INHALATIONAL ANESTHETICS PHYSIOLOGICAL EFFECTS AND CLINICAL COMPARISONS

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INHALATIONAL ANESTHETICSPHYSIOLOGICAL
EFFECTSAND CLINICAL COMPARISONS

• DENNIS STEVENS MSN, CRNA, ARNP
• SEPTEMBER 2006
• FLORIDA INTERNATIONAL UNIVERSITY
• PHARMACOLOGY OF ANESTHESIOLOGY NURSING
• NGR 6173

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OBJECTIVES

• Discuss the discovery and early development of
  inhalational anesthetics.
• Explain theories of anesthetic action related to
  inhalational anesthetics.
• Define MAC and respective percentages for
  volatile anesthetic agents.
• Compare and contrast the physical properties of
  inhalational anesthetics and their effects on
  organ systems.
• Discuss biotransformation and contraindications
  related to specific volatile anesthetic agents.

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HISTORY

• 1840S
• Nitrous oxide
• Diethyl Ether
• Chloroform
• 1920s 1940s
• Ethylene
• Cyclopropane
• Divinyl Ether
• 1950s
• Discoveries in fluorine chemistry

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INHALATIONAL AGENTS

• Nitrous Oxide (N20)
• Halothane (Fluothane)
• Enflurane (Ethrane)
• Isoflurane (Forane)
• Desflurane (Suprane)
• Sevoflurane (Ultane)

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CHEMICAL STRUCTURE OFINHALATIONAL AGENTS
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PROPOSED MECHANISMS OF INHALATION ANESTHETIC
ACTION

• General anesthesia is an altered physiologic
  state characterized by reversible loss of
  consciousness, analgesia of the entire body,
  amnesia, and to some degree muscle relaxation
• Meyer-Overton Rule (Critical Volume Hypothesis)
• Protein Receptor Hypothesis (Agent Specific
  Theory)
• Microcrystaline Theory
• Alteration in Neurotransmitter Availability

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MINIMUM ALVEOLAR CONCENTRATION

• MAC defined as
• MAC mirrors brain partial pressure, allows
  comparisons of potency between agents, and
  provides a standard for experimental evaluations
• Patient specific
• MAC
• N2O
• Halothane
• Ethrane
• Forane
• Desflurane
• Sevoflurane
• Factors affecting MAC

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NITROUS OXIDE

• Physical Properties
• Effects on Organ Systems
• Cardiovascular
• Respiratory
• Cerebral
• Neuromuscular
• Renal
• Hepatic
• Gastrointestinal
• Biotransformation and Toxicity
• Contraindications
• Drug Interactions

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HALOTHANE

• Physical Properties
• Effects on Organ Systems
• Cardiovascular
• Respiratory
• Cerebral
• Neuromuscular
• Renal
• Hepatic
• Biotransformation and Toxicity
• Contraindications
• Drug Interactions

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ETHRANE

• Physical Properties
• Effects on Organ Systems
• Cardiovascular
• Respiratory
• Cerebral
• Neuromuscular
• Renal
• Hepatic
• Biotransformation and Toxicity
• Contraindications
• Drug Interactions

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FORANE

• Physical Properties
• Effects on Organ Systems
• Cardiovascular
• Respiratory
• Cerebral
• Neuromuscular
• Renal
• Hepatic
• Biotransformation and Toxicity
• Contraindications
• Drug Interactions

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DESFLURANE

• Physical Properties
• Effects on Organ Systems
• Cardiovascular
• Respiratory
• Cerebral
• Neuromuscular
• Renal
• Hepatic
• Biotransformation and Toxicity
• Contraindications
• Drug Interactions

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SEVOFLURANE

• Physical Properties
• Effects on Organ Systems
• Cardiovascular
• Respiratory
• Cerebral
• Neuromuscular
• Renal
• Hepatic
• Biotransformation and Toxicity
• Contraindications
• Drug Interactions

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Inhalation Agent CV Respiratory Cerebral Neuromuscular Renal Hepatic Metabolism
Nitrous Oxide
Halothane
Enflurane
Isoflurane
Desflurane
Sevoflurane
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Inhalation Agent Induction Emergence Highlights
Nitrous Oxide
Halothane
Enflurane
Isoflurane
Desflurane
Sevoflurane
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IDEAL INHALATIONAL ANESTHETIC

• Rapid onset rapid recovery
• Easy to administer
• Possess clear indication of anesthetic depth
• No significant effect on organ systems
• High margin of safety for all age groups
• Inexpensive

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CLINCAL CASE STUDIES

• 78 year old male presents to OR from ED diagnosed
  with a small bowel obstruction. PMH CHF, CAD,
  and history of seizures 2 years prior to
  admission.
• 26 year old female presents to OR for emergent
  cesarean section. General anesthesia is initiated
  due to fetal distress (bradycardia and acidosis).
  PMH negative.
• 47 year old male presents to OR for elective
  colon resection. PMH CRF and arthritis.
• 6 year old female presents to the OR for elective
  adenoidectomy and tonsillectomy. PMH negative.

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REFERENCES

• Morgan, G.E., Mikhail, M.S., and Murray, M.J.
  (2006). Clinical Anesthesiology. (4th ed.) New
  York, NY McGraw-Hill.
• Stoelting, R.K. (1999). Pharmacology Physiology
  in Anesthetic Practice. (3rd ed.) Philadelphia,
  PA
• J.B. Lippincott Company.