Inhalant anaesthetics
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Transcript of Inhalant anaesthetics
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) GasesN2O (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
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
Vapour Pressure & BP
Agent BP (0C) VP (20 0C)
Halothane 50 243
Enflurane 56 175
Isoflurane 48 238
Sevoflurane 58 160
Desflurane 23 664
Nitrous Oxide -89
Xenon -107
Solubility of Inhaled Drugssolubility (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 N2O
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 diseasesKidney: decreases urine outputLiver: Minimum effect, decreases liver
glycogenHeart: Initially increases cardiac output, then
decreases card. output, suppresses vasomotor center.
EtherEther 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.
HalothaneProperties: nonflammable, expensive,
colorless, nonexplosive, nonirritating, decomposes by light, Solubility 2.3; MAC 0.87%
Pharmacodynamics: Lungs: Progressive depression, acidosis, decrease pH, given with N2O, O2
Heart: Myocardial depression, decreases cardiac output (CO), hypotension, sensitizes myocardiumLiver: hepatitis by repeated administration.
HalothaneGeneral 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 myocardiumLiver: decreased hepatic function, forms free
fluoride ionsKidney:decreased flow, metabolites cause
dysfunction and renal vasoconstriction.
Methoxyflurane
•General information:
Was extensively used in large animals, better agents are available nowintroduced in 1964 slow induction and recovery Stage II is bypassed, less CNS stimulationexcellent muscle relaxation, very good analgesicvaporization difficult safe for fetus, compatible with other agents.
EtheraneProperties: 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
effectHeart: less sensitization, CO decreased, less effect
on BPLiver: no adverse effect, hepatic necrosis upon
repeated administrationKidney: no adverse effects, decreases renal flow.
EtheraneGeneral 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.
IsofluraneProperties: widely used now, an isomer
of enfllurane colorless, less soluble, nonflammable, stable, mild pungent odor, MAC 1.5%
Pharmacodynamics:Lungs: mostly exhaled as suchHeart: lesser effects, does not sensitizes, Liver and Kidney: not injurious.
IsofluraneGeneral 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 InhalantsDesflurane (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 OxideProperties: colorless, nonirritant,
nonflammable, sweet odor, partition coefficient .45, MAC 188%
Pharmacodynamics: Lungs: least effect,exhaled as suchHeart: do not sensitize, minimum effectLiver: minimum effect, not metabolizedKidney: no effect.
Nitrous OxideGeneral 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% O2 given during recovery to prevent diffusion hypoxia.
Inhalant Anesthetics