Pharmacology MBBS for BAMS students

1. ANAESTHESIA
FOR SECOND PROFESSIONAL
BAMS STUDENTS
Dr. Remya Krishnan MD PhD (Ay)

2. WHAT DOES ANESTHESIA
MEAN?
The word anaesthesia is derived from the
Greek: meaning insensible or without
feeling.
The adjective will be ANAESTHETIC .
The means employed would properly be
called the anti-aesthetic agent but it is
allowable to say anaesthetic or in
American anesthetic

3. Definition of Anaesthesia
Insensible does not necessary imply loss of
consciousness.
So General Anaesthesia can be defined as :
Totally Reversible Induced Pharmacological
type of Unconsciousness so it can be
differentiated from sleep, head injury,
hypnosis, drug poisoning , coma or
acupuncture

4. COMPONENTS OF ANAESTHESIA
The famous components of general anaesthesia are
TRIAD
1. UNCOSCOUSNESS.
2. ANALGESIA
3. MUSCLE RELAXATION.
But those triad are under modifications
Unconsciousness replaced by amnesia or loss of awareness
Analgesia replaced by no stress autonomic response
Muscle relaxation replaced by no movement in response to
surgical stimuli

5. General Anaesthetics
1.Agents which produce a reversible loss of
conciousness so as to enable surgical
operation .
a. Stage of Analgesia
b.Stage of delerium or excitement
c.Stage of surgical anasthesia
d.Stage of respiratory paralysis

6. Procedures
Stage 1-period between starting of administration of drug to
the onset of surgical anaesthesia . The patient progresses
from analgesia without amnesia to analgesia with amnesia
Stage 2- Stage of delirium and involuntary excitement
followed by loss of consciousness . Respiration and heart
rate becomes irregular, uncontrolled movements, breath
holding and papillary dilatation.Rapidly acting drugs
minimize the duration of the stage
Stage 3- of surgical anasthesia – relaxation of skeletal
muscles and depression of CNS and respiration
Stage 4- Overdose- Severe brain stem and medullary
depression caused by excess medication . Cardiovascular
collapse can happen unless cardiovascular and respiratory
support is rendered on time

7. •
A general anaesthetic (or anesthetic) is a drug that
has the ability to bring about a reversible loss of
consciousness. Anesthesiologists administer these
drugs to induce or maintain general anaesthesia to
facilitate surgery.
•
The patient gets unconscious and unaware of the
surroundings

8. •
Injectable anaesthetics are used for the induction
and maintenance of a state of unconsciousness by
inhaled gas anaesthetics and IV drugs .
•
Anaesthetists prefer to use intravenous injections,
as they are faster, generally less painful and more
reliable than intramuscular or subcutaneous
injections.

9. Membrane potential

When a neuron is at rest, there is a considerable
difference between ion concentration inside and outside

The difference is partly the result of unequal distribution
of potassium ions and sodium ions on either side of the
membrane

In resting neurons, the potassium ions inside the cell is
about 28-30 times greater than it is outside

The sodium ion concentration is 14 times greater
outside than inside

The sodium potassium pump is the membrane system by
which sodium and potassium ions are actively
transported simultaneously

10. Neuronal Excitability
•
There is always a difference in charge on either side of
the membrane , net positive outside and net negative
inside and this difference in the charge is called resting
membrane potential and the membrane is said to be
polarized.
•
The ability of neurons to respond to stimuli and convert
into nerve impulse is called excitability.
•
If an excitatory stimulus is applied to polarised
membrane,the membrane’s permeability of
sodium ions increases at the point of stimulation
and sodium channels open and permit the influx
of sodium ions by diffusion

11. Neuronal excitability
•
As more sodium ions are entering inside
the resting membrane potential inside
membrane shifts from -70mV towards 0-
Depolarisation.
•
The inside becomes more positive
and outside negative , the potential
increases upto +30mV and it requires
only a time period of 0.5 mSec

12. Repolarisation
•
By the time the nerve impulse travels from one point to
the next, the previous pointe becomes repolarised and
its resting potential is restored.
•
Repolarisation happens by the action of voltage
sensitive potassium channels which opens and rapid
passage of potassium ions to exterior happens but along
with this voltage sensitive sodium ions become
inactivated causing an inhibition to further entry of
sodium ions .
•
Thus the outer surface becomes more positive
owing to potassium ions and loss of potassium
ions from inside result in inner surface of
membrane negative again restoring the
membrane potential of -70mV

13. GABA –Action
•
The potassium ions that have leaked to outside
membrane and sodium ions that are leaked to
inside membrane get restored to original sites of
the membrane by the action of sodium
potassium pump
•
A substance called Gamma Amino Butyric Acid
(GABA) leads to the inhibition of certain neurons
in the CNS by hyperpolarising (making more
negative) the synaptic membrane

14. MOA
•
It is postulated that general anaesthetics
exert their action by the activation of
inhibitory central nervous system (CNS)
receptors, and the inactivation of CNS
excitatory receptors. The relative roles of
different receptors is still under much
debate

15. Hyperpolarization
•
These channels regulate membrane
excitability, and halothane has been found
to reduce neuronal firing by
hyperpolarizing neurons

16. Mode of action
Sensitise GABA RECEPTORS
GABA is inhibitory neurotransmitter
Opening of chloride ion channels leads to
hyperpolarisation of neuronal membrane .
Opening of potassium ion channels leading
to hyperpolarisation of neuronal
membranes

17. TOOLS OF ANAESTHESIA
Knowing physiology, pathology ,and
pharmacology is not enough to
communicate safe anesthesia
But there is need for two important tools:
1. Anaesthetic machine.
2. Monitoring system.

