Transcript General Anesthetics

Chapter 12
General Anesthetics
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General Anesthetics
….. Reversible Loss of Consciousness and
Insensibility to Painful Stimuli …..
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General Anesthetics
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Guedel’s Stages and Planes of Anesthesia
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Stage 1
• This stage is characterized by the development of analgesia or
a reduced sensation to pain.
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Stage II
• This stage begins with unconsciousness and is associated
with involuntary movement and excitement.
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Stage III
• This is the stage where general surgery is performed.
• It is divided into 4 planes that are based upon eye movement,
depth of respiration, and muscle relaxation.
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Stage IV
• This stage is characterized by respiratory or medullary
paralysis.
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General Anesthetics
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Current Levels of Anesthesia
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Induction
• This level encompasses the administration of preoperative
medications, adjunctive drugs to anesthesia, and the
anesthetics required for surgery.
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Maintenance
• This level begins when the patient has achieved a depth of
anesthesia sufficient to allow the surgery to begin and
ends upon the completion of the surgical procedure.
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Recovery
• The recovery phase begins with the termination of the
surgical procedure and continues throughout the
postoperative recovery period until the patient is fully
responsive to his or her environment.
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General Anesthetics
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Adverse Reactions
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The goals of general anesthesia are to provide
good patient control, adequate muscle
relaxation, and pain relief.
 In order to do this, potent CNS depressants are
given in relatively high doses and many drug
combinations are used in balanced anesthesia.
 As a result, the patient is at high risk for
adverse effects.
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General Anesthetics
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Adverse Reactions
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Adverse reactions are many and primarily affect the
heart and lungs.
They include cardiovascular collapse and arrest,
ventricular fibrillation, hyper or hypotension, respiratory
depression or arrest, and laryngospasm.
Chronic exposure can lead to teratogenicity in men or
women.
Hepatotoxicity can occur with repeated exposure,
especially in operating room personnel.
Other adverse reaction include headache, fatigue,
irritability, and the risk of addiction.
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General Anesthetics
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Physical Factors
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The concentration of the anesthetic in the inspired
mixture is proportionate to its partial pressure.
The depth of anesthesia is a function of the partial
pressure in the brain.
Those physical factors that most influence brain
anesthetic partial pressure are the partial pressure of the
inspired anesthetic, rate and volume of delivery to the
lungs, and solubility in body tissues.
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General Anesthetics
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Nitrous Oxide
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Nitrous oxide is a colorless gas with little or no
odor.
It is administered with oxygen.
Nitrous oxide provides the patient with anxiety
relief.
It is the primary part of dental office conscious
sedation.
It lightly sedates and relaxes the patient while
providing some degree of analgesia.
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General Anesthetics
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Nitrous Oxide
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Nitrous oxide is administered in combination with oxygen
(N2O-O2).
100% oxygen is administered for 2-3 minutes and
nitrous oxide is gradually added at 5%-10% increments
until the desired level of patient sedation is achieved.
At the end of the procedure the nitrous oxide is
discontinued first and the patient should then be placed
on 100% oxygen for 5 minutes.
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General Anesthetics
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Advantages of Nitrous Oxide
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It has a rapid onset of action (< 5 minutes).
It is easy to administer because the patient breathes it
through his or her nose.
It is easy to control by adjusting the percentage of
nitrous oxide administered.
Patient’s recovery almost immediate.
It is of value in nervous children provided they are not
hysterical.
Relaxed patients mean a much less stressed dental
environment and staff.
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General Anesthetics
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Nitrous Oxide
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Pharmacologic Effects
• Sedation is the main pharmacologic effect.
• Nausea and vomiting can occur but it is uncommon.
• Analgesia occurs at concentrations of 30% nitrous
oxide.
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General Anesthetics
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Nitrous Oxide
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Adverse Reactions
• There have been reports of dental health
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practitioners abusing nitrous oxide.
Faulty equipment can lead to complications.
Headache with the abrupt discontinuation of N2O-O2
can occur.
Nausea and vomiting have been reported.
Spontaneous miscarriage can occur in pregnant
patients and dental health practitioners.
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General Anesthetics
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Nitrous Oxide
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Contraindications
• Respiratory obstruction such as a stuffy nose prevents the
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patient from inhaling the anesthetic.
Chronic obstructive pulmonary disease compromises the
patient’s ventilation and increases carbon dioxide partial
pressure.
Patients with emotional instability can experience euphoria
or an altered sensorium.
Pregnancy is a contraindication because of the high rate of
spontaneous miscarriage.
Patients with a history of substance abuse, especially with
nitrous oxide, should not be given this drug.
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General Anesthetics
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Halogenated Hydrocarbons
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These inhaled general anesthetics are called volatile
liquids.
Volatile general anesthetics are liquids that evaporate
easily at room temperature because of their low boiling
points.
They are potent agents that have limited solubility in
body tissues.
These drugs in their odor, induction and recovery times,
have an adverse effect profile.
They are all metabolized in the liver to a varying extent.
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General Anesthetics
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Ultrashort-Acting Barbiturates
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These drugs have a rapid onset of action when
given intravenously and are highly lipidsoluble.
 Recovery is prolonged with these drugs.
 They do not provide the patient with analgesia.
 Serious adverse effects include bronchospasm
and laryngospasm.
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General Anesthetics
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Propofol
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This is an intravenous anesthetic that is not
related to other general anesthetics.
It has a very rapid onset (<30 seconds) and a
duration of action of 5 minutes.
Patients feel better faster.
There is less nausea and vomiting with this
drug.
It can cause a significant drop in blood
pressure because it causes vasodilation.
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General Anesthetics
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Ketamine
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This intravenously administered general
anesthetic is chemically related to
phencyclidine.
It produces a dissociate anesthesia.
The patient experiences excessive salivation.
Patients can experience delirium and
hallucinations during recovery.
Psychiatric disorders may be a contraindication
to ketamine use.
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General Anesthetics
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Other Intravenous General Anesthetics
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Opioid Analgesics
• These drugs are given during the induction phase and
during surgery to provide analgesia.
• They can cause prolonged respiratory depression.
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Droperidol Plus Fentanyl
• This combination produces neuroleptoanalgesia which is a
“wakeful” anesthetic state.
• Adverse effects are serious and include respiratory
depression and extrapyramidal effects.
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Benzodiazepines
• These are used as an integral part of conscious sedation.
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General Anesthetics
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Balanced Anesthesia
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The goals of surgical anesthesia are to achieve
good patient control, adequate muscle
relaxation, and pain relief.
 Patients should readily pass from stage I to
stage III, skipping over phase II which is
uncomfortable.
 The patient should then recover from
anesthesia with a minimal amount of adverse
effects.
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