EYE

Ophthalmic Anesthesia Overview

Anesthesia Considerations for Eye Surgery

  • Patient range: from premature neonates (retinopathies) to elderly (cataracts).

  • Important subgroup: traumatic eye injuries requiring special anesthetic considerations.

  • Types of anesthetic techniques:

    • Topical anesthetics

    • Sedation

    • Regional anesthesia

    • General anesthesia

  • Significant statistic: One-third of closed-case claims for eye injury associated with anesthesia were due to patient movement during procedures, resulting in blindness.

  • Anesthetic technique is crucial for patient outcomes.

Chambers of the Eye

  • Types of Chambers:

    1. Anterior Chamber

    2. Posterior Chamber

    3. Vitreous Cavity

Anterior Chamber

  • Location: Between the posterior cornea and the iris-lens plane.

  • Filled with: Aqueous humor.

  • Volume: Approximately 250 μl.

Posterior Chamber

  • Location: Anterior to the iris, lateral to the ciliary body, and posterior to the anterior vitreous face.

  • Contains: Approximately 60 μl of aqueous humor.

Vitreous Cavity

  • Description: Largest cavity of the eye, containing 2/3 of the eye volume.

  • Volume: About 4 ml.

  • Filled with: Vitreous humor, a gel composed of 98% water, hyaluronic acid, and collagen fibers.

Blood Supply of the Eye

  • Arterial Supply:

    • Main source: Ophthalmic artery (first intracranial branch of internal carotid artery).

  • Venous Drainage:

    • Via the superior ophthalmic vein.

Blood Supply to the Retina

  • Choroidal circulation:

    • Supplies 2/3 of retinal arterial supply (nourishing outer retina).

  • Central retinal artery:

    • Supplies remaining 1/3 through the optic nerve head to inner retina.

Optic Nerve

  • Definition and Location:

    • CN II, a white matter tract from retina to optic chiasm.

    • Features meningeal coverings and subarachnoid space communicating with CNS.

  • Function: Transmits visual signals from retina to occipital cortex.

Optic Chiasm

  • Functionality:

    • Nasal (medial) retina fibers cross to opposite sides; combines with opposite temporal (lateral) retina fibers to form optic tracts.

    • This partial decussation enables processing of visual fields for both eyes in left and right visual systems.

Extraocular Muscles

  • Muscle Count: Six extraocular muscles controlling eyeball movement, supplied by cranial nerves.

  • Muscle Functions: New Format Includes Specific Directions:

    • Superior Rectus: Moves the eye upward (located at 12-o’clock position).

    • Medial Rectus: Moves the eye inward (90° laterally to 12-o’clock position).

    • Inferior Rectus: Moves the eye downward (located at 6-o’clock position).

    • Lateral Rectus: Abducts eye (90° laterally to 12 o’clock position).

    • Superior Oblique: Moves downward and outward (on superior aspect).

    • Inferior Oblique: Moves upward and outward (on inferior aspect).

Autonomic Innervation of the Eye

  • Sympathetic Innervation:

    • Passes through superior cervical ganglion; promotes dilation (mydriasis).

  • Parasympathetic Innervation:

    • Via oculomotor nerve (CN III); promotes constriction (miosis).

Sensory Innervation of the Eye

  • Afferent pathways:

    • Comprised of long and short ciliary nerves.

  • Ciliary ganglion:

    • A major location for regional blocks of the eye.

Oculocardiac Reflex

  • Clinical Presentation:

    • Bradycardia, cardiac arrhythmia, or asystole due to ocular stimulation.

    • Triggered by pressure on the globe or traction on extraocular muscles (especially medial rectus).

    • Most common in children undergoing strabismus surgery.

    • Mediated through trigeminal (V) afferent and vagal (X) efferent pathways.

    • Can occur under local or general anesthesia.

  • Factors that can trigger reflex:

    • Retrobulbar anesthesia administration.

    • Reflex lessens with repeated stimulation (probably from fatigue).

    • Augmented by hypercarbia and hypoxemia; pressure in the empty orbit can also invoke it.

  • Pretreatment Options:

    • Use of anticholinergic drugs (e.g., atropine 0.02 mg/kg or glycopyrrolate 0.01 mg/kg) is controversial and may risk serious cardiac arrhythmias, especially in elderly patients.

Oculocardiac Reflex Treatment

  1. Immediate cessation of operative manipulation until heart rate normalizes.

  2. Confirm adequate ventilation, oxygenation, and depth of anesthesia.

  3. If reflex persists, administer atropine (0.007-0.01 mg/kg) or glycopyrrolate (0.01 mg/kg).

  4. Consider direct infiltration of rectus muscles with local anesthetic.

Intraocular Pressure (IOP)

  • Factors Influencing IOP:

    • Movement of aqueous humor.

