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Sub-Tenon's administration of local anaesthetic: a review of the technique

2003; Elsevier BV; Volume: 90; Issue: 6 Linguagem: Inglês

10.1093/bja/aeg105

1471-6771

K Canavan, A Dark, Magnus Garrioch,

Anesthesia and Pain Management

Local anaesthesia is the anaesthetic technique of choice for surgery on the eye in many instances. The expansion of day-case facilities has encouraged its use, and the development of less invasive surgical techniques has rendered general anaesthesia largely unnecessary. Retrobulbar and peribulbar blocks are commonly practiced.10Eke T Thompson JR The National Survey of Local Anaesthesia for Ocular Surgery: (i) survey methodology and current practice.Eye. 1999; 13: 189-195Crossref PubMed Scopus (61) Google Scholar 27Mawer RJ Coombes AGA Local anaesthesia for routine ocular surgery.Br J Anaesth. 1998; 81: 485Crossref PubMed Google Scholar While providing excellent conditions for operating on the eye, these techniques are associated with serious but uncommon side-effects. The most dangerous is respiratory arrest as a result of brain stem anaesthesia.19Hamilton RC Gimbel HV Strunin L Regional anaesthesia for 12,000 cataract extraction and intraocular lens implantation procedures.Can J Anaesth. 1988; 35: 615-623Crossref PubMed Scopus (195) Google Scholar 43Rubin AP Complications of local anaesthetics for ophthalmic surgery.Br J Anaesth. 1995; 75: 93Crossref PubMed Scopus (128) Google Scholar Less invasive techniques for providing local anaesthesia, such as subconjunctival or topical application of local anaesthetic, are devoid of such risks but fail to provide adequate immobility of the eye and postoperative analgesia. Recent reports suggest that the use of Sub-Tenon's block is becoming more widespread amongst anaesthetists and ophthalmological surgeons.7Dark A Local anaesthesia for routine ocular surgery.Br J Anaesth. 1999; 82: 153-154Crossref PubMed Scopus (21) Google Scholar 10Eke T Thompson JR The National Survey of Local Anaesthesia for Ocular Surgery: (i) survey methodology and current practice.Eye. 1999; 13: 189-195Crossref PubMed Scopus (61) Google Scholar It has been suggested that it has a more acceptable risk profile than traditional ophthalmic anaesthesia techniques.7Dark A Local anaesthesia for routine ocular surgery.Br J Anaesth. 1999; 82: 153-154Crossref PubMed Scopus (21) Google Scholar This article reviews the technique with special focus on possible complications. Tenon's capsule is a fascial layer of connective tissue surrounding the globe and extra-ocular muscles. It is attached anteriorly to the limbus of the eye and extends posteriorly over the surface of the globe until it fuses with the dura surrounding the optic nerve (Fig. 1.) The Sub-Tenon's or episcleral space is a potential cavity bound by Tenon's capsule and the sclera. It is divided into anterior and posterior segments at the insertion of the extra-ocular muscles and their associated fasciae. In the anterior segment the extra-ocular muscle fascia may continue forward to be inserted around the limbus, imposing a fascial layer within Sub-Tenon's space. In the posterior segment the Tenon's capsule is in direct apposition, but unattached, to the sclera, where it forms the base of the orbital cone and is thinner than it is anteriorly. It is possible that with age the posterior Tenon's capsule degenerates and becomes fenestrated which aids diffusion of anaesthetic into the retrobulbar cone. Sensory innervation to the globe and its internal structures is derived from the ophthalmic branch of the trigeminal nerve via the long nasociliary and short ciliary nerves. The ciliary ganglion lies near the apex of the retrobulbar cone and is associated with the optic nerve and artery. It is composed of sympathetic fibres, sensory fibres, and parasympathetic fibres. Whereas the sympathetic and sensory fibres transit through the ganglion, the parasympathetic fibres synapse within it. The efferent nerve, the short ciliary nerve, progresses anteriorly to provide sensation to the globe and autonomic motor function to the iris. Its path to the anterior segment is diffuse, but traverses both the retrobulbar cone and Sub-Tenon's space where it is susceptible to block by local anaesthetic agents. The patient should be assessed for anaesthesia in the standard manner. Non-consent, inability to comply with the anaesthetist's instructions as, for example, a result of deafness or mental incapacity, inability to lie flat, allergy to local anaesthetics, lack of i.v. access, or excessive uncontrollable anxiety are absolute contraindications