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Anterior Sub- Tenon’s Anaesthesia (ASTA) for Cataract Surgery

Dr S Wu. FACRRM, FRACGP Dr KC Tang. FRANZCO, Clinical lecturer School of Rural Health, University of Sydney. Anterior Sub- Tenon’s Anaesthesia (ASTA) for Cataract Surgery. Introduction. Ocular regional blocks 1 = Anterior Sub- Tenon’s Anaesthesia (ASTA)

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Anterior Sub- Tenon’s Anaesthesia (ASTA) for Cataract Surgery

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  1. Dr S Wu. FACRRM, FRACGP Dr KC Tang. FRANZCO, Clinical lecturer School of Rural Health, University of Sydney Anterior Sub-Tenon’s Anaesthesia (ASTA)for Cataract Surgery

  2. Introduction • Ocular regional blocks • 1 = Anterior Sub-Tenon’s Anaesthesia (ASTA) • 2 = Steven’s sub-Tenons Technique. • 3 = Retrobulbar • 4 = Peribulbar

  3. Tenon’s Capsule • Like a glove for the whole eye • Starts at the limbus and lid muscles • Initially fused to conjunctiva • Loose matrix • Follows sclera around the globe • Sleeves around rectus and oblique muscles • Attaches to optic nerve sheaths

  4. Posterior instrumentation unnecessary for Sub-Tenon’s (ST) Block • McNeela et al (2004) N=59 • Successful ST blocks • 6mmultra-short cannula • Kumar et al (2004) N=151 compared 3 sub-Tenon’scannulae lengths: • 25mm • 18mm • 12mm Sub-Tenon’s space accessed anteriorly!!! Short cannula achieved similaranaesthesia and akinesia

  5. Needle sub-Tenon’s injection • Ripart et al (1996) N=151 • Unlike cannula ST techniques • 25G needle without dissection • Medial canthus sub-Tenon’s injection • Mean depth 15-20mm • 92% - total akinesia Dissection not necessary for sub-Tenon’s block

  6. Ripart (1998) • CT images of fresh cadavers • 9mls contrast given by MC sub-Tenon’s injection spread to: • Episcleral space • Optic nerve sheath • Rectus muscle sheath • Lid muscles- orbicularisocculi & levatorpalpabrae • Subconjunctival space

  7. Short needle 25G 16mm

  8. Methods • Case series • 60 adult elective cataract patients • All received ASTA by author • Using 2 common local anaesthetics • 30 – lignocaine 2% +hyalase 30 iu/ml • 30 – bupivacaine 0.5% + lignocaine 2% + hyalase 30 iu/ml • Approved by regional HERC • ANZCTR

  9. Preparation • Routine pre op care • Supine, eye pillow • ½ strength iodine • Head stabilised by nurse • Amethocaine 1% x1 drop • Optional light sedation (midazolam)

  10. ASTA Technique Outline • Lift upper lid, look down • Pierce conjunctiva and Tenon’s capsule in upper outer quadrant • 5-7mm from limbus • Advance needle about 5mm supero-medially • Following curve of sclera • Visually check needle position by forming a small bleb of L.A. • Inject L.A. VERY SLOWLY, guided by patient comfort

  11. Vol. 6-10mls, diff in each patient, guided by 3 signs of filling up the ST space as described by Ripart : • Mod. proptosis + lid fullness + mod. chemosis

  12. At the end of ASTA injection, complete lid drop evident

  13. Excess chemosis Mostly resolves with gentle massage

  14. Akinesia • Scored 10min post ASTA, using Aggregated Motility Score (AMS) • Validated scale used by Kumar, MaNeela, Brahma etc • Lid + Globe mvt in 4 directions: up, down, medial, lateral • 0 = no mvt • 1 = twitch <1mm • 2 = partial mvt • 3 = full mvt • Total akinesia = 0, adequate akinesia < =4, max mvt = 15

  15. Pain • Rated as it occurred during operation • Numeric Verbal Rating Scale • 0 = no pain • 1-3 = mild • 4-6 = moderate • 7-9 = severe • 10 = worst

  16. Results • Mean age 74, equal gender. • All successfully completed surgery without supplemental anaesthesia • No major anaesthetic complications • No surgical complications due to ASTA • Main complication = Sub conjunctivalhaemorrhage in 5% pts. • 48% on warfarin or antiplatelet Rx

  17. Akinesia 10min post ASTA • 95% - AMS ≤4/15 • 100% - lid paralysis : levatorpalpabrae and orbicularisocculi

  18. Pain during operation • 58/60 pain free • 2 patients- Transient mild pain 1-2/10 • End of procedure • No supplementation required

  19. Discussion • ASTA comparable to other sub-Tenons blocks • Akinesia - 95% AMS ≤ 4 • Learning curve • McNeela et al (2004) • 98% AMS<4 • Kumar 3 cannulae (2004) • 92-100% AMS<4 • Koh et al, Concord Hosp, 2005, Steven’s sub-Tenon’s block • Akinesia - 88% AMS≤4 • Anaesthesia – 7% needed topical amethocaine supp.

  20. ASTA - Comprehensive all-in-one block • Relatively large volume • Av = 9mls (similar to Ripart) • One injection delivers LA to: • Lid muscles, no need VII inj. • Sub-conjunctival space • Muscle sheaths • Episcleral space • Retrobulbar space

  21. Implications for Safety • ASTA • Anterior • Visually guided • Short needle • Less invasive – no dissection • Improve Aesthetics & healing • Reduce infection • Avoids vulnerable anatomy • Optic and other nerves • CSF • Blood vessels • Retina / macula • Should be safer

  22. Potential Advantages • Globe perforation • Anterior • Peripheral retina • Visible • Haemorrhage - anterior • Seen • Compressed • No need to stop Warfarin or antiplatelets • ?Safer in axial length ≥ 26mm • Equipment is cheap & readily available – beneficial for developing nations • Easily topped up anytime • ?Role in patients with difficult access • Previous surgery • Adhesions • Scleral buckles

  23. Conclusion • Small study • ASTA • Simple • Effective • Safe • Phaecoemulsification cataract surgery • Further research to elucidate its wider application

  24. “Simplicity is achieving maximal effect with minimal means” Dr Kawana Zen Garden Master. Contact: drwu@bigpond.com

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