General anesthesia involves administering anesthetic agents to induce a reversible state of unconsciousness and loss of pain sensation. It progresses through four stages from analgesia to respiratory and vasomotor paralysis. Anesthetic agents act primarily by potentiating the GABA receptor or inhibiting the NMDA receptor. They can be administered via various routes including intravenous, inhalation, rectal or intramuscular injection to produce depression of the brain. Common inhalational agents include nitrous oxide, halothane, sevoflurane and desflurane while intravenous agents used for induction and maintenance include propofol, thiopental and ketamine. General anesthesia provides unconsciousness, analgesia, amnesia and muscle relaxation during surgery.

1. GENERALANESTHESIA

2. GENERAL ANESTHESIA
 Definition: reversible state of
unconsciousness produced by
anesthetic agents, with loss of the
sensation of pain over the whole
body

3. Order of Descending Depression
Cortical and Psychic Centers
↓
Basal Ganglia and Cerebellum
↓
Spinal cord
↓
Medullary centers

4. Anesthesiology
Stages of anesthesia:
 Stage I : Analgesia
 Stage II : Excitement, combative
behavior – dangerous state
 Stage III : Surgical anesthesia
 Stage IV : Medullary paralysis –
respiratory and vasomotor
control ceases.

5. Anesthesiology
Molecular mechanism of the GA :
 GABA –A : Potentiation by Halothane,
Propofol, Etomidate, Barbiturates, Sodium
hydroxybutirate
 NMDA receptors : inhibited by Ketamine

6.  Anesthetic agents introduced either of
the following routes, producing a
depression of the brain
1. Oral
2. Rectal
3. Intramuscular
4. Intravenous
5. Inhalational
Mask Inhalational
Nasal Insufflation
Endotracheal Intubation

7. INDICATIONS FOR GENERAL
ANESTHESIA
 Infants and children
 Adults who prefer GA
 Extensive surgical procedures
 Patients with mental disease
 Long duration of surgery
 Surgery for which LA is impractical or
unsatisfactory
 History of toxic or allergic reactions to LA drugs
 Anticoagulant treatment

8. Anesthesiology
Hallmark of anesthesia:
 Amnesia / unconsciousness
 Analgesia
 Muscle relaxation

9. Clinical Signs of General
Anesthesia
a. Insufficient Depth – breath holding,
delirium, involuntary movement, retching and
increase mucus secretion
b. Sufficient Depth – stable Cardiovascular
response, adequate muscle relaxation, amnesia
and absence of troublesome reflexes
c. Excessive Depth – no response, nor ability to
resume normal respiratory function at the end
of the operation with decrease blood pressure.

10. Maintenance of AIRWAY in GA
Jaw thrust Head tilt–chin lift

11. Oropharyngeal Airway

12. Nasopharyngeal Airway

13. Laryngeal Mask Airway (LMA)

14. Esophageal-Tracheal Combitube

15. Endotracheal Intubation “Aligning Axes of the Airway”

16. Endotracheal Intubation “Laryngoscopes” with curved
and stright blades

17. Endotracheal Intubation
“Visualization of the Vocal Cords”

18. Correct position of the
endotracheal tube

19. ADVANTAGES of ENDOTRACHEAL
INTUBATION
1. Airway patency is assured
2. Protection from aspiration
3. Gastric distention is prevented

20. Complications of tracheal intubation
1. Trauma during intubation
2. Endobronchial intubation
3. Esophageal intubation
4. Endotracheal tube obstruction
5. Laryngospasm

21. Induction agents
 Opioids – fentanyl
 Propofol, Thiopental and Etomidate
 Muscle relaxants:
Depolarizing
Nondepolarizing

22. Induction
 IV induction
 Inhalation induction

23. General Anesthesia
 Reversible loss of consciousness
 Analgesia
 Amnesia
 Some degree of muscle relaxation

24. Intraoperative management
 Maintenance
Inhalation agents: N2O, Sevo, Deso, Iso
Total IV agents: Propofol
Opioids: Fentanyl, Morphine
Muscle relaxants
Balance anesthesia

