The document discusses general anesthetics and their stages and classifications. It describes the four stages of general anesthesia: analgesia and amnesia, delirium or excitement, surgical anesthesia, and medullary paralysis. It classifies general anesthetics based on their route of administration as volatile/inhalational (ether, halothane, cyclopropane, nitrous oxide) or non-volatile/intravenous (barbiturates, ketamine). It outlines the properties of ideal general anesthetics and discusses advantages and disadvantages of specific anesthetics. It also discusses pre-anesthetic medications that are used prior to anesthesia administration.

1. 2. DRUGS ACTING ON CNS
A) GENERAL ANAESTHETICS
Prepared by – Mr. Digambar Jadhav ( M.Pharm)
HOD
Padmini College of Pharmacy,
Dighanchi.

3.  ANAESTHETICS
 Definition –
The drugs which are used to produce
anaesthesia are known as anaesthetics.
Anaesthetics
General Anaesthetics Local Anaesthetics

4.  GENERAL ANAESTHETICS
 Def :- “ These are pharmacological agents which
when administered externally produces loss of
sensation of pain with reversible loss of
consciousness.”
 Stages of General anaesthesia :
1. Stage of Analgesia and amnesia
2. Stage of Delirium or excitement
3. Stage of Surgical anaesthesia
4. Stage of medullary paralysis

5. 1. STAGE OF ANALGESIA
 This stage is in between induction of anaesthetics
to loss of consciousness.
 It is characterized by loss of consciousness with
feeling floating, numbness and analgesia.
 All reflexes are present
 This stage is suitable for dental surgery.

6. 2. STAGE OF DELIRIUM OR EXCITEMENTS
 This stage is in between loss of consciousness and
stage of surgical anaesthesia
 This stage start with loss of consciousness
 It is characterized by psychomotor excitement and
hyperactivity of respiratory and cardiovascular
reflexes
 This stage is not suitable for any surgical
procedure.

7. 3. STAGE OF SURGICAL ANAESTHESIA
 This stage is starts when patients excitement is
stopped and breathing is regularized
 It is characterized by fixed eye ball and shallow
abdominal breathing
 All reflexes are completely abolished
 This stage is most suitable for major operation

8. 4. STAGE OF MEDULLARY PARALYSIS
 It is a stage of overdose beyond the stage of
surgical anaesthesia in which medullary centres are
completely paralysed
 It is characterized by stoppage of breathing, fall of
blood pressure to zero level and cardiovascular
collapse. It leads to death
 Vigorous and prompt measure only can save the
patient from this stage.

9. CLASSIFICATION
 Classification of General anesthetic is based on
route of administration.
 General anesthetic drugs can be administered by
Inhalation Intravenous

10. CLASSIFICATION
( A ) Volatile or Inhalatory anesthetics
1. Liquid :
 Ether
 Chloroform
 Halothane
2. Gases :
 Cyclopropane
 Nitrous oxide
( B ) Non-Volatile or Intravenous anesthetic
1. Barbiturate
 Thiopentone
 Kemithal
2. Non-barbiturate
 Propanedid
 Ketamine

11. PROPERTIES OF IDEAL GENERAL ANESTHETIC
 Easy for administer
 Should produce rapid and smooth induction and
recovery
 Should be non-inflammable & non-irritating
 Should possess good analgesic effect
 Should possess adequate muscle relaxation
 Should possess sufficient margin of safety between
stage of surgical anesthesia and stage of medullary
paralysis
 Should be potent anasthetic with adequate duration of
action
 Signs and stages of anesthesia should be clear

12. A ) VOLATILE OR INHALATORY ANESTHETICS
1. Ether
 Physical Properties :
 It is colourless, volatile liquid with pungent odour
 It boils at 350C and vapours are irritant
 When ether is exposed to air, moisture or light, it
get converted to ether peroxides and acetic
aldehyde, which is irritant in nature
 Ether is highly explosive.
 It is stored in amber coloured bottles covered with
black paper.

13. 1.ETHER
 Advantages
 It is the safest anaesthetic agent with wide margin
of safety even in unexperienced hands
90 mg/ 100 ml blood- induces anaesthesia
190 mg/ 100 ml blood- causes respiratory arrest
 It is not only a safe anaesthetic but a good
analgesic also
 Ether does not modify blood pressure
 It does not have any effect on liver, kidney & heart
 It is an economical agent

14. 1. ETHER
 Disadvantages
 Induction is very slow and stormy
 Ether vapours are irritant and may increase
salivary, bronchial secreation. Accumulation of
secreation may induce cough & larynegal spasm
 Recovery is slow and is associate with high
incidences of nausea & vomiting
 In children it may produce convulsions.

