This document discusses various general anesthetics used in medicine including their classification, mechanisms of action, advantages, and disadvantages. It covers inhalational anesthetics like nitrous oxide, halothane, isoflurane, desflurane, and sevoflurane. It also discusses intravenous anesthetics such as thiopentone, propofol, benzodiazepines, and opioids. The document provides details on the stages of anesthesia, potency measures, and important considerations for different anesthetics.

1. General anesthetics
Dr Chintan Doshi

3. Loss of all sensation, especially pain
Unconsciousness
Amnesia
Immobility & muscle relaxation
Abolition of reflexes
General Anaesthesia
Balanced anaesthesia - with combination of drugs

4. Mechanism of
General Anaesthesia
GABAA receptor - open Cl¯ channels
– hyperpolarisation
N2O & Ketamine - NMDA receptor antagonism
Activation of glycine receptors

7. Minimum alveolar concentration
• Lowest concentration of the anaesthetic in
pulmonary alveoli needed to produce
immobility in response to a painful stimulus
(surgical incision) in 50% individuals
• Measure of potency

8. Stages
• Stages of analgesia
• Stage of delirium
• Surgical anesthesia
• Medullary paralysis

13. Classification
Inhalational
1. Gas: Nitrous Oxide
2. Volatile liquids:
Ether
Halothane
Enflurane
Isoflurane
Desflurane
Sevoflurane

14. Intravenous
• Faster acting
 Thiopentone,
 Methohexitone sodium,
 propofol
 etomidate
• Slower acting
a. Benzodiazapines
 Diazepam,
 Lorazepam,
 Midazolam
b. Opioid analgesic
 Fentanyl
 Ramifentanyl
c. Dissociation anesthetic
 Ketamine

15. Nitrous oxide
• Colourless, odourless inorganic gas with sweet
taste
• Noninflammable and nonirritating, but of low
potency
• Very potent analgesic, but not potent anaesthetic
• Carrier and adjuvant to other anaesthetics –70%
N2O+ 25-30% O2 + 0.2-2% another agent
• As a single agent used wit O2 in dental
extraction and in obstetrics

16. Advantages Disadvantages
Non-inflammable and
nonirritant
Not potent alone
Rapid induction and
recovery
Not good muscle relaxant
Very potent analgesic Hypoxia
No effect on heart rate and
respiration
Gas filled spaces expansion
(pneumothorax) - dangerous
No nausea and vomiting Inhibits vitamin B-12
metabolism
Nontoxic to liver, kidney
and brain
Bone marrow depression
Peripheral neuropathy: by depressing
methionine synthase activity

17. Important feature

18. Halothane
• Fluorinated volatile liquid with sweet odour
• Non-irritant ,non-inflammable and supplied in
amber coloured bottle
• Potent anaesthetic
• Delivered by the use of a special vapourizer
• Not good analgesic or relaxants
• Potentiates NM blockers

19. Advantages Disadvantages
Non-inflammable and nonirritant Poor analgesic and muscle relaxant
Bronchodilatation –
preferred in asthmatics
Myocardial depression
Potent and speedy
induction & recovery
Hypotension
Cheap: Popular anesthetic in
developing countries
Heart rate – reduced
Can be used in children for
induction and maintenance
Arrythmia - Sensitize heart to Adrenaline
Respiratory depression
Decreased urine formation
Hepatitis: 1 in 10,000
Malignant hyperthermia: Abnormal
Ryanodine Receptor
Prolong labour

20. Isoflurane
Cardiac output -- maintained
* Preferred for cardiac surgery
Hypotension
‘coronary steal’ phenomenon

21. Desflurane
- Induction & recovery fast
- Coughing , laryngospam
- Day care surgery
Sevoflurane
- For induction in children
- Good muscle relaxation

22. Inhalational anaesthetics that
can precipitate seizures
• S – Sevoflorane
• E – Enflurane (Maximum)
• I – Isoflurane

23. Intravenous
Anaesthetics

25. Advantages Disadvantages
Rapid induction Depth of anesthesia
difficult to judge
Does not sensitize
myocardium to adrenaline
Pharyngeal and laryngeal
reflexes persists - apnoea
No nausea and vomiting Respiratory depression
Non-explosive and nonirritant Hypotension
Short operations: alone used Cardiovascular collapse if shock or
sepsis present
Poor analgesic and muscle
relaxant

