2 - Local Anaesthetics Flashcards
Local anaesthetics are either:
(1) Injectable
(2) Topical
True
Injectable anaesthetics are:
(1) Amide - Bupivacaine, Lignocaine, Mepivacaine
(2) Ester - Procaine, Cocaine, Tetracaine
(3) Antihistamines - Diphenhydramine
True
Topical anaesthetics are:
(1) Amide - Dibucaine, Lignocaine, Mixture of Lignocaine + Prilocaine (EMLA)
(2) Ester - Benzocaine
(3) Ether - Pramoxine
(4) Ketone - Diclonine
(5) Antihistamines - Diphenhydramine, Doxepine
(6) Substance P depletors - Capsaicin
True
EMLA = eutectic mixture of local anaesthetics
Both amide (lignocaine, Mepivacaine, Bupivacaine) and ester (procaine, benzocaine) local anaesthetic compounds have an aromatic (lipophilic) portion, an amine (hydrophilic) portion, and an intermediate chain (ester or amide)
True
Lipophilicity (from protein binding) appears to correlate with the intrinsic potency of the anaesthetic
True (Bupivacaine is highly lipophilic compared to lignocaine and therefore much more potent, with a longer duration of action)
Absorption of lignocaine (amide) and other injectable local anaesthetics into the systemic circulation in influenced by properties of the agent itself
True
Absorption of lignocaine (amide) and other injectable local anaesthetics into the systemic circulation in influenced by presence of a vasoconstrictor in the injected solution
True (adrenaline reduces absorption)
Absorption of lignocaine (amide) and other injectable local anaesthetics into the systemic circulation in influenced by quantity of the drug injected
True
Absorption of lignocaine (amide) and other injectable local anaesthetics into the systemic circulation in influenced by technique of the injection
True
With the exception of cocaine (has potent vasoconstrictive effects), all other local anaesthetics have varying degrees of vasodilator effects and adrenaline is often added for its haemostatic effect
True
The vasoconstriction caused by adrenaline delays the absorption of the anaesthetic agent, thereby prolonging the anaesthetic effect
True
Without adrenaline, the approximate duration of action of lignocaine is 30-60 mins
True
With adrenaline, the duration of action of lignocaine is extended to 120-360 mins
True (Without adrenaline, the approximate duration of action of lignocaine is 30-60 mins)
Skin and subcutaneous tissues of the face and scalp exhibit higher significant absorption than the trunk or extremities owing to the increase relative density of blood vessels, therefore duration of anaesthesia may be briefer in these highly vascularised areas
True
Injection of the Anaesthetic agents too deeply into subcutaneous fat may give inadequate analgesia particularly on the scalp, resulting in the requiremeant for larger volumes of local anaesthetic injection and increased systemic drug absorption
True
Incorrect local anaesthetic infiltration technique may also lead to direct intravascular injection and risking systemic toxicity
True
Protein binding is the property of local anaesthetics that relates to the relative lipophilicity of the agent
True
Lignocaine = 60-80% protein bound with elimination half-life of 1.5-2 hours
Bupivacaine = 82-96% protein bound with elimination half-life of 5 hours
Amide local anaesthetics (lignocaine, Bupivacaine, Mepivacaine, prilocaine) is metabolised in the liver through hydrolysis by hepatic microsomal enzymes (Cytochrome P450) in the endoplasmic reticulum of hepatocytes
True (metabolism can be dramatically impaired in patients with significant liver dysfunction, therefore putting the patients at risk for systemic toxicity when relatively high volumes are used)
Metabolism of amide local anaesthetics (lignocaine, Bupivacaine, Mepivacaine, prilocaine) can be dramatically impaired in patients with significant liver dysfunction, therefore putting the patients at risk for systemic toxicity when relatively high volumes are used
True (metabolised in the liver by microsomal Cytochrome P450 enzymes)
Lignocaine is specifically metabolised by CYP3A4
True (substrate of CYP3A4)
Ester local anaesthetics (procaine, benzocaine) are metabolised very rapidly in the blood by pseudocholinesterase through hydrolysis to form aromatic acids and amino alcohols
True (in contrast, amides are metabolised in the liver) - approx 4% of the population is deficient in pseudocholinesterase, potentially resulting in slow metabolism
Both amides (lignocaine, Bupivacaine, Mepivacaine, prilocaine) and esters (procaine, benzocaine) are eliminated through renal excretion
True
