Anaesthesia and Analgesia Flashcards
Local anaesthetics reversibly interrupt propagation of nerve impulses by interfering with sodium ion influx into peripheral nerve cells.
T
Topical anaesthesia is generally less effective for mucosal surfaces.
F
Very effective dt enhanced absorption.
Intradermal infiltration of anaesthesia causes less pain thn subcutaneous infiltration
F
Other way around
Intradermal infiltration of anaesthesia is more immediate in onset and more prolonged than subcutaneous infiltration
T
The chemical structure of most local anaesthetic agents consists of an aromatic portion, an intermediate chain, and an amine portion.
T
The amine portion of the local anaesthetic compound provides most of its lipophilic properties.
F
Aromatic end.
The aromatic end of the local anaesthetic compound facilitates the diffusion of the anaesthetic through membranes, which correlates to the potency of the anaesthetic.
T
The hydrophilic end of the local anaesthetic compound is involved in binding within the sodium channel.
T
This is usually a tertiary amine.
The intermediate chain of the local anaesthetic compound consists of either an ester or an amide.
T
Amide-type compounds tend to have a shorter duration of action because they are rapidly hydrolyzed by plasma pseudocholinesterases to form metabolites excreted by the kidneys. .
F
This is true for esters. Pts with decreased levels of pseudocholinesterase may be prone to their toxic effects
PABA is the major metabolite product of the ester-type anaesthetics and is responsible for their higher incidence of allergies.
T
related to PPD - cross reacts with ester anaesthetics
suphonylureas and thiazides alos cross react with this group
Ester derivatives are metabolised by microsomal enzymes in the liver and excreted by the kidneys.
F
This is true for amides.
Individuals with compromised liver function are more susceptible to the toxic effects of ester anaesthetics.
F
This is true for amides.
Highly protein-bound anaesthetics, such as bupivacaine, are tightly associated with the neural membrane, leading to a longer duration of action.
T
Shorter-acting anaesthetics tend to have a longer action of onset and more toxicity.
F
Shorter onset of action, less toxicity.
Local anaesthetics are weak bases, with a pKa between 7.7 and 9.1.
T
Prepared with hydrochloride salts though so become acidic.
A lower pKa correlates to a higher concentration of base and a faster onset of action.
T
Tissue pH does not affect the action of local anaesthetics.
F
Eg. infected tissue more acidic
Local anaesthetics can cross the placenta.
T
Local anaesthetics can be excreted in breast milk.
T
Procaine, tetracaine, benzocaine, chloroprocaine, and cocaine are types of amide anaesthetics.
F
Esters
Lignocaine, bupivacaine, mupivacaine and prilocaine are types of ester anaesthetics.
F
Amides
Procaine has a faster onset of action than lignocaine.
F
Procaine 5 mins, lignocaine
Procaine lasts longer than lignocaine.
F
Procaine 15-30mins, ligno 30-120 mins.
Bupivacaine and mepivacaine last longer than lignocaine.
T
There is significant benefit of adding vasoconstrictors to lipid-soluble anaesthetics (bupivacaine/ropivacaine) to prolong their effect
F
They are already highly tissue bound
The maximum dose of adrenaline for LA should not exceed 1mg over approximately 8-10hours
T
The recommended maximum dose for procaine is 10mg/kg for adults, without adrenaline.
T
14mg/kg with adrenaline.
The recommended maximum dose for lignocaine is 7mg/kg for adults, without adrenaline.
F
5mg/kg
7mg/kg with adrenaline.
The recommended maximum dose for bupivacaine is 2.5mg/kg for adults, without adrenaline.
T
3mg/kg with adrenaline.
The recommended maximum dose for mepivacaine is 10mg/kg for adults, without adrenaline.
F
6mg/kg.
8mg/kg with adrenaline.
A and B nerve fibres are myelinated and C fibres are unmyelinated.
T
Smaller myelinated fibres are easier to block than larger myelinated fibres, therefore pain and temperature sensation may be eliminated before the loss of vibration and pressure.
T
The A-alpha fibres primarily conduct light touch and pressure.
F
Motor impulses.
The A-beta fibres conduct motor impulses.
F
Light touch and pressure.
The A-gamma fibres are responsible for joint proprioception.