    • Changes in choroidal blood volume.

    • Central venous pressure.

    • Extraocular muscle tone.

  • Physiological determinant: The balance between production and drainage of aqueous humor.

  • Resistance to outflow: Particularly in peripheral corners of the eye maintaining IOP within physiological ranges.

Normal IOP Ranges

  • Normal IOP: 10 to 20 mm Hg.

  • Abnormal IOP: >22 mmHg (pathological >25 mmHg).

  • Variations:

    • IOP fluctuates 1 to 2 mmHg with each cardiac cycle.

    • Supine position increases IOP by 2 to 4 mmHg.

Effects on IOP Variations

  • Increased venous pressure raises IOP by affecting aqueous drainage and choroidal blood volume.

  • Events like vomiting, coughing, or bucking on an endotracheal tube can elevate IOP by 30 to 40 mmHg.

  • Laryngoscopy, intubation, airway obstruction, or Trendelenburg position can also significantly increase IOP.

  • Autoregulation: Blood pressure in the eye aids stability of IOP, although extreme changes in systemic blood pressure and ventilation can affect IOP.

  • Choroidal arteries react:

    • Vasodilate in response to hypercapnea.

    • Constrict with hypocapnea, affecting intraocular pressure.

Considerations for Anesthesia & IOP

  • Most anesthetic drugs reduce or have no effect on IOP.

  • Exception: Succinylcholine increases IOP by 5 to 10 mmHg for 5-10 minutes post-use.

  • Ketamine: Controversial regarding its effect on IOP due to inducing nystagmus and blepharospasm.

  • Inhalation agents: Reduce IOP with increased dosage due to effects on blood pressure, relaxation of extraocular muscles, and pupil constriction facilitating aqueous outflow.

Effects of Anesthetic Agents on IOP

  • Inhaled anesthetics: Decrease IOP.

  • Volatile agents: Similar effect; specific agents may vary.

  • Nitrous oxide: Requires caution; variable effects on IOP.

  • Intravenous anesthetics:

    • Barbiturates, benzodiazepines generally decrease IOP.

    • Ketamine may have conflicting reports.

  • Muscle relaxants:

    • Depolarizers (e.g., succinylcholine) notably increase IOP.

    • Non-depolarizers have varied effects.

Glaucoma Overview

  • Definition: Pathological increase in IOP owing to resistance against aqueous humor outflow.

  • Types of Glaucoma:

    • Open-angle glaucoma:

    • Typically caused by trabecular tissue sclerosis affecting aqueous drainage despite an open chamber.

    • Most common form, accounting for 70-80% of chronic cases.

    • Treatment: Medications (e.g., Timolol, Epinephrine) and procedural interventions (e.g., laser trabeculoplasty).

    • Closed-angle glaucoma:

    • Involves iris contact with the cornea, obstructing aqueous outflow.

    • Treatment involves medications that constrict the pupil (e.g., pilocarpine) and surgical interventions (e.g., iridotomy).

Anesthesia Considerations for Glaucoma Patients

  • Atropine: Previously contraindicated in patients with glaucoma due to its mydriatic effect; newer data suggest clinical doses (0.4 mg) pose no risk.

  • Scopolamine: Not recommended for closed-angle glaucoma due to stronger mydriatic effects.

Ophthalmic Drugs

  • Rate of Absorption: Eye drops have a higher absorption rate compared to IV or SQ injections due to concentrated medications.

  • Examples of Ophthalmic Drugs:

    • Phenylephrine: Mydriatic agent with side effects like hypertension and arrhythmias.

    • Echothiophate: Anticholinesterase that decreases IOP and prolongs action of succinylcholine.

    • Pilocarpine: Miotic agent reducing IOP with minimal side effects.

    • Beta Blockers: Treat glaucoma, lower aqueous humor production.

    • Acetazolamide (Diamox): Carbonic anhydrase inhibitor that can cause metabolic side effects.

Complications of Ophthalmic Drugs

  • Significant Considerations:

    • Phenylephrine: Can cause severe hypertension and arrhythmias.

    • Echothiophate: Irreversibly affects cholinesterase activity for 4-6 weeks following treatment.

    • Acetazolamide: Risks of Stevens-Johnson syndrome among other side effects; contraindicated in sulfa allergies.

Anesthetic Management: Monitoring

  • Standard monitoring is essential for both local and general anesthesia:

    • Bed position is adjusted to avoid obstructing anesthesia machine; patient vigilance is critical.

    • Monitoring tools include:

    • EKG, SpO2, NIBP, precordial stethoscope, ETCO2 via nasal cannula.

