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Flashcards in ENT I Deck (33)
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1

What are the 3 main chambers of the eye?

What are the 3 layers of the wall of the globe?

  • 3 main chambers:
    • Vitreous chamber
    • Anterior chamber
      • cornea to iris
      • filled with aqueous humor
      • aqueous humor drains from anterior chamber thru schlemm's canal into venous system
    • Posterior chamber
      • Iris to lens and ciliary process
  • 3 layers of wall of globe
    • Sclera
    • Uveal tract
      • choroid- layer of blood vessels
      • Iris- controls light entry
      • Ciliary body- produces aqueous humor
    • Retina

2

What are the different parts of the eye?

Conjunctiva

cornea

aqueous humor

Schlemm's canal

pupil

lens

  • Conjunctiva is clear membrane that covers the sclera in the front of the eye
  • Cornea (part of sclera) is a strong clear bulge located at the pront of the eye
  • Aqueous humor is a watery substance located in the anterior chamber of the eye
  • Schlemm's canal is a channel in the eye that collects aqueous humor from the anterior chamber and delivers it into the bloodstream
  • pupil is formed by the iris
  • lens of the eye is a flexible unit that consists of layers of tissue enclosed in a tough capsule

3

What are the 6 extraocular muscles of the eye?

CN innervation?

movement?

  • Innervated by oculomotor nerve--CN III
    • Eye movements, pupil constriction, opens eyelids
      • Superior rectus
      • inferior rectus
      • medial rectus
      • inferior oblique
  • Innervated by Trochlear nerve--CN IV
    • moves eye down and out
      • superior oblique
  • innervated by abducens nerve-- CNVI
    • moves eye lateral
      • lateral rectus

4

What nerve provides sensory innervation to the eye?

  • Trigeminal nerve CN V
    • Opthalmic branch- upper eyelid, conjunctiva, and cornea
      • Nosociliary branch of opthalmic nerve is sensory to medial canthus, lacrimal sac, and ciliary ganglion
    • Maxillary branch- lower lid

5

What is the function of Cranial Nerve II?

  • Optic nerve
    • vision
    • It is part of the optic chiasm along with the artery, vein, and sympathetic nerves
    • Injury to the optic nerve can cause total blindness

6

Aqueous humor

How is it produced?

How is it eliminated?

  • Production:
    • 1/3 produced in the posterior chamber by the ciliary body and then actively moved from posterior chamber to anterior chamber by an active sodium pump mechanism
    • 1.3 comes from passive filtration through vessels in the iris
    • produced at rate of 2 µL/min
  • Elimination:
    • fluid drains out of the eye through a spongy tissue called the trabecular meshwork into canal of Schlemm's and the episcleral venous system located in the anterior chamber, eventually ending up at the SVC and RA

7

What is IOP measuring?

How is it measured?

  • IOP is the measurement of the fluid pressure inside the eye
    •  the globe is a relatively noncompliant compartment and the volume of the internal structures is fixed, except for the aqueous fluid and choroidal blood volume
    • The quantity of the aqueous fluid and choroidal blood volume regulates intraocular pressure
  • IOP determined by:
    • production of aqueous humor
    • drainage of aqueous humor
    • changes in choroidal blood volume or pressure
    • extraocular muscle tone
  • Normal IOP: 10-20 mmHg

8

What can increase intraocular pressure?

What can decrease intraocular pressure?

  • Increase:
    • drugs- ketamine, succ
    • position changes
    • coughing
    • valsalva, straining
    • vomiting
    • HTN
    • LA
    • laryngoscopy
    • hypercarbia/hypoventilation/hypoxia
    • lid pressure
    • eye compression
    • mydriasis (dilation)
  • Decreased:
    • drugs- most anesthetic drugs, NDMR, hypertonic solutions, dextra, mannitol
    • hypotension
    • hypothermia
    • hyperventilation
    • pupil miosis (constriction)

9

Topical opthalmic drugs:

Acetazolamide (diamox)

