Sub-Tenon Block: A Learning Curve of 100 Cases

Assessment of the learning curve of peribulbar blocks using the Learning-Curve Cumulative Sum Method (LC-CUSUM): an observational study

INTRODUCTION

This study aimed to assess the learning curves of peribulbar anesthesia and estimate the number of blocks needed to attain proficiency.

METHODS

Anonymized records of sequential peribulbar blocks performed by first-year anesthesia residents were analyzed. The block sequential number and the outcomes were extracted from each record. Success was defined as a complete sensory and motor block of the eye, and failure was defined as an incomplete block requiring supplemental local anesthetic injections or general anesthesia. Learning curves using the LC-CUSUM method were constructed, aiming for acceptable and unacceptable failure rates of 10% and 20%, and 10% probability of type I and II errors. Simulations were used to determine the proficiency limit h0. Residents whose curves reached h0 were considered proficient. The Sequential Probability Ratio Test Cumulative Sum Method (SPRT-CUSUM) was used for follow-up.

RESULTS

Thirty-nine residents performed 2076 blocks (median = 52 blocks per resident; Interquartile Range (IQR) [range] = 27-78 [4-132]). Thirty residents (77%) achieved proficiency after a median of 13 blocks (13-24 [13-24]).

CONCLUSIONS

The LC-CUSUM is a robust method for detecting resident proficiency at peribulbar anesthesia, defined as success rates exceeding 90%. Accordingly, 13 to 24 supervised double-injection peribulbar blocks are needed to attain competence at peribulbar anesthesia.

Regional Anesthesia for Pediatric Ophthalmic Surgery: A Review of the Literature

Ophthalmic pediatric regional anesthesia has been widely described, but infrequently used. This review summarizes the available evidence supporting the use of conduction anesthesia in pediatric ophthalmic surgery. Key anatomic differences in axial length, intraocular pressure, and available orbital space between young children and adults impact conduct of ophthalmic regional anesthesia. The eye is near adult size at birth and completes its growth rapidly while the orbit does not. This results in significantly diminished extraocular orbital volumes for local anesthetic deposition. Needle-based blocks are categorized by relation of the needle to the extraocular muscle cone (ie, intraconal or extraconal) and in the cannula-based block, by description of the potential space deep to the Tenon capsule. In children, blocks are placed after induction of anesthesia by a pediatric anesthesiologist or ophthalmologist, via anatomic landmarks or under ultrasonography. Ocular conduction anesthesia confers several advantages for eye surgery including analgesia, akinesia, ablation of the oculocardiac reflex, and reduction of postoperative nausea and vomiting. Short (16 mm), blunt-tip needles are preferred because of altered globe-to-orbit ratios in children. Soft-tip cannulae of varying length have been demonstrated as safe in sub-Tenon blockade. Ultrasound technology facilitates direct, real-time visualization of needle position and local anesthetic spread and reduces inadvertent intraconal needle placement. The developing eye is vulnerable to thermal and mechanical insults, so ocular-rated transducers are mandated. The adjuvant hyaluronidase improves ocular akinesia, decreases local anesthetic dosage requirements, and improves initial block success; meanwhile, dexmedetomidine increases local anesthetic potency and prolongs duration of analgesia without an increase in adverse events. Intraconal blockade is a relative contraindication in neonates and infants, retinoblastoma surgery, and in the presence of posterior staphylomas and buphthalmos. Specific considerations include pertinent pediatric ophthalmologic topics, block placement in the syndromic child, and potential adverse effects associated with each technique. Recommendations based on our experience at a busy academic ophthalmologic tertiary referral center are provided.

DEVELOPMENT OF RETROBULBAR AND AURICULOPALPEBRAL NERVE BLOCKS IN CALIFORNIA SEA LIONS (ZALOPHUS CALIFORNIANUS)

Eye lesions are commonly observed in pinnipeds. Clinical assessment is challenging because animals are often blepharospastic and under inhalant anesthesia the globe rotates ventrally, making observation difficult. Retrobulbar and auriculopalpebral nerve block techniques have been developed in other species to alleviate these difficulties and allow for a more thorough ophthalmic exam. Ocular nerve block techniques were developed for California sea lions (CSLs) (Zalophus californianus) using lidocaine hydrochloride 2%. To develop the retrobulbar block, a variety of needle sizes, anatomic approaches, and volumes of methylene blue were injected into the orbits of 10 CSL cadavers. An optimal technique, based on desired distribution of methylene blue dye into periocular muscles and tissues, was determined to be a two-point (ventrolateral and ventromedial) transpalpebral injection with a 20-ga, 1 1/2-inch needle. This technique was then tested using lidocaine on 26 anesthetized animals prior to euthanasia, and on one case with clinical ocular disease. A dose of 4 mg/kg of lidocaine was considered ideal, with positive results and minimal complications. The retrobulbar block had a 76.9% rate of success (using 4 mg/kg of lidocaine), which was defined as the globe returning at least halfway to its central orientation with mydriasis. No systemic adverse effects were noted with this technique. The auriculopalpebral nerve block was also adapted for CSLs from techniques described in dogs, cattle, and horses. Lidocaine was injected (2-3 ml) by subcutaneous infiltration lateral to the orbital rim, where the auriculopalpebral nerve branch courses over the zygomatic arch. This block was used in five blepharospastic animals that were anesthetized for ophthalmic examinations. The auriculopalpebral nerve block was successful in 60% of the cases, which was defined as reduction or elimination of blepharospasm for up to 3 hr. Success appeared to be dependent more on the location of injection rather than on the dose administered.