Preoperative Medications

  • Patient Anxiety Management:

    • Consider premedication with Versed (1-3 mg) with optional narcotic (fentanyl 12.5-25 mcg), reducing doses for elderly patients.

    • Propofol (10 mg increments) provides rapid onset for regional anesthesia placement.

    • Ensure sedation aligns with surgical needs, avoiding excessive levels to prevent movement risks.

Fire Hazards in Eye Surgery

  • Oxygen administration through nasal prongs can create a flammable environment under drapes, warranting caution.

  • Caution needed with use of cautery or laser; oxygen supply should be shut off 5 minutes prior to its use.

Types of Anesthesia

Topical Anesthesia

  • Advantages: Easy application, rapid onset, minimal discomfort.

  • Effectively provides analgesia by blocking trigeminal nerve endings but does not affect optic nerve; ocular motility remains intact.

  • Ideal for uncomplicated cataract procedures.

Regional Eye Blocks

  • Provide akinesia and analgesia within the globe and orbit.

  • Possible complications can arise, posing risks to vision and life.

  • Key muscles and nerves within the ocular cone must be understood for effective blocking methods.

  • Techniques:

    • Retrobulbar anesthesia: Injection within the muscle cone.

    • Peribulbar anesthesia: Injection outside the muscle cone.

Retrobulbar Block

  • Injection of local anesthetic (3-5 mL) targeting ciliary nerves.

    • Must ensure correct needle advancement and pressure application post-injection to minimize hemorrhage risk.

Complications of Retrobulbar Block

  • Contraindications:

    • Bleeding disorders, extreme myopia, open eye injury risks.

  • Potential complications include:

    • Retrobulbar hemorrhage, stimulation of the oculocardiac reflex, retinal detachment, seizures, globe perforation.

Management of Retrobulbar Hemorrhage

  • Treatment includes lateral canthotomy or anterior chamber paracentesis if warranted; monitoring IOP is critical.

Brain Stem Anesthesia

  • Serious complication from inadvertent CNS access can lead to respiratory complications.

  • Symptoms may emerge within 10 minutes, lasting varying durations; avoids overtreatment of hemodynamic changes.

  • Pathways affected:

    • Optic chiasm: paresis of extraocular muscles.

    • Glossopharyngeal nerve: swallowing and speech issues.

Globe Perforation Risks

  • Potential result of all eye blocks leading to serious complications including visual impairment.

  • Symptoms include extreme pain and patient restlessness.

Facial Nerve Block

  • Employed alongside retrobulbar block for eyelid akinesia, allows smooth procedure.

General Anesthesia Indication & Management

Indications for General Anesthesia

  • Patient type considerations:

    • Pediatric, uncooperative, emergent cases, or lengthy/painful procedures.

  • Situational aspects include end of procedures affecting extent of guidance.

General Anesthesia Key Points

  • Ensure absolute attention to IOP management during induction and maintenance phases.

  • All non-depolarizing muscle relaxants typically lower IOP; succinylcholine use requires strict location-specific precautions.

Anesthesia Emergence Management

  • Strategies to manage anesthesia emergence include managing cough reflex and postoperative nausea; prevent respiratory impacts.

  • Attention to eye pain, corneal abrasions must not be neglected, as can lead to significant patient discomfort.

Specific Surgical Procedures

Cataract Extraction

  • Defines the process; performed under local/sedation; general anesthesia used for uncooperative cases.

Retinal Detachment Surgery

  • Immediate intervention is crucial for patients; take account of dietary management pre-operatively.

Scleral Buckle Surgery

  • Surgical physical repair of retinal detachment; regional anesthesia noted for postoperative pain management challenges.

Vitrectomy

  • Used in various ocular conditions; common complications include cataract formation and elevated IOP.

Gas Bubble Techniques in Surgery

  • Description of gas bubbles injected during retinal surgeries for healing; important precautions with surgical gases like N2O outlined.

Repair of Open Globe and Strabismus Surgeries

  • Specific requirements for anesthesia techniques; attention to risks such as aspiration strategies and use of neuromuscular blockers is critically reviewed.

Managing Retinopathy of Prematurity

  • Importance of timely surgical intervention under proper conditions for the affected infant demographic.

Corneal Transplant Procedure

  • Overview of keratoplasty procedures; sedation/version management discussed for a successful implantation.

Complications of Eye Surgery

  • Comprehensive analysis of complications related to ocular anesthesia.

    • Risk of retrobulbar hemorrhage, intravascular injection leading to severe outcomes, optic nerve trauma, ocular ischemia, extraocular muscle palsies, and potential corneal abrasions must be highlighted.

Conclusion

  • Anesthesia for eye surgery requires significant vigilance and consideration across multiple domains; understanding patient needs and complications remains a central theme.