Inhalant anaesthetics
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Inhalant anaesthetics

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Inhalant anaesthetics

Inhalant anaesthetics

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Inhalant anaesthetics Inhalant anaesthetics Presentation Transcript

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