Local anesthetics Flashcards
what is the goal of local anesthesia
to tremporarily block pain and feeling in a specific area during minor medical procedures
why do we not just use analgesics instead of local anesthetics
- systemic side effects we can avoid
- can be addictive
why do we not just use general anesthetics instead of local?
- can still feel some pain
- longer recovery
- it is ok if patient is concious for procedure
general features of local anesthetics
- inhibit the transmission of all electrical signals in nerve and muscle
- administered peripherally as opposed to IV
- inhibit pain without producing unconcssiousness
- all are derivatives of cocaine that do not produce euphoria
local anesthetics mechanism of action
- ionized LAs competitively inhibit Na+ channels at level of PNS
- reversible and concentration-dependent
- binding site is on cytoplasmic surface of the receptor
- LAs block the channel until they diffuse away from site of administration
what happens when low vs, high concentrations of local anesthetics are administered
- at lower concentrations, small nerve fibers are blocked to inhibit pain
- at higher concentrations, motor fivers are blocked to inhibit movements
what is the benefit of combining LAs with epinephrine
- LAs act on SM and cause vasodilation
- epinephrine is a vasoconstrictor so it reverses this
- slows the removal of drug to prolong action
- Con: can delay healing by reducing blood flow
types of local anesthetics
surface anesthesia
infiltration anesthesia
feild block
nerve block
characteristics of surface anesthesia
- topical gel
- short lasting
- penetrates a few mm
- without epinephrine local anesthetics increase blood flow to skin - improves perfusion of burned skin for better healing
characteristics of infiltration anesthesia
- inject subcutaneously at region where inscision is to be made
- epinephrine doubles duration
- uncommon but large doses may be toxic
characteristics of field block anesthetics
- inject subcutaneously
- goal is to prevent transmission coming from more peripheral sites
- small amounts or anesthetic are injected into nerve fibres in the feild around the incision site
characteristics of nerve block anesthetics
- inject drug in immediate vacinity of nerve
- blocks transmission of all signals distal to block
- less drug needed
- required good anatomical knowledge
Epidural: nerve block example
- inject into epidural space
- can use a variety of drugs - commonly lidocaine and bupivacaine
- blocks APs arriving at spinal cord from peripheral nerves
- also diffuses across dura into subarachnopid space
- manages pain in caudal body structures (childbirth and knee or hip surgery)
adverse effects on CNS if local anesthetic diffuses into bloodstream
- as dose increases, the first systemic effect is drowsiness and numbness around mouth
- at higher concentrations: agitation then seizures due to release of intracellular Ca2+ in CNS causeing excess glutamate release
- RARE: at massive doses CNS depression and respiratory failure
adverse effects on CV system if local anesthetic diffuses into bloodstream
- decreased excitability of myocardium - may casue arrhythmias
- if bolus IV is accidentaly injected and travels to heart causes cardiac arrest
Lidocaine can be used to treat cardiac arrythmias which might have been an adverse effect of local anesthetics…
- used to inhibit depolarization of cardiac myocytes
- damaged heart tissue might lead to premature APs causing some arrythmias
- signals from these damaged regions of myocardium are blocked at low drug concentrations because channels are open for longer
properties of cocaine as a local anesthetic
- all LAs are derivatives of cocaine
- used topically today
- applied to oral/nasal muscoa for nose and throat procedures
- inhibits NE re-uptake, stimulates vasoconstriction, less bleeding
- can cause local necrosis and produce severe CVS toxicity
properties of Procaine as a local anesthetic
- ester-linked anesthetic
- low potency
- low tissue solubility
- still used for some dental procedures but replaced largely by lidocaine
properties of Lidocaine as a local anesthetic
- most widely used local anesthetic
- amide-linked instead of either (better for allergies)
- numerous routes of administration
- moderate solubility
- faster onset and longer duration of action than procaine
- injectible form provides 30-60 minutes of effect
properties of bupivicaine as a local anesthetic
- almost as widely used as lidocaine but prefered for longer procedures
- can be administered a variety of ways except topical
- highly soluble and highly potent
- slower onset but longer duration than lidocaine
- greater CVS toxicity risk (IV bolus - severe arrhythmias)
local anesthetics in order from shortest to longest duration of action
Procaine
Lidocaine
Bupivicaine
