Local Anaesthetic

Question 1

What is the corneal epithelium innervated by

Answer 1

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)

Question 2

what are the local anaesthetics available to use

Answer 2

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

Question 2

what do local aesthetics produce

Answer 2

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

Question 3

describe the structure of local anaesthetics

Answer 3

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

Question 4

describe all features of a local aesthetic

Answer 4

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

Question 5

describe the relationship between the structure of local anaesthetics and how they are processed in the liver

Answer 5

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

Question 6

describe the relationship between amines and water solubiility

Answer 6

because amines are not very soluble in water , the hydrochloride salt is used inc all local anesthetic preparations

Question 7

why is the linkage type important In local anesthetics

Answer 7

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

Question 8

describe the mode of action of local anestthetics

Answer 8

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

Question 9

what is the duration of LA action proportional to

Answer 9

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

Question 9

how are local anesthetics clinically used

Answer 9

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

Question 10

what medicines are used in the use of Goldmann aplantion tonometry

Answer 10

fluroscein is needed to visualise the contact area so 1 drop lid lidocaine with fluroscein is frequently used

Question 11

how long does it take to anaesthetise the cornea after installation of lidocaine

Answer 11

the cornea is sufficiently anaesthetised 1 minute post instillation

Question 12

what are other uses of local anesthetics

Answer 12

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

Question 13

when multiple drops are to be instilled what are the methods of instillatiion

Answer 13

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

Question 14

what is done to the cornea the multiple drops are to be installed q

Answer 14

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

Question 15

when multiple eye drops are to be instilled why are local anesthetics instilled first

Answer 15

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

Question 16

why has it been suggested that local anesthetics instillation prior to mydriatics is advised

Answer 16

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

Question 17

what patient advice should you give

Answer 17

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

Question 17

how should local anestheitcs be stored

Answer 17

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

Question 18

what is one of the expients in chloramphenicol

Answer 18

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

Question 19

what does modified release mean

Answer 19

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

Question 20

where does chloramphenicol need to be kept

Answer 20

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

Question 21

which of the following has to be kept between 2 and 8 degrees

Answer 21

chloramphenicol

Question 22

why should you pay attention to unilateral vs bilateral presentations of pink eye

Answer 22

unilateral tends to be more sinister in nature

Question 23

what does the anterior chamber being Clear tell you

Answer 23

that there is an external infection

Question 24

what type of disease is acute bacterial conjunctivitis

Answer 24

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

Question 25

what factors would you consider when deciding to supply chloramphenicol

Answer 25

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

Question 26

what is antimicrobial stweardship

Answer 26

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.

Question 27

chloramphenicol is contraindicated in what patients

Answer 27

contraindicated in pregnancy and breast feeding mothers and in patients with history of blood dyscrasia e.g. anemia

Question 28

what local anesthetic has to be refrigerated

Answer 28

proxymetacaine - 2-8 degrees

Question 29

if you are going to do a procedure that is longer how many drops are you going to use

Answer 29

you will use more more than one drop , length if time of anaesthetic will increase with increased contact of the drop