Anesthesia for Eyes Flashcards
What is the outermost layer of the eye called?
Sclera
What surgery is the most common in the elderly?
Eye Surgery
What is the anterior-most portion of the eye called?
Cornea
What is the middle layer of the eye called?
Uveal Tract
What are the layers of the Uveal Tract?
- Choroid
- Iris
- Ciliary Body
What is the function of the Choroid?
A layer of blood vessels located posteriorly that provides blood flow to the eye
What can bleeding in the Choroid lead too?
Intraoperative Explusive Hemorhage
Where do sympathetic fibers of the iris originate from?
Carotid Plexus
Where do parasympathetic fibers of the iris originate from?
Oculomotor Nerve
The sympathetic fibers of the iris travel through the ciliary ganglion to innervate this muscle.
What does this muscle do when contracted?
- Dilator Muscle
- Contraction of Dilator Muscle dilates the pupil
The parasympathetic fibers synapse in the ciliary ganglion to innervate this muscle.
What does this muscle do when contracted?
- Iris Sphincter Muscle
- Contraction of iris sphincter causes pupillary constriction.
What does the ciliary body of the eye produce?
Aqueous Humor
What is the center of the eye filled with?
Vitreous Gel
How many extraocular muscles are there?
6 extraocular muscles
The ophthalmic artery is branched from where?
Branch from the internal carotid artery
What supplies the majority of blood to orbital structures?
Ophthalmic artery
The ophthalmic vein drains blood directly into a _________.
cavernous sinus
Which CN transmits neural signals from the retina?
Optic Nerve (CN II)
Which CN controls extraocular muscle movement?
- Oculomotor Nerve (CN III)
- Trochlear Nerve (CN IV)
- Abducens Nerve (CN VI)
Which CN is responsible for touch and pain sensation?
- Trigeminal Nerve (CN V)
Which CN is responsible for motor innervation to orbicularis muscle via zygomatic branch?
- Facial Nerve (VII)
A blockade on CN VII will prevent this from “squeezing”.
Eyelid
Which nerve provides sensation to the upper eyelid
Frontal branch of ophthalmic nerve
Which nerve provides sensation to the lower eyelid
Maxillary nerve
What is normal intraocular pressure (IOP)?
10-20 mmHg
At what pressure is IOP considered pathological and will need treatment?
Greater than 25 mmHg
In anesthesia, what factors can increase intraocular pressure?
What two factors cause the most significant increase in IOP?
- Direct Laryngoscopy and Emergence
- Changes in intraocular content
- External pressure (masking)
- Patient Positioning (prone)
- Coughing, straining, vomiting
- Hypercapnia
- Hypoxia
- Hypertension
- Drugs (Sux, Ketamine, Neostigmine/Atropine, etc)
Intraocular perfusion pressure formula
MAP - IOP
Blood supply to the retina and optic nerve depends on ______________ Pressure
Blood supply to the retina and optic nerve depends on Intraocular Perfusion Pressure
What is believed to cause the chronic pressure elevation in open-angle glaucoma?
Sclerosis of the trabecular mesh network
___________ is primarily regulated by the resistance at the trabecular meshwork
Intraocular Pressure
What fluids in the eye help regulate IOP
- Quantity of Aqueous Fluid
- Choroidal Blood Volume
How much increase in IOP would be caused by coughing, straining, and vomiting?
30-40 mmHg
How does hypercapnia increase IOP?
Hypercapnia causes choroidal congestion, which causes an increase in IOP.
Intravenous succinylcholine causes IOP to increase by ________ mmHg (range)
8-10 mmHg
How does succinylcholine increase IOP?
- Reduced aqueous humor outflow
- Increased choroidal blood volume
- Increased central venous pressure
How long does the increased IOP last if succinylcholine is administered?
5-10 minutes
Intravenous ketamine causes IOP to increase by ________ mmHg (range)
What is the increase in IOP from ketamine related to?
- 2-3 mmHg
- Increase BP from the effects of ketamine
How does Sugammadex increase IOP?
Trick question.
Sugammadex does not increase IOP.
Ocular blocks increase IOP by ______ mmHg (range).
IOP will return to baseline within _____ mins.
