1.
GENERAL ANESTHETICS
Prof. Amol B. Deore
Department of Pharmacology
MVP’s Institute of Pharmaceutical Sciences, Nashik

2.
General anesthesia is a medically induced reversible loss of
consciousness and loss of protective reflexes over the entire body,
resulting from the administration of general anesthetic agents.
The optimal combination of these agents for any given patient and
procedure is typically selected by an anesthesiologist.

3.
General anesthesia has many purposes including:
•Pain relief (analgesia)
•Blocking memory of the procedure (amnesia)
•Producing reversible unconsciousness
•Inhibiting normal body reflexes to make surgery
safe and easier to perform
•Relaxing the muscles of the body

4.
STAGES OF GENERAL ANAESTHESIA
General anesthesia affects the
entire body, so there are different
stages a person goes through.

5.
Stage 1 or Induction
stage:
Stage 2 or Excitement
stage:
Stage 3 or Surgical
anesthesia:
Stage 4 or Overdose:

6.
Stage and depth of anesthesia

7.
Stage 1 or Induction (Analgesia)
• Loss of pain sensation results from interference with sensory transmission
in the spinothalamic tract.
• The patient progresses from conscious and conversational to drowsiness.
• Amnesia and reduced awareness of pain occur as stage II is approached.

8.
Stage 2 or Excitement (Delirium उत्तेजना)
• The patient displays delirium and possibly aggressive behavior (लढाऊ
वर्तन). A rise and irregularity in blood pressure and respiration occur, as
well as a risk of laryngospasm.
• Breathing and heart rate become irregular. In addition, there may be
uncontrolled movements, vomiting, breath holding, pupil dilation
(mydriasis), coughing, salivation, defecation, stretching, vocalization,
and shouting.
• Tachycardia may develop, due to release of adrenaline.
• No operation and surgery is carried in this stage.
• They can be minimized by proper pre-anesthetic medication and
rapidly increasing concentration of anesthetic agents.

9.
Stage 3 or Surgical anesthesia:
•This stage is characterized by regular respiration,
a gradual loss of reflexes, and relaxation of the
skeletal muscles. Reflex activity is lost.
•This stage is usually employed for surgical
procedures.

10.
Stage 3 is divided into four planes:
•Plane I - starts from onset of automatic
respiration to loss of eyeball movements. Eyelid
reflex is lost, swallowing reflex is lost.
•Plane II - starts from loss of eyeball movements
to beginning of paralysis of intercostal muscles.
Laryngeal reflex and corneal reflex are lost.
Secretion of tears increases.

11.
Plane III - starts from beginning to paralysis of intercostal
muscle, pupils’ dilation and negative light reflex.
Plane IV - starts from complete intercostal muscle paralysis
to diaphragmatic paralysis (apnea).

12.
Stage 4- Respiratory Paralysis
•In this stage where too much medication has been
given and the patient has severe brain stem or
medullary depression.
•This results in a cessation of respiration (respiratory
center paralysis), hypotension and cardiovascular
collapse (vasomotor center paralysis).
•This stage is dangerous without cardiovascular and
respiratory support.

13.
PROPERTIES OF IDEAL GENERAL ANESTHETIC
For the patients
• It should be pleasant and non-irritating.
• It should not cause nausea and vomiting.
• Induction and recovery should be fast.
• There should not be any adverse drug reaction.
For the surgeon
• It should provide adequate analgesia.
• It should cause immobility and muscle relaxation.
• It should be noninflammable and non-explosive.

14.
For the anesthetist
•It should be easy for administration.
•It should have wide margin of safety.
•It should be potent and effective at low
concentration.
•It should be cheap, stable and easily stored.
•It should not show any effect on the heart, lung and
liver.

15.
GENERAL ANESTHETICS
General anesthetics depress the central nervous
system leading to reversible loss of
consciousness, analgesia and protective reflexes
in order for surgeons to operate on a patient.

