ENT Part I Flashcards
How many muscles of the eye are there?
6
These muscles are innervated by the oculomotor nerve
Oculomotor nerve = CN III
- Superior rectus
- medial rectus
- inferior rectus
- inferior oblique.
This muscle is innervated by the abducens nerve
abducens nerve = CN VI
- Lateral rectus (LR6)
- Moves the eye down and outward.
This muscle is innervated by the trochlear nerve
trochlear nerve = CN IV
- Superior oblique (SO4)
- moves the eye down and out
Functions of the oculomotor nerve.
- Innervates 4 of the eye muscles
- superior rectus
- medial rectus
- inferior rectus
- inferior oblique
- Also causes pupillary constriction and eyelid opening.
Innervation of the trigeminal nerve
3 branches total, but two SENSORY branches for the eye
-
Ophthalmic branch
- Innervates upper eyelid, conjunctiva, and cornea
-
Nasociliary branch of the ophthalmic nerve
- sensory to the medial canthus, lacrimal sac, and ciliary gangion (cornea, iris, and ciliary body)
- Also reulates oculocardiac reflex
- Maxillary branch - Sensory to lower lid
Topical anesthesia eye drops do a great job at blocking this, but not this
- Good for blocking the trigeminal nerve, which innervates the cornea.
- Bad at blocking the eyelids = Need extra anesthesia to relax the lids for traction.
Injury to this nerve can result in total blindness
-
Optic nerve (CN II) which is part of the optic chiasm
- nerve, artery, and sympathetic nerves
Where is aqueous humor produced?
-
2/3 is made in the posterior chamber by the ciliary body.
- Once produced, it is actively moved from the posterior to the anterior chamber via an active sodium pump mechanism.
- 1/3 is produced by passive filtration through vessels in the iris
How fast is aqueous humor produced?
2uL/min
This is the same as 0.12mL per hour.
Sooooo not very fast!
How is aqueous humor eliminated?
- It drains out of the eye through a spongy tissue called the trabecular meshwork.
- From the meshwork, it drains into Schlemm’s canal and the episcleral venous system located in the anterior chamber, eventually ending up at the SVC and RA.
What is normal IOP and what factors determine it?
Normal IOP is 10-20mmHg
-
4 players in determining IOP:
- Production of aqueous humor
- Drainage of aqueous humor
- Changes in the choroidal blood volume or pressure
- EOM (extraocular muslce) tone
The globe of the eye is a pretty non-compliant structure, the volume of the compartments is fixed, with these two exceptions
- Aqueous fluid
- Choroidal blood volume.
These volumes can change and regulate the IOP.
These factors can increase IOP
Major problem if the globe of the eye is exposed (in eye trauma) because it will lead to spillage of contents of the eye. Gross!
- Drugs:
- Ketamine
- Sux (up to 8mmHg increase in IOP d/t fasciculations.
- Other:
- Position changes
- coughing
- valsalva maneuver
- straining, vomiting
- HTN
- injection of local anesthesia
- laryngoscopy
- hypercarbia
- lid pressure, eye compression, forceful eyelid squeeze
These factors will decrease IOP
Drugs:
- Most anesthetic drugs
- NDMRs
- Hypertonic solutions (3%NS, mannitol, etc)
Other:
- Hypotension
- hypothermia
- hyperventilation (low CO2 –> similar to decreasing ICP!)
Examples of topical ophthalmic drugs and their effects
-
Acetazolamide
- Used to tx glaucoma
- Induces diuresis
- May cause K+ depletion
- want preop labs
-
Ecothiophate
- Used to tx glaucoma
- Topical anticholinesterase
- maintains miosis
- May cause inhibition of plasma cholinesterase;
- caution with succinylcholine and toxicity with ester-type local anesthetics
-
Phenylephrine - Alpha agonist;
- causes mydriasis
- Associated with severe HTN
-
Acetylcholine - Cholinergic drugs
- constrict pupil
- Can cause bradycardia and acute bronchospasm
-
Timolol - Used in the tx glaucoma
- Topical beta blocker
- May cause bradycardia, bronchospasm, CHF
-
Ketorolac and Diclofenac
- Both are NSAIDs - Used for inflammation
- Mitomycin C - Chemotherapeutic drug
- Atropine = Pupil dilation
- Cyclopentolate = Potent pupil dilation
This glaucoma med must be stopped 4-6 weeks prior to surgery
Ecothiophate
- topical anticholinesterase
-
inhibition of plasma cholinesterases d/t systemic absorption
- sux (prolonged NMB)
- ester-type LA toxicity (because the ESTERs and metabolized by plasma ESTERases)
This chemo agent is used ophthalmically to promote smooth healing of the eye
Mitomycin C.
- prevents excessive cellular proliferation results in scarring.
