anaesthetics

■ The term anaesthesia is derived from two
words [an (absence) + aesthesia (sensation
of pain)] meaning ‘absence of pain
sensation’.
■ The drugs which are used to produce
anaesthesia are known as anaesthetics or
anaesthetic drugs.

■ General anaesthesia is defined as reversible
loss of all the sensations and consciousness.
– It is produced by the drugs, which act at
CNS level and are known as general
anaesthetic drugs.
■ Local anaesthesia is the defined as
reversible loss of all the local sensations
without loss of consciousness.
– It is produced by the drugs, which act at
peripheral level and are known as local
anaesthetic drugs.

GENERAL
ANAESTHETICS (GAs)
■ General anaesthesia is the reversible loss of all
the sensations and consciousness.
■ This involves following special components:
– Analgesia (loss of pain sensations)
– Unconsciousness (Loss of consciousness)
– Amnesia
– Immobility & skeletal muscles relaxation
– Loss of all somatic & autonomic reflexes

■ An ideal anaesthetic drug should be able to
induce the unconsciousness smoothly &
rapidly with prompt recovery from anaesthesia
whenever required.
■ The drug, which is unable to produce the
above effects, is not considered as general
anaesthetic drug.
■ There is no anaesthetic agent, which can
produce all the above effects individually
without producing toxicity. Hence, in the
modern day anaesthetic practice, several
different categories of drugs are used
simultaneously to produce ‘balanced
anaesthesia’.

■ The drug regimen for balanced
anaesthesia is made by keeping in view
the advantage of:
– the individual beneficial effects of
different drugs and
– minimizing their individual toxic effects.
■ This is usually made by making a
combination of Intravenous and inhaled
drugs.

Steps of GAs:
■ Pre-anaesthetic medication.
■ Induction of anaesthesia
– IV route for adults
– Inhalational for children.
■ Maintenance of all phases of
anaesthesia.
■ Reversal of anaesthesia

STAGES OF
ANAESTHESIA
■ Traditionally, the anaesthetic drugs produce
sequential effects as a part of increasing
depth of CNS depression.
■ These stages of anaesthesia were described
by Guedel in 1920 and ether was used as an
anaesthetic agent at that time. These are
known as Guedel’s signs.
■ In Modern anaesthesia, all these stages may
not be seen very clearly and even the
sequence may differ in some.

■ Stage of analgesia:
– It remains from beginning of anesthesia
to loss of consciousness.
– Patient remains conscious and feels a
dream like state.
– Very short procedures can be carried out
during this stage.

■ Stage of excitement:
– During this stage,
■ patient appears delirious or
■ may lose consciousness and
■ sympathetic activity is increased which is
manifested in the form of
– shouts, struggle, jerky breathing, vomiting,
involuntary micturation or defecation.
– Heart rate and BP may rise and pupils dilate
due to sympathetic stimulation.
– No operative procedure can be carried out
during this stage.

■ Stage of surgical anaesthesia:
– This stage begins with
■ slowing of respiration and
■ heart rate and
■ extends to complete cessation of spontaneous
respiration (apnoea).
– It has been further subdivided into four planes
depending upon changes in ocular movements,
eye reflexes and pupil size indicating the depth
of anaesthesia.
– Most of the surgical procedures are performed in
this stage

■ Stage of medullary paralysis:
– Due to increasing depth of
■ CNS depression, and
■ depression of respiration &
■ vasomotor center,
■ respiratory and circulatory failure occurs.
– Without respiratory and circulatory
support, it progresses to death.

Minimum alveolar
concentration (MAC)
■ It is the lowest concentration of any anesthetic that
produces immobility or loss of consciousness in 50%
individuals.
■ The potency of any inhalational anesthetic depends
upon their MAC.
■ MAC is inversely proportional to potency of drugs.
– Example: nitrous oxide has high MAC [104], and
is very less potent; while methoxyflurane has
very low MAC [0.13] and is most potent
inhalational anaesthetic.

Blood Gas Solubility [BGS]
■ It is the solubility of inhalational anesthetic
gases into the blood.
■ BGS determines the speed of induction and
recovery by the inhalational agent.
■ If the inhalational anesthetic gas is less
soluble into the blood, it will induce quickly
and vice-versa.
– Example, N2O, sevoflurane, and
desflurane are used for quick induction,
as these are less blood soluble.