to Sub-Tenon's anaesthesia. The procedure should be explained to the patient to allay anxiety and assist the anaesthetist in carrying out the block. The injection is made on a supine patient with an i.v. cannula in situ. The conjunctiva is anaesthetized with topical anaesthetic solution. An eyelid speculum should be inserted at this point to improve access. Throughout the procedure, the patient is asked to look up and outwards to expose the infero-nasal quadrant. A small tent of conjunctiva is raised with a pair of fine non-toothed forceps approximately mid-way between the limbus of the eye and the visible edge of the inferonasal portion of the conjunctiva. A small incision is made in the tented conjunctiva with a pair of ophthalmic scissors (Fig. 2). The closed scissors are introduced through the aperture created and a tunnel is fashioned to the bare sclera by blunt dissection through Tenon's capsule. A curved, blunt irrigating cannula is then inserted with the syringe of anaesthetic solution attached (Fig. 3). Stevens describes a metal cannula designed for this purpose48Stevens JD Curved Sub-Tenon cannula for local anaesthesia.Ophthalmic Surg. 1993; 24: 121-123PubMed Google Scholar (Visitec™ Sub-Tenon's Anaesthesia Cannula 19 g × 25 mm) (Fig. 4). The cannula is introduced along the contour of the globe and gentle contact of its tip is maintained with the sclera until it lies in the posterior segment (Fig. 1). Occasionally, resistance to the needle is felt around the equator where a fibrous band can form as the ocular muscles broach the capsule. This is usually easily overcome by gentle pressure.Fig 3Tenon's capsule has been dissected in a blunt fashion through the aperture created in the previous figure. The cannula is about to be inserted and guided through the Sub-Tenon's space around the globe until it lies posterior to the equator, at the base of the orbital cone.View Large Image Figure ViewerDownload (PPT)Fig 4The Visitec™ curved Sub-Tenon's cannula.48View Large Image Figure ViewerDownload (PPT) To reduce the risk of trauma to soft tissues, flexible cannulae have been used.1Amin S Minihan M Lesnik-Oberstein S Carr C A new technique for delivering sub-Tenon's anaesthesia in ophthalmic surgery.Br J Ophthalmol. 2001; 86: 119-120Crossref Scopus (9) Google Scholar, 16Greenbaum S Parabulbar anesthesia.Am J Ophthalmol. 1992; 114: 776Abstract Full Text PDF PubMed Google Scholar, 24Kumar CM Dodds C A disposable plastic sub-Tenon cannula.Anaesthesia. 2001; 56: 399-400Crossref PubMed Scopus (18) Google Scholar These have two potential problems: the precise site of injection may be unpredictable, and with an anterior injection the volume administered could be limited by swelling of the conjunctiva (chemosis). For anterior segment procedures, where absolute immobility of the eye (akinesis) may not be required, these factors are unlikely to be significant. Normally, little resistance is found to injection. If resistance is felt, withdrawal and re-insertion of the needle using gentle pressure of the tip against the globe to ensure entry into the correct tissue plane will help. Slight proptosis of the eyeball is normal after a correctly sited injection. There may be slight leakage of solution from the tunnelled point of entry of the cannula into the conjunctiva. Should ballooning of the conjunctiva occur, the solution might be in the incorrect tissue plane. After removal of the cannula, pressure is applied by massaging the globe. To ensure flaccidity of the extra-ocular muscles, an additional facial nerve block was originally described,47Stevens J A new local anaesthesia technique for cataract extraction by one quadrant sub-Tenon's infiltration.Br J Ophthalmol. 1992; 76: 620-624Google Scholar but is rarely necessary in our experience. Common pitfalls relate to the positioning of the conjunctival incision and the confirmation of dissection down to the sclera. The incision must be made at a sufficient distance from the limbus to avoid the oblique insertion of Tenon's capsule into the sclera. A distance of 7–10 mm from the limbus is acceptable. Detecting the end-point of dissection comes with experience. The sclera has a different, more fibrous, and whiter appearance than either the capsule, or the continuation of the fascial layer of the extra-ocular muscles. Good illumination is very important for this difference to be apparent. While some ophthalmologists may prefer to use magnification, the procedure is normally performed satisfactorily with the naked eye. Extra care should be taken with myopic patients. They have longer and thinner globes, and there is an increased risk of