Anesthesia For Eye Surgery Flashcards
1
Q
Where bone is the eye located in? What is the size of the eye?
A
- Located in the pyramidal bony orbit
- 24 mm in diameter
2
Q
What are the 3 layers of the eye wall?
A
- Sclera
- Uveal tract (middle layer)
- Retina
3
Q
What is the center of the eye filled with? And what is it attached to?
A
- Filled with vitreous gel
- attached to blood vessels & optic nerve
4
Q
What can traction of vitreous & retina cause?
A
Retinal detachment
5
Q
What is scarring, bleeding, or pacification of vitreous treated with?
A
Vitrectomy
6
Q
Where is the sclera located?
What is the most anterior part of the sclera?
A
- Outermost layer of the eye
- cornea is most anterior
7
Q
What part of the eye provides the most focusing power?
A
The curvature of the cornea
8
Q
Where is the uveal tract located?
What are the 3 structures found in the uveal tract?
A
- Located in the middle layer of the eye
1. Choroid
2. Ciliary body
3. Iris
9
Q
What is the choroid?
Where is it located in the eye?
A
- Layer of blood vessels, located posteriorly
- Found in the middle layer of the eye wall
10
Q
What does the ciliary body produce?
Where is it located?
What does it do?
A
- produces aqueous humor
- Located behind the iris
- Adjusts focus on lens by reducing tension on suspension fibers/zonules of the lens
11
Q
Where is the iris located?
What is unique about it?
What does it do?
A
- Located in the uveal tract, in front of the ciliary body
- it is pigmented
- controls light entry into eye
12
Q
What happens to the iris with sympathetic stimulation?
A
Causes the iris dilator muscle to contract = dilation or mydriasis
13
Q
What is mydriasis
A
Dilation of the iris
14
Q
What happens to the iris with parasympathetic stimulation?
A
Iris sphincter muscle contracts = pupilary constriction or miosis
15
Q
What is miosis?
A
Pupilary constriction
16
Q
Where is the retina located?
What important receptors are located in the retina?
A
- innermost layer of the outer eye, ends 4 mm behind iris
- photoreceptors are located here
17
Q
- What are photoreceptors located?
- what are they responsible for?
A
- Located in the retina
- light activates them to produce neural signal
18
Q
- Where is the pars plans located?
- What makes this area special?
A
- Located in retina, between limbus (edge) of cornea & end of retina
- area of safe entropy for vitectromy procedures
19
Q
When can ocular cardiac reflex occur?
A
With any stimulation of orbital contents including lid and periosteum
20
Q
What is the route of afferent impulses of ocular cardiac reflex (5)?
A
- Afferent impulse originates in orbital contents (via long and short ciliary nerves)
- To ciliary ganglion
- To ophthalmic division of trigeminal nerve
- To sensory nucleus of trigeminal nerve near fourth ventricle
- To visceral motor nuclei of the vagus
21
Q
What is the efferent limb of the ocular cardiac reflex?
A
Vagus nerve to the heart
22
Q
Does the ocular cardiac reflex occur more frequently in children or adults?
A
Children
23
Q
T/F OCR seen during more frequently during topical and general anesthesia vs. retrobulbar blocks?
A
True
24
Q
T/F Orbital injections (including retrobulbar blocks) CANNOT stimulate OCR?
A
False
25
Ocular cardiac reflex is considered a ____________ .
Trigeminovagal
26
What 3 things were mentioned to WORSEN OCR?
1. Hypoxemia
2. Hypercarbia
3. Medial rectus traction
27
What is normal intraocular pressure?
What is pathological IOP?
What regulates IOP?
- normal = 10-22
- pathologic > 25
- The quantity of aqueous and blood volume regulate IOP (everything else in eye is a relatively fixed volume)
28
Is production of aqueous humor constant? What is it’s production facilitated by?
- Production is constant
| - Production facilitated by carbonic anhydrase
29
What does increased IOP lead to?
- ocular HTN
| - Structural changes (optic disc and nerve fiber atrophy + optic artery occlusion)
30
What does decreased IOP lead to?
Fluid accumulation in the eye
31
What specific anesthetic events increased IOP? (5)
1. Events that increase BP
2. Laryngoscopy + intubation
3. Trendelenburg position
4. Coughing, straining, breath holding, vomiting
5. Direct pressure on eye from PRONE POSITION
32
Which 2 commonly used drugs are known to increase IOP?
1. Ketamine may as it usually increases BP & does NOT relax intraocular muscles
2. Succinylcholine increases IOP 5-10 mmHg for 5-10 mins d/t prolonged contracture of extraocular muscles
33
Which drug is associated with myoclonus and may not be appropriate for open globe procedures?
- Etomidate
34
By what 3 mechanisms do inhalation agents drop IOP?
1. Lower BP = decrease choroidal volume
2. Relax extraocular muscles and lower wall tension
3. Pupil constriction enables aqueous outflow
35
T/F most anesthetic drugs LOWER IOP, including IA, IV agents (propofol), and opioids?
