ANAESTHETICS
What are Anaesthetics?
 Anaesthetics
are drugs that
causes reversible loss of
sensation with or without
reversible loss of consciousness
Classification
a) General Anaesthetics
These are drugs that causes reversible loss of
sensation, along with reversible loss of
consciousness, affecting the whole body
b) Local Anaesthetics
These are drugs that causes reversible loss of
sensation, without loss of consciousness,
affecting a localized area
Classification of General Anaesthetics
I) Inhalational General Anaesthetics

Volatile Liquids:
Chloroform, Diethyl ether, Ethyl chloride,
Trichloroethylene, halothane, Enflurane,
Isoflurane

Gases:
Cyclopropane, Nitrous oxide
Classification of General Anaesthetics
II) Intravenous anaesthetics

Barbiturates
Thiopentone sodium, Methohexital

Non – barbiturates
Midazolam
Ketamine
Etomidate
Propofol
Classification of Local Anaesthetics
I. Injectable
•
Low potency, short duration
Procaine, Chloroprocaine
•
Intermediate potency and duration
Lignocaine, Prilocaine
•
High Potency, Long duration
Tetracaine , Bupivacaine, Ropivacaine,
Dibucaine
Classification of Local Anaesthetics
II)
a)
III)
Surface Anaesthetic
Soluble
Cocaine
Lignocaine
Tetracaine
Benoxinate
b) Insoluble
Benzocaine
Butylaminobenzoate
(Butamben)
Oxethazine
Other Drugs
Propranolol, Chlorpromazine, Quinine
General Anaesthetics
2.
Site of action
Area of body
involved
3.
Consciousness
1.
4.
5.
6.
7.
8.
Care of vital
functions
Physiological
trespass
Poor health
patient
Use in non –
cooperative
patient
Major surgery
Local Anaesthetics

CNS
 Whole body
Lost
Peripheral nerves
Restricted area
Unaltered
Essential
Usually not needed
High
Low
Risky
Safer
Possible
Not possible
Preferred
Cannot be used
preferred
Stages of general Anaesthesia

Stage of Analgesia
Loss of pain sensation
Stage of Delirium
↑ BP & ↑ respiratory rates
Stage of surgical
anaesthesia
Regular respiration
Skeletal muscle relaxation
Progressive loss of eye
reflexes
Cessation of eye movements

Fixed Pupil
1.

2.

3.



4.


Medullary Paralysis Respiratory
centre
Severe depression
DEATH
Vasomotor
centre
Properties of an Ideal Anaesthetic
Pleasant
Non – irritating
Non – inflammable
Good anaesthetic, analgesic, skeletal muscle
relaxant
No action on heart, BP, respiration
Smooth induction
No post anaesthetic nausea and vomiting
Cheap
Nitrous Oxide
Colorless , Non-irritating gas
Odourless, Non – inflammable
Low potency anaesthetic
Good analgesic
Poor skeletal muscle relaxant
Low blood solubility, Quick onset
Rapid recovery
No effect on other organs
Shows second gas effect & Diffusion hypoxia
Used as an adjuvant/carrier
ALONE in dental and Obstetric analgesia
Cheap , very commonly used
Second Gas Effect
When certain anaesthetics like N2O are
administered in high concentrations,the
other anaesthetic which is given along
with N2O ,is also pullen & its alveolar
tension rises more rapidly than when it
(second anaesthetic) is given alone.This
is known as second gas effect
 ↓ concentration of second anaesthetic
 ↓ adverse effects

