOS2 inhibitor. Nuclear factor kappa B p65 (NF-κB p65), phosphorylated NF-κB p65, phospho-protein kinase B (AKT), NOS2, nitrotyrosine, and cleaved caspase-3 protein levels were evaluated by immunofluorescence staining and/or western blot analysis. Interleukin-6 (IL-6) and nitrated protein levels were quantified using an immunoassay, whereas caspase-3 activity and nitrite/nitrate levels were measured using a fluorometric method. A significant increase in NF-κB p65, and phosphorylated NF-κB p65 and AKT levels due to PRL toxicity was observed. Similarly, IL-6, NOS2, nitrite/nitrate, and nitrotyrosine levels were significantly higher in PRL-treated cells than in control cells. Application of ASP to PRL-treated cells reduced NF-κB p65, and phosphorylated NF-κB p65 and AKT to basal levels. IL-6, NOS2, nitrite/nitrate, and nitrotyrosine levels also considerably decreased following ASP treatment in cells experiencing PRL-induced toxicity. Moreover, the caspase-3-dependent apoptotic pathway was not activated. Our results indicate that ASP could ameliorate PRL-induced activation of NF-κB p65 that led to inflammation in cultured ARPE-19 cells.

Tracheal Sound Analysis for Automatic Detection of Respiratory Depression in Adult Patients during Cataract Surgery under Sedation

Background

Tracheal sound analysis is a simple way to study the abnormalities of upper airway like airway obstruction. Hence, it may be an effective method for detection of alveolar hypoventilation and respiratory depression. This study was designed to investigate the importance of tracheal sound analysis to detect respiratory depression during cataract surgery under sedation. Methods: After Institutional Ethical Committee approval and informed patients' consent, we studied thirty adults American Society of Anesthesiologists I and II patients scheduled for cataract surgery under sedation anesthesia. Recording of tracheal sounds started 1 min before administration of sedative drugs using a microphone. Recorded sounds were examined by the anesthesiologist to detect periods of respiratory depression longer than 10 s. Then, tracheal sound signals converted to spectrogram images, and image processing was done to detect respiratory depression. Finally, depression periods detected from tracheal sound analysis were compared to the depression periods detected by the anesthesiologist.

Results

We extracted five features from spectrogram images of tracheal sounds for the detection of respiratory depression. Then, decision tree and support vector machine (SVM) with Radial Basis Function (RBF) kernel were used to classify the data using these features, where the designed decision tree outperforms the SVM with a sensitivity of 89% and specificity of 97%.

Conclusions

The results of this study show that morphological processing of spectrogram images of tracheal sound signals from a microphone placed over suprasternal notch may reliably provide an early warning of respiratory depression and the onset of airway obstruction in patients under sedation.

Sub-Tenon's injection in equine cadaver eyes: MRI visualization of anesthetic fluid distribution and comparison of two different volumes

OBJECTIVE

To compare the localization and distribution of two different anesthetic fluid volumes around equine cadaver eyes to determine an appropriate volume for a single sub-Tenon's injection in horses.

PROCEDURE

A single sub-Tenon's injection of 2% lidocaine was performed in 10 equine cadaver heads (20 eyes) using two different volumes (7 mL on one side and 10 mL on the opposite side). The posterior circular distribution of the anesthetic was quantified in sagittal, dorsal, and transverse MRI (T2W-TSE) sequences and evaluated independently by three board-certified radiologists. The distribution of the two fluid volumes was compared via a paired Student's t-test. The interobserver reliability was evaluated via a Kruskal-Wallis test.

RESULTS

Extension of the injection fluid was observed along the dorsal and temporal quadrants of the globe within the subconjunctival space, the anterior and posterior sub-Tenon's space, and into the muscle sheaths along the extraocular muscles. Accumulation of anesthetic fluid directly surrounding the optic nerve was detected in three of 20 cadaver eyes. Circular distribution of the 7 and 10 mL anesthetic volumes was not significantly different (P = 0.849). More retrograde leakage of the anesthetic was observed using the 10 mL volume. Evaluation of interobserver reliability revealed no significant differences between observers (P = 0.21-0.92).

