GENERAL ANAESTHETIC AGENTS / DRUG WHICH INDUCES GENERAL ANAESTHESIA for B.Pharm & Pharm.D

1. -By: Dr.S.Kameshwaran

2. GENERAL ANAESTHETICS
“GENERAL ANAESTHETICS ARE DRUGS WHICH
PRODUCE REVERSIBLE LOSS OF ALL SENSATION &
CONSCIOUSNESS”
It renders the patient
 LOSS OF ALL SENSATION
 ANALGESIC,
 SLEEP (UNCONSCIOUSNESS)
 AMNESIC,
 UNCONSCIOUSNESS,
 PROVIDE MUSCLE RELAXATION, IMMOBILITY &
 SUPRESSION OF UNDESIRABLE REFLEXES
General anaesthesia is achieved by using
combination of Inhaled & IV Drugs.

3. STAGES OF ANAESTHESIA
GENERAL ANAESTHETICS:
“IRREGULARLY DESCENDING DEPRESSION OF THE
CNS”
• Higher functions are lost first and progressively
lower segments are affected
• The vital centre's located in the medulla are
paralysed the last as the depth of anaesthesia
increases

4. GUEDEL (1920)
described the four stages of anaesthesia
I – STAGE OF ANALGESIA
II – STAGE OF DELIRIUM
III – SURGICAL ANAESTHESIA
IV – MEDULLARY PARALYSIS

5. I - STAGES OF ANALGESIA
Starts from: Beginning of anaesthetic
inhalation lasts up to the loss of consciousness.
Pain – Progressively Abolished.
Patient remains conscious, can hear & see.
At the end of this stage AMNESIA develops.
Respiration & Reflexes – normal.
Minor operations can be carried out in this
stage.

6. II – STAGE OF DELIRIUM
Stage starts from: Loss of consciousness lasts
up to the: Beginning of regular respiration
Excitement is produced in this stage
Patient may Shout, Struggle, Increase in
muscle tone, Jaws are tightly closed.
Breathing is jerky
Vomiting & involuntary defecation may occur
Increase in HR & BP,
Pupils are dilated

7. III - SURGICAL ANAESTHESIA
 Stage starts from: Onset of regular respiration lasts
up to: Cessation of spontaneous Breathing
 This stage is divided in to FOUR PLANES
 PLANE 1: Roving eye balls, when eye balls become
fixed this plane ends
 PLANE 2: Loss of corneal & laryngeal reflexes
 PLANE 3: Pupil- starts dilating & loss of light reflex
 PLANE 4:
Intercostal muscle paralysis,
Shallow abdominal breath,
Dilated pupil

8. Deep Anesthesia:
Muscle tone decreases,
BP falls,
HR increases,
respiration decreases

9. IV – MEDULLARY PARALYSIS
Stage starts from: Cessation of breathing lasts
up to: Failure of circulation & death
Pupils widely dilated
Muscles tone are totally flabby
Pulse – unpredictable
BP – very low
Medullary paralysis & death.

10. STAGES OF ANAESTHESIA

11. CLASSIFICATION
INHALATIONAL ANAESTHETICS
GAS
Nitrous Oxide
VOLATILE LIQUIDS
Ether
Halothane
Enflurane
Isoflurane
Desflurane
Sevoflurane

12. INTRA VENOUS ANAESTHETICS (iv)
INDUCING AGENTS
Thiopentone sod
Methohexitone sod
Propofol
Etomidate
SLOWER ACTING DRUGS
BENZODIAZEPINES
Diazepam
Lorazepam
Midazolam
DISSOCIATIVE ANAESTHESIA
Ketamine
OPIOID ANALGESIA
Fentanyl

13. INHALATION ANAESTHETICS:
NITROUS OXIDE (N20)
It is a potent analgesic but a weak anaesthetics
Also known as Laughing Gas
Unconsciousness cannot be produced in all
patients
Produced analgesic activity equal to that of
morphine
It is a poor muscle relaxant
Frequently combined with other anesthetics
Quick onset of action
Smooth mixture of 70% N2O +25 – 30 % O2 + 0.2 –
2% another potent anesthetics is employed for
most surgical procedures.

