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General Anesthetics PowerPoint Presentation

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Description : Anesthesia

Tags : ANESTHESIA

Published on : May 04, 2019 | Views : 3003 | Downloads : 5

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Slide 1-

GENERAL ANESTHETICS
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Primary Effects Analgesia Inhibition of autonomic reflex Amnesia Unconciousness Skeletal Muscle Relaxation
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General Anesthetics :TERMS
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TERMS CONSCIOUS SEDATION Alleviation of Anxiety and Pain Less alteration with level of consciousness by using smaller doses of sedative medications Patient maintain patent airway Patient is responsive to verbal commands DEEP SEDATION Decreased consciousness Patient is not easily aroused Loss of verbal responsiveness Loss of protective airway reflexes Loss ability to maintain patent airway
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TYPES General Ansthetics Inhaled Anesthetics Intravenous Anesthetics Volatile Gaseous
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VOLATILE ANESTHETICS Low vapor pressures High boiling points Liquid at room temperature Halothane Enflurane Isoflurane Desflurane Seveflurane
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GASEOUS ANESTHETICS High vapor pressures Low boiling points Gas form at room temperature Nirous Oxide Xenon
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NITROUS OXIDE ADVANTAGES Good analgesia Rapid onset/ Recovery Safe, non irritating PHARMACOLOGY DISADVANTAGES Incomplete anesthesia No muscle relaxation Must be used with other anesthetics for surgical anesthesia
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HALOTHANE ADVANTAGES Has a pleasant odor Has fair analgesic and skeletal muscle and uterine relaxant properties Has excellent hypnotic properties DISADVANTAGES Reduces hepatic and renal blood flow Lowers blood pressure Sensitizes myocardium to action of cathecolamine Hepatic Toxicity Arrythmias
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ENFLURANE ADVANTAGES Produces a rapid induction and recovery with little excitation Produces good analgesia muscle relaxation, hypnosis Less likely to sensitize the heart to cathecolamine or cause arrythmias DISADVANTAGES Pungent Produces CNS stimulation with mild twitching or tonic-clonic movements Contraindicated in patients with renal failure
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ADVANTAGES Good muscle relaxation Rapid recovery Stability of cardiac output Does not raise intracranial pressure No sensitization of heart to epinephrine ISOFLURANE DISADVANTAGES Has a pungent odor
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DESFLURANE ADVANTAGES Produces more rapid induction and emergence Often preferred for out patient surgical procedures Undergoes minimal metabolism and therefore rarely produce organ toxicity DISADVANTAGES Irritating to the airway and may cause coughing, laryngospasm, and increased secretions with breath holding Special dispensing equipment for desflurane is necessary because of its low boiling point ( 23.5 ℃)
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SEVOFLURANE ADVANTAGES Bronchial smooth muscle relaxation good for patients with asthma Rapid onset/recovery Not irritating; useful in children DISADVANTAGES Potential renal toxicity at low level
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MECHANISM OF ACTION Primary focus has been on the SYNAPSE Principal molecular target are neuronal ion channels that mediate impulse conduction in the CNS PRESYNAPTIC ACTION Alters the release of neuro transmitter POSTSYNAPTIC ACTION Change the frequency or amplitude of impulses exiting the synapse
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1. INSPIRED CONCENTRATION AND VENTILATION - driving force for uptake = RATIO between INSPIRED and ALVEOLAR CONCENTRATION - important gases delivered by anesthesia machine • 70% nitrous oxide • 29% oxygen •1% isoflurane at normal barometric pressure (760 mmHg) UPTAKE AND DISTRIBUTTION A. Factors Controlling Uptake
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2. Solubility - Agents with low solubility in blood, quickly saturate the blood. - halothene > isoflurane > sevoflurane > nitrous oxide > desflurane
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3. Cardiac Output - the increased uptake of anesthetic into the blood will be distributed to all tissues - increased anesthesia uptake caused by cardiac output will predominantly be distributed to the tissues that are not involved in the site of action of anesthetics 4. Alveolar Venous Partial Pressure Difference -dependent mainly on the uptake of the anesthetic by tissue including neuronal tissue
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Recovery depends on the rate of elimination of anesthetic from the brain important factor- Blood: Gas Partition coefficient of the anesthetic agent B. Elimination Ventilation 1. Concentration of the anesthetic in the inspired gas 2. Alveolar ventilation HYPERVENTILATION is the only way to speed recovery Contribute to the elimination and recovery from some older anesthetics. Metabolism
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STAGE I ( ANALGESIA) - Patient experiences analgesia without amnesia STAGE II (EXCITEMENT) - Patient appears delirious and may vocalized but is completely amnesic. Respiration is rapid, heart rate and BP increase. STAGE III (SURGICAL ANESTHESIA) - begins with slowing of respiration and heart rate extends to complete cessation of spontaneous respiration. STAGE IV ( MEDULLARY DEPRESSION) - represents severe depression of the CNS, including the vasomotor center in the medulla and respiratory center in the brainstem PHARMACODYNAMICS A. CNS Effects
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All volatile agents tends to decrease mean arterial pressure in direct proportion to their alveolar concentration B. Cardiovascular Effects C. Respiratory Effects All volatile anesthetics posses varying degrees of bronchodilating properties, an effect value in patients with active wheezing and in status asthmaticus. D. Renal Effects Inhaled anesthetics tend to decrease glomerular filtration rate (GFR) and urine flow.
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Nephrotoxicity - reported only for enflurane with prolonged exposure Hematotoxicity - Prolonged exposure to nitrous oxide decrease methionine synthase activity which could cause megaloblastic anemia. Malignant Hypothermia - heritable genetic disorder, occurs in individuals exposed to volatile anesthetics while undergoing general anesthesia Hepatotoxicity ( Halothane Hepatits) - caused by hypovolemic shock, infection conferred by blood transfussion or other surgical stresses TOXICITY OF ANESTHETICS AGENTS Acute Toxicity
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Mutagenecity, Tetranogenecity, and Reproductive Effects Carcinogenecity Chronic Toxicity