26. ADR
Laryngospasm
• can be prevented by atropine premedication
and administration of succinylcholine
immediately after thiopentone
• Succinylcholine and thiopentone react
chemically— should not be mixed in the same
syringe

27. Contd.
Shivering and delirium
Pain in the postoperative period
Precipitate acute intermittent porphyria in
susceptible individuals

28. Other uses
• Convulsions
• Narcoanalysis in criminal patients

29. Methohexitone sod
• Similar to thiopentone
• 3 times more potent
• Quicker and briefer (5–8 min) action

30. Propofol
• Replacing thiopentone now – induction and
maintenance
• Intermittent or continuous infusion – Total IV
anaesthesia (supplemented by fentanyl)
• Oily liquid used as 1% emulsion
• Rapid induction :15 – 45 seconds and lasts for
5–10 minutes
• Rapid distribution

31. Contd.
• Dose: Induction - 2mg/kg bolus i.v.
• Metabolized by hepatic conjugation of the
inactive glucuronide metabolites

36. Benzodiazapines
• Lorazepam
• Diazepam
• Midazolam

40. • The following causes increased intra ocular
pressure:
• (a) Thiopentone
• (b) Althesin
• (c) Ketamine
• (d) Barbiturate

41. • Nitrous oxide is contraindicated in patients
with pneumothorax, pneumopericardium or
intestinal obstruction, because it:
• (a) Depresses an already compromised
myocardium
• (b) Permits the use of limited FIO2 only
• (c) Is less soluble than nitrogen
• (d) Causes the expansion of air filled body
cavities

42. • Regarding propofol, which one of the
following is false:
• (a) It is used as an intravenous induction agent
• (b) It causes severe vomiting
• (c) It is painful on injecting intravenously
• (d) It has no muscle relaxant property

43. • All of the following are intravenous
anesthetic induction agents except:
• (a) Thiopentone sodium
• (b) Ketamine
• (c) Etomidate
• (d) Bupivacaine

44. • Ketamine produces
• (a) Emergence delirium
• (b) Pain on injection
• (c) Bronchoconstriciton
• (d) Depression of cardiovascular system

45. • True statements regarding halothane is:
• (a) Hepatitis occurs in susceptible individuals
after repeated dose
• (b) It potentiates competitive neuromuscular
blockers
• (c) Causes respiratory depression
• d) All of the above

46. • Induction agent of choice in day care surgery
is:
• (a) Ketamine
• (b) Propofol
• (c) Methohexitone
• (d) Thiopentone sodium

47. • An i.v. bolus dose of thiopentone leads to
loss of consciousness within 10-15 sec. The
patient regains consciousness in just a few
minutes. This is because it is:
• (a) Renally excreted
• (b) Exhaled rapidly
• (c) Rapidly metabolised by hepatic enzymes
• (d) Redistributed from brain to other body
tissues

48. • Ketamine should be avoided in
• (a) The presence of increased arterial pressure
• (b) Pregnancy
• (c) Hypovolemic shock
• (d) Asthmatic

49. • Which one of the following inhalational
anesthetics is most likely to cause fluoride
ion nephrotoxicity?
• (a) Methoxyflurane
• (b) Enflurane
• (c) Halothane
• (d) Isoflurane

50. • Anaesthetic having epileptogenic potential is:
• (a) Desflurane
• (b) Sevoflurane
• (c) Ether
• (d) Halothane

51. • Which of the following increase the speed of
induction with an inhalational agent?
• (a) Opiate pre-medication
• (b) Increased alveolar ventilation
• (c) Increased cardiac output
• (d) Reduced FIO2

52. • Thiopental sodium is administered
intravenously as:
• (a) 25% solution
• (b) 2.5% solution
• (c) 0.25% solution
• (d) 0.025% solution

53. • Which of the following drugs are believed to
be effective in the treatment of post
operative shivering?
• (a) Ondansetron
• (b) Diclofenac sodium
• (c) Pethidine
• (d) Paracetamol

54. • Malignant hyperthermia is a rare
complication of the use of the following
anaesthetic:
• (a) Ketamine
• (b) Thiopentone sodium
• (c) Halothane
• (d) Ether