CONCLUSIONS

Sub-Tenon's anesthesia can have potential as an alternative to retrobulbar anesthesia for ophthalmic surgeries in equines. A 7- to 10-mL injection volume should be appropriate based on the results of this study. The distribution of the anesthetic solution in live tissues, the clinical effects, and the potential for complications will have to be evaluated in vivo.

PRESSÃO INTRAOCULAR, PRESSÃO ARTERIAL MÉDIA E DIÂMETRO PUPILAR EM COELHOS ( (Oryctolagus cuniculus) ) SUBMETIDOS AO BLOQUEIO RETROBULBAR COM DIFERENTES PROTOCOLOS ANESTÉSICOS

Resumo O objetivo deste estudo foi buscar novos protocolos de anestesia loco regional para procedimentos oftálmicos que proporcionem segurança e manutenção das funções vitais, além de manter a pressão intraocular estável, com centralização do bulbo do olho e acinesia palpebral. Foram utilizados 20 coelhos da raça Nova Zelândia para a realização de quatro protocolos de anestesia local através do bloqueio retrobulbar com lidocaína 2% com vasoconstritor, lidocaína 2% sem vasoconstritor associada ao tramadol, ropivacaína 1% e bupivacaína 0,5%, cada animal recebeu o volume anestésico de 1,0 mL. Todos os protocolos anestésicos utilizados promoveram acinesia palpebral e centralização do bulbo do olho durante todo o período de avaliação. A realização do bloqueio retrobulbar com os protocolos anestésicos demonstrou ser factível e segura quanto à manutenção da pressão intraocular, pressão arterial invasiva e diâmetro pupilar e pode ser utilizada para realização de cirurgias intraoculares. Os anestésicos proporcionaram bom bloqueio retrobulbar, entretanto a bupivacaína foi o anestésico que ocasionou o maior diâmetro pupilar comparativamente aos demais fármacos testados.

Corneal Anesthesia With Site 1 Sodium Channel Blockers and Dexmedetomidine

PURPOSE

Amino-amide or amino-ester local anesthetics, which are currently used for topical ocular anesthesia, are short acting and may delay corneal healing with long-term use. In contrast, site 1 sodium channel blockers (S1SCBs) are potent local anesthetics with minimal adverse tissue reaction. In this study, we examined topical local anesthesia with two S1SCBs, tetrodotoxin (TTX) or saxitoxin (STX) individually or in combination with α2-adrenergic receptor agonists (dexmedetomidine or clonidine), and compared them with the amino-ester ocular anesthetic proparacaine. The effect of test solutions on corneal healing was also studied.

METHODS

Solutions of TTX ± dexmedetomidine, TTX ± clonidine, STX ± dexmedetomidine, dexmedetomidine, or proparacaine were applied to the rat cornea. Tactile sensitivity was measured by recording the blink response to probing of the cornea with a Cochet-Bonnet esthesiometer. The duration of corneal anesthesia was calculated. Cytotoxicity from anesthetic solutions was measured in vitro. The effect on corneal healing was measured in vivo after corneal debridement followed by repeated drug administration.

RESULTS

Addition of dexmedetomidine to TTX or STX significantly prolonged corneal anesthesia beyond that of either drug alone, whereas clonidine did not. Tetrodotoxin or STX coadministered with dexmedetomidine resulted in two to three times longer corneal anesthesia than did proparacaine. S1SCB-dexmedetomidine formulations were not cytotoxic. Corneal healing was not delayed significantly by any of the test solutions.

CONCLUSIONS

Coadministration of S1SCBs with dexmedetomidine provided prolonged corneal anesthesia without delaying corneal wound healing. Such formulations may be useful for the management of acute surgical and nonsurgical corneal pain.