25. Intraoperative management
 Monitoring
 Position – supine, lateral, prone, sitting, Litho
 Fluid management
- Crystalloid vs colloid
- NPO fluid replacement: 1st 10kg weight-
4ml/kg/hr, 2nd 10kg weight-2ml/kg/hr and
1ml/kg/hr thereafter
- Intraoperative fluid replacement: minor
procedures 1-3ml/kg/hr, major procedures 4-
6ml/kg/hr, major abdominal procedures 7-10/kg/ml

26. Intraoperative management
Emergence
 Turn off the agent (inhalation or IV agents)
 Reverse the muscle relaxants
 Return to spontaneous ventilation with
adequate ventilation and oxygenation
 Suction upper airway
 Wait for pts to wake up and follow command
 Hemodynamically stable

27. Postoperative management
 Post-anesthesia care unit (PACU)
- Oxygen supplement
- Pain control
- Nausea and vomiting
- Hypertension and hypotension
- Agitation
 Surgical intensive care unit (SICU)
- Mechanical ventilation
- Hemodynamic monitoring

28. Complications of General
Anesthesia
A. Intra-operative Complications
1. Respiratory Difficulties – hypoventilation due
to respiratory depression
2. Airway Obstruction
a. Upper Airway Obstruction
1) Falling back of the tongue
2) Foreign bodies above glottis
3) Endobronchial intubation
4) Larryngeal spasm & hiccups

29. b. Lower Airway Obstruction
1) Aspiration
2) Bronchospasm
3. Cardiovascular Complications
a. Hypotension
b. Hypertension
c. Arrhythmias
4. Ocular Complications
5. Malignant Hyperthermia

30. B. Post-operative Complications
1. Respiratory Complications
a. Atelectasis
b. Pneumothorax
2. Post Anesthesia Shivering
3. Post Operative Nausea and Vomiting

31. Prevention of Post-operative
Complications in GA
1. Continuous monitoring – BP, PR, RR, T
2. Avoid excessive sedation
3. O2 inhalation
4. Turn from side to side
5. Deep breathing
6. Steam Inhalation to liquefy sputum
secretions

32. INHALATIONAL
ANESTHETICS

33. Anesthesiology
The main target of inhalation anesthetics is
the brain.

34. Anesthesiology
Inhalational anesthetics :
Non-halogenated gas:
 Nitrous oxide
Halogenated hydrocarbons:
 Halothane
 Enflurane
 Isoflurane
 Desflurane
 Sevoflurane
 Methoxyflurane – nephrotoxicity.

35. Anesthesiology
The important characteristics of
Inhalational anesthetics which govern
the anesthesia are :
 Solubility in the blood
(blood : gas partition co-efficient)
 Solubility in the fat (oil : gas partition
co-efficient)

36. Anesthesiology
Blood : gas partition co-efficient:
 It is a measure of solubility in the blood.
 It determines the rate of induction and
recovery of Inhalational anesthetics.
 Lower the blood : gas co-efficient – faster
the induction and recovery – Nitrous oxide.
 Higher the blood : gas co-efficient – slower
induction and recovery – Halothane.

37. BLOOD GAS PARTITION CO-EFFICIENT

38. Anesthesiology
Oil: gas partition co-efficient:
 It is a measure of lipid solubility.
 Lipid solubility - correlates strongly with
the potency of the anesthetic.
 Higher the lipid solubility – potent
anesthetic. e.g., halothane

39. Anesthesiology
 MAC value is a measure of inhalational
anesthetic potency.
 It is defined as the minimum alveolar
anesthetic concentration ( % of the
inspired air) at which 50% of patients do
not respond to a surgical stimulus.
 MAC values are additive and lower in the
presence of opioids.

