Eye Surgery Flashcards
Sclera
outermost layer
tough, fibrous, white of the eye
cornea - most anterior part
Focus power
from curvature of cornea
Middle Layers of the Eye
choroid
ciliary body
iris
Choroid
layer of blood vessels
located posteriorly
Ciliary Body
- behind iris, produces aqueous humor
- adjusts focus on lens by reducing tension on suspension fibers or zonules of the lens
Iris
pigmented, controls light entry
Iris: Parasympathetic Stimulation
- iris sphincter muscle contracts
- miosis = pupillary constriction
Iris: Sympathetic Stimulation
- Iris dilator muscle contracts
- mydriasis or dilatation
Innermost Layer of the Eye
Retina
- photoreceptors –> neural firing
- no capillaries –> choroid layer gives o2 (detachment can cause vision loss)
- pars plana –>area btwn edge of cornea and end of retina
Where does safe entry for vitrectomy occur?
Pars Plana
Center of the eye
- vitreous gel
- attaches to vessels and optic nerve
- traction of vitreous on retina = detachment
- vitrectomy tx for scarring, bleeding or opacification
OCR
Ocular Cardiac Reflex
cause: globe pressure or traction of extraocular muscles or any orbital contents
s/s: bradycardia, AV block, ventricular ectopy, asystole
-more frequent in peds
Which muscle manipulation is seen commonly with OCR?
medial rectus traction
Which nerve is involved with triggering OCR?
trigeminal-vagal reflex
What factors can worsen OCR response?
hypoxia and hypercarbia
OCR Tx
- Ask surgeon to stop, asses, deepen anesthetic
- If persists - atropine
- consider robinul
Pretreatment for OCR?
atropine or robinul, esp if pt has conduction block or BB
Blood supply to the eye is dependent on…
Intraocular perfusion pressure
MAP - IOP
What regulates IOP?
amount of aqeous and blood volume
Normal IOP
10-22 mmHg
> 25 is pathological
Productino of aqeous humor?
constant, regulated by carbonic anhydrase
IOP: Arterial Pressure
- sudden increase in B/P–> increase IOP, drains quick
- sudden decrease in B/P–> drop IOP, loss of autoreg
IOP: Venous Pressure
- increased CVP increases IOP (more than B/P does)
- coughing –> no drain –> increase IOP up to 40x
IOP: Respiration & CO2 tension
Decreased PaCO2 –> fast drop in IOP (choroidal vasoconstriction)
Increased PaCO2–> slow increase in IOP
*fast RR may increase IOP from insufficient venous drainage
IOP: Acid Base
Metabolic Acidosis –> decreases choroid vessel volume, therefore IOP
Metabolic Alkalosis–> increases the choroid volume and IOP
IOP: External Forces
lid retraction
blocks
hemorrhage
etc..
IOP: Anesthetic Drugs
-most lower or do not effect IOP
-inhalation agents–> lower B/P, therefore choroidal vol
relax muscles
pupil constriction - enables aqueous outflow
IOP: IV agents
propofol- decreases IOP
ketamine - may increase (raise b/p, doesnt relax muscles
etomidate - myoclonus, maybe not a good idea
opioids - generally decrease IOP
IOP: Muscle Relaxants
- intubation will increase IOP (b/p) regardless of NMB if pt isnt deep enough
- NDNMB do not alter IOP (except curare - decrease)
- Sch increases IOP
IOP: Succinycholine
increase IOP
starts w/i 1 minute
-increases 5-10 mmHg for 5-10 mins due to contraction
-glaucoma pt rxn is about the same
Acetazolamide (Diamox)
- carbonic anhydrase inhibitor
- decreases aqueuos production - inhibits Na pump responsible
- decreases IOP
- dose = 500 mg, acts w/i minutes
What should you watch for with use of acetazolamide (diamox)?
- lyte disturbances
- chronic use depletes K, Na and bicard –> met acidosis
Mannitol
- osmotic diuretic
- can use intraop to drop IOP
- increases circulating blood volume (CHF)
- max effect 30-45 min, baseline within 5-6 hrs
Topical eye drop absorption
subq < topical eye < IV
Echothiophate
- topical anticholinesterase drug
- maintains miosis, for glaucoma
Caution with echothiophate…
- systemic absorption –> total inhib of plasma cholinesterases (think sch, bad)
- may dispose to ester-type local toxicity
- long acting, 4-6 weeks until normal enzyme activity
Phenylephrine
- used topically to dilate pupil
- alpha adrenergic agonist
Drugs used to constrict pupil…
pilocarpine & acetycholine
- cholinergic drugs
- bronchospasm and acute bradycardia reported
Timolol
- beta blocker, used topically to reduce IOP
- systemic absorption –> brady, bronchospasm, CHF exacerbation
Flomax (Tamsulosin hydrochloride)
-selective alpha antagonistic properties
-binds to iris dilator muscles
-effects iris dilation and complicates surgery
“floppy iris” 7-24 days after d/c
Preop Indications: EKG
-new chest pain, decreased exercise tolerance, palpitations, near syncope, fatigue, etc.
