Local Anaesthetics

shevyatiwari's version from 2015-10-28 11:14


Question Answer
Lignocaine is an esterF, amide. Remember I before Caine = AMIDE
Esters include cocaine, procaine, tetracaine, benzocaineT
Esters inclue lignocaine, mepivacaine, bupivacaine, etidocaine, prilocaineF, amdies. As 'I ' comes before CAINE in AMIDES
All LA are hydrophilicF, hydrophilic and lipophilic components
The more lipophilic the agent, the more potent it isT
Bupivacaine is highly hydrophilic and therefore highly potent and has a long duration of actionF, lipophilic and highly potent
Technique of injection determines absorptionT, as well as properties of the agent, presence of a vasoconstrictor, site of injection, quantity of drug injected, technique of injection
Cocaine is a potent vasodilatorF, vasoconstrictor
All local anaesthetics have vasodilatory effectsF, cocaine does not. COCAINE vasoCOnstricts
W/out adrenaline, the duration of action of lignocaine is 120-360 minutesF, that is with lignocaine. Without - 30-60 minutes
Duration of anaesthesia is brief in highly vascularised areasT such as scalp
Lignocaine is 60-80% protein boundT
Lignocaine has T1/2 of 1.5-2 hoursT
Bupivacaine is highly protein boundT, 82-96%
Amdies and esters are metabolised in the same wayF
Amides are hydrolysed by hepatic microsomal enzymes in ER of hepatocytesT
Lignocaine is metabolised faster than bupivacaineT
Lignocaine is metabolised faster than prilocaineF
Lignocaine is metabolised by CYP3A4T
Esters are hydrolysed in the blood by pseudocholinesterase T
Procaine has a long half lifeF, <1 minute
PABA is a metabolite of lignocaineF, of procaine
PABA undergoes no metabolismF, hepatic metabolism
Pseudocholinesterase deficiency -> impaired metabolism of amidesF of esters. Think PseduocholinESTERASE DEFICIENCY impaired ESTER metabolism
96% of the population has pseudocholinesterase deficiencyF, 4%
0.1% of the population has a complete pseudocholinesterase defieciencyT. Can cause prolonged effect of succinylcholine
Predominantly renal excretionT
Local anaesthetics block conduction by maximising influx of Na ionsF, minimise influx
Smaller fibre nerves are more responsive to LAT - temperature and pain
Touch, pressure and finally motor function are the most resistantT
Unmyelinated fibres are more susceptible to LAT
TeratogenicF, cat b
Hyperthyroidism, and myasthenia gravis as well as cardiac impariment and hepatic impairment are relative C/IT
Dermal injections create more distortion but are rapidT
Sodium bicarbonate as a buffer lasts 1 week at room temperatureT. 25% decline in epinephrine every week. Refrigeration extends life to 2 weeks
Warming local anaesthetic improves painT
Hyaluronidese causes increased tissue distortionF
Hyaluronidease may increase pain and reduce duration of anaesthesiaT
Ring blocks may be beneficial for MCST there may be antibacterial effects in the preservatives
Nerve blocks generally need lower concentrations of LAF, higher
Tumuscent analgesia leads to delayed peak plasma levels 12-14 hoursT
Safe dose is 35-50mg/kg for tumescent analgesiaT
Adverse effects are more likely to be due to LA than the vasoconstrictorF
Tinnitus and circumoral paraesthesia are more likely due to lignocaine than adrenalineT
IV lipid emulsion can be used if overdose of LAT
Bupivacaine is 2 times more potent than lignocaineF, 4. Bupivicaine is 4 time smore potent than lignocaine
Esters cause more allergic reactions than amidesT. Think of Ester - mediterraneans more reactive
Epinephrine Sx resolve in a short time - can be given SL diazepamT
In tumuscent analgesia doses should be reduced by 30-40% in men and women who are on CYP3A4 inhibitorsF only for women. 10-20% for males