Nerves that mediate the oculocardiac reflex (OCR)
- Trigeminal (afferent)
- Vagal (efferent)
S/S of the OCR
- Bradycardia
- AV block
- ventricular ectopy
- asystole
What triggers the OCR?
- Pressure on the globe
- pain
- traction on the EOMs
- retrobulbar block
- eye trauma
- hypoventilation
- ( hypercarbia increases IOPs)
OCR occur most often during this type of surgery****
Strabismus surgery
(due to manipulation of the EOMs) This was italicized on the ppt. Possible test question.
How can you try to prevent the OCR, and how do you treat the OCR if it happens?
Prevention:
- Maintain normal EtCO2
- Pretreat with anticholinergics like Glyco (this is not normally necessary)
Treatment:
- Tell surgeon to stop the stimulus. Let them know what is happening.
- Assess their ventilatory status (what is their EtCO2 looking like?) –> may want to hyperventilate
- Atropine if necessary in 7mcg/kg increments -
- Injection of LA into the EOMs
What is a big thing you need to assess for before an eye surgery?
- Is the patient able to cooperate and lie still?
- If not, do a general anesthetic.
- Conditions it is difficult to lie supine and lie still:
- SOB, OSA, chronic cough, nasal drip, reflux, nausea, Parkinson’s, Alzheimer’s or claustrophobia, mentally disabled, back pain, pediatric patients
What to tell you patient regarding before eye surgery?
- continue their home medication regimen
- Let them know they need to lie still and may be awake for the procedure.
- Avoid overhydration –> awake and may have to pee
Goals of anesthesia for eye surgery
- Safety (ability to manage airway with limited access),
- control HTN
- avoid overhydration
- akinesia
- analgesia
- taking steps to avoid the OCR
- preventing increase in IOP
- smooth emergence (avoiding retching, vomiting, coughing etc than can increase IOP and rupture stitches)
- awareness of drug interactions (ecothiophate and sux/ester-LAs)
Advantage of regional over general anesthesia for eye surgeries
- Provides good analgesia
- Less occurance of N/V
- Faster recovery and discharge
- Cheaper
Anesthesia/sedation for retrobulbar block
- Usually, patient sedated for the block and then wake them back up.
- They are supine with HOB up 10-15 degrees. Nasal cannula in place with ASA monitors.
-
Propofol can be given in small increments (20mg).
- no analgesia = patient may startle on needle insertion.
-
Remifentanyl is another option (.3-.5mcg/kg).
- Lasts 2-5 minutes, long enough for placement of the block.
- Can give midazolam in addition to these two meds depending on the pt’s age.
- Infusions are not necessary because we want the patient to be aware an unobtunded during the procedure.
Local anesthesia for retrobulbar block
- LA deposited posterior to the eye in the orbital cone.
- 2% lido with 0.75% bupivicaine in a 1:1 ratio.
- 2-3cc total are deposited.
- Hyaluronidase can be added for tissue penetration.
- This block provides excellent akinesia and analgesia.
- “Conan’s Cup” puts pressure on eye to spread the local
Complications of retrobulbar block
- Retrobulbar hemorrhage most common*
- Globe perforation
- OCR
- Seizures (d/t subarachnoid injection)
- Resp arrest
- Optic nerve dammage
Peribulbar block
- Safer than retrobulbar → it is not injected within the cone.
- Requires higher volumes of LA.
- Onset is slower.
- Lower incidence of eye akinesia
- Most common complications
- globe perforation
- block failure → may not hit the top part of the eye (lower parts and muscles will be anesthetized, but top will not)
Subtendon blockade
- LA is injected under the Tenon’s fascia
- Excellent analgesia for the iris and anterior eye
- Can cause conjunctival edema
- This is not common anymore because topicals work so well.
Facial nerve block
- Gives anesthesia to the eyelids.
- Not very common.
- 2-3cc of LA is given where the facial nerve exits the chondyle of the mandible.
- Complications include:
- facial droop
- vocal cord paralysis
- respiratory distress
Let the patient know that they will have facial droop after the procedure**
Topical anesthetics for eye surgery
- Proparacaine, tetracaine, and lidocaine are commonly used
- Provides anesthesia to the cornea and conjunctiva ONLY**
- Need to provide extra sedation so the pt is still/cooperative.
- Disadvantage of this is that the eye can still move
- no akinesia
- pt may have increased anxiety and discomfort
Sedation for eye surgeries
- Have the pt position themselves comfortably
- ASA monitors and nasal cannula
- Propofol bolus of 0.5mg/kg for block placement only
- Midazolam 0.5-1mg and/or fentanyl 12.5-50mcg
- Avoid build-up of CO2 under the drapes.
- May need suction under the drapes.