scleral perforation. The technique is relatively contraindicated where there is a history of scleral disease with possible scarring and friability of the sclera. Previous retinal detachment surgery can be associated with scleral buckles and adhesions, which may hinder dissection or spread of anaesthetic solution, and increase the risk of globe perforation in the quadrant dissected. While the extensive experience of Guise and colleagues17Guise P Single quadrant Sub-Tenon's block. Evaluation of a new local anaesthetic technique for eye surgery.Anaesth Intensive Care. 1996; 24: 241-244PubMed Google Scholar and Friedberg and colleagues12Freidberg MA Spellman FA Pilkerton AR Perrault Jr, LE Stephens RF An alternative technique of local anaesthesia for vitreoretinal surgery.Arch Opthalmol. 1991; 109: 1615-1616Crossref PubMed Scopus (49) Google Scholar supports the safe use of Sub-Tenon's block in patients with scleral pathologies, a recent case report of scleral perforation should be viewed with concern.14Frieman BJ Friedberg MA Globe perforation associated with Sub Tenon's anaesthesia.Am J Ophthalmol. 2001; 131: 520-521Abstract Full Text Full Text PDF PubMed Scopus (102) Google Scholar This is discussed more fully below. Spread of the local anaesthetic solution into the retro-orbital space through the thin posterior section of Tenon's capsule may occur.50Stevens JD Restori M Ultrasound imaging of no needle one quadrant sub Tenon local anaesthetic for cataract surgery.Eur J Implant Ref Surg. 1993; 5: 35-38Abstract Full Text PDF Scopus (21) Google Scholar This accounts for the further development of the sensory block, supplementing the direct effect on sensory nerves within the sclera.37Ripart J Prat-Pradal D Vivien B Charavel P Eladjam J Medial canthus episcleral (sub-Tenon) anesthesia imaging.Clin Anat. 1998; 11: 390-395Crossref PubMed Scopus (28) Google Scholar 53Winder S Walker SB Atta HR Ultrasonic localization of anaesthetic fluid in Sub-Tenon's, peribulbar and retrobulbar techniques.J Cataract Refract Surg. 1999; 25: 56-59Abstract Full Text PDF PubMed Scopus (56) Google Scholar The development of akinesia is related to direct spread into the Tenon's sheaths surrounding the insertion of the extra-ocular muscles, and to effects within the retrobulbar cone on both these muscles and their motor nerves.38Ripart J Benbabaali M Muller L Letter.Ophthalmology. 2002; 109: 215-216Abstract Full Text Full Text PDF PubMed Scopus (4) Google Scholar Diffusion of solution into the periorbital tissues has been demonstrated, which explains the akinesia of the eyelids.36Rauz S Subramaniam S Sub-Tenon's anesthesia and orbicularis oculi function.Ophthalm Surg Lasers. 1997; 28: 727-730PubMed Google Scholar Many studies use an anaesthetic mixture compromising of lidocaine and bupivacaine in equal volumes to a total of 4 ml. Hyaluronidase (75–150 iu) is added to promote the rate and extent of diffusion to the peri- and retro-orbital tissues.9Dutton GN Sub-Tenon's infiltration of local anaesthetic with hyaluronidase.Br J Ophthalmol. 1994; 78: 238Crossref PubMed Scopus (7) Google Scholar 18Guise P Laurent S Sub-Tenon's block: the effect of hyaluronidase on speed of onset and block quality.Anaesth Intensive Care. 1999; 27: 179-181Crossref PubMed Google Scholar This practice has been used to reduce the need for a facial nerve block.3Bearn MA Shetty TT Hasan M Arunagiri G Sub-Tenon's anaesthesia.Eye. 1997; 11: 761Crossref PubMed Google Scholar 21Khoo BK Lim TH Yong V Sub-Tenon's versus retrobulbar anaesthesia for cataract surgery.Ophthalm Surg Lasers. 1996; 27: 773-777PubMed Google Scholar 41Rowley SA Hale JE Sub-Tenon's local anaesthesia: the effect of hyaluronidase.Br J Ophthalmol. 2000; 84: 435-436Crossref PubMed Scopus (34) Google Scholar In our hospitals, lidocaine 2% and bupivacaine 0.75% are mixed in equal volumes then a small volume (0.2–0.4 ml) of hyaluronidase is added. There is a relationship between the volume of local anaesthetic injected into the orbital cavity and the rise in intra-ocular pressure. When 3 ml of anaesthetic solution is slowly administered, a similar volume to a retrobulbar block, there is a similar rise in intra-ocular pressure. Peribulbar injection requires a larger volume to be administered, and the degree of intra-ocular hypertension is correspondingly greater.49Stevens JD Giubilei M Lanigan L Hykin P Sub-Tenon, retrobulbar and peribulbar local anaesthesia: the effect upon intraocular pressure.Eur J Implant Ref Surg. 1993; 5: 25-28Abstract Full Text PDF Scopus (24) Google Scholar On administration of anaesthetic solution to the Sub-Tenon's space, analgesia develops rapidly and effectively. Roman and colleagues40Roman SJ Chong Sit DA Bourea CM Auclin FX Ullern MM Sub-Tenon's anaesthesia; an efficient and safe technique.Br J Ophthalmol. 