A qualitative study of regional anaesthesia for vitreo-retinal surgery

AIM

The aim of this research was to collect experiential knowledge about regional ocular anaesthesia - an integral component of most vitreo-retinal surgery.

BACKGROUND

Anaesthesia for vitreo-retinal surgery has predominantly used general anaesthesia, because of the length and complexity of the surgical procedure. However, recent advances in surgical instrumentation and techniques have reduced surgical times; this decision has led to the adoption of regional ocular anaesthesia for vitreo-retinal day surgery. Although regional ocular anaesthesia has been studied from several perspectives, knowledge about patients' experience of the procedure is limited.

DESIGN

An interpretive qualitative research methodology underpinned by Gadamer's philosophical hermeneutics.

METHODS

Eighteen participants were interviewed in-depth between July 2006-December 2007 following regional ocular anaesthesia. Interview data were thematically analysed by coding and grouping concepts.

FINDINGS

Four themes were identified: 'not knowing': the time prior to the experience of a regional eye block; 'experiencing': the experience of regional ocular anaesthesia; 'enduring': the capacity participants displayed to endure regional ocular anaesthesia with the hope that their vision would be restored; and 'knowing': when further surgery was required and past experiences were recalled.

CONCLUSIONS

The experience of regional ocular anaesthesia had the capacity to invoke anxiety in the participants in this study. Many found the experience overwhelming and painful. What became clear was the participant's capacity to stoically 'endure' regional ocular anaesthesia, indicating the value people placed on visual function.

Sub-Tenon's anaesthesia: complications and their prevention

The advent of a new technique that is considered much safer than previously established one leads to its rapid adoption. This usually leads to the identification of previously unreported complications of the new technique, and a re-assessment of its position in clinical care, which is precisely the state of play with the sub-Tenon's block. The sub-Tenon's block was introduced into the clinical practice in early 1990. A systematic recent search of subject headings such as complications of sub-Tenon's block, subtenon, orbital block, orbital block complications, and orbital anaesthesia was performed in Medline, EMBASE, and Cochrane database. Indeed there are complications of sub-Tenon's block published as case reports and the exact incidence of these complications is not known. Management and preventive measures of these complications are described. Although the sub-Tenon's block appears to be relatively safer than needle-based blocks but a proper prospective, randomized, double-blind controlled trial is essential for scientific proof that sub-Tenon's block is better than needle-based blocks.

Adverse events associated with regional ophthalmic anaesthesia in an Australian teaching hospital

This study prospectively audited 3339 peribulbar and 2688 sub-Tenon's eye blocks in an Australian teaching hospital with regard to the occurrence of adverse events. Complications were classified into three groups: ocular complications directly due to the eye block technique, systemic medical complications possibly associated with block technique and adverse events which were unlikely to have been associated with block technique. Five serious ocular complications were associated with peribulbar block compared to none with sub-Tenon's block (P = 0.07).

Combination auriculopalpebral nerve block and local anesthesia for placement of a nictitating membrane-to-superotemporal bulbar conjunctiva flap in dogs

The purpose of this study was to evaluate the efficacy of combined local anesthesia in dogs undergoing nictitating membrane (NM)-to-superotemporal bulbar conjunctiva flap construction. Medical records of 47 dogs that had received local anesthesia for NM-to-superotemporal bulbar conjunctiva flap were reviewed. Combined local anesthetic technique included auriculopalpebral nerve block, topical anesthesia of the eye, and infiltration anesthesia of the superotemporal bulbar conjunctiva and palpebral surface of the NM. Forty-two (89.3%) dogs complied with the anesthetic procedures and underwent NM flap without general anesthesia or sedation. No complications were related to the combined local anesthesia. Combined local anesthesia for NM-to-superotemporal bulbar conjunctiva flap may be a time- and cost-effective method that produces both analgesia of the surgical site and akinesia of the eyelid.