Question 1

What are the main differences between topical and nerve-blocking local anesthetics?

Accepted Answer

Topical local anesthetics like dyclonine and benzocaine are rapidly absorbed through mucous membranes and skin, producing short-lived anesthesia suitable for over-the-counter applications. Nerve-blocking agents such as lidocaine and bupivacaine provide prolonged anesthesia and pain control for medical procedures but are used at low concentrations due to transient neurologic pain.

Question 2

How does tissue vascularity affect the duration of ophthalmic anesthesia?

Accepted Answer

Tissue vascularity directly determines anesthesia duration in ophthalmic applications. Normal cornea has the longest duration, while inflamed conjunctiva has the shortest, requiring repeated applications of agents like proparacaine and tetracaine. Higher blood flow in inflamed tissue increases drug absorption and reduces anesthetic effect.

Question 3

Why is lidocaine often combined with vasoconstrictors in clinical practice?

Accepted Answer

Lidocaine readily escapes into systemic circulation from muscles, gastrointestinal, and respiratory tracts. Adding vasoconstrictors like epinephrine constricts blood vessels, reducing absorption and systemic toxicity. This combination allows lidocaine to maintain localized anesthetic effects while minimizing adverse systemic exposure and improving clinical efficacy.

Question 4

What makes bupivacaine suitable for prolonged anesthesia procedures?

Accepted Answer

Bupivacaine is an amide-linked local anesthetic that preferentially blocks sensory fibers over motor fibers, making it ideal for extended pain control. It can be continuously infused through catheters to provide adequate anesthesia for several days, making it valuable for procedures requiring sustained anesthetic coverage.

Question 5

Why are topical local anesthetics unsuitable for sensitive eye areas?

Accepted Answer

Most topical anesthetics are irritants and cannot be directly applied to sensitive areas like the eyes. Specialized ophthalmic agents such as proparacaine and tetracaine are formulated specifically for ocular use and applied as single drops to avoid tissue damage and irritation.

Question 6

How do benzocaine and other low-solubility topical agents maintain localized anesthesia?

Accepted Answer

Topical local anesthetics with low aqueous solubility, such as benzocaine, can be applied directly to wounds where they remain localized and produce sustained effects. Their poor water solubility prevents rapid absorption through tissue, allowing prolonged local anesthetic action at the application site.

Question 7

What are the clinical advantages of cocaine as a topical local anesthetic?

Accepted Answer

Cocaine is an ester of benzoic acid and methylecgogine that provides both anesthesia and vasoconstriction locally. It is particularly beneficial for upper respiratory tract surgeries, where it anesthetizes tissue while shrinking the mucosa. Available as 1%, 4%, and 10% solutions, the lower concentrations are preferred to reduce toxicity.

التخدير الموضعي: العوامل الشائعة وتطبيقاتها

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