True
36
Do nondepolarizing NMBs alter IOP?
No, with the exception of curare, which decreases it
37
How does a sudden increase in arterial pressure affect IOP?
Increases IOP, but soon dissipates due to drainage system
38
How does a sudden decrease in arterial pressure < 90 mmHg affect IOP?
- Drops IOP due to loss of autoregulation
39
What does a 60 systolic BP do to IOP?
Causes a 3-4 mmHgdrop in IOP due to decreased blood flow in eye
40
How is IOP affected by increased PaCO2?
Results in a slow increase in IOP
41
How is IOP affected by a fast RR?
May increase IOP due to insufficient venous drainage
42
How does a decreased CO2 affect IOP?
A FAST drop in IOP from choroidal vasoconstriction
43
How does metabolic alkalosis affect IOP?
Increases IOP due to increased choroid volume
44
How does metabolic acidosis affect IOP?
Decreases IOP due to decreased choroid vessel volume
45
Acetazolamide (diamond)
- Drug class?
- mechanism of action?
- Special considerations?
- carbonic anhydrase inhibitor
- decreases aqueous production by inhibiting Na+ pump responsible for secretion of aqueous humor==> decrease IOP
- IV dose = 500mg; woks in minutes; Check electrolytes as with chronic use Na, K, and bicarb are depleted leading to metabolic acidosis
46
What 3 electrolytes/compounds are affected by chronic use of carbonic anhydrase inhibitors?
- Depletion of Na+, K+, and bicarb
47
Mannitol
- Class?
- Mechanism?
- Considerations?
- Osmotic diuretic
- Used IV intraop to drop IOP
- increases circulating blood volume (CHF); max effect 30-45 minutes (baseline 5-6 hours); may require urinary catheter
48
Echothipate
- Class?
- Mechanism?
- Considerations?
- Topical anticholinesterase
- Maintains miosis for glaucoma
- Systemic absorption leads to total inhibition of plasma cholinesterase = prolonged muscle paralysis after Succs; may dispose to ester-type local toxicity; Very long acting (4-6 weeks for normal enzyme activity)
49
Phenylephrine
- Drug class?
- Mechanism?
- Considerations?
- Alpha adrenergic agonist
- Topically used to dilate pupil
- 2.5% causes less HTN than 10%, but will still aggravate BP in some
50
Pilocarpine and Acetylcholine
- Class?
- Mechanism?
- Considerations?
- Cholinergic
- Constricts pupil
- Bradycardia (M2) and acute bronchospasm (M3) have been reported
51
Timolol
- class?
- Mechanism?
- Considerations?
- Topical beta blocker
- used for glaucoma
- systemic absorption can cause bradycardia, bronchospasm, and CHF exacerbation
52
Flomax (Tamsulosin hydrochloride)
- class?
- Mechanism?
- Considerations?
- selective alpha antagonistic properties
- Binds to the iris dilator muscles, affecting iris dilation
- Complicates cataract surgery, iris remains floppy even after 7-28 days off therapy
53
Severe HTN can lead to postop complications. At what point should pt be rescheduled?
Stage 3 HTN (SBP > 180 or DBP > 110 mmHg)
| Reschedule sustained stage 3 client until 2 weeks of antihypertension prescription
54
Where should blood glucose level be maintained for diabetic patients?
150 - 250 mmHg
55
What are considered critical serum glucose levels?
< 46 mg/dL; >484 mg/dL
56
What are considered critical H&H results?
- Hct < 18% or > 61%
| - Hgb < 6.6 mg/dL or > 19.9 mg/dL
57
- Which eye surgeries are considered a serious hemorrhage risk?
- “. “ intermediate risk
- “. “ least hemorrhage risk
- Serious risk in orbital and oculoplastic surgery
- intermediate risk in vitreoretinal, glaucoma, corneal transplant
- least risk in cataracts (most agree safe to do cataracts with pt on warfarin)
58
T/F: Most agree it is safe to do cataract procedure with pt on warfarin?
True
59
What meds should be given in conjunction with regional for eye surgeries?
- Midazolam (0.5-1 mg)
- fentanyl (25-50 mcg)
- propofol (30-50 mg)
For amnesia and sedation
* Omit versed and fentanyl with limited cognitive reserve*
60
When are facial nerve blocks utilized?
When complete akinesis of the eyelids are desired (can’t squeeze eye shut/squint)
61
What are the 4 mentioned blocks that are used?
| What is the general difference between them?
1. Van Lint
2. Atkinson
3. O’Brien ———> these block orbicular oculi muscle
4. Nadbath Rehman Block -> block entire trunk of facial nerve
62
What is the major complication of Van Lint, Atkinson, and O’Brien facial nerve blocks?
Subcutaneous hemorrhage
63
What should be expected with Nadbath Rehman Blocks?
| What are major complications of Nadbath Rehman Blocks? Why?
- Expect lower facial droop postop for several hours
- Associated with vocal cord paralysis, laryngospasm, dysphagia & respiratory distress —> b/c injection is close to vagus and glossopharyngeal nerves
64
What is a retrobulbar block? What is the procedure?
