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60 Cards in this Set
- Front
- Back
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Check out the pharm LA cards because I'm not rewriting all of these. . . .
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What is the chronology of events of local anesthetics?
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1) LA deposited near nerve. Drug diffuses away d/t tissue binding, circulation, and local hydrolysis. what's left penetrates the nerve sheath. 2) LA molecules permeate nerve's axon membranes and reside there and in the axoplasm. Speed and extent depend on pKa and lipophilicity. 3) Ionized LA binds to voltage-gated Na channels and prevent opening by inhibiting conformational change. They bind in the channel's pore and block the Na path. 4) onset and recovery are governed by slow diffusion of LA in and out of whole nerve |
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Why are LAs usually prepared with a hydrochloride salt?
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they are basic in nature and not readily water soluble
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What is the pKa range for LAs?
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7.6-8.9
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What does adding sodium bicarbonate do to lidocaine?
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increase non-ionized portion of drug -speeds onset -improves quality of block -may decrease pain on injection of local |
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What happens when epinephrine is added to LA by manufacturer?
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they are acidic with pH around 4.5 -slows onset time |
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What is the duration of LAs related to?
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its degree of protein binding -proteins serve as reservoirs for LAs -if there are a lot of proteins in the vicinity of the nerve axon, can result in prolonged conduction blockade |
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What is the onset of action of local anesthetics related to?
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pKa value
also lipid solubility |
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What is potency of local anesthetics related to?
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lipid solubilitiy
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What protein is of most interest for LAs?
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alpha-I-glycoprotein
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Which LAs do not produce relaxation of vascular smooth muscle resulting in vasodilation?
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lidocaine, ropivacaine and cocaine
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What does the vasodilation produced by LAs result in?
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an increase in the drug's absorption, limited duration of action and increased chance of toxicity
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List the areas in order from most vascular to least vascular. (also low to high tissue binding)
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intravenous > tracheal > interpleural > intercostal > caudal > epidural > brachial plexus > femoral/sciatic > subcutaneous
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What does the degree of systemic absorption of LA depend on?
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dose administered - vascularity of injection site - presence of vasoconstrictor - physiochemical properties of the LA
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Does adding a vasoconstrictor to LA have any analgesic effect?
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it may occur from interaction with alpha adrenergic receptors in the brain and spinal cord
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Which ester LA is not metabolized by cholinesterase enzyme?
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cocaine - it's metabolized by liver
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What patients is plasma cholinesterase activity slowed in?
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atypical plasma cholinesterase - on chemo treatments - OB pts - liver disease or increased BUN
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What organ can extract LAs from the circulation?
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the lungs.. .. .this can limit concentration of drug reaching the systemic circulation for distribution to brain and heart
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What is an acidotic fetus?
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LA crosses placenta and cannot cross back to mom = larger amount of ionized form staying in fetal plasma and tissues. Called ion trapping. Rate and degree of diffusion across placenta is influenced by plasma protein binding. |
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What is methhemoglobinemia?
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condition where ferrous form of Hgb is oxidized to the ferric form and a high concentration of methemoglobin occurs in the blood. -results in reduced oxygen carrying capacity and shift to the left. s/s: cyanosis, chocolate blood, increased RR, coma, death cause: benzocaine (not dose related, seen with topicals) and prilocaine (d/t metabolite, dose related (2.5mg/kg), don't use w/ peds or pregos treatment: methylene blue (causes reforming of ferrous form) 1-2mg/kg |
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What is a differential block?
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nerves have different sensitivites to LAs sensory nerves could be blocked but not motor nerves . . .thus, differential block |
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What is Cm?
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the minimum concentration of LA necessary to produce conduction blockade of nerve impulses -depends on nerve fiber diameter and tissue pH -Cm of motor fibers is 2x that of sensory |
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We know that nerve fiber diameter and pH play a part in how much LA is required. What else can?
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a minimum length of myelinated nerve fiber must be exposed to adequate concentration ~ 2-3 nodes of Ranvier with A fibers pain producing fibers need similar concentrations B fibers more readily blocked than any other |
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What is the order of sensory loss?
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pain heat/cold touch pressure **restored in reverse order** |
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What is the order of nerve blockade?
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B fibers (venodilation, low BP) A-delta fibers (fast, sharp pain) C-fibers (slow, dull pain) A-gamma (muscle tone) A-beta (motor and proprioception) A-alpha (motor and proprioception) |
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What is LAST?
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local anesthetic systemic toxicity caused by: accidental IV injection during peripheral nerve blocks or epidural anesthisa (and less commonly from absorption of local from injection site) |
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What are the s/s of LAST?
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CNS before CV (CV are late signs) at low plasma toxicity: numbness of tongue/lips, ringing in ears, anti-arrhythmic property, lightheadedness as concentration increases: muscle twitching, unconsciousness, sz, coma, depressed conduction and automaticity excessive lidocaine: Prolonged PR, QRS complex |
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What happens with accidental bupivacaine injection?
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rapid hypotension, cardiac dysrhythmias, AV block **little warning before VT or VF** *prolonged CPR needed. . . |
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What factors increase the risk of LAST?
