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Volatile Anesthesia- Basic.pptx

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Volatile Anesthesia- Basic.pptx

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Discussing the history of modern volatile anesthetics, Halothane, Enflurane, Desflurane Isoflurane, and Sevoflurane.
Discussing the general points about volatile anesthetics, the MAC , partition co-efficient.
Factors affecting MAC.
Factors affecting the speed of induction and recovery from volatile anesthesia.

Discussing the history of modern volatile anesthetics, Halothane, Enflurane, Desflurane Isoflurane, and Sevoflurane.
Discussing the general points about volatile anesthetics, the MAC , partition co-efficient.
Factors affecting MAC.
Factors affecting the speed of induction and recovery from volatile anesthesia.

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Volatile Anesthesia- Basic.pptx

  1. 1. Inhalational Anesthetics Basic Mahmood Hasan Taha H.D Anesthesia Zakho General H. Aug 2022
  2. 2. Halothane (Fluothane)
  3. 3. • First synthesized by C.W. Suckling in 1951 in Widens , England. • First used clinically by M. Johnston in 1956 Manchester. • Nonflammable. • In many parts of the word it has been largely replaced by newer agents since the 1980s.
  4. 4. • May be still used in developing countries and in veterinary surgery because of its lower cost • It is on the World Health Organization's List of Essential Medicines. • No longer commercially available in the United States.
  5. 5. Recent Agents • In 1963 Ohio Medical products assigned the work to two senior chemists, Ross C. Terrell and Louise Speers Croix who worked for 10 - 15 years to synthesize several hundred fluorinated hydrocarbons, four among which were Enflurane, Isoflurane, Desflurane and Sevoflurane.
  6. 6. Enflurane (Ethrane) First used clinically in 1966 increased in 1970s and 1980s but is no longer in common use.
  7. 7. Isoflurane (Forane) AnIsomerofEnflurane. Approved for medical use in United States in 1979. Approved by FDA for clinical use in 1981.
  8. 8. Desflurane (Suprane) Introduced for clinical use in 1992.
  9. 9. Sevoflurane (Ultane) was discovered as a new anesthetic agent in 1971. However, because Isoflurane and Enflurane were approved for use as inhalational anesthetics about the same time, clinical studies on Sevoflurane were not performed and it was not released for clinical use until the early 1990s.
  10. 10. Desflurane together with Sevoflurane , it is gradually replacing Isoflurane, for human use, except in economically undeveloped areas, where it high cost precludes its use, it has the most onset and offset.
  11. 11. General Points about volatile anesthetics • Halogenation→ ↓flammability. • Fluorination→ ↓solubility & ↓potency. • All are liquid at 20ċ. • Vapor pressure depend on the temperature & the physical characteristics of a liquid, not on atmospheric pressure . (↑ in temperature → Vapor pressure).
  12. 12. • MAC: is a measure of the potency. • Partition - Coefficient (P.C): Halothane ≈ 220 , Isoflurane ≈ 91, Sevoflurane ≈ 58 • Solubility in the Blood ( Blood: Gas P.C). • Solubility in the Fat ( Oil : Gas P.C).
  13. 13. Blood : Gas P.C • Measure the solubility in Blood. • Determine the rate of induction & recovery. • E.g.: N2O vs. Halothane.
  14. 14. Figure 1: Volatile Anesthetic cycle
  15. 15. Figure 2 : Induction and Recovery Halothane Vs N2O circuit Blood Brain N2O(rapid) Halothane(slow)
  16. 16. Ideal volatile anesthetic agent ? Induction – Recovery: N2O > Des > Sevo > Iso > H. Partition - Coefficient (potency): H> Iso > Sevo > Des > N2O
  17. 17. • Lipid solubility ꞊ potency of anesthetic gas. ↑ lipid solubility ꞊ ↑ the potency (e.g. Halothane). • Rubber & Plastic : Halothane , Isoflurane : minor problem. • N2O, Desflurane, Sevoflurane: no problem. • Respiratory irritation: 1 MAC: no irritation. 2 MAC: Isoflurane → 50% irritation
  18. 18. • Environment: Ozone destruction: Halothane > Enf > Iso. Environmental friendly : Sevflurane, Desflurane. • Exposure: More exposure time (prolonged Surgery): More time needed for recovery.
  19. 19. Factors affecting volatile anesthetic uptake: 1. Solubility in blood. 2. Alveolar blood flow. 3. Difference in partial pressure between alveolar gas & venous blood.
  20. 20. Factors affecting speed of induction & recovery: 1. Elimination of rebreathing. 2. ↑ FGF. 3. Low anesthetic circuit volume. 4. Low absorption by anesthetic circuit. 5. ↓ Solubility. 6. ↑ CBF. 7. ↑ Ventilation.
  21. 21. Elimination Sites: 1. Alveolar (exhalation). 2. Liver (biotransformation). 3. Skin (transcutaneous) insignificant.
  22. 22. MAC: the minimum alveolar concentration of an inhaled anesthetic that prevents movement in 50% of patients in presence of surgical stimulation (incision).
  23. 23. Factors affecting MAC: • Temperature: hypothermia ↓MAC, hyperthermia ↓MAC if > 42ċ. • Age: young ↑MAC , old age ↓MAC. • Alcohol: Acute ↓ MAC , Chronic ↑ MAC. • Anemia: ↓MAC if hematocrit <10%. • PaO2 < 40 mmHg ↓MAC. • PaCO2 > 95 mmHg ↓MAC.
  24. 24. • Thyroid: no change whether hyper or hypothyroidism. • B.P: MAP < 40 mmHg → ↓MAC. • Electrolytes: ↑ Ca++ → ↓MAC , ↑Na++→ ↑MAC , ↓Na++→ ↓MAC . • Pregnancy : MAC ↓ 1/3 at 8 weeks of gestational age, return normal after 72 hr. of postpartum.
  25. 25. Drugs: • Local anesthetics, Opioid, Ketamine, Pentothal, propofol, Benzodiaz. , Methyldopa:→ ↓MAC. • Cocaine, Ephedrine: → ↑MAC. • NB: MAC decrease 6% per decade of age regardless of volatile anesthetic.

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