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Published byWinfred Peters Modified over 9 years ago
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Induction Recovery
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Concentration = Partial pressure x Solubility tissue
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Pulmonary ventilation Respiratory rate V tidal – V dead space Anesthetic concentration Blood-gas partition coefficient Concentration effect Second gas effect
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Table 1 Characteristics of Inhalational Anesthetics AnestheticsMAC (% of 1 atm) Oil:Gas Partition Coefficient Blood:Gas Partition Coefficient Desflurane7.0190.42 Ether1.96512 Enflurane1.7981.9 Halothane0.752252.3 Isoflurane1.2981.4 Methoxyflurane0.1682513 Nitrous oxide1051.40.47 Sevoflurane2.0530.63
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Pulmonary ventilation Concentration effect Second gas effect Respiratory rate V tidal – V dead space Anesthetic concentration Blood-gas partition coefficient Pulmonary blood flow Gradient of P arterial / P venous Cardiac output
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Anesthetic concentration Pulmonary ventilation Concentration effect Second gas effect Blood-gas partition coefficient Tissue blood flow Gradient of P arterial / P Tissue Redistribution Diffusion hypoxia Pulmonary blood flow Gradient of P arterial / P venous Cardiac output Tissue-Blood partition coefficient
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Stages of Ether Anesthesia Stage IAnalgesiaClouding Spinal cord sensory neurons (Substantia gelatinosa) Stage IIDelirium (Excitement) Loss of consciousness Hypersensitive small Golgi type interneurons excitatory neurons Stage IIISurgical anesthesia Loss of somatic pain Ascending pathway of recticular activating system Spinal reflex Stage IVMedullary depression Loss of visceral pain Medulla (respiratory, cardiovascular center)
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AnestheticsMAC (% of 1 atm) Oil:Gas Partition Coefficient Blood:Gas Partition Coefficient Desflurane7.0190.42 Ether1.96512 Enflurane1.7981.9 Halothane0.752252.3 Isoflurane1.2981.4 Methoxyflurane0.1682513 Nitrous oxide1051.40.47 Sevoflurane2.0530.63 Table 1 Characteristics of Inhalational Anesthetics
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Stages of Ether Anesthesia Stage IAnalgesiaClouding Spinal cord sensory neurons (Substantia gelatinosa) Stage IIDelirium (Excitement) Loss of consciousness Hypersensitive small Golgi type interneurons excitatory neurons Stage IIISurgical anesthesia Loss of somatic pain Ascending pathway of recticular activating system Spinal reflex Stage IVMedullary depression Loss of visceral pain Medulla (respiratory, cardiovascular center)
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Mechanisms of Action Lipid bilayer-Meyer and Overton Theory Membrane fluidity Membrane expansion Voltage-gated ion channels Na + K + GIRK TASK, TREK: 2P, pH-sensitive, open rectifier Ca +2 Ligand-gated ion channels NMDA nACh Glycine 5HT3 GABA A
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TASK-1 Activated by inhalational anesthetics (0.1-0.4 mM) Two pore background K + channels pH-sensitive, pH o <7, channels close Open rectifier, instaneous activation No time dependence Slight outward rectification TASK-2 might also be the target Time-dependent outward rectifier
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TREK-1 Activated by inhalational anesthetics (higher) pH-sensitive, pH i <7, channels open Outward rectification
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Gaseous anesthetics Nitrous oxide (N 2 O) Volatile anesthetics Ether Chloroform Halothane Enflurane Isoflurane Desflurane Sevoflurane Inhalational Anesthetics
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Nitrous Oxide Benefits No CV side effect Rapid induction Second gas effect Harms Weak potency Diffusion hypoxia Megaloblastic anemia N 2 O pockets formed in closed spaces Occluded middle ear Pneumothorax Embolism Pneumoencephaly Obstructed intestine
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Nitrous Oxide Normal N2N2 N2N2 N2N2 N2ON2O Blood vessel
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Nitrous Oxide Benefits No CV side effect Rapid induction Second gas effect Harms Weak potency Diffusion hypoxia Megaloblastic anemia N 2 O pockets formed in closed spaces Occluded middle ear Pneumothorax Embolism Pneumoencephaly Obstructed intestine
