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General Anaesthesia

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A slideshow on how general anaesthesia works and its history, modern usage and procedure. This slide gives a concise and comprehensive review on General anaesthesia

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General Anaesthesia

  1. 1. General Anaesthesia Adityadeb Ghosh B. Pharm Guru Nanak Institute of Pharmaceutical Science and Technology, Kolkata, IN
  3. 3. 1. What is Anaesthesia? Introduction and history of anaesthesia.
  4. 4. Introduction General anaesthesia is a medically induced state of unconsciousness with loss of protective reflexes, resulting from the administration of one or more general anaesthetic agents. It is carried out to allow medical procedures that would otherwise be intolerably painful for the patient.
  5. 5. History  Before 19th century, alcohol, opium, cannabis, even concussion and asphyxia were used to prevent surgical pain.  In the 19th century, invention of antiseptics and advances in pharmacology and physiology led to massive development in general anaesthesia and pain management.  On November 14, 1804, Hanaoka Seishū, a Japanese doctor, performed the first successful surgery using general anesthesia.
  6. 6. Timeline of Anaesthetics 1884 1846 1956 N2O Ether 1847 Chloroform 1929 Cyclopropane Halothane These were the most popular early anaesthetics. The first I.V. anaesthetic thiopentone was introduced in 1935.
  7. 7. 2. How it works? Mechanism of action of anaesthesia.
  8. 8. Mechanism of action ▪ Blocking cation channels of nicotinic cholinergic receptors. ▪ Blocking excitatory NMDA type of glutamate receptor. ▪ Enhancement of inhibitory transmission through GABAA receptor. ▪ Interrupting functions of cerebral cortex, thalamus, reticular activating system, and spinal cord
  9. 9. Minimum Alveolar Concentration ▪ Lowest concentration of the drug in pulmonary alveoli needed to produce immobility in response to a painful stimulus in 50% individuals. ▪ It is a measure of potency and the capacity of an anaesthetic to enter into CNS and attain certain concentration in neuronal membrane. ▪ Declines with age beyond 50 years.
  10. 10. 3. How is it done? Procedure, premedication and stages of anaesthesia.
  11. 11. Fig: Anaesthesia workstation
  12. 12. Premedication ▪ Clonidine - reduces postoperative shivering, nausea and vomiting, and emergence delirium. ▪ Midazolam - reduces preoperative anxiety, including separation anxiety in children. ▪ Melatonin - hypnotic, anxiolytic, sedative, antinociceptive, and anticonvulsant. ▪ β-blockers – reduces postoperative hypertension, cardiac dysrhythmia, or myocardial infarction.
  13. 13. Procedure Anaesthetic agents may be administered by : Inhalation, injection (intravenous, intramuscular, or subcutaneous), oral, and rectal routes. Once they enter the circulatory system, the agents are transported to their biochemical sites of action in the central and autonomic nervous systems. An example sequence of induction drugs: • Pre-oxygenation to fill lungs with oxygen. • Lidocaine for sedation and systemic analgesia for intubation. • Fentanyl for systemic analgesia for intubation. • Propofol for sedation for intubation. • Switching from oxygen to a mixture of oxygen and inhalational anesthetic.
  14. 14. STAGES ▪ Stage of analgesia – pain is abolished, patient is awake in a dreamy state. Amnesia imminent. ▪ Stage of delirium – patient may shout, struggle and hold his breath. HR and BP rises, pupils dialate. No procedure done. ▪ Surgical Anaesthesia – 4 planes : ▸Plane 1 – Roving eyeballs, eyelids closed, reflexes present. ▸Plane 2 – Loss of corneal and laryngeal reflexes. ▸Plane 3 – Pupil dialates, light refles lost, H.R rises. ▸Plane 4 – Intercostal paralysis, shallow abdominal respiration. ▪ Medullary Paralysis – Cessation of respiration and potential cardiovascular collapse. This stage is lethal without cardiovascular and respiratory support.
  15. 15. Fig : Physiological changes during stages of general anaesthesia with ether.
  16. 16. Maintenance and emergence ▪Anaesthesia is maintained for the required time by continuously applying inhalation or intravenous anaesthetics. ▪Emergence usually takes 1-30 min, when the concentration of the drug falls below a certain level. ▪Symptoms like shivering, confusion, aphasia, dyspnoea and arrhythmia occur during emergence. ▪NSAIDS, Opiates and other pain management drugs are administered to reduce post operative pain.
  17. 17. CONCLUSION Attempts at producing a state of general anaesthesia can be traced throughout recorded history in the writings of the ancient Sumerians, Babylonians, Assyrians, Egyptians, Greeks, Romans, Indians, and Chinese. Rapid advancement in modern anaesthetic techniques has ensured painless surgeries and eliminated the horrible consequences arising from surgeries performed without anaesthesia.
  18. 18. Thank You! References:  Tripathi K.D.; Essentials of Medical Pharmacology; 7th Edition; Jaypee brothers medical publishers ltd.; 2014.  Anesthesiology; August 2007; Volume 107; Issue 2.
  19. 19. “Alcohol is the anaesthesia by which we endure the operation of life - George Bernard Shaw
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A slideshow on how general anaesthesia works and its history, modern usage and procedure. This slide gives a concise and comprehensive review on General anaesthesia


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