General anesthesia goals during eye surgery
induction
maintinence
emergence
post-op
Induction
- Smooth intubation
- avoid SNS response which can increase IOP).
- blunt responses to airway maneuvers.
- Avoid ketamine and sux (can increase IOP) -
- Avoid N2O
- LMA is ok
Maintenance
- AVOID hypoventilation (will increase EtCO2 and IOP) -
- Treat HTN promptly
- Avoid bucking and patient movement
Emergence
- Prevent coughing, bucking, and vomiting
- Pre-treat with antiemetics
- Ask the surgeon how much coughing patient can tolerate.
- For some procedures, it is more important to prevent coughing/bucking than others.
Post-op - Treat pain and PONV
What is open-angle glaucoma, and how is it treated?
- Slow development caused by sclerosis of the trabecular meshwork
- resulting in blockage of drainage of the aqueous humor.
- Treatment
- miosis (pupillary constriction)
- decreasing production of aqueous hummor
- stretching of the trabecular meshwork
What is closed-angle glaucoma, and how is it treated?
- This is an acute process where the peripheral aspect of the iris bulges forward and prevent drainage of the aqueous humor.
- Treatment involves immediate surgery.
Anesthesia goals for glaucoma surgery
- Continue medical management to maintain miosis
- Limit the use of anticholinergics like glyco and atropine (cause dilation)
- AVOID increases in IOP
- Severe attack = Mannitol or Acetazolamide (Diamox)
What is the leading cause of treatable blindness?
Glaucoma
Usual anesthesia given for glaucoma surgery
Regional or topical block with sedation
Surgical treatments for retinal detachment
- Scleral buckle
- vitrectomy
- pneumatic retinopexy
- cryotherapy
These gases can be used for intravitreal injection of gases to treat retinal detachment
-
Sulfur hexafluoride (SF3)
- No N2O for 10 days post-injection
-
Perfluoropropane (C3F8)
- No N2O for 30 days post-injection
- If patient has had surgery for retinal detachment, it’s important to know when that was, and what gas was used if within the last month. But no one uses nitrous anymore anyway, so who the fuck cares.
Anesthesia considerations for open globe eye injury
- Pt is probably a full stomach.
-
RSI should be performed, but we don’t want increased IOP, so no ketamine or sux.
- Probs use high dose Roc.
- If sux necessary, give defasciculating dose of roc
- Eye blocks are usually contraindicated in open globe injury.
Considerations for strabismus surgery
- Strabismus is often due to myopathy of the EOMs
- Common surgery for pediatrics
- High incidence of PONV
- Risk for MH
- Highest risk for OCR d/t muscle manipulation
The superior laryngeal nerve innervates this muscle. Damage causes this.
Cricothyroid muscle.
- This muscle normally elongates and tenses the cords.
- Thus, unilateral damage causes a weak, lower pitched voice, and puts the patient at risk for aspiration.
This nerve inneravtes all intrinsic muscles muscles of the larynx, except the cricothyroid muscle. Damage results in this.
Recurrent laryngeal nerve.
- Unilateral injury causes a paralyzed VC and vocal hoarseness.
- Bilateral injury results in respiratory distress.
Treatment of corneal abrasion.
Give antibiotic ointment and cover the eye.
Chemical injury to the eye is often from
Betadyne or chlorprep getting in the eye.
What is the principal concern for ALL ENT surgeries??
Providing a clear, free, and unobstructed airway***
General Principles of ENT Surgery
SIMPLE
- Provide complete control of airway with no risk of aspiration
- Control ventilation with adequate oxygenation and CO2 removal
- Provide smooth induction and maintenance of anesthesia
- Provide a clear, motionless surgical field, free of secretions
- Not impose time restrictions on the surgeon
- Not be associated with any risk of airway fire or CV instability
- Allow safe emergence with no coughing, bucking, breath holding, laryngospasm
- Produce a pain-free, comfortable, alert patient at the end
Pre-op assessment and planning for airway surgery
Pre-Op Assessment
- NEED EXCELLENT AIRWAY ASSESSMENT
- Size, mobility, location of any airway lesions
- If stridor is present, it implies an airway diameter of pharynx reduved
Considerations for maintenance of airway surgery
- Anticholinergics – reduce vagal tone, secretions, and cause bronchodilation
- Corticosteroids – Decrease edema, reduce PONV, and prolong the effects of LAs
-
PONV – give antiemetics
- pt may have blood in the stomach causing N/V
- throat packing may be in place
- Surgeon may want controlled hypotension
- A-line – Nitroglycerin, nitroprusside, etc.
Post-op considerations for airway surgery
- Observe for edema and bleeding
- Steroids and racemic epi can help control laryngeal edema
- Head up to decrease edema
- Give humidified O2
- Watch for pneumothorax and resp failure
Is jet ventilation considered an open or closed system?