- injection of LA w/in the muscle cone
| - Atkinson needle placed through skin and orbital septum close to bone at inferior temporal margin.
65
What meds are used for retrobulbar block?
1: 1 ratio of:
1. Bupivicaine (0.75%)
2. Lidocain (2%) plain
AND Hyaluronidase (to speed tissue penetration)
66
What is the result of a retrobulbar block?
Produces anesthesia of the globe, akinesia of the extraocular muscle and hypotonic (drop in IOP) from relaxation of extraocular muscles and decreased production of aqueous humor
67
Which muscle may not be blocked by retrobulbar block? How would you know?
- superior rectus muscle (outside the muscle cone)
| - able to tell if able to produce intorsion on downward gaze
68
What is the most common complication of retrobulbar block? What should you watch for?
What are 2 more complications of this block?
- Retrobulbar hemorrhage
- watch for OCR
- proptosis (downward displacement) and subconjunctival hemorrhage
69
What happens with arterial injection of local with retrobulbar block?
High brain levels via retrograde flow in internal carotid artery = CNS excitation and seizure possibly - usually transient
70
What happens with accidental injection into optic nerve shear with retrobulbar block (4)?
Why?
1. Contralateral amaurosis (complete lack of vision)
2. Obtundation
3. Respiratory arrest (occurs w/in 20 minutes, resolves w/in one hour)
4. Vascular collapse from depressant effect on medulla (total spinal)
- Can occur because optic nerve shear is continuous with subarachnoid space
71
What are the 3 contraindications to retrobulbar block?
1. Bleeding d/o (r/o RB hemorrhage)
2. Extreme myopia (longer globe more at risk of perforation)
3. Open eye injury (pressure of fluid behind eye may force intraocular contents out through wound)
72
- How is a peribulbar block performed?
| - Describe this Block in regards to it’s safety (3)
- multiple injections made around eye w/o entering the muscular cone
- safer approach, less r/o RB hemorrhage; globe perforations have been reported; increased likelihood of ecchymosis
73
Compare onset and degree of block of peribulbar block vs. retrobulbar block:
- onset of peribulbar block is longer (9-12 minutes) vs. retrobulbar block
- peribulbar block has less complete akinesia
74
- Describe Sub-Tenon’s Block procedure:
- Tenon’s fascia surrounds globe & extraocular muscles
- LA diffuses into retrobulbar space
- Blunt cannula placed under Tenon’s fascia
75
- Compare complications of Sub-Tenon’s Block vs. RBB and peribulbar block
Avoids use of sharp needles and less complications than RBB and peribulbar block
76
When is topical anesthesia acceptable to use in anesthesia? (2)
Small incision surgery and phacoemulsion
77
What are the advantages of topical anesthesia in eye surgeries?
- Avoids Complications of a block
| - Improved vision almost immediately after procedure
78
What are the disadvantages of topical anesthesia?
- Potential patient movement
| - increased anxiety and discomfort from microscope light
79
What meds are used and in what order for topical local for eye surgeries?
- Tetracaine 0.5% and lidocaine 4%
- 2 drops tetracaine given initially followed by 3 more doses of tetracaine or lidocaine every 5 mins just before surgery
80
Neither GA nor regional anesthesia for eye surgeries are shown to be safer, except in which case??
- Normally ruptured globes are done under general with ETT as the only choice
81
What 4 medications with doses are suggested for use to limit IOP increase to laryngoscopy?
1. Lidocaine (1.5 mg/kg)
2. Fentanyl (1-3 mcg/kg)
3. Alfentanil (20 mcg/kg)
4. Remifentanil (0.5-1 mcg/kg)
82
What advantages can an LMA offer vs. tube with eye surgeries? Disadvantages?
- advantage is that there is less coughing on emergence
| - disadvantage is potential for aspiration or laryngospasm and decreased access to airway
83
What eye procedure is emesis from vagal stimulation especially common?
Strabismus surgery — aggressively prevent and treat nausea
84
Severe post op pain us unusual in eye surgeries with the exception of these 3 procedures?
1. Sclera buckling
2. Enucleation
3. Ruptured globe repair
85
What can severe pain after eye surgery indicate? (3)
1. IO hypotension
2. Corneal abrasion
3. Other complications
86
Which types of surgeries should you consider not using N2O in?
Certain vitreoretinal procedures - retinal surgery
87
What are the 2 types of gas used for air bubbles for certain eye surgeries? And when should N2O be avoided with these?
1. Sulfur hexafluoride - D/c N2O 15 mins prior to bubble placement and avoid 7-10 days after
2. Perfluoropropane (C3F6) - Avoid N2O for 1 month after bubble placement
88
What is the purpose of air bubble injection in certain vitreoretinal procedures?
To tamponade the detached retina unto the globe
89
What is major consideration for open globe eye surgeries?
They are normally emergent with full stomachs, RSI indicated, controversy over use of succs