Inhalational anesthetic
Gases
MAC BGS
Xenon 71 0.13-0.20
Desflurane 5.8 0.42
Nitrous oxide 105 0.45
Sevoflurane 2 0.63
Isoflurane 1.12 1.4
Halothane 0.74 2.25

Second gas effect and
diffusion hypoxia
■ In the initial part of induction, diffusion gradient from
alveoli to blood is high and larger quantity of
anaesthetic is entering blood.
■ If the concentration of inhaled anaesthetic is high, it
will more dissolved to the blood and unable to reach
at target region to produce anaesthetics effect.
■ As the solubility of N2) is very less, about 1 litre/min
of N2O enters blood in the first few minutes.
■ As such, gas flow is 1 litre/min higher than minute
volume. If another potent anaesthetic, e.g.
halothane (1–2%) is being given at the same time, it
also will be delivered to blood at a rate 1 litre/min
higher than minute volume and induction will be
faster. This is called ‘second gas effect’

CLASSIFICATION OF
ANAESTHETICS
General Anaesthetics Agents
Inhalational Agents Parenteral agents
Carrying gas
 Nitrous
oxide
 Xenon
Volatile liquids
 Halothane
 Isoflurane
 Desflurane
 Sevoflurane
 Ether
Inducing agents
 Thiopentone
sodium
 Propofol
 Etomidate
Short acting
agents
 Benzodiazepin
e [Diazepam,
Midazolam,
Lorazepam].
 Opioids
[Fentanyl,
Remifentanil,
Sufentanil].
 Ketamine

CARRYING GASES
(Nitrous oxide, Xenon)

Nitrous oxide [N2O]
■ It is noninflammable, colourless, odorless & non-
irritating gas.
■ It is used as carrying agent for inhalational
anaesthetics.
■ It has good analgesic with poor muscle relaxant
property.
■ In major surgical procedure, it is used in a mixture of
70% N2O + 25–30% O2 + 0.2–2% another potent
anaesthetic.
■ The onset of action is quick and smooth with rapid
recovery.
■ Post anaesthetic nausea is not seen with this agent.

Cont..
■ It has a wide margin of safety as it has minimal effect on
heart, blood pressure, respiration and is not toxic to liver,
brain & kidney.
■ Second gas effect and diffusion hypoxia is seen with this
agent.
■ It is contraindicated in
– air embolism,
– pneumothorax and
– intestinal obstruction
■ as it moves very swiftly from blood into these
compartments and aggravates these conditions.
■ The commercially preparation of N2O gas comes in blue
coloured cylinder.

Xenon gas
■ It is an inert gas.
■ Being least soluble in blood, it has very rapid
inducing action.
■ It is commercially available in white body with
green-black shoulder cylinder.
■ It has to be extracted from air and is very
expensive than other carrying agents.
■ It is rarely used.

STANDARD COLOR CODES
OF THE GAS CYLINDERS

VOLATILE LIQUIDS
(Halothane, Isoflurane, Desflurane,
Sevoflurane, Ether)

Halothane
■ It is a noninflammable, volatile liquid with sweet odour
& nonirritant in nature.
■ The induction with this agent can be achieved quickly
and pleasantly due to intermediate solubility.
■ 2–4% of halothane is given for induction and 0.5–1%
for maintenance.
■ It is delivered by the use of a special vaporizer.
■ Being highly potent, precise control of administered
concentration of halothane is very important as slight
deviation from the required concentration can be
harmful.

■ It causes hypotension to the extent of 20–30 mmHg
drop.
■ It is a preferred agent for asthmatics as it dilates the
bronchi but respiratory depression can also occur.
■ It can prolong delivery and increase postpartal blood
loss; if used during labour.
■ It is used to facilitate external or internal podalic
version during late pregnancy due its property of
inhibition of uterine contractions.
■ In genetically predisposed individuals,
– hepatitis and
– malignant hyperthermia can occur.

■ Malignant hyperthermia is treated by:
– Rapid external cooling
– Bicarbonate infusion
– 100% O2 inhalation
– IV dantrolene (1 mg/kg repeated as
required).
■ In children, it is suitable for both for induction as
well as maintenance.
■ In adults, it is mainly used for maintenance after
IV induction.
■ Practically, halothane is quite common in use.

Isoflurane
■ Isoflurane is commonly used anaesthetic agent as it
produces relatively rapid induction and recovery as
compared to halothane.
■ It is administered through a special vaporizer.
■ 1.5–3% of isoflurane is given for induction and 1–2% for
maintenance.
■ Hypotension is similar to halothane with prominent
respiratory depression.
■ It is not preferred for induction because of its pungent
nature.
■ It is a good maintenance anaesthetic, and is suitable for
neurosurgery.