1997; 81: 673-676Crossref PubMed Scopus (108) Google Scholar reported that 99.1% of 109 patients scored the anaesthetic procedure as painless, and 97% reported the various operative procedures as devoid of pain. Stevens assessed analgesia by visual analogue pain scoring (scale 0–10) in 50 patients for cataract surgery.47Stevens J A new local anaesthesia technique for cataract extraction by one quadrant sub-Tenon's infiltration.Br J Ophthalmol. 1992; 76: 620-624Google Scholar Insertion of the block produced a mean and median score of 1 (range 0–5). Forty-one patients scored 1 or less. When pain associated with the anaesthetic injection is compared, Sub-Tenon's is comparable with topical,6Chittenden HB Meacock WR Govan JA Topical anaesthesia with oxybuprocaine versus Sub Tenon's infiltration with 2% lignocaine for small incision cataract surgery.Br J Ophthalmol. 1997; 81: 288-290Crossref PubMed Scopus (23) Google Scholar 26Manners TD Burton RL Randomised trial of topical versus Sub Tenon's local anaesthesia for small-incision cataract surgery.Eye. 1996; 10: 367-370Crossref PubMed Scopus (58) Google Scholar 32Nielsen PJ Allerod CW Evaluation of local anaesthetic techniques for small incision cataract surgery.J Cataract Refract Surg. 1998; 24: 1136-1144Abstract Full Text PDF PubMed Scopus (40) Google Scholar or subconjunctival52Winder S Noble DW Sim MJ Church WH Sub-Tenon's versus peribulbar anaesthesia for cataract surgery.Eye. 1998; 12: 486-488Crossref PubMed Scopus (5) Google Scholar anaesthesia and appears less painful than both peribulbar2Azmon B Alster Y Lazar M Geyer O Effectiveness of sub-Tenon's versus peribulbar anesthesia in extracapsular cataract surgery.J Cataract Refract Surg. 1999; 25: 1646-1650Abstract Full Text Full Text PDF PubMed Scopus (21) Google Scholar, 5Briggs MC Beck SA Esakowitz L Sub-Tenon's versus peribulbar anaesthesia for cataract surgery.Eye. 1997; 11: 636-643Google Scholar, 22Kollarits CR Jaweed S Kollarits FJ Comparison of pain, motility and preoperative sedation in cataract phacoemulsification patients receiving peribulbar or sub-Tenon's anesthesia.Ophthalm Surg Lasers. 1998; 29: 462-465PubMed Google Scholar, 32Nielsen PJ Allerod CW Evaluation of local anaesthetic techniques for small incision cataract surgery.J Cataract Refract Surg. 1998; 24: 1136-1144Abstract Full Text PDF PubMed Scopus (40) Google Scholar, 52Winder S Noble DW Sim MJ Church WH Sub-Tenon's versus peribulbar anaesthesia for cataract surgery.Eye. 1998; 12: 486-488Crossref PubMed Scopus (5) Google Scholar or retrobulbar20Kapran Z Uyar M Eltutar K Dincer N One quadrant Sub-Tenon's anaesthesia in anterior segment surgery.Eur J Ophthalmol. 1996; 6: 131-136PubMed Google Scholar, 21Khoo BK Lim TH Yong V Sub-Tenon's versus retrobulbar anaesthesia for cataract surgery.Ophthalm Surg Lasers. 1996; 27: 773-777PubMed Google Scholar, 52Winder S Noble DW Sim MJ Church WH Sub-Tenon's versus peribulbar anaesthesia for cataract surgery.Eye. 1998; 12: 486-488Crossref PubMed Scopus (5) Google Scholar blocks (Fig. 5). Sub-Tenon's provides a similar degree of intra-operative analgesia to retrobulbar,20Kapran Z Uyar M Eltutar K Dincer N One quadrant Sub-Tenon's anaesthesia in anterior segment surgery.Eur J Ophthalmol. 1996; 6: 131-136PubMed Google Scholar 21Khoo BK Lim TH Yong V Sub-Tenon's versus retrobulbar anaesthesia for cataract surgery.Ophthalm Surg Lasers. 1996; 27: 773-777PubMed Google Scholar 52Winder S Noble DW Sim MJ Church WH Sub-Tenon's versus peribulbar anaesthesia for cataract surgery.Eye. 1998; 12: 486-488Crossref PubMed Scopus (5) Google Scholar and peribulbar blocks,2Azmon B Alster Y Lazar M Geyer O Effectiveness of sub-Tenon's versus peribulbar anesthesia in extracapsular cataract surgery.J Cataract Refract Surg. 1999; 25: 1646-1650Abstract Full Text Full Text PDF PubMed Scopus (21) Google Scholar, 5Briggs MC Beck SA Esakowitz L Sub-Tenon's versus peribulbar anaesthesia for cataract surgery.Eye. 1997; 11: 636-643Google Scholar, 22Kollarits CR Jaweed S Kollarits FJ Comparison of pain, motility and preoperative sedation in cataract phacoemulsification patients receiving peribulbar or sub-Tenon's anesthesia.Ophthalm Surg Lasers. 