15. 1. ETHER
 Preparation :
 Anaesthetic ether, I.P.
 Spirit of ether, I.P
 Dose : 1-4 ml
 Therapeutic uses :
 As General anaesthetic
 As rubefacients
 Used as solvent
 As cleansing agent

16. 2. HALOTHANE
 Physical properties :
 It is heavy, colourless liquid.
 It is an inflammable, non-toxic fluorinated
hydrocarbon.
 It has sweet, fruity odour and boils at 500C.
 It affects most metals including stainless steel, brass
and copper. It also affects rubber.

17. 2. HALOTHANE
 Advantages :
 Induction is very smooth as it has sweet, fruity
odour.
 Recovery is also fast, smooth with low incidences
of nausea and vomiting.
 It does not cause irritation of respiratory passage.
 It does not produce bronchospasm, hence can be
used in patients with bronchial asthma.

18. 2. HALOTHANE
 Disadvantage :
 Muscular relaxation is inadequate.
 It causes respiratory, cardiovascular depression.
 Mental recovery is delayed
 Shivering during recovery is very common
 It is a poor analgesic
 It is expensive, need special apparatus for
administration.

19. 3. CHLOROFORM
 It is no more used for therapy because of its :
 Hepatotoxicity
 Nephrotoxicity
 cardiotoxicity

20. 4. CYCLOPROPANE
 Physical properties :
 It is a colourless gas with sweet odour and taste.
 It is available as liquid under pressure and administered in
closed circuit.
 Advantages :
 It is a potent anaesthetic agents.
 Induction is pleasant and quicker.
 Recovery is rapid and smooth
 Does not irritate respiratory passage
 Incidences of nausea and vomiting are less
 It produces adequate muscular relaxation
 It does not affect blood pressure and cardiac contractility.

21. 4. CYCLOPROPANE
 Disadvantages :
 The signs of anaesthesia are not clear.
 Rapid induction may produce laryngospasm, breath
holding, coughing
 Stages of anaesthesia are not clear , as induction is
very smooth.

22. 5. NITROUS OXIDE
 Physical properties :
 It is colourless gas with sweet odour and taste
 It is non-inflammable
 Advantages :
 It is non-inflammable and non-irritant.
 It produces rapid induction and recovery.
 It has good analgesic effects & hence can be used
in dental practice.
 It is safest anaesthetic agent.
 Incidences of nausea & vomiting are rare

23. 5. NITROUS OXIDE
 Disadvantages :
 Pre-anesthetic medication is required as it is not a
potent anaesthetic.
 Excitement may be violent.
 Special apparatus is required.

24. B) NON –VOLATILE / INTRAVENOUS
ANAESTHETICS
 Advantages :
 Easy for administration
 Induction is rapid and smooth
 Post-anaesthetic complication are rare
 Recovery is very fast
 Respiratory and myocardial functions remains
unaffected
 No irritation of respiratory passage.

25. B) NON –VOLATILE / INTRAVENOUS ANAESTHETICS
 Disadvantages :
 Usual stages of anaesthesia are not clear.
 Coughing, apnea is common during induction
 Muscular relaxation is very poor.
 Injection around nerve may produces pain.
 Preparations
 Thiopenton sodium : 2.5% solution
 Methohexitone : 1% solution
 Propanidid : 4 mg/kg
 Ketamine : 1.2 mg/kg

26.  PREANAESTHETIC MEDICATION
 Def :- “ These are the drugs used prior to the
administration of an anesthetic agent, with the
important object of making anesthesia safe and
more agreeable to the patient.”

27.  AIM & OBJECTIVE
 For sedation – to reduce anxiety
 To obtain an additive or synergestic effect
 To minimise pre and post operative complication
 To facilitate smooth and rapid induction
 To overcome secretary effects of general
anaesthetics.

28.  Various agents preferred as preanaesthetic
anaesthetics are as follows
Sr. No Type Drug
1 Opioid analgesic Morphine
2 Anxiolytic Diazepam
3 Anti-emetic Promethazine
4 Antisecretory Atropine
5 Skeletal muscle relaxant D-tubocurarine