General anesthetics are agents that cause reversible loss of sensation and consciousness. Ideal anesthetics provide analgesia, immobility, muscle relaxation and are safe, easy to administer, and inexpensive. Anesthetics are classified as inhalational gases/liquids like nitrous oxide and ether or intravenous inducing agents like thiopentone sodium. Nitrous oxide provides rapid, smooth induction while ether has potent effects but an unpleasant induction. Thiopentone sodium quickly induces unconsciousness while ketamine provides analgesia without respiratory depression. Fentanyl with droperidol or benzodiazepines like lorazepam can be used to induce or supplement anesthesia.

1. GENERAL ANAESTHETICS
 General anaethetics are the agents that bring about reversible
loss of sensation and consciousness.
 Before 1846:
 Alcohol, opium, packing a limb with ice, and concussion were used to relieve
surgical pain.
 Ideal anaethetic:
 Should be pleasant
 Non-irritant
 Provide adequate analgesia, immobility and muscle relaxation.
 Non inflammable
 Administration should be easy and controllable
 Should have wide margin of safety
 Should not affect CVS functions
 Induction and recovery should be smooth
 Should be inexpensive

2. CLASSIFICATION:
Inhalational:
 Gases: Nitrous oxide, Cyclopropane.
 Liquids: Ether, Halothane, Enflurane, Isoflurane,
Methoxyflurane.
Intravenous:
 Inducing agents: Thiopentone sodium, Methohexitone.
 Dissociative anaesthesia: Ketamine.
 Neuroleptanalgesia: Fentanyl + Droperidol.
 Benzodiazepines: Diazepam, Lorazepam.

3. INHALATIONAL ANAESTHETICS:
Nitrous oxide: (gas)
 It is a gas with slightly sweetish odor.
 Produces light anesthesia without significant depression of
respiration or vasomotor center.
 Advantages:
 Strong analgesic. Induction is rapid and smooth.
 Non-irritating and non-inflammable. Recovery is rapid.
 Has little effect on respiration and CVS functions.
 Non toxic to liver, kidney, brain and is quickly removed from lungs
 Disadvantages:
 Less potent
 Should be used with other agents (used along with 30% oxygen)
 Poor muscle relaxant.

4. Ether: (liquid)
 Is a colorless volatile liquid.
 Advantages:
 Potent and reliable anesthetic.
 Effect on respiratory and CVS are not significant.
 It is a bronchodilator.
 Provides full muscle relaxation in deep anaesthesia.
 Easy to administer and relatively safer
 Inexpensive.
 Disadvantages:
 Induction is slow and unpleasant
 It is irritating, hence enhances respiratory secretions
 Post operative nausea and vomiting are frequent.
 Highly flammable

5. INTRAVENOUS ANAESTHETICS:
 These are used for induction because of rapid onset of action (11
seconds) and anesthesia is maintained by an inhalational agent.
Thiopentone sodium: (Inducing agents)
 Rapidly induces anesthesia without analgesia.
 Produces unconsciousness in 20-30 seconds.
 Duration of action is 4-7 minutes.
 Highly lipid soluble.
 Advantages: quick onset, smooth induction, rapid and pleasant.
 Disadvantages: not good analgesic, not a muscular relaxant,
causes respiratory and circulatory depression hypotension
(cannot be used alone)

6. Ketamine: (dissociative anesthesia)
Ketamine is a phencyclidine derivative.
Produces dissociative anaesthesia characterized by
analgesia, immobility, amnesia and feeling of
dissociation from ones own body and surroundings.
Onset of action: 3-5 minutes.
Duration of action: 10-15 minutes. (amnesia: 1-2 hours)
Advantages: analgesia, respiration is not depressed, no
hypotension, no vomiting, no bronchospasm (can be
used in asthmatic patients)
Disadvantages: hallucinations and involuntary
movement during recovery. Raises BP (hence dangerous
in hypertension)

7. Fentanyl + Droperidol: (Neuroleptanalgesia)
 Fentanyl (0.05 mg/ml) is a short acting (30-50 min) and
potent opioid analgesic.
 Droperidol (2.5 mg/ml) is a rapidly acting, potent
neuroleptic.
 4-6 ml of mixture is infused IV over 10 minutes.
 Both in combination produces Neuroleptanalgesia
characterized by calmness, psychic indifference and
intense analgesia without loss of consciousness.
 Patient is drowsy but cooperative.
 Disadvantages: respiratory depression, slight fall in BP and
HR.
 Addition of 65% N2O and 35% O2 produces
neuroleptanaesthesia.

8. Lorazepam and Diazepam (Benzodiazepines)
Used to induce supplement anaesthesia.
Causes sedation, amnesia and reduce anxiety.
Also used as pre anaethetic medications.
IV Midazolam is particularly preferred as it is faster
and shorter acting, more potent and does not cause
pain or irritation to the injection sites.