Lignocaine has a complex excretion process as it is metabolised by CYP3A4 in the liver and then excreted into the bile , but is then reabsorbed from the GI tract and excreted in the urine
True (simplified version = metabolised in the liver, excreted in the kidneys)
Amide and Ester Local anaesthetics prevent nerve depolarisation/block conduction in nerves by minimising or preventing the influx of sodium ions into the nerve axon cell membrane
True (lipophilic portion of the drug allows penetration of the cell membrane, hydrophilic portion of the drug interact with the sodium channels on the inner surface of the cell membrane)
Through prevention of nerve depolarisation, amide and ester local anaesthetics block type C pain and itch nerve fibres
True
Local anaesthetics work on all nerves although have different propensities to block conduction depending on the nerve characteristics
True (Small diameter myelinated nerves such as pain and temperature fibres I.e. Type A delta fibres are more sensitive to blockade by local anaesthetics)
Small diameter myelinated nerves are more sensitive to blockade by local anaesthetics
True (relevant small myelinated nerve fibres are the type A delta fibres that carry pain and temperature sensations)
The larger myelinated nerve fibres are more resistant to blockade by local anaesthetics
True (larger myelinated nerve fibres are the type A alpha fibres that carry touch and pressure sensations)
The largest myelinated nerve fibres are most resistant to local anaesthetic blockade
True (the largest and most resistant myelinated nerve fibres are the type A alpha fibres that control propioception and motor function)
Myelinated nerve fibres are more resistant to local anaesthetics that unmyelinated nerve fibres
True
Temporary motor paresis may occur if high volumes of local anaesthetic are used
True
Temporary motor paresis may occur if dep placement of the local anaesthetic occurs in an area where deeper motor fibres are present under the more superficial sensory cutaneous nerves
True (can be seen commonly when anaesthetising skin on the temple overlying the temporal branch of the facial nerve)
The maximum dose of lignocaine without adrenaline is 4.5mg/kg (up to 300mg)
True (lignocaine concentration is 1mg/ml)
The maximum dose of lignocaine with adrenaline is 7mg/kg (up to 500mg)
True (lignocaine concentration is 1mg/ml)
The duration of action of Bupivacaine is 120-240 mins when used without adrenaline
True
The duration of action of Bupivacaine is 180-420 mins when used with adrenaline
True
The maximum dose of Bupivacaine without adrenaline is 175mg
True
The maximum dose of Bupivacaine with adrenaline is 225mg
True
The onset of action of lignocaine is <2 mins
True
The onset of action of Bupivacaine is 5 mins
True
Lignocaine is FDA approved for:
(1) infiltrative anaesthesia
(2) regional nerve block
(3) topical anaesthesia
True
Lignocaine is used off-label for:
(1) tumescent anaesthesia
(2) postherpetic neuralgia
(3) pruritus
True
Papillary dermal injection is most painful and creates more tissue distortion but gives instantaneous anaesthesia and such a depth of injection may be indicated in situations that require very rapid onset of anaesthesia
True
Subcutaneous is the least painful plane of injection, however this depth of injection provides less effective anaesthesia for epidermal and dermal procedures unless the anaesthetic is allowed to diffuse into adjacent tissue planes over several minutes
True
A favoured method of infiltration involves injection anaesthetic slowly as the needle is advanced into the deep dermis at the junction of the subcutaneous tissue as this method strikes a balance allowing relatively rapid onset of anaesthesia with less injection pain
True
Use of pH-buffered lignocaine (achieved using 1 part sodium bicarbonate with 9 parts lignocaine) reduces pain of injection
True
Warming the local anaesthetic to 40 degree Celsius can reduce injection pain
True
Adding hyaluronidase to lignocaine results in enhanced tissue dispersion of lignocaine and less tissue distortion, although it increases the pain of injection and reduces the duration of anaesthesia
True (also contains thimerosal, to which patents may be allergic)
Placing lignocaine-soaked gauze in an open wound for several minutes to allow topical absorption of the local anaesthetic prior to re-injection for lacerations and in MOHs surgery
True
Ring blocks may be useful in obtaining skin biopsies for microbiologic culture as direct infiltration of the anaesthetic with preservatives into the tissue to be smokes may lead to false negative bacterial cultures owing to the antibacterial effects of the preservatives
