1.
Inhalational Anesthetics
Basic
Mahmood Hasan Taha
H.D Anesthesia
Zakho General H.
Aug 2022

2.
Halothane (Fluothane)

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.
• 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.
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.
Enflurane (Ethrane)
First used clinically in 1966
increased in 1970s and 1980s
but is no longer in common use.

7.
Isoflurane (Forane)
AnIsomerofEnflurane.
Approved for medical use in
United States in 1979.
Approved by FDA for clinical
use in 1981.

8.
Desflurane (Suprane)
Introduced for clinical use
in 1992.

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.
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.
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.
• 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.
Blood : Gas P.C
• Measure the solubility in Blood.
• Determine the rate of induction & recovery.
• E.g.: N2O vs. Halothane.

14.
Figure 1: Volatile Anesthetic cycle

15.
Figure 2 : Induction and Recovery
Halothane Vs N2O
circuit Blood Brain
N2O(rapid)
Halothane(slow)

16.
Ideal volatile anesthetic agent ?
Induction – Recovery:
N2O > Des > Sevo > Iso > H.
Partition - Coefficient (potency):
H> Iso > Sevo > Des > N2O

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.
• Environment:
Ozone destruction: Halothane > Enf > Iso.
Environmental friendly : Sevflurane, Desflurane.
• Exposure: More exposure time (prolonged
Surgery): More time needed for recovery.

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.
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.
Elimination Sites:
1. Alveolar (exhalation).
2. Liver (biotransformation).
3. Skin (transcutaneous) insignificant.

22.
MAC: the minimum alveolar concentration of
an inhaled anesthetic that prevents movement
in 50% of patients in presence of surgical
stimulation (incision).

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.
• 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.
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.