Prostaglandin inhibitors are a class of analgesics, not general anesthetic agents. Opioids, ultrashort-acting barbiturates, and benzodiazepines are central nervous system depressants that are used for induction and short periods of general anesthesia.
The tissue solubility of isoflurane (Forane) is poor, which allows for rapid induction and recovery. Its odor limits induction concentration because of the potential for coughing. Because only about 15% of isoflurane is metabolized in the liver, hepatoxicity is not a problem.
Respiratory paralysis would result in patient death, so is not a desired component of general anesthesia. The goals of surgical anesthesia are loss of consciousness, adequate muscle relaxation, good patient control, and pain cessation.
Loss of consciousness
Loss of pain sensation
Good patient control
Skeletal muscle relaxation
Propofol is a general anesthetic agent that is unrelated to any other general anesthetic and has the advantage of allowing patients to "feel better" and ambulate sooner than with other agents. It is an IV anesthetic that has a rapid onset and duration of about 5 minutes. It is also used for IV sedation and for induction and maintenance of balanced anesthesia. Enflurane and halothane are both classified as volatile liquid anesthetics. Ketamine is chemically related to phencyclidine (PCP) and produces analgesia without loss of consciousness. Morphine is an opioid that is used as an adjunctive drug to general anesthetic.
Nitrous oxide has low blood solubility, which allows rapid onset and quick recovery. It is popular in dental offices because of its analgesic and anxiolytic properties, ease of administration, and the retention of consciousness and protective reflexes.
Short period of onset and recovery
Long period of onset and recovery
Ease of administration
Retained consciousness and protective reflexes
The patient should be placed on 100% oxygen for at least 5 minutes at the termination of a procedure using nitrous oxide sedation to prevent the phenomenon known as diffusion hypoxia. The rapid outflow of nitrous oxide accompanied by oxygen and carbon dioxide can cause severe headache and other adverse effects.
Increasing the percentage of nitrous oxide to 100% for 5 minutes
Administering two aspirins at the end of treatment
Increasing the percentage of OXYGEN to 100% for 5 minutes
Administering an additional cartridge of local anesthetic
Nitrous oxide equipment today has built-in safety features, including a minimal concentration of 30% oxygen flow, or the machine's fail-safe system will shut off the flow of nitrous oxide.
Analgesia is not included in Flagg's stages of general anesthesia. Flagg's stages describe more rapidly acting anesthetic agents than those used when Guedel's stages were developed, and they include the following:(1) Induction—all preparation and medication for the patient up to the beginning of the operation, including preoperative medications, adjunctive drugs to anesthesia, and anesthetics required for induction.(2) Maintenance—this phase begins with the patient at the depth of anesthesia sufficient to allow surgical manipulation and continues to the completion of the procedure.(3) Recovery—this phase begins with the termination of the surgical procedure and continues throughout the postoperative period until the patient is fully responsive to the environment.
Chronic nitrous oxide abuse can cause nitrous-induced neuropathy symptoms, including numbness and paresthesias of the hands and legs that progresses to more serious neurologic symptoms with continued abuse. Liver and kidney problems have also been associated with nitrous oxide abuse.
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Stage IV is characterized by respiratory and circulatory failure; if this stage is not immediately reversed, the patient will die. Stage I analgesia is characterized by analgesia or reduced pain sensation. The patient is conscious and responsive. Stage II delirium or excitement begins with unconsciousness and is associated with involuntary movement and excitement. Stage III surgical anesthesia is the stage during which most major surgery occurs.
The percentage of nitrous oxide required for patient comfort may range from 10% to 50%, with the average being 35%. At levels higher than 50%, increased adverse effects such as vomiting and loss of consciousness may occur.
Stage II is the excitement or delirium stage of general anesthesia, beginning with loss of consciousness and associated with involuntary movement and sympathetic stimulation. Tachycardia, hypertension, emesis, and incontinence can occur. Having a rapid and smooth passage through stage II into stage III (i.e., surgical anesthesia) is important for patient comfort.
The intravenous use of barbiturates as an adjunct to general anesthesia is limited because repeated dosing of these drugs can greatly prolong the patient's recovery.
Repeated dosing leads to prolonged recovery
Central nervous system stimulation
Balanced general anesthesia uses several agents to help the patient pass smoothly into general anesthesia and decrease adverse effects. The ultrashort-acting barbiturates combined with nitrous oxide and oxygen are used to move the patient easily from stage I to stage III, skipping stage II. Volatile inhalation anesthetics are then administered to produce profound general anesthesia.
Volatile inhalation anesthetics
The most serious disadvantage of opioids as adjunctive drugs to general anesthesia is prolonged respiratory depression, which can lead to death if the patient is not carefully monitored. Miosis, abuse potential, and decreased gastrointestinal motility are additional, less serious adverse drug effects.
Decreased gastrointestinal motility
Prolonged respiratory depression
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