Open.
- Remember there MUST be a way for the air to be exhaled passively.
- Because you must have an exit, you also have an entrance for air to be entrained into the system with each burst from the jet ventilator d/t the venturi effect
Advantages and disadvantages of a closed system with a cuffed ETT
Advantages:
- Routine technique
- Protection of lower airway
- Control of airway
- Control of ventilation
- Minimal pollution by volatile anesthetics
Disadvantages:
- Surgical access and visibility limited
- High inflation pressures needed with small ETT tubes
- Vocal cord damage with intubation
- Risk of laser airway fire
These are the only types of cuffs that are resistant to lasers
Cuffs wrapped in metal foil (usually aluminum or copper).
- Also, cuff will be filled with methyline blue.
- This helps detect cuff rupture and the liquid helps prevent airway fire.
Examples of open systems
Natural airway with insufflation
Jet ventilation
Technique of spontaneous ventilation with insufflation of anesthetic gases
Patient has natural airway, and anesthetic gases are insufflated via one of these mechanisms:
- Nasal trumpet
- A small catheter in nasopharynx that terminates just above the laryngeal opening
- A ETT tube that is cut short and placed in nasopharynx, extending just beyond the soft palate
- Gases can also be insufflated via the side-arm channel of a laryngoscope or bronchoscope
What are some of the vessels through which jet ventilation can take place?
- A jetting needle attached to a laryngoscope or bronchoscope
- Transtracheal catheter through the cricothyroid membrane
- A small-diameter cuffed ETT specifically designed for jet ventilation
Jet ventilation can provide respiratory rates as high as
- 100-150 breaths per minute
- Automated high-frequency ventilators have alarms that will automatically interrupt ventilation if pressure limits are reached
Anesthetic technique with jet ventilation
- Preoxygenation
- IV induction
- NDMR***
- Laryngoscopy
- Topical local anesthesia
- LMA or ETT inserted
- Ventilation with 100% oxygen until surgeon ready to site the rigid laryngoscope with jetting needle
- Anesthesia maintained with propofol infusion + remifentanil infusion
- At the end of surgery: LMA reinserted, NDMR antagonized, Anesthetic infusions stopped, Smooth awakening and LMA/ ETT removal
How can you continuously assess that your jet ventilation is adequate?
- Observing chest movements
- O2 sats
- Listening for changes in sounds during air entrainment and exhalation
- Observing airway patency
Complications of jet ventilation
- Crepitus
- Pneumothorax
- Gastric distention
Why are lasers used in airway surgery?
Usually for their thermal effects to cut, coagulate, and vaporize tissues.
What are some of the advantages of laser use in airway surgery?
- Very precise
- minimal edema
- minimal bleeding.
What are some of the characteristics of the laser beams used?
- They have one wavelength
- they move in the same direction, and its beam is parallel
Why are CO2 lasers common in airway surgeries?
D/t extreme precision and shallow depth of burn
What are some of the hazards of laser use in airway surgery?
- AIRWAY FIRE!!!**
- Atmospheric contamination
- Plume of smoke and fine particulates
- Deposition in lungs
- Leads to pneumonia, inflammation, viral infections
- Perforation of a vessel or structure
- Embolism
- Inappropriate energy transfer
- Reflection and scatter of beams can cause immediate or delayed injury to normal tissue, especially the eyes
- CO2-reacts at surface causing corneal damage
- Nd: YAG/argon-pass thru the cornea to the retina
- TAPE PT EYES CLOSED AND COVER WITH WET GAUZE
- Pt may need special goggles as well – PROTECT YOUR OWN EYES
Risks for airway fire and damage it can cause
Risks/damage
- Lasers cause intense heat that can ignite a fire
- CO2 lasers can penetrate an ETT and ignite a fire.
- N2O supports fires!!!!
- Damage is usually caused to the subglottic, epiglottic, and oropharyngeal structures
- Smoke inhalation can result in bronchospasm and chemical injury that can lead to respiratory failure
Strategies to reduce the incidence of airway fires
- Reduce the flammability of the ETT
- metal wrapping, fluid filled cuff, etc
- Remove flammable materials from the airway
- ex– making do without an ETT by using jet ventilation or intermittent extubation.
- Pt may experience periods of apnea.
- Use lowest tolerated O2 concentrations
Treatment of airway fires
- Remove burning ETT and/or other material from airway
- Stop ventilation D/C oxygen
- Flush the pharynx with cold saline
- Mask with 100% O2
- Laryngoscopy and bronchoscopy to assess damage
- Administer humidified gas, steroids, antibiotic
- May need to reintubate, or even trach, and control ventilation
- Check ABGs, SpO2, CXray, etc
