Local anaesthesia is defined as any technique that induces loss of sensation in a specific part of the body. Even though this definition is correct in general terms local anaesthesia also causes loss of other sensations as well. Local anaesthesia can be induced by drugs. Ideal local anaesthesia for surgical treatment purposes should be reversible. The first local anaesthetic to be used was Cocaine. Cocaine was isolated from Coca leaves. It was originally popular with residents of Andes mountain area. Australian surgeon Koller  was the first to perform a surgery in the eye after administration of cocaine. This caused a spurt in the use of cocaine as local anaesthetic agent in United States and Great Britain. Soon the complications of cocaine became evident including its addictive potential. Initially it was commonly used as a local anaesthetic agent by dentists to be followed by otolaryngologists as topical anaesthetic agent in the nasal cavity.
This drug was widely preferred in nasal surgeries because of its associated vasoconstrictive property. Initially cocaine for otolaryngological use was available in two concentrations (4% and 10%). Since nasal mucosa provided a vast absorptive surface the incidence of toxicity following use of cocaine was rather high . Despite the high levels of toxicity Halstead started to use it as nerve block for his surgeries in United States in 1885. The irony was Halstead himself became an addict to cocaine due to his self experimentations . Search for safer synthetic alternatives lead to the synthesis of the first synthetic derivative to cocaine. It was named as Procaine (1904). Lidocaine which is still commonly used local anaesthetic was developed by Lofgren and was put to extensive use during the Second World War.
Local anaesthetics induce anaesthesia by inhibiting excitation of nerve endings / blocking conduction in peripheral nerves. This is usually caused due to reversible binding and inactivation of sodium channels. Normal functioning of sodium channels in a nerve is important for depolarization process which causes nerve conduction.
All local anaesthetics have an intermediate chain linking an amine to one end and aromatic ring on the other. The amine end is hydrophilic and the aromatic end is lipophilic. Chemical variations to amine end / aromatic end causes changes to the chemical activity of the drug.
In chemical terms there are two classes of local anaesthetics available:
Amino amides: This group has an amide link between the intermediate chain and the aromatic end
Amino esters: This group has an ester link between the intermediate chain and the aromatic end
Lipid solubility: Potency is directly related to lipid solubility. It should be remembered that 90% of nerve cell membrane is composed of lipid .
Protein binding: Is usually related to the duration of
action. If the drug binds firmly to the protein of sodium
channel the effect of local anaesthesia would be longer.
Ionization at physiological pH: Chemically local
anaesthetics exist in ionized and non ionized forms. The
proportion of these two forms depends on the pH of the
environment. The non-ionized form of local anaesthetic
is that one that is capable of diffusing across nerve cell
membrane causing local anaesthesia. Local anaesthetics
with larger amounts of non-ionized components are
capable of inducing faster anaesthesia. Ideally local
anaesthetic drugs should be available in non-ionized
form in physiologic pH. A decrease in pH shifts the local
anaesthetic drug to its ionized form there by reducing
its potency. This is the reason why the action of local
anaesthetics is suboptimal in inflamed tissues. Addition of
sodium bicarbonate to the local anaesthetic drug would
increase its potency as this would increase the pH at the
Vasodilating properties: All local anaesthetics except
cocaine are known to cause vasodilatation. Vasodilatation
occurs due to relaxation of peripheral arteriolar smooth
muscle fibres. Greater vasodilatation causes rapid
absorption of the drug thereby shortening its action.
Hence vasoconstrictors like adrenaline are added to local
anaesthetic drug to increase their duration of action.
Ideally it is the duty of the surgeon to find the smallest dose
of local anaesthetic drug possible whose local anaesthetic effect
could last the entire duration of surgery. It should be stated
here that addition of adrenaline increases the margin of safety
and prolongs the duration of action of the drug. To increase the
shelf life of local anaesthetic drugs the pH is deliberately kept in
the range between 4-5. This when injected will not only reduce
the potency of the drug but also can cause undesirable burning
sensation if administered in awake patients. Addition of sodium
bicarbonate 1cc of a 1 mEQ/ml solution for every 9 ml of local
anaesthetic taken will not only increase the potency of the drug
but also would minimize the burning sensation.
Anaesthesia of nose and nasal cavity are indicated for various
diagnostic and surgical procedures involving the nose. Some of
these indications include:
Using 10% xylocaine nasal spray: Topical surface
anaesthesia just lasts for about 45 mins. This type of
anaesthesia is preferred while performing diagnostic
nasal endoscopy / minor procedures involving the nasal
cavity like nasal packing.
Nasal packing using cottonoids / pledgets soaked in
4% xylocaine mixed with 1 in 10000 adrenaline is useful
for performing minor surgical procedures inside the nasal
cavity. Cottonoids are comparatively better than cotton
pledgets. Each nasal cavity should be packed with 3 packs.
One is placed in the floor of the nasal cavity, the next one is
placed over it to encroach into the middle meatus and the
last one is placed above the second one to anaesthetize the
frontal recess area. Presence of adrenaline in the mixtureshrinks the nasal mucosa and prolongs the duration of
Infiltration anaesthesia is preferred while performing
surgeries inside the nasal cavity. 2% xylocaine mixed with
1 in 10000 adrenaline is used for infiltration. Infiltration
can be used to anaesthetize the anterior ethmoidal nerve,
infraorbital nerve via the canine fossa. This is very useful
during reduction of fracture nasal bone(Figure 2).
Caution: While using 4% topical xylocaine for anaesthesia
the maximum volume of the drug used should not exceed 7
ml. Pharyngeal wall mucosa gets anaesthetized when pledgets
dipped in 4% xylocaine is used to pack the nose. This may cause
the patient to aspirate blood and secretions. Periodical suction
should be applied to the patient’s throat while performing nasal
surgeries under local anaesthesia.