Sevoflurane
■ It has pleasant odour and it is more suitable anaesthetic
agent for induction in children.
■ It is administered through a face mask.
■ It is intermediate between isoflurane and desflurane in
different pharmacological properties.
■ The solubility in blood and potency are less than
isoflurane but more than desflurane.
■ It is good agent for induction as well as maintenance with
quick recovery.
■ It is suitable both for outpatient as well as inpatient
surgery.
■ It is very expensive; rarely used in government hospitals
while commonly used in corporate hospitals.

Desflurane
■ It has pungent odour and is not suitable for
induction.
■ It is 5 times less potent than isoflurane.
■ It is administered in the vapour form along
with carrier gas (N2O+O2) mixture.
■ The induction and recovery is very fast due
to very low solubility in blood.
■ It is most commonly used as an anaesthetic
for outpatient surgery.

COMPARATIVE FEATURES OF
DIFFERENT INHALATIONAL
AGENTSProperties Halothane Isoflurane Sevoflurane Desflurane
Chemical
structure
Halogenated ether Isomer of enflurane Halogenated ether It is a structure
analogue of Isoflurane
with replacement of
chloride to Fluoride.
Boiling point 50°C 48°C 59°C 24°C (Room
temperature) to prevent
it from boiling TEC-6
vaporizer is used.
MAC 0.75 1.12 2 5.8
BGS 2.25 1.4 0.63 0.42
Colour code Red Purple Yellow Magenta blue
Muscles
relaxant
Least potent More than
halothane
More than
Isoflurane
Most potent
Malignant
hyperthermia
More common Less common than
halothane
Less common than
Isoflurane
Least common

 All inhalational anaesthetics are respiratory depressant.
 Isoflurane causes Coronary steal phenomenon; hence
contraindicated in MI.
 Sevoflurane is the inhalational agent of choice for
induction of GA.
 Desflurane is used as maintenance of choice for GAs.
 Desflurane is the inhalational agent of choice for
 surgery in elderly patient,
 renal impaired and
 day care surgery.
 Halothane is potent bronchodilator and best uterine
relaxant may cause
 uterine atony
 post partum hemorrhage.

 Malignant hyperthermia is more common with
halothane, which presents as fever, hypertension and
tachycardia and is managed by IV injection of
Dantrolene.
 Propofol is a DOC for malignant hyperthermia during
anaesthesia.
 Methoxyflurane is more potent than other inhalational
anaesthetics but it is not used nowadays due to severe
nephrotoxicity.
 Enflurane: It is also inhalational anaesthetic,
absolutes nowadays due to epileptogenic effects.

Ether
■ Ether is an inflammable and highly volatile liquid.
■ It has potent anaesthetic, analgesic and muscle
relaxant properties.
■ It is not used nowadays due to its potent side
effects.
ADVANTAGE AND DISADVANTAGE OF ETHER
Advantage Disadvantage
 It is cardiovascular stable drug.
 It does not depress respiratory
center; no hypoxia is seen.
 It obeys all five criteria of GAs.
 It is a good bronchodilator.
 It is quite economical.
 Both induction and recovery are
slow as it is highly soluble in
blood.
 It produces irritant vapors and
increases the tracheobronchial
secretions; prior atropine is
required.
 It is a highly inflammable agent.

PARENTERAL
ANAESTHETICS
INDUCING AGENTS
(Thiopentone sodium,
Propofol, Etomidate)

Thiopentone sodium
■ It is most commonly used ultra short acting
thiobarbiturate.
■ The solution for injection (2.5%) should be freshly
prepared.
■ The solution is alkaline in nature with a pH of 10.5.
■ It produces induction within 10-12 seconds after IV
injection.
■ It has short duration of action and the
consciousness is regained within 6-8 minutes.
■ It is given in a dose of 3-5 mg/kg.

■ It decreases cerebral blood flow as well as cerebral
oxygen demand; cerebral perfusion is maintained as
per the requirement.
■ It also causes hypotension and tachycardia due to
peripheral vasodilatory effects.
■ It is useful for
– induction of anaesthesia,
– narcoanalysis (used as truth serum),
– management of status epilepticus,
– electroconvulsive therapy and
– brain surgery.
■ Most commonly seen adverse effects are
– delirium and
– shivering during reversal of anaesthesia.