True
Regional nerve blocks are commonly used on the face, wrist, ankle, and digits and is useful to treat large areas such as for facial laser resurfacing
True (2% lignocaine commonly used -no need for adrenaline as no vasoconstriction needed)
The main risks with regional nerve block include laceration of nerve trunks
True
The main risks with regional nerve block include intravascular injection
True
The main risks with regional nerve block include temporary motor paralysis
True
The tumescent technique achieves longer lasting regional anaesthesia by direct infiltration of large volumes of dilute lignocaine with lower concentrations of adrenaline
True
Adverse effects of local anaesthetics are uncommon
True (adverse effects of the vasoconstrictive agent is more common than the actual anaesthetic agent itself)
Adverse reactions to local anaesthetics can be toxic or allergic in nature
True
Lignocaine toxicity primarily involves CNS toxicity and Cardiotoxicity
True
CNS toxicity = drowsiness, circumoral paraesthesia, lingual paraesthesia, tinnitus, nystagmus, ataxia, hallucinations, twitching, anxiety, restlessness, tremor, seizures, coma, apnoea
The is an overlap between the signs and symptoms of lignocaine toxicity and systemic effects of adrenaline such as anxiety, restlessness and tremor
True (given that the lignocaine dose limit is not exceeded, it can be assumed that these symptoms are from adrenaline + the absence of tinnitus and circumoral paraesthesia also supports the effects are due to adrenaline instead)
IV lipid emulsion (20%) infusion has been safely used and effectively improve survival and reverse the CNS and cardiovascular symptoms of lignocaine toxicity
True
The effects of lignocaine toxicity on the cardiovascular system are due to blocking of sodium channels which leads to decreased cardiac contractility, hypotension, bradycardia, and respiratory depression
True (Bupivacaine also exerts the sa,e effect, but 4 X more potency than lignocaine as a reflection of its potency compared to lignocaine)
Bupivacaine toxicity may also cause fatal dysrhythmias (ventricular fibrillation) as it dissociates more slowly/incompletely from the sodium channels
True
Allergic reaction make up <1% of all adverse reactions to local anaesthetics
True
Local anaesthetic allergic reaction may either be due to the:
(1) anaesthetic itself (true anaesthetic allergy)
(2) preservatives such as parabens and sulfites
True (esters are more commonly associated with allergic reactions)
Esters are more commonly associated with allergic reactions than amides
True (one of the primary factors leading to decline in usage of esters)
The 2 types of allergic reaction to local anaesthetics are:
1) anaphylactic reactions (type I IgE hypersensitivity
(2) delayed reactions (type IV hypersensitivity)
True
There is no cross-reaction between amides and esters
True (from patch testing results) - although if the patient has had an anaphylactic reaction then thorough evaluation by an allergist is recommended as class switching in anaphylaxis reactions has never been proven to be completely safe
If no safe local anaesthetic can be determined based on allergic reaction history, infiltration of diphenhydramine (antihistamine) or even saline can provide reasonable local anaesthesia in selected instances
True
Transient or minor reactions frequently caused by adrenaline include anxiety
True
Transient or minor reactions frequently caused by adrenaline include headache
True
Transient or minor reactions frequently caused by adrenaline include tremor
True
Transient or minor reactions frequently caused by adrenaline include restlessness
True
Transient or minor reactions frequently caused by adrenaline include palpitations
True
Vasovagal reactions may occur due to the injection procedure and are not an effect of the local anaesthetic agent
True
Drugs that induce CYP3A4 system may theoretically increase lignocaine clearance and reduce lignocaine blood levels
True (lignocaine is a substrate of CYP3A4 metabolism in the liver) - this has no clinical signifance in dermatologic use as rapid clearance would only enhance the safety profile of its use
Drugs that inhibit CYP3A4 system may theoretically reduce lignocaine clearance and increase lignocaine blood levels
True (consider reducing the doses lignocaine for tumescent anaesthesia and when administering large volumes of infiltrative anaesthesia)
Bupivacaine offers prolonged duration of anaesthesia as much as 4X the duration of plain lignocaine, although it’s onset of action may be slower
True (due to lipid solubility)