ENT Part I Flashcards
How many muscles of the eye are there?
6
These muscles are innervated by the oculomotor nerve (CN III)
Superior rectus, inferior rectus, medial rectus, and inferior oblique.
This muscle is innervated by the abducens nerve (CN VI)
Lateral rectus. Moves the eye down and outward.
This muscle is innervated by the trochlear nerve (CN IV)
Superior oblique (moves the eye down and out)
Functions of the oculomotor nerve.
Innervates 4 of the eye muscles (superior rectus, inferior rectus, medial rectus, and inferior oblique).
Also causes pupillary constriction and eyelid opening.
Innervation of the trigeminal nerve
This is a SENSORY nerve with two branches
1) Ophthalmic branch
- Innervates upper eyelid, conjunctiva, and cornea
- Nasociliary branch of the ophthalmic nerve gives sensory to the medial canthus, lacrimal sac, and ciliary gangion (cornea, iris, and ciliary body)
2) 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 for 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)
Where is aqueous humor produced?
2/3 is made in the posterior chamber by the ciliary body. Once produced, it is then 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 IOP and what factors determine it?
Normal IOP is 10-20mmHg.
4 players in determining IOP:
- Production of aqueous humor
- Drainage of aqueous humor
- Changed is the choroidal blood volume or pressure
- EOM (extraocular muslce) tone
The globe of the eye is a pretty non-compliant structure, and the volume of the compartments is fixed, with these two exceptions
Aqueous fluid and choroidal blood volume.
These volumes can change and regulate the IOP.
These factors can increase the IOP
Drugs:
- Ketamine
- Sux (This can actually cause a 8mmHg increase in IOP d/t fasciculations. This can be a 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!)
Other factors that increase IOP:
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 the 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 glaucome med must be stopped 4-6 weeks prior to surgery
Ecothiophate
This med is a topical anticholinesterase. It causes inhibition of plasma cholinesterases d/t systemic absorption. This can lead to problems with sux and 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. It aids by preventing excessive cellular proliferation that could result in scarring.
Nerves that mediate the oculocardiac reflex (OCR)
Trigeminal and vagal
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 (remember that hypercarbia will result in increased 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 the surgeon to stop the stimulus. Let them know what is happening.
- Assess their ventilatory status (what is their EtCO2 looking like?)
- 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, you’ll probably have to do a general anesthetic.
Conditions that make it 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?
Make sure they continue their home medication regimen. Let the patient know that they need to lie still and may be awake for the procedure.
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, we put the patient out 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). However, this provides no analgesia, so the patient may startle on needle insertion.
Remifentanyl is another option (.3-.5mcg/kg). Lasts 2-5 minutes, which is 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 given for retrobulbar block
LA is 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.
Complications of retrobulbar block
Retrobulbar hemorrhage most common* Globe perforation OCR Seizures (d/t subarachnoid injection) Resp arrest
Peribulbar block
Safer than retrobulbar because it is not injected within the cone.
Requires higher volumes of LA.
Onset is slower.
Lower incidence of eye akinesia
Most common complications are globe perforation and block failure.
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, and 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 that the pt is still and 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 .5mg/kg for block placement only
Midazolam .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
- Smooth intubation (want to avoid SNS response that can increase IOP). Want to 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
- Can ask the surgeon how much coughing the patient is able to 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
If severe attack, Mannitol or Acetazolamide (Diamox)
What is the leading cause of treatable blindness?
Glaucoma
Usual anesthesia given for glaucome surgery
Regional block or topical 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 is necessary, then give fasciculating dose of roc first.
Eye blocks are usually contraindicate 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
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
Head up to decrease edema Observe for edema and bleeding Give humidified O2 Watch for pneumothorax and resp failure Steroids and racemic epi can help control laryngeal edema
Is jet ventilation considered an open or closed system?
Open.
Remember that you MUST have 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.
These are 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:
1) Nasal trumpet
2) A small catheter in nasopharynx that terminates just above the laryngeal opening
3) A ETT tube that is cut short and placed in nasopharynx, extending just beyond the soft palate
4) 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?
1) A jetting needle attached to a laryngoscope or bronchoscope
2) Transtracheal catheter through the cricothyroid membrane
3) 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, and minimal bleeding.
What are some of the characteristics of the laser beams used?
They have one wavelength, the 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
1) Reduce the flammability of the ETT (metal wrapping, fluid filled cuff, etc)
2) 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.
3) 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, antibiotics
May need to reintubate, or even trach, and control ventilation
Check ABGs, SpO2, CXray, etc
