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General Anesth Lecture for 3rd year MBBS


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surgery and allied

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General Anesth Lecture for 3rd year MBBS

  1. 1. General Principles of anaesthesia DR.NADIR MEHMOOD Asst professor Department ofSurgery, RMC
  2. 2. L Os What we will cover  History  Definition of Anesthesia  Why is it important?  Mechanism & stages  Planning & pre-op fasting  Equipment used  Analgesia  What is anesthetics?
  3. 3. Historical information People always wanted to overcome the sufferings caused by pain. The history of civilization left numerous documented evidences of permanent search for ways and methods of anesthesia. The first written mention of the pain relieving medicines was found in Egypt (described in Ebers papyrus 4 - 5 thousand years ago). Use of wine, mandrake root, opium, Indian hemp, henbane and thorn-apple. In the East, in the mountains of Tibet, acupuncture and massage were widely used with anesthetic aim.
  4. 4. History of Anesthesia • Ether synthesized in 1540 by Cordus • Ether used as anesthetic in 1842 by Dr. Crawford W. Long • Ether publicized as anesthetic in 1846 by Dr. William Morton • Chloroform used as anesthetic in 1853 by Dr. John Snow
  5. 5. • In the Crimean-Turkish war (1853 – 1856) compatriot performed hundreds of successful ether anesthesia during surgeries on gunshot injuries. • In 1937 Guedel determined the clinical stages of ether narcosis, which are still considered to be classic. • Since that time anesthesiology has begun its scientific development. • For 150 years of anesthesiology history, scientists proposed and implemented in clinical practice dozens of anesthetic preparations, both inhalation and non-inhalation, as various types and methods of pain relief. This stimulated development of operative surgery and allowed various range of surgical interventions in all organs and systems of the body.
  6. 6. History of Anesthesia • Endotracheal tube invented in 1878 • Local anesthesia with cocaine in 1885 • Thiopental first used in 1934 • Curare first used in 1942 - opened the “Age of Anesthesia”
  7. 7. Anesthesiology It is a science that studies how to protect the organism from operating injuries. It improves the well-known and develops new methods of preparing patients for surgeries, providing anesthesia, controlling the body functions during the operation and in postoperative period.
  8. 8. The 16th of October, 1846 is considered to be the birthday of anesthesiology.
  9. 9. History of Anesthesia, 16th October 1846
  10. 10. So why no anesthesia until 1846? No real concept of “anesthesia” in late 1700’s / early 1800’s how can you achieve a state which you assume impossible or cannot envisage achieving Numerous Institutes concerned with treatment of disease by “Physicians” - surgery did not have same standing and therefore influence State of surgery - almost inevitably fatal - why encourage them? General moral / religious beliefs and fear / concerns about animal experimentation World Anesthesia Day 16th Oct
  20. 20. Basic Principles of Anesthesia • Anesthesia defined as the targetedly induced loss of perception of all modalities (touch, heat, cold, pain) of sensation • a) reversible • b) permanent (tumour pain) • “Triad of General Anesthesia” – need for unconsciousness – need for analgesia – need for muscle relaxation • Analgesia defined as the abolition of pain
  21. 21. Stages of GA (Guedel I-IV ) • obviously present in ether monoanaesthesia (history) • nowadays shortcut stage I, suppressed stage II I. stage of analgesia (induction) • from the initial administration to the loss of consciousness • normally responsive pupils, later dilation • tachycardia • tachypnoea • unchanged skin reflexes • marked analgesia – minute operations (e.g: painfull re-bandage)