■ It is contraindicated in-patients with asthma
as it may cause laryngospasm due to
increased respiratory secretions.
■ It is also contraindicated in shock and
porphyria.
■ Thiopentone sodium should be
administered only into the vein; if
accidentally injected into the artery, intense
pain, necrosis and gangrene can occur.
■ The first symptom, which appears after
injection into the artery, is severe pain and
first sign is pallor.

Management
■ Leave the cannula in situ.
■ Stat injection of 500unit of heparin.
■ 1% Lignocaine 10ml given; causes
vasodilation and reduces pain.
■ Ganglionic block may be done by
blocking stellate ganglion.

Propofol
■ It is preferred over thiopentone for induction.
■ It is used for both induction and maintenance
purpose.
■ It is oily in nature and commercially prepared from
the egg extract; painful during injection.
■ The patient becomes unconscious within 15–45
second and the effect lasts for 5–10 min.
■ It is given in a dose of 2 mg/kg in 1-2%
concentration bolus i.v. for induction; 100–200
μg/kg/min for maintenance.
■ The recovery with Propofol is pleasant; hence, it
is a drug of choice for day care surgery.

■ It relaxes the upper airways; it is agent of choice for
endoscopy, intubation and in asthmatics. Higher doses
may produce respiratory depression also.
■ It also decreases cerebral metabolic O2 demand, cerebral
blood flow and ICT as thiopentone.
■ The incidence of postoperative nausea and vomiting is
very low.
■ The cardiac effects are similar to thiopentone.
■ In high dose, it may lead to metabolic acidosis, lipaemia
and heart failure even in adults.
■ It is contraindicated in shock.
■ Intermittent injection or continuous infusion of propofol
with fentanyl supplementation is used to produce total i.v.
anaesthesia.

Etomidate
■ It is also ultra-short acting anaesthetic with brief
duration of action.
■ It is given in a dose of 0.2–0.5mg/kg.
■ It produces less cardiovascular and respiratory
depression.
■ It is not used these days due to:
– Pain on injection.
– Excessive muscles movement on induction.
– Nausea, vomiting on recovery.
– Adrenocortical suppression if infusion is given for
prolonged period.

SHORT ACTING AGENTS
(Benzodiazepine, Opioids,
Ketamine)

Benzodiazepines
[Diazepam, Midazolam,
Lorazepam]■ These agents are used in pre-anaesthetic
medication, induction, maintaining and
supplementing anaesthesia as well as for
‘conscious sedation’.
■ They slightly decrease respiration, blood pressure
and cardiac contractility when given in combination
with opioids.
■ They produce amnesia, sedation and
unconsciousness within 5-10 minutes, when given
in slightly higher doses.

■ The side effects such as nausea or vomiting
are uncommon with BZDs.
■ The common indications of BZDs are
endoscopies, angiography, cardiac
catheterization, setting of fractures,
local/regional anaesthesia.
■ BZDs are also an important component of
balanced anaesthesia.
■ Flumazenil in a dose of 0.5–2 mg IV is used
for the reversal of anaesthetic effects of
BZDs.

■ Diazepam
– Administered in a running IV infusion in
a dose of 0.2–0.5 mg/kg slowly to
prevent thrombophlebitis.
■ Lorazepam
– It is a slow acting, less irritant and 3-
times more potent than diazepam.
– It is given in a dose of 2-4 mg IV.
– It has potent amnesic effect.

Midazolam
■ It is short acting, nonirritant to veins and water
soluble BZD.
■ It is 3 times more potent than diazepam.
■ It is given in a dose of 1–2.5 mg IV, while 0.02–
0.1 mg/kg/hour continuous IV infusion is given in
the critical care anaesthesia.
■ It is also used for the sedation of
■ intubated and
■ mechanically ventilated patients, and
■ for debridement &
■ dressing of burn wounds.
■ It is preferred over diazepam for anaesthetic
use.

OPIOIDS [Fentanyl,
Remifentanil, Sufentanil].
■ Fentanyl
– It is more lipid soluble and easily crosses BBB;
produces analgesic effects within 5 minutes after IV
injection.
– It is given in a dose of 2–4 μg/kg and can be used in
combination with BZDs.
– It is used for endoscopic, angiographic and minor
surgical procedures in low risk patients.
– It is used as adjunct in nerve block, spinal block and
for the management of postoperative pain.
■ Alfentanil, Sufentanil and Remifentanil are still shorter
acting analogues, which can be used in place of fentanyl.