T
The A-delta fibres conduct pain and temperature. They are the smallest of the A fibres.
T
A fibres are the largest of the nerve fibres.
T
B-fibres are preganglionic sympathetic fibres.
T
C-fibres are the smallest and conduct pain and temperature.
T
All local anaesthetic promote vasodilation by relaxation of vascular smooth muscle.
F
Cocaine doesn’t.
Vasoconstrictors added to local anaesthetic impair the absorption of the anaesthetic and prolong its duration.
T
Sodium bicarbonate 10.5% is used in a dosage of 1mL for every 10mL of 1% lignocaine with adrenaline.
F
8.4%, to decrease pain with infiltration of acidic solution.
Full vasoconstriction with adrenaline typically requires only 30-60 seconds.
F
7-15 minutes.
Adrenaline can reduce uterine blood flow and induce premature labour, therefore non-urgent procedures requiring the use of adrenaline should be postponed until after pregnancy.
T
Hyaluronidase facilitates local diffusion of anaesthetics.
T
Adding sodium bicarbonate to local anaesthetics allows for increased amounts of uncharged, lipid-soluble base, which more readily crosses the nerve membrane, leading to faster onset of action.
T
There is no need to patch test hyaluronidase prior to use.
F
Contains allergen thimerosal.
Hyaluronidase decreases the duration of anaesthesia and potentially increases the risk of anaesthetic toxicity as a result of increased absorption
T
Uniform dose of hyaluronidase is 10u/ml
F
There is no uniform dosage, but 150units in 20-30mls of anaesthetic has been used
Hyalmuronidase contains the preservative thimerosal which is a contact allergen
T
Because rare allergic reaction have been reported, preoperative skin testing has been recommended
Hyaluronidase is recommended for tumescent liposuction.
F
See above for why it isn’t.
Cocaine is primarily used as a topical anaesthesia in nasal surgery as a 4% and 10% solution.
T
Anaesthesia within 5 mins of application, lasts up to 30mins.
The recommended maximum dose of cocaine is 200mg/kg.
T
Use of topical benzocaine can cause contact sensitisation.
T
Benzocaine-containing preparations can be safely used in infants.
F
Risk of methaemoglobinaemia.
Lignocaine is available in a 2% and 5% gel, ointment or viscous solution.
T
Onset of action is 1-2 mins, duration 15-20 mins.
EMLA is a eutectic mixture of 2.5% lignocaine and 2.5% prilocaine.
T
Oil-in-water emulsion cream.
A eutectic mixture is a formulation that melts at a lower temperature than any of its individual components.
T
The depth of analgesia after 60mins of EMLA application is 5.0mm. .
F
3mm. 120 mins gives 5mm
EMLA should be used with caution in infants due to the risk of methaemoglobinaemia.
T
EMLA can be applied to eyes.
F
Risk alkaline injury.
LMX 5% is a topical anaesthetic containing lignocaine encapsulated in a liposomal delivery system.
T
LMX has a slower onset of action than EMLA.
F
Faster – 30min application time.
LMX has a shorter duration of action than EMLA.
F
Longer.
LMX can be applied without the need for occlusion.
T
LMX use in a child weighing less than 20kg should be limited to an area less than 100cm2 for a single application.
T
Tetracaine, a long-acting ester anaesthetic, is available in a 0.5% solution and is used most commonly for ophthalmic procedures.
T
Common topical eye preparations include lignocaine
F
Proparacaine 0.5%, tetracaine 0.5%, benoxinate 0.25%
Topical eye preparations have an onset time of 30seconds
T
Field or ring block involves placement of anaesthesia circumferentially around the operative site.
T
Tetracaine can provide anaesthesia to mucous membranes for up to 45 mins.
T
An eye patch must be worn following anaesthesia to the eye to protect the cornea
T
Topical eye preparations usually last 15mins or longer
T
Local infiltration is suitable for infected or inflamed tissue
F
Field blocks are appropriate
Tumescent anaesthesia involves the delivery of large volumes of dilute anaesthesia (usually 0.05%-0.1% lignocaine with 1:1 000 000 adrenaline) into subcutaneous fat until it distends.
T
Safe upper limit of lignocaine with tumescent anaesthesia is estimated to be 35mg/kg
F
55mg/kg
