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ANESTHETICS. Dr.Shadi- Sarahroodi Pharm.D & PhD PUBLISHED BY www.medicalppt.blogspot.com. General Anesthetics. Signs and Stages of Anesthesia (Somewhat related to the response from Diethyl Ether): Stage I—Analgesia Stage II—Excitement Stage III—Surgical anesthesia

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anesthetics

ANESTHETICS

Dr.Shadi- Sarahroodi

Pharm.D & PhD

PUBLISHED BY

www.medicalppt.blogspot.com

www.medicalppt.blogspot.com for more lectures

general anesthetics
General Anesthetics

Signs and Stages of Anesthesia (Somewhat related to the response from Diethyl Ether):

  • Stage I—Analgesia
  • Stage II—Excitement
  • Stage III—Surgical anesthesia
  • Stage IV—Medullary paralysis

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patient factors in selection of anesthesia
Patient Factors in Selection of Anesthesia
  • Liver and kidney
  • Respiratory system
  • Cardiovascular system
  • Nervous system
  • Pregnancy

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summary of anesthetics
Summary of anesthetics

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slide5
MOA
  • modulating ligand-gated ion channels
  • activating GABA channels (hyperpolarizing cells)
  • blocking excitatory receptors (like NMDA-glutamate receptors).

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inhalation anesthetics
Inhalation Anesthetics
  • Modern inhalation anesthetics are nonflammable, nonexplosive
  • nitrous oxide
  • halothane, desflurane, enflurane, isoflurane, sevoflurane, and methoxyflurane (easily vaporized liquid halo-genated hydrocarbons)

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inhalation anesthetics8
Inhalation Anesthetics
  • ether [which is highly flammable]
  • chloroform [which has toxic properties]
  • are no longer used as general anesthetics

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important concepts
important concepts
  • minimal alveolar concentration (MAC)
  • blood:gas partition coefficient

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mac minimal alveolar concentration
MAC(minimal alveolar concentration)
  • concentration of anesthetic agent that renders 50% of patients immobile during surgery
  • this is measured as the percentage of the agent in inspired air
  • MAC is a direct measure of the potency of a drug
  • influenced by the age and physiologic state of the patient and by the presence of other pharmacologic agents

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blood gas partition coefficient
blood:gas partition coefficient
  • solubility of the agent in blood
  • and is a measure of how quickly the inhalation anesthetic will equilibrate between lungs and blood and ultimately the target site in the brain
  • low blood:gas coefficient (e.g., desflurane) equilibrate quickly
  • lower the blood:gas coefficient faster the induction and the faster the recovery

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speed of induction of anesthetic effects
speed of induction of anesthetic effects
  • Solubility
  • Inspired gas partial pressure-high partial pressure in the lungs rapid achievement of anesthetic levels in the blood
  • Ventilation rate
  • Pulmonary blood flow—high pulmonary blood flows onset of anesthesia is reduced.

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alveolar blood concentration
Alveolar Blood Concentration

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elimination
elimination
  • redistribution of the drug from the brain to the blood and elimination of the drug through the lungs.

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slide18

desflurane, sevoflurane low blood solubility shorter recovery

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effects of inhaled anesthetics
effects of inhaled anesthetics
  • CNS effects:
  • decrease brain metabolic rate.
  • reduce vascular resistance increase cerebral blood flow.
  • High concentrations of enflurane may cause spike-and-wave activity and muscle twitching,
  • nitrous oxide has low anesthetic potency (ie, a high MAC), it exerts marked analgesic and amnestic actions.

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effects of inhaled anesthetics20
effects of inhaled anesthetics
  • Cardiovascular effects
  • decrease arterial blood pressure moderately
  • Enflurane and halothane: myocardial depressants
  • isoflurane, desflurane, and sevoflurane: peripheral vasodilation
  • Nitrous oxide: less likely to lower blood pressure

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effects of inhaled anesthetics21
effects of inhaled anesthetics
  • Respiratory effects:
  • dose-dependent decrease in tidal volume and minute ventilation increase in arterial CO2 tension
  • Bronchodilation except desflurane(pulmonary irritant).

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toxicities
Toxicities
  • Halothane: Postoperative hepatitis (rarely)

(formation of reactive metabolites that cause direct toxicity or initiate immune-mediated responses.)

  • Methoxyflurane, enflurane and sevoflurane: Fluoride release renal insuffi­ciency
  • nitrous oxide: megaloblastic anemia
  • anesthetics + neuromuscular blockers (Susceptible patients): malignant hyperthermia

mutations in the gene loci corresponding to the ryanodine receptor (RyRl)

Dantrolene

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intravenous anesthetics
Intravenous Anesthetics
  • Barbiturates: Thiopental and methohexital
  • Benzodiazepines: Midazolam
  • ketamine
  • Opioids: Morphine and fentanyl
  • propofol
  • etomidate

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barbiturates
Barbiturates
  • high lipid solubility rapid entry into the brain surgical anesthesia in one circulation time (< 1 min).
  • short surgical procedures
  • hepatic metabolism
  • respiratory and circulatory depressants
  • depress cerebral blood flow
  • decrease intracranial pressure.

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redistribution of thiopental
Redistribution of Thiopental

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benzodiazepines
Benzodiazepines
  • The onset of its CNS effects is slower than that of thiopental
  • flumazenil, accelerates recovery from midazolam and other benzodiazcpines.

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ketamine
ketamine
  • dissociative anesthesia
  • patient remains conscious
  • marked catatonia, analgesia, and amnesia.
  • phencyclidine (PCP)
  • cardiovascular stimulant
  • increase in intracranial pressure.
  • disorientation, excitation, and hallucinations occur during recovery

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opioids
opioids
  • Morphine and fentanyl
  • Intravenous opioids :chest wall rigidity
  • Respiratory depression
  • Neuroleptanesthesia(state of analgesia and amnesia):fentanyl is used with droperidol and nitrous oxide.
  • Alfentanil and remifentanil (NEW)

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propofol
propofol
  • Rapid as the intravenous barbiturates
  • antiemetic
  • prolonged sedation
  • marked hypotension during induction of anesthesia
  • Total body clearance is greater than hepatic blood flow, suggesting elimination includes other mechanisms in addition to metabolism by liver enzymes.

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etomidate
etomidate
  • rapid induction
  • minimal change in cardiac function
  • minimal change in respiratory rate
  • not analgesic
  • cause pain and myoclonus on injection and nausea postoperatively
  • Prolonged administration may cause adrenal suppression.

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slide34

PUBLISHED BY

www.medicalppt.blogspot.com

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