local anesthetics

Question 1

nerve cell is depolarized by flow of what current?

Answer 1

flow of Na current into intracellular space. repolarization is caused by outflow of K ions from intracellular to extracellular space.

Question 2

mechanism of action of local anesthetic

Answer 2

diffusion of unionized (uncharged) base form across nerve sheath –> re-equilibration of base to ionized (cation) form –> binding of ionized form to INSIDE if Na channel resulting it its blockade –> no Na can flow in and depolarize

Question 3

what terms onset time of local anesthetics?

Answer 3

pKa - the closer the pKa is to tissue p the more rapid the onset time.
pKa is defined as the pH at which the ionized and non-ionized forms exist in equal concentrations.

Question 4

which regional anesthetic blocks are associated with the greatest degree of systemic vascular absorption of local anesthetic?

Answer 4

intercostal > caudal > epidural > brachial plexus . sciatic-femoral > subcutaneous

Question 5

manifestations of local anesthetic toxicity (in chronologic order)

Answer 5

CNS tox: lightheadedness, tinnitus, perioral numbness, confusion; muscle twitching, hallucinations, tonic-clonic seizures, –> unconsciousness, respiratory arrest, –> cardiotoxicity, hypertension, tachycardia, decreased contractility and cardiac output, hypotension, sinus brady, ventricular dysrhythmias, circulatory arrest.

Question 6

what local anesthetic is associated with the risk of methemoglobinemia?

Answer 6

prilocaine and benzocaine (often used as spray for topical anesthesia)