1998; 29: 462-465PubMed Google Scholar, 32Nielsen PJ Allerod CW Evaluation of local anaesthetic techniques for small incision cataract surgery.J Cataract Refract Surg. 1998; 24: 1136-1144Abstract Full Text PDF PubMed Scopus (40) Google Scholar, 52Winder S Noble DW Sim MJ Church WH Sub-Tenon's versus peribulbar anaesthesia for cataract surgery.Eye. 1998; 12: 486-488Crossref PubMed Scopus (5) Google Scholar and more adequate analgesia than topical methods6Chittenden HB Meacock WR Govan JA Topical anaesthesia with oxybuprocaine versus Sub Tenon's infiltration with 2% lignocaine for small incision cataract surgery.Br J Ophthalmol. 1997; 81: 288-290Crossref PubMed Scopus (23) Google Scholar 26Manners TD Burton RL Randomised trial of topical versus Sub Tenon's local anaesthesia for small-incision cataract surgery.Eye. 1996; 10: 367-370Crossref PubMed Scopus (58) Google Scholar 32Nielsen PJ Allerod CW Evaluation of local anaesthetic techniques for small incision cataract surgery.J Cataract Refract Surg. 1998; 24: 1136-1144Abstract Full Text PDF PubMed Scopus (40) Google Scholar 52Winder S Noble DW Sim MJ Church WH Sub-Tenon's versus peribulbar anaesthesia for cataract surgery.Eye. 1998; 12: 486-488Crossref PubMed Scopus (5) Google Scholar (Fig. 5Briggs MC Beck SA Esakowitz L Sub-Tenon's versus peribulbar anaesthesia for cataract surgery.Eye. 1997; 11: 636-643Google Scholar) particularly if scleral cautery is used.5Briggs MC Beck SA Esakowitz L Sub-Tenon's versus peribulbar anaesthesia for cataract surgery.Eye. 1997; 11: 636-643Google Scholar 6Chittenden HB Meacock WR Govan JA Topical anaesthesia with oxybuprocaine versus Sub Tenon's infiltration with 2% lignocaine for small incision cataract surgery.Br J Ophthalmol. 1997; 81: 288-290Crossref PubMed Scopus (23) Google Scholar Postoperative analgesia provided by Sub-Tenon's block is generally reported to be excellent although there is a suggestion that anaesthetic volume and composition may be important.5Briggs MC Beck SA Esakowitz L Sub-Tenon's versus peribulbar anaesthesia for cataract surgery.Eye. 1997; 11: 636-643Google Scholar Kwok and colleagues23Kwok AKH Mylan R Lam DSC Fan D Sub-Tenon's anaesthesia in vitreoretinal surgery, a needleless technique.Retina. 1999; 19: 291-296Crossref PubMed Google Scholar have demonstrated minimal use of postoperative analgesia in the first 24 h after Sub-Tenon's block. In this uncontrolled study, 90% of patients received either no analgesia or acetaminophen, 4% received a single dose of codeine, and 6% received two or more doses of codeine. Akinesia is less consistent than the production of adequate analgesia. Maximal akinesia will develop over 5–15 min. The site of injection, its timing relative to surgery, and the composition and volume of solution administered are each important in producing immobility of the globe. With standard volumes of 2–3 ml of solution and an inferonasal approach, a degree of lateral rectus function may prevail. The muscles most affected are normally adjacent to the site of injection. This can be an advantage for strabismus surgery.15Fujishama H Yagi Y Yang HY Toda I Shimaka J Tsubota K Direct Sub Tenon's ocular anaesthesia for strabismus surgery.Ophthalmologica. 1995; 209: 208-211Crossref PubMed Scopus (9) Google Scholar 39Ritch R Leibman JM Sub Tenon's anaesthesia for strabismus surgery.Ophthalmic Surg. 1992; 23: 502-504PubMed Google Scholar 46Steele MA Lavrich J Nelson L Koller H Sub-Tenon's infusion of local anaesthetic for strabismus surgery.Ophthalmic Surg. 1992; 23: 40-43PubMed Google Scholar Volume appears critical, with Li and colleagues25Li HK Abouleish A Grady J et al.Sub-Tenon's injection for local anesthesia in posterior segment surgery.Ophthalmology. 2000; 107: 41-46Abstract Full Text Full Text PDF PubMed Scopus (52) Google Scholar reporting reliable akinesia with 11 ml of solution injected for posterior segment surgery. Inadequate blocks can be successfully managed by supplementing the anaesthetic with a 1–1.5 ml extra of solution via the tract already prepared through the conjunctiva and Sub-Tenon's space. Supplemental injections are no more commonly needed than with peribulbar blocks,5Briggs MC Beck SA Esakowitz L Sub-Tenon's versus peribulbar anaesthesia for cataract surgery.Eye. 1997; 11: 636-643Google Scholar and with a Sub-Tenon's block the ability to place solution through the pathway already prepared has the advantage of producing less pain and fewer complications. A polyethylene catheter fixed into the Sub-Tenon's space, permits extension of anaesthesia perioperatively for a theoretically unlimited period.4Behndig A Sub-Tenon's anaesthesia with a retained catheter in ocular surgery of longer duration.J Cataract Refract Surg. 1998; 24: 1307-1309Abstract Full Text PDF PubMed Scopus (14) Google Scholar Behndig also suggests that infusion of anaesthetic solution through such a catheter, rather than bolus