5: Local Anesthetics - Smith Flashcards
define local anesthetic
- block n conduction when applied locally to n tissue in appropriate concentrations and act on any part of nervous system and on every type of n fiber
have two “I”s in chemical name
amides
where are amides and esters metabolized?
amides - liver (i)
esters - in bloody by pseudocholinesterase
MOA anesthetics
- inhibit excitation (generation) and conduction of n impulse by increasing the threshold for depolarization
- cell membrane
- prevents increase in permeability of membranes to Na+ (sodium channels)
- can act on K+ channels
which n fibers are more sensitive to anesthetic?
small and unmyelinated
order of function
pain temp touch propioception deep pressure movement
increasing pH will ______ effectiveness of anesthetic
decrease
why use epinephrine with local anesthetic?
- increases duration of action
- decreases systemic toxicity
- provides hemostasis
where should epinephrine not be used?
ears
nose
penis
toes/fingers
concentration of epi
1:100,000 - safer at 1:200,000
dilute to 1:200,000 by (ex) drawing 5 cc of epi and lidocaine and 5 cc lidocaine
\_\_ % contains \_\_mg/ml or cc 0.25% 0.50% 1% 2%
2.5 mg/ml or cc
5
10
20
10 cc of 1% lidocaine contains _____ mg
100 mg
how many mg of drug in …
- 15cc of 2% lidocaine
- 15cc of 0.50% marcaine
- 10cc of 0.25% marcaine
- 10cc of 50/50 mix 2% lidocaine and 0.50% marcaine
- 300
- 75
- 25
- 100 lido, 25 marc
toxic dose lidocaine
4.5 mg/kg
= 300mg plain
= 500 mg w/ epi
toxic dose marcaine
2.5 mg/kgk
= 175 mg plain
= 225 mg w/ epi
how many cc of 2% lidocaine plain can be given before toxic dose reached?
15cc
how many cc of 0.50% marcaine plain cna be give before toxic dose reached?
35 cc
Lidocaine/xylocaine
onset =
DOA =
risk =
3- 5 min
3-4 hr
- vfib, cardiac arrest
bupivacaine/marcaine/sensorcaine
onset =
DOA =
5-10 min
6-8 hr
- often mixed with lidocaine to increase DOA and prolong anesthesia
what could you add to make an injection less painful?
- topical refrigerant (ethyl chloride)
- sodium bicarb (buffer solution)
- also use right syringe and smallest needle
- warm the anesthetic
injection technique
- antiseptic
- needle inserted and wheal raised
- aspiration to prevent intravascular injection
- needle advanced forward and anesthetic deposited
- redirection of needle
describe mayo block/ring block
- used for bunion surgery
- proximal first interspace and advanced plantarly
- needle redirected medially along dorsal aspect of metatarsal
- needle directed from dorsal to plantar on medial side of met
- needle directed from medial to lateral on plantar side of met
- deep peroneal n block at distal interspace
“ring block around 1st met plus one more”
6 nerves blocked with ankle block ***
posterior tibial n. saphenous n. medial dorsal cutaneous n. intermediate dorsal cutaneous n. sural n. deep peroneal n.
5 nerves blocked with ankle block ***
post tibial n. saphenous n. superficial peroneal n. sural n. deep peroneal n.
where do you do a post tibial n. block?
- palpate pulse of post tib a and inject POSTERIOR to artery
where do you do a saphenous n block?
- lateral to great spahenous v
- anterior and lateral to medial malleolus
where do you do a superficial peroneal n block?
- lateral to EHL tendon to get medial dorsal cutaneous n
- 1 to 1.5cm anteriro to lateral malleolus for intermediate dorsal cutaneous n
lemont’s n
plantarflec and invert foot to visualize n
where do you do a sural n block?
1 to 1.5 cm posterior and inferior to lateral malleolus
where do you do a deep peroneal n block?
- inject b/w EDL and EHL just lateral to ant tibial a (palpate pulse)
what is an infiltration block?
injection of anesthetic directly at procedure site for example, excision of wart of biopsy
complications assoc with local anesthetics
- syncope
- allergic rxn
- arrhythmia (PVC, lwo pulse, low oxygen, chest pain, vfib)
- cardiac arrest