Bupivacaine is more cardiotoxic and CNS toxic than lignocaineT
Mixing 2 anaesthetics together has no positive effectT
Bupivacaine and mepavicaine are okay to use in pregancyF contraindicated due to risk of fetal bradycardia
LA should be avoided in first trimesterF, during days 15-56 (organogenesis period)
Pregnant patients should lie on their R sideF, L side to avoid vena caval and aortic compression
adrenaline is cat BF, C
EMLA is a eutectic mixture of 2.5% lignocaine and 2.5% prilocainet
The amount of EMLA absorbed is related to the amount applied F, area and duration
EMLA absorbs slowest on the faceF, fastest
Prilocaine is metabolised faster than lignocaineT
EMLA is cat BT
Depth of analgesia is a maximum of 5mmT
EMLA is useful prior to vaccinations in childrenF
EMLA carries a risk of haemolytic anaemaiF, methaemoglobinaemia
O-toluidine is a metabolite of prilocaine which causes methemoglobinemiaT
EMLA is safe under 12 monthsT, but not if on a methemoglobin inducing agent
EMLA is not to be used in those with congenital or idiopathic methemoglobinemiat
Panadol increases the risk of methemoglobiemiaT
Methemoglobinemia can be treated with IV methylene blueT
COrneal abrasions and conjunctivitis are a risk of EMLAT
LMX4 and LMX5 don't require occlusion unlike EMLAT
LMX4/5 have a slower onset of action than EMLAF, faster, approx 30 minutes
Synera = eutectic mixture of lignocaine and tetracaineT
Synera has a rapid onset of actionT, 20-30 minutes
Lidoderm 5% patch is for postherpetic neuralgiaT
Lidoderm provides rapid onset analgesiaF, provides extended analgesia
Lidoderm is a potential agent for dermatologic surgeryF
Benzocaine is an ester which can cause allergyT
Allergy to benzocaine - high risk of cross reaction to other estersT
Cross reaction to benzocaine is for Type 1 reactionsF, type 4
Topical benzocaine can cause methemoglobinemiaT
Dyclonine is a ketoneT
Dyclonine causes more pain relief than lignocaine in chemo and radiation induced stomatitist
Dyclonine is useful in oral ulcersT
Dyclonine is free of risk from ACDF
Pramoxine is a topical etherT
Dibucaine is a topical esterF
Dibucaine is used in haemorrhoid cream preparationst
Dyclonine is safe for use in the conjunctivaF
Adrenaline's B adrenergic properties cause vasoconstrictionF, a adrenergic
Maximum effect of adrenaline is 7-15 minutesT
Duration of action of adrenalnie is short (approx 60 minutes)T
Adrenaline is rapidly inactivated in tissue to metanephrine and normetanephrineT
Adrenaline's metabolites are conjugated in the liverT
Adrenaline is metabolised by MAOT
Adrenaline is excreted in the urineT. Adrenaline - urine
Adrenaline is more effective with bupivacaine than lignocaineF, more effective with lignocaine than bupivacaine and etidocaine (these arleady have delayed onset of action due to higher protein binding)
Mixing adrenaline and lignocaine just before injection improves painT
Phaeochromocytoma and hyperthyroidism -> risk of IHDF, risk of hypertension
Non selective B blockers can potentially cause malignant hypertensionT, no need to stop them before
TCA's can impair excretion of LAF, can increase cardiac effects of LA
Antihistamines, thyroid replacement can potentiate sympathomimetic effects of epinephrineT
Antipsychotics can reverse adrenaline's effectsT
Digitalis and quinidine can potentate the cardiac effects of adrenalineT
Burning of capsaicin reduces after 1-2 weeksT
Capsaicin can be applied to broken skinF
Adequate trial of capsaicin should be 4-6 weeksT
Capsaicin lasts 30 minutesF 3-6 hours
Diphenhydramine can cause necrosis in S/C, or ACD as a topicalT

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