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

Ocular regional blocks

1 = Anterior Sub-Tenon’s Anaesthesia (ASTA)2 = Steven’s sub-Tenons Technique.3 = Retrobulbar4 = Peribulbar

Introduction

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

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

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

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

Short needle25G 16mm

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

PreparationRoutine pre op care

Supine, eye pillow

½ strength iodine

Head stabilised by nurse

Amethocaine 1% x1 drop

Optional light sedation (midazolam)

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

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

At the end of ASTA injection, complete lid drop evident

Excess chemosis Mostly resolves with

gentle massage

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

PainRated as it occurred during operation

Numeric Verbal Rating Scale0 = no pain

1-3 = mild

4-6 = moderate

7-9 = severe

10 = worst

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

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

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

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.

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

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

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

ConclusionSmall study

ASTA SimpleEffective SafePhaecoemulsification cataract surgery

Further research to elucidate its wider application

“Simplicity is achieving maximal

effect with minimal means”

Dr Kawana

Zen Garden Master.Contact: drwu@bigpond.com