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General Anaesthetics.pptx

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General Anaesthetics.pptx

  1. 1. General Anaesthetics Dr Farhan
  2. 2. General Anaesthesia  It refers to drug induced reversible loss of consciousness and all sensations.  There is no single agent that can produce all the above effects. Hence we have an anaesthetic protocol  Premedication, Induction of anaesthesia, Maintenance of anaesthesia, skeletal muscle relaxation, Analgesics as premedication-during and post operatively, Drugs to reverse effects
  3. 3. GUEDEL’S STAGES OF ANAESTHESIA  Stage 1 – Analgesia or disorientation  Stage 2 – Excitement or delirium*  Stage 3 – Surgical Anaesthesia# – Plane 1,2,3 & 4  Stage 4 – Medullary Depression  *Induction & #Maintenance
  4. 4. CLASSIFICATION  INHALATIONAL ANAESTHETICS – GAS – Nitrous Oxide LIQUID – Ether, Halothane, Fluranes  INTRAVENOUS ANAESTHETICS – INDUCERS – FAST – Thiopentone (Barb) Propofol, Etomidate (Non – Barb) INDUCERS – SLOW – Diazepam, Lorazepam, Midazolam (Benzos) OPIOIDS – Fentanyl NEUROLEPTIC AGENT – Droperidol
  5. 5. Inhalational Agents  Minimum Alveolar Concentration (MAC) – It is the minimum concentration of inhalational anaesthetic in the alveoli that is required to produce immobility in response to a painful stimulus in 50% patients. It indicates the potency of the inhalational general anaesthetic. Greater is the MAC, lesser is the potency. Nitrous oxide – High MAC, Least Potent Methoxyflurane – Low MAC, Most Potent  Blood Gas Partition Coefficient – It determines the solubility of an agent in the blood. It indicates the speed of onset and recovery of an anaesthetic drug. Greater is the blood gas partition coefficient, lesser is the speed of onset and recovery Methoxyflurane – High BGPC, Slow Acting Desflurane – Low BGPC, Fastest Acting
  6. 6. Ether  Highly inflammable, Pungent smell, Explosive agent  Effective analgesic, Muscle relaxant  Slow inducer  Good bronchodilator. Safer in asthmatics  Inexpensive  C/I – Diabetics (causes Hyperglycaemia)
  7. 7. Nitrous Oxide  Colourless, Non Irritating, Non Inflammable gas – Laughing Gas  Effective analgesic at low concentration – Labour Pain  Weak Muscle Relaxant, Fast Inducer & Faster recovery due to High BGPC  It takes time to produce surgical anaesthesia and hence combined with others (50- 65% N20 + 33% O2) CONCENTRATION EFFECT – When N2O is administered in high dose, then it diffuses from alveoli to blood that generates negative pressure in the alveoli that results in more gas removal from the cylinder or source SECOND GAS EFFECT – When N2O is given along with other inhalational agent like halothane, then due to generation of negative pressure, the second gas is also taken in from the cylinder or source  ADVERSE EFFECTS – If N2O is suddenly stopped while recovery from anaesthesia then more negative pressure is generated in the alveoli which removes alveoli from blood, results in diffusional hypoxia. It can be prevented by giving 100% oxygen a few minutes before discontinuing the nitrous oxide Presence of impurities cause methemoglobinemia and laryngospasm Bone Marrow Suppression + Megaloblastic Anaemia = Subacute Combined Degeneration of spinal cord
  8. 8. Halothane  Colourless, Non Irritant, Non Inflammable, Pleasant smelling volatile liquid  High therapeutic efficacy with weak analgesic effect  Excellent choice for induction of anaesthesia in children – rapid & smooth  Agent of choice in asthma  Agent of choice in internal version and manual removal of placenta as is relaxes the placenta. C/I during labour  ADVERSE EFFECTS – Pruritis, sensitizes the heart to catecholamines and can cause arrhythmias C/I in pheochromocytoma; Cardio depressant effect resulting in hypotension and bradycardia Malignant Hyperthermia; Post anaesthetic chills and shivering
  9. 9. FLURANES  Enflurane, Isoflurane, Desflurane, Sevoflurane  ISOFLURANE – Isomer of enflurane. Medium rate of onset and recovery.  Maintains cardiac output, produces least intracranial tension and hence an agent of choice for cardiac and neurosurgery Used for producing controlled hypotension Safe in pheochromocytoma Lacks proconvulsive property  Adverse effects – Coronary steal phenomenon – divert blood away from myocardium – ischemia in patients with CAD
  10. 10. INTRAVENOUS ANAESTHETICS  Thiopentone – Ultra short acting barbiturate and is the most widely used. 3-5mg/kg; 5-10 min  High lipid solubility, rapidly crosses BBB but terminates its action very quickly due to redistribution  Recovery time – 5 minutes  Safe in pregnancy  Decreases ICP – agent of choice for cerebral protection, also reduces cerebral oxygen consumption  Hyperalgesia at subanaesthetic doses  Adverse effects – Hypotension, respiratory depression, apnoea  C/I – Acute intermittent Porphyria  VTIG - SH
  11. 11. INTRAVENOUS ANAESTHETICS  Propofol – It has fast onset within 15 sec and lasts for 5-10 min because of redistribution. 2mg/kg  IV Drug of choice for day care surgery, for sedation in ICU, and in patients with malignant hyperthermia  Used with ALFENTANIL to produce TIVA  It has antiemetic action  Indicated for those procedures where return to a preoperative mental status is desirable  Bronchodilator property  Cerebroprotective activity; no muscle relaxing property  Can cross placenta but safe in pregnancy  Anti convulsant property  Adverse effects – Apnoea and pain at the site of injection, marked fall in BP, Bradycardia
  12. 12. INTRAVENOUS ANAESTHETICS - KETAMINE  It is a phencyclidine derivative that is often abused  Its primary site of action is the cortex and limbic system. It acts by blocking the action of Glutamate at NMDA receptor  It is a highly lipophilic drug  After its fast diffusion into brain it is subsequently redistributed in various body compartments with simultaneous hepatic metabolism followed by urinary and biliary excretion.  Its usual induction dose is 1-2mg/kg
  13. 13. INTRAVENOUS ANAESTHETICS - KETAMINE  It produces dissociative anaesthesia which is characterized by a feeling of dissociation from the surroundings, profound analgesia, immobility and amnesia with light sleep.  It is a potent analgesic, potent bronchodilator  It significantly increases HR, BP and cardiac output (can be used in SHOCK) along with marked increase in cerebral blood flow and ICP. Hence it is C/I in patients of hypertension, IHD, Schizophrenia and Epilepsy.  It is the drug of choice for induction in children. At Sub doses, it is used for painful procedures of short duration like dressing of burn, radiotherapy, minor orthopaedic procedures  Adverse Effects – Emergence delirium characterized by vivid dreams, hallucinations, disorientation and sensory illusions. (use diazepam or midazolam)
  14. 14. NEUROLEPT ANALGESIA NEUROLEPT ANAESTHESIA  A fixed dose combination of opioid analgesic FENTANYL (50mcg/ml) and a neuroleptic DROPERIDOL (2.5mg/ml) is used to produce a state of neurolept- analgesia. It is diluted in a glucose solution and infused IV over 10-15 minutes.  It is characterized by a state of calmness, psychic indifference to the surroundings and profound analgesia without any loss of consciousness.  Alfentanil, Sufentanil, Remifentanil can also be used in place of Fenatanyl  This is utilized for endoscopies, angiographies, burn dressings and minor surgical procedures.  Neurolept-analgesia + 65% nitrous oxide + 35% oxygen = Neurolept- anaesthesia
  15. 15. PRE ANAESTHETIC MEDICATION comfort and less adr to patient  Antianxiety drugs – diazepam (5-10mg oral) lorazepam (2mg IM) midazolam (70-100 mcg/kg IV)  Sedative Hypnotics – Promethazine (25mg IM)  Opioid Analgesics – Morphine (8-12mg IM) Pethidine (50-100 mg IM)  Anticholinergics – Atropine (0.5 mg IM) Hyoscine (0.5mg IM) Glycopyrrolate (0.1-0.3 mg IM)  Anti emetics – Metaclopramide (10 mg IM) Domperidone (10 mg oral) Ondansetron (4-8 mg IV)  H2 Receptor blockers – Ranitidine (150-300 mg oral) omeprazole (20mg)

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