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118 Cards in this Set
- Front
- Back
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anaphylaxis is...?
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a Type 1 allergic reaction to systemically administred antigen
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anaphylaxis - what cellular process starts it off?
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mast cells degranulate
inflammatory mediators released |
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anaphylaxis - main adverse effects?
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Bronchospasm
Uticaria Swelling Hypotension |
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Anaphylaxis occurs during LA injection - what should you do?
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give IV adrenaline
get help |
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Give 2 reasons for toxic side effects following admin of LA.
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1. Hypersensitivity to drug
2. Accidental injection into vein/artery |
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Give 3 actions of adrenaline when added to LA.
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1. Longer lasting
2. Less bleeding 3. Less systemic absorption |
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Give 2 symptoms of early CNS toxicity from LA.
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1. CNS - perioral numbness
2. CNS - visual/aural disturbance |
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What is the purpose of aspiration?
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Prevention of intravascular injection which would cause toxicity
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What is the relevance of pKa to the action of the LA?
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pKa determines the amount of free drug
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Relevance of tissue pH on LA action?
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Affects the effectiveness of the LA. The more acid the tissue the less effective the LA agent.
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LA agents - do they act preferentially on any types of nerve fibre?
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Yes - small diameter fibres
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MSD of Bupivicaine?
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2mg/kg
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MSD of Lignocaine?
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3mg/kg
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On whom would you NOT use Bupivicaine?
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Patients with Heart Disease
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Bupivicaine - why not use on heart disease patients?
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Bupivicaine selectively blocks Na/Ca/K channels in cardiac muscle
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Bupivicaine - known as...?
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Marcaine
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Prilocaine - known as...?
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Citanest
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Mepivicaine - known as...?
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Scandonest
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LA dosage good practice mantra?
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use minimum dose
to avoid toxicity and tissue damage |
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Max tourniquet time?
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15-20 mins
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MSD equation?
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mg = ml x % x 10
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Bupivicaine is _ times as potent as Lidocaine?
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4
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Bupivicaine in pregnancy?
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No!
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Name 2 drugs that reduce LA clearance...
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Beta-blockers
Cimetidine |
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What type of neurones are last to be affacted by LA?
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motor neurones
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Name three side effects of poor injection technique.
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1- nerve injury
2- infection 3- pain |
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Action of adrenaline?
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vasoconstrictor
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If pus is present in local tissue, how does this affect the LA?
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pus = acidic
changes pH of tissue reduces un-ionised % of drug longer onset & less effective |
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MSDs apply to what time period?
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24hr period
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Upper MSD weight limit for calculations?
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70kg
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LA mechanism of action?
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block voltage gated sodium channels in PNS, CNS & heart
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Advice on Citanest/Prilocaine for children?
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Don't use if under 6mths
MSD 5mg/kg over 6mths |
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Advice on Scandonest/Mepivicaine for children?
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not licensed for podiatric use on children
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Advice on Marcaine/Bupivacaine for children?
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use as for adults
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Bupivacaine - effect on heart?
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irreversibly blocks
Ca/Na/K channels changes heart output, rate & resistance |
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LA administration in pregnancy?
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avoid in early pregnancy
& use with caution later |
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Two main contraindications to minor surgery under LA
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1- local inflammation/infection
2- known hypersensitivity to LA |
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Use LAs with caution if...?
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1- liver (LA metabolism)
2- kidney (LA excretion) 3- chronic alcoholism |
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Signs of hypoglycemic attack?
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(FUCDA)
Fits Unconscious Confused Drowsy Aggressive |
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Three-stage action in cases of hypoglycemic attack?
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1) rapid glucose by mouth
2) check levels every 15mins 3) call 999 if drowsy |
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Usual duration of epileptic fit?
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1 minute
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If epileptic fit continues past 1 minute you should...?
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call ambulance
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Proper response to syncope is...?
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trendelenberg
recovery & oxygen |
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What 2 drugs reduce hepatic LA clearance & increase plasma levels?
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Beta-blockers & cimetidine
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What 4 drugs reduce the effectiveness of local anaesthetic drugs, by increasing hepatic clearance & reducing plasma levels?
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Phenobarbitol
Phenytoin Isoproterenol Rifampicin |
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Levo-Bupivicaine MSD?
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2mg/Kg
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MSD Ropivacaine?
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3-4mg/Kg
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Effect of Beta-blockers on LA?
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Reduce hepatic clearance
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Effect of cimetidine on LA?
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reduces clearance
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Effect of Rifampicin on LA?
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increases clearance
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Effect of Phenytoin on LA?
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increases clearance
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Mepivicaine (Scandonest) - max mls per digit?
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4.4ml
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Digital pressure necrosis - caused by?
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injecting too much LA into digit
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Define "local anaesthetic"
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a drug used to provide
reversible depression of nerve conduction when applied to a nerve fibre |
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advantage of using amide LA agents?
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fewer allergic reactions
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Bupivacaine - onset?
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10-30 mins
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Bupivacaine - duration?
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up to 10hrs
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pKa is...?
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pH at which 50% of the drug is in un-ionised form
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Most LAs are weak bases. How is this relevant?
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drug exists simultaneously in both ionised and un-ionised forms
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In tissues, only __________ LA drug molecules can diffuse into the nerve fibre.
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Un-ionised
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MSD Prilocaine?
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6mg/kg
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MSD Mepivacaine?