administration by injection, could minimize chemosis and provide better akinesia. An almost painless block, along with adequate analgesia for the surgical procedure, reduces patient anxiety and sedation requirements; this is particularly advantageous for day case patients. Improved patient cooperation minimizes both residual eye movement and blepharospasm during the surgical procedure. The quality of the data comparing different regional anaesthesia techniques for ophthalmic surgery is limited by a scarcity of randomized controlled trials. Use of Sub-Tenon's block is currently based on cohort studies and this limits its undisputed recommendation.13Friedman DS Bass EB Lubomski LH et al.Synthesis of the literature on the effectiveness of regional anaesthesia for cataract surgery.Ophthalmology. 2001; 108: 519-529Abstract Full Text Full Text PDF PubMed Scopus (64) Google Scholar 42The Royal College of Anaesthesists and the Royal College of Ophthalmologists. Report on Local Anaesthesia for Intraocular Surgery. London: 2001Google Scholar 44Scottish Intercollegiate Guidelines Network. Day Case Cataract Surgery, A National Clinical Guideline. Edinburgh: 2001Google Scholar Guidelines concerning the technique are therefore based on Level B+ evidence with inadequate grounds for Grade 1 recommendations. A large, correctly conducted randomized trial would add hugely to the validity of the technique. Sub-Tenon's block is perceived as having an acceptable safety profile because a sharp needle is not placed within the orbital cavity. The design of the catheter and the nature of the blunt dissection suggest that intradural puncture is unlikely if not impossible. As a consequence, intradural, subarachnoid, and central nervous system injection is improbable. Intravascular or intraneural injection is also unlikely and the risk of scleral perforation is reduced. Swelling of the conjunctiva has an incidence of 39.4% with Sub-Tenon's blocks.40Roman SJ Chong Sit DA Bourea CM Auclin FX Ullern MM Sub-Tenon's anaesthesia; an efficient and safe technique.Br J Ophthalmol. 1997; 81: 673-676Crossref PubMed Scopus (108) Google Scholar Some chemosis is attributable to anterior leak of injectate but its extent can be much greater if the solution is administered incorrectly into either the anterior compartment of the Sub-Tenon's space, or the subconjunctival space. It does not usually impede the surgical field. Chemosis might be reduced by fashioning a radial conjunctival incision.38Ripart J Benbabaali M Muller L Letter.Ophthalmology. 2002; 109: 215-216Abstract Full Text Full Text PDF PubMed Scopus (4) Google Scholar Subconjunctival haemorrhage occurs in 32–56% of cases.40Roman SJ Chong Sit DA Bourea CM Auclin FX Ullern MM Sub-Tenon's anaesthesia; an efficient and safe technique.Br J Ophthalmol. 1997; 81: 673-676Crossref PubMed Scopus (108) Google Scholar 47Stevens J A new local anaesthesia technique for cataract extraction by one quadrant sub-Tenon's infiltration.Br J Ophthalmol. 1992; 76: 620-624Google Scholar Bleeding is usually localized and infrequently associated with significant consequences. To reduce haemorrhage, cauterization of the conjunctival incision has been advocated.51Stevens JD Parabulbar anesthesia.Am J Ophthalmol. 1992; 114: 776Abstract Full Text PDF PubMed Scopus (69) Google Scholar Using a standard i.v. cannula (22 G Venflon) to puncture the anaesthetized and tented conjunctiva may reduce the occurrence of chemosis and subconjunctival haemorrhage.1Amin S Minihan M Lesnik-Oberstein S Carr C A new technique for delivering sub-Tenon's anaesthesia in ophthalmic surgery.Br J Ophthalmol. 2001; 86: 119-120Crossref Scopus (9) Google Scholar While the tip of the needle is kept in position and visible under the conjunctiva, the cannula is advanced posteriorly in the Sub-Tenon's space, before administration of anaesthetic solution. Use of a sharp needle to access the Sub-Tenon's space is associated with the risk of globe perforation. This complication is reduced by keeping the needle tip in constant view. A vortex vein in the sclera may be ruptured during the blunt dissection. This is less likely in the inferonasal quadrant. Should retrobulbar bleeding occur, it might decompress anteriorly through the path dissected by the catheter. If patients are receiving anticoagulants, which cannot be reversed safely, and akinesia is desirable, Sub-Tenon's anaesthesia is often considered to be the method of choice.22Kollarits CR Jaweed S Kollarits FJ Comparison of pain, motility and preoperative sedation in cataract phacoemulsification patients receiving peribulbar or sub-Tenon's anesthesia.Ophthalm Surg Lasers. 