anterior sub- tenon’s anaesthesia (asta) for cataract surgery
DESCRIPTION
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) - PowerPoint PPT PresentationTRANSCRIPT
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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
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Ocular regional blocks
1 = Anterior Sub-Tenon’s Anaesthesia (ASTA)2 = Steven’s sub-Tenons Technique.3 = Retrobulbar4 = Peribulbar
Introduction
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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
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Posterior instrumentation unnecessary for Sub-Tenon’s
(ST) BlockMcNeela et al (2004) N=59
Successful ST blocks
6mm ultra-short cannula
Kumar et al (2004) N=151 compared 3 sub-Tenon’s cannulae lengths:
25mm
18mm
12mm
Sub-Tenon’s space accessed
anteriorly!!!
Short cannula achieved
similar anaesthesia and akinesia
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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
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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- orbicularis occuli & levator palpabrae
Subconjunctival space
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Short needle25G 16mm
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MethodsCase 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
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PreparationRoutine pre op care
Supine, eye pillow
½ strength iodine
Head stabilised by nurse
Amethocaine 1% x1 drop
Optional light sedation (midazolam)
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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
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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
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At the end of ASTA injection, complete lid drop evident
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Excess chemosis Mostly resolves with
gentle massage
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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
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PainRated as it occurred during operation
Numeric Verbal Rating Scale0 = no pain
1-3 = mild
4-6 = moderate
7-9 = severe
10 = worst
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ResultsMean age 74, equal gender.
All successfully completed surgery without supplemental anaesthesia
No major anaesthetic complications
No surgical complications due to ASTA
Main complication = Sub conjunctival haemorrhage in 5% pts.
48% on warfarin or antiplatelet Rx
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Akinesia 10min post ASTA
AMS 0
AMS 1
AMS 2
AMS 3
AMS 4
AMS 5
AMS 7
0
2
4
6
8
10
12
14
16
18
LignocaineLignocaine/Bupivicaine
•95% - AMS ≤4/15
•100% - lid paralysis : levator palpabrae and orbicularis occuli
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Pain during operation
Pain
0
Pain
20
5
10
15
20
25
30
35
Lignocaine
Lignocaine/bupivacaine
•58/60 pain free
•2 patients- Transient mild pain 1-2/10
•End of procedure
•No supplementation required
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DiscussionASTA comparable to other sub-Tenons blocks
Akinesia - 95% AMS ≤ 4Learning curve
McNeela et al (2004)98% AMS<4
Kumar 3 cannulae (2004)
92-100% AMS<4Koh et al, Concord Hosp, 2005, Steven’s sub-Tenon’s block
Akinesia - 88% AMS≤4Anaesthesia – 7% needed topical amethocaine supp.
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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
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Implications for Safety
ASTA AnteriorVisually guidedShort needleLess invasive – no dissection
Improve Aesthetics & healing
Reduce infection
Avoids vulnerable anatomy
Optic and other nerves CSF Blood vesselsRetina / macula
Should be safer
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Potential Advantages
Globe perforation Anterior
Peripheral retina
Visible
Haemorrhage - anteriorSeen
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
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ConclusionSmall study
ASTA SimpleEffective SafePhaecoemulsification cataract surgery
Further research to elucidate its wider application
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“Simplicity is achieving maximal
effect with minimal means”
Dr Kawana
Zen Garden Master.Contact: [email protected]