- 5-10 mmHg
- 5 minutes
Which block will cause the greatest increase in IOP?
What is this due to?
- Peribulbar Block
- D/t large volume of LA that is injected
What patient position will increase IOP?
- Supine
- Prone
- Trendelenburg
Normal blink increases IOP by ____ mmHg
10 mmHg
Forceful lid squeeze increases IOP by ________ mmHg
70 mmHg
In anesthesia, what factors can decrease intraocular pressure?
- Volatile agents & IV anesthetics
- Short-acting opioids
- Mannitol
- Acetazolamide
- Echothiophate
- Timolol
How does VA decrease IOP?
Depression of CNS ocular centers → relaxation of extraocular muscle tone
Volatile agents & IV anesthetics can cause a dose-dependent reduction of IOP by ________% (range)
30-40%
Mannitol causes a decrease in IOP lasting ______hours (range)
5-6 hours
Effects of Midazolam, Nitrous Oxide, and Nondepolarizing neuromuscular blocking agents (NMBA) on IOP.
No effect
What is another name for the oculocardiac reflex?
Trigeminovagal Reflex
What are the triggers for the oculocardiac reflex?
- Traction on extraocular muscles (specifically the medial rectus muscle)
- Pressure on globe
- Retrobulbar block
The oculocardiac reflex may be accompanied by _______ in the awake patient.
Nausea
The oculocardiac reflex is most commonly seen in children for this surgery.
Strabismus repair
Clinical presentation of the oculocardiac reflex during surgery.
- Bradycardia
- AV block
- Ventricular Ectopy
- Asystole
Give the pathophysiology of the oculocardiac reflex.
- Afferent limb of the reflex limb arises from the ophthalmic division of the trigeminal nerve and travels to the Gasserian ganglion and the sensory nucleus of the trigeminal nerve near the fourth ventricle where it synapses with the motor nucleus of the vagus nerve
- Efferent limb is via the vagus nerve to the heart → decreases in HR and contractility
Oculocardiac Reflex Managment
- IV pretreatment with atropine / glycopyrrolate before surgery begins
- STOP surgery
- Assess ventilation (worsened by hypercapnia/hypoxia)
- Surgeon will infiltrate retus muscle w/ LA
How will the oculocardiac reflex fatigue itself?
Repeated stimulation will decrease the reflex response
Atropine dose for intraoperative oculocardiac reflex
- 7-10 mcg/kg IV incrementally
- Faster onset than glycopyrrolate
Glycopyrrolate dose for intraoperative oculocardiac reflex
0.2 mg IV incrementally
What is another name for Open Angle Glaucoma
Chronic Glaucoma
How is Open Angle Glaucoma characterized?
Optic neuropathy characterized by progressive peripheral visual field loss followed by central field loss in a typical pattern
How does Open Angle Glaucoma cause visual loss?
- Trabecular meshwork sclerosis causes chronic pressure elevation
- This process is usually gradual and painless
Treatment for Open Angle Glaucoma
- Lower IOP / decrease fluid production
- Trabeculoplasty / trabeculectomy
How is closed-angle glaucoma characterized?
- Obstruction to aqueous drainage from closure of the anterior chamber angle
- Caused by acute dilation of iris that blocks drainage
- Rapid rise in IOP, PAINFUL
- Blindness <24 hours if not treated
Treatment for Closed Angle Glaucoma
Iridotomy
Describe an iridotomy procedure to treat closed-angle glaucoma.
Laser peripheral iridotomy to create a small hole in the iris to allow fluid to flow more freely into the front chamber of the eye where it then can drain.
Pew Pew
What medication and substances should patients avoid if they have closed-angle glaucoma.
- DO NOT USE SCOPOLAMINE
- Antihistamines & decongestants may cause increase in IOP d/t pupillary dilation
- Antidepressants d/t anticholinergic effect – pupillary dilation & increased aqueous production
- Benzodiazepines d/t relaxation of sphincter muscle of iris & mild anticholinergic effect
- Coke, X, & MJ
- Ipratropium bromide
During strabismus repair for a 10 yo, the patient’s heart rate decreases from 89 bpm to 30 bpm. What is the cause?