1998; 29: 462-465PubMed Google Scholar 34O'Reilly J Logan P Sub-Tenon's anaesthesia.Br J Ophthalmol. 1998; 82: 589-590Crossref PubMed Scopus (1) Google Scholar The International Normalized Ratio should be appropriately controlled and conjunctival cautery is recommended. The serious complications associated with sharp needle techniques are rare (Table 1). User-dependent factors, such as inexperience of the operator and the frequency of performing particular blocks, contribute to the incidence of complications. Such extensive practical and published experience has yet to be accrued for Sub-Tenon's blocks, and it is conceivable that significant but rare complications may yet be uncovered.Table 1Incidence of complications of sharp needle blocks (%)Retrobulbar blockPeribulbar blockRetrobulbar haemorrhage1.730Morgan CM Schatz H Vine AK et al.Ocular complications associated with retrobulbar injections.Ophthalmology. 1998; 95: 660-665Abstract Full Text PDF Scopus (245) Google Scholar 43Rubin AP Complications of local anaesthetics for ophthalmic surgery.Br J Anaesth. 1995; 75: 93Crossref PubMed Scopus (128) Google Scholar0.008Davis DB Mandel MR Efficacy and complication rate of 16624 consecutive peribulbar blocks, a prospective multi centre trial.J Cataract Refract Surg. 1994; 20: 327-337Abstract Full Text PDF PubMed Scopus (213) Google Scholar 11Eke T Thompson JR The National Survey of Local Anaesthesia for Ocular Surgery: (ii) safety profiles of local anaesthetic techniques.Eye. 1999; 13: 196-204Crossref PubMed Scopus (93) Google ScholarGlobe perforation0.7519Hamilton RC Gimbel HV Strunin L Regional anaesthesia for 12,000 cataract extraction and intraocular lens implantation procedures.Can J Anaesth. 1988; 35: 615-623Crossref PubMed Scopus (195) Google Scholar0.000819Hamilton RC Gimbel HV Strunin L Regional anaesthesia for 12,000 cataract extraction and intraocular lens implantation procedures.Can J Anaesth. 1988; 35: 615-623Crossref PubMed Scopus (195) Google ScholarCentral nervous involvement0.331Nicoll JMV Acharya PA Ahlen K Bagenuid S Edge KR Central nervous system complications after 6000 retro bulbar blocks.Anesth Analg. 1987; 66: 1298-1302Crossref PubMed Scopus (170) Google Scholar Open table in a new tab Concern has been expressed that the dissection of the conjunctiva, muscular fascia, and Tenon's capsule may pose a risk of globe perforation.28Mawer RJ Local anaesthesia for routine ocular surgery.Br J Anaesth. 1999; 82: 153-154Crossref PubMed Google Scholar It has been suggested that anaesthetists may not have practiced the fine motor skills or have acquaintance with the equipment necessary to undertake this procedure safely, and that it may be better performed by ophthalmologists.28Mawer RJ Local anaesthesia for routine ocular surgery.Br J Anaesth. 1999; 82: 153-154Crossref PubMed Google Scholar It has been shown that this is not the case.7Dark A Local anaesthesia for routine ocular surgery.Br J Anaesth. 1999; 82: 153-154Crossref PubMed Scopus (21) Google Scholar 35Price SR Miller CD Local anaesthesia for routine ocular surgery.Br J Anaesth. 1999; 82: 156Crossref Scopus (3) Google Scholar We have identified four case reports of complications attributed to the administration of a Sub-Tenon's block. Frieman and Friedberg14Frieman BJ Friedberg MA Globe perforation associated with Sub Tenon's anaesthesia.Am J Ophthalmol. 2001; 131: 520-521Abstract Full Text Full Text PDF PubMed Scopus (102) Google Scholar reported an episode of globe perforation associated with a Sub-Tenon's procedure. A patient with scleral scarring as a result of previous retinal detachment surgery presented with symptoms attributable to recurrence. Initially, the procedure was uneventful and the sclera was accessed by blunt dissection with Westcott scissors. These were then passed posteriorly and resistance was met because of scleral adhesions, which were cut with the scissors. The surgeon continued to advance the scissors posteriorly and encountered a sudden loss of resistance due to scleral perforation. While no long-term visual deficit was reported, prolonged management, including laser treatment to the associated retinal tear, was required. Once the sclera has been exposed, we believe it is unnecessary and unwise to use the scissors to dissect posteriorly in Sub-Tenon's space, particularly when scleral scarring is present. The use of Sub-Tenon's block in patients with previous retinal detachment surgery is not fully established and randomized trials in these patients would be of particular value. There has been one case report of significant retrobulbar haemorrhage associated with Sub-Tenon's block.33Olitsky SE Juneja RG Orbital haemorrhage after the administration of sub-Tenon's infusion in anaesthesia.Ophthalmic Surg Lasers. 