Week 5 - MAC and Ophthalmic Anesthesia Flashcards
What is the definition of MAC?
A specific anesthesia service in which an anesthesiologist has been requested to participate in the care of a patient undergoing a diagnostic or therapeutic procedure
Anesthesia care that includes the monitoring of the patient by a practitioner who is qualified to administer anesthesia — provider of MAC must be able to convert to general when necessary
What is the difference between minimal, moderate, and deep sedation?
Minimal: normal response to verbal stimulation, unaffected airway/ventilation/cardiovascular function
Moderate: purposeful response to verbal or tactile stimulation, no airway intervention required, adequate spont ventilation, usually maintained CV function
Deep: purposeful response after repeated or painful stimulation, airway intervention may be required, spont ventilation may be inadequate, CV function is usually maintained
What are the goals of MAC?
- # 1 is Safety (maintenance of respiration and physiological reflexes
- Comfort (physiological and psychological)
- Cooperation
- Communication (with surgeon and patient) – set expectations
What is the dosing of Precedex for non-intubated procedural sedation?
Loading dose = 1mcg/kg over 10 mintues (adult)
Maintenance dose = 0.6 mcg/kg/hr and titrate 0.2-1 mcg/kg/hr
What is a normal intraocular pressure?
12-20 mmHg (16 +/-5mmHg)
- determined by volume of aqueous humor, vitreous and blood within the eye, scleral compliance, extraocular muscle tone exerting inward pressure
- increased pressure damages blood vessels
How can anesthesia increase IOP?
- Venous congestion (coughing or bucking can cause transient increases up to 40mmHg)
- Mechanical pressure on eye
- Extraocular muscle contraction (succinylcholine can produce an increase of about 9mmHg in 1-4 min after admin)
- Hypertension, Hypoxemia, Hypoventilation
- Ketamine? (does cause nystagmus)
What anesthetic agents decrease intraocular pressure? Which increase it?
Decrease IOP:
- Inhaled anesthetics (volatile agents > nitrous oxide)
- Propofol, Benzos, Opioids
Increase IOP:
-Succinylcholine
**NDMRs have no or minimal effect on IOP
What is the Oculocardiac Reflex? What can it be triggered by?
“Five and Dime” – trigeminal nerve (ophthalmic division) provides the afferent limb of OCR and vagus nerve provides the efferent limb
-Causes bradycardia, and other arrhythmias including junctional, AV blockade, multifocal PVCs, V-tach, or asystole
-can be triggered by pressure on the globe, traction on extraocular muscles, conjunctiva, or orbital structures, regional ophthalmic anesthesia such as a retrobulbar or peribulbar block, ocular trauma, or pressure on tissue within the orbital apex after enucleation
How do you manage the oculocardiac reflex?
1 notify surgeon to stop ocular manipulation
If bradycardia doesn’t resolve (and hypertensive) administer atropine or glycopyrrolate 10-20mcg/kg
Optimize oxygenation
CPR if necessary
What is the MOA and systemic effect of acetylcholine for ocular procedures?
Cholinergic Agonist – causes miosis
Effect: bronchospasm, bradycardia, hypotension
What is the MOA and systemic effect of acetazolamide for ocular procedures?
Carbonic Anhydrase Inhibitor – decreases IOP
Effect: diuresis, hypokalemic metabolic acidosis
What is the MOA and systemic effect of atropine for ocular procedures?
Anticholinergic – causes mydriasis
Effect: central anticholinergic syndrome
What is the MOA and systemic effect of cyclopentolate for ocular procedures?
Anticholinergic – causes mydriasis
Effect: disorientation, psychosis, convulsions
What is the MOA and systemic effect of echothiophate for ocular procedures?
Cholinesterase Inhibitor – causes miosis and decreases IOP
Effect: prolongation of succinylcholine and mivacurium paralysis, bronchospasm
What is the MOA and systemic effect of epinephrine for ocular procedures?
Sympathetic Agonist – causes mydriasis and decreases IOP
Effect: HTN, bradycardia, tachycardia, headache
What is the MOA and systemic effect of Phenylephrine for ocular procedures?
Alpha-Adrenergic Agonist – causes mydriasis and vasoconstriction
Effect: HTN, tachycardia, dysrhythmias
What is the MOA and systemic effect of scopolamine for ocular procedures?
Anticholinergic – causes mydriasis and vasoconstriction
Effect: central anticholinergic syndrome
What is the MOA and systemic effect of timolol for ocular procedures?
Beta-Adrenergic Blocking Agent – decreases IOP
Effect: bradycardia, asthma, CHF
What are the regional eye anesthetics?
“Needle Based” Blocks: Retrobulbar block (intraconal) and Peribulbar block (extraconal)
“Cannula Based” Block: local anesthetic is instilled via a blunt cannula and Sub-Tenon’s block
What are complications of a retrobulbar block?
- OCR (Initial pressure can cause OCR, then anesthetic effects ablate the response)
- Retrobulbar or superficial hemorrhage
- Patient on anticoagulants?
- Intraocular injection (globe puncture)
- Optic nerve trauma
- Intravascular injection
- Brainstem anesthesia
What will you see with Brainstem Anesthesia with a RBB?
Loss of consciousness
Apnea
Cardiac instability
Possible contralateral mydriasis and contralateral eye block
What will you see with Intravascular Injection with a RBB?
Loss of consciousness
Possible apnea
Possible cardiac instability
Seizure activity
What is a Sub Tenon’s Block?
Instilling LA through a blunt cannula into the space between the sclera and the sub-Tenon’s capsule
What are anesthetic considerations for cataract surgery?
- Relatively short cases 15-45 minutes
- Mainly topical anesthetic with RN sedation or MAC (Small doses of versed or no sedation at all)
- Retrobulbar or peribulbar anesthesia for difficult cases or when akinesia is desired (Short acting sedative and/or narcotic while block is placed, then versed as needed)
What are anesthetic considerations for retinal surgery?
- Retinal detachment due to trauma or chronic disease such as diabetes
- Longer case (~2-3 hours) and requires akinesa
- Usually done under regional block with sedation or GA
- Surgical interventions: sceleral buckle, vitrectomy, laser, cryotheraphy, and injection of intravitreal gas
- Keep MAP at baseline to ensure optic nerve perfusion
**avoid nitrous oxide if surgeon injects sulfur hexafluouride into the aqueous humor (gas bubble can take 10-28 days to reabsorb)
What is a scleral buckle?
- The element pushes in, or “buckles,” the sclera toward the middle of the eye
- This buckling effect on the sclera relieves the pull (traction) on the retina, allowing the retinal tear to settle against the wall of the eye
*The buckle effect may cover only the area behind the detachment, or it may encircle the eyeball like a ring
What are anesthetic considerations for glaucoma surgery?
- Can be done under sedation with ocular block (typically RBB), or GA
- Make sure not to contribute to increased IOP — “Smooth” GA induction and remind patient not to cough, or to warn surgeon and team if they need to cough
- Be aware of IOP and pharmacology – avoid drugs that cause midriasis (caution with scopolamine)
What are anesthetic considerations for strabismus surgery “squint”?
- GA
- High incidence of OCR
- High incidence of PONV
- Increased risk of MH?
- Goal to have patient awake and alert for adjustments as soon as possible
- Some surgeons will inject local at end, or topical tetracaine
What are anesthetic considerations for eye trauma open globe injuries?
- Balance of risk of IOP with RSI
- Control of airway supersedes
- Consider pretreatment with non-depolarizer
- Consider slight rev. Trendelenburg with induction
- Continuation of muscle relaxation for case
