ENT I Flashcards by Maggie McDonell

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

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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

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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

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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

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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

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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

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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

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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)

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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

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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

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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

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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

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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

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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

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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.

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What are the goals of anesthesia for an eye surgery?

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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

Retrobulbar block:

positioning

sedation

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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

Retrobulbar block:

Procedure

complications

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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

Peribulbar block:

compared to retrobulbar

onset time

complications

Technique

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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.

Sub-tenon block:

Where is it done?

What does it do?

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

What block provides anesthesia to the eyelids?

Complications?

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

How is topical anesthesia done for eye surgery?

What does it anesthetize?

disadvantage?

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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

How should you do the sedation for eye surgery?

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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

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

Induction

Maintenance

emergence

Post-op

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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

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

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

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

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

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

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

What is Strabismus? What are they at higher risk for?

* Misalignment of visual axis with ambylopia, diplopia, and loss of stereopsis * generally a myopathy of extraocular muscles * Higher risk: * MH * PONV * OCR from direct muscle manipulation

What are some eye complications in non-ophthalmic procedures?

* Corneal abrasions * blindness * chemical injury * thermal injury * hemorrhagic tetinopathy * retinal ishcemia * acute glaucoma attack

ENT I Flashcards

(33 cards)