16.
1. Inhalation anesthetics
• Gases-
• Ex. Nitrous oxide, Xenon, Cyclopropane
• Volatile liquids
• Ex. Isoflurane, Enflurane, Desflurane, Methoxyflurane, Sevoflurane
2. Intravenous anesthetics
• Ultra short acting barbiturates
• Ex. Thiopental, Thiamylal, Methohexital
• Benzodiazepines
• Ex. Diazepam, Lorazepam, Midazolam
• Neuroleptic analgesia/anaesthesia
• Ex. Ketamine, Fentanyl/ Droperidol
• Opioid analgesics
• Ex. Morphine, Alfentanil, Remifentanil, Sufentanil
• Miscellaneous sedative hypnotics
• Ex. Etomidate, Propofol

17.
Mode of administration
• Agents used for general anesthesia may be either
gases or volatile liquids that are vaporized and
inhaled with oxygen, or drugs delivered
intravenously.
• A combination of inhaled anesthetic gases and
intravenous drugs are usually delivered during
general anesthesia; this practice is called
balanced anesthesia and is used because it takes
advantage of the beneficial effects of each
anesthetic agent to reach surgical anesthesia.

18.
Mechanism of action

19.
It appears that a variety of molecular mechanisms may contribute to
the activity of general anesthetics.
At clinically effective concentrations, general anesthetics increase
the sensitivity of the γ-aminobutyric acid (GABAA) receptors to the
inhibitory neurotransmitter GABA.
This increases chloride ion influx and hyperpolarization of neurons.
Postsynaptic neuronal excitability and, thus, CNS activity are
diminished

20.
PREANESTHETIC MEDICATIONS
The preanesthetic medications involve administration of
certain drugs before the inducing general anesthesia to
manage stage-2 complications. The preanesthetic
medications are given to assist the induction and
maintenance of anesthesia and to minimize adverse effects.

21.
To relieve anxiety ex. anxiolytic drug like benzodiazepines
(midazolam, diazepam, lorazepam)
Reduction in salivary and bronchial mucus secretion ex.
anticholinergic drug like atropine, hyoscine, glycopyrrolate.
To potentiate the action of anesthetics: benzodiazepines,
barbiturates, analgesics, α2-receptor agonists.
To suppress cough secretion- ex. codeine phosphate
To depress CNS, to produce sedation and analgesia ex., fentanyl,
pethidine etc.

22.
To control nausea and vomiting ex. antiemetic like chlorpromazine,
metoclopramide
To prevent bacterial infection ex. anti-infective like cefixime, cefazoline or
metronidazole
Skeletal muscle relaxant like succinylcholine, gallamine
For constipation ex. laxative and stool softeners like bisacodyl, MgO
To control abdominal distention and urinary retention ex. cholinergic drugs like
bethanechol
To suppress postoperative pain (opioid: e.g., fentanyl; tramadol, NSAID: e.g.,
ketorolac)

23.
Chloroform is not used nowadays as general
anesthetics. Why?
• Signs and stages of chloroform induced general anesthesia are
not clear. It shows major toxic effects on heart, lungs, liver
and kidney. It produces cardiac arrhythmia, hypotension, and
cardiac arrest.
• Chloroform causes respiratory depression, bronchospasm,
layngospasm and breath holding. Due to these toxic effects,
Chloroform is not a good anesthetic and not used nowadays.

24.
Atropine is used as preanaesthetic medication. Why?
• Atropine is anti-muscarinic agent which inhibits exocrine gland
secretions. Hence show antisecretory action.
• The inhalational anesthetics show irritation to respiratory mucosa
and case excessive mucus secretion. This interferes with normal
breathing.
• Intravenous anesthetics do not cause excessive secretion of mucus.
But in the stage of delirium, vomiting, & unconscious, they can
block respiratory passageway.
• Atropine inhibits all these secretions and assists in anesthesia.

25.
Thank You