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HalothaneEnfluraneIsofluraneDesfluraneSevoflurane Analgesia+/-++++ Muscle relaxation-+++ Fast Induction-+++++++++ Potency+++++++/-++++/-++ Metabolism+++++++/--++(+) Airway irritation++-+/-- Nausea, vomiting+---- Malignant Hyperthermia++--- Arrhythmia++++++/- - Hypotension+++++ Cardiac output decrease++ --- Hepatic toxicity+++--+/- Renal toxicity++ --+/- dantrolene
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Malignant hyperthermia Genetic susceptibility: 1 in 15,000 to 50,000 Failure of Ca 2+ uptake by sarcoplastic recticulum in skeletal muscle, genetic mutation of ryanodine receptors Treatment with dantrolene Incidence if coadministration with succinylcholine
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HalothaneEnfluraneIsofluraneDesfluraneSevoflurane Analgesia+/-++++ Muscle relaxation-+++ Fast Induction-+++++++++ Potency+++++++/-++++/-++ Metabolism+++++++/--++(+) Airway irritation++-+/-- Nausea, vomiting+---- Malignant Hyperthermia++--- Arrhythmia++++++/- - Hypotension+++++ Cardiac output decrease++ --- Hepatic toxicity+++--+/- Renal toxicity++ --+/- Seizure F-F- Cough
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Intravenous Anesthetics Barbiturates Thiopental (Pentothal) Methohexital (Brietal) Thiamylal (Surital) Benzodiazepines Diazepam (Valium) Lorazepam (Ativan) Midazolam (Dormicum) Dissociate anesthetic Ketamine (Ketaral) Etomidate (Hypnomidate) Propofol (Diprivan) Butyrophenones Droperidol Opioids Fentanyl
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Ultrashort Barbiturates GABA A -Cl - current Contraindication Porphyria Shock Respirator not available Pain threshold Laryngeal spasm Unpurpose movement Thiopental Redistribution Slow recovery Short t 1/2 Methohexital Rapid recovery Hiccup
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Benzodiazepines GABA A -Cl - current Diazepam Amnesia Reflex No analgesic action Endoscopy,Cardiocatheter respiration CV function Midazolam More rapid onset Shorter duration More potent Water soluble Antidote: flumazenil Emergency room
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Ketamine NMDA receptor blocker Dissociation anesthesia Sedation Analgesic CV stimulation Muscle tone Nightmare Trauma, Emergency, Radiotherapy
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Etomidate GABA uptake inhibitor Onset rapid (< 5min), redistribution No CV and respiratory depression No analgesia Nausea vomiting, myoclonic twitch Adrenocortical supprssion Sedative-hypnotic in ICU Used in hypovolumic shock, Burn trama
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Propofol GABA uptake inhibitor Rapid psychomotor recovery Unpurpose movement Allergic reaction Antiemetic Not suggested in obstetrical procedures Respiratory and cardiovascular depression
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Neuroleptic Analgesia Droperidol D2 receptor blocker Antiemetic Antianxiety, Indifference motor activity Antifibrilation Anticonvusion Diagnosis only when used alone Extrapyramidal dyskinesia Fentanyl Opioid receptor agonist Nausea vomitting Skeletal muscle rigidity Analgesia
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Premedication of Anesthesia Benzodiazepine: Diazepam Barbiturates: Secobarbital, Phenobarbital Narcotics: Meperidine, Morphine Anticholinergics: Atropine, scopolamine Antihistamines: H 1 antagonists, H 2 antagonists Antiemetics: Benzquinamide, Odansetron, diphenhydramine, metocloprmide
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Mechanism of Action: GABA A receptor TM2 segment of 2 1 subunit of GABA A receptor Binding site different to that of GABA Potentiating GABA effect at low concentrations Directly inducing GABA current at high concentrations Preventing GABA A receptor desensitization
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Discovery of Inhalational Anesthetics 1842 Crawford W. Long Surgeon 1844 Horace Wells Dentist 1846 Willium T. G. Morton Charles J. Jackson Mr. ifs N2ON2OEther Time: 1846, October 16 Place: Massachusetts General Hospital Surgeon: John Collins Warren
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Concentration Effect N 2 O (blood/gas =0.5) 40 % 20 % 0.2 * 40 % = 8 % 80 % 40 % 0.4 * 80 % = 32 % P alveola P blood
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