Ketamine
■ It induces ‘dissociative anaesthesia’, which is
characterized by dissociation from the body and
surroundings with profound analgesia, immobility,
amnesia and light sleep.
■ The primary site of action is in the cortex and
subcortical areas; not in the reticular activating
system, which is the site of action of barbiturates.
■ It acts by inhibition of NMDA receptor complex.
■ Respiration is not depressed, bronchi dilate, airway
reflexes are maintained, muscle tone increases.

■ A dose of 1–2 mg/kg IV or 3–5 mg/kg IM produces
the above effects within a minute, and recovery
starts after 10–15 min, but patient remains amnesic
for 1–2 hr.
■ Ketamine has been used for operations on the
– head and neck,
– in asthmatics (relieves bronchospasm),
– in those who do not want to lose
consciousness and for short operations.
■ It is the only IV anaesthetic that produces
analgesic effects.

■ Ketamine increases the cerebral blood flow, intraocular
pressure (IOP) and intracranial tension (ICT).
■ Therefore, it is contraindicated in patients with
– hypertension,
– ischemic heart disease,
– glaucoma and
– neurosurgical procedures but
■ suitable for patient of hypovolumic shock.
■ It is used in combination with diazepam for
angiographies, cardiac catheterization and trauma
surgery.
■ Children tolerate this drug better than adults.

CONSCIOUS SEDATION
■ ‘Conscious sedation’ is a state of altered
consciousness that is used in minor procedures
(localized surgical or therapeutic procedure) which
do not require proper anaesthesia.
■ In this condition the patient is in conscious state but
doesn’t feel any pain stimulus.
■ This is due to CNS depressant effects by the drugs
without interfering the level of consciousness of
patient.

Drugs used for conscious
sedation are
■ Fentanyl: At 1–2 μg/kg every 15–30 min
with/without combination of other drugs
[Propofol, Midazolam].
■ Nitrous oxide: 10% nitrous oxide [maximum up to
50%] in combination with 100% oxygen. The
effects last only for ≤ 1 hour.
■ Propofol: Given as continuous IV infusion till the
procedure is performed. It has very short action.
As soon as Propofol is withdrawn, patient
recovers within minutes.

■ Diazepam: 1-2 mg slow IV infusion in small repeated
doses produces satisfactory sedative effects like
slurring of speech, ptosis, muscles relaxation, etc.
– The further administration is stopped after this
observation.
– The effects of diazepam persist for an hour while
the psychomotor impairment persists for 6–24
hour.
■ Midazolam: It is used as an alternative to diazepam.

Dexmedetomidine is a centrally active
selective α2A agonist that has been
introduced for sedating critically
ill/ventilated patients in intensive care
units.

■ Preanaesthetic medications are the drugs given before
anaesthesia to make patient calm and to make the
anaesthesia more pleasant and safe.
■ It is given:
– To decrease the level of anxiety and apprehension
– To facilitate induction
– For pre- and postoperative amnesia
– To decrease the requirement of anaesthetic drugs
– To decrease gastric and respiratory secretions and
antiemetic effect.
■ Depending upon the need of patient and type of surgery
being performed, different combination of drugs are
used as pre-anaesthetic medications.

Sedative-antianxiety drugs
■ Benzodiazepines like diazepam, lorazepam,
midazolam, and promethazine are commonly
used drug as preanaesthetic medications for
their tranquilizer and smooth induction
property.
■ Diazepam (5–10 mg oral) or lorazepam (2 mg
oral or 0.05 mg/kg IM) are used one hour
before the surgery.

■ Midazolam is commonly used
intravenously due to it shorter action and
water solubility. It is used along with
pethidine/fentanyl for a variety of minor
surgical and endoscopic procedures
■ Promethazine having antihistaminic,
antiemetic anticholinergic and sedative
effects is used in a dose of 50 mg
intramuscularly.

Anticholinergics
■ These drugs are less frequently used
nowadays due to availability of non-irritant
anaesthetics drugs.
■ The commonly used anticholinergics for
preanaesthetics are atropine or hyoscine
or glycopyrrolate.
■ These drugs are used to reduce GI and
bronchial secretions to prevent aspiration.

■ Atropine or hyoscine given in a dose of 0.6
mg or 10–20 μg/kg IM/IV and glycopyrrolate
at 0.2–0.3 mg or 5–10 μ g/kg IM/IV.
■ Glycopyrrolate is more preferred than
atropine due to its lesser side effects and
good anti-secretory action after IM injection.
■ Hyoscine having both antiemetic and
amnestic effects but may lead to delirium
and disorientation; hence less frequently
used.