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older age - HF - ischemic heart disease - cardiac dysfxn - conduction abnorm - metabolic dx - liver dx - low plasma protein concentration - metabolic or resp acidosis - medications that inhibit Na channels
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List some things to prevent LAST.
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-know max safe dose -use vasoconstrictor if possible -aspirate and test dose -ultrasound -fractionate dose -proper monitoring -correct LA chosen -least dose necessary given -prepare for possible resuscitation |
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What is the maximum safe dose of 2-Chloroprocaine?
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12mg/kg
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What is the maximum safe dose of lidocaine with and without epi?
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4mg/kg without 7mg/kg with |
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What is the maximum safe dose of mepivacaine with and without epi?
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4mg/kg without 7mg/kg with |
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What is the maximum safe dose of bupivacaine?
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3mg/kg
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What is the maximum safe dose of ropivacaine?
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3mg/kg
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What is a lipid infusion?
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one of the main treatments for LAST an emulsion in water comprised of soybean oil, egg yolk phospholipid, fat droplets creates a "lipid sink" that sequesters the toxins of high lipophilicity in an expanded plasma liquid phase administer 20% lipid emulsion (bolus 1.5ml/kg over one minute with continuous infusion of .25ml/kg/min) |
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Do you give epinephrine when treating for LAST?
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no you should avoid it because it can impair resuscitation and reduce efficacy of lipid rescue also avoid: vasopressin, CCBs, BBs, LAs, |
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What is neurotoxicity?
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results from injecting LA into epidural and subarachnoid spaces more common with spinals s/s: patchy groin numbness, persistent muscle weakness, transient radicular irritation, cauda equina syndrome |
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What is transient radicular irritation?
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moderate to severe low back pain radiating down legs that appears w/in 24 hrs after complete recovery from spinal anesthetic with lidocaine -associated with lithotomy position -related to neuro-inflammatory process -treatment is supportive and NSAIDs -resolves w/in 1 week |
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What is cauda equine syndrome?
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neurotoxicity following continuous infusion of lidocaine through microcatheters for spinal anesthesia -sensory deficits, bowel and bladder sphincter dysfxn, paraplegia |
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Where is the chief site of action for spinal anesthetics?
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on spinal cord and emerging roots
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List the LAs in order of which is better for a sensory block.
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bupivacaine > lidocaine > tetracine
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List the LAs in order of which is better for a motor block.
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tetracaine > lidocaine > bupivacaine
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In regards to spinals, what does a greater dosage of LA do?
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faster onset - longer duration - denser block - increased spread *if there is too few mgs then the block is spotty and poor* |
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In regards to spinals, which LAs last longest?
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tetracaine (4hr) > bupivacaine (2hr) > lidocaine (1hr)
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What is specific gravity?
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the ratio of density of a solution to the known density of water at a specified temperature
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What is baricity?
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the ratio of the density of a solution to the density of CSF at a specified temperature
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What direction will LA solution migrate if it is hypobaric?
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up baricity is < 1, specific gravity is < 1.003-1.009 |
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What direction will LA solution migrate if it is hyperbaric?
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down baricity > 1, specific gravity > 1.003-1.009 |
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What direction will LA solution migrate if it is isobaric?
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it shouldn't migrate baricity is 1, same specific gravity of CSF |
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What do you know about using Lidocaine 5% in 7.5% dextrose in spinals?
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commonly used it is hyperbaric: baricity 1.0262 dose is 50-100mg duration: 60-75 mins, 90-120 with epi may dilute it with CSF to make it isobaric |
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What do you know about using Lidocaine 2% in spinals?
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it's isobaric, baricity 1.0004 dose 40-100mg duration 60-120 mins minimal to no spread very fast onset |
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What do you know about bupivacaine 0.75% in 8.25% dextrose in spinals?
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commonly used hyperbaric, baricity 1.0230 dose 10-15mg duration 120-150 mins *lay pt down immediately for T4 level otherwise it will sink down |
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What do you know about tetracaine 0.5-1% in 5-10% dextrose in spinals? |
hyperbaric, baricity 1.0133 dose 5-20mg duration 120-180 mins, 240-360 with epi 0.5% can be neurotoxic if used in a continuous spinal |
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What are the sites of action for epidurals?
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spinal nerves, roots, spinal cord placed in proximity of site of action diffusion through dura and dural root sleeves -> nerves, root, cord *takes time *much of the drug carried away by blood and absorbed by fat |
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What do you not add to epidurals that get added to spinals?
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dextrose and CSF
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Can epinephrine be added to spinals or epidurals?
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both in spinals use as a wash or 0.1 to 0.2 mls of 1:1000 |
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Can fentanyl be added to spinals or epidurals?
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both adds quality to block may add to duration because of quality effects gone after 4 hours |
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Can sodium bicarbonate be added to spinals or epidurals?
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only epidurals to hasten onset (allows more drug in non-ionized form) |
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What other meds can be added to spinals?
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clonidine: prolongs motor and sensory blockdecadron: prolongs blockdextran: prolongs blockhyaluronidase: facilitates spread of LA into tissue
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