General anaesthesia

1. General
Anaesthesia
Dr. Jervin

2. History
• Before middle 90s: Alcohol, Opium, Cannabis and
Asphyxia: Operations were Horrible.
• Horrace Wells (1844): Nitrous oxide.
• Mortan (1846): Ether
• Simpson (1846): Chloroform
• New Generation Anaesthetics: Halothane (1956)
• First i.v. Anaesthetic: thiopentone (1935)

3. Ques
 MAC
 Stages of anaesthesia
 Second gas effect
 Ideal anaesthetic?
 Inhalational anaesthetic*
 IV anaesthesia
 Complications of GA
 Consciuos sedation
 Pre Aanaesthetic Medication

4. Definition
Are the drugs which produce Reversible
loss
of all the sensation and consciousness.

5. MAC
• MAC: Minimal alveolar concentration of the
anaesthetic in the pulmonary alveoli to produce
immobility to the painful stimulus in 50% of the
individuals.
• Accepted as the valid measure of the potency
because it remains fairly constant for given
species.

6. Guedel (1920) with ether
 I. Stage of Analgesia: Administration of GA to loss of
consciousness
 II. Stage of Delirium: Loss of consciousness to
onset of regular respiration
 III. Stage of Surgical Anaesthesia: Onset of regular
respiration to cessation of spontaneous breathing
 IV. Medullary Paralysis: Cessation of respiration to
failure of circulation and death

7. Properties of the Ideal
Anaesthetic
For the patient
 Pleasant
 Non-irritating
 Should not cause nausea or vomiting.
 Induction and recovery should be fast.

8. Properties of the Ideal
Anaesthetic
For the Surgeon
 Should provide adequate analgesia.
 Immobility
 Muscle relaxation
 Should be noninflammable and
nonexplosive.

9. Properties of the Ideal
Anaesthetic
For the Anaesthetist
 Ease of administration, controllable, versatile
 Potent at low concentrations
 Rapid adjustments in depth of anaesthesia
 Wide safety margin
 No effect on vital organs
 Cheap, Stable
 Ease of storage
 Should not react with rubber tubing or soda lime

10. Preanaesthetic medication
 Decrease anxiety : BZDs- diazepam; Antihistamine:
Promethazine
 Provide amnesia
 Analgesia: Relieve preoperative pain : Opiods
 Prevent aspiration: decrease secretions : Anticholinergics
 Antiemetic: Metaclopromide, domperidone, ondansetron
 Reduce gastric acidity: H2 blockers, PPIs

11. CLASSIFICATION INHALATIONAL
Gas: Nitrous oxide
Volatile liquids: Ether, Halothane, Enflurane, Isoflurane, Desflurane,
Sevoflurane
 INTRAVENOUS
Inducing agents: Thiopentone sodium, Methohexitone sod., Propofol,
Etomidate
Slower acting drugs:
Benzodiazepines – Diazepam, Lorazepam, Midazolam
Dissociative anaesthetic – Ketamine
Opioid analgesic - Fentanyl

12. MOA
• Ligand gated Ion channels are the major targets of the
anaesthetic action.
• Inhalational Anaesthetics: Potentiate the action of the
Inhibitory Neurotransmitter GABA.
• Also augment the action of the Glycine in the spinal cord.
• Certain fluorinated anaesthetics: Inhibits Cation channel
gated Nicotinic cholinergic receptor.

