Ophthalmic Procedures under MAC

Procedures

Cataract extraction, corneal transplant, trabeculectomy (for glaucoma), ectropion-entropion repair, ptosis surgery, eyelid reconstruction, pterygium (raised, wedge-shaped growth of the conjunctiva) excision

Akinesia required

• Retrobulbar and peribulbar injections
  • Risk of inadvertent intrathecal injection, orbital hemorrhage, need for heavy sedation during placement, delayed return of vision post-op
• Topical anesthesia
  • Lower bleeding risk: patients can be on anticoagulants
  • Works best in surgical techniques not requiring akinesia

Contraindications for regional/MAC

• Bleeding disorders, open-eye injuries, claustrophobia, chronic cough, inability to lie flat, pt refusal

Intraocular pressure

Normal 12-20 mmHg

Influenced by changes in BP and ventilation

• Hypoventilation increases (high CO₂)
• Hyperventilation decreases (low CO₂)

PaO₂ decrease will increase IOP

Low ophthalmic artery pressure increases the risk of retinal ischemia

Increases in IOP will try to decrease intraocular volume by increased drainage of aqueous or extrusion of vitreous (gel between lens and retina) through the wound. Latter is a serious complication that can permanently worsen vision

Anesthetic considerations

Local versus general

Note: Succinylcholine causes increased IOP for 5-10 min (false high measurements, extrusion of content from open wound)

• Do not use it for open-eye injuries

Elderly population

Respiratory

• Increased incidence of hiatal hernia = increased risk of aspiration
• Chronic cough, unable to lie flat

Cardiac

• CAD, HTN, CHF
• Check exercise tolerance

Diabetes

• Increased risk for MI and pulmonary aspiration secondary to delayed emptying of the stomach
• Monitor BS, possibly D₅LR

Musculoskeletal

• Arthritic changes, position carefully with good padding

Hematologic

• Check coagulation status

Labs

As indicated per H&P

Limit fluid administration to avoid full bladder = increased BP

Communicate with pt, but instruct NO head movement

Oculocardiac reflex

• Caused by traction on extraocular muscles or pressure on the eyeball
• Trigeminal afferent and vagal efferent
• Decreased HR, BP, and arrhythmias - seen primarily on strabismus surgeries
• May cause nausea

Consider premedication with IV atropine or glycopyrrolate

• Note: CAD in elderly

Treatment

Stop the procedure, check the anesthetic level, and give IV atropine 10 mcg/kg

Intraocular gas expansion

Injection of a gas bubble into the posterior chamber - flattens detached retina, helps healing

If N₂O is given, this can seep into a bubble, increase size, and increase pressure

No N₂O at least 15 min before insertion of bubble and 5-10 days post, depending on the type of gas bubble

Sulfur hexafluoride (SF6) is another gas that can be injected, and it lasts up to 10 days

Extubation

• Deep, if possible, to prevent coughing
• Premedicate with lidocaine 1.5 mg/kg/IV to blunt
• Antiemetics

Systemic effects of ophthalmic drugs (topical application)

Topically applied medications absorbed at a rate intermediate between IV and SQ administration

Acetylcholine

Cholinergic agonist (miosis) - causes bronchospasm and bradycardia. hypotension

Atropine

Anticholinergic (mydriasis) to help with examination and surgery.

Central anticholinergic syndrome (dry mouth, tachycardia, agitation, delirium, hallucinations to unconsciousness)

• Physostigmine 0.01-.03 mg/kg/IV will increase central acetylcholine and reverse the symptoms

Acetazolamide

Carbonic anhydrase inhibitors are used to decrease IOP (decreased CO2)

Hypokalemia, metabolic acidosis

Betaxolol

Oculospecific Beta-blocker to decrease IOP

Cyclopentolate

Anticholinergic (mydriasis)

• Potential for disorientation, psychosis, convulsions

Echothiophate

Irreversible cholinesterase inhibitor, which prolongs the effect of Succinylcholine

It is used to cause miosis and decreased IOP

Inhibition lasts for 3-7 weeks post discontinuation

Causes paralysis and bronchospasm

Epinephrine

Sympathetic agonist (mydriasis, decreased IOP)

It causes HTN, bradycardia, tachycardia, and headache

Phenylephrine

Alpha-adrenergic agonist causes mydriasis (pupil dilation) and vasoconstriction

It can cause HTN, tachycardia, and dysrhythmias

Scopolamine (see Atropine)

Timolol

Non-selective beta-blocker that reduces IOP by decreasing the production of aqueous humor

Rarely associated with atropine-resistant bradycardia, hypotension, asthma, CHF, and bronchospasm.