General anesthetics cause reversible loss of consciousness through pain relief, muscle relaxation, relaxation of reflexes, and induced deep sleep. They are commonly used during surgery. There are four stages of general anesthesia: analgesia, disinhibition, surgical anesthesia, and medullary depression. The main categories of anesthetics are inhalation agents (gases or vapors, usually halogenated) and intravenous agents (injections of anesthetics or induction agents). Inhalation anesthetics are inhaled as liquids or gases and act by activating potassium channels and blocking sodium channels. Intravenous anesthetics like propofol and thiopental sodium exert their actions by potentiating GABA-A receptors. Both inhalation and

1. Anesthetics
Prepared by
Chayan Dhar Clinton
B.Pharm (Hon’s)
Department of pharmacy, IIUC

2. General Anesthetics
 A drug that brings about a reversible loss of
consciousness
 Causes one or more of the following
 Pain relief
 Muscle relaxation
 Relaxation of reflexes
 Deep sleep
 Commonly used during surgery

3. Pathway for general
Anaesthetic

4. Stages of General
Anesthesia
 Stage I - Analgesia
 Stage II - Disinhibition
 Stage III - Surgical anesthesia
 Stage IV - Medullary depression

5. Main Categories
 Inhalation Anesthetics
 Gasses or Vapors
 Usually Halogenated
 Intravenous Anesthetics
 Injections
 Anesthetics or induction agents

6. Inhalation Anesthetics
 Inhaled – may be liquid or gas
 Nitrous oxide – gas
 Halothane – liquid
 Several others that end with –ane
 Inhaled drugs are used together with IV
drugs to provide the best level of sedation
for the patient & procedure = Balanced
Anesthesia

7. Mechanisms of Action
o Activate K+
channels
o Block Na+
channels
o Disrupt membrane lipids
o In general, all general anesthetics increase
the cellular threshold for firing, thus
decreasing neuronal activity.

8. General Actions of Inhaled
Anesthetics
 Respiration
 Depressed respiration and response to CO2
 Kidney
 Depression of renal blood flow and urine output
 Muscle
 High enough concentrations will relax skeletal muscle
 Cardiovascular System
 Generalized reduction in arterial pressure and peripheral vascular
resistance. Isoflurane maintains CO and coronary function better than other
agents
 Central Nervous System
 Increased cerebral blood flow and decreased cerebral metabolism

9. Intravenous Anaesthetics
 Commonly used IV induction agents
– Propofol
– Thiopental sodium
– Ketamine
 Most exert their actions by potentiating GABAA receptor
 GABAergic actions may be similar to those of volatile
anesthetics, but act at different sites on receptor

10. Organ effects
 Most decrease cerebral metabolism and
intracranial pressure
 Most cause respiratory depression
 May cause apnea after induction of anesthesia
 Barbiturates, benzodiazepines and propofol cause
cardiovascular depression.

11. Thiopental sodium
 rapid onset (20 sec)
 short-acting
 Effect terminated not by metabolism but by
redistribution
 repeated administration or prolonged infusion
approached equilibrium at redistribution sites
 Build-up in adipose tissue = very long emergence
from anesthesia

12. Propofol
 Short-acting agent used for the induction
 maintenance of GA and sedation
The onset of its action begins after 30 s.
 After a single dose patient recovers
after 5 min with a clear head
and no hangover.

13. Purpose
 Overall purposes of intravenous general
anaesthetic
 Opioid analgesic – pain relief
 Benzodiazepine – amnesia
 Anticholinergic – decreases secretions
 Opioid analgesics – lighter pain relief
 Sedative/hypnotic – lighter amnesia/sedation

14. Toxicity and side effects
 Depression of respiratory drive
 Decreased CO2 drive (medullary chemoreceptor's),
Takes MORE CO2 to stimulate respiration
 Depressed cardiovascular drive
 Gaseous space enlargement by NO
 Fluoride-ion toxicity from methoxyflurane
 Metabolized in liver = release of Fluoride ions
 Decreased renal function allows fluoride to accumulate =
nephrotoxicity
 Malignant hyperthermia
 Rapidly cool the individual and administer Dantrolene to
block S.R. release of Calcium.

15. Local Anaesthetic
• Local Anaesthetics are drugs which
reversibly prevent the transmission of pain
stimuli locally at their site of administration.
• The clinical uses and responses of LA s
depend both on the drug selected and the
site of administration.

16. Esters
NH2
O
O CH2 CH2
N
CH2
CH2
CH3
CH3
Amides
CH3
CH3
NH CH2
CH2
N
CH2
CH3
CH2 CH3
Procaine
Lidocaine

17. Mode of Action
 Block ! Initiation & propagation of action potential
(AP) by preventing voltage-gated Na+
channels.
 Bind to specific sites on channel protein
 Prevent formation of open channel
 Inhibit influx of sodium ions into the neuron
 Reduce depolarization of membrane in response
to action potential
 Prevent propagation of action potential.

18. Choice of local
Anaesthetic
 Onset
 Duration
 Regional anesthetic technique
 Sensory vs. motor block
 Potential for toxicity

20. Local Anaesthetic major
toxicity
 Allergy
 CNS toxicity
 Cardiovascular toxicity.
 Excitation – anxiety, agitation, restlessness
 Convulsions
 Reduced myocardial contractility
 Vasodilatation

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