7- Local Anaesthetics Flashcards
Why is the corneal epithelium considered one of the most innervated tissues in the human body?
It has approximately 2.2 million nerve endings, making it highly sensitive to stimuli like chemical, mechanical, and temperature changes.
What types of stimuli do the sensory fibers in the corneal epithelium respond to?
C,M,T
Chemical, mechanical, and temperature stimuli
Which nerve supplies the cornea, and what is its pathway?
LPC nerve
The long posterior ciliary nerve, which originates from the nasociliary branch of the ophthalmic division of the trigeminal nerve.
At what temperature should cloranfenocol and proxymetacaine be stored?
Between 2°C and 8°C and in the fridge.
How long can proxymetacaine be stored at room temperature, and what should be done afterward?
It can be stored below 25°C for one month, after which it must be discarded.
How should all local anaesthetics be disposed of?
As clinical waste, following the guidelines for Prescription Only Medicines (POM)
What are the common clinical procedures that use local anaesthetics?
Changing/removing sutures, applanation tonometry, and gonioscopy.
What is the role of local anaesthetics in Goldmann applanation tonometry (GAT)?
They anesthetize the cornea for measurement of intraocular pressure by flattening a 3.06 mm diameter circle of the cornea.
How can local anaesthetics enhance the uptake of mydriatic medicines?
By increasing corneal permeability, leading to better drug absorption and enhanced pupil dilation.
Why are local anaesthetics helpful when administering multiple ocular drops?
They reduce discomfort, minimize tearing reflex, and enhance drug retention in the conjunctival sac.
What are the four criteria for an ideal local anaesthetic?
Fast-acting, sustained effect long enough for procedures, totally reversible, and no systemic or local side effects.
What are the components and type of lidocaine with fluorescein?
4% lidocaine hydrochloride and 0.25% fluorescein, classified as an amide-type anaesthetic.
What is the concentration and type of oxybuprocaine?
0.4% oxybuprocaine hydrochloride, an ester-type anaesthetic.
What is the concentration and type of proxymetacaine?
0.5% proxymetacaine hydrochloride, an ester-type anaesthetic.
In what concentrations is tetracaine available, and what type is it?
0.5% and 1.0% tetracaine hydrochloride, an ester-type anaesthetic.
What are the three key components of a local anaesthetic’s structure?
A,I,H
Aromatic hydrophobic portion, intermediate linkage, and hydrophilic amine.
What is the role of the aromatic hydrophobic portion in a local anaesthetic?
It provides the anaesthetic effect by interacting with nerve membranes.
What are the two types of intermediate linkages in local anaesthetics, and how do they affect metabolism?
Ester linkages (metabolised by plasma cholinesterases) and amide linkages (metabolised in the liver).
Why are local anaesthetics formulated as hydrochloride salts?
To increase water solubility and extend their shelf life.
Why is it important to determine hypersensitivity to ester or amide local anaesthetics?
Hypersensitivity to one type can affect the choice of anaesthetic for future treatments.
How do local anaesthetics block nerve impulses?
**By preventing the temporary increase in sodium ion permeability, thus blocking depolarisation of the nerve membrane.
Where on the nerve cell do local anaesthetics exert their effect?
They bind to a specific site on the nerve cell membrane.
How does the duration of local anaesthetic action relate to its contact time with nerve tissue?
Longer contact with nerve tissue results in a longer duration of action.
What is the systemic and ocular toxicity of local anaesthetics when applied topically?
They have low systemic and ocular toxicity.
Why are local anaesthetics considered stable in solution if stored correctly?
Because the hydrochloride salt formulation resists degradation.
What should patients expect after the instillation of a local anaesthetic?
A temporary stinging sensation and lachrymation.
Why should patients avoid rubbing their eyes after local anaesthetic use?
They lose the protective blink reflex and cannot feel corneal abrasions.
What specific activities should patients avoid post-local anaesthetic use?
Activities like swimming or exposure to airborne irritants that could increase the risk of corneal injury.
How should the cornea be examined if there is doubt about its condition after anaesthetic use?
Use fluorescein to check for abrasions before the patient leaves.
Which local anaesthetic requires refrigeration for optimal storage?
Proxymetacaine.
At what temperature should lidocaine, oxybuprocaine, and tetracaine be stored?
Below 25°C.
Why is it critical to store local anaesthetics correctly?
To maintain their stability and efficacy over time.
How does local anaesthesia improve the retention of cycloplegic drugs like cyclopentolate?
By reducing tearing reflex and irritation, allowing more drug to remain in the conjunctival sac.
Why is it important to consider iris pigmentation when using local anaesthetics and mydriatics?
Iris pigmentation can influence the uptake of drugs and pupil dilation.
What is the primary use of fluorescein with lidocaine in Goldmann tonometry?
To visualize the corneal contact area during intraocular pressure measurement.
What are the risks associated with hypersensitivity reactions to ester-type local anaesthetics?
Though uncommon, they may necessitate avoiding ester-type anaesthetics in the future.
Why is it important that local anaesthetics do not tend to interact with other drugs?
It ensures their safe use in combination with other ocular treatments.
How does the use of a topical anaesthetic improve the efficiency of subsequent ocular procedures?
It numbs the cornea, reducing discomfort and improving drug absorption.
What is the clinical significance of lachrymation after local anaesthetic use?
Lachrymation dilutes the drug, potentially reducing its effectiveness if excessive.
What should clinicians consider when using multiple doses of local anaesthetics?
The potential for cumulative effects and ensuring proper spacing to maintain efficacy.
