Local Anaesthetic Flashcards
What is the corneal epithelium innervated by
the corneal epithelium is innervated with approximately 2.2 million nerve endings which make it one of the most innervated tissues of the human body
the majority of these fibres are sensory and respond to chemical , mechanical and temperature stimuli
they form posterior cillary nerve from the nasocillary branch of the 1st division (ophthalmic) of the fifth cranial nerve (trigeminal)
what are the local anaesthetics available to use
lidocaine with flurocein - 4% lidocaine hydrochloride and 0.25% fluroscien (amide type)
oxybuporcraine - 0.4% oxybupocraine hydrochycloride (ester types)
proxymetacaine - 0.5% proxymetacaine hydrochloride (ester type)
tetracaine - 0.5% and 1.0% tetracaine hydrochloride (ester type)
all available as minims therefore single use preparations
what do local aesthetics produce
local anaesthetics produce a reversible block of the conduction of nerve impulses
an ideal local anesthetic will be fast acting
sustain there effect for enough time to complete the clinical procedure
be totally reversible
have no systemic or local Side effects
describe the structure of local anaesthetics
all of the local anaesthetics available to use are synthetic , not very water soluble , and they from weakly based amines
they consist of an aromatic hydrophobic portion , an intermediate linkage and a hydrophilic amine
the hydrophobic portion must be an aromatic ring and creates anaesthetic effect
describe all features of a local aesthetic
synethetic
not water soluble
form weakly based aromatic amines
have hydrophobia portion , intermediate linkage and hydrophilic amine
hydrophobic portion must be an aromatic ring creating the anaesthetic effect
describe the relationship between the structure of local anaesthetics and how they are processed in the liver
the intermediate chain is an ester type link or an amide type link which can affect drug metabolism , amides must be metabolised into the liver whereas the ester type can bemestabolised buy plasma cholinesterase’s and esterase’s in the liver
describe the relationship between amines and water solubiility
because amines are not very soluble in water , the hydrochloride salt is used inc all local anesthetic preparations
why is the linkage type important In local anesthetics
the linkage type is important as patients may be hypersensitive t one which will affect the future choices of the local anesthetic
although these reactions are uncommon , they are mainly associated with the ester type
describe the mode of action of local anestthetics
LA’S prevent the creation and transmission of nerve impulses
they work at the cell membrane by blocking the temporal increase in membrane permeability to sodium ions that cause the depolarisation of the nerve cell membrane
it is thought that this is accomplished by the binding of the LA to a specific binding site on the cell membrane
what is the duration of LA action proportional to
the duration of LA action is proportional to the time they are in contact with the nerve tissue
when applied topically to the eye all of the LA’S have low systemic and ocular toxicity
they have sufficent action time and are relatively low cost
also they are stable in solution if stored correctlyy and do not tend to interact with the action of other drugs
how are local anesthetics clinically used
the main use of local anesthetics by orthoptists are in the measurement of intraocular pressure (iop) by Goldmann applantion tonometry
the usual method of iop measurement within hospital clinical and work by placing a probe onto the corneal surface and measuring force required to flatten a circle , 3.06 mm diameter of the cornea
what medicines are used in the use of Goldmann aplantion tonometry
fluroscein is needed to visualise the contact area so 1 drop lid lidocaine with fluroscein is frequently used
how long does it take to anaesthetise the cornea after installation of lidocaine
the cornea is sufficiently anaesthetised 1 minute post instillation
what are other uses of local anesthetics
other uses include gonioscopy carried out in glaucoma clinical to visualise the anterior angle to differentiate between open angle and closed angle glaucoma , a gone lens needs to be placed onto the cornea and requires corneal anesthesisa
ultrasound is still in use and the probable also needs to be in contact with cornea
foreign body and suture removal also necessitates the use of a local anesthetic
when multiple drops are to be instilled what are the methods of instillatiion
either 2 or more doses of the same medicine is indicated or when two different ocular medicines are required then instilling a local anesthetic first allows subsequent drops to be installed painlessly
what is done to the cornea the multiple drops are to be installed q
it is not uncommon practice to anaesthetise the cornea when multiple drops are indicated
this may be siin darkly pigmented irises when the chance of effective cycloplegia with a single drop is reduced
when multiple eye drops are to be instilled why are local anesthetics instilled first
the use of an initial anesthetic results in only one uncomfortable eye drop and subsequent drops may be instilled with no other discomfort
tropical anaesthetic when given with a well tolerated medicine such as proxymetacaines has been suggested to reduced the tearing reflex and reduce ocular irritation thus meaning that more than cyclopentolate is retained in the conuctical sac and more effective cycloplegia is complained
why has it been suggested that local anesthetics instillation prior to mydriatics is advised
it has been suggested that giving a topical anaesthetic prior to mydriatic medicine enhances the permeability of the cornea therefore giving a Bette uptake of the mydriatc and enhancing pupil dilation
however this effect has not always been replicated and may be influenced by iris colour and combinations of patients within the study groups
what patient advice should you give
all local anesthetics will sting on instillation and cause lacyhrmation which dilutes the drug
patients should be advised that the stinging is temporary
the length of duration of anesthesia is important as patients lose the protective blink reflex and are unable to feel any corneal abrasion
therefore you must advise all patients not to tub their eyes for up to one hour after instillation
(check emc/bnf) for specific times for different LAS and drop regiem
how should local anestheitcs be stored
proxymertacine should be stored at 2-8 degrees whereas the other three can be stored below 25 degrees
proxymetacaine can be stored at room tempreturee but only for one month and them must be discarded
all Local Anaesthetics are prescription only medicines and should be disposed of as clinical waste
what is one of the expients in chloramphenicol
expeients = something in medicines that helps to stablise it on chormomphenicol boric acid is put into hot and in some literature it suggests that it should be removed from supply from 2 year olds but that is now been superseded so … now its safe to use
what does modified release mean
modified release action means it is released more slowly for example fusidic acid consistency is on between drop and ointment formulation and is therefore more viscous
where does chloramphenicol need to be kept
chloramphenicol needs to be kept in the fridge between 2 and 8 degrees if its not refrigerated you can use if up to 28 days fusidic acid can be stored at room tempreture
which of the following has to be kept between 2 and 8 degrees
chloramphenicol
why should you pay attention to unilateral vs bilateral presentations of pink eye
unilateral tends to be more sinister in nature
what does the anterior chamber being Clear tell you
that there is an external infection
what type of disease is acute bacterial conjunctivitis
it is a self limiting disease meaning that it is not going to go and from other forms of eye disease it is not sight threatening and it dosnt need treatment
what factors would you consider when deciding to supply chloramphenicol
how long they have had it?
-more than 10days
important to tell patient the if condition detritoriates /vision to call
red flags= vision affected , and pain
what is antimicrobial stweardship
antimicrobial stewardship promotes the effective use of antimicrobials (including antibiotics) in children , young people and adults and aims to change prescribing practice to help slow the emergence of antimicrobial resistance and ensure that antomicrobials remain an effective treatment for infection
in addition pts eexpectations also need to be modified , its quite common for carers to expect to receive a medicine product when there is a obvious disease and this needs to change in cases of acute bacterial conjuctivitis.
chloramphenicol is contraindicated in what patients
contraindicated in pregnancy and breast feeding mothers and in patients with history of blood dyscrasia e.g. anemia
what local anesthetic has to be refrigerated
proxymetacaine - 2-8 degrees
if you are going to do a procedure that is longer how many drops are you going to use
you will use more more than one drop , length if time of anaesthetic will increase with increased contact of the drop
