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General anaesthesia

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General anaesthesia

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General anaesthesia

  1. 1. General Anaesthesia Dr. Jervin
  2. 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. 3. Ques  MAC  Stages of anaesthesia  Second gas effect  Ideal anaesthetic?  Inhalational anaesthetic*  IV anaesthesia  Complications of GA  Consciuos sedation  Pre Aanaesthetic Medication
  4. 4. Definition Are the drugs which produce Reversible loss of all the sensation and consciousness.
  5. 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. 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. 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. 8. Properties of the Ideal Anaesthetic For the Surgeon  Should provide adequate analgesia.  Immobility  Muscle relaxation  Should be noninflammable and nonexplosive.
  9. 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. 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. 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. 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. 13.  N2O and Ketamine: Selectively inhibits the excitatory NMDA type of glutamate receptor.
  14. 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. 15.  Disadvantages: Low potency No bronchodilatation Poor Muscle relaxation 2nd gas effect Diffusion hypoxia Megaloblastic anaemia
  16. 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. 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. 18. HALOTHANE Disadvantages: During labour - Prolongs delivery, PPH Post operative shivering MALIGNANT HYPERTHERMIA
  19. 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. 20. Propofol  Propofol causes rapid induction/recovery with LESS HANGOVER  MILK OF AMNESIA  Anti-emetic and anti-convulsant property  Day care surgery  Anaphylaxis
  21. 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. 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. 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. 24. Complications of ga  During anaesthesia  After anaesthesia DRUG INTERACTIONS  Antihypertensives  CNS depressants  Neuroleptics, MAOIs
  25. 25. Conscious sedation  CNS depression + Local anaesthesia  Ad: Airway patent, reflexes present  Drugs:  Diazepam/midazolam  Propofol  N2O  Fentanyl
  26. 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. 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. 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.
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General anaesthesia

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