H2 blockers/proton pump
inhibitors
■ These agents are mainly indicated in the individuals who
are at high risk of gastric regurgitation and aspiration
pneumonia usually seen after prolonged GI surgery,
caesarian section and obese patients.
■ The commonly prescribed drugs are pantoprazole (40
mg) or Ranitidine (150 mg) or famotidine (20 mg) or
omeprazole (20 mg). These are given night before and in
the morning or preferably 12 hours before any procedure.
■ They reduce GI secretions as well as pH; hence routinely
prescribed nowadays.
■ They are also beneficial to prevented stress ulcer.

Antiemetics
■ The commonly prescribed drugs are
metoclopramide, ondansetron and domperidone.
Metoclopramide Ondansetron Domperidone
 Preoperatively 10–
20 mg IM is given
to counteract
postoperative
vomiting.
 It increases LES
tone and promoting
gastric emptying.
 It may use in
combination with
H2 blockers.
 Preoperatively 4–8
mg IV is given to
counteract
postoperative
nausea and
vomiting.
 It selectively
inhibits5-HT3
receptors.
 It has very few
side effects; hence
most commonly
used.
 Domperidone is
nearly as
effective and
does not produce
extrapyramidal
side effects.

Opioids
■ Nowadays opioids are less commonly used in
postoperative pain; fentanyl is used only if
specifically indicated.
■ Opioids are used for induction, pre-and post-
operative analgesia and to manage preoperative
anxiety.
■ Commonly intramuscularly morphine (10 mg) or
pethidine (50-100 mg) are used.
■ They may cause respiratory depression, biliary
spasm, hypotension and may precipitate
asthma.
■ Morphine may cause postoperative vomiting,
urinary retention and constipation; while
pethidine induces tachycardia.

Neuroleptics
■ These agents have great potency to
develop hypotension and respiratory
depression; hence infrequently used
nowadays.
■ In children muscles dystonia and
involuntary movements may be seen.
■ These agents are used as antiemetics,
antianxiety and for induction.
■ The commonly used preanaesthetic drugs
are chlorpromazine (25 mg), triflupromazine
(10 mg) or haloperidol (2–4mg) given
intramuscularly.

■ Local anesthesia refers to a reversible loss
of sensations in limited areas of the body.
■ The local anaesthetic drugs block
generation and conduction of nerve impulse
at any part of the neuron with which they
come in contact, without causing any
structural damage to the nerve.
■ When a LA is applied to a mixed nerve, both
sensory and motor impulses are interrupted
which results in muscular paralysis and loss
of autonomic control as well.

■ Local anesthesia can be achieved by
several different methods:
– Topical administration,
– infiltration,
– field block,
– nerve block, and
– intravenous regional anesthesia.

Topical Administration
■ Topical local anesthesia involves the
application of a cream, lotion, ointment, or
drop of a local anesthetic to skin or
mucous membrane to relieve pain or to
anesthetize the area to facilitate a
medical procedure.
■ Although systemic absorption is rare with
topical application, it can occur if there is
damage or breakdown of the tissues in
the area.

Infiltration anaesthesia
■ Infiltration local anesthesia involves
injecting the anesthetic drug directly into
the tissues to be anaesthetized.
■ The infiltrated anesthetic comes into
contact with the nerve endings in the area
and prevents them from transmitting
nerve impulses to the brain.

Field Block
■ Field block local anesthesia involves
injecting the anesthetic drug all around
the area, which needs to be anesthetized
for procedure or surgery.
■ Example: block for tooth extractions.

Nerve Block
■ Nerve block local anesthesia involves
injecting the anesthetic drug at some
point along the nerve or nerves that run to
and from the region in which the loss of
pain sensation or muscle paralysis is
desired.
■ The blocks are given at some distance
from the field to be operated.

Several types of nerve blocks
are possible:
■ Peripheral nerve block: for relief of pain or for
diagnostic purposes.
■ Central nerve block: injection of anesthetic into the
roots of the nerves in the spinal cord.
■ Epidural anesthesia: Injection of the drug into the
epidural space where the nerves emerge from the
spinal cord.
■ Caudal block: Injection of anesthetic into the sacral
canal, below the epidural area.
■ Spinal anesthesia: Injection of anesthetic into the
spinal subarachnoid space.

Intravenous Regional Local
Anesthesia
■ Intravenous regional local anesthesia
involves carefully draining all of the blood
from the patient’s arm or leg, securing a
tourniquet to prevent the anesthetic from
entering the general circulation, and then
injecting the anesthetic into the vein of the
arm or leg.
■ This technique is used for very specific
surgical procedures.