Diffusion hypoxia

When anaesthetics like N2O is
discontinued after prolonged use- N2O
having low blood solubility ,rapidly back
diffuses into alveoli & dilutes alveolar air
(↓ oxygen content) hypoxia
Ether
Colorless , volatile liquid
Pungent odour
Highly irritant & Inflammable
Potent anaesthetic
Good analgesic & skeletal muscle relaxant
action
↑ respiratory rate
BP & heart rate are well maintained
No interference with uterine contractility
Cheap
Shouldn’t be given in Alcoholics
Halothane
Fluorinated volatile liquid
Structurally similar to chloroform
Sweet fruity odour
Non – irritant & Non – inflammable
Potent anaesthetic
Poor analgesic & muscle relaxant
↓ solubility in blood
Smooth induction
Rapid recovery
Halothane
Depresses myocardial contractility
↓ BP & heart rate
Arrhythmia
Respiratory depression
↓ urine formation
HEPATITIS
Malignant hyperthermia
Most popular anaesthetic
Nitrous Oxide and Diethyl ether
Nitrous Oxide
Diethyl ether
Colorless, Odourless,
noninflammable gas &
nonirritating
Highly volatile liquid
produces irritating vapors care inflammable
It is a inhalational
anaesthetic
It is a inhalational
anaesthetic
Low potency anaesthetic
Potent anaesthetic
Good analgesic but poor
muscle relaxant
Good analgesic & marked
muscle relaxation
Nitrous Oxide
Diethyl Ether
Action is quick & smooth
Induction is prolonged &
unpleasant
Recovery is rapid
Recovery is Slow
Post anaesthetic nausea is Post anaesthetic nausea &
not marked
vomiting are marked
Little effect on respiration, BP & respiration are
heart & BP
generally well maintained
Nontoxic to liver, kidney
and brain
Not hepatotoxic
Cheap and commonly
used
Cheap but not used as such
Nitrous Oxide & Halothane
Nitrous Oxide
Halothane
It is a inhalational
anaesthetic
Colorless, Odourless &
nonflammable gas
Nonirritating, low potency
anaesthetic
It is a inhalational
anaesthetic
Noninflammable, volatile
liquid with sweet
odour
Nonirritating potent
anaesthetic
Good analgesic but a poor
muscle relaxant
Not a good analgesic or
muscle relaxant
Nitrous Oxide
Halothane
Action is quick & smooth
Induction is quick &
pleasant
Little effect on respiration, BP falls & greater
heart & BP
depression of
respiration
Nontoxic to lever, kidney Hepatitis occurs in
& brain
susceptible individuals
Recovery is quick
Recovery is smooth &
quick
Post anaesthetic nausea is Shivering may occur
not marked
but nausea & vomiting
are rare
Ether & Halothane
Ether
Halothane
It is a inhalational
anaesthetic
It is a inhalational
anaesthetics
Produce irritating vapours
which are inflammable
Nonirritant &
Noninflammable
Potent anaesthetic, good
analgesic & marked muscle
relaxation
Potent anaesthetic, but not a
good analgesic or muscle
relaxation
BP & respiration are well
maintained
BP falls and greater
depression of respiration
Does not sensitize the
heart to Adrenaline
Sensitize the heart to the
arrhythmogenic action of
Adrenaline
Not hepatotoxic
Hepatitis occurs in
susceptible individuals
Induction is prolonged &
unpleasant
Induction is reasonable
quick and pleasant
Nitrous Oxide & Halothane
Nitrous Oxide
Halothane
It is a inhalational
anaesthetic
Colorless, Odourless &
nonflammable gas
Nonirritating, low potency
anaesthetic
It is a inhalational
anaesthetic
Noninflammable, volatile
liquid with sweet
odour
Nonirritating potent
anaesthetic
Good analgesic but a poor
muscle relaxant
Not a good analgesic or
muscle relaxant
Nitrous Oxide
Halothane
Action is quick & smooth
Induction is quick & pleasant
Little effect on respiration, heart &
BP
BP falls & greater depression of
respiration
Nontoxic to lever, kidney & brain
Hepatitis occurs in susceptible
individuals
Recovery is quick
Recovery is smooth & quick
Post anaesthetic nausea is not
marked
Shivering may occur but nausea
& vomiting are rare
Ether & Halothane
Ether
Halothane
It is a inhalational
anaesthetic
It is a inhalational
anaesthetics
Produce irritating vapours
which are inflammable
Nonirritant &
Noninflammable
Potent anaesthetic, good
analgesic & marked muscle
relaxation
Potent anaesthetic, but not a
good analgesic or muscle
relaxation
BP & respiration are well
maintained
BP falls and greater
depression of respiration
Does not sensitize the heart to Sensitize the heart to the
Adrenaline
arrhythmogenic action of
Adrenaline
Not hepatotoxic
Hepatitis occurs in susceptible
individuals
Induction is prolonged &
unpleasant
Induction is reasonable quick
and pleasant
Thiopentone Sodium