Ecothiophate

  • Acetazolamide (Diamox)
    • topical carbonic anhydrase inhibitor
    • used to treat gloucoma
    • induces diuresis, decreases IOP, reduces aqueous humor production
    • may cause K depeletion, want pre-op labs
  • Ecothiophate
    • topical plasma cholinesterase inhibitor
    • used to tx gloucoma
    • produces miosis
    • systemic absorption may cause total body inhibition of plasma cholinesterase
      • caution with Succ, mivacuronium, and toxicity with ester-type anesthetics
      • very long duration of action, stop 4-6 wks preop

10

Topical Ophthalmic drugs:

Phenylephrine

Acetylcholine

Timolol

  • Phenylephrine
    • topical alpha agonist
    • produces mydriasis
    • associated with severe HTN
  • Acetylcholine
    • produces miosis
    • Can cause bradycardia and acute bronchospasm
  • Timolol
    • topical beta blocker
      • used to tx gloucoma
      • produces miosis; reduction of aqueous humor production
      • may cause bradycardia, bronchospasm, exacerbation of CHF, hearth block

11

Topical ophthalmic drugs

Ketorolac and diclofenac

Mitomycin C

Atropine and Cyclopentolate

  • Ketorolac and Diclofenac
    • used for inflammation
  • Mitomycin C
    • chemotherapeutic drug
  • Atropine and cyclopentolate
    • cycloplegic (paralizes ciliary muscles of the eye)
    • pupil dilation
    • SE: agitation, disorientation, psychotic reactions

12

What is the Oculocardiac reflex?

  • Trigeminal-vagal reflex
  • Pressure on the globe of the eye, pain, or traction on the extraocular muscles causes bradycardia, atrioventricular block, ventricular ectopy, negative inotropy or asystole
  • Can also be caused by:
    • retrobulbar block
    • orbital injections
    • trauma
    • hypoventilation
  • Occurs most often during strabismus surgery
    • esp under topical anesthesia

13

Oculorcardiac Reflex:

How can you reduce occurence?

How can you treat?

  • To reduce occurence:
    • maintain normal ETCO2, SpO2
    • pretreat with anticholinergic (atropine or glyco)
  • Treatment
    • stop stimuus
    • assess ventilation
    • Atropine 7µg/kg
    • LA (lidocaine) into muscle

14

What should your pre-op assessment include for an opthalmic case?

  • May be high risk population
  • Elderly have co-morbidites
    • may not be able to lie still or supine w/some chronic conditions
    • SOB, cough, nasal drip, reflux, OSA, back pain
  • Pediatric patient may be difficult to get to cooperate

15

How should you prepare for an opthalmic case?

  • make sure pre-op ophthalmic drops are given
  • continue home medications
  • educate pt about being awake/still during to surgery
  • avoid over-hydration
  • control HTN
  • control BS
  • No steroid coverage needed
  • dry secretions
  • treat reflux
  • good operative positioning.

16

What are the goals of anesthesia for an eye surgery?

  • safety
  • akinesia
  • analgesia
  • minimal bleeding
  • avoidance or obtundation of the oculocardiac reflex
  • prevent increase IOP
  • awareness of drug interactions
  • smooth emergance
    • avoid retching, vomiting, coughing

17

Retrobulbar block:

positioning

sedation

 

  • Supine with HOB up 10-15 degrees
  • Sedation:
    • propofol in small increments (20mg) but no analgesia, pt may startle with needle insertion
    • Remifentanil (0.3-0.5 µg/kg) lasts 2-5 minutes while block is going in
    • Caution with versed, may use depending on age
    • infusions not necessary, you want pt aware during surgery

18

Retrobulbar block:

Procedure

complications

  • Procedure:
    • LA instilled by injection posterior to eye directly into the orbital cone
    • 2% lidocaine/0.75% bupivicaine, 1:1 ration, 2-3 ml
    • hyaluronidase assed for tissue penetration
    • provides akinesia and analgesia
  • Complications
    • Retrobulbar hemorrhage (most common)
    • Globe perforation
    • OCR
    • sz
    • resp arrest

19

Peribulbar block:

compared to retrobulbar

onset time

complications

Technique

  • Safer than retrobulbar block b/c muscle cone is not penetrated (it goes into the extraconal space)
  • Slower onset of action (10 min vs 5 min)
  • requires higher volumes of LA
  • Lower incidence of complete akinesia of eye
  • Globe perforation and failure of block are most common complications
  • Technique:
    •  blunt needle is  inserted thru skin and advanced along the orbit floor directed parallel to the globe, thru the lower lid, toward the sphenoid bone.  Local anesthetic is instilled into the extraconal space (outside the muscle cone) and will slowly penetrate toward the optic nerve.