CLASSIFICATION
■ Injectable anaesthetics
■ Surface anaesthetics
Low potency and
short duration
 Procaine
 Chloroprocaine
Intermediate
potency and
duration
 Lidocaine
(Lignocaine)
 Prilocaine
High potency and long
duration
 Tetracaine
 Bupivacaine
 Ropivacaine
 Dibucaine
Soluble
 Cocaine
 Lidocaine
 Tetracaine
 Benoxinate
Insoluble
 Benzocaine
 Oxethazaine
 Butylaminobenzoate

Deference between Ester and
Amide of Local Anaesthetics
Properties Ester Amide
Onset of action Slow Fast
Duration of
action
Short Intermediate
Tissue
penetration
Poor Good
Metabolism By cholinesterase By liver microsomal
enzyme
Allergic reactions Common Uncommon
Drugs Cocaine, Procaine,
Benzocaine,
Tetracaine
Chloroprocaine
Lidocaine, Dibucaine,
Bupivacaine,
Ropivacaine, Prilocaine ,
Articaine

Mechanism of Action
■ Local anaesthetics [LAs] interfere with the
sodium ions entry during action potential
and this leads to inhibition of nerve
conduction.
■ They mainly act on the voltage gated
sodium channel and open it, leading to
efflux of positive ions and cell become
negative inside causing hyperpolarization.

■ Mostly, the LAs are used for their local
action, but after systemic absorption from
the local site, some systemic effects may
be seen.
■ The systemic actions are seen depending
up on the concentration attained in
plasma and tissues.
■ All LAs produce CNS stimulation followed
by depression.

■ The LAs act as cardiac depressants
– if they achieve concentration 2-3 times
higher than that producing CNS effects or
accidently these are injected intravenously.
■ They decrease:
– automaticity,
– excitability,
– contractility,
– conductivity and
– prolong effective refractory period (ERP).
■ By causing vasodilation, they cause
hypotension.

The local anaesthetic agents are not
able to provide adequate pain control
in inflamed tissues.
■ This occurs due to following reasons:
– Due to inflammation, the pH of the tissues
becomes acidic which causes ionization of
greater fraction of the LA. This hinders the
diffusion of LAs into the axolemma of nerve.
– The LA is removed more rapidly from the site
due to increased blood flow to the inflamed
area.
– Inflammatory mediators may oppose LA action.

Usually, adrenaline is added to the local
anaesthetic solutions.
■ The adrenaline acts as vasoconstrictor in a ratio
of 1:50,000 to 1:200,000 and the addition of a
vasoconstrictor offers following advantages as
compared to plain local anaesthetic solution:
– It prolongs the duration of action of LAs by decreasing
their rate of removal from the local site. It increases
the intensity of nerve block.
– As the rate of absorption is reduced, the plasma
concentration remains on the lower side and the
systemic toxicity of LAs is reduced.

Cont…
– Due to intense local vasoconstriction, the
field of surgery remains bloodless.
– Simultaneously, there are disadvantages of
this combination in the form of
■ local tissue edema,
■ necrosis,
■ delay in wound healing due to local tissue
hypoxia and
■ rise in blood pressure and
■ arrhythmias in the susceptible individuals

Precautions while using LAs
■ Before injecting the LAs, aspiration test
should be performed to avoid intravascular
injection.
■ Inject the LA slowly and take care not to
exceed the maximum safe dose, especially
in children.
■ Propranolol (probably other β blockers also)
may reduce metabolism of lidocaine and
other amide LAs by reducing hepatic blood
flow.

Cont…
■ Vasoconstrictor (adrenaline) containing LA
should be avoided for patients with
– ischemic heart disease,
– cardiac arrhythmia,
– thyrotoxicosis,
– uncontrolled hypertension, and
– those receiving
■ β blockers (rise in BP can occur due to
unopposed α action) or
■ tricyclic antidepressants (uptake blockade
and potentiation of Adr).

Reasons of failure in induction
of local anaesthesia
Causes of failure of local
anaesthesia
Management of failed local
anaesthesia
 Wrong technique &
anatomical variations
 Inadequate dose
 Sepsis
 Injection in blood
vessels
 Anxiety [reduces patient
pain threshold]
 Check anatomical
landmarks.
 Repeat injection.
 Settle pain and
inflammation and try
again about a week later.
 Manage accordingly.
 Consider whether
anxiety may be
contributory.