18. ANAESTHETIC MACHINE
1. Oxygen gas supply.
2. Nitrous oxide gas supply.
3. Flow meter
4. Vaporizer specific for every agent
5. Mechanical ventilator
6. Tubes for connection.

19. Anaesthesia
Machine
An anaesthesia machine allows
composing a mixture of oxygen,
anaesthetics and ambient air,
delivering it to the patient and
monitoring patient and machine
parameters.
Liquid anaesthetics are vapourized in
the machine.
All of these agents share the property
of being quite hydrophobic (i.e., as
liquids, they are not freely miscible—
or mixable—in water, and as gases
they dissolve in oils better than in
water).

20. MONITORING
1. Pulse, ECG
2. Blood pressure
3. Oxygen saturation.
4. End tidal CO2
5. Temperature
6. Urine output, CVP, EEG, bispectral index,
muscle tone, ECHO, drug concentration.

21. HOW CAN WE ACHIEVE
ANAESTHESIA?
1. General anaesthesia
a) Inhalational: by gas or vapor
b) IV ,IM or P/R
2. Regional anaesthesia
3. Local anaesthesia
Or to combine between them

22. INHALATIONAL ANAESTHESIA
- Inhalational anaesthesia is achieved
through airway tract by facemask,
laryngeal mask or endotracheal tube.
- The agent used is a gas like nitrous oxide
or volatile vapor like chloroform, ether, or
flothane.
- Inhalational anaesthesia depresses the
brain from up [cortex] to down [the
medulla] by increasing dose.

23. Inhalational Anaesthetics
1. Volatile liquids- Ether, Halothane.
2. Gases – Nitric oxide .

24. Intravenous Anaesthetics
Intravenous anaesthetics act quicker than
inhalationa anaesthetics .
1. Thiopentone
2. Ketamine
Once Anaesthesia is induced, the status is
maintained by an inhalational agent.

25. INTRVENOUS ANAESTHESIA
-Very rapid: 10 seconds, for 10 minutes
-Irreversible dose
-It is used in short operation or in induction
of anaesthesia and anaesthesia
maintained by inhalational route
-New agent now can be used in
maintenance by infusion

26. LOCAL ANAESTHETIC
As anaesthesia means no sense, so there are
drugs which can block the nerve conduction
peripherally with no need of brain depression .
So patient will be conscious
• MOA- They block the nerve conduction by
preventing increase in membrane
permeability to sodium ions that normally
leads to a nerve impulse.

27. The attack of nerve may be at
the level of:
1. Spinal cord: By injection of local drug in sub -
arachnoid space in CSF, this must be bellow L 2
2. Epidural: The drug is injected outside dura [no
puncture] to block the nerve roots at its exit
from spinal cord.
3. Nerve plexus: Cervical, brachial, lumbosacral
4. Peripheral nerve: Radial, ulnar, median, sciatic,
femoral, popletial, facial, mandibular.
5. Injection into tissues, skin, subcutaneous.

28. Spinal, Epidural Anaesthesia
•
Used for lower abdominal, pelvic , rectal or lower
extremity surgery.
•
Injecting a single dose of anaesthetic agent directly
into the spinal cord in the lower back causing
numbness in the lower body.
•
Epidural and caudal anaesthetic are similar to spinal
for labor and lower limb surgery
•
Continuos infusion of a drug through a thin catheter
that has been placed into the space surrounding
spinal cord causing numbness in lower body

29. Spinal Needles Epidural Needles

30. Spinal
Epidural

31. REGIONAL AND LOCAL
ANAESTHESIA
- The subarachnoid, epidural or plexus block are
called REGIONAL ANAESTHESIA
- Some called it regional analgesia as patient is
conscious.
- Some use sedative with regional analgesia to be
anaesthesia.
- Local anaesthesia means block of peripheral
nerve or tissue infiltration as in lipoma,
circumcision, teeth, eye even craniotomy.

32. NEW TRENDS IN ANAESTHESIA
1. Balanced anaesthesia:
- Use of different potent drugs for every
component of anaesthesia :
Unconsciousness by low inhalational
Analgesia by narcotics or nitrous oxide
Muscle relaxation by muscle relaxant.
-So we can get best results with less side
effects and can be reversed.

33. 33
What are Sedative-Hypnotics?
A sedative-hypnotic is a substance that
depresses the central nervous system (CNS)
They exert their effect on the brain by
interacting with receptors for the
neurotransmitter GABA
Their effect at the receptors enhances the
action of GABA as an inhibitory
neurotransmitter and results in depression of
brain activity

34. Sedation
•
Relieve pain, decrease anxiety and
agitation, provide amnesia, reduce patient-
ventilator dysynchrony, decrease
respiratory muscle oxygen consumption,
facilitate nursing care.
•
May prolong mechanical ventilation and
increase costs.

35. Hypnotics & Sedatives
Drugs which produces drowsiness and
facilitates the onset and maintenance of a
state of sleep resembling natural sleep.
Drugs which reduce excitement and calms
the recepient without
producing sleep .
Mode of action – Depression of CNS

36. Therapeutic uses
Sedation
Hypnosis
Anticonvulsant effect
Pre anaesthetic effect
Potentiation of analgesic effect
Neonatal jaundice

37. Adverse reactions
Nausea
Headache
Diarrhoea
Drug dependence
Withdrawal symptoms

38. Benzodiazepines
Act as sedative, hypnotic, amnestic,
anticonvulsant, anxiolytic.
No analgesia.
Develop tolerance.
Synergistic effect with opiates.
Lipid soluble, metabolized in the liver,
excreted in the urine.
Interact with erythro, propranolol, theo