Inhalant anaesthetics

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Inhalant anaesthetics

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Inhalant anaesthetics

  1. 1. Inhalant Anesthetics
  2. 2. Inhalant Anesthetics <ul><li>1) Volatile liquids </li></ul><ul><li>Ether (prototype – not used) </li></ul><ul><li>Halothane, Methoxyflurane (Old) </li></ul><ul><li>Enflurane (new) </li></ul><ul><li>Isoflurane (Newer) </li></ul><ul><li>Desflurane (Suprane) (Newest) </li></ul><ul><li>Sevoflurane (Ultane) (Newest) </li></ul><ul><li>2) Gases </li></ul><ul><li>N 2 O (still used) </li></ul><ul><li>Cyclopropane (not in use) </li></ul>
  3. 3. Physicochemical characteristics <ul><li>The action and margin of safety </li></ul><ul><li>How they are supplied </li></ul><ul><li>Equipment needed for safe delivery </li></ul><ul><li>How they are taken up by the lung, distributed within the body, and eliminated </li></ul>
  4. 4. Vapour Pressure & BP <ul><li>Pressure exerted by the molecules of the vapor phase at equilibrium of molecules moving in and out of liquid phase </li></ul><ul><li>Vapor Pressure dependent on temperature and physical characteristics of liquid, independent of atmospheric pressure </li></ul><ul><li>↑ Temperature->↑ Vapor Pressure </li></ul><ul><li>Vapor pressure is a measure of the agent’s ability to evaporate (volatility) .The greater is the vapor pressure, the greater the concentration of inhalant deliverable to the patient (and environment). </li></ul><ul><li>Boiling Point: Temperature at which vapor pressure equals atmospheric pressure </li></ul>
  5. 5. Vapour Pressure & BP Agent BP ( 0 C) VP (20 0 C) Halothane 50 243 Enflurane 56 175 Isoflurane 48 238 Sevoflurane 58 160 Desflurane 23 664 Nitrous Oxide -89 Xenon -107
  6. 6. Solubility of Inhaled Drugs <ul><li>solubility (partition) coefficient - the extent to which a gas will dissolve in a given solvent </li></ul><ul><li>Predicts the speed of induction, recovery, and change in anesthetic depth for an inhalant. </li></ul><ul><li>Ideal inhaled anesthetics should have low blood/gas and low tissue/blood solubility and low solubility in plastic and rubber. </li></ul><ul><li>Low solubility means rapid induction and emergence and more precise control </li></ul>
  7. 7. Solubility of Inhaled Drugs
  8. 8. Solubility of Inhaled Drugs Halo Enflur Isoflur Sevofl Desfl N 2 O Blood/Gas 2.54 1.8 1.4 0.69 0.42 0.47 Brain/Blood 1.9 - 1.6 1.7 1.3 0.5 Fat/ Blood 51 - 45 48 27 2.3
  9. 9. MAC <ul><li>Defined as the minimum alveolar concentration of an anesthetic agent at one atmosphere that produces immobility in 50% of patients exposed to a noxious stimulus. </li></ul><ul><li>Measurement of inhalation agent potency, which refers to the quantity of an agent required to produce a desired effect. </li></ul><ul><li>methoxyflurane (MAC = 0.23) currently is the most potent inhalant agent available. </li></ul>
  10. 10. Ether <ul><li>Properties : Colorless, highly volatile, pungent odor, flammable, explosive, stored in cool area. </li></ul><ul><ul><li>Solubility 12; MAC 2-3% </li></ul></ul><ul><li>Pharmacodynamics: </li></ul><ul><li>Lungs: Stimulates resp, increases secretion, not good in respiratory diseases </li></ul><ul><li>Kidney: decreases urine output </li></ul><ul><li>Liver: Minimum effect, decreases liver glycogen </li></ul><ul><li>Heart: Initially increases cardiac output, then decreases card. output, suppresses vasomotor center. </li></ul>
  11. 11. Ether <ul><li>Ether as an anesthetic </li></ul><ul><li>Advantage : CNS depression, excellent muscle relaxant , causes surgical anesthesia </li></ul><ul><li>Disadvantage : Flammable, irritates mucus membrane , breath holding, induces nausea & vomiting </li></ul><ul><li>Contraindications : Resp., kidney and liver diseases </li></ul><ul><li>Better agents are available now, so not used now. </li></ul>
  12. 12. Halothane <ul><li>Properties : nonflammable, expensive, colorless, nonexplosive, nonirritating, decomposes by light, Solubility 2.3; MAC 0.87% </li></ul><ul><li>Pharmacodynamics : </li></ul><ul><li>Lungs: Progressive depression, acidosis, decrease pH, given with N 2 O, O 2 </li></ul><ul><li>Heart: Myocardial depression, decreases cardiac output (CO), hypotension, sensitizes myocardium </li></ul><ul><li>Liver: hepatitis by repeated administration. </li></ul>
  13. 13. Halothane <ul><li>General Information : </li></ul><ul><li>Introduced in 1957 </li></ul><ul><li>Rapid induction and recovery </li></ul><ul><li>Low solubility in plasma </li></ul><ul><li>Sensitizes myocardium, good muscle relaxation </li></ul><ul><li>70% exhaled as such , 30% metabolized in liver </li></ul><ul><li>Malignant hyperthermia in swine reported, give Dantrolene , a phenytoin derivative of sk.mus.relax. </li></ul><ul><li>Exposure during pregnancy cautioned. </li></ul>
