LA Flashcards
What is LA
any technique to induce absence of sensation in a specific part of the body
What are some non pharmacological methods of inducing LA
electrical nerve stimulation, nerve ablation, pulsed radiofrequency
What do LA drugs do
loss of nociception, blocks afferent activity in peripheral and CNS
What are some adverse effects of LA
prolonged anesthesia/paresthesia due to ( inflection, hematoma, excessive fluid pressure in a confined cavity)
- systemic reaction ( could inadvertently enter the systemic circulation when injected into blood vessel or region of highly vascularised area), leading to depressed CNS syndrome, allergic reaaction, vasovagal episode, cyanosis due to LA toxicity
what is the chemistry of LA
consists of lipophilic group connected via an ester or amide to an ionisable group
whats the difference in the duration of action between ester links and amide links
ester links have shorter duration of action as they are more prone to hydrolysis
what kind of LA are ester group
cocaine, procaine, chloroprocaine, tetracaine
what kind of LA are amide group
lidocaine, mepivacaine, bupivacaine, etidocaine, prilocaine
What form of LA is the most active
charged form as it cannot readily exit closed Na channel
What form of LA is important for rapid penetration of lipid membrane
Uncharged form, less effective when injected into acidic tissue as smaller proportion will be non ionised and available for diffusion into the nerve
What is LA onset of action determined by
offset of action and systemic toxicity, and not by absorption or distribution as LA are usually injected around nerves
What is systemic absorption of LA dependent on
dosage, site of injection, tissue binding, local blood flow, use of vasoconstrictors like epinephrine, drug properties
What is ester type LA hydrolysed by
circulating butyrylcholinesterases into inactive metabolites in the blood
What is amide type LA metabolised by
microsomal CYP450 isoenzymes in the liver.
What type of patients will experience reduced metabolism for amid type LA
reduced metabolism in patients with liver disease, reduced hepatic blood low, or if they are taking concomitant medications competing for or inhibiting cyp450 enzymes