Drugs Groups Duration
of action
(minutes)
Onset
of
action
Special features
Procaine Ester 15-30 Slow  It was the first synthetic LA.
 It slows the absorption of
penicillin making it OD dose.
 Presented as injection PPF
(procaine penicillin fortified).
Chloroprocaine Ester 15-30 Rapid  Low toxicity due to rapid
metabolism.
Lidocaine
(Lignocaine)
Amide 30-60 Rapid  Most widely used LA.
 Both surface and injectable
forms are available.
 Used for most of the surgical
procedures.
Prilocaine Amide 30-90 Interm
ediate
 Used for infiltration, nerve block
and intravenous regional
anaesthesia.

Drugs Groups Duration
of action
(minutes)
Onset
of
action
Special features
Tetracaine Ester 120-240 Very
slow
 Use is restricted to eye, nose,
throat and tracheobronchial tree.
Bupivacaine Amide 120-240 Interm
ediate
 Epidural injection (0.25-0.5%)
provides analgesia- painless
vaginal delivery.
 Cardiotoxic at ≥0.75%
concentration.
Ropivacaine Amide 120-360 Interm
ediate
 Similar to bupivacaine with less
cardiotoxicity, preferred over
bupivacaine in postoperative
pain and painless vaginal
delivery.
Dibucaine Amide 180–600 Slow  It is most potent, most toxic and
longest acting LA.
 Used only topically

Drugs Onset of
action
Special features
Cocaine Fast  Rarely used as anaesthetic agent.
 Produces drug dependence and abuse.
Benoxinate Rapid  0.4% solution is used for corneal
anaesthesia for tonometry (intraocular
pressure measurement procedure).
Tetracaine Very slow  0.5% solution is used for eye, nose, throat
and tracheobronchial tree.
Lidocaine (Lignocaine) Rapid  Topical: 4%, jelly & viscous form: 2%,
ointment: 5%, spray: 10% available in the
market.
 Transdermal patch is used in post-herpetic
neuralgia.
Benzocaine Intermediate  It is not absorbed from mucous membrane.
 Used as lozenges for stomatitis, sore throat.
 As powder/ointment for wound/ulcerated
surface and suppository for anorectal
lesions.
Butylaminobenzoate Intermediate  Same as above
Oxethazaine Slow  It is active even at low pH. Hence, used
along with antacids for anesthetizing gastric
mucosa.

EMLA
(Eutectic mixture of local anaesthetics
lignocaine 2.5% and pilocaine 2.5%)
■ Eutectic mixture is made by mixing 2.5%
lidocaine and 2.5% prilocaine in equal
proportions at 25°C.
■ This lowers the melting point of these two
drugs.
■ The resulting oil is emulsified into water to
form a cream.

■ This preparation can anaesthetize intact skin
after surface application.
■ The method of application of this cream is
unique.
■ The EMLA cream is applied under occlusive
dressing for 1 hr before the requirement of
anaesthesia in conditions such as
– split skin graft harvesting,
– painless IV cannulation and
– other superficial procedures.

Cont..
■ The part remains anaesthetized for 1-2
hours after removal of occlusive dressing.
■ It is used as an alternative to lidocaine
infiltration.
■ It should not be used on
– mucous membranes and
– abraded skin.
■ It is available in 5% concentration.

ADVERSE EFFECTS OF
LOCAL ANAESTHETICS
■ The rapidly absorbed LAs with slow
metabolism are more toxic and produce
side effects when they come in circulation
and reach to various organs such as
CNS, CVS etc.

■ CNS effects: Dizziness, mental confusion,
disorientation, shivering, twitching,
auditory and visual disturbances,
convulsions and respiratory arrest.
– This is treated by diazepam.
■ Cardiovascular toxicity of LAs presents as
– bradycardia,
– hypotension,
– cardiac arrhythmias and
– vascular collapse.

■ Injection of LAs is painful and addition of
vasoconstrictor enhances the local tissue damage.
■ The lignocaine with adrenaline combination should not
be used for
– infiltration in ring block of hands, feet, fingers, toes,
in pinna and penis.
■ Hypersensitivity reactions and rarely anaphylaxis can
also occur.
– These reactions are more common with ester-
linked LAs, but rare with lidocaine or its congeners.
■ Cross reactivity is frequent among ester compounds,
but not with amide-linked LAs.
■ The cause of allergic reaction is methylparaben, which
is added as preservative in certain LA solutions.

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