- Oculocardiac Reflex
- This reflex is triggered by traction on the extraocular muscles, particularly the medial rectus muscle, or pressure on the globe.
Name drugs that are used to treat glaucoma.
- Acetazolamide (drainage)
- Echothiophate (maintains miosis)
- Timolol
- Netarsudil
MOA of Acetazolamide
- Carbonic Anhydrase Inhibitor
- It reduces the production of aqueous humor
S/E of Acetazolamide
- Alkaline diuresis → K+ depletion
- PONV
Systemic absorption of Acetazolamide is possible through ________ or __________
- Conjunctiva
- Nasal Mucosa
MOA of Echothiophate
- Anticholinesterase Inhibitor
- Increased ACh → contraction of the ciliary muscle (miosis) → outflow of aqueous humor through the trabecular meshwork
Anesthesia Considerations for Echothiophate
- Systemic absorption → inhibition of plasma cholinesterase
- Succinylcholine can cause prolonged paralysis
- Inhibition of the metabolism of Ester-type LA → toxicity
- Return of normal enzyme activity in 4-6 wks after d/c
MOA of Timolol
- Non-selective β blocker
- Reduces the production of aqueous humor
S/E of Timolol
- Bradycardia
- Bronchospasm
- CHF exacerbation
Timolol is contraindicated in what patient population?
- Asthma
- CHF
- Conduction defects
MOA of Netarsudil
- Rho Kinase Inhibitor
- ↓ IOP by increasing the outflow of aqueous humor through the trabecular meshwork
Effects of Phenylephrine on the eyes
Pupillary Dilation
Concentration of Phenylephrine eye drops
2.5%
- Administration 10% phenylephrine contains 5 mg
- 10% administration can result in hypertension, arrhythmias, and adverse cardiac
What drugs cause pupillary constriction and are used for intraoperative lens extraction?
What are the S/E?
- Pilocarpine/ Acetylcholine
- Bradycardia, Bronchospasm
What are cataracts?
The opacity of the crystalline lens of the eye
A modern cataract surgery technique that uses ultrasonic energy to break up and remove a cataractous lens from the eye
Phacoemulsification
Anesthesia for Cataract surgery
- Topical or regional
- Minimal IV medications
- General is rare
Cataract Anesthesia consideration
- No supplemental O2 if femtosecond laser is being used to make the corneal incision, capsulotomy, and fragmenting the lens
- Fire risk
What is a corneal transplant called?
Keratoplasty
What medication is used to maintain low and stable IOP during a corneal transplant?
Mannitol
Anesthesia for Keratoplasty surgery
- Complete eye akinesia required
- Good analgesia postop
- Prevent eye squeezing
- No coughing / movement
- Eye protection w/adequate perfusion
- Prevent oculocardiac reflex
- Usually a regional block is used
Why is topical anesthesia not recommended for keratoplasty?
Poor option d/t duration & pain at end
Criteria for GETA for a Keratoplasty?
- Unable to lie flat
- Restless w/tremor
- Claustrophobic
- Pediatrics
What are the regional block options for a keratoplasty?
How much will IOP increase w/ each block?
- Retrobulbar Block (4-6 mmHg)
- Peribulbar Block (5-22 mmHg)
- Sub-Tenon’s Block (no change in IOP)
What are the advantages of using a regional block for a keratoplasty?
- Intraop & postop analgesia
- Akinesia
- No oculocardiac reflex
- Less PONV
- Quicker recovery & discharge
A 69-year-old male presents for a trabeculectomy. His medications include echothiophate eye drops. Which medication should be avoided in his anesthesia plan?
- Any Ester-type LA may predispose a patient to local anesthetic toxicity (Procaine, Chloroprocaine, Tetracaine)
- Don’t use Succinylcholine, prolonged muscle paralysis
Remember: Ester LA have only one “i”
If medications fail to treat chronic glaucoma, what type of surgery may the patient be a candidate for to increase drainage of aqueous humor to reduce IOP?
Trabeculectomy
What is used to decrease/ prevent flap scarring of a trabeculectomy?
- Mitomycin-C
- 5-FU
What is Pytergium?
What is another name for it?
