Inhalational Anesthesia School of Medicine The University of Jordan February, 2018 mgharaib@ju.edu.jo
Inhalational Anesthesia n Gases or volatile liquids n Administration and Elimination is by the lungs n Metabolism is slow n 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. 2
n MAC = Minimum Alveolar Concentration A measure of anesthetic potency. Alveolar tension required to produce surgical anesthesia(skin incision) in 50% of patients. 3
MAC= Minimal Alveolar Concentration 4
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Anesthesia Cycle n Delivering System n Alveoli n Blood -------- CNS n Tissues 6
n Anesthesia Machine 7
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Inhalational Anesthesia Alveolar Tension corresponds to Brain Tension Rate of Rise in Alveolar Tension Depends on: n Inspired tension. n Pulmonary ventilation n Transfer from alveoli to Blood: a. Pulmonary BF b. Solubility in blood. n Loss from blood to tissues 9
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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. 12
The alveolar anesthetic concentration approaches the inspired anesthetic concentration fastest for the least soluble agents 13
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Halogenated Anesthetics Halothane First practical anesthetist, Widely used n Non flammable, Non toxic, Sweet odor. n Complete anesthetist only in high doses. n Cardiorespiratory depressant, Sensitizes the heart to NE. 19
Halothane Hepatic Necrosis(1/35.000). Hypersensitivity: ABs detected. Abortion : In animals. 20
n More N.M. Blockade Enflurane n Rapid Induction & emergence n Sensitizes heart to catecholamines. n EEG Changes------ seizures. n Releases fluoride ions, so nephrotoxic. 21
Isoflurane n Similar but: maintains C.O n Less metabolized i.e. less heptotoxicity n Less nephrotoxicity n Most popular 22
Desflurane n Low solubility n Rapid Induction & Emergence n Outpatient procedures. n Irritating 23
n Sweet smelling Methoxyflurane n Slow induction & emergence due to high solubility. n Profound analgesia. n BP is maintained. n Renal toxicity. Sevoflurane 24
Nonhalogenated Anesthetics Nitrous 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. 25
n Historical(1846). Ether n Irritant, Flammable, Explosive. n Complete anesthetic. n Safe except for postoperative nausea, vomiting and bad odor. Cyclopropane. Chloroform. 26