13.  N2O and Ketamine: Selectively inhibits the excitatory
NMDA type of glutamate receptor.

14. Nitrous Oxide
 Physical characteristics: Colourless, odourless,
heavier than air, non-inflammable, non-irritating
 Uses: + 30% oxygen ± other volatile GAs ± Muscle
relaxant
 Advantages:
Fast and smooth induction
Fast recovery (4 mins)
Good analgesia
↓ need for volatile anaesthetics
No AEs on CVS, RS, Kidney, Liver
No arrhythmogenic action

15.  Disadvantages:
Low potency
No bronchodilatation
Poor Muscle relaxation
2nd gas effect
Diffusion hypoxia
Megaloblastic anaemia

16. HALOTHANE
 Physical characteristics:
Volatile liquid, mild sweetish odour, non-irritant, non-inflammable
 Advantages:
High potency
Pleasant induction
Smooth recovery
Bronchodilatation
Inhibits intestinal and uterine contractions
Cheap

17. HALOTHANE
 Disadvantages:
Slow Induction and recovery
Poor analgesic
Poor muscle relaxant
Vagomimetic - ↓BP, HR
Sensitises myocardium to arrhythmogenic action of
CAs
Hepatotoxic (repeated use)

18. HALOTHANE
Disadvantages:
During labour - Prolongs delivery, PPH
Post operative shivering
MALIGNANT HYPERTHERMIA

19. Thiopentone sodium
 Ultra-short acting barbiturate
 High lipid solubility and REDISTRIBUTION
 Pleasant induction, fast recovery
 Poor analgesic, poor muscle relaxant
 REFLEXES INTACT
 Respiratory centre and VMC ↓, myocardium ↓
 BP and respiration ↓ initially, recover
 Restlessness, delirium, shivering on prolonged
anaesthesia

20. Propofol
 Propofol causes rapid induction/recovery with LESS
HANGOVER
 MILK OF AMNESIA
 Anti-emetic and anti-convulsant property
 Day care surgery
 Anaphylaxis

21. Benzodiazepines
 Diazepam, lorazepam, midazolam
 Induction, maintenance, supplementation of
anaesthesia
 Poor analgesic, poor muscle relaxant
 NO CV or respiratory ↓↓
 NO nausea/vomiting, involuntary movements post-
op
 Reversed by FLUMAZENIL
 Endoscopy, angiography, cardiac catheterisation

22. Ketamine
 Related to Phencyclidine (hallucinogen)
 Blocks NMDA subtype of glutamate receptor in cortex (limbic system)
and sub-cortical areas
 DISSOCIATIVE ANAESTHESIA
 Reflexes INTACT
 Respiration unaffected, relieves bronchospasm, CVS ++ (↑HR, CO,
BP)
 Cardiac Catheterisation, bronchoscopy, burn dressings, forceps
delivery
 SHOCK patients, BRONCHIAL ASTHMA
 Emergence delirium, hallucinations
 ↑ IOP, ICT

23. Fentanyl
 Opioid analgesic with potency, X 80-100 Morphine
 Good analgesic, poor muscle relaxant
 ↓ respiration, HR, BP
 Diagnostic procedures, endoscopy, angiography, burn dressing
 NALOXONE
 NEUROLEPT ANALGESIA
 NEUROLEPT ANAESTHESIA
 QT prolongation
 Remifentanyl, Sulfentanil, Alfentanil

24. Complications of ga
 During anaesthesia
 After anaesthesia
DRUG INTERACTIONS
 Antihypertensives
 CNS depressants
 Neuroleptics, MAOIs

25. Conscious sedation
 CNS depression + Local anaesthesia
 Ad: Airway patent, reflexes present
 Drugs:
 Diazepam/midazolam
 Propofol
 N2O
 Fentanyl

26. Nueroleptanalgesia
 Characterised by quiescence, psychic
indifference and intense analgesia without loss of
consciousness.
 The combination causes significant respiratory
depression, hypotension, bradycardia and EPS
during recovery.

27. Nueroleptanaesthesia
 Addition of 65% N2O + 35% O2 to the above
combination
 Benzodiazepines
 For inducing or supplementing
 They cause sedation, amnesia and reduce anxiety

28.  IV midazolam is preferred as it is faster and
shorter acting, more potent, does not cause
significant respiratory and cardiovascular
depression and does not cause pain or irritation at
the injection sites.
 Also used as preanaesthetic medication.