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6mg/kg
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What tissue response indicates you are injecting LA into subcutaneous tissue?
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blanching
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Which part of the proximal phalanx do you inject into?
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the thinnest part
b4 the flare of its base |
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Action of an LA drug?
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reversibly stop nerve conduction & propagation by blocking sodium channels in axon membrane
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What form of LA drug blocks the sodium channel?
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charged
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What form of the LA drug can diffuse across the axon membrane?
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uncharged lipophilic
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Binding of LA agent to the socium channel prevents...?
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sodium influx and membrane depolarisation
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Which nerve function is the first to be supressed on application of LA?
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pain sensation
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Which nerve function is lost last with LA?
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skeletal muscle tone
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Why might the % of charged/uncharged drug not be exactly equal to each other?
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differences between the drug and tissue pH
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Equation for LA agent dissociation?
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BH˖ <--> B + H˖
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At physiological pH (7.4) all local anaesthetics are more _______ than _______.
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more ionised than un-ionised
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In what form does LA drug pass through the lipid axon membrane more readily?
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un-ionised
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Why does lidocaine have a faster onset of action than bupivacaine?
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At pH 7.4, Lidocaine has a higher % of uncharged drug molecules than Bupivicaine.
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At physiological pH a drug which is more charged than uncharged will reach its target quicker or slower?
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slower
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What effect - acid tissue pH?
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reduces the uncharged fraction of the drug
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What effect - basic tissue pH?
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increases the uncharged fraction of the drug
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Infected tissue - why might LA not be effective?
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acidic pH reduces uncharged drug fraction
& hyperemia removes LA from area |
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What aspect of amide LA drug structure increases its lipid solubility?
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aromatic ring
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the more lipophilic, the more...?
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potent
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What is the most important factor affecting LA duration of action?
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the protein binding ability of the drug
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The more protein bound a drug, the _______ the duration of action.
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longer
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LA drugs - metabolised where?
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liver
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LA drugs - excreted via where?
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kidney
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What type of LA drugs readily cross the placenta?
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less protein-bound amides
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Adrenaline - effect on LA agents?
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vasoconstrictor
longer duration of action slows systemic absorption |
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Peri-oral numbness
Unconsciousness Slurred speech Seizures ..are signs of the effect of LA on which system? |
Central Nervous System (CNS)
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arrhythmias and reduced myocardial contractility - what type of LA effects?
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cardiovascular
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Name the 3 factors that affect the possibility of LA toxicity?
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The DOSE, the RATE and the injection SITE
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State 3 reasons why you would use Adrenaline with LA?
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1. it reduces systemic absorption
2. it prolongs duration of action 3. it reduces local bleeding at operation site |
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adrenaline used for digital ring blocks causes...?
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ischaemia
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Adrenaline is used with which LA agents?
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Lidocaine & Bupivacaine
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name the 4 main symptoms of anaphylaxis
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Bronchospasm
Uticaria Swelling (oedema) Hypotension |
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Early CNS toxicity symptoms?
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lightheadeness
dizziness visual/auditory disturbance shivers |
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Late CNS toxicity symptoms?
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convulsions
respiratory arrest |
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Cardiovascular toxicity effects?
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negative inotropic action
depress pacemaker activity |
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Adrenaline - overall action?
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Alpha and Beta adrenoceptor agonist.
Vasoconstrictor Reverses anaphylaxis |
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Adrenaline - Two main alpha adrenoceptor effects?
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reduces laryngeal oedema
reduces peripheral vasodilation |
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Adrenaline - three main Beta adrenoceptor effects?
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dilates airways
positively inotropic histamine suppression |
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Toxic levels of LA drug first affect the _____ and then the _____
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brain then heart
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Define toxicity
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The rapid uptake of drugs or doses exceeding the body's capacity to metabolise them.
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Main CV toxicity effects of LA drugs?
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Conduction block
Vascular dilatation |
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Are LA drugs selective for neuronal Na+ channels?
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No.
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Clinical significance of LA drugs not being selective for neuronal Na+ channels?
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if systemically absorbed can cause CV and CNS effects
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What to do if patient has anaphylaxis?
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give adrenaline IM
call 999 |
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Anaphylaxis is due to?
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massive systemic vasodilatation caused by widespread histamine release from mast cells
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What LA drugs can be given to children?
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Bupivacaine
Lidocaine (not >3mg/kg) Prilocaine (not <6mths) |
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Why is alcohol a problem with LA drugs?
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systemic acidosis
vasodilation by alcohol |
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three patient groups who should be given LA with caution
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liver disease
kidney disease alcoholics |
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Two drugs that reduce clearance of amide LA drugs?
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Cimetidine
Propanolol (Reduce clearance) |
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Clearance rate is...?
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plasma volume cleared, per unit of time
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signs of hypoglycemia?
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drowsiness, slurred speech, confusion, blurred vision, fits
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Hypoglycemia - immediate treatment?
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if conscious
give rapid glucose by mouth check glucose every 15 mins |
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when should you call 999 for a patient having an epileptic seizure?
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if the fit doesn't stop in 1 min
or if they fit immediately |
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what should you do if a patient faints?
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raise legs above heart until conscious
then recovery position & give oxygen |
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action if patient has a CVA, TIA, MI?
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call 999
give life support start 30 chest compressions & 2 breaths |
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what medication can reduce the effect of Lidocaine?
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diuretic therapy
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