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1. General Anesthetics (GA)
General anesthesia is a state of drug-induced reversible
inhibition of CNS function, during which surgical
procedures can be carried out in the absence of:
• Consciousness
•Memory
• Responsiveness to pain
•Defensive or involuntary movements

2. • The discovery of general anesthesia must be
regarded as one of the most significant events
that made modern surgical practice possible.
• Prior to this discovery, surgical procedures
were horrifically painful and often met with
limited success.
• Preparation for surgery often consisted of
simple physical restraint of the patient.

3. GENERAL ANESTHESIA REPRESENTS A
NECESSITY TO THE SURGICAL PRACTICE AS IT
RENDERS PATIENTS
• Analgesic
• Amnesic
• Unconscious
• Suppresses muscle tone (muscle relaxation)
• Not achieved by a single drug

4. Concomitant use of drugs
Multiple adjunct agents
• Commonly, surgical patients receive the following
preanesthetic medications:
• benzodiazepines, such as midazolam or
diazepam, to allay anxiety and facilitate amnesia;
• barbiturates, such as pentobarbital, for sedation;
• Anticholinergics such as atropine to decrease
bronchial secretion
• ranitidine, to reduce gastric acidity;

5. • Antiemetics to prevent the possible aspiration of
stomach contents;
• opioids, such as fentanyl for analgesia; and propofol
for sedation
• These agents facilitate smooth induction of
anesthesia.
• In addition preanaesthetic medications also lower the
dose of anesthetic required to maintain the desired
level of surgical (Stage III) anesthesia.

6. • Most aneasthetics enhance the inhibitory functions
of such receptors as GABAA receptor which appears
to be an important target for such agents as
propofol, thiopental and etomidate.
• Inhaled anesthetics, barbiturates, benzodiazepines,
etomidate, and propofol facilitate GABA-mediated
inhibition at GABAA receptor sites.
• General anaesthetic also Inhibit the function of
excitatory receptors e.g. ionotropic glutamate
receptors (ketamone, nitrous oxide)
MECHANISM OF ACTION OF GENERAL ANESTHETIC DRUGS

7. PHASES OF GENERAL ANAESTHESIA
1- Induction:
• It is defined as the period from the onset of
administration of anesthesia to the production
of effective surgical anesthesia.
• Thiopental is an excellent inducer (onset 25
seconds) which is then followed by the agent
of choice to attain the depth of anesthesia
(stage III).

8. 2-Maintenance:
• defined as the period of sustained surgical
anesthesia.
• During this period the patient is monitored for
reflexes and vital signs all throughout the
surgical procedure.
• Preferably volatile anesthetics are used since
they offer (minute-to-minute control).
• Should there be a use for additional pain
relief, Fentanyl used to relieve pain.

9. I- INTRAVENOUS ANESTHETICS
• Used for rapid induction which is then maintained with
inhalation anesthetics.
• Thiopental, etomidate and propofol are most commonly
used; all act within 20-30 seconds if given intravenously
1. Barbiturates:
• Thiopental is the prototype used for induction.
• Being an ultrashort barbiturate causes rapid induction
(<1 minute).
• Barbiturates are not significantly analgesic and hence
require supplementary analgesia.
• Minor cardiovascular effects but may contribute to severe
hypotension in hypovolemic or shock patients.
CLASSES OF ANESTHETICS

10. Thiopental
– barbiturate with very high lipid solubility
– rapid action due to rapid transfer across blood-brain
barrier; short duration (about 5 minutes) due to
redistribution, mainly to muscle , no analgesic effect
– narrow margin between anaesthetic dose and dose
causing CVS depression

11. 2. Etomidate:
• Hypnotic agent that lacks analgesic effect.
• Similar to thiopental but more quickly
metabolised
• Less risk of cardiovascular depression
• Only used for patients with coronary artery
disease or cardiac dysfunction such as shock.
• Its adverse effects include a decrease in
plasma cortisol and aldosterone levels due to
inhibition of 11-ß-hydroxylase.

12. 3.Ketamine: (inhibiting the function of exicatatory
recptors ) , this is MoA action of G.A
• Induces a state of dissociative anesthesia in
which the patient appears to be awake but feels
no pain.
• This state provides analgesia, amnesia, sedation
and immobility.
• Action differs from other agents, probably related to
effect on NMDA-type glutamate receptors
• Onset of effect is relatively slow (2-5 minutes)
• Produces 'dissociative' anaesthesia, in which patient
may remain conscious although amnesic and insensitive
to pain

13. 4. Propofol:
• It has widely replaced thiopental because it produces a
euphoric feeling in the patient and does not cause
postanesthetic nausea and vomiting.
• Onset is smooth and rapid (40 seconds).
• Supplementation with opioids for analgesia is
required.
• Propofol facilitates depression in the CNS.
• Rapidly metabolised , very rapid recovery; no
cumulative effect
• Useful for day case surgery

14. 5. Benzodiazepines
• The benzodiazepines are used in conjunction
with anesthetics to sedate the patient.
• The most commonly employed is midazolam,
which is available in many formulations,
including oral.
• Diazepam and lorazepam are alternatives.
• All three facilitate amnesia while causing
sedation.

15. 6. Opioids
• Because of their analgesic property, opioids are
frequently used together with
otheranesthetics;
• for example, the combination of opiods and
nitrous oxide provides good anesthesia for
cardiac surgery.
• Fentanyl most commonly used
• The choice of opioid used preoperatively is
based primarily on the duration of action
needed

16. II- INHALATION ANESTHETICS:
• Inhaled gases are the mainstay of anesthesia
and are used primarily for the maintenance of
anesthesia after the administration of an
intravenous agent.
• They offer the advantage of tight control, i.e.
unlike intravenous anesthetics the depth of
anesthesia can be controlled, they are
reversible and rapidly eliminated from the
body.

17. Common features of inhaled anesthetics:
• Modern agents are nonflammable, non-explosive.
• They include nitrous oxide and halogenated
hydrocarbons.
• These agents decrease cerebrovascular resistance,
resulting in increased perfusion of the brain.
• Movement of such agents into different body
compartments depends on solubility in blood,
solubility in tissues and blood flow.
• These factors play an important role in induction and
recovery.

18. REPRESENTATIVE DRUGS USED AS INHALATION
ANESTHETICS
1. halogenated hydrocarbons are volatile liquids
• Halothane
• Isoflurane
• Sevoflurane
• Enflurane
• Desflurane
• Ether
2.Nitrous Oxide (laughing gas) has rapid action
and recovery

19. Undesirable effects of GA
• The margin between surgical anaesthesia and
potentially fatal respiratory and circulatory
depression is quite narrow, requiring careful
monitoring by the anaesthetist and rapid
adjustment of the level of anaesthesia, as
required.
• At supra-anaesthetic doses, all anaesthetic
agents can cause death by loss of cardiovascular
reflexes and respiratory paralysis.

20. • Halothane is a widely used inhalation
anaesthetic, but its use is now declining
• Halothane is a potent anesthetic but a relatively
weak analgesic
• Has high blood:gas partition coefficients show
slow induction and recovery
• Nitrous oxide (N2O) is rapid in action because of
its low blood:gas partition coefficient, and is an
effective analgesic with weak anaesthetic
activity