1997; 28: 145-146PubMed Google Scholar Acute pain was the presenting symptom which occurred immediately on injection of 3 ml of local anaesthetic. There was no bleeding at the site of incision and lateral canthotomy and cantholysis were performed successfully to reduce intra-orbital pressure. Mein and Woodcock29Mein CE Woodcock MG Local anesthesia for vitreoretinal surgery.Retina. 1990; 10: 47-49Crossref PubMed Scopus (71) Google Scholar reported one patient in their series of 58 who developed raised intra-orbital and intra-ocular pressures on injection of 1.5 ml of perilimbal anaesthetic solution. Lateral canthotomy and anterior paracentesis were performed, but there was no evidence of intra-ocular haemorrhage, and the scleral buckle procedure was completed successfully. A self-limiting strabismus associated with clinical palsy of the ipsilateral superior oblique muscle occurred in a 68-yr-old man who underwent phacoemulsification and intra-ocular lens implantation.45Spierer A Schwalb E Superior oblique muscle paresis after sub-Tenon's anesthesia for cataract surgery.J Cataract Refract Surg. 1999; 25: 144-145Abstract Full Text PDF PubMed Scopus (37) Google Scholar The Sub-Tenon's injection was administered through the superior temporal quadrant and direct trauma to the muscle–tendon complex or the trochlear nerve by the needle were the most likely causes. His symptoms resolved within 4 weeks. The National Survey of Local Anaesthesia for Ocular Surgery by the Clinical Sub-Committee of the Royal College of Ophthalmologists10Eke T Thompson JR The National Survey of Local Anaesthesia for Ocular Surgery: (i) survey methodology and current practice.Eye. 1999; 13: 189-195Crossref PubMed Scopus (61) Google Scholar 11Eke T Thompson JR The National Survey of Local Anaesthesia for Ocular Surgery: (ii) safety profiles of local anaesthetic techniques.Eye. 1999; 13: 196-204Crossref PubMed Scopus (93) Google Scholar provides substantial evidence of the relative safety of the Sub-Tenon's block. In an estimated population of 4384 patients receiving Sub-Tenon's block, Eke and colleagues11Eke T Thompson JR The National Survey of Local Anaesthesia for Ocular Surgery: (ii) safety profiles of local anaesthetic techniques.Eye. 1999; 13: 196-204Crossref PubMed Scopus (93) Google Scholar report one major expulsive haemorrhage. Because of the confidential nature of reporting to this audit, no further information is available. No life-threatening complications of the block itself were reported. Severe systemic effects such as hypertension, claustrophobia, and confusion were reported, Sub-Tenon's producing a similar incidence to other blocks. There was no evidence of inadequate block of the oculocardiac reflex. There is one further suggestion of a significant complication attributable to Sub-Tenon's block.28Mawer RJ Local anaesthesia for routine ocular surgery.Br J Anaesth. 1999; 82: 153-154Crossref PubMed Google Scholar A verbal report of globe perforation was made at a meeting of the European Society of Anaesthetists (ESA) but, unfortunately, does not seem to have been reported further. The perceived safety of Sub-Tenon's block has led to its endorsement by The Royal Colleges of Ophthalmologists and Anaesthetists as a procedure where an anaesthetist need not be present,42The Royal College of Anaesthesists and the Royal College of Ophthalmologists. Report on Local Anaesthesia for Intraocular Surgery. London: 2001Google Scholar when appropriate patient selection has occurred. An anaesthetist must be present if i.v. sedation, performance of a sharp needle block, or general anaesthesia is required. The anaesthetist therefore continues to have an important role in the multidisciplinary team, and the appropriate administration of local anaesthetic is an important part of this role. Anaesthetists frequently perform Sub-Tenon's block for a variety of ophthalmological procedures. It is a relatively pain-free block to perform and is effective in producing sensory block sufficient for surgery without the use of sedation. Total akinesia may not be obtained. The patient should be warned of chemosis and conjunctival haemorrhage occurring although these do not normally impede the procedure. The technique of blunt dissection and the type of cannula used to perform the block avoid the potentially serious side effects of retro- or peribulbar blocks. The relatively few complications reported in the 11 yr since the technique was first described suggest that it is safe.