Test 3: Ophthalmology Flashcards
What is the oculocardiac reflex?
-Caused by pressure on the globe & traction on the extraocular muscles
-“Five & dime” – Afferent limb (CN 5 Trigeminal N) & Efferent limb (CN 10 Vagus N)
-May occur under local, regional, or general anesthesia
What is the afferent limb of the oculocardiac reflex?
Trigeminal Nerve (CN V)
What is the efferent limb of the oculocardiac reflex?
Vagus Nerve (CN X)
What is the most common symptom associated with the oculocardiac reflex?
Bradycardia
What increases the incidence of the oculocardiac reflex?
Incidence may be increased with hypoxia, hypercarbia, or light anesthesia
Explain the effect of blocks on the oculocardiac reflex.
-Performing a block can cause the reflex, however the block may be protective from future stimulus.
-reflex arc will fatigue w repeated stimulus
-Pretreatment w atropine or retrobulbar block is not useful
What is the treatment of the oculocardiac reflex?
-Release the pressure/stop eye manipulation
-Atropine 10 mcg/kg up to 2-3 mg in complete vagal block, can use glyco
-In refractory bradycardia, can infiltrate the rectus muscles w local anesthetic
What is a normal intraocular pressure?
Normal = 10-20 mmHg
What are the determinants of intraocular pressure?
IOP is determined by aqueous humor dynamics, changes in choroidal blood volume, central venous pressure, and extraocular muscle tone
What is the MOST IMPORTANT determinant of IOP?
The most important determinant of IOP is the balance between production, drainage, & reabsorption of aqueous humor
Blood supply to the retina & optic nerve are dependent on ?
intraocular perfusion pressure
How do you calculate IPP (Intraocular Perfusion Pressure)?
IPP = MAP - IOP
What has a greater effect on IPP, CVP or ABP?
CVP has a greater effect than arterial blood pressure (increase CVP = decreased drainage)
High IOP impairs blood supply and can cause what?
Loss of optic nerve function
What are the S/Sx of increased IOP?
Hypercarbia, hypoxia → could prolapse eye contents = blindness
What things increase IOP to 30-40?
Coughing, straining, vomiting, intubation
What is the effect of Volatile Inhalation Agents on IOP?
Dose-related decreases in IOP
What is the effect of N2O on IOP?
Increased risk for PONV (Which increases IOP)
What is the effect of propofol on IOP?
Lowers IOP
What is the effect of Ketamine on IOP?
Increases in IOP are controversial. Not an optimal agent d/t nystagmus, blepharospasm
What is the effect of benzos on IOP?
Lower IOP
What is the effect of etomidate on IOP?
Significant reduction in IOP (despite pain and myoclonus)
What is the effect of opioids on IOP?
Lower IOP
What is the effect of Succ on IOP?
Increases IOP (Avoid it!!!!!)
What is the effect of Rocuronium on IOP?
Causes mild decrease to no effect on IOP.
What is the most common form of glaucoma?
Open angle
Describe open angle glaucoma.
The gradual blockage of outflow of aqueous humor d/t sclerosis of trabecular tissue
-Medication goal: enhanced drainage or reduced production of aqueous humor
-miosis via alpha 2 agonists and beta blockers
Describe Closed Angle Glaucoma.
“narrow angle” (acute), can appear suddenly & is often painful; obstruction from posterior chamber to anterior chamber; worsens w mydriasis
-IV reversal of neuromuscular blockade = okay
-Ocular emergency!!!
What is the effect of Cholinesterase Inhibitors on the formation of aqueous humor?
Produce miosis (constriction) by allowing Ach to continually stimulate iris/ciliary muscles, improving uveoscleral outflow of Aqueous humor.
What is the effect of Beta Blockers on the formation of aqueous humor?
Reduces aqueous humor production.
What is the effect of Cholinergic Agonists on the formation of aqueous humor?
Constriction of pupil
What is the effect of beta-2 stimulation and muscarinic receptor stimulation on the formation of aqueous humor?
Reduces aqueous humor production & increases outflow
What are the anesthetic implications for ocular surgery associated with Miochol-E (Acetylcholine)?
-Causes contraction of the ciliary muscle - miosis
-Increased outflow d/t pulling the iris away from the anterior chamber
-Systemic effects (may cause cholinergic syndrome) – bradycardia w hotn, salivation, bronchospasm, bronchial secretions → reversed w atropine
What are the anesthetic implications for ocular surgery associated with Echothiophate?
-irreversible inhibition of cholinesterase
-Produces miosis by allowing Ach to continually stimulate iris/ciliary muscles
-Long-acting anticholinesterase may prolong the action of Sch
-Plasma pseudocholinesterase activity may be below 5% of normal
-4-6 weeks for normal enzyme activity to return after stopping this med
-Delay in metabolism of ester local anesthetics
What are the anesthetic implications for ocular surgery associated with Epinephrine?
Decreased production (vasoconstriction of ciliary body)
What are the anesthetic implications for ocular surgery associated with Non-selective Beta 2 antagonists? (Timolol)
-Reduces aqueous humor production
-Be careful w asthma, COPD, heart block, heart failure, hotn
What are the anesthetic implications for ocular surgery associated with Acetazolamide (carbonic anhydrase inhibitor)
-Reduces aqueous humor production
-MOA: ciliary body of the eye secretes HCO3 from the blood into the aqueous humor and formation of CSF by the choroid plexus involve HCO3 secretion
-These processes are inhibited
-Can cause potassium depletion
What is the most common ocular complication of general anesthesia?