14. MECHANISM OF ACTION:
GENERAL ANAESTHETICS

INCREASE THE SENSITIVITY OF GABA-A RECEPTORS
TO THE NEUROTRANSMITTER GABA

MORE ENTRY OF CHLORIDE IONS IN TO THE NEURON

HYPER POLARIZATION OF CELL & DIFFICULT TO
DEPOLARIZE

DECREASED NEURAL EXCITABILITY

INDUCTION OF GENERAL ANAESTHESIA

15. PHARMOKINETICS:
Non toxic to liver , kidney & brain
Metabolism of N2O does not occur
Removed from body by lungs
Cheap & commonly used
ADR:
Arrhythmia
Hypotension
Hepatotoxicity

16. INTRAVENOUS ANAESTHETICS
“INTRAVENOUS ANAESTHETICS ON IV INJECTION
PRODUCE LOSS OF CONSCIOUSNESS IN ONE ARM
BRAIN CIRCULATION TIME ( 11 SECONDS)”
Generally used for the induction of anaesthesia
because of rapidity of onset of action
Induced anaesthesia is maintained by inhalation
anaesthetic agent,
It is supplemented with analgesics and muscle
relaxants

17. THIOPENTONE SODIUM:
 Ultra short acting thiobarbiturate
 Highly soluble in water
 Must be prepared freshly before injection
 IV injection of 2.5% solution produces
unconsciousness in 15-20 sec
 Highly lipid soluble drug so enters the brain
immediately
 Consciousness retained in 6-10 min
 It is a poor analgesic
 Weak muscle relaxant
 BP falls immediatly after injection

18. PHARMACOKINETICS:
Given through IV injection
Undergo hepatic metabolism
t ½ - 7-12 hrs
ADR:
Shivering
Delirium
Restlessness
Nausea,
Vomiting

20. PRE ANAESTHETIC MEDICATION
“USE OF DRUGS BEFORE ANAESTHESIA TO MAKE IT
MORE PLEASANT AND SAFE”
AIMS OF PRE ANAESTHETIC MEDICATIONS:
• Relief of anxiety & apprehension (anxiety or fear
that something bad or unpleasant will happen)
• Amnesia
• Supplement analgesic action of anaesthetic
agent, which facilitates the anaesthetic dose
reduction
• Decrease secretions and vagal stimulation
caused by anaesthetics
• Decrease the volume of gastric juice

21. SEDATIVE & ANTI ANXIETY DRUGS:
Diazepam 5-10 mg oral (or) Lorazepam 2mg i.m
 Used to produce smooth induction of
anaesthesia
Midazolam:
 It is a good amnesic with potent and short
lasting action
 It is also better suited for i.v injection
OPIOIDS
 Morphine 10 mg, Pethidine 50-100mg i.m.
 Produce pre and post operative analgesia
 Reduce the dose of anesthetics required

22. ANTI CHOLINERGICS:
Atropine / Hyoscine 0.6mg i.m./ i.v
Used reduce salivary & bronchial secretion
Now used to prevent vagal bradycardia and
hypotension and prophylaxis of
laryngospasm
Glycopyrrolate (0.1-0.3mg i.m.) is a long
acting atropine substitute also used now
NEUROLEPTICS:
Chlorpromazine 25 mg, Haloperidol 2-4 mg
i.m. are frequently used
They allay anxiety, have anti emetic action

23. H2 BLOCKERS:
 Ranitidine 150mg / Famotidine 20mg
 Given night before and in the morning
 Patients undergoing prolonged operations,
caesarian section this H2 blockers were used
 It raises the gastric PH, reduce its volume and
prevent the chance of regurgitation
 Prevention of stress ulcer
 They are now routinely used before prolonged
surgery

25. ANTI EMETICS:
Metoclopranide 10-20 mg i.m. /
Domperidone / Ondansetron 4-8 mg. i.v.
Effective in reducing post operative vomiting
Combined use of metoclopramide and H2
blockers is more effective

26. THANK YOU