anaesthesia for ophthalmic surgery

Anaesthesia for Ophthalmic

SurgeryAnatomy, Physiology and Practice

T Mphanza FRCA, FFICM

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Special Considerations

•Proximity to airway

•Age

•Anatomy

•Physiology

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Anatomy

•Orbit - irregular pyramid

•Base at the front

•Axis - points postero-medially

•Optic foramen forms the apex

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Anatomy

•Orbit - irregular pyramid

•40 - 50 mm deep

•Volume - 30 mls

•globe - 7 mls

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Anatomy

•Globe

•Anteriorly

•Closer to the roof

•Nearer to the lateral wall

•Axial length - 25 mm

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Anatomy

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Anatomy

•Extraocular muscles

•4 rectus muscles

•2 oblique muscles

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LR6(SO4)3

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Sensory Innervation

•Trigeminal

•V1

•Supratrochlear, Supraorbital, Long ciliary, Nasociliary, Infratrochlear, Lacrimal

•V2

• Infraorbital, Zygomatic

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Autonomic Innervation

•Sympathetic

•Superior cervical ganglion

•Mydriasis

•Parasympathetic

•Fibres from III

•Miosis

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Blood Vessels

•Arterial

•Ophthalmic artery

•Venous

•Ophthalmic veins

•Superior

•Inferior

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Anatomy and Physiology

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Physiology

•Aqueous humour

•Produced by ciliary body

•Carbonic anhydrase

•Drainage

•Venous channels

•SVC

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Physiology

•Intraocular pressure (IOP)

•Range 10 - 20 mmHg

•Increases with age

•Direct correlation with axial length

•Main determinant is aqueous humour

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Physiology

•Factors affecting IOP

•Arterial BP

•Auto-regulation

•Venous BP

•Valsalva, coughing, straining

•Partial pressures - CO2 , O2

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Events that Decrease IOP

• IV anaesthetics

• Volatile anaesthetics

•Mannitol

• Timolol

• Betaxolol

•NDMR

•Hyperventilation

•Hypothermia

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Events that Increase IOP

• Succinylcholine

• Direct laryngoscopy

• Hypoventilation

• Arterial hypoxaemia

• Increased venous pressure

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Oculomedullary Reflexes

•Oculocardiac

•Trigemino-vagal:

•Bradycardia, ectopics, sinus arrest

•Oculorespiratory

•Oculoemetic

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Anaesthetic Ramifications of

Ophthalmic Drugs

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•Ecothiopate

•Anticholinesterase miotic

•Cyclopentolate

•Mydriatic

•Phenylephrine

•Mydriatic

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•Acetazolamide

•Carbonic anhydrase inhibitor

•Timolol

•Beta blocker

•Sulphur hexafluoride

•Inert gas

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Requirements for Ophthalmic

Surgery

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•Akinesia

•Profound analgesia

•Minimal bleeding

•Avoidance of oculocardiac reflex

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•Control of IOP

•Awareness of drug interactions

•Emergence without coughing, straining or vomiting

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•General

•Local

•Topical

•Regional

Anaesthesia Techniques

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Factors that Influence Choice of

Anaesthesia•Nature and duration of procedure

•Coagulation status

•Patient’s choice

•Ability to communicate and cooperate

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General Anaesthesia

•Volatile vs TIVA

•ETT vs LMA

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General Anaesthesia

•Special consideration

•Head up tilt

•Avoid hypercapnoea

•Avoid N2O in vitreoretinal surgery

•Smooth emergence

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Topical Anaesthesia

•Instillation of LA drops

•Advantages

•Minimal complications

•Limitations

•Lack of akinesia

•Only suitable for uncomplicated cases

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Regional Anaesthesia

•Sub-Tenon

•Peribulbar (Extra-conal)

•Retrobulbar (Intra-conal)

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Sub-Tenon’s Block

•Tenon’s capsule

•Dense fascial sheath surrounding the globe and extraocular muscles from the limbus to the optic nerve

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Sub-Tenon’s Block

•Sensory block

•Short-ciliary nerves pass through Tenon’s capsule to globe

•Akinesia

•Direct blockade of ant. nerve fibres as they enter extra-ocular muscles

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Retro & Peribulbar Blocks

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Retrobulbar Block

Complications of Regional Blocks

•Stimulation of oculocardiac reflex

•Haemorrhage

•Superficial

•Retrobulbar

•Retinal perfusion compromise

•Loss of vision

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Complications of Regional Blocks

•Globe penetration

•Intra-arterial injection

•Trauma to optic nerve

•Optic sheath injection

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Complications of Regional Blocks

•Extraocular muscle injury

•Central retinal artery occlusion

•Accidental brainstem anaesthesia

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Anaesthetic Management of

Specific Situations

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•Open Eye, Full Stomach

•Aspiration vs Blindness

•Strabismus surgery

•OCR

•MH

•PONV

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•Intraocular Surgery

•Glaucoma, vitrectomy, cataracts

•IOP control

•Complete akinesia

•Continuation of miotics

•Provide an antiemetic effect

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•Retinal Detachment Surgery

•SF6 injection for tamponade

•IV acetazolamide or mannitol

•Akinesia is not critical

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General Vs. Regional

Anaesthesia

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•Regional Techniques

•Day stay surgery

•Better akinesia

•Less PONV

•Less effect on IOP

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•Cochrane Reviews

•Peribulbar Vs. Retrobulbar

•Sub-Tenon’s Vs. Topical

Evidence Based Medicine

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Evidence Based Medicine - CRTs

•General Vs Regional for Cataract Surgery

•Cognitive Function

•Perioperative MI

•Plasma catecholamine response

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Summary

•Anatomy and Physiology

•Drug interactions

•Special Requirements

•Management of Specific Situations

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