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AP 1 > Test 3: Ophthalmology > Flashcards

Test 3: Ophthalmology Flashcards

1
Q

What is the oculocardiac reflex?

A

-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

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2
Q

What is the afferent limb of the oculocardiac reflex?

A

Trigeminal Nerve (CN V)

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3
Q

What is the efferent limb of the oculocardiac reflex?

A

Vagus Nerve (CN X)

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4
Q

What is the most common symptom associated with the oculocardiac reflex?

A

Bradycardia

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5
Q

What increases the incidence of the oculocardiac reflex?

A

Incidence may be increased with hypoxia, hypercarbia, or light anesthesia

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6
Q

Explain the effect of blocks on the oculocardiac reflex.

A

-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

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7
Q

What is the treatment of the oculocardiac reflex?

A

-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

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8
Q

What is a normal intraocular pressure?

A

Normal = 10-20 mmHg

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9
Q

What are the determinants of intraocular pressure?

A

IOP is determined by aqueous humor dynamics, changes in choroidal blood volume, central venous pressure, and extraocular muscle tone

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10
Q

What is the MOST IMPORTANT determinant of IOP?

A

The most important determinant of IOP is the balance between production, drainage, & reabsorption of aqueous humor

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11
Q

Blood supply to the retina & optic nerve are dependent on ?

A

intraocular perfusion pressure

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12
Q

How do you calculate IPP (Intraocular Perfusion Pressure)?

A

IPP = MAP - IOP

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13
Q

What has a greater effect on IPP, CVP or ABP?

A

CVP has a greater effect than arterial blood pressure (increase CVP = decreased drainage)

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14
Q

High IOP impairs blood supply and can cause what?

A

Loss of optic nerve function

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15
Q

What are the S/Sx of increased IOP?

A

Hypercarbia, hypoxia → could prolapse eye contents = blindness

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16
Q

What things increase IOP to 30-40?

A

Coughing, straining, vomiting, intubation

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17
Q

What is the effect of Volatile Inhalation Agents on IOP?

A

Dose-related decreases in IOP

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18
Q

What is the effect of N2O on IOP?

A

Increased risk for PONV (Which increases IOP)

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19
Q

What is the effect of propofol on IOP?

A

Lowers IOP

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20
Q

What is the effect of Ketamine on IOP?

A

Increases in IOP are controversial. Not an optimal agent d/t nystagmus, blepharospasm

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21
Q

What is the effect of benzos on IOP?

A

Lower IOP

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22
Q

What is the effect of etomidate on IOP?

A

Significant reduction in IOP (despite pain and myoclonus)

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23
Q

What is the effect of opioids on IOP?

A

Lower IOP

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24
Q

What is the effect of Succ on IOP?

A

Increases IOP (Avoid it!!!!!)

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25
Q

What is the effect of Rocuronium on IOP?

A

Causes mild decrease to no effect on IOP.

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26
Q

What is the most common form of glaucoma?

A

Open angle

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27
Q

Describe open angle glaucoma.

A

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

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28
Q

Describe Closed Angle Glaucoma.

A

“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!!!

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29
Q

What is the effect of Cholinesterase Inhibitors on the formation of aqueous humor?

A

Produce miosis (constriction) by allowing Ach to continually stimulate iris/ciliary muscles, improving uveoscleral outflow of Aqueous humor.

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30
Q

What is the effect of Beta Blockers on the formation of aqueous humor?

A

Reduces aqueous humor production.

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31
Q

What is the effect of Cholinergic Agonists on the formation of aqueous humor?

A

Constriction of pupil

32
Q

What is the effect of beta-2 stimulation and muscarinic receptor stimulation on the formation of aqueous humor?

A

Reduces aqueous humor production & increases outflow

33
Q

What are the anesthetic implications for ocular surgery associated with Miochol-E (Acetylcholine)?

A

-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

34
Q

What are the anesthetic implications for ocular surgery associated with Echothiophate?

A

-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

35
Q

What are the anesthetic implications for ocular surgery associated with Epinephrine?

A

Decreased production (vasoconstriction of ciliary body)

36
Q

What are the anesthetic implications for ocular surgery associated with Non-selective Beta 2 antagonists? (Timolol)

A

-Reduces aqueous humor production
-Be careful w asthma, COPD, heart block, heart failure, hotn

37
Q

What are the anesthetic implications for ocular surgery associated with Acetazolamide (carbonic anhydrase inhibitor)

A

-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

38
Q

What is the most common ocular complication of general anesthesia?