  14. 14. Methoxyflurane <ul><li>Properties : clear, sweet odor, partition coefficient 13, MAC 0.23% </li></ul><ul><li>Pharmacodynamics : </li></ul><ul><li>Lungs: gradually depressed, decreases tidal volume, respiratory acidosis, ventilation required </li></ul><ul><li>Heart:decreases CO, BP, sensitizes myocardium </li></ul><ul><li>Liver: decreased hepatic function, forms free fluoride ions </li></ul><ul><li>Kidney:decreased flow, metabolites cause dysfunction and renal vasoconstriction. </li></ul>
  15. 15. Methoxyflurane <ul><li>General information : </li></ul><ul><ul><li>Was extensively used in large animals, better agents are available now </li></ul></ul><ul><ul><li>introduced in 1964 </li></ul></ul><ul><ul><li>slow induction and recovery </li></ul></ul><ul><ul><li>Stage II is bypassed, less CNS stimulation </li></ul></ul><ul><ul><li>excellent muscle relaxation, very good analgesic </li></ul></ul><ul><ul><li>vaporization difficult </li></ul></ul><ul><ul><li>safe for fetus, compatible with other agents. </li></ul></ul>
  16. 16. Etherane <ul><li>Properties: colorless, nonflammable, mild sweet odor, volatile liquid, extremely stable, no reaction with metals, Partition coefficient 1.78, MAC 2.2% </li></ul><ul><li>Pharmacodynamics: </li></ul><ul><li>Lungs: nonirritating, gradually depresses, no toxic effect </li></ul><ul><li>Heart: less sensitization, CO decreased, less effect on BP </li></ul><ul><li>Liver: no adverse effect, hepatic necrosis upon repeated administration </li></ul><ul><li>Kidney: no adverse effects, decreases renal flow. </li></ul>
  17. 17. Etherane <ul><li>General information : </li></ul><ul><li>-Introduced in 1973 </li></ul><ul><li>-approved in horses in 1981 </li></ul><ul><li>-seizure activity at high doses </li></ul><ul><li>- contraindicated in patients with seizure history </li></ul><ul><li>-rapid and smooth induction </li></ul><ul><li>- adequate muscle relaxation. </li></ul>
  18. 18. Isoflurane <ul><li>Properties: widely used now, an isomer of enfllurane colorless, less soluble, nonflammable, stable, mild pungent odor, MAC 1.5% </li></ul><ul><li>Pharmacodynamics: </li></ul><ul><li>Lungs: mostly exhaled as such </li></ul><ul><li>Heart: lesser effects, does not sensitizes, </li></ul><ul><li>Liver and Kidney: not injurious. </li></ul>
  19. 19. Isoflurane <ul><li>General information: </li></ul><ul><li>-Approved in 1985 for veterinary practice </li></ul><ul><li>-not a convulsive agent </li></ul><ul><li>- malignant hyperthermia in swine reported </li></ul><ul><li>-adequate muscle relaxation </li></ul><ul><li>- rapid and smooth induction </li></ul><ul><li>-rapid and smooth recovery </li></ul>
  20. 20. Newest Inhalants <ul><li>Desflurane (Suprane) </li></ul><ul><li>-Needs special vaporizer </li></ul><ul><li>-Partition coefficient 0.42; MAC 7.20 </li></ul><ul><li>-Rapid and smooth induction and recovery </li></ul><ul><li>-Causes least cardiovascular or cardiac sensitization to epinephrine </li></ul><ul><li>-Increases intracranial pressure ( ↑ ICP) </li></ul><ul><li>-requires temperature controlled, pressurized vaporizer </li></ul>
  21. 21. Desflurane <ul><li>Close to isoflurane </li></ul><ul><li>Reduces blood solubility almost to N2O </li></ul><ul><li>Recovery is twice rapid as isoflurane </li></ul><ul><li>Blood pressure decreases dose-dependently </li></ul><ul><li>Does not predispose to ventricular arrhythmia </li></ul><ul><li>Increase in intracranial pressure </li></ul><ul><li>Resp. depression, irritation to airways </li></ul>
  22. 22. Sevoflurane (Ultane) <ul><li>Nonflammable, nonirritating, does not increase heart rate </li></ul><ul><li>Rapid and smooth induction & recovery, partition coefficient 0.68; MAC 2.36 </li></ul><ul><li>Unstable when exposed to soda lime and toxic metabolites ( compound A ) are formed (renal toxicity) </li></ul>
  23. 23. Sevoflurane <ul><li>Increases intracranial pressure ( ↑ ICP) </li></ul><ul><li>Metabolized (3%) more than desflurane, (<1%) least effects on cardiovascular system </li></ul><ul><li>Increases plasma and urinary fluoride ions (renal and hepatic injury) </li></ul><ul><li>Being tried in Avian and exotic species. </li></ul>
  24. 24. Nitrous Oxide <ul><li>Properties: colorless, nonirritant, nonflammable, sweet odor, partition coefficient .45, MAC 188% </li></ul><ul><li>Pharmacodynamics: </li></ul><ul><li>Lungs: least effect,exhaled as such </li></ul><ul><li>Heart: do not sensitize, minimum effect </li></ul><ul><li>Liver: minimum effect, not metabolized </li></ul><ul><li>Kidney: no effect. </li></ul>
  25. 25. Nitrous Oxide <ul><li>General information: </li></ul><ul><li>-used for faster induction </li></ul><ul><li>-it reduces the dose and depressant effect of halothane on cardiopulmonary system </li></ul><ul><li>-requires preanesthetic medication </li></ul><ul><li>-not a good muscle relaxant </li></ul><ul><li>-cough reflex remains </li></ul><ul><li>-100% O 2 given during recovery to prevent diffusion hypoxia. </li></ul>
  26. 26. Inhalant Anesthetics
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