Anesthetics Flashcards
What is the chemical structure of an anesthetic?
lipophilic synthetic aromatic or heterocyclic residue, intermediate ester or amide linkage and a weakly basic tertiary amine terminal
Why is lipophilicity of key component of anesthetics?
it can penetrate cells (corneal layers), skin, CNS, and blood brain barrier
What does myelin do to anesthetics?
enhances its sensitivity independent of diameter (lipid myelin attracts lipophilicity)
Are small diameter nerves more or less sensitive than large diameter nerves?
small (highly active) are more sensitive to anesthetics = fire more rapid and has repeated opportunity to bind drug (large = recover quicker - usually have life giving functions)
What is the order of effects for anesthetic targets?
pain > cold > warmth > touch > deep pressure > motor
what does the intermediate chain linkage on an anesthetic link?
a lipophilic aromatic residue with a hydrophilic amino group - longer linkage enhances potency
Is the receptor on the nerve lipophilic or hydrophilic?
hydrophilic - the more lipophilic the more effective (potency)
How are ester linkage anesthetics metabolized?
locally by pseudocholinesterase (PChE)
What are the 3 parent structures in the ester group? and which anesthetics are in those groups?
PABA (tetracaine, procaine, benzocaine, and benoxinate), MABA (proparacine), and BA (cocaine)
How are the amide linked anesthetics metabolized?
hepatic metabolism, urinary and biliary excretion
What is the most common eye-care amide anesthetic?
lidocaine
What is the difference in action between esters and amides?
amides are longer acting, have greater systemic effects and readily cross the blood brain barrier
How do anesthetics increase absorption and intercellular permeability?
break the corneal epithelium tight junctions
What is the schirmer I test?
without anesthetic = measures basal tearing + reflex tearing
with anesthetic = measures basal tearing (neurogenic reflex tearing is suppressed)
What is the best anesthetic to use when collecting cultures?
Preservative free proparacine - least antibacterial/antifungal effects
What are proparacine and tetracaine used for?
tonometry, gonio, sutures, nasolacrimal massage, ultrasound
what is an advantage of proparacine over tetracaine?
proparacaine has less sting - but has potential to increase corneal thickness (cause swelling) and affects goldmann and pachymetry
what is an advantage of tetracaine over proparacaine?
tetracaine has greater corneal toxicity but penetrates more than proparacaine
Which ester anesthetic produces the least amount of corneal compromise but has the potential to increase thickness?
benoxinate
what is the onset and duration for topical anesthetics?
(mainly esters) - 30sec onset and about 15min duration (procaine is longer)
Why are amide anesthetics usually longer lasting and take longer to take effect?
they are not locally metabolized - need to go to liver
How can you double lidocaine duration?
use with epinephrine for vasoconstriction
If a patient has a red eye following anesthetic use - are they allergic to the drop?
not necessarily - vasodilation of lidocaine may relax nerves responsible for vascular tine and if it was a long half-life anesthetic they may have a red eye
Why would you pair an anesthetic with a vasoconstrictor?
reduce absorption and systemic toxicity, reduce metabolism, keep effect localized, and reduce bleeding at injection site
What is the only anesthetic that vasoconstricts instead of vasodilates?
cocaine
what are the systemic adverse effects of cocaine?
excitement, convulsions, rapid palpitations, nausea, and delirium
what are the ocular adverse effects of cocaine?
desquamation, mydriasis, lid retraction (unilateral)
Why do TCADs, MAOIs, epinephrine, phenylephrine, Guanethidine, and Reserpine cause adverse reactions with cocaine?
these drugs also excite the sympathetic nervous system - amplify the effects of cocaine and cause serious damage
what are some adverse effects of cocaine on ocular tissues?
desquamation, corneal edema, conjunctival hyperemia, allergic conjunctivitis, and lacrimation
who is more susceptible to desquamation?
patients over age 50 - reduced blink rate (cells die), reduced tear production, and increased evaporation
How do you determine if your patient has conjunctival hyperemia vs. allergic conjunctivitis from an anesthetic?
allergic conjunctivitis will itch (both will be red eyes)
Why do you need to know what anesthetics your patient may have been on for surgeries or procedures?
they may have nystagmus or visual hallucinations from long lasting (long half-life) anesthetics
what are the cardiovascular anesthetic adverse effects (except from cocaine)?
decreased excitability, decreased cardio force/conduction –> hypotension = cardio collapse
what are some anesthetic cautions?
cholinesterase deficiency, hyperthyroidism, cardiac disease, allergy history, and sensitivity to similar drugs
What is the primary sign of anesthetic abuse syndrome?
yellow-white stromal ring at the active site
What are some signs and symptoms of anesthetic abuse syndrome?
corneal epithelium defect (stromal edema and descemet’s folds), disciform stromal infiltrates, KP, hypopyon, hyphema, lid edema, neovascularization, discharge
What are some non-anesthetic alternatives (allergy to amide/esters)?
Injectable = 1% Benadryl or saline Topicals = EMLA, lidoderm patch, or iontophoresis
