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Inhalational anaesthetic agents
Inhalational anaesthetic agents
Inhalational anaesthetic agents
Inhalational anaesthetic agents
Inhalational anaesthetic agents
Inhalational anaesthetic agents
Inhalational anaesthetic agents
Inhalational anaesthetic agents
Inhalational anaesthetic agents
Inhalational anaesthetic agents
Inhalational anaesthetic agents
Inhalational anaesthetic agents
Inhalational anaesthetic agents
Inhalational anaesthetic agents
Inhalational anaesthetic agents
Inhalational anaesthetic agents
Inhalational anaesthetic agents
Inhalational anaesthetic agents
Inhalational anaesthetic agents
Inhalational anaesthetic agents
Inhalational anaesthetic agents
Inhalational anaesthetic agents
Inhalational anaesthetic agents
Inhalational anaesthetic agents
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Inhalational anaesthetic agents

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  • 1. INHALATIONAL ANAESTHETIC AGENTS History & Minimum alveolar concentration Presenter: Dr.Anoop Kumar Moderator:Dr.Anand Kulkarni
  • 2. History
    • Jean Baptiste Van Helmont(1577-1644)
    • invented the word Gas
    • Boyle, Dalton & Charles out lined the basic properties of gases
    • Joseph priestley & Carl scheele (1742-1786) performed first investigation on gas inhalation
  • 3. History Contd ..
    • On Dec 10 th ,1844 Prof Colton presented his exhibit featuring inhalation of nitrous oxide at union hall in Hartford, Connecticut.
    • On Oct 16 th 1846 Morton demonstrated Ether anaesthesia at Massachusetts general hospital.
  • 4.  
  • 5. History contd…
    • Wells, Morton and Jackson all claimed to have discovered anaesthesia.
    • In 1847 David Waldie at Edinburgh Medical school England suggested Chloroform as an alternative agent.
  • 6. History contd…
    • In 1951 Halothane was synthesised by Suckling and introduced into clinical practice in 1956
    • Between 1959 & 1966 Terrell and colleagues at Ohio medical products synthesised more than 700 products
  • 7. History contd…
    • 347 th and 469 th compounds were Enflurane & Isoflurane
    • Wallin and colleagues at Travenol laboratories described other new compounds in 1970-Sevoflurane
    • Desflurane was introduced in 1993
  • 8. Minimum Alveolar concentration (MAC)
    • Eger and colleagues defined this concept.
    • “ The alveolar concentration of an inhaled anaesthetic at 1 atm pressure in 100%Oxygen at equilibrium, that produces immoblity in 50% of those subjects exposed to a standardized noxious stimuli. ”
  • 9. Determination of MAC
    • For humans the noxious stimulus is a surgical incision of the abdomen.
    • In animals it is usually produced by clamping of tail or passing electric current through subcutaneous electrodes.
  • 10. MAC Contd…
    • It mirrors brain partial pressure after a period of equilibration.
    • Best estimate of anaesthetic potency of an inhalational anaesthetic.
    • Allows comparison between agents and provides a standard for experimental evaluation.
  • 11. MAC Contd…
    • MAC values are roughly additive.
    • MAC for other response parameter are not additive.
    • Relatively constant within species and between species.
  • 12. MAC contd..
    • Analogous to ED 50 expressed for intravenous drugs.
    • 1.3 MAC would prevent 95 % subjects from moving and is equivalent to ED 95.
  • 13. MAC Awake
    • MAC of anaesthetic that would allow opening of eyes on verbal commands during emergence from anaesthesia
    • =0.3-0.4 MAC
    • MAC Intubation
    • MAC that would inhibit movement and coughing during endotracheal intubation.=1.3 MAC
  • 14. MAC Bar
    • MAC of anaesthetic necessary to prevent adrenergic response to skin incision, as measured by conc. of catecholamine in venous blood =1.5 MAC
    • When different agents are compared the ratio of MAC skin incision to MAC intubation or MAC awake is relatively constant
  • 15. MAC Rationale Why this measures anaesthetic potency?
    • Alveolar conc. can be easily measured
    • Near equilibrium alveolar and brain tension are virtually equal
    • High cerebral blood flow produces rapid equilibration
  • 16. Factors supporting use of MAC
    • MAC is invariant with variety of noxious stimuli.
    • Individual variability is small.
    • Doses of anaesthetic in MAC are additive.
  • 17.
    • Hypothermia
    • Hyperthermia(If >42 0 C)
    • Hyponatremia & Hypocalcemia
    • Hypoxia(PaO 2 <38mm of Hg)
    • Induced hypotension (MAP<50mmHg)
    Factors affecting MAC MAC
  • 18. Factors sing MAC contd…
    • Hypercarbia(PaCO 2 >95mm of Hg)
    • Anemia(Hematocrit<10%)
    • Pregnancy
    • Acute ethanol administration
    • Hypo osmolality
    • Increasing age(max. at 6months)
  • 19.
    • Local anaesthetics(except cocaine)
    • Opioids.
    • Ketamine,Barbiturates,Benzodiazapines.
    • Sympatholytics.
    • Verapamil, Lithium.
    • c/c administration of amphetamine.
    Drugs MAC
  • 20. Factors MAC
    • Chronic ethanol use.
    • Hypernatremia.
    • a/c admin. of amphetamine.
    • Cocaine.
    • Ephedrine.
    • MAO inhibitors.
    • Levodopa.
  • 21. No changes in MAC
    • Gender.
    • Hypo/Hyper thyroidism.
    • Duration of inhaled anaesthetic Administration.
    • Hypercalcemia.
    • Metabolic alkalosis.
  • 22. Clinical implications of MAC
    • Understanding of MAC helps in prevention of awareness.(will not occur at end tidal conc. of 1MAC).
    • Tool to measure anaesthetic potency.
    • Helps to study side effects of inhalational anaesthetics at equipotent doses.
    • Combinations are additive.
  • 23. MAC of common inhalational anaesthetics 2 Sevoflurane 1.2 Isoflurane 0.75 Halothane 105 N2O 1.6 Enflurane
  • 24. Thank you

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