20

Sub-tenon block:

Where is it done?

What does it do?

SE

  • LA injected under Tenon's fascia
  • Analgesia for the iris and anterior eye
  • SE: some conjunctival edema

21

What block provides anesthesia to the eyelids?

Complications?

  • Facial nerve block (CN VII)
  • Complications:
    • facial droop
    • vocal cord paralysis
    • respiratory distress

22

How is topical anesthesia done for eye surgery?

What does it anesthetize?

disadvantage?

  • Instillation of LA onto the eye
    • proparacaine
    • tetracaine
    • lidocaine
  • Anesthetizes only the cornea and the conjunctiva
  • Sedation may be requires- pt needs to be cooperative but still
  • Disadvantage:
    • potential eye movement
    • increased patient anxiety and discomfort

23

How should you do the sedation for eye surgery?

  • Propofol bolus of 0.5 mg/kg for block placement only
  • versed 0.5-1 mg and/or fentanyl 12.5-50 mcg
  • Avoid CO2 buildup under the drapes

24

What should you consider when providing general anesthesia for an eye procedure?

Induction

Maintenance

emergence

Post-op

  • Induction:
    • smooth intubation
    • LMA ok
    • avoid ketamine and Sch
    • blunt responses to airway maneuvers
    • avoid pressure on eye
    • avoid N2O
  • Maintenance:
    • avoid hypoventilation/may want mild hyperventilation
    • treath HTN
    • avoid bucking or moving
    • avoid direct pressure on eye
  • Emergence
    • smooth
    • pretreat with antiemetics
  • Post-op
    • Treat PONV
    • good pain control

25

What is Gloucoma?

  • Increased IOP
  • Open-angle
    • Sclerosis of trabecular tissue- develops slowly and bilaterally
    • Angle btwn iris and cornea is correct, but drainage canals become clogged
    • Tx: miosis, decrease production of aqueous humor, and trabecular stretching
  • Angle closure or closed angle
    • peripheral iris moves into direct contact with cornea, mechanically obstructing aqueous flow
      • acute process
    • Tx: immediate surgery

26

What are the surgeries for Gloucoma?

How is the anesthetic managed?

  • Surgery:
    • laser trabeculoplasty
    • Trabeculectomy
    • Tube-shunt surgery
  • Anesthetic management
    • continue medical management to maintain miosis
    • limit use of anticholinergics (b/c they cause dilation)
    • Avoid increases in IOP
    • If severe acute gloucoma attack (dry pale painful eye) treat with Mannito or acetazolamide

27

What are Cataracts?

What are the surgeries?

How is anesthetic managed?

  • Opacification of the crystalline lens
    • Cataracts are the leading cause of treatable blindness
  • Surgery: Surgical removal of the lense
    • ICCE w/IOL
    • ECCE w/IOL- more often used
  • Anesthetic management
    • Topical block with minimal sedation or regional block

28

What is Retinal detachment?

What are the surgical treatments?

  • A separation of the retina from its attachments to its underlying tissue within the eye
    • most are result of a retinal break, hole, or tear
  • Surgical treatments:
    • scleral buckle
    • vitrectomy
    • pneumatic retinopexy
    • cryotherapy

29

What is intravitreal injection of gas?

When can you use N2O after this procedure?

  • Also called pneumatic retinopexy, used to treat detatched retina
    • insoluble or poorly diffusible gas is injected to tamponade retinal break against the wall of the globe
  • Nitrous after this procedure
    • Sulfur hexafluoride (SF3) wait 10 days
    • Perfluoropropane(C3F8) wait 30 days
    • Air wait 5 days

30

What is an open globe injury?

What is the concern?

Anesthetic goals?

  • Open globe: when the integrity of the outer membranes of they eye is disrupted by blunt or penetrating trauma
  • Concern with wanting to treat the open eye injury but pt may have full stomach
    • May not be able to use Sch- increased IOP and fasiculations might push out eye fluid
  • Ophthalmic blocks usually contraindicated
  • Goals:
    • limit increase in IOP
    • need motionless surgical field