  22. 22. Stages of GA (Guedel I-IV ) II. stage of excitement • from the loss of consciousness to the beginning of the automatic respiration • extremely marked excitation and motor agitation • hypersalivation, increased emetic reflex • arrhytmia, circulatory instability • irregular respiration • No action is allowed during this stage. Rapidly acting drugs are used to minimize time in this stage and reach stage 3 as fast as possible.
  23. 23. Stages of GA (Guedel I-IV ) III. stage of surgical anaesthesia • automatic respiration to respiration arrest • absent eye-lid and corneal reflex • absent reaction to pain • rhythmical eye-balls movements, sometimes nystagmus • In this stage operations including tracheal intubation are being done.
  24. 24. Stages of GA (Guedel I-IV ) IV. stage of paralysis (overdose) • after stage III if administration of medication continues • respiratory depression, first thoracic breathing, later abdominal breathing • cessation of respiration & circulatory collapse • lethal without cardiovascular and respiratory support • Warning signs: maximally dilated pupils, fading photoreaction, irregular heart action, urinary & faecal incontinence
  25. 25. STAGES OF GENERAL ANESTHESIA (Guedel) • Stage I: Analgesia • Stage II: Excitement/ Delirium • Stage III: Surgical Anesthesia – Plane I:reg. breathing  loss of eye movement – Plane II initiation of IC muscle paralysis – Plane III:  completion ICM paralysis – Plane IV:  diaphragmatic paralysis • Stage IV: Medullary Paralysis
  26. 26. Evaluation of inhalational anaesthetics efficiency Minimum alveolar concentration (MAC) • Concentration of anaesthetic in alveolar space, that prevents the reaction to a standard surgical stimulus (skin incision) in 50% of subjects • the lower MAC, the more potent anaesthetic • immobility in 95% subjects: increasing concentration of anaesthetic 30% over MAC • before inhalational induction 2-5 minutes 100% oxygen-> denitrogenation -> faster induction • at the end of anaesthesia again 100% oxygen -> faster excretion of anaesthetic and waking up
  27. 27. Groups of intravenous anaesthics in use 1. barbiturates – thiopental 2. imidazoles – etomidat 3. alkyled phenols – propofol 4. steroids– althesin 5. eugenols – propanidid 6. phenylcyclidines – ketamine 7. benzodiazepines- midazolam
  28. 28. Anesthesia Components – Frame – Regulator – Flowmeter – Oxygen Flush Assembly – Vaporizer – Anesthetic Supply System – Scavenging System • Anesthesia Machine
  29. 29. Anesthesia Components • Anesthesia Machine – Frame – Regulator • Placed on O2 tanks to decrease pressure from tank • 2 types of tanks – “E” Tanks » 650L @ 1800PSI – “H” Tanks » 7100L @ 2200PSI • Output pressure adjusted with knob
  30. 30. Anesthesia Components • Anesthesia Machine – Frame – Regulator – Flowmeter • Controls the amount of air released into the anesthetic circuit • Calculation: (Tidal volume - mL) x (Breathes per minute) / (1000mL/Liter)= Liters Resp. per Minute
  31. 31. Anesthesia Components • Anesthesia Machine – Flowmeter – Oxygen Flush Assembly – Vaporizer • Changes liquid agent to a vapor • Delivers the vapor into the moving steam of oxygen in controlled amounts • Must be serviced to maintain accuracy of delivery and safety • Caution with refurbished models
  32. 32. Anesthesia Components • Anesthesia Machine – Oxygen Flush Assembly – Vaporizer – Anesthetic Supply System • a.k.a Breathing circuits • Rebreathing – Exhaled air is cleaned and reused with the patient • Non-rebreathing – Exhaled air is taken by scavenging system
  33. 33. Anesthetic Supply Systems Rebreathing Circuit Non-Rebreathing Circuit
  34. 34. The future Anesthesia in the 21st Century Crystal ball  new and better drugs “anaesthesia” perhaps not priority it was NDMR(non dep musc relx) version of Suxamethonium analgesia and PONV  more TCI (Total comfort installation)  “closing the loop” techniques  new airway management techniques  new monitoring - anesthetic depth World Anesthesia Day 16th Oct
  35. 35. Anaesthesia in the 21st Century • Staffing and workload issues – increased demand for “anaesthetic services” – questioning of roles outside theatre – questioning of roles within theatre World Anesthesia Day 16th Oct
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