General Anaesthesia

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General Anaesthesia

  1. 1. Anesthesiology[Gk . an-, not + aisthesis-, perception+ logia, study]
  2. 2. General Anaesthesia An artificial state of unresponsiveness, followed by amnesia, maintained by the continuing presence of chemical agents in the brain
  3. 3. Pharmacology1. Intravenous Agents2. Inhalational Agents3. ( Analgesics )4. Muscle Relaxants
  4. 4. Intravenous anaesthetics1. Thiopentone2. Propofol3. Ketamine
  5. 5. Thiopentone• Proven track record• Rapid onset of action with fast recovery due to redistribution• Repeated doses need to be smaller as accumulation occurs• Extravasation may cause necrosis• Potent anticonvulsant
  6. 6. Propofol• Fast onset of action with rapid recovery due to redistribution and high clearance• Clear headed recovery• Low incidence of nausea and vomiting• Suitable for short procedures especially day surgery• Pain on injection and occasional involuntary movements
  7. 7. Target-controlled Infusion (TCI)
  8. 8. Inhalational anaesthetics1. Nitrous oxide2. Volatile anaesthetics - Sevoflurane - Desflurane - Isoflurane - Enflurane - Halothane
  9. 9. Nitrous oxide• “ Laughing Gas”• Gaseous anaesthetic.• Piped gas supply or blue cylinders. 
  10. 10. Isoflurane• Volatile anaesthetic• Require vaporiser• Isoflurane commonly used• Faster recovery compared to halothane and enflurane• Irritating vapour, therefore not commonly used for induction.
  11. 11. Newer agents• Sevoflurane - Fast onset and offset of effect - Non-irritating, useful for inhalational induction, especially in children.• Desflurane - Boiling point near room temperature - Need special vaporiser
  12. 12. Older agents• Halothane - May cause arrhythmias intraoperatively and hepatitis postoperatively• Enflurane - May cause seizures and renal impairment
  13. 13. Muscle relaxants• Useful for aiding insertion of Endotracheal tube and ventilation• Will cause apnoea, therefore assisted ventilation mandatory.
  14. 14. Muscle relaxants• Suxamethonium - Rapid onset of action - Used in rapid sequence induction - Potential problems include arrhythmias
  15. 15. Muscle relaxants• Non-depolarising muscle relaxants - - Atracurium - Vecuronium - Mivacurium - Rocuronium• Fast onset with intermediate duration of action
  16. 16. Reversal of neuromuscularblockade• Neostigmine : - Anticholinesterase - Used for reversal of muscle relaxation by non-depolarising muscle relaxants - Atropine given together to counter bradycardia
  17. 17. Anaesthetic Technique1. Induction2. Maintenance3. Reversal
  18. 18. Induction of Anaesthesia• Intravenous hypnotic ± narcotic, or• Inhalational anaesthetic ± narcotic ± Muscle relaxant if required
  19. 19. Maintenance ofAnaesthesia• Inhalational anaesthetic ± analgesic, or• Intravenous anaesthetic ± analgesic, or• Inhalational anaesthetic + Intravenous anaesthetic ± analgesic ± Muscle relaxant if required
  20. 20. Reversal of Anaesthetic• Switch off Inhalational / Intravenous Anaesthetic• Reverse neuromuscular blockage• Consider other specific antagonists if necessary - Naloxone, Flumazenil
  21. 21. Complications ofGeneral Anaesthesia1. Central Nervous System2. Cardiovascular System3. Respiratory System
  22. 22. EffectsCentral Nervous System1. Depression - loss of consciousness - Cardiovascular depression - Respiratory depression2. Stimulation - seizures
  23. 23. EffectsCardiovascular System1. Myocardial depression2. Vasodilatation3. Arrhythmias hypotension, decreased perfusion
  24. 24. EffectsRespiratory System1. Decreased Rate & Apnoea2. Decreased Tidal Volume3. Ventilation – Perfusion mismatch4. Increased Work of Breathing hypoventilation, hypoxia
  25. 25. Intraoperative Monitoring1. Clinical2. Cardiovascular System3. Respiratory System
  26. 26. MonitoringClinical1. Pulse rate, Blood Pressure2. Respiratory rate3. Colour: - Pallor, cyanosis4. Perfusion: - Capillary refill, Temperature - Urine output
  27. 27. MonitoringCardiovascular System 1. Non-invasive: - ECG - Pulse rate, Heart rate - Blood pressure 2. Invasive: - Intra-arterial pressure - Central Venous Pressure, PCWP
  28. 28. MonitoringRespiratory System1. Pressure / Flow monitors: - Tidal volume, Airway pressure2. Gas analyser: - Inspiratory O 2 concentration, - End-tidal CO 2 partial pressure, - Anaesthetic gas concentration3. Pulse Oximeter - Arterial O 2 saturation
  29. 29. Ventilation• Spontaneous ventilation• Intermittent positive pressure ventilation - IPPV
  30. 30. Ventilation - IPPV• Requires endotracheal intubation in most cases• Useful when needed to: - protect the lungs from aspiration of material from stomach or upper airways - ensure adequate ventilation of the lungs
  31. 31. Ventilation - IPPV• Ventilator generates a positive pressure which drives gas / oxygen mixture into lungs • Dangers include: - failure of intubation / ventilation leading to hypoxia - injury to lungs if airway pressure is excessive

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