Mosby items and derived items © 2007 by Mosby, Inc., an affiliate of Elsevier Inc. Chapter 12 General Anesthetics

Mosby items and derived items © 2007 by Mosby, Inc., an affiliate of Elsevier Inc. General Anesthetics ….. Reversible Loss of Consciousness and Insensibility to Painful Stimuli ….. 2

Mosby items and derived items © 2007 by Mosby, Inc., an affiliate of Elsevier Inc. General Anesthetics  Guedel’s Stages and Planes of Anesthesia  Stage 1 This stage is characterized by the development of analgesia or a reduced sensation to pain. This stage is characterized by the development of analgesia or a reduced sensation to pain.  Stage II This stage begins with unconsciousness and is associated with involuntary movement and excitement. This stage begins with unconsciousness and is associated with involuntary movement and excitement.  Stage III This is the stage where general surgery is performed. 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. It is divided into 4 planes that are based upon eye movement, depth of respiration, and muscle relaxation.  Stage IV This stage is characterized by respiratory or medullary paralysis. This stage is characterized by respiratory or medullary paralysis. 3

Mosby items and derived items © 2007 by Mosby, Inc., an affiliate of Elsevier Inc. General Anesthetics  Current Levels of Anesthesia  Induction This level encompasses the administration of preoperative medications, adjunctive drugs to anesthesia, and the anesthetics required for surgery. This level encompasses the administration of preoperative medications, adjunctive drugs to anesthesia, and the anesthetics required for surgery.  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. 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.  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. 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. 4

Mosby items and derived items © 2007 by Mosby, Inc., an affiliate of Elsevier Inc. General Anesthetics  Adverse Reactions  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. 5

Mosby items and derived items © 2007 by Mosby, Inc., an affiliate of Elsevier Inc. General Anesthetics  Adverse Reactions  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. 6

Mosby items and derived items © 2007 by Mosby, Inc., an affiliate of Elsevier Inc. General Anesthetics  Physical Factors  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. 7

Mosby items and derived items © 2007 by Mosby, Inc., an affiliate of Elsevier Inc. General Anesthetics  Nitrous Oxide  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. 8

Mosby items and derived items © 2007 by Mosby, Inc., an affiliate of Elsevier Inc. General Anesthetics  Nitrous Oxide  Nitrous oxide is administered in combination with oxygen (N 2 O-O 2 ).  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. 9

Mosby items and derived items © 2007 by Mosby, Inc., an affiliate of Elsevier Inc. General Anesthetics  Advantages of Nitrous Oxide  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. 10

Mosby items and derived items © 2007 by Mosby, Inc., an affiliate of Elsevier Inc. General Anesthetics  Nitrous Oxide  Pharmacologic Effects Sedation is the main pharmacologic effect. Sedation is the main pharmacologic effect. Nausea and vomiting can occur but it is uncommon. Nausea and vomiting can occur but it is uncommon. Analgesia occurs at concentrations of 30% nitrous oxide. Analgesia occurs at concentrations of 30% nitrous oxide. 11

Mosby items and derived items © 2007 by Mosby, Inc., an affiliate of Elsevier Inc. General Anesthetics  Nitrous Oxide  Adverse Reactions There have been reports of dental health practitioners abusing nitrous oxide. There have been reports of dental health practitioners abusing nitrous oxide. Faulty equipment can lead to complications. Faulty equipment can lead to complications. Headache with the abrupt discontinuation of N 2 O-O 2 can occur. Headache with the abrupt discontinuation of N 2 O-O 2 can occur. Nausea and vomiting have been reported. Nausea and vomiting have been reported. Spontaneous miscarriage can occur in pregnant patients and dental health practitioners. Spontaneous miscarriage can occur in pregnant patients and dental health practitioners. 12

Mosby items and derived items © 2007 by Mosby, Inc., an affiliate of Elsevier Inc. General Anesthetics  Nitrous Oxide  Contraindications Respiratory obstruction such as a stuffy nose prevents the patient from inhaling the anesthetic. Respiratory obstruction such as a stuffy nose prevents the patient from inhaling the anesthetic. Chronic obstructive pulmonary disease compromises the patient’s ventilation and increases carbon dioxide partial pressure. 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. Patients with emotional instability can experience euphoria or an altered sensorium. Pregnancy is a contraindication because of the high rate of spontaneous miscarriage. 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. Patients with a history of substance abuse, especially with nitrous oxide, should not be given this drug. 13

Mosby items and derived items © 2007 by Mosby, Inc., an affiliate of Elsevier Inc. General Anesthetics  Halogenated Hydrocarbons  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. 14

Mosby items and derived items © 2007 by Mosby, Inc., an affiliate of Elsevier Inc. General Anesthetics  Ultrashort-Acting Barbiturates  These drugs have a rapid onset of action when given intravenously and are highly lipid- soluble.  Recovery is prolonged with these drugs.  They do not provide the patient with analgesia.  Serious adverse effects include bronchospasm and laryngospasm. 15

Mosby items and derived items © 2007 by Mosby, Inc., an affiliate of Elsevier Inc. General Anesthetics  Propofol  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. 16

Mosby items and derived items © 2007 by Mosby, Inc., an affiliate of Elsevier Inc. General Anesthetics  Ketamine  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. 17

Mosby items and derived items © 2007 by Mosby, Inc., an affiliate of Elsevier Inc. General Anesthetics  Other Intravenous General Anesthetics  Opioid Analgesics These drugs are given during the induction phase and during surgery to provide analgesia. These drugs are given during the induction phase and during surgery to provide analgesia. They can cause prolonged respiratory depression. They can cause prolonged respiratory depression.  Droperidol Plus Fentanyl This combination produces neuroleptoanalgesia which is a “wakeful” anesthetic state. This combination produces neuroleptoanalgesia which is a “wakeful” anesthetic state. Adverse effects are serious and include respiratory depression and extrapyramidal effects. Adverse effects are serious and include respiratory depression and extrapyramidal effects.  Benzodiazepines These are used as an integral part of conscious sedation. These are used as an integral part of conscious sedation. 18

Mosby items and derived items © 2007 by Mosby, Inc., an affiliate of Elsevier Inc. General Anesthetics  Balanced Anesthesia  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. 19