40. OIL GAS PARTITION CO-EFFICIENT
Higher the Oil: Gas
Partition Co-efficient
lower the MAC . E.g.,
Halothane
1.4 220
0.8

41. Inhalation
Anesthetic
MAC value
%
Oil: Gas
partition
Nitrous
oxide
>100 1.4
Desflurane 7.2 23
Sevoflurane 2.5 53
Isoflurane 1.3 91
Halothane 0.8 220

42. Inhalational anesthetics
Nitrous oxide:
 Safest inhalational anesthetic.
 Weak anesthetic but a good analgesic.
 No toxic effect on the heart, liver and
kidney.
 Caution about diffusional hypoxia
megaloblastic anemia.

43. Inhalational anesthetics
Halothane:
 It is a potent anesthetic.
 Induction is pleasant.
 It sensitizes the heart to catecholamines.
 It dilates bronchus – preferred in asthmatics.
 It inhibits uterine contractions.
 Halothane hepatitis and malignant
hyperthermia can occur.

44. Inhalational anesthetics
Enflurane:
 Sweet and ethereal odor.
 Generally do not sensitizes the heart to
catecholamines.
 Seizures occurs at deeper levels –
contraindicated in epileptics.
 Caution in renal failure due to fluoride.

45. Inhalational anesthetics
Isoflurane:
 It is commonly used with oxygen or
nitrous oxide.
 It do not sensitize the heart to
catecholamines.
 Its pungency can irritate the respiratory
system.

46. Inhalational anesthetics
Desflurane:
 It is delivered through special vaporizer.
 It is a popular anesthetic for day care
surgery.
 Induction and recovery is fast, cognitive
and motor impairment are short lived
 It irritates the air passages producing
cough and laryngospasm.

47. Inhalational anesthetics
Sevoflurane:
 Induction and recovery is fast.
 It is pleasant and acceptable due to lack
of pungency.
 It do not cause air way irritancy.
 Concerns about nephrotoxicity.
 Reacts with CO2 absorbents to form a special
halokene (COMPOUND A)  metabolized to
nephrotoxins which can lead to Kidney damage

48. Inhalational anesthetics
Xenon:
 Short duration of action
 Very expensive

49. Anesthetic B:G PC O:G PC Features Notes
Halothane 2.3 220 PLEASANT Arrhythmia
Hepatitis
Hyperthermia
Enflurane 1.9 98 PUNGENT Seizures
Hyperthermia
Isoflurane 1.4 91 PUNGENT Widely used
Sevoflurane 0.62 53 PLEASANT Ideal
Desflurane 0.42 23 IRRITANT Cough
Nitrous 0.47 1.4 PLEASANT Anemia

50. Non-Inhalational
(intravenous)
general anesthetics

51. Parenteral anesthetics
(IV):
 These are used for induction and
maintenance of anesthesia.
 Rapid onset of action.
 Recovery is mainly by redistribution.
 Also reduce the amount of inhalation
anesthetic for maintenance.
 E.g., includes thiopental, midazolam
propofol, etomidate, ketamine, sodium
hydroxybutyrate.

52. Anesthesiology
Thiopental (Pentothal):
 It is an ultra short acting barbiturates.
 Consciousness regained within 10-20 mins
by redistribution to skeletal muscle.
 It does not increase ICP.
 It is eliminated slowly from the body by
metabolism.
 It can be used for rapid control of
seizures.

53. Intravenous anesthetics
Propofol (Diprivan):
 Most commonly used IV anesthetic.
 Unconsciousness in ~ 45 seconds and
lasts ~15 minutes.
 Anti-emetic in action.
 Suited for day care surgery - residual
impairment is less marked.

54. Intravenous anesthetics
Sodium hydroxybutyrate (Gamma-Oxy-
Butiric-Acid):
 Most commonly used IV anesthetic in
post-soviet countries.
 Unconsciousness in ~ 120 seconds and
lasts ~45-120 minutes.
 Increases ICP.

55. Intravenous anesthetics
Etomidate:
 It is a short acting anesthetic.
 It suppress the production of steroids from
the adrenal gland and no repeated
injections.
 It is a pro-convulsant and emetic.
 Cardio-Vascular System stability is the main
advantage over anesthetics.