Preop Eval: HTN
-severe HTN –> postop complications
stage 3 = syst > 180 or diast >110
-reschedule until 2 wks of antihtn therapy
Preop Eval: DM
-check fasting BG, use insulin to maintain BG 150-250
Preop Eval: Steroid Use
- don’t usually need stress dose, just use regular
- may need if unexpected hypotension, fatigue and nausea
Critical Lyte Results
Na < 120 or > 158
K < 2.8 or > 6.2
Urea Nitrogen
s/s renal decompensation
-critical if > 104
Polydipsia, polyuria, wt loss…
-check BG
critical if < 46 or > 484
H&H critical result
Hct < 18% or > 61%
Hgb < 6.6 or > 19.9
Hemorrhage potential
serious –> orbital and oculoplastic
intermed–> vitreoretinal, glaucoma, corneal transplant
least–> cataract surgery
Is if safe to perform cataract surgery if pt is on warfarin?
Yes, most agree it is safe
Regional Techniques
akinesia (immobility)
lessens nausea, keeps em comfy
midaz, fent, prop
Facial Nerve Block
- useful when complete immobility of eyelids is necessary
- blocks: orbicularis oculi
Facial Blocks Typically used…
- Van Lint
- Atkinson
- O’Brien
biggest risk is subcutaneous hemorrhage
Nadbath Rehman Blocks
- type of facial block - blocks entire trunk of facial nerve - expect facial droop for several hours
- close to vagus and glossopharyngeal - associated with vocal cord paralysis, laryngospasm, dysphagia and resp distress
Retrobulbar Block
- LA injected into muscle cone
- Atkinson needle, 1:1 mix bupivacaine 0.75% and lidocaine 2% plain
- result: anesthesia to globe, akinesia of extraocular muscle (drop IOP)
- superior rectus muscle may not be blocked –> intorsion on downward gaze
RBB Complications
- retrobulbar hemorrhage is most common
- OCR!
- proptosis (downward displacement)
- IV injection
- arterial injection
- optic nerve injection
- ocular perforation
- post-op strabismus from local tox
What monitoring is specific to and mandatory for RBB?
IOP, if no elevation then may proceed
RBB Optic Nerve injection
- optic nerve sheath is continuous with subarachnoid space–>
- contralateral amaurosis (no vision)
- obtundation
- resp arrest (occurs w/i 20 mins, resolves in 1 hr)
- vascular collapse (total spinal, medulla)
RBB Post Operative Strabismus
- from myotoxicity (bupivicaine)
- day after surgery -> vertical, double vision worsening over 2 months
RBB Contraindications
- bleeding disorders
- extreme myopia (longer glober = more risk)
- open eye injury
Peribulbar Block
- safer, less risk of RB hemorrhage
- multiple injection around eye, none to muscular cone
- onset = 9-12 min
- less complete akinesia
- more bruising
Sub-Tenon’s Block
- tennon’s fascia - surrounds globe and extraocular muscles
- LA diffuses into retrobulbar space
- blunt cannula
- less complications
Topical
- ok for small incision and phacoemulsion
- tetracaine 0.5% and lidocaine 4%
Ways to limit IOP response to larygoscopy
lidocaine 1.5 mg/kg
fentanyl 1-3 mcg/kg
alfentenil 20 mcg/kg
remifentanil 0.5-1 mcg/kg
Which procedure is emesis common after? Why?
Strabismus surgery, d/t vagal stim
Painful eye surgeries
scleral buckling
enucleation
open globe repair
Nitrous Oxide and Sulfur Hexaflouride
- d/c 15 minutes prior
- avoid for 7-10 days after
Nitrous Oxide and Perfluoropropane (C3F6)
-avoid nitrous for a month
Strabismus surgery
- extraocular
- shorten and lengthen opposite muscle
- OCR
- oral rae, avoid Sch
Retinal Detachment
extraocular
1-2 hrs
Vitrectomy
intraocular
gas bubble placed
1-2 hrs