Quick and pleasant induction

hypnosis deep sleep anesthesia

Consciousness lost first  reflex activity
muscle tone  medullary centres
depressed

Pupils contracted to light

Cerebral blood flow and cerebral metabolic
rate ↓↓ intra cranial tension↓

Absence of eye lid reflex sign of
adequate induction
Absorption,fate,excretion

Very short duration of action high lipid
solubility

With successive doses of drug ,body fat
depots get saturated with drug

Slow release back into plasma
drowsiness after cessation

Cross placental barrier
Therapeutic uses
 For
Induction
 As anesthetic agent, for operations of short
duration
 As an anesthetic, in patients with malignant
hyperthermia
 As
an Anticonvulsant
Advantages

Quiet respiration ,non-explosive
Disadvantages

Pharyngeal, laryngeal reflexes persist
coughing ,laryngospasm

Depression of respiratory centre
KETAMINE
Pharmacologically related to hallucinogen
phencyclidine
 Anesthesia induced by im(5-10mg/kg) or
iv (1-2mg/kg)
 Site of action: cerebral cortex, limbic
system
 Analgesic in sub narcotic doses,
immobility, amnesia with light sleep

 Given
iv quick acting ,following single
dose dissociative anesthesia 
complete analgesia & amnesia
 Analgesia
40 minutes; anesthesia
15 minutes
 No
CVS & respiratory depression
 Bronchodilator
 BP
,HR,CO  noradrenaline
 Used
in shock
Disadvantages of Ketamine
Involuntary movements ,hypertonus
 Delirium ,hallucinations during induction
and recovery ; avoided by diazepam
 Poor muscle relaxation ,intra ocular
pressures & intra cranial pressures

PROPOFOL
Rapid induction & recovery, small
hangover effect
 Used for induction & maintenance of GA
 Dose dependent cortical depression,
anticonvulsant
 Metabolized by liver 88%
 Adv: antiemetic action, daycare surgery,
safe during pregnancy

NEUROLEPTANALGESIA
Method of IV anesthesia combining
neuroleptics & opioids.
 Conscious & cooperative during anesthesia
 Droperidol + Fentanyl

Fentanyl
Opioid supplementary analgesic in
inducing GA
 100 times more potent than morphine
 Droperidol 2.5mg & fentanyl citrate 50mcg
in 1 ml
Advantage
 Smooth onset and rapid post operative
recovery


Less danger of hypotension ,suppression of
coughing ,vomiting

Continued analgesia in post operative period

Patient’s co-operation

Useful in old people
Adverse reactions
Extra pyramidal disturbances ,respiratory
depression
 Fentanyl has shorter duration of analgesic
action; supplementary doses of fentanyl
has to be given

PREANAESTHETIC MEDICATION
Defined as “preanaesthetic medication",
drugs with specific pharmacological actions
administered preoperatively with specific
goals to achieve.
GOALS OR OBJECTIVES OF PREMEDICATION
1.
2.
3.
4.
5.
6.
7.
RELIEF OF APPREHENSION OR ANXIETY
SEDATION
ANALGESIA
ANTISIALOGOGUE EFFECT
REDUCTION OF GASTRIC ACIDITY & VOLUME
PREVENTION OF NAUSEA & VOMITING
FACILITATION OF ANESTHETIC INDUCTION
OPIOIDS– morphine (10mg),or pethidine(50mg-100mg),fentanyl
ANTIANXIETY DRUGS– BZDs,diazepam(5-10mg)
Diazepam is anxiolytic ,amnesic &sedative
SEDATIVE-HYPNOTIC– pentobarbitone(100mg).
night before and in morning to calm the patient.
ANTICHOLINERGICS– atropine or hyoscine(0.6mg
i.m or i.v.) TO PREVENT VAGAL BRADYCARDIA& HYPOTENSION.
Decrease salivary & bronchial secretion.
H2 BLOCKERS – ranitidine(150mg) or famotidine(20mg)
Raises gastric pH, reduce gastric volume gastroesophageal reflux.
ANTIEMETICS– metoclopramide(10-20mg) i.m preoperatively,
is effective in reducing post operative vomiting