A

Corneal Abrasion

39
Q

What are the causes of a corneal abrasion?

A

D/t variety of mechanisms: drying of exposed cornea or from direct trauma

Prevention: tape eyes, pulse ox probe on ring finger

40
Q

What are the s/sx of a corneal abrasion?

A

foreign-body sensation, photophobia, pain

41
Q

What is the treatment of a corneal abrasion?

A

Consult & fluorescein exam, ointments, eye patch

42
Q

What are the anesthetic considerations for a patient who has had an intraocular injection of perfluropropane

A

N2O must be avoided for 30-70 days after perfluropropane.
Used for retinal detachment – intravitreal insufflation to tamponade retina in place

43
Q

What are the anesthetic considerations for a patient who has had an intraocular injection of sulfur hexafluoride?

A

-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

44
Q

Describe the advantages of a Retrobulbar Block.

A

-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

45
Q

What are the complications associated with a Retrobulbar Block?

A

Trauma to optic nerve/blood vessels/globe → loss of vision

46
Q

What is the anesthetic technique for a Retrobulbar Block?

A

-Have patient look directly forward when doing block
-1 inch needle depth decreases the risk of contact w deep orbital structures

47
Q

Describe the advantages associated with a Peribulbar Block (Extraconal)

A

-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

48
Q

Describe the disadvantages associated with a Peribulbar Block (Extraconal)

A

-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

49
Q

What is Tenon’s capsule?

A

thin membrane that forms a socket for the globe, separating it from the orbital fat

50
Q

Where is Sub-Tenon located?

A

A potential space between tenon’s capsule & the sclera

51
Q

Describe a Sub-Tenon Block

A

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

52
Q

What are the risks associated with regional anesthesia and ocular surgery?

A

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

53
Q

What occurs with inadvertent brainstem anesthesia?

A

Inadvertent brainstem anesthesia – onset of respiratory arrest is usually within 2-5 min after injection (neurologic, CV, pulm collapse)

54
Q

What should you observe prior to an Ocular Block?

A

The contralateral pupil.
-Pupil may be constricted and if it dilates after block, you must assume subarachnoid injection occurred & be prepared for respiratory arrest

55
Q

What is the anesthetic technique of choice for an open globe injury?

A

GETA = technique of choice but some places use regional

56
Q

T/F: Open globe injury is an emergency.

A

True; Protect patient from aspiration & avoid increased IOP that could result in expulsion of intraocular contents

57
Q

What anesthetic medications decrease IOP and should be utilized in an open globe injury?

A

Inhalational agents & narcotics decrease IOP

58
Q

What are the physiologic benefits to using inhalational agents and narcotics for an open globe injury?

A

-Relaxation of extraocular muscles
-decrease in aqueous humor production
-lower CVP

59
Q

Should you use Succ with an open globe injury?

A

A balance of risk.
-Not ideal to use Succ because it increases IOP, and can cause expulsion of eye contents.

60
Q

Why are NDMR preferred over Succ for an open globe injury?

A

Decreases IOP or no effect on IOP
-Can be reversed with Sugammadex

61
Q

What is the indication for a scleral buckle procedure?

A

Treatment of retinal detachment

62
Q

Describe the Scleral Buckle.

A

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

63
Q

The 6 extraocular muscles are innervated by what CN?

A

Innervated by CN3, except for LR6 and SO4

64
Q

Which muscle raises upper eyelids (no akinesia needed)?

A

Levator Muscle

65
Q

Which muscle causes contraction of eyelid?

A

Orbicular Muscle

66
Q

What can happen with any anesthetic agent that is injected into the optic nerve sheath?

A

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

67
Q

What is unique about the venous system of the orbit?

A

It is valveless. Blood flow = determined by pressure gradient

68
Q

What is contained in the Orbit?

A

30 mL
muscle, vessel, nerve, fat

69
Q

How many mL are in the Globe?

A

7 mL

70
Q

The outer fibrinous protective layer. White, opaque, posterior

A

Sclera

71
Q

The outer fibrinous protective layer. Anterior, transparent, colorless

A

Cornea

72
Q

The middle, vascular layer

A

Choroid

73
Q

The inner layer of posterior half of eye

A

Retina

74
Q

The junction between cornea & sclera

A

Limbal Area

75
Q

The thin, transparent mucous membrane

A

Conjunctiva

76
Q

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

A

Tenon Capsule

AP 1 (32 decks)

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