ISSN 2398-2942      

Anesthesia: in ophthalmic surgery

icanis

Introduction

Alternatives

Topical analgesia

  • Action: desensitizes conjunctiva and cornea only.
  • Uses:
    • Examination of painful eye.
    • To collect samples.
    • Remove foreign bodies.
    • Cannulate and flush nasolacrimal duct.
      Not suitable if sharp instruments are to be used because animal may move suddenly.
  • Agents:
    • Short acting (<30 minutes): proxymetacaine (0.5%) Proparacaine , lidocaine Lidocaine , oxybuprocaine (0.4%), proparacaine (0.5%) Proparacaine.
    • Amethocaine (0.5-1%) has a similar duration of action as proxymetacaine but produces more discomfort on initial application.

Infiltration of local anesthetic

  • Uses: minor/superficial extraorbital surgery if sharp instruments will not be used next to the eye itself
    EitherFor very debilitated or deeply sedated patients
    OrIn combination with neuroleptanalgesia.
  • Agents: lidocaine (1-2%), direct injection of small volumes (0.1-0.3 ml) at site of intended incision.

Supra-orbitalnerve block

  • Action: blocks sensation to upper eyelid.
  • Use: alternative to infiltration at the site for minor sugical procedures in the upper eyelid.
  • Agent: lidocaine Lidocaine (1-2%), bupivacaine Bupivacaine 0.5%: inject an appropriate small volume (<0.5 ml) close to the nerve.
  • Sedation/precautions as for infiltration above.

Retrobulbar Local anesthesia: retrobulbar

  • Action:
    • Decreases intra-ocular pressure - beneficial.
    • Causes midriasis - requirement for intra-ocular surgery.
  • Use: alternative to neuro-muscular blocking agents (muscle relaxants) Anesthesia: non-depolarizing neuromuscular blockade if eye surgery is difficult due to retraction into orbit.
  • Agent: general anesthesia is required as an injection of an appropriate small volume of lidocaine Lidocaine (1-2%) is made via the conjunctival sac into the retrobulbar space.
  • Small bore needle required, eg 25 g to minimize trauma.
    Do not inject intravascularly.

Auriculo-palpebral Local anesthesia: auriculopalpebral

  • Action: blocks a branch of the facial motor nerve ’ prevents blepharospasm.
  • Uses:
    • Prevents tightly closed lids putting pressure on the eye in the post-operative period.
    • Assists in removal of foreign bodies from conjunctival sac.
      Not an alternative to anesthesia as motor blockade only without any analgesia.

Preparation

Risk assessment

  • Many patients for ophthalmic surgery are old +/- have other conditions, eg diabetes mellitus (cataract surgery).
  • Full pre-anesthetic evaluation is necessary.

Pre-operative considerations

  • Pupil dilatationmay be required - give pre-op atropine Atropine 1% or sodium fluroiprofen 0.03%.
  • Eye positionmay be crucial.
  • Anesthesia ’ enophthalmus, globe retraction, nictitating membrane protrusion.
  • Stay sutures in sclera to rectus muscles or the use of neuromuscular blockade may help to maintain good eye position.

Specific pre-operative preparation

Consider possible interactions between drugs being used to treat the ophthalmic condition and drugs which may be used in pre-medication and anesthesia.
  • Pros:
    • Epinephrine: decreases production of aqueous humor in glaucoma; controls hemorrhage in intra-ocular surgery.
    • Phenylephrine Phenylephrine : decreases production of aqueous humor in glaucoma.
  • Cons:
    • Increase likelihood of hypertension and cardiac dysrhythmias.

Anticholinesterases

  • Physostigmine, ecothiopate.
  • Constrict pupil and increase drainage of aqueous humor.
    Prolong the action of drugs metabolized by cholinesterase, eg procaine , suxamethonium Suxamethonium.

Diuretics

  • Dichlorophenamide, acetazolamide Acetazolamide.
  • Decrease the production of aqueous humor; diuresis may ’ hypokalemia and hypovolemia with prolonged use.
    Monitor potassium status and fluid balance; correct imbalance before anesthetic induction.

Corticosteroids

  • If already being administered avoid sudden withdrawal - risk of decreased animal ability to cope with stress response triggered by anesthesia and surgery. May require perioperative supplementation in addition.
  • Monitor blood pressure. If non-invasive methods are not available place central venous catheter +/- arterial catheter at this stage.

Requirements

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Pre-medication

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Induction

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Maintenance

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Recovery

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Further Reading

Publications

Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Clutton R E, Boyd C, Richards D L et al (1988) Significance of the oculocardiac reflex during ophthalmic surgery in the dog. JSAP 29 (9), 573-579 VetMedResource.
  • Crispin S M (1981) Anaesthesia for Ophthalmic Surgery. Veterinary Anaesthesia and Analgesia (1), 170-183 Wiley Online Library.
  • Brunson D B (1980) Anesthesia in Ophthalmic Surgery. Vet Clin North Am Small Anim Pract 10 (2), 481-495 PubMed.

Other sources of information

  • Gelatt K N & Gelatt J P (2001) Anesthesia for ophthalmic surgery. In: Small Animal Ophthalmic Surgery: Practical techniques for the Veterinarian. Chapter 3. Butterworth Heinemann.
  • Weaver B M Q (1989) In:Manual of Anaesthesia for Small Animal Practice, Anaesthesia for Ophthalmic surgery. British Small Animal Veterinary Association. pp 101-105.

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