- Triangular wedge of fibrovascular conjunctival tissue, r/t chronic sun exposure
- Surfer’s eye
What is used to prevent the recurrence of Ptyergium?
Mitomycin-C (MMC)
Ptyergium has a 30-80% recurrence rate – MMC is alkylated agent and inhibits DNA synthesis
What type of anesthesia would be used for Ptyergium Excision?
Topical Anesthetic
What term describes the lower eyelid turned outward d/t the effects of aging?
Ectropion
What term describes the lower eyelid turned inward d/t the effects of aging?
Entropion
What type of anesthesia would be used for Ectropion and Entropion Repair?
Local Anesthetic w/ Sedation
Procedure that corrects defect, deformity, or disfiguration of eyelids. Removes redundant tissue of the eyelids
Blepharoplasty
- Considered plastic surgery
- Transconjunctival vs Skin approach
- Local w/ sedation or GETA
Dystrophy of this muscle will cause ptosis (droopy eye).
Levator Muscle
What type of anesthesia would be used for Ptosis Repair?
Local Anesthetic w/ Sedation
What term describes malalignment of the visual axis causing diplopia (double vision)?
Strabismus
What is the most common eye surgery in children?
Strabismus Repair
Children with strabismus will have what other underlying disorder?
- Trisomy 21 (Downs)
- Cerebral palsy
- Hydrocephalus
- Malignant hyperthermia
- Myotonic dystrophy
May need to be cautious w/ Sux of VA for these patients
What type of anesthesia would be used for Strabismus Repair?
Post-op Considerations for Strabismus Repair
- General + Regional Anesthesia
- No severe post-op pain
- Severe PONV (50-80%)
- Minimize opioids. Consider Ketorolac
Anesthesia Considerations for Eye Trauma.
- Considered full stomach
- Sux vs. RSI Roc dose
- GETA vs Regional
- Decrease gastric volume/acidity (Bicitra)
- Use Oral Rae Tube
- Avoid hypercapnia, light sedation (↑ IOP)
What advantages does regional anesthesia have over general anesthesia for eye procedures?
- Significant postoperative analgesia
- Nausea and vomiting are infrequent.
- Return to ambulation faster
What is often placed with the outlet on the chest to eliminate carbon dioxide and oxygen buildup under the drapes and to prevent claustrophobia?
Air Blower
What makes up the local anesthetic used for regional eye blocks?
1:1 ratio of bupivacaine 0.75% and lidocaine 2% without epinephrine
Why is Hyaluronidase added to local anesthetic for eye procedures?
- Speed tissue penetration
- Prevent anesthetic-related damage to the extraocular muscles
How much Hyaluronidase is needed to facilitate permeability & quality of the block?
7.5 units/ mL of LA
Name this block
Retrobulbar Block
Name this block
Peribulbar Block
PERribulbar is PERfectly Straight
PERibulbar is also on the PERimeter of the Cone
Describe the placement of a retrobulbar block
- Behind globe of the eye
- Inside the muscular cone
The retrobulbar block will cause akinesia of the extraocular muscles. What CN will be involved?
- II
- III
- VI
The retrobulbar block will provide a sensory block for these structures.
- Conjunctiva
- Cornea
Complications of a Retrobulbar Block. What is the most common?
- Retrobulbar Hemorrhage (monitor for IOP elevation)
- Hematoma
- Optic nerve injury
- Globe penetration
- LAST (seizures, CNS excitation)
With a retrobulbar block, this will be expected because the superior oblique muscle outside the muscle cone may not be blocked.
Some intorsion on downgaze
Describe the placement of a peribulbar block
Inject above & below orbit
The peribulbar block will cause akinesia to what CN?
- III
- VI
Incomplete akinesia, peribular block will not block CN II
Pros of Peribulbar Block
- Easier and Less painful to perform
- ↓ Risk of Retrobulbar Hemorrhage
Complications of Peribulbar Block
- High spinal
- Intraocular injection
What topical anesthetic is typically used for the eyes?
0.5% Proparacaine
Topical Anesthetic is limited to these structures of the eye.
- Conjunctiva
- Cornea
- Anterior Sclera
Topical Anesthetic do not block these eye structures.
- Iris
- Ciliary Body