Ophthalmic regional blocks: management, challenges, and solutions

In the past decade ophthalmic anesthesia has witnessed a major transformation. The sun has set on the landscape of ophthalmic procedures performed under general anesthesia at in-hospital settings. In its place a new dawn has ushered in the panorama of eye surgeries conducted under regional and topical anesthesia at specialty eye care centers. The impact of the burgeoning geriatric population is that an increasing number of elderly patients will present for eye surgery. In order to accommodate increased patient volumes and simultaneously satisfy administrative initiatives directed at economic frugality, administrators will seek assistance from anesthesia providers in adopting measures that enhance operating room efficiency. The performance of eye blocks in a holding suite meets many of these objectives. Unfortunately, most practicing anesthesiologists resist performing ophthalmic regional blocks because they lack formal training. In future, anesthesiologists will need to block eyes and manage common medical conditions because economic pressures will eliminate routine preoperative testing. This review addresses a variety of topical issues in ophthalmic anesthesia with special emphasis on cannula and needle-based blocks and the new-generation antithrombotic agents. In a constantly evolving arena, the sub-Tenon's block has gained popularity while the deep angulated intraconal (retrobulbar) block has been largely superseded by the shallower extraconal (peribulbar) approach. Improvements in surgical technique have also impacted anesthetic practice. For example, phacoemulsification techniques facilitate the conduct of cataract surgery under topical anesthesia, and suture-free vitrectomy ports may cause venous air embolism during air/fluid exchange. Hyaluronidase is a useful adjuvant because it promotes local anesthetic diffusion and hastens block onset time but it is allergenic. Ultrasound-guided eye blocks afford real-time visualization of needle position and local anesthetic spread. An advantage of sonic guidance is that it may eliminate the hazard of globe perforation by identifying abnormal anatomy, such as staphyloma.

Convulsions during cataract surgery under peribulbar anesthesia: a case report

INTRODUCTION

Locoregional anesthesia techniques are increasingly used for cataract surgery. From these techniques, peribulbar anesthesia has been very successful over the retrobulbar anesthesia seen its effectiveness and safety. However, peribulbar anesthesia is not without risk.

CASE PRESENTATION

A 70-year-old African man was scheduled for cataract surgery and lens implant for his right eye. His medical history included hypertension, diabetes mellitus and gall bladder surgery. There were no personal or family antecedents of allergy, epilepsy or taking food or toxic drug. No abnormalities were detected in his preoperative evaluation. In the operating room, standard monitoring was installed and a peripheral venous catheter 18g was inserted. Peribulbar anesthesia was realized with two injections in primary gaze position. The anesthetic mixture contained lidocaine 2% and bupivacaine 0.5%. The needle used was 25GA, 19mm, ¾ inch. The first injection was performed in his lower temporal peribulbar space with 5mL of mixture; the second injection was performed with 3mL of mixture in his upper nasal peribulbar space. These injections were performed after a negative aspiration test and followed by manual compression of his globe for 5 minutes. Five minutes after peribulbar anesthesia, his blood pressure increased to 209/115mmHg requiring three bolus of nicardipine (3.0mg) to reduce his blood pressure to 134/56mmHg. One minute after, he had generalized tonic-clonic seizures. Tracheal intubation was performed. His capillary blood glucose was 170mg/dL, axillary temperature was 36.5°C, and his serum electrolytes were normal. He recovered spontaneous ventilation 1.5 hours later. A neurological examination noted no deficit. Extubation was performed 15 minutes later without incident. A brain computed tomography and electroencephalogram were unremarkable. He was discharged on the second day and operated on 1 month later under general anesthesia.

CONCLUSIONS

Various serious complications can occur during locoregional anesthesia techniques in ophthalmic surgery. The mastering and perfecting of these techniques by practitioners and compliance with safety standards in anesthesia are the only way to guarantee the prevention of such complications.

Are ocular injection anesthetic blocks obsolete? Indications and guidelines

PURPOSE OF REVIEW

In this era of topical anesthesia for ocular surgery, anesthetic ocular blocks are still important when profound anesthesia and akinesia are required. Although injection ocular blocks, retrobulbar and peribulbar anesthesia, have been supplanted for most ocular surgery in many centers by sub-Tenon's irrigation block because of its superior safety profile, still worldwide, injection blocks remain popular.