Corneal Abrasion
What are the causes of a corneal abrasion?
D/t variety of mechanisms: drying of exposed cornea or from direct trauma
Prevention: tape eyes, pulse ox probe on ring finger
What are the s/sx of a corneal abrasion?
foreign-body sensation, photophobia, pain
What is the treatment of a corneal abrasion?
Consult & fluorescein exam, ointments, eye patch
What are the anesthetic considerations for a patient who has had an intraocular injection of perfluropropane
N2O must be avoided for 30-70 days after perfluropropane.
Used for retinal detachment – intravitreal insufflation to tamponade retina in place
What are the anesthetic considerations for a patient who has had an intraocular injection of sulfur hexafluoride?
-N2O must be stopped at least 15 min prior to injection, No N2O for 5 days after air bubble
-No N2O for 10 days after sulfur injection
Describe the advantages of a Retrobulbar Block.
-intraconal
-Achieve analgesia and akinesia
-Requires smaller volumes (3-5mL), Rapid onset (2 min), Intense anesthesia depth
-Lower risk of block failure, Higher risk of retrobulbar hemorrhage
What are the complications associated with a Retrobulbar Block?
Trauma to optic nerve/blood vessels/globe → loss of vision
What is the anesthetic technique for a Retrobulbar Block?
-Have patient look directly forward when doing block
-1 inch needle depth decreases the risk of contact w deep orbital structures
Describe the advantages associated with a Peribulbar Block (Extraconal)
-Injected anesthetic creates a positive extraconal pressure that spreads the agents inside the muscle cone to anesthetize the cranial nerves
-Less risk of retrobulbar hemorrhage
Describe the disadvantages associated with a Peribulbar Block (Extraconal)
-Requires larger volumes (8-12mL), Onset (10 min)
-Due to the many septal divisions of the orbit, the anesthetic flow may not adequately diffuse into the intramuscular cone → less consistent & higher risk of block failure
What is Tenon’s capsule?
thin membrane that forms a socket for the globe, separating it from the orbital fat
Where is Sub-Tenon located?
A potential space between tenon’s capsule & the sclera
Describe a Sub-Tenon Block
Performed between rectus muscles of the globe
-3-4 mL up to 10mL LA injected into sub–tenon space
-Motor movement of the globe may still be present
What are the risks associated with regional anesthesia and ocular surgery?
Intravascular injection
Globe puncture
Optic nerve injury
Retrobulbar hemorrhage
Retinal vascular events
Muscle palsy
Loss of vision
Respiratory arrest
Stimulation of oculocardiac reflex
Extraocular muscle injury
Central Retinal artery occlusion
Superficial hemorrhage
Optic nerve sheath injection
What occurs with inadvertent brainstem anesthesia?
Inadvertent brainstem anesthesia – onset of respiratory arrest is usually within 2-5 min after injection (neurologic, CV, pulm collapse)
What should you observe prior to an Ocular Block?
The contralateral pupil.
-Pupil may be constricted and if it dilates after block, you must assume subarachnoid injection occurred & be prepared for respiratory arrest
What is the anesthetic technique of choice for an open globe injury?
GETA = technique of choice but some places use regional
T/F: Open globe injury is an emergency.
True; Protect patient from aspiration & avoid increased IOP that could result in expulsion of intraocular contents
What anesthetic medications decrease IOP and should be utilized in an open globe injury?
Inhalational agents & narcotics decrease IOP
What are the physiologic benefits to using inhalational agents and narcotics for an open globe injury?
-Relaxation of extraocular muscles
-decrease in aqueous humor production
-lower CVP
Should you use Succ with an open globe injury?
A balance of risk.
-Not ideal to use Succ because it increases IOP, and can cause expulsion of eye contents.
Why are NDMR preferred over Succ for an open globe injury?
Decreases IOP or no effect on IOP
-Can be reversed with Sugammadex
What is the indication for a scleral buckle procedure?
Treatment of retinal detachment
Describe the Scleral Buckle.
A silicone band sewn around the sclera which creates a dimple on the eye wall.
-buckle is secured under the conjunctiva, so it moves the wall of the eye closer to the detached retina
-Use of laser therapy to create permanent adhesion
-Injection of expandable gas
The 6 extraocular muscles are innervated by what CN?
Innervated by CN3, except for LR6 and SO4
Which muscle raises upper eyelids (no akinesia needed)?
Levator Muscle
Which muscle causes contraction of eyelid?
Orbicular Muscle
What can happen with any anesthetic agent that is injected into the optic nerve sheath?
Optic nerve is covered by meninges. Any anesthetic agent injected into optic nerve sheath can find its way back to midbrain through CSF → CNS depression & resp arrest
What is unique about the venous system of the orbit?
It is valveless. Blood flow = determined by pressure gradient
What is contained in the Orbit?
30 mL
muscle, vessel, nerve, fat
How many mL are in the Globe?
7 mL
The outer fibrinous protective layer. White, opaque, posterior
Sclera
The outer fibrinous protective layer. Anterior, transparent, colorless
Cornea
The middle, vascular layer
Choroid
The inner layer of posterior half of eye
Retina
The junction between cornea & sclera
Limbal Area
The thin, transparent mucous membrane
Conjunctiva
Fibrous connective tissue that covers the eye from near the corneal limbus-fused to conjunctiva & extends behind the eye.
-The cavity in which the eye moves
Tenon Capsule
