Inhalational Anesthesia

Munir Gharaibeh, MD, PhD, MHPESchool of Medicine

The University of JordanFebruary, 2018

mgharaib@ju.edu.jo

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Inhalational Anesthesian Gases or volatile liquids n Administration and Elimination is by the

lungsn Metabolism is slown Equilibrate with tissues.n Interaction with tissues and liquids is by

non specific physical interactions with membrane components– Some work on GABA or NMDA

receptors or through potassium channels activation.February 18 Munir Gharaibeh, MD, PhD, MHPE

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n MAC = Minimum Alveolar Concentration –A measure of anesthetic potency.–Alveolar tension required to

produce surgical anesthesia(skin incision) in 50% of patients.

February 18 Munir Gharaibeh, MD, PhD, MHPE

MAC= Minimal Alveolar Concentration

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Anesthesia Cycle

n Delivering System

n Alveoli

n Blood -------- CNS

n Tissues

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n Anesthesia Machine

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Inhalational AnesthesiaAlveolar Tension corresponds to Brain TensionRate of Rise in Alveolar Tension Depends

on:n Inspired tension.n Pulmonary ventilation n Transfer from alveoli to Blood:

a. Pulmonary BFb. Solubility in blood.

n Loss from blood to tissues

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Induction of anesthesia is slower with more soluble anesthetic gases

n Solubility in blood is represented by the relative size of the blood compartment (the more soluble, the larger the compartment).

n Relative partial pressures of the agents in the compartments are indicated by the degree of filling of each compartment.

n For a given concentration or partial pressure of the two anesthetic gases in the inspired air, it will take much longer for the blood partial pressure of the more soluble gas (halothane) to rise to the same partial pressure as in the alveoli.

n Since the concentration of the anesthetic agent in the brain can rise no faster than the concentration in the blood, the onset of anesthesia will be slower with halothane than with nitrous oxide.

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The alveolar anesthetic concentration approaches the inspired anesthetic concentration fastest for the least soluble agents

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Halogenated AnestheticsHalothane

First practical anesthetist, Widely usedn Non flammable , Non toxic , Sweet odor .n Complete anesthetist only in high doses .n Cardiorespiratory depressant , Sensitizes

the heart to NE.

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Halothane

Hepatic Necrosis(1/35.000).Hypersensitivity: ABs detected.

Abortion : In animals.

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Enfluranen More N.M. Blockaden Rapid Induction & emergence n Sensitizes heart to catecholamines.n EEG Changes------ seizures. n Releases fluoride ions, so nephrotoxic.

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Isofluranen Similar but: maintains C.On Less metabolized i.e. less heptotoxicityn Less nephrotoxicity n Most popular

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Desflurane

n Low solubility n Rapid Induction & Emergence n Outpatient procedures. n Irritating

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Methoxyfluranen Sweet smelling n Slow induction & emergence due to high

solubility. n Profound analgesia. n BP is maintained.n Renal toxicity.

Sevoflurane

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Nonhalogenated AnestheticsNitrous Oxide:

n Cardiac depressant but stimulates the sympathetic system.

n Lowers tidal volume but increases respiratory rate.

n Very weak, MAC = 105%.n Very easy to use.n Almost insoluble in blood so very rapid in onset.n Analgesic (25% of Morphine) n Used in dentistry and Labor n Used in combination and for induction.

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Ethern Historical(1846).n Irritant , Flammable , Explosive.n Complete anesthetic.n Safe except for postoperative nausea,

vomiting and bad odor.

Cyclopropane.Chloroform.

February 18 Munir Gharaibeh, MD, PhD, MHPE