56. Intravenous anesthetics
Ketamine : Dissociative anesthesia
 Produce - profound analgesia, cataleptic
state, immobility, amnesia with light sleep.
 Acts by blocking NMDA receptors
 Heart rate and BP are elevated due to
sympathetic stimulation.
 Respiration is not depressed and reflexes
are not abolished.

57. Intravenous anesthetics
Ketamine:
 Emergence delirium, hallucinations
and involuntary movements occurs in 50%
cases during recovery.
 It is useful for burn dressing and trauma
surgery, in hypovolemic patients.
 Dangerous for hypertensive and increased
Intra-Cranial Pressure.

58. Intravenous anesthetics
Neuroleptanalgesia :
 It is characterized by general quiescence,
psychic indifference and intense analgesia
without total loss of consciousness.
 Combination of Fentanyl and Droperidol.

59. Intravenous anesthetics
Neuroleptanalgesia :
 It is associated with decreased motor
functions, suppressed autonomic reflexes,
cardiovascular stability with mild amnesia.
 It causes drowsiness but respond to
commands.
 Used for endoscopies, angiography and
minor operations.

60. Anesthetic
I.V
Duration
mins
Analgesia Muscle
relaxation
Others
Thiopental 5 - 10 --- --- Respiratory
depression
Propofol 5-10 --- --- Respiratory
depression
Ketamine 5-10 +++ --- Hallucinatio
ns
Midazolam 5-20 --- +++ Amnesia
Na
hydroxybut
yrate
40-60 --- --- Increases
ICP

61. Analgesia
1. Opiods
• Classification
 AGONISTS
 AGONIST/ANTAGONIST
 ANTAGONIST

62. Morphine
– Central actions and side effects
 DEPRESSANT EFFECT  analgesia, sedation,
depresses respiration & cough reflex, decreases
GI motility
 EXCITATORY EFFECT  euphoria, miosis,
nausea & vomiting, bradycardia, release of ADH
 Increases smooth muscle tone
 HISTAMINE RELEASE  broncospasm,
erythema

63. Meperidine
– Actions similar to morphine
– Shorter duration of respiratory depression
– Not as marked euphoria
– More pronounced nausea & vomiting
– Less histamine release
– Less or no GIT actions

64. Short-action opioids for fast-
track surgery
 Fentanyl
 Su-fentanyl
 Remi-fentanyl

65. AGONIST/ANTAGONISTS
 Buprenorphine
 Nalbuphine
 Limited analgesic potency
 Less respiratory depression

66. Naloxone (Pure opioid Antagonist)
– Competitive antagonists at the opioid
receptor sites

67. Muscle Relaxants – Neuromuscular
blockers
• Types of Neuromuscular Blockers (NMB)
a. Depolarizer: prolongs depolarization/ mimic Ach
action reduces sensitivity of the post-junctional
membrane to Ach
b. Non-depolarizer: acts by competitive inhibition

68. SUCCINYLCHOLINE – ONLY DEPOLARIZING
AGENT IN CLINICAL USE
– Depolarization of the membrane persists
until the drug diffuses away
– Manifest 1st muscle twitching and
fasciculation
– Elimination: enzymatic destruction by
PSEUDOCHOLINESTERASE
– Onset of action: 30 secs Duration: 5 mins
– Recovery within 5 to 10 mins

69. b. Non-Depolarizers
• Reversed by Anticholinesterases
(prostigmine, neostigmine)
• Do not cause muscular contractions
(fasciculations)

70. Types of non-depolarizers
a) Long acting (45 mins)
Pancuronium – eliminated via kidney
b) Intermediate acting (20-30 mins)
1) Atracurium – eliminated via HOFFMAN elimination
pathway
2) Vecuronium – eliminated through the biliary
3) Rocuronium – eliminated through the kidney
c) Short Acting (15- 20 minutes)
Mivacurium – eliminated by pseudocholinesterases

71. Clinical Uses
 Facilitate tracheal intubation
 Provide skeletal muscle relaxation during
surgery (adjunct to GA)
 Used in intensive care units

72. Thank you