RECENT FINDINGS

We present here the results of a survey of the literature published over the last 5 years to assess current international preferences for ocular anesthesia injection blocks. We discuss the reasons why sub-Tenon's anesthesia is not more universally popular and advocate for its greater acceptance because of safety. Specific narrow indications for performing injection ocular blocks are presented. Also, guidelines for performing retrobulbar anesthesia which reduce the risk of serious ocular complications are provided as well as our rationale for preferring retrobulbar to peribulbar anesthesia.

SUMMARY

Sub-Tenon's block should be performed in the operating theatre in preference to retrobulbar or peribulbar anesthesia except for limited indications. When injection ocular block is deemed necessary, we feel that retrobulbar anesthesia with the technique described may be safer than peribulbar anesthesia.

Overview of ocular anesthesia: past and present

PURPOSE OF REVIEW

Many choices of ocular anesthetic techniques are available to the ophthalmologist. This study reviews currently used techniques of topical, subconjunctival and regional block anesthesia used in ophthalmic procedures.

RECENT FINDINGS

The choices of anesthetics that are available are considered and a new ocular anesthetic gel is described that provides sustained ocular surface anesthesia, minimal side-effects and may also have antimicrobial properties.

SUMMARY

Consideration of ocular anesthetic techniques and anesthetic choice plays a critical role for the success and safety of ophthalmic surgery.

[Sub-tenon block for ocular globe anesthesia: a review]

Sub-Tenon anesthesia is an effective, well-tolerated technique for surgery in the anterior or posterior compartments of the eye. The advantages of this block are comparable to those of peribulbar and retrobulbar anesthesia and complications are minimal. Sub-Tenon anesthesia provides better analgesia than akinesia. Most studies suggest that sub-Tenon anesthesia is a good technique to choose, given that potential adverse effects are fewer than for other regional blocks and analgesia and akinesia are superior.

Needle-based blocks for the 21st century ophthalmology

PURPOSE

This paper reviews history of the needle orbital blocks used in the earlier centuries and how they have evolved towards safer anaesthesia in the modern clinical practice.

METHODS

Material is derived from literature searches from major ophthalmic and anaesthetic journals on the use of orbital needle blocks over earlier centuries.

RESULTS

Needle-based anaesthetic techniques were described shortly after the invention of reliable medical needles. Atkinson popularized the classical retrobulbar block in a series of papers published in the early 20th century. This technique,which utilises a relatively long needle inserted towards the apex of the muscle cone behind the globe, has been criticized by some as unsuitable for modern 21st century ophthalmic surgery because of the extremely rare potential for serious complications. Satisfactory anaesthesia and akinesia can be obtained with short sharp or dull needles with slightly higher volumes of local anaesthetic agent placed in the farthest inferotemporal quadrant.

CONCLUSION

Aside from relative safety, modern needle blocks offer the advantage of lid akinesia without a need for a second injection for the seventh nerve that is often performed con-comitantly with retrobulbar block.

Sub-Tenon's anaesthesia: a well tolerated and effective procedure for ophthalmic surgery

PURPOSE OF REVIEW

To report recent advancements with sub-Tenon's anaesthesia for ocular surgery, accentuating the efficacy and safety of this technique. Further clinical implications are reviewed with regard to its technique, indications, benefits, and reported complications.

RECENT FINDINGS

Sub-Tenon's anaesthesia, a versatile and technically easy procedure to master, has gained popularity with both ophthalmic surgeons and anaesthetists. This block is achieving repute as the block of choice, providing anaesthesia as well as akinesia during ophthalmic surgery. As the technique has further evolved and novel cannulae introduced, increasing complications have been documented.

SUMMARY

Currently, there is no absolutely well tolerated orbital regional block technique. However, well founded evidence appears to support sub-Tenon's block as a safer option. Sound knowledge of orbital anatomy, pharmacology of anaesthetic agents, and prevention of potential complications are therefore crucial to perform sub-Tenon's block effectively and safely.