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General anaesthetics

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General anaesthetics

  1. 1. GENERAL ANAESTHETICS By Dr .Elza Joy Munjely, JR II, Govt. Medical College ,Kottayam.
  2. 2. CARDINAL FEATURES Immobility Amnesia Attenuation of autonomic responses Analgesia unconsciousness
  3. 3. Balanced anaesthesia- • All these modalities achieved • Using combination of anaesthetic drugs • So that the dose of individual drugs can be reduced along with their side effects
  4. 4. HISTORY Humphrey Davy • 1800 • First person to make N2O • Noted – Euphoria,analgesia,LOC
  5. 5. HISTORY Horace Wells • American dentist • 1844 • First used N2O to patients for dental extraction
  6. 6. HISTORY William Morton • 1846 • American Dentist • Ether- tooth extraction
  7. 7. HISTORY John Collins Warren • Chief surgeon of Massachusetts • 16 th October 1846- ETHER DAY =WORLD ANAESTHESIA DAY • Operation theatre-ETHER DOME
  8. 8. HISTORY James Simpson • Professor of midwifery at Edinburgh university • 1847 • Chloroform • To relieve pain of childbirth
  9. 9. HISTORY John Snow • Calculated dosages for the use of ether and chloroform as surgical anaesthetics • Designed the apparatus to administer ether & mask to administer chloroform • 1853 • administered chloroform to Queen Victoria during her 8th delivery
  10. 10. STAGES OF ANAESTHESIA
  11. 11. STAGE 1-Stage of analgesia From inhalation –LOC Pain progressively abolished Dream like state STAGE 2-Stage of delirium From LOC -beginning of regular respiration Apparent excitement STAGE 3-Surgical anaesthesia From regular respiration-loss of spontaneous respiration Divided into 4 planes STAGE 4-Medullary paralysis Loss of spontaneous respiration – failure of circulation & death
  12. 12. MEASUREMENT OF ANAESTHETIC POTENCY
  13. 13. MAC- MINIMAL ALVEOLAR CONCENTRATION The alveolar partial pressure of a gas at which 50% of humans do not respond to a surgical incision
  14. 14. Two important characteristics of Inhalational anaesthetics which govern the anaesthesia are : 1. Solubility in the fat (oil : gas partition coefficient) 2. Solubility in the blood (blood : gas partition coefficient)
  15. 15. OIL-GAS PARTITION COEFFICIENTS • It is a measure of lipid solubility of the anaesthetic • Measure of anaesthetic potency • solubility of general anaesthetics in lipid is the potency
  16. 16. BLOOD-GAS PARTITION COEFFICIENT • Ratio conc. in blood conc. in gas • Lower the Blood-gas partition coefficient faster the induction & faster the recovery.
  17. 17. Anaesthetic Blood/Gas Oil/gas Nitrous oxide 0.47 1.4 Halothane 2.4 224 Isoflurane 1.4 97 Sevoflurane .65 42 Desflurane .42 18.7
  18. 18. MECHANISM OF ACTION
  19. 19. EFFECT OF ION CHANNELS Potentiation of GABA at GABAA receptors- almost all anaesthetics (except cyclopropane,ketamine,Xenon,N2O)
  20. 20. EFFECT OF ION CHANNELS Activation of Two – pore Domain potassium channels- can be directly activated by low conc. of volatile & gaseous anaesthetics, thus reducing memb. excitability
  21. 21. EFFECT OF ION CHANNELS Inhibition of excitatory NMDA receptors- • Competitive antagonist for glycine - Xenon • Noncompetitive antagonist of glutamate- Ketamine • NMDA channel blocker-N2O
  22. 22. EFFECT OF ION CHANNELS • Other ion channels-ligand-gated channels including glycine,nicotinic & 5HTreceptors as well as at cyclic nucleotide –gated K+ channels • Inhibition of presynaptic Na channels inhibition of NT release at excitatory synapses
  23. 23. CLASSIFICATION
  24. 24. INHALATIONAL GAS • Nitrous oxide • Xenon VOLATILE LIQUIDS • Ether • Halothane • Isoflurane • Desflurane • Sevoflurane
  25. 25. INTRAVENOUS Fast acting drugs • Thiopentone sod. • Methohexitone sod. • Propofol • Etomidate Slower acting drugs BENZODIAZEPINES • Diazepam • Lorazepam • Midazolam DISSOCIATIVE ANAESTHESIA • Ketamine OPIOID ANALGESIA • Fentanyl • Alfentanil • Sufentanil • Remifentanil Cyclopropane,trichloroethylene,methoxyflurane & enflurane are no longer used
  26. 26. INHALATIONAL ANAESTHETICS
  27. 27. PHARMACOKINETICS
  28. 28. DEPTH OF ANAESTHESIA DEPENDS ON POTENCY OF THE AGENT PARTIAL PRESSURE IN THE BRAIN
  29. 29. INDUCTION & RECOVERY DEPENDS ON RATE OF CHANGE OF PARTIAL PRESSURE IN THE BRAIN
  30. 30. ALVEOLI BRAINBLOOD
  31. 31. FACTORS AFFECTING THE PP OF ANAESTHETIC ATTAINED IN THE BRAIN 1. PP of anaesthetic in inspired gas 2. Pulmonary ventilation 3. Alveolar exchange 4. Solubility in blood 5. Solubility of anaesthetic in tissues 6. Cerebral blood flow
  32. 32. ELIMINATION • Same factors which govern induction also govern recovery. • Most GA eliminated unchanged • Halothane >20% metabolised in liver
  33. 33. SECOND GAS EFFECT • Occurs when another inhalational anaesthetic is used with N2O • Rapid uptake of N2O produces a vaccum in the alveoli • Second gas also undergoes rapid uptake along with N2O
  34. 34. DIFFUSION HYPOXIA • Reverse of second gas effect occurs when N2O is discontinued after prolonged anaesthesia • N2O rapidly diffuses out the alveoli & dilutes the alveolar air. PP of O2 reduced in alveoli Diffusion Hypoxia
  35. 35. Anaesthetic MA C Oil:Gas Partition Coeff. Blood:Gas Partition Coeff. Induction Muscle Relaxation Remarks Ether 1.9 65 12.1 Slow V.Good Irritating,inflammable & explosive Potent,Good analgesia,pungent Safe ininexperienced hands-no need for special equipment Halothane 0.75 224 2.3 Interm Fair Nonirritant,Potent,preferred for asthmatics Malignant hyperthermia,hepatotoxic Isoflurane 1.2 99 1.4 Interm Good Safe in MI, Preferred in neurosurgery Desflurane 6 19 0.42 Fast Good Out patient surgery,irritant Sevoflurane 2 50 0.68 Fast Good Pleasant,can be used in paediatric patients N2O 105 1.4 0.47 fast Poor Least potent Good analgesic,breathing & respiration better maintained Expand pneumothorax
  36. 36. I.V ANAESTHETICS
  37. 37. INDUCING AGENTS • Drugs on IV injection produce LOC in one arm- brain circulation time, 11 sec • Thiopentone sod. • Methohexitone sod. • Propofol • Etomidate
  38. 38. DRUG INDUCTI ON MAJOR UNWANTED EFFECTS REMARKS PROPOFOL Fast CVS & R.S depression Propofol infusion syndrome Used for total IV anaesthesia along with fentanyl Preferred for OP surgeries DOC for sedating intubated pts. In ICU,preferred in asthmatics THIOPENTAL Fast hangover CVS & R.S Depression, can precipitate AIP Necrosis on extravasation Other uses – to control convulsions, Narcoanalysis ETOMIDATE Fast Excitatory effects During induction & recovery Adrenocortical suppression Aneurysm surgeries & cardiac disease
  39. 39. KETAMINE Slow Psychomimetic effects Postop nausea, vomiting Salivation Raised ICT Dissociative anaesthesia Muscle tone ↑ HR,CO,BP,ICT ↑ Preferredfor head & neck surgeries,hypovolaemic pts,Asthmatics MIDAZOLAM slow Preferred for endoscopies fracture settings angiographies, ECT FENTANYL Anaesthetic awareness with dreadful recall Opioid analgesic To supplement balanced anaesthesia Nerolept analgesia –along with Droperidol
  40. 40. CONSCIOUS SEDATION • Monitored state of altered consciousness that can be employed to carryout diagnostic/short therapeutic/dental procedures in apprehensive subjects or medically compromised patients – Diazepam – Propofol